Academic literature on the topic 'Facteur de transcription EB (TFEB)'

The kinase PINK1 and ubiquitin ligase Parkin can regulate the selective elimination of damaged mitochondria through autophagy (mitophagy). Because of the demand on lysosomal function by mitophagy, we investigated a role for the transcription factor EB (TFEB), a master regulator of lysosomal biogenesis, in this process. We show that during mitophagy TFEB translocates to the nucleus and displays transcriptional activity in a PINK1- and Parkin-dependent manner. MITF and TFE3, homologues of TFEB belonging to the same microphthalmia/transcription factor E (MiT/TFE) family, are similarly regulated during mitophagy. Unlike TFEB translocation after starvation-induced mammalian target of rapamycin complex 1 inhibition, Parkin-mediated TFEB relocalization required Atg9A and Atg5 activity. However, constitutively active Rag guanosine triphosphatases prevented TFEB translocation during mitophagy, suggesting cross talk between these two MiT/TFE activation pathways. Analysis of clustered regularly interspaced short palindromic repeats–generated TFEB/MITF/TFE3/TFEC single, double, and triple knockout cell lines revealed that these proteins partly facilitate Parkin-mediated mitochondrial clearance. These results illuminate a pathway leading to MiT/TFE transcription factor activation, distinct from starvation-induced autophagy, which occurs during mitophagy.

In response to the increased energy demands of contractions, skeletal muscle adapts remarkably well through acutely regulating metabolic pathways to maintain energy balance and in the longer term by regulating metabolic reprogramming, such as remodeling and expanding the mitochondrial network. This long-term adaptive response involves modulation of gene expression at least partly through the regulation of specific transcription factors and transcriptional coactivators. The AMPK-peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α) pathway has long been known to orchestrate contraction-mediated adaptive responses, although AMPK- and PGC1α-independent pathways have also been proposed. Transcription factor EB (TFEB) and TFE3, known as important regulators of lysosomal biogenesis and autophagic processes, have emerged as new metabolic coordinators. The activity of TFEB/TFE3 is regulated through posttranslational modifications (i.e., phosphorylation) and spatial organization. Under nutrient and energy stress, TFEB and TFE3 are dephosphorylated and translocate to the nucleus, where they activate transcription of their target genes. It has recently been reported that exercise promotes nuclear translocation and activation of TFEB/TFE3 in mouse skeletal muscle through the Ca2+-stimulated protein phosphatase calcineurin. Skeletal muscle-specific ablation of TFEB exhibits impaired glucose homeostasis and mitochondrial biogenesis with reduced metabolic flexibility during exercise, and global TFE3 depletion results in diminished endurance and abolished exercise-induced metabolic benefits. Transcriptomic analysis of the muscle-specific TFEB-null mice has demonstrated that TFEB regulates the expression of genes involved in glucose metabolism and mitochondrial homeostasis. This review aims to summarize and discuss emerging roles for TFEB/TFE3 in metabolic and adaptive responses to exercise and contractile activity in skeletal muscle.

The autophagy-lysosome pathway is a major protein degradation pathway stimulated by multiple cellular stresses, including nutrient or growth factor deprivation, hypoxia, misfolded proteins, damaged organelles, and intracellular pathogens. Recent studies have revealed that transcription factor EB (TFEB) and transcription factor E3 (TFE3) play a pivotal role in the biogenesis and functions of autophagosome and lysosome. Here we report that three translation inhibitors (cycloheximide, lactimidomycin, and rocaglamide A) can facilitate the nuclear translocation of TFEB/TFE3 via dephosphorylation and 14-3-3 dissociation. In addition, the inhibitor-mediated TFEB/TFE3 nuclear translocation significantly increases the transcriptional expression of their downstream genes involved in the biogenesis and function of autophagosome and lysosome. Furthermore, we demonstrated that translation inhibition increased autophagosome biogenesis but impaired the degradative autolysosome formation because of lysosomal dysfunction. These results highlight the previously unrecognized function of the translation inhibitors as activators of TFEB/TFE3, suggesting a novel biological role of translation inhibition in autophagy regulation.

The transcription factor EB (TFEB) promotes protein degradation by the autophagy and lysosomal pathway (ALP) and overexpression of TFEB was suggested for the treatment of ALP-related diseases that often affect the heart. However, TFEB-mediated ALP induction may perturb cardiac stress response. We used adeno-associated viral vectors type 9 (AAV9) to overexpress TFEB (AAV9-Tfeb) or Luciferase-control (AAV9-Luc) in cardiomyocytes of 12-week-old male mice. Mice were subjected to transverse aortic constriction (TAC, 27G; AAV9-Luc: n = 9; AAV9-Tfeb: n = 14) or sham (AAV9-Luc: n = 9; AAV9-Tfeb: n = 9) surgery for 28 days. Heart morphology, echocardiography, gene expression, and protein levels were monitored. AAV9-Tfeb had no effect on cardiac structure and function in sham animals. TAC resulted in compensated left ventricular hypertrophy in AAV9-Luc mice. AAV9-Tfeb TAC mice showed a reduced LV ejection fraction and increased left ventricular diameters. Morphological, histological, and real-time PCR analyses showed increased heart weights, exaggerated fibrosis, and higher expression of stress markers and remodeling genes in AAV9-Tfeb TAC compared to AAV9-Luc TAC. RNA-sequencing, real-time PCR and Western Blot revealed a stronger ALP activation in the hearts of AAV9-Tfeb TAC mice. Cardiomyocyte-specific TFEB-overexpression promoted ALP gene expression during TAC, which was associated with heart failure. Treatment of ALP-related diseases by overexpression of TFEB warrants careful consideration.

Background/Aims: This study determined the role and mechanism of action of transcription factor EB (TFEB) in H2O2-induced neuronal apoptosis. Methods: SH-SY5Y cells were treated with Akt inhibitor/activator and different concentrations of H2O2. Cell apoptosis was detected by flow cytometric analysis. Akt and TFEB phosphorylation and PARP cleavage were determined by Western blotting. HEK293T cells were transfected with different truncated TFEB mutants and HA-Akt-WT; SH-SY5Y cells were transfected with Flag-vector, Flag-TFEB, Flag-TFEB-S467A or Flag-TFEB-S467D; and TFEB interaction with Akt was determined by co-immunoprecipitation and GST pull-down assays. Results: A low concentration of H2O2 induces TFEB phosphorylation at Ser467 and nuclear translocation, facilitating neuronal survival, whereas a high concentration of H2O2 promotes SH-SY5Y cell apoptosis via suppressing TFEB Ser467 phosphorylation and nuclear translocation. The TFEB-S467D mutant is more easily translocated into the nucleus than the non-phosphorylated TFEB-S467A mutant. Further, Akt physically binds to TFEB via its C-terminal tail interaction with the HLH domain of TFEB and phosphorylates TFEB at Ser467. Mutation of TFEB-Ser467 can prevent the phosphorylation of TFEB by Akt, preventing inhibition of oxidative stress-induced apoptosis. Conclusions: Oxidative stress induces neuronal apoptosis through suppressing TFEB phosphorylation at Ser467 by Akt, providing a novel therapeutic strategy for neurodegenerative diseases.

To determine the roles of transcription factor EB (TFEB) in colorectal cancer (CRC), we collected samples of tumor tissues and normal tissues from 40 patients with CRC. The expression of TFEB in these samples was analyzed by using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. Furthermore, we explored the expression of TFEB mRNA in CCD-18Co normal cells and HT-29, HCT-8, C2BBe1 cancer cells. HT-29, HCT-8, and C2BBe1 cancer cells were transfected with a TFEB-specific small interference RNA (siRNA) and scrambled siRNA, then the TFEB expression was confirmed by Western blot. The migration and invasion abilities of cells transfected with TFEB-siRNA were examined by transwell method and wound-healing assay. The subsequent effect of TFEB silencing on the tumor growth was also detected in mice xenograft model in vivo. Our study found that TFEB expression was significantly increased ( P < 0.05) in colorectal tumor tissues compared with normal tissues. Consistent with TFEB expression in tissues, compared with the normal CCD-18Co cells, TFEB mRNA expression was also significantly augmented in CRC cells. TFEB protein expression was markedly reduced in HT-29, HCT-8, and C2BBe1 cells after TFEB-siRNA transfection. In addition, inhibition of TFEB expression resulted in decrease of cells migration and invasion abilities. In vivo study, compared with the negative control group, the tumor weight, and volume were also reduced after inhibiting the TFEB expression. Our research suggested that TFEB expression is related to the occurrence and development of colorectal adenocarcinoma. The migration and invasion abilities of cancer cells, the weight and volume of tumor were all decreased when inhibiting TFEB expression. Thus, TFEB serves as an important factor in the development of CRC by modulating cancer cell migration and invasion, showing the potential therapeutic target of CRC in clinical.

The stress-responsive transcription factor EB (TFEB) is a master controller of lysosomal biogenesis and autophagy and plays a major role in several cancer-associated diseases. TFEB is regulated at the posttranslational level by the nutrient-sensitive kinase complex mTORC1. However, little is known about the regulation of TFEB transcription. Here, through integrative genomic approaches, we identify the immediate-early gene EGR1 as a positive transcriptional regulator of TFEB expression in human cells and demonstrate that, in the absence of EGR1, TFEB-mediated transcriptional response to starvation is impaired. Remarkably, both genetic and pharmacological inhibition of EGR1, using the MEK1/2 inhibitor Trametinib, significantly reduced the proliferation of 2D and 3D cultures of cells displaying constitutive activation of TFEB, including those from a patient with Birt-Hogg-Dubé (BHD) syndrome, a TFEB-driven inherited cancer condition. Overall, we uncover an additional layer of TFEB regulation consisting in modulating its transcription via EGR1 and propose that interfering with the EGR1-TFEB axis may represent a therapeutic strategy to counteract constitutive TFEB activation in cancer-associated conditions.

Niemann–Pick type C disease (NPCD) is a lysosomal storage disease (LSD) characterized by abnormal cholesterol accumulation in lysosomes, impaired autophagy flux, and lysosomal dysfunction. The activation of transcription factor EB (TFEB), a master lysosomal function regulator, reduces the accumulation of lysosomal substrates in LSDs where the degradative capacity of the cells is compromised. Genistein can pass the blood–brain barrier and activate TFEB. Hence, we investigated the effect of TFEB activation by genistein toward correcting the NPC phenotype. We show that genistein promotes TFEB translocation to the nucleus in HeLa TFEB-GFP, Huh7, and SHSY-5Y cells treated with U18666A and NPC1 patient fibroblasts. Genistein treatment improved lysosomal protein expression and autophagic flux, decreasing p62 levels and increasing those of the LC3-II in NPC1 patient fibroblasts. Genistein induced an increase in β-hexosaminidase activity in the culture media of NPC1 patient fibroblasts, suggesting an increase in lysosomal exocytosis, which correlated with a decrease in cholesterol accumulation after filipin staining, including cells treated with U18666A and NPC1 patient fibroblasts. These results support that genistein-mediated TFEB activation corrects pathological phenotypes in NPC models and substantiates the need for further studies on this isoflavonoid as a potential therapeutic agent to treat NPCD and other LSDs with neurological compromise.

Cisplatin, a widely used anticancer agent, can cause nephrotoxicity, including both acute kidney injury (AKI) and chronic kidney diseases, by accumulating in renal tubular epithelial cells (TECs). Mitochondrial pathology plays an important role in the pathogenesis of AKI. Based on the regulatory role of transcription factor EB (TFEB) in mitochondria, we investigated whether TFEB is involved in cisplatin-induced TEC damage. The results show that the expression of TFEB decreased in a concentration-dependent manner in both mouse kidney tissue and HK-2 cells when treated with cisplatin. A knockdown of TFEB aggravated cisplatin-induced renal TEC injury, which was partially reversed by TFEB overexpression in HK-2 cells. It was further observed that the TFEB knockdown also exacerbated cisplatin-induced mitochondrial damage in vitro, and included the depolarization of membrane potential, mitochondrial fragmentation and swelling, and the production of reactive oxygen species. In contrast, TFEB overexpression alleviated cisplatin-induced mitochondrial damage in TECs. These findings suggest that decreased TFEB expression may be a key mechanism of mitochondrial dysfunction in cisplatin-induced AKI, and that upregulation of TFEB has the potential to act as a therapeutic target to alleviate mitochondrial dysfunction and cisplatin-induced TEC injury. This study is important for developing therapeutic strategies to manipulate mitochondria through TFEB to delay AKI progression.

The oncogenic Transcription Factor EB (TFEB), a member of MITF-TFE family, is known to be the most important regulator of the transcription of genes responsible for the control of lysosomal biogenesis and functions, autophagy, and vesicles flux. TFEB activation occurs in response to stress factors such as nutrient and growth factor deficiency, hypoxia, lysosomal stress, and mitochondrial damage. To reach the final functional status, TFEB is regulated in multimodal ways, including transcriptional rate, post-transcriptional regulation, and post-translational modifications. Post-transcriptional regulation is in part mediated by miRNAs. miRNAs have been linked to many cellular processes involved both in physiology and pathology, such as cell migration, proliferation, differentiation, and apoptosis. miRNAs also play a significant role in autophagy, which exerts a crucial role in cell behaviour during stress or survival responses. In particular, several miRNAs directly recognise TFEB transcript or indirectly regulate its function by targeting accessory molecules or enzymes involved in its post-translational modifications. Moreover, the transcriptional programs triggered by TFEB may be influenced by the miRNA-mediated regulation of TFEB targets. Finally, recent important studies indicate that the transcription of many miRNAs is regulated by TFEB itself. In this review, we describe the interplay between miRNAs with TFEB and focus on how these types of crosstalk affect TFEB activation and cellular functions.

Skeletal muscle is the most abundant tissue in the whole organism representing more than 40% of the total body mass. This organ is responsible for the 30% of metabolic rate in basal condition, suggesting its great relevance not only for locomotor activity, but also for the control of whole body metabolism. Indeed skeletal muscle is a highly dynamic tissue that modulates its metabolism and mass as a consequence of different physiopathological conditions. One stimulus that triggers major adaptations is exercise, which is also well known to activate autophagy (Grumati, Coletto, Schiavinato, et al., 2011). Physical exercise elicits several beneficial effects acting on mitochondrial content/function, fatty acid oxidation and glucose uptake; however it is considered a disruptive trigger for myofiber homeostasis that needs to be counterbalanced through the activation of transcriptionally regulated pathways ready to contrast mechanical and metabolic stresses produced during contraction. The role of FoxOs transcription factors and TFEB in regulating protein breakdown and autophagy is known (Milan et al., 2015; Settembre et al., 2011). However the role of TFEB in skeletal muscle and its possible effects in controlling exercise-dependent adaptations in this tissue were not proved. TFEB has been proposed as the key factor that coordinates autophagy to lysosomal biogenesis in cell culture, with different evidences showing the regulation of its activity. In particular it is known that an mTORC1 phosphorylation is able to prevent TFEB function by retaining it in the cytoplasm. However, there were no evidences concerning the possible phosphatases involved in TFEB activation. Using a cellular high content screening able to monitor TFEB nuclear translocation during starvation, we identified PPP3CB, the catalytic subunit of calcineurin, as one of the highest hit for TFEB nuclear relocalization. We demonstrated that calcineurin activity is necessary and sufficient to push TFEB in the nucleus, where it can complete its function. Nevertheless, calcineurin is known to be active in skeletal muscle during contraction as a consequence of calcium oscillations. For this reason we wondered whether calcineurin activity could affect TFEB translocation also in adult skeletal muscle during exercise. Using muscles transfected with a TFEB-GFP reporter, we demonstrated that calcineurin activity is necessary and sufficient to promote TFEB nuclear translocation even in adult skeletal muscle during coxntraction. However, the physiological meaning of this nuclear translocation in skeletal muscle remained to be addressed. To answer this question we used gain and loss of function approaches, by mean of viral infection of TFEB overesxpressing vectors, muscle specific TFEB knockout animals and tamoxifen inducible muscle specific TFEB transgenic animals. From microarray analysis of muscles overexpressing and lacking TFEB, we realized that the major pathways affected by genetic manipulation are related to mitochondrial biogenesis and function, lipid utilization and glucose homeostasis. Thus we started to dissect the function of TFEB in skeletal muscle proving that its activation is required for mitochondrial biogenesis that is indeed increased in transgenic muscle. We also found an augmented mitochondrial number and size in transgenic muscle, with only a small percentage of dysfunctional mitochondria in KO animals. These changes were paralleled by a TFEB signature in gene expression of genes involved in mitochondrial biogenesis and functionality. Moreover, these morphometric and gene expression evidences correlate with increased mitochondrial respiration and higher activity of respiratory chain complexes. For this reason transgenic muscles produce more ATP than normal mice, while KO muscles have a lower ATP synthesis because mitochondria present a leak in mitochondrial membrane that dissipate membrane potential. Nevertheless, in order to understand if TFEB is able to promote this mitochondrial program independently from PGC1α, we checked the expression of NRF1/2, TFAM and other genes involved in mitochondrial biogenesis in a model of PGC1α ablation during TFEB overexpression. These data, and complexes activity measurements, demonstrate that TFEB is able per se to activate the transcriptional program directly binding to NRF1 and NRF2 genes promoters without the need of the transcriptional co-activator. At this point, we challenged mice with exercise finding that transgenic mice are more resistant to exhaustive contraction than control; conversely muscle specific TFEB-KO animals display pronounced exercise intolerance due to their lack in ATP production. In order to better explain this latter finding, thanks to metabolic measurements we realized that KO muscles rely more on glucose oxidation both in basal condition and during the first phases of exercise thus explaining the observed exercise intolerance triggered by glycogen storage depletion. Furthermore lactate quantification in serum before and after exercise suggests that KO animal depend more on anaerobic glycolysis with respect to control and transgenic counterpart. To deeply investigate the role of glucose oxidation that seems the cause of exercise intolerance, we monitored glycogen levels in muscle of KO animals in resting condition, revealing a reduction of glycogen storage. For this reason after the early stages of exercise TFEB-KO animals need to rapidly shift their metabolism to fatty acid oxidation that however cannot support energy demand because of the presence of dysfunctional mitochondria. Altogether these findings indicate that TFEB is impinging more on metabolism rather than autophagy, that indeed is not affected by TFEB genetic modulation; more in detail TFEB seems to significantly modulate muscular glucose homeostasis that is altered in KO animals. Reduced glucose uptake and glycogen synthesis during EU clamps explains why glycogen storages are depleted in KO animals, while the transgenic counterpart present more glycogen accumulation. This phenotypic effect is paralleled by a change in glucose related genes expression, with higher levels of glucose transporters and glycogen synthesis regulator in transgenic muscles, even in the absence of PGC1α. Nevertheless TFEB overexpression is also able to drive factors such as nNOS and AMPK activity, thus modulating not only the expression but also the signalling pathways related to glucose homeostasis. In conclusion all these findings strongly support a new vision of TFEB as master regulator of metabolic flexibility during physical exercise in a PGC1α-independent fashion.
Il muscolo scheletrico è il tessuto più abbondante dell’organismo e rappresenta più del 40% della massa corporea. Questo organo è responsabile del 30% della spesa energetica a riposo, suggerendo la sua importanza non solo a livello di locomozione ma anche nel controllo del metabolismo a livello sistemico. Infatti il muscolo scheletrico è un tessuto estremamente dinamico, capace di modulare il suo metabolismo in seguito a stimoli di diversa natura. Uno stimolo che attiva maggiori adattamenti metabolici è l’esercizio, che è noto attivare anche l’autofagia. L’esercizio fisico stimola molti effetti benefici sul contenuto e funzionalità mitocondriale, ossidazione degli acidi grassi e assorbimento del glucosio; tuttavia, è considerato uno stimolo che danneggia la normale omeostasi delle fibre muscolari per cui necessita di essere controbilanciato dall’attivazione di meccanismi trascrizionalmente controllati che contrastano gli stress meccanici e metabolici prodotti durante la contrazione. Il ruolo dei fattori di trascrizione FoxO e TFEB nel regolare la degradazione proteica e l’autofagia è largamente conosciuto. Tuttavia, il ruolo di TFEB nel muscolo scheletrico e i suoi possibili effetti nel regolare gli adattamenti derivanti dall’esercizio in questo tessuto non sono ancora chiari. TFEB è stato proposto come fattore chiave nel coordinare autofagia e biogenesi lisosomiale in cellule in coltura, con diverse evidenze che dimostrano la regolazione della sua attività. In particolare è noto come la fosforilazione operata da mTORC1 sia in grado di prevenire l’attivazione di TFEB sequestrandolo nel citoplasma. Tuttavia, non esistono dati riguardanti le possibili fosfatasi coinvolte nell’attivazione di TFEB. Mediante l’utilizzo di uno High Content Screening in grado di monitorare la traslocazione di TFEB nel nucleo durante la starvation, abbiamo identificato il gene PPP3CB, codificante la subunità catalitica della calcineurina, come uno dei migliori geni coinvolti nella rilocalizzazione di TFEB. Abbiamo dimostrato che l’attività della calcineurina è necessaria e sufficiente per spingere TFEB nel nucleo, dove può espletare la sua funzione. Tuttavia, la calcineurina è noto essere attiva nel muscolo scheletrico durante la contrazione come conseguenza dei transienti di calcio. Per questo motivo ci siamo chiesti se l’attività della calcineurina possa influenzare la traslocazione di TFEB nel nucleo anche nel muscolo scheletrico durante l’esercizio fisico. Utilizzando un reporter TFEB-GFP abbiamo dimostrato che l’attività della calcineurina è necessaria e sufficiente a promuovere la traslocazione nucleare di TFEB anche nel muscolo scheletrico durante la contrazione. Tuttavia il significato fisiologico di questo avvenimento rimane da essere spiegato. Per rispondere a questa domanda abbiamo usato degli approcci di gain e loss of function utilizzando infezioni virali con vettori per l’overespressione di TFEB, una linea di topi con delezione muscolo specifica di TFEB e un’altra linea in cui l’overespressione di TFEB può essere attivata in muscolo grazie al tamoxifen. Da uno studio di espressione genica in muscoli overesprimenti TFEB e TFEB deficienti, abbiamo trovato che le vie di segnale principalmente coinvolte dalle manipolazioni genetiche erano quelle correlate alla biogenesi mitocondriale, utilizzo dei lipidi e omeostasi del glucosio. Abbiamo perciò cominciato a dissezionare il ruolo di TFEB nel muscolo scheletrico provando che la sua attivazione è richiesta per la biogenesi mitocondriale, che è per l'appunto aumentata nei muscoli transgenici. Infatti, in questi abbiamo trovato un aumento nel numero e nella dimensione dei mitocondri, mentre abbiamo riportato solo una piccola percentuale di mitocondri disfunzionali nei muscoli knockout. Questi cambiamenti sono accompagnati da un’attivazione dei geni TFEB-dipendenti responsabili per la biogenesi e funzionalità mitocondriale. Inoltre, questi cambiamenti morfometrici e di espressione genica correlano con un aumento nella respirazione mitocondriale e nell’attività dei complessi della catena respiratoria. Per questo motivo i muscoli transgenici producono più ATP dei wildtype, mentre i muscoli KO presentano una ridotta sintesi di ATP a causa di una disfunzionalità della membrana mitocondriale che dissipa il gradiente protonico. Tuttavia, per capire se questi cambiamenti dipendono direttamente da TFEB indipendentemente da PGC1α, abbiamo monitorato l’espressione di NRF1/2, TFAM e altri geni coinvolti nella biogenesi mitocondriale in un modello in cui PGC1α è deleto e TFEB overespresso. Questi dati di espressione uniti alle misure delle attività dei complessi dimostrano che TFEB è in grado di indurre autonomamente la biogenesi mitocondriale legandosi direttamente ai promotori dei geni NRF1 e NRF2. A questo punto abbiamo sottoposto a esercizio i topi riscontrando che gli animali transgenici resistono maggiormente all’attività fisica; al contrario i topi KO presentano una marcata intolleranza all’esercizio a causa della scarsa produzione di ATP. Per spiegare meglio questo fenomeno, grazie a misurazioni di parametri metabolici abbiamo riscontrato che i topi KO fanno affidamento maggiormente nell’ossidazione del glucosio sia a riposo che durante le fasi iniziali dell’esercizio fisico, spiegando l’intolleranza con la fine delle riserve di glicogeno. Inoltre, le quantificazioni del lattato nel siero prima e dopo l’esercizio suggeriscono che i muscoli KO dipendono maggiormente dalla glicolisi anaerobia a differenza delle controparti wildtype e transgenica. A questo punto, per investigare più in dettaglio il ruolo dell’ossidazione del glucosio che sembra essere alla base dell’intolleranza all’esercizio, abbiamo misurato i livelli di glucosio intramuscolare negli animali KO, notando che a riposo questi presentano una riduzione considerevole delle riserve. Per questo motivo gli animali KO, dopo i primi momenti di esercizio, sono costretti a cambiare il loro metabolismo verso una maggiore ossidazione degli acidi grassi che comunque non riesce a supportare la domanda energetica a causa dei mitocondri disfunzionali. Tutte queste evidenze indicano che TFEB controlla più il metabolismo rispetto all’autofagia la quale non è influenzata dalla modulazione genetica di TFEB; più in dettaglio TFEB sembra controllare direttamente il metabolismo del glucosio che è alterato negli animali TFEB-deficienti. Un ridotto assorbimento del glucosio e una ridotta sintesi del glicogeno durante gli EU-clamps spiegano perché le riserve di glicogeno sono ridotte negli animali KO mentre la controparte transgenica ne accumula in più. Questi effetti fenotipici sono accompagnati da un cambiamento nell’espressione di geni connessi all’omeostasi del glucosio, con maggiore presenza di trascritti per i trasportatori di glucosio and regolatori della sintesi del glicogeno nei muscoli transgenici, anche in assenza di PGC1α. Inoltre, l’overespressione di TFEB è in grado di modulare anche l’attività di nNOS e AMPK, influenzando l’omeostasi del glucosio non solo dal punto di visto trascrizionale, ma impattando anche sulle vie di segnale ad esso correlate. In conclusione tutte queste scoperte sostengono fortemente una nuova visione di TFEB come un fattore chiave nella regolazione della flessibilità metabolica durante l’esercizio fisico in modo indipendente da PGC1α.

Plusieurs études ont suggéré une implication des glycogène synthase kinases 3 (GSK3) dans la carcinogenèse, notamment du pancréas. Des études ont rapporté des résultats contradictoires quant à l’impact des GSK3 sur la survie cellulaire. Au niveau du pancréas, il a été observé que l’inhibition des GSK3 inhibe la croissance entre autres via la régulation de la voie JNK ou NFkB. Les inhibiteurs des GSK3 sont présentement à l’étude comme traitement de différentes pathologies, notamment pour le cancer pancréatique. Une meilleure compréhension des voies de signalisation régulées par les GSK3 sera donc nécessaire. Nous avons entrepris ces travaux afin de mieux comprendre les mécanismes impliqués dans la régulation de la survie des cellules pancréatiques tumorales par les GSK3. Nous avons démontré que l’inhibition des GSK3 induit l’apoptose et l’autophagie dans les cellules pancréatiques tumorales humaines. L’inhibition des GSK3 stimule l’autophagie autant dans les cellules pancréatiques tumorales que non tumorales, alors que l’apoptose est induite spécifiquement dans les cellules tumorales. Contrairement à l’apoptose, l’autophagie est induite indépendamment de la voie JNK-cJUN suite à l’inhibition des GSK3. Nos résultats démontrent que l’inhibition des GSK3 mène à l’inactivation de la voie mTORC1 qui pourrait contribuer à l’induction de l’autophagie. D’autre part, nos travaux ont démontré pour la première fois que les GSK3 régulent le facteur de transcription EB (TFEB) dans les cellules pancréatiques tumorales. En effet, l’inhibition des GSK3 entraîne la déphosphorylation de TFEB, notamment sur la Ser211, la dissociation des 14-3- 3 et sa translocation nucléaire. Nos résultats suggèrent que la régulation de TFEB par les GSK3 impliquerait des Ser/Thr phosphatases et pourrait être indépendante de l’activité mTORC1. L’inhibition de l’autophagie ou la déplétion de l’expression de TFEB sensibilise les cellules pancréatiques tumorales à l’apoptose induite suite à l’inhibition des GSK3 suggérant un rôle pro-survie de l’autophagie et de TFEB dans ces cellules. Enfin, l’inhibition des GSK3 semble mener à l’inhibition de la glycolyse qui contribuerait à l’induction de l’apoptose. En résumé, nos résultats démontrent que l’inhibition des GSK3 induit à la fois des signaux pro-apoptotiques et pro-survie suggérant que l’équilibre entre ces signaux dicterait l’impact des GSK3 sur la survie des cellules pancréatiques tumorales humaines.

Les lysosomes jouent un rôle central dans la régulation des processus anaboliques et cataboliques, la signalisation cellulaire ainsi que dans la mise en œuvre des programmes transcriptionnels au sein des cellules. Ils favorisent l’adaptation des cellules cancéreuses lors des variations du microenvironnement en leur fournissant les métabolites essentiels et l’énergie nécessaire à leur survie et à leur prolifération. Un acteur majeur dans la réponse adaptative des lysosomes est le facteur de transcription EB (TFEB). TFEB coordonne l’expression de gènes associés à la fonction et à la biogenèse des lysosomes, y compris ceux impliqués dans l’autophagie, un processus catabolique majeur des cellules qui dépend des lysosomes. TFEB et l’autophagie fonctionnent comme des mécanismes adaptatifs visant à rétablir l’homéostasie cellulaire en réponse à un stress. Cependant, la biogenèse des lysosomes et l'augmentation de leur taille induite par TFEB peuvent rendre les cellules cancéreuses plus vulnérables aux composés ciblant les lysosomes. Cette vulnérabilité ouvre la porte au développement de nouvelles stratégies pour lutter contre le cancer en ciblant simultanément les lysosomes et en activant TFEB. L’objectif initial de cette étude a été de découvrir de nouveaux agents pharmacologiques agonistes de TFEB, manifestant une cytotoxicité significative contre les cellules cancéreuses. Par un criblage de la bibliothèque Prestwick comprenant 1200 composés approuvés par la « Food and Drug Administration » (FDA), nous avons identifié deux antidépresseurs, la sertraline et l’indatraline, qui agissent en tant que puissants activateurs de la translocation de TFEB vers le noyau. Les deux composés induisent une accumulation de cholestérol au sein des lysosomes, entraînant la perméabilisation de leurs membranes et une perturbation du flux autophagique. L’analyse de modélisation moléculaire a révélé que les deux composés pourraient inhiber le trafic du cholestérol en se liant au site de fixation du cholestérol des transporteurs, Niemann-Pick type C1 (NPC1) et NPC2. Dans les cellules cancéreuses, la sertraline et l’indatraline provoquent une mort cellulaire immunogénique, en transformant les cellules mourantes en vaccins prophylactiques capables de protéger contre la croissance tumorale chez la souris. Dans un contexte thérapeutique, une dose unique de ces composés était suffisante pour ralentir de façon significative la croissance tumorale de manière dépendante des lymphocytes T. Ces résultats caractérisent la sertraline et l’indatraline comme des agents immunostimulants qui agissent à travers un mécanisme novateur connectant l’accumulation du cholestérol lysosomal aux dommages lysosomaux, entraînant ainsi la mort immunogénique des cellules cancéreuses. Ces résultats soutiennent le repositionnement de ces deux molécules en tant qu’agents immunostimulants pour le traitement du cancer et encouragent l’extension de cette étude à d’autres inhibiteurs du transport lysosomal du cholestérol
Lysosomes serve as an intracellular platform that coordinates anabolic and catabolic processes, cell signaling, and transcriptional programs. These organelles allow the adaptation of cancer cells to a changing microenvironment by supplying them with essential metabolites and energy for their survival and proliferation. A major player in the lysosomal adaptive response is the transcription factor EB (TFEB), which is part of the microphthalmia/transcription factor E (MIT/TFE) family of transcription factors. TFEB plays a pivotal role in driving the expression of several genes associated with lysosome function and biogenesis, including those participating in autophagy. The latter is a critical lysosomal catabolic process in the cell. While TFEB and autophagy function as adaptive mechanisms to reestablish cellular homeostasis in response to stressors, TFEB-induced lysosomal biogenesis and enlargement can render cancer cells more vulnerable to compounds targeting lysosomes. This vulnerability opens the door for developing new strategies to combat cancers by simultaneously targeting the lysosome and activating TFEB. This study initially aimed to uncover novel pharmacological agents that function as agonists of TFEB and exhibit substantial cytotoxicity against cancer cells. By conducting cell-based drug screening of the Prestwick library, consisting of 1200 Food and Drug Administration (FDA)-approved compounds, we identified two antidepressants, sertraline and indatraline, as potent inducers of TFEB nuclear translocation. Both compounds promoted cholesterol accumulation within lysosomes, resulting in lysosomal membrane permeabilization, disruption of autophagy, and cell death. Molecular docking analysis unveiled that indatraline and sertraline may inhibit cholesterol traffic by binding to the same cavity where cholesterol typically binds to the lysosomal cholesterol transporters, Niemann-Pick type C1 (NPC1) and NPC2. In cancer cells, sertraline and indatraline elicited immunogenic cell death, converting dying cells into prophylactic vaccines that were able to protect against tumor growth in mice. In a therapeutic setting, a single dose of each compound was sufficient to significantly reduce the outgrowth of established tumors in a T cell-dependent manner. These results identify sertraline and indatraline as immunostimulatory agents that operate through a novel mechanism that connects lysosomal cholesterol accumulation to lysosomal membrane permeabilization, ultimately leading to immunogenic cell death. These results support the repositioning of sertraline and indatraline as immunostimulatory agents for cancer treatment and encourage the broadening of this study to other lysosomal cholesterol transport inhibitors

Die Komposition der Skelettmuskulatur resultiert aus der fein abgestimmten Balance von Proteinauf- und Abbaumechanismen. Die Skelettmuskelatrophie kann in verschiedenen Situationen entstehen bzw. von diversen Krankheiten ausgelöst werden (Altern, Hunger, Krebs, Nervenschädigung, Kachexie) und ist meist die Folge von gesteigertem Proteinabbau, der die Proteinsynthese überwiegt. Der Muskelabbau ist physiologisch teilweise sinnvoll und dient der Notversorgung von lebenswichtigen Organen mit Lipiden, Aminosäuren und Glukose. Insgesamt ist eine funktionsfähige Muskulatur sehr wichtig, sowohl für Gesunde als auch Erkrankte, da bei Muskelatrophie auslösenden Erkrankungen das Gesamtüberleben wesentlich verringert ist und die Lebensqualität der Patienten enorm reduziert ist. Der Abbau von strukturellen Muskelproteinen wurde hauptsächlich dem Ubiquitin-Proteasom System zugeschrieben, dessen Regulation und von seinen einzelnen Enzymen muss genauestens verstanden sein, um in der Zukunft zielgerichtete Therapien entwickeln zu können. Eines der zentralen Enzyme in der Skelett- und Herzmuskelatrophie ist die E3 Ubiquitin Ligase MuRF1. In nahezu allen Modellen für Muskelatrophie wurde eine starke Zunahme der Expression von MuRF1 beschrieben. Betrachtet man die sehr zentrale Rolle von MuRF1 im UPS, dort vermittelt MuRF1 den Abbau von strukturellen Proteinen des Sarkomers, und der beobachteten starken Regulation bei diversen Atrophie-Modellen, wird klar, wie wichtig das Verständnis der transkriptionellen Regulation von MuRF1 selbst ist. In den letzten Jahren wurden bereits einige Transkriptionsfaktoren identifiziert, die an der Regulation von MuRF1 bei verschiedenen Atrophie-Modellen beteiligt sind, die Studien zeigten aber auch, dass noch nicht alle Modelle erklärt werden konnten. Um die verbleibenden Wissenslücken zu füllen, wurde in dieser Studie nach neuen transkriptionellen Regulatoren von MuRF1 gesucht und deren Beteiligung an bereits bekannten Signalwegen analysiert.
Skeletal muscle mass is permanently balanced as a result of fine tuned protein synthesis and degradation mechanisms. Skeletal muscle atrophy occurs when protein degradation exceeds protein synthesis, which happens in a variety of conditions, such as aging, starvation, cancer, cachexia or denervation. Degradation of muscle mass can sometimes be useful, e.g. as source for lipids, amino acids and glucose in case of critical malnutrition as well as several other physiological conditions. But a solid composition and thereby functional maintenance of muscles is necessary for healthy individuals as well as individuals suffering from atrophy releasing diseases as to retain their mobility and to preserve full heart functions. Since degradation of structural proteins in muscle tissue has been addressed mainly to the ubiquitin-proteasome-system, the regulation of the participating components needs to be understood in detail to develop constructive treatments and therapies for atrophy prevention. One of the key enzymes in skeletal and heart muscle atrophy is the E3 ubiquitin ligase MuRF1. Its expression levels and protein content was found to be elevated in almost every know atrophy model. MuRF1 is very critical for the muscles composition and thus their functional integrity, as it marks and initiates degradation of structural and contractile proteins via the UPS. Since MuRF1 plays a prominent role in muscle atrophy, its transcriptional regulation needs to be well understood to develop effective therapies for all the different atrophy models MuRF1 has been linked to. Several transcription factors have been identified to regulate MuRF1 at different ratios and in diverse atrophy models. Importantly, they do not explain all MuRF1 inducing events observed. To fill some of the remaining knowledge gaps, the studies aims were to find new transcriptional regulators for MuRF1 and to analyze potential involvements of the obtained candidates in pathways affecting skeletal muscle atrophy.

La maladie d’Alzheimer (MA) se caractérise par l’accumulation dans le cerveau d’agrégats extracellulaires et intraneuronaux (Aβ et Tau). Dans la cellule, la principale voie de dégradation des protéines agrégées est la voie lysosomale-autophagique, qui est altérée de façon précoce chez les patients Alzheimer. Des études récentes de mon laboratoire ont montré que ce dysfonctionnement serait à la fois la cause et la conséquence de l’accumulation du précurseur direct de l’Aβ, appelé C99 ou APP-CTFβ. De par sa toxicité, le C99 semble donc jouer un rôle crucial dans l’étiologie de la maladie. Son accumulation se produit majoritairement dans les compartiments endolysosomaux mais de façon intéressante, un marquage extracellulaire associé au C99 a également été observé à des stades plus avancés de la maladie ou en présence d’un inhibiteur de la γ-sécrétase (enzyme clivant le C99 en Aβ). Le premier axe de mon travail de thèse a donc consisté à étudier l’efficacité d’une restauration du système lysosomal-autophagique sur l’accumulation du C99. Dans ce but, nous avons utilisé une stratégie virale visant à exprimer le facteur de transcription EB (TFEB) dans un modèle murin de la MA (3xTg-AD). Ce facteur est le principal régulateur de la biogenèse lysosomale et de l’autophagie. Deux approches ont été testées cherchant à exprimer le TFEB avant ou après le début de l’accumulation du C99, grâce à une injection de virus exprimant le TFEB, soit en intracérébroventriculaire dès la naissance, soit par stéréotaxie à l’âge de 4 mois. Ces études ont montré une réduction importante de l’accumulation intraneuronale du C99 chez les souris 3xTg-AD, que ce soit via l’approche "préventive" ou "curative". Le deuxième axe de mon travail de thèse a cherché à comprendre l’origine du marquage extracellulaire observé dans le cerveau et associé au C99. Nous avons émis l’hypothèse que ce marquage correspondrait à des exosomes enrichis en C99. Les exosomes sont des vésicules extracellulaires, d’origine endosomale et sécrétées par les cellules, ayant déjà été décrites comme transportant des protéines neurotoxiques. Grâce à des approches pharmacologiques, immunocytochimiques et génétiques, nous avons confirmé cette hypothèse et mis en évidence la présence de C99 et de son dérivé le C83 (APP-CTFα) dans les exosomes purifiés à partir de modèles cellulaires ou murins de la MA, sous forme monomérique et oligomérique. Nos travaux montrent également que la charge des exosomes en oligomères est fortement amplifiée en présence d’une inhibition de la γ-sécrétase, expliquant ainsi le marquage extracellulaire. En conclusion, mes travaux de thèse (1) proposent une potentielle stratégie thérapeutique, basée sur l’activation du TFEB et visant à empêcher l’accumulation du C99, (2) montrent la présence de monomères et d’oligomères de C99 dans les exosomes ainsi qu’un lien entre la γ-sécrétase et l’oligomérisation. Les futures études devront déterminer le rôle exact de ces exosomes enrichis en C99
Alzheimer’s disease (AD) is characterized by the pathological accumulation of extracellular and intracellular aggregates (Aβ and Tau) in the brain. AD is also associated with an early alteration of the major degradation pathway of aggregated proteins, the autophagic-lysosomal pathway. Recent works have suggested that this defectcouldbothbeacauseandaconsequenceofearlyintraneuronalaccumulation of C99 (also named as APP-CTFβ), the direct precursor of Aβ. Due to its toxicity, C99 could be a possible key player of AD etiology. The accumulation of this product occurs mainly within organelles of the endolysosomal network, but our recent observations also indicate an extracellular accumulation of C99 in later stages of the disease, or in conditions where the Aβ-generating enzyme, γ-secretase, is blocked. The first aim of my PhD project was to investigate the possible beneficial effect of restoringlysosomal-autophagicfunctiononC99accumulation. Tothisend, weused a viral strategy to overexpress TFEB, a master regulator of both lysosome biogenesis and autophagy, in a mouse model of AD (3xTg-AD mouse). Two approaches were tested aiming to express TFEB either before or after the beginning of C99 accumulation, by injecting AAV-TFEBs into the ventricles of newborn mice or by stereotaxic injection into 3 month-old mice, respectively. These studies have shown a strong TFEB-mediated reduction of C99 accumulation when using both the preventive and curative approach. The aim of the second part of my PhD work was to understand the reasons of the extracellular accumulation of C99. We postulated that this C99-associated immunostaining could correspond to exosomal-associated C99. Exosomes are nanosizedvesiclesofendocyticoriginthatarereleasedfromcellsandknowntotransport neurotoxic proteins. In our study based on pharmacological, immunocytochemical and genetic approaches, we have confirmed this hypothesis and have shown the presence of C99, and of its direct derived-fragment C83 (APP-CTFα), existing as both monomers and oligomers, in exosomes purified from AD cell and mouse models. Moreover, our data have shown that the levels of these APP-CTFs are strongly increased by γ-secretase inhibition, thus explaining the higher levels of extracellular staining in γ-secretase treated animals. In conclusion, my PhD work shows 1) a new potential therapeutic strategy based on TFEB activation aiming to reduce early C99 accumulation and 2) the presence of monomeric and oligomeric C99 in exosomes in AD models and a link between γ-secretase inhibition and oligomerisation. Future studies are needed to elucidate the exact role of these C99-enriched exosomes in AD