Littérature scientifique sur le sujet « CELLULE STAMINALE »

La ricerca sulle cellule staminali rappresenta uno dei settori più promettenti della biotecnologia, in quanto offre la possibilità di sviluppare nuovi metodi per riparare o sostituire le cellule o i tessuti lesionati o malati e per curare alcune patologie croniche gravi. Tale ricerca può anche fornire un contributo importante alla scienza di base, aiutando a comprendere i meccanismi di proliferazione e differenziazione cellulare. Gli embrioni umani preimpanto rappresentano una delle possibili fonti di cellule staminali. Tuttavia, laddove questa ricerca prevede l’utilizzo di embrioni umani, essa solleva la questione dei principi etici in gioco e dei limiti e delle condizioni cui questa deve essere soggetta. Gli stati europei hanno adottato posizioni diverse in merito alla regolamentazione della ricerca sulle cellule staminali embrionali. Tale disparità, che riflette le tradizioni etiche, filosofiche e religiose alle quali gli stati si ispirano, conferma l’esistenza di punti di vista divergenti in Europa su quanto sia o meno eticamente suscettibile di tutela. Questo articolo esamina le legislazioni e le posizioni etiche esistenti a tal proposito in Europa, oltre che i nuovi orientamenti sui principi da applicare nella concessione di finanziamenti comunitari (nell’ambito del VI Programma quadro di ricerca europeo –FP6) per progetti di ricerca implicanti l’uso di embrioni umani e di cellule staminali embrionali. Tale studio intende altresì fornire degli spunti di riflessione sui nuovi traguardi dell’integrazione europea nel settore della ricerca biomedica.

La Gran Bretagna ha recentemente aperto alla possibilità di clonare embrioni umani nella prospettiva di ottenere tessuti da trapiantare in malati per i quali vi sia una indicazione clinica. Gli Stati uniti, con lo stesso scopo, intendono finanziare la ricerca sugli embrioni soprannumerari derivanti dalle tecnologie di fecondazione artificiale. In questo lavoro, sostenuto dalla più recente letteratura disponibile, l’autore sostiene che esistono modalità di ottenimento dei tessuti meno controverse da punto di vista etico per raggiungere gli stessi obiettivi terapeutici e denuncia gli interessi che spingono ad offrire una informazione parziale su questa materia, peraltro assai rilevante per la medicina del futuro.

Negli ultimi anni, l’editing genetico nelle cellule staminali/progenitrici ematopoietiche umane (HSPC) per il trattamento di malattie genetiche del sangue è migliorato drasticamente trasformando inserzioni genetiche casuali in precise e mirate modificazioni del genoma. La modifica mirata dei geni mutati ereditati consente la correzione in situ e la ricostituzione funzionale con il mantenimento del controllo endogeno dell'espressione. Recentemente abbiamo dimostrato che sia le rotture del DNA a doppio filamento indotte dall’editing che il genoma stesso dell’Adeno-Associated Virus 6 (AAV) innescano una risposta dipendente da p53 nell'HSPC che risulta in un ritardo della proliferazione con conseguente diminuzione della ricostituzione ematopoietica dopo il trapianto delle cellule editate in animali immuno-compromessi. Per cui, abbiamo quindi dimostrato come la soppressione di questa risposta mediante l’espressione transitoria della forma negativa dominante di p53 preservi la ricostituzione del lineage ematopoietico. Tuttavia, la biologia sottostante è rimasta sconosciuta, così come l'impatto dell'editing genetico sulle dinamiche clonali dell'HSPC modificate con riparo diretto per omologia (Homology Directed Repair, HDR) al momento del trapianto. Inoltre, lo stato quiescente delle HSC primitive costituisce un limite per l’editing genetico mediato da HDR, riducendo le sue possibili applicazioni cliniche. In questo lavoro, abbiamo prima superato tale limite esprimendo transitoriamente la proteina dell'adenovirus 5 E4orf6/7, che regola il principale controllore del ciclo cellulare, E2F, insieme alla nucleasi. Mediante un'analisi dell'espressione genica globale e mirata, abbiamo dimostrato come E4orf6/7 spinga le cellule in fase S/G2 con concomitante sovra-regolazione di tutti i principali componenti del macchinario HDR, aumentando così l'efficienza dell'inserimento del transgene in cellule precedentemente quiescenti. Nel contesto dello xenotrapianto, l'espressione combinata di E4orf6/7 e l'inibizione di p53 hanno migliorato l'efficienza del HDR (>50%) all'interno dell'innesto umano totale, superando i livelli riportati fino ad ora in letteratura. Tale risultato è stato riprodotto in diversi donatori da diverse fonti di HSPC e sono stati modificati più loci genomici, dimostrando la maggior versatilità di questa piattaforma se paragonata ad altre strategie di editing. In parallelo, abbiamo ideato una nuova tecnologia (BAR-seq) che consente il monitoraggio clonale di singole HSC modificate con HDR. Questo approccio prevede l’introduzione di un codice a barre ereditabile univoco (BAR) nel templato AAV6 necessario al HDR. Il sequenziamento ad alta copertura di tali sequenze negli xenotrapianti ha mostrato come l’editing genetico risulti in un attecchimento di pochi cloni dominanti. Mentre l'inibizione transitoria di p53 durante l’editing ha consentito un aumento sostanziale della composizione clonale dell'innesto senza alterare la capacità ripopolante delle HSC. Inoltre, questi dati suggeriscono come la risposta mediata da p53 sia responsabile di un'ematopoiesi oligoclonale. È importante sottolineare che il BAR-seq ha fornito la prima prova diretta che le HSC umane modificate con HDR mantengono un potenziale multilineage e subiscono più cicli di divisioni simmetriche e asimmetriche nei trapianti primari e secondari. In conclusione, auspichiamo che i miglioramenti messi a punto nel nostro protocollo di editing possano ampliare le possibili applicazioni cliniche dell’editing genetico.
The scope of genome engineering in hematopoietic stem/progenitor cells (HSPCs) has broadened from random to precise genome insertions for treating genetic diseases of the blood lineages. Targeted editing of inherited mutant genes allows in situ correction and functional reconstitution with preserved expression control. We recently showed that both the induced double-strand DNA breaks and the AAV6 genome trigger a p53-dependent DNA damage response in HSPC delaying proliferation and decreasing hematopoietic reconstitution after xenotransplantation. Suppression of this response by transient expression of a dominant negative p53 released cell-cycle block and rescued hematopoietic reconstitution. Yet, the underlying biology remained unknown as well as the impact of gene editing on clonal dynamics of HDR-edited HSPC upon transplantation. Moreover, it has long been contended that the quiescence of primitive HSC constrains HDR-mediated gene editing, thus limiting its perspective clinical applications in several diseases. Here, we first overcame such constraints by transiently expressing the adenovirus 5 protein E4orf6/7, which operates the major cell cycle controller E2F, together with the nuclease. By global and targeted gene expression analysis we showed engagement of targeted cells in S/G2 phases with concomitant upregulation of all major components of the HDR machinery, thus increasing the efficiency of targeted transgene insertion. Combined E4orf6/7 expression and p53 inhibition enhanced >50% HDR efficiency within human graft surpassing the levels reported until now in the literature. Such outcome was reproducible across several HSPC donors and sources, genomic loci and conceivably portable to most types of editing platforms. In parallel, we devised a novel technology (BAR-seq) which enables clonal tracking of individual HDR-edited HSC by introducing a unique heritable barcode in the AAV6 template. Deep sequencing of integrated BARs in human hematochimeric mice showed that only few (5-10) dominant clones of edited HSC robustly contributed to the hematopoietic graft long-term after transplant. Transient p53 inhibition during editing enabled substantial increase in polyclonal graft composition without altering individual HSC output, thus explaining the improved engraftment and highlighting the p53-mediated response as culprit of an otherwise oligoclonal hematopoiesis. Importantly, BAR-seq provided the first direct evidence that human HDR-edited HSC maintain multilineage potential and undergo multiple rounds of symmetric and asymmetric divisions in primary and secondary xenogeneic hosts. Altogether, we expect that the substantial gains obtained in HDR efficiency and polyclonal repopulation by our improved editing protocol should broaden applicability of HSC gene editing and pave its way to clinical translation.

Recent progress in stem cell research makes it possible to use them in cardiac therapy. Our aim was to characterize the pacemaker current (If) and HCN channels distribution in murine embryonic stem cells and cardiac adult mesoangioblasts following differentiation towards a pacemaker-like phenotype. Mouse embryonic stem cells (mESCs) are pluripotent stem cells and they were differentiated through formation of embryoid bodies (EBs). A fraction of these cells exhibited action potentials characterized by a slow diastolic depolarization typical of pacemaker myocytes and expressed the If current. Immunofluorescence analysis revealed that both the HCN1 and HCN4 isoforms of the pacemaker channel are expressed. Rhythmic cells responded to β-adrenergic and muscarinic agonists: isoproterenol accelerated and acetylcholine slowed spontaneous rate. Accordingly, β1- and β2-adrenergic, and M2-muscarinic receptors were detected by immunofluorescence. Cardiac mesoangioblasts are vessel-associated clonogenic, self-renewing progenitor cells identified in the post-natal murine heart, which can be induced to differentiate into cardiac myocytes. A subpopulation of cardiac mesoangioblasts induced to differentiate in vitro into cardiomyocytes acquires a phenotype with specific pacemaker cells properties, such as the presence of If current and the expression of the HCN4 isoform of pacemaker channels. As in native cardiac pacemaker cells, f-channel modulation by autonomic transmitters, in these cells, contributes to control of spontaneous rate. These results show that both of these cell types express proteins which underlie generation and modulation of heart rhythm, and can represent a potential substrate for a biological pacemaker.

Over the past few years, in veterinary medicine there has been an increased interest in understanding the biology of mesenchymal stem cells (MSCs). This interest comes from their potential clinical use especially in wound repair, tissue engineering and application in therapeutics fields, including regenerative surgery. MSCs can be isolated directly from bone marrow aspirates, adipose tissue, umbilical cord and various foetal tissues. In this study, mesenchymal stem cells were isolated from equine bone marrow, adipose tissue, cord blood, Wharton’s Jelly and, for the first time, amniotic fluid. All these cell lines underwent in vitro differentiation in chondrocytes, osteocytes and adipocytes. After molecular characterization, cells resulted positive for mesenchymal markers such as CD90, CD105, CD44 and negative for CD45, CD14, CD34 and CD73. Adipose tissue and bone marrow mesenchymal stem cells were successfully applied in the treatment of tendinitis in race horses. Furthermore, for the first time in the horse, skin wounds of septicemic foal, were treated applying amniotic stem cells. Finally, results never reported have been obtained in the present study, isolating mesenchymal stem cells from domestic cat foetal fluid and membranes. All cell lines underwent in vitro differentiation and expressed mesenchymal molecular markers.

Over the past few years, in veterinary medicine there has been an increased interest in understanding the biology of mesenchymal stem cells (MSCs). This interest comes from their potential clinical use especially in wound repair, tissue engineering and application in therapeutics fields, including regenerative surgery. MSCs can be isolated directly from bone marrow aspirates, adipose tissue, umbilical cord and various foetal tissues. In this study, mesenchymal stem cells were isolated from equine bone marrow, adipose tissue, cord blood, Wharton’s Jelly and, for the first time, amniotic fluid. All these cell lines underwent in vitro differentiation in chondrocytes, osteocytes and adipocytes. After molecular characterization, cells resulted positive for mesenchymal markers such as CD90, CD105, CD44 and negative for CD45, CD14, CD34 and CD73. Adipose tissue and bone marrow mesenchymal stem cells were successfully applied in the treatment of tendinitis in race horses. Furthermore, for the first time in the horse, skin wounds of septicemic foal, were treated applying amniotic stem cells. Finally, results never reported have been obtained in the present study, isolating mesenchymal stem cells from domestic cat foetal fluid and membranes. All cell lines underwent in vitro differentiation and expressed mesenchymal molecular markers.

One of the most important challenges in modern medicine is the identification of cell therapy protocols, enabling identification of personalized treatment strategies. WIthin this context, adult stem cells (ASC) have a large applicative potential. Contrary to ESCs (embryonic stem cells) and IPSCs (induced pluripotent stem cells), ASCs can be easily extracted from different tissues (bone marrow, skin, adipose tissue, muscle) without raising ethical issues . Moreover, they can be used for autologous transplantation, eliminating the complications associated with autoimmune reactions. Mesenchymal stem cells (MSC,), are an ASC population present in the bone marrow, adipose tissue and other tissues. MSCs are readily available and are able to self-replicate and differentiate, supported by the presence of appropriate stimuli, into cell lines derived from mesodermal lineage (osteoblasts, chondrocytes, adipocytes, and muscle cells). In the last decade it has also been observed that MSCs are able to trans-differentiate into cell types of ectodermal and endodermal origin (transdifferentiation).. The purpose of my work was to develop and define the conditions which can induce trans-differentiation of MSCs extracted from rat adipose tissue toward the neuronal phenotype. The study is part of a major project of regenerative medicine focused on identifying new strategies aimed at restoring functionality in degenerated brain tissue. Initially, MSCs have been characterized by the induction of osteoblastic differentiation, one of their physiological differentiations, and their interaction with biocompatible materials ( titanium dioxide) was analyzed, in order to assess their possible application in medicine for the creation, for example, of prothesic solutions. Subsequently, we sought to devise a GMP compliant cell culturing medium for MSC proliferation, crucial in order to obtain a clinically relevant cell number to differentiate following isolation from adipose tissue. For that reason we tried to induce the differentiation of MSCs into a neural phenotype; a first approach has been to apply protocols already known in literature for the differentiation of different types of stem cells toward the neuronal phenotype.. We considered both the direct differentiation protocols, as well as those that encompassed intermediate stages (sphere-forming). The protocols of differentiation by sphere formation resulted in differentiated MSC expressing glial markers (GFAP), but the protocol was too long(30 days) and a number of differentiated cells very low.. A second approach has been to develop a proprietary differentiation medium (NZ4) using the knowledge and expertise gained from the literature and from the negative results previously obtained The cells maintained in NZ4 differentiation medium , showed a clear morphological change and a high vitality; moreover they expressed both markers of specific neurons in the early stages of development (nestin, doublecortin) as well as markers expressed by mature neurons (βIIItubulin, VAMP2, Sinaptotagmin). Furthermore, the efficiency of the differentiation protocol has been functionally characterized by means of qualitative analysis of the dynamics of intracellular calcium and with quantitative analysis of the resting membrane potential The functional characterization clearly showed that MSC exposed to NZ4 differentiation medium have comparable behavior as primary neurons undergoing in vitro maturation. Given the future direction of the project will be to inject in an animal model the cell undergoing differentiation in order to attempt a partial recovery of the damaged neuronal tissue (i.e. ischemia) we characterized the behavior of MSC encapsulated in a biocompatible bioresorbable hydrogel matrix. The cells were encapsulated for different time periods, recovered, and heir survival as well as maintenance of stemness potential following retrieval was assessed . There are still other issues to be clarified n in particular, it will be necessary to verify in an in vivo setting the the efficacv of the differentiation protocol as well as to characterize the process of MSCs homing and to perform more detailed studies on behavioral changes of the same animal model. However, preliminary data obtained during this thesis allows to deepen the knowledge concerning the differentiation process of MSC from adipose tissue toward a neuronal phenotype.

Bone marrow-derived mesenchymal stem cells (MSCs) account for a small population of cells of the non-hematopoietic component of bone marrow. MSCs are multipotent stem cells endowed with neurotrophic potential combined to immunological properties, making them a promising therapeutic tool for neurodegenerative disorders. Although the mechanisms by which they act are still largely unknown, trans-differentiation, paracrine and autocrine actions have been hypothesized. Here we focus on the study of the effects exerted by rat MSCs on CNS neurons and oligodendrocytes by using a simplified in vitro co-culture system that precludes any direct contact between different cell types. The analysis of hippocampal synaptogenesis, synaptic vesicle recycling and electrical activity show that MSCs by themselves, efficiently support morphological and functional neuronal differentiation. Our observations demonstrate that MSCs selectively and directly increased hippocampal GABAergic presynapses and inhibitory transmission. In fact, this increment correlated to a higher expression of the potassium/chloride KCC2 cotransporter and to an enhancement of both the frequency and the amplitude of mIPSC and sIPSC. The decreased of GABA synapses following the treatment with a widely used Trk-neurotrophin receptor blocker, K252a, and the more specific TrkB receptor bodies prompt for the involvement of the brain derived neurotrophic factor (BDNF) in mediating such effects. The involvement of this neurotrophin is also strengthened by test ELISA on the culture medium collected from MSC-neuron co-cultures in which an higher BDNF concentration was detected, when compared to astrocyte-neuron co-cultures. The results obtained indicate that MSC-secreted factors induce glial-dependent neuronal survival and directly trigger an augmented GABAergic transmission in hippocampal cultures, highlighting a new effect by which MSCs could cooperate in CNS repair. Additionally, MSCs have been described to improve the clinical course of some demyelinating pathologies and to promote tissue repair through immunological mechanisms and neuroprotective effects. Following these evidences we performed in vitro and in vivo experiments to assess whether MSCs exert their actions through the support of oligodendrocytes (OLs), the myelinating CNS cells, and participate in the regulation of their proliferation and maturation. Through the analysis of specific proteins typically used as markers of the different stages of proliferation, maturation and differentiation (specifically, the membrane glycoprotein O4, the proteoglycan NG2 and myelin basic protein MBP, respectively), it has been noticed that MSCs are capable to prolong the proliferation phase of OPCs and also to anticipate OL differentiation, with respect to standard astrocyte/OL co-cultures. Moreover we investigated a possible molecular mechanism underlying these phenomena focusing on neurotrophin pathways. Trk receptors activation was analyzed in order to find out a possible role of neurotrophins in MSC-mediated effects on OLs, as it happens in neuronal cultures. We focused on the changes in the phosphorylation level of ERK (Extracellular signaling-regulated kinases), one of the activated effectors by TrK receptors. Our observations show that, in OLs co-cultured with MSCs, ERK is highly phosphorylated with respect to astrocyte/OL co-cultures, suggesting a MSC-induced activation of the pathways regulated by this protein. These data, although preliminary, suggest that MSCs positively act on the regulation of proliferation and maturation of OLs and, due to the observed effects on the regulation of synaptogenesis (see above), make these cells an interesting model for the identification of molecules involved in MSC neuroprotective processes. This may open new therapeutic approaches in the treatment of neurodegenerative diseases involving not only a synaptic imbalance, as it happens in various forms of epilepsy, but also in demyelinating diseases. Thus, in this research project, we aimed at characterising the molecular mechanisms underlying MSC actions that could participate in the recovery of neurological disorders or demyelinating pathologies.

Cell therapy is an attractive perspective for the treatment of life threatening disorders. In this context, foetal tissues are gaining interest as sources of cells for auto- and allo-transplantation, because of their pluripotency, proliferative capability and their low, if any, immunogenicity. Recently a pluripotent stem cell population has been isolated from Amniotic Fluid (AF). It is able to proliferate for more than 18 months, maintaining their differentiative ability as well as a normal karyotype. In term of differentiation potential, we succeeded in obtaining in vitro mesenchymal-, ectodermal- and endodermal-derived tissues from human Amniotic Fluid Stem (AFS) cells. Furthermore, murine AFS cells injected in blastocytes took part to the formation not only of several different foetal organs, but also of the placenta and the umbilical cord. In the present study we investigated the possibility of differentiating AFS cells towards the hematopoietic pathway. AFS cells isolated from human amniotic fluid, collected during routine diagnostic procedures and obtained under informed consent, were firstly expanded in vitro and selected on the basis of their ckit expression. We achieved a reproducible erythroid differentiation by culturing hAFSCs as embryoid bodies (EBs) under serum free conditions with haematopoietic cytokines. Erythroid cells expressing CD235a constituted 70% of the total hAFSCs forming EBs showing also a co-expression of CD36 and CD71. Furthermore, human erythrocytes (human CD235a) were isolated from bone marrow and spleen of sublethally irradiated NOD/SCID mice at 3 months after the injection of hAFSCs. To determine if the expansion procedure had led to a restriction of the hematopoietic potential towards the erythroid pathway, we compared expanded AFSCs and freshly isolated cKit+ Lin- (AFKL) cells. We also harvested cKit+ Lin- KL cells from the membrane surrounding the AF, the Amnion, in search for a possible origin. We compared the hematopoietic potential of mAFKL and mAmKL to Fetal Liver KL, the main source of fetal HSC. When cultivated immediatly after their sorting, freshly isolated murine AFKL and AmKL cells gave rise to all the different hematopoietic lineages both in vitro and in vivo. Actually, when cocultivated with OP9(d)1 cells, AFKL and AmKL undergo complete T cell differentiation within 2 weeks. They also generate myeloid and erythroid colonies when cultivated in methylcellulose for clonogenic assay. The erythroid restricted potential of human AFS cells was thus probably linked to the in vitro expansion procedure. Moreover, cells belonging to all the three hematopoietic lineages (lymphoid, myeloid and erythroid) and arising from freshly isolated mAFKL and mAmKL are found in the peripheral blood of sublethally irradiated RAG1 deficient mice only 4 weeks after transplantation. Four month later, transplanted mice showed mAFKL-derived lymphoid, myeloid and erythroid cells, in all the hematopoietic organs. Successful econdary transplantation strongly suggest that mAFKL and mAmKL comprise HSC, with self-renewal ability. Those results were very similar to those obtained with mFLKL, confirming the strong hematopoietic potential of mAFKL and mAmKL. Experiments with freshly isolated hAFKL gave good results in the in vitro assays being able to give rise to erythroid, myeloid and lymphoid lineages, but failed to reconstitute the hematopoietic system in irradiated NOD/SCID mice, probably due to the poor amount of cells injected. This is the first report demonstrating that AFKL and AmKL do have an haematopoietic potential, supporting the idea that AF and Am may be an excellent source for therapeutic application.