Dissertationen zum Thema „Bones Pathophysiology“

Includes bibliographical references (leaves 226-273.) Investigates the regulation of the expression of CYP27B1, CYP24 and vitamin D receptor (VDR) mRNA, both in the bone and in the kidney, with the aim to determine whether the regulation of the vitamin D metabolism in the bone is independent from that in the kidney. The effects of age, dietary calcium and vitamin D status on the expression of these genes in both the kidney and the bone, as well as on a number of biochemical factors known to regulate the renal metabolism of 1,25D, such as PTH, calcium and 1,25D itself, were examined. CYP27B1 mRNA expression was also studied in histological sections of rat femoral bone.

To enhance our understanding of the pathophysiology of bone disease associated with liver transplantation and of the mechanisms underlying bone loss in the three month period following transplantation, this prospective study was undertaken as follows: (1) bone pathophysiology was evaluated pre- and three months post-transplantation in transiliac biopsies using tetracycline-assisted histomorphometry; (2) cellular activities of bone formation and resorption pre- and post- transplantation were studied using quantitative enzyme cytochemistry in combination with histomorphometric methods; (3) cellular activities for markers of bone energy metabolism and biosynthesis and/or cell proliferation were investigated using quantitative enzyme cytochemistry; (4) plasma markers for bone metabolism were investigated at regular intervals in collaboration with other laboratories. It was concluded from this study that rapid bone loss early after transplantation is due both to increased bone turnover and a negative remodelling balance at the individual bone remodelling site. These changes were at least partially mediated by increased PTH levels secondary to a negative balance in plasma calcium. Cyclosporin A is known to increase intracellular calcium levels and inhibit calcium release from mitochondria. It also reduces glomerular filtration rate which could be sufficient to depress extracellular calcium levels and thereby cause the observed rise in PTH levels. The consequences of this for post transplant bone remodelling is a markedly enhanced risk of osteoporosis in these patients. Ensuring replete calcium and vitamin D levels pre-transplantation and supplementation of cyclosporin A treatment with vitamin D metabolites and calcium post-transplantation followed by careful monitoring of plasma calcium concentrations might offer a better overall outcome for preventing transplantation-associated osteoporosis at this early stage post transplantation.

One of the most common complications of fibrous dysplasia of bone (FD) is bone pain. Usual pain killers are often of inadequate efficacy to control this bone pain. The mechanism of bone pain in FD remains uncertain, but by analogy with bone tumors one may consider that ectopic sprouting and formation of neuroma-like structures by sensory and sympathetic nerve fibers also occur in the dysplastic skeleton. Bone pain has been reported in up to 81% of adults and 49% of children. It affects predominantly the lower limbs and the spine. The degree of pain is highly variable and adults reports more pain than children. Bisphosphonates have been shown to reduce bone pain in uncontrolled studies. Their influence on bone strength remains unknown. In a randomized trial testing alendronate, bone pain was not significantly improved. Another trial assessing the effect of risedronate is ongoing. Possible future therapies include tocilizumab, denosumab and drugs targeting nerve growth factor and its receptor TrkA.

Cysteine rich with EGF-like domains 2 (Creld2) is a novel endoplasmic reticulum (ER) resident molecular chaperone that has been recently implicated in the ER stress signalling response (ERSS) and the unfolded protein response (UPR). Global transcriptomic data derived from in vivo mouse models of rare chondrodysplasias; Multiple Epiphyseal Dysplasia (MED Matn3 p.V194D) and Metaphyseal chondrodysplasia type Schmid (MCDS Col10a1 p.N617K), identified a significant upregulation in Creld2 expression in mutant chondrocytes. These chondrodysplasias share a common disease signature consisting of aberrant folding of a matrix component often as a result of inappropriate alignment of intramolecular disulphide bonds. This in turn culminates in toxic protein aggregation, intracellular retention mutant polypeptides and a classical ER stress response. The aim of this study was to further analyse the function of Creld2 in cartilage development and chondrodysplasias in which endochondral bone growth is perturbed. Protein disulphide isomerases (PDIAs) were amongst the most up-regulated genes in the MED and MCDS mouse models, consistent with the prolonged exposure of normally 'buried' cysteine residues. This led to the hypothesis that Creld2 was functioning as a novel PDI-like oxidoreductase to assist in the correct folding and maturation of aggregated misfolded polypeptide chains through REDOX regulated thiol disulphide exchange. A series of Creld2-CXXA substrate trapping mutants were generated in order to determine whether Creld2 possessed inherent isomerase activity. Here potential substrates interacting with Creld2 were 'trapped' as mixed disulphide intermediates, then isolated by immunoprecipitation and identified by mass spectrometry analysis. It was demonstrated that Creld2 possessed a catalytic active CXXC motif in its N-terminus that enabled the molecular chaperone to participate in REDOX regulated thiol disulphide exchange with at least 20 potential substrates including; laminin (alpha3,β3,γ2), thrombospondin 1, integrin alpha3 and type VI collagen. There was also numerous co-chaperones and foldases thought to be part of a specialised protein-protein interactome (PPI) for folding nascent polypeptides translocating the ER lumen. Moreover, co-immunoprecipitation experiments supported a protein-protein interaction between Creld2 and mutant matrilin-3, thereby inferring a potential chondro-protective role in resolving non-native disulphide bonded aggregates in MED. An established biochemical approach was employed to test the hypothesis that all MATN3-MED disease causing mutations have a generic cellular response to the β-sheet V194D mutation, consisting of intracellular retention, protein aggregation and ER stress induction. Several missense mutations were selected for analyses which encompassed a spectrum of disease severity and included examples of both β-sheet and alpha helical mutations. It was possible to define a reliable and reproducible assay for categorising MATN3 missense mutations into pathological or benign based on these basic parameters. This study was extended further to determine whether there were common pathological mechanisms behind MED and Bethlem myopathy (BM) caused by missense mutations in von Willebrand Factor A domain (vWF-A) containing proteins (matrilin-3 and type VI collagen respectively). We chose to compare and contrast the effects of an archetypal MATN3-MED causing mutation (R121W) with the equivalent COL6A2-BM causing mutation (R876H). These mutations compromised protein folding and maturation, resulting in the familiar disease profile of intracellular retention, protein aggregation and an ER stress response in an artificial overexpression system. However, the mutant C2 domain was efficiently targeted for degradation whilst mutant matrilin-3 vWF-A domain appeared to be resistant to these molecular processes.Molecular genetics was employed to study the role of Creld2 in vivo. Creld2-/- null mice (both global and conditional) were generated to directly examine the role of Creld2 in endochondral bone growth. Global knock-out mice were viable with no overt phenotype at birth. However, female Creld2-/- null mice showed a significant reduction in body weight and tibia bone length at 3 weeks of age. A cartilage specific knock-out was generated to determine whether these skeletal abnormalities were attributed to a systemic or a direct effect on cartilage development. [Creld2Flox/Flox Col2Cre (+)] demonstrated a severe chondrodysplasia with significantly reduced body weight and long bone growth compared to control littermates. Morphological and histochemical analysis of mutant growth plates revealed gross disorganisation of the chondrocyte columns with extensive regions of hypocellularity. These pathological features were confirmed to be the result of reduced chondrocyte proliferation and increased/spatially dysregulated apoptosis throughout all zones of differentiation. Taken together, these data provide evidence that Creld2 possesses isomerase activity and exhibits distinct substrate specificity. Furthermore, Creld2 has a fundamental role in post-natal cartilage development and chondrocyte differentiation in the growth plate.

Vascular calcification (VC) is an important complication of chronic renal failure (CRF), and a risk factor for reduced survival. Osteoblast-like cells in the vessel wall derived from resident vascular smooth muscle cells (VSMC) are considered central to the pathogenesis of VC, which is exacerbated by mineral ion abnormalities inherent in renal osteodystrophy (ROD). Nevertheless, its aetiology is incompletely understood, and no effective therapies exist. Recently, CRF has been characterised as a state of Bone Morphogenetic Protein 7 (BMP7) deficiency, and animal studies have shown that administration of this renal morphogen is efficacious in treating several aspects of renal failure, including progressive renal fibrosis and ROD. The hypothesis of this thesis is that BMP7 deficiency contributes to the pathogenesis of VC, by facilitating the emergence of the osteoblast-like cell, and that exogenous BMP7 administration abrogates it by normalising VSMC behaviour. This hypothesis was tested in atherosclerotic Low Density Lipoprotein Receptor Null (ldlf/j) mice. Uraemia was superimposed surgically to generate VC. Animals received BMP7 or vehicle over 15 weeks. Untreated uraemic animals had increased VC on histological and chemical grounds, and demonstrated increased expression of the characteristic osteoblast protein osteocalcin was demonstrated in vascular tissues. Both changes were reversed by BMP7 administration. Uraemic animals were shown to have an adynamic form of ROD, also reversed by BMP7 administration, suggesting that normalisation of mineral ion abnormalities may underlie the benefits of BMP7 on VC in CRF. In addition, in vitro studies showed that BMP7 can act directly on vascular cells to reduce extracellular calcification under conducive conditions. Finally, in an appendix, preliminary data is presented showing that expression of LRP5, a protein involved in the control of normal bone mineralization, may be increased in Idlf1 animals, suggesting that consequences of this genotype may be important to VC pathogenesis in this model.

This is an original study to quantify and grade defect healing in a large animal cranial bone substitute model. The study of various therapies to heal cranial defects requires an appropriate ?critical? animal model. An experimental animal model should be analogous and recognizable as an appropriate challenge to human physiology. In addition, the defect must fail to heal unless treated with the tissue engineering therapy under study. Sheep as a large animal model was chosen because of its ability to tolerate creation of large skull defects analogous to clinical scenario, and its biology of healing as a high order mammal would be closer human beings. There is no agreement on the critical size limits for cranial defects. Various sizes have been termed "critical" in publications utilizing sheep. These ranged from 20-22mm. This study will investigate whether a 20mm defect is adequate. Bilateral circular cranial defects of 10, 20 and 25mm diameters were created in 12 adult sheep. Based on guided tissue engineering principles, defect protection was utilized to prevent in-growth of fibroblasts and other connective tissue cells from the surroundings. As bone tissue regeneration strategies usually involve osteoconduction element, an animal model that considered the defect protection role of osteoconduction would be more appropriate. Repopulation and regeneration of the defect was maximized as an added challenge Bioresorbable polylactic acid co-polymer mesh (MacroPoreTM) and Titanium mesh (TiMeshTM) was used as defect protection. The cranial defects were harvested at 8 and 16 weeks. The end-point analysis included Faxitron X-ray images, DEXA (Dual Energy X-ray Absorptiometry), and histology. The defects were graded to assess their ability to eventually heal. 10mm defects fully healed at 16 weeks. There was new bone formation spanning the entire defect seen on histology. 25mm defects were spanned by thin fibrous tissue only. There was variability in the healing potential of 20mm defect. Based on presence of bone islands within the defect, half of the 20mm defects demonstrated ability to heal while the other half actually had new bone spanning the defects on histology. Critical size cranial defect in sheep for the study of bone graft substitute has to be larger than 25mm diameter. The model is then utilized to study the use of Pro Osteon and AGF compared with the gold standard of autologous bone graft.

Indiana University-Purdue University Indianapolis (IUPUI)
Bone is a dynamic tissue that is constantly remodeling to repair damage and strengthen regions exposed to loads during everyday activities. However, certain conditions, including long-term unloading of the skeleton, hormonal imbalances, and aging can disrupt the normal bone remodeling cycle and lead to low bone mass and osteoporosis, increasing risk of fracture. While numerous treatments for low bone mass have been devised, dynamic mechanical loading modalities, such as axial loading of long bones and lateral loading of joints, have recently been examined as potential methods of stimulating bone formation. The effectiveness of mechanical loading in strengthening bone is dependent both on the structural and geometric characteristics of the bone and the properties of the applied load. For instance, curvature in the structure of a bone causes bending and increased strain in response to an axial load, which may contribute to increased bone formation. In addition, frequency of the applied load has been determined to impact the degree of new bone formation; however, the mechanism behind this relationship remains unknown. In this thesis, the application of mechanical loading to treat osteoporotic conditions is examined and two questions are addressed: What role does the structural geometry of bone play in the mechanical damping of forces applied during loading? Does mechanical resonance enhance geometric effects, leading to localized areas of elevated bone formation dependent on loading frequency? Curvature in the structure of bone was hypothesized to enhance its damping ability and lead to increased bone formation through bending. In addition, loading at frequencies near the resonant frequencies of bone was predicted to cause increased bone formation, specifically in areas that experienced high principal strains due to localized displacements during resonant vibration. To test the hypothesis, mechanical loading experiments and simulations using finite element (FE) analysis were conducted to characterize the dynamic properties of bone. Results demonstrate that while surrounding joints contribute to the greatest portion of the damping capacity of the lower limb, bone absorbs a significant amount of energy through curvature-driven bending. In addition, results show that enhanced mechanical responses at loading frequencies near the resonant frequencies of bone may lead to increased bone formation in areas that experience the greatest principal strain during vibration. These findings demonstrate the potential therapeutic effects of mechanical loading in preventing costly osteoporotic fractures, and explore characteristics of bone that may lead to optimization of mechanical loading techniques. Further investigation of biomechanical properties of bone may lead to the prescribing of personalized mechanical loading treatments to treat osteoporotic diseases.

Indiana University-Purdue University Indianapolis (IUPUI)
Mechanical loading associated with exercise is known to benefit bone health; however, most studies explore exercise benefits on bone mass independent of bone structure and strength. The purpose of this dissertation is to explore the response of the skeleton to exercise across the translational divide between animal- and human-based studies, with a particular emphasis on exercise-induced changes in bone structure and estimated strength. To explore the skeletal benefits of exercise, models were used wherein loading is introduced unilaterally to one extremity. Unilateral exercise enables the contralateral, non-exercised extremity to be used as an internal control site for the influences of systemic factors, such as genetics and circulating hormones. In study 1, a dose response between load magnitude and tibial midshaft cortical bone adaptation was observed in mice that had their right tibia loaded in axial compression at one of three load magnitudes for 3 d/wk over 4 weeks. In study 2, the ability of peripheral quantitative computed tomography to provide very good prediction of midshaft humerus mechanical properties with good short-term precision in human subjects was demonstrated. In study 3, collegiate-level jumping (long and/or high jump) athletes were shown to have larger side-to-side differences in tibial midshaft structure and estimated strength between their jump and lead legs than observed in non-jumping athletes. In study 4, prepubertal baseball players followed for 12 months were shown to gain more bone mass, structure and estimated strength in their throwing arm relative to their nonthrowing arm over the course of 12 months. These cumulative data using a combination of experimental models ranging from animal to cross-sectional and longitudinal human models demonstrate the ability of the skeleton to adapt its structure and estimated strength to the mechanical loading associated with exercise. Study of these models in future work may aid in optimizing skeletal responses to exercise.

Indiana University-Purdue University Indianapolis (IUPUI)
Skeletal manifestations including short stature, osteoporosis, kyphoscoliosis, and tibial dysplasia cumulatively affect approximately 70% of patients with neurofibromatosis type 1 (NF1). Tibial pseudarthrosis, the chronic non-union of a spontaneous fracture, is a debilitating skeletal malady affecting young children with NF1. These non-healing fractures respond poorly to treatment and often require amputation of the affected limb due to limited understanding of the causative mechanisms. To better understand the cellular and molecular pathogenesis of these osseous defects, we have established a new mouse model which recapitulates a spectrum of skeletal pathologies frequently observed in patients with NF1. Nf1flox/-;Col2.3Cre mice, harboring Nf1 nullizygous osteoblasts on a Nf1+/- background, exhibit multiple osseous defects which are closely reminiscent of those found in NF1 patients, including runting (short stature), bone mass deficits, spinal deformities, and tibial fracture non-union. Through adoptive bone marrow transfer studies, we have demonstrated that the Nf1 haploinsufficient hematopoietic system pivotally mediates the pathogenesis of bone loss and fracture non-union in Nf1flox/-;Col2.3Cre mice. By genetic ablation of a single Nf1 allele in early myeloid development, under the control of LysMCre, we have further delineated that Nf1 haploinsufficient myeloid progenitors and osteoclasts are the culprit lineages mediating accelerated bone loss. Interestingly, conditional Nf1 haploinsufficiency in mature osteoclasts, induced by CtskCre, was insufficient to trigger enhanced lytic activity. These data provide direct genetic evidence for Nf1’s temporal significance as a gatekeeper of the osteoclast progenitor pool in primitive myelopoiesis. On the molecular level, we found that transforming growth factor-beta1 (TGF-β1), a primary mediator in the spatiotemporal coupling of bone remodeling, is pathologically overexpressed by five- to six- fold in both NF1 patients and in mice. Nf1 deficient osteoblasts, the principal source of TGF-β1 in the bone matrix, overexpress TGF-β1 in a gene dosage dependent fashion. Moreover, p21Ras dependent hyperactivation of the Smad pathway accentuates responses to pathological TGF-β1 signals in Nf1 deficient bone cells. As a proof of concept, we demonstrate that pharmacologic TβRI kinase inhibition can rescue bone mass defects and prevent tibial fracture non-union in Nf1flox/-;Col2.3Cre mice, suggesting that targeting TGF-β1 signaling in myeloid lineages may provide therapeutic benefit for treating NF1 skeletal defects.

Includes articles co-authored by the author during the preparation of this thesis.
Includes erratum on back leaf.
Includes bibliographical references (leaves 257-299).
xvii, 300 [27] leaves : ill. (some col.) ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Examines regional variations in trabecular bone remodelling and bone loss following oophorectomy in the distal femur of the rat. The studies reveal a complex interaction between weight bearing and ovarian hormone deficiency, and show that physiological signals exist which can negate all adverse effects of postmenopausal osteoporosis
Thesis (Ph.D.)--Adelaide University, Dept. of Physiology, 2001

Trabalho final de mestrado integrado em Medicina (Hematologia), apresentado à Faculdade de Medicina da Universidade de Coimbra.
Aplastic anemia (AA) is a rare hematopoietic disease characterized by a pancytopenia and a hypoplastic bone marrow. AA can be congenital (CAA) or acquired (AAA). Acquired AA comprises those cases where a causative factor is identified (Secondary AA) and also idiopathic cases (Idiopathic AA). There was a marked improvement on treatment options in the last years that had resulted on increased overall survival rates. It is known that a correct management of this entity is directly related with an efficient diagnostic investigation, and for that, it is fundamental to be aware of the most effective strategies or techniques available nowadays. Therefore, the aim of this review is to make a state of art of the most recent available data concerning this disorder, particularly IAA, including all the sub-topics inherent: etiology, pathophysiology mechanisms, differential diagnosis, management and treatment options.
A Anemia Aplásica (AA) é uma doença hematopoiética rara caracterizada por pancitopenia e hipocelularidade da medula óssea. A AA pode ser congénita ou adquirida. A AA Adquirida inclui os casos em que é possível identificar um fator causal (AA Secundária) e também os casos idiopáticos (AA Idiopática). Nos últimos anos tem havido uma melhoria notável nas opções de tratamento o que tem conduzido a melhores taxas de sobrevivência. É também um facto estabelecido que uma orientação clínica correta está diretamente relacionada com uma investigação diagnóstica eficiente, o que por sua vez exige um conhecimento sobre as estratégias e técnicas mais eficazes disponíveis na atualidade. O objetivo desta revisão é fazer um estado da arte das publicações e dados mais recentes relacionados com esta doença, especificamente em relação à Anemia Aplásica Idiopática, incluindo assim todos os subtópicos inerentes: etiologia, mecanismos fisiopatológicos, diagnóstico diferencial, conduta e opções de tratamento.

Tese de Doutoramento em Ciências Veterinárias
Os biomarcadores de remodelagem óssea (BTM) são produtos da actividade celular e são geralmente subdivididos em três categorias: biomarcadores de reabsorção óssea, formação óssea e proteínas reguladoras da actividade dos osteoclastos. Em vários estudos foi demonstrado que s BTM são capazes de reflectir o processo de cicatrização óssea, com os seus níveis dependentes da localização, tamanho e tipo da fractura. Além disso, a variação dos seus níveis tem, também, sido avaliada por alguns autores quanto à sua capacidade de prever precocemente o processo de cicatrização prejudicada. O principal objetivo deste trabalho consistiu em investigar a eficácia clínica de BTM para acompanhar a evolução do processo de cicatrização de fraturas ósseas após eventos traumáticos e identificar precocemente doentes em risco de processos de cicatrização prejudicado. Com isto em mente, o objectivo principal deste trabalho foi investigar a eficácia clínica dos BTM para monitorizar o processo de cicatrização das fracturas de etiologia traumática e identificar os doentes em risco de desenvolvimento de processos de cicatrização comprometida. Este trabalho teve, também, como objetivo adicional avaliar se um painel económico de marcadores bioquímicos de remodelação óssea se poderia apresentar como um método simples, acessível e preciso no seguimento do processo de consolidação das fracturas ósseas de etiologia traumática. A fim de alcançar o objectivo proposto, numa primeira fase, um modelo animal de nãounião foi criado através da realização de um de defeito crítico na diáfise da tíbia da ovelha e foi comparada a evolução serológica dos BTM neste grupo com outro grupo de animais com um processo de consolidação de fraturas em que se previa uma normal evolução no sentido de uma completa cicatrização ao longo de doze semanas. As ovelhas têm sido amplamente utilizadas em estudos científicos na Ciência Animal e Veterinária e também como um animal de grande porte para a investigação em Ortopedia, envolvendo a determinação de marcadores bioquímicos de remodelação óssea. Um dos marcadores de formação óssea mais amplamente utilizado e mais sensível é a isoforma óssea da fosfatase alcalina (BALP). Tendo isto em mente, este trabalho pretendeu, adicionalmente, avaliar se a actividade da BALP poderia reflectir o aumento da atividade osteoblástica de formação óssea durante o normal crescimento e durante os diferentes estádios fisiológicos da ovelha, a fim de melhorar o conhecimento sobre a variação deste marcador bioquímico ao longo da vida da ovelha como modelo animal. Em resumo, este trabalho demonstrou que a alta variabilidade subjacente aos marcadores bioquímicos de remodelação óssea limita a sua aplicação por rotina na prática clínica. No entanto, estes marcadores podem ser usados como ferramentas sensíveis em estudos experimentais, uma vez que proporcionam informação não invasiva sobre o processo de remodelação óssea, numa abordagem em tempo real. Adicionalmente, uma vez que a remodelação óssea é um processo dinâmico, as mudanças nos níveis séricos destes marcadores ocorrem mais cedo do que aquelas observadas pelas diferentes técnicas de imagem utilizadas para avaliar este processo, tais como os raios X simples ou as técnicas de densitometria óssea.
Bone turnover markers (BTM) are products of bone cells activity and are generally subdivided into three categories: bone resorption and bone formation markers and osteoclasts regulatory proteins. In several studies were demonstrated that serum or urinary BTM are capable to reflect the healing process with their levels being dependent on the localization, type and size of the fracture. Additionally, the variation in the levels of BTM has, also, been assessed by some authors for their ability to early predict impaired fracture healing processes, but the conclusions are not consensual. The main goal of this work was to investigate the clinical effectiveness of BTM to monitor the evolution of fracture healing process after traumatic events and to precociously identify patients at risk of development impaired healing processes. With this in mind, the present work aimed to achieve the value of BTM to assess the fracture healing process. In order to achieve the proposed objective, in a first stage, a non-union animal model was created through the realization of a critical size-defect in the diaphysis of sheep tibia and compared the serological evolution of BTM in this group with another group of animals with a normall fracture healing process during twelve week period. Sheep have been used in several animal science studies and also as a large animal for orthopedic research also involving measurements of BTM. One of the most widely used biomarker of bone formation is a membrane-bound enzyme - BALP. Additionally, BALP is, also, one of the most sensitive markers of bone formation. With this in mind, this work aimed to assess if BALP activity could mirror the increase in osteoblastic activity during normal growth and during different physiologic status over sheep lifespan, in order to improve the knowledge about the variation of these biomarkers. In summary, this work demonstrated that the high variability of BTM limits its routine application into the clinical practice. However, these bone markers can be used as valuable tools in experimental studies, since they provide non-invasive information about bone remodeling process in a real-time approach. Additionally, since bone turnover is a dynamic process, the changes in BTM levels occur earlier than those observed by the different techniques used to assess this process, namely plain X-rays and bone densitometry techniques.
The research described in this Thesis was financially supported by the Portuguese Foundation for Science and Technology (FCT)

Chronic patellar tendinopathy is a degenerative tendon disorder characterized by chronic activity-related, anterior knee pain associated with localized tenderness, swelling and impaired performance, which is a common clinical problem in athletes. The pathogenesis of patellar tendinopathy is still largely unknown, although tendon overuse is the most commonly suggested etiological factor, and treatment is usually symptomatic.
Histopathologically, the predominant feature of patellar tendinopathy is tendinosis, which is characterized by progressive tissue degeneration with a failed healing response and the absence of inflammatory cells. Hypercellularity with non-tenocyte phenotype cells and tissue metaplasia, including hyaline metaplasia, fibrocartilaginous metaplasia and bony metaplasia were observed in clinical patellar tendinopathy samples. The degeneration of patellar tendon in patellar tendinopathy is an active cell-mediated process rather than a passive degenerative process. Using a patellar tendinopathy animal model, we observed the presence of chondrocytic and osteoblastic phenotype / markers in patellar tendinopathy samples with or without ossification, which was consistent with the findings in clinical samples. Interestingly, chondrocyte makers were expressed by healing tendon cells at week 2 which became round prior to their expression in the chondrocyte-like cells at week 4. This leads us to speculate that erroneous differentiation of tendon-derived stem cells (TDSCs) identified recently in tendon tissues by our group, to chondrocyte / osteoblasts, due to alteration of mechanical and biological microenvironment during overuse, may lead to the ectopic chondro-ossification and failed healing in patellar tendinopathy. Osteo-chondrogenic BMPs, such as BMP-2, BMP-4 and BMP-7 might be possible factors regulating the osteo-chondrogenic differentiation of TDSCs in the pathogenesis of patellar tendinopathy.
In conclusion, our results have provided new insights about the pathological mechanisms of patellar tendinopathy involving the resident stem cells, osteo-chondrogenic BMPs and mechanical overloading. Erroneous differentiation of TDSCs to chondrocytes / osteoblasts due to ectopic osteo-chondrogenic BMP-2 expression, which were induced by repetitive tensile loading stimulation, might account for the chondro-ossification and failed healing in patellar tendinopathy. Re-directing of stem cells for tenogenic differentiation by blocking the ectopic expression of osteo-chondrogenic BMPs may help to promote tendon healing in patellar tendinoapthy.
In this study, we hypothesized that (1) TDSCs isolated from pathological patellar tendon of the CI model will exhibit higher osteogenic and chondrogenic differentiation potential but lower proliferative capacity compared to TDSCs isolated from healthy patellar tendon. Rat pathological tendon in our collagenase-induced failed healing animal model will harbor more TDSCs compared to healthy patellar tendon. (2) Osteo-chondrogenic BMPs, such as BMP-2, BMP-4, and BMP-7, will be expressed ectopically in both preclinical and clinical samples of patellar tendinopathy. (3) BMP-2 will promote osteo-chondrogenic differentiation and inhibit tenogenic differentiation of TDSCs in vitro. (4) Repetitive tensile loading will increase the expression of BMP-2 in TDSCs in vitro.
Our results showed that TDSCs isolated from the collagenase-induced tendinopathic patellar tendon of the animal model exhibited higher osteogenic/chondrogenic differentiation potential as well as lower proliferative capacity, supporting that there might be some defects in the TDSCs from the animal model, which might undergo osteo-chondrogenic differentiation and hence reduced the pool of TDSCs for tendon repair in the development of patellar tendinopathy. The higher clonogenicity and increased yield of TDSCs in tendinopathic patellar tendon might be caused by a compensation for the impaired differentiation potential and proliferative capacity of TDSCs. The histopathological features of our clinical patellar tendinopathy were characterized by tissue degeneration. Non-tenocyte phenotype cells and tissue metaplasia, such as chondrocyte-like cells and endochondral ossification were also observed. We observed the ectopic expression of osteo-chondrogenic BMP-2, BMP-4 and BMP-7 in both our animal model and clinical samples of patellar tendinopathy, which might trigger the erroneous differentiation of TDSCs to non-tenocytes. Indeed, we further showed that BMP-2 could promote the osteo-chondrogenic and inhibit tenogenic differentiation of TDSCs in vitro, which might provide a possible explanation for ectopic chondro-ossification and failed healing in patellar tendinopathy. In addition, our results also showed that in vitro repetitive cyclic tensile loading could increase the expression of BMP-2 in TDSCs, which might provide a possible explanation for the ectopic expression of BMP-2 in patellar tendinopathy.
This study aimed to compare the osteogenic / chondrogenic differentiation potential, proliferative capacity and yield of TDSCs isolated from rat healthy patellar tendon and pathological tendon in our collagenase-induced failed tendon healing animal model of patellar tendinopathy in vitro. The histopathological characteristics of our clinical patellar tendinopathy with or without ossification were examined. The ectopic expression of BMP-2, BMP-4, and BMP-7 in both human and rat samples of patellar tendinopathy was also examined. The effects of BMP-2 on the osteogenic, chondrogenic and tenogenic differentiation of TDSCs was further investigated in vitro. The effect of repetitive tensile loading on the expression of BMP-2 in TDSCs was studied in vitro.
Rui, Yunfeng.
Advisers: Kai Ming Chan; Po Yee Lui.
Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: .
Thesis (Ph.D.)--Chinese University of Hong Kong, 2011.
Includes bibliographical references (leaves 172-193).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.

Indiana University-Purdue University Indianapolis (IUPUI)
Reactive gliosis is known to have a beneficial and a degenerative effect following injury to neurons. Although many factors have been implicated in reactive gliosis, their role in regulating this change is still unclear. We investigated the role of bone morphogenetic proteins in reactive gliosis in vivo and in vitro. In vivo, IHC analysis indicated reactive gliosis in the 6 week Ins2Akita mouse and WPK rat retinas. Expression of BMP7 was upregulated in these models, leading to an increase in the phosphorylation of downstream SMAD1. In vitro, treatment of murine retinal astrocyte cells with a strong oxidizing agent such as sodium peroxynitrite regulated RNA levels of various markers, including GFAP, CSPGs, MMPs and TIMPs. BMP7 treatment also regulated RNA levels to a similar extent, suggesting reactive gliosis. Treatment with high glucose DMEM and BMP4, however, did not elicit increase in levels to a similar degree. Increase in SMAD levels and downstream targets of SMAD signaling such as ID1, ID3 and MSX2 was also observed following treatment with sodium peroxynitrite in vitro and in the 6 week Ins2Akita mouse retinas in vivo. These data concur with previously established data which show an increase in BMP7 levels following injury. It also demonstrates a role for BMP7 in gliosis following disease. Further, it suggests SMAD signaling to play a role in initiating reactivity in astrocytes as well as in remodeling the extracellular matrix following injury and in a disease condition.