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Juvenile osteochondritis dissecans (JOCD) is a pediatric disease, which begins with an osteonecrotic lesion in the secondary ossification center which, over time, results in the separation of the necrotic fragment from the parent bone. JOCD predisposes to early-onset osteoarthritis. However, the knowledge gap in JOCD pathomechanisms severely limits current therapeutic strategies. To elucidate its etiology, we conducted a study with induced pluripotent stem cells (iPSCs) from JOCD and control patients. iPSCs from skin biopsies were differentiated to iMSCs (iPSC-derived mesenchymal stromal cells) and subjected to chondrogenic and endochondral ossification, and endoplasmic reticulum (ER)-stress induction assays. Our study, using 3 JOCD donors, showed that JOCD cells have lower chondrogenic capability and their endochondral ossification process differs from control cells; yet, JOCD- and control-cells accomplish osteogenesis of similar quality. Our findings show that endoplasmic reticulum stress sensing and response mechanisms in JOCD cells, which partially regulate chondrocyte and osteoblast differentiation, are related to these differences. We suggest that JOCD cells are more sensitive to ER stress than control cells, and in pathological microenvironments, such as microtrauma and micro-ischemia, JOCD pathogenesis pathways may be initiated. This study is the first, to the best of our knowledge, to realize the important role that resident cells and their differentiating counterparts play in JOCD and to put forth a novel etiological hypothesis that seeks to consolidate and explain previously postulated hypotheses. Furthermore, our results establish well-characterized JOCD-specific iPSC-derived in vitro models and identified potential targets which could be used to improve diagnostic tools and therapeutic strategies in JOCD.

Mesenchymal stromal cells (MSCs) are considered promising candidates for regenerative medicine applications. Their clinical performance post-implantation, however, has been disappointing. This lack of therapeutic efficacy is most likely due to suboptimal formulations of MSC-containing material constructs. Tissue engineers, therefore, have developed strategies addressing/incorporating optimized cell-, micro-environmental-, biochemical, - and biophysical- cues/stimuli to enhance MSC-containing construct performance. Such approaches have had limited success because they overlooked that maintenance of MSC viability after implantation for a sufficient time is necessary for MSCs to develop their regenerative functionalities fully. Following a brief overview of glucose metabolism and regulation in MSCs, the present literature review includes recent pertinent findings that challenge old paradigms and notions. We hereby report that glucose is the primary energy substrate for MSCs, provides precursors for biomass generation, and regulates MSC functions, including proliferation, differentiation, and immunosuppressive properties. More importantly, glucose metabolism is central in controlling

Osteoarthritis (OA) is a widespread disease that continues to lack approved and efficacious treatments that modify disease progression. Micronized dehydrated human amnion/chorion membrane (μ-dHACM) has been shown to be effective in reducing OA progression, but many of the engineering design parameters have not been explored. The objectives of this study were to characterize the particle size distributions of two μ-dHACM formulations and to investigate the influence of these distributions on the

Summary Objective To characterize local disease progression of the medial meniscus transection (MMT) model of post-traumatic osteoarthritis (OA) at the molecular level, in order to establish a baseline for therapeutic testing at the preclinical stage. Design Weight-matched male Lewis rats underwent MMT or sham surgery on the left limb with the right leg as contralateral control. At 1 and 3 weeks post-surgery, tissues were harvested from different areas of the articular cartilage (medial and lateral tibial plateaus, and medial osteophyte region) and synovium (medial and lateral), and analyzed separately. RNA was extracted and used for microarray (RT-PCR) analysis. Results Gene expression changes due to surgery were isolated to the medial side of the joint. Gene changes in chondrocyte phenotype of the medial tibial plateau cartilage preceded changes in tissue composition genes. Differences in inflammatory markers were only observed at the osteophyte region at 3 weeks post-surgery. There was surgical noise in the synovium at week 1, which dissipated at week 3. At this later timepoint, meniscal instability resulted in elevated expression of matrix degradation proteins and osteogenic markers in the synovium and cartilage. Conclusion These results suggest feedback interactions between joint tissues during disease progression. Regional tissue expression differences found in MMT joints indicated similar pathophysiology to human OA, and provided novel insights about this degeneration model. The examination of gene expression at a localized level in multiple tissues provides a well-characterized baseline to evaluate mechanistic effects of potential therapeutic agents on OA disease progression in the MMT model.

International audience; Repair and reconstruction of large bone defects remain a significant challenge. Cell construct, containing mesenchymal stem cells (MSCs) and scaffold, is a promising strategy for addressing and treating major orthopedic clinical conditions. However, the design of an ideal cell construct for engineering bone faces two critical challenges (i) matching the scaffold degradation rate to that of new bone formation and (ii) preventing the massive cell death post-implantation (caused by disruption of oxygen and nutrient supply). We will hereby primarily focus on the challenge of survival of MSCs post-implantation. Increasing evidence indicates that metabolic regulation plays a critical role in cell fate and functions. In cell metabolism, glucose is considered the major metabolic substrate to produce ATP via glycolysis when the availability of oxygen is limited. In this paper, we delineate the essential roles of glucose on MSC survival. We aim to provide a different perspective which highlights the importance of considering glucose in the development of tissue engineering strategies in order to improve the efficiency of MSC-based cell constructs in the repair of large bone defects.

International audience; In tissue engineering and regenerative medicine, stem cell-specifically, mesenchymal stromal/stem cells (MSCs)-therapies have fallen short of their initial promise and hype. The observed marginal, to no benefit, success in several applications has been attributed primarily to poor cell survival and engraftment at transplantation sites. MSCs have a metabolism that is flexible enough to enable them to fulfill their various cellular functions and remarkably sensitive to different cellular and environmental cues. At the transplantation sites, MSCs experience hostile environments devoid or, at the very least, severely depleted of oxygen and nutrients. The impact of this particular setting on MSC metabolism ultimately affects their survival and function. In order to develop the next generation of cell-delivery materials and methods, scientists must have a better understanding of the metabolic switches MSCs experience upon transplantation. By designing treatment strategies with cell metabolism in mind, scientists may improve survival and the overall therapeutic potential of MSCs. Here, we provide a comprehensive review of plausible metabolic switches in response to implantation and of the various strategies currently used to leverage MSC metabolism to improve stem cell-based therapeutics. Significance statement: Lack of success of stem cell-based therapies has been largely attributed to the massive cell death observed post-transplantation, which is caused by the metabolic shock these cells experience as they transition from in vitro to a hostile, injured site in vivo. The metabolism in mesenchymal stem cells (MSCs), specifically, is highly sensitive to cellular and environmental cues. In order to improve cell survival rate posttransplantation, it is important that scientists understand, and take into account, the needs and demands of MSC metabolism as they design the next generation of MSC-based therapies.

Disease-specific pluripotent stem cells can be derived through genetic manipulation of embryonic stem cells or by reprogramming somatic cells (induced pluripotent stem cells). These cells are a valuable tool to study human diseases in vitro in order to dissect their pathomechanisms and develop novel therapeutics. Although pluripotent stem cell-derived models have successfully recapitulated the abnormalities of some skeletal diseases in vitro, this field is still at its early stages, and it could greatly benefit from the direct application of biomaterial research. Biomaterial-based systems may be utilized to enhance the differentiation processes of pluripotent stem cells in order to create more homogeneous and physiologically relevant in vitro disease models. Moreover, inducing the disease phenotype may be facilitated by the guidance of biomaterials. This review presents a comprehensive summary of existing biomaterial applications in human disease modeling and their potential on skeletal disease models. By utilizing disease-specific pluripotent stem cells, current biomaterial-based systems for in vitro models could be extrapolated to study skeletal diseases in a petri dish.

Characterization of articular cartilage morphology and composition using microcomputed tomography (microCT) techniques requires the use of contrast agents to enhance X-ray attenuation of the tissue. This chapter describes the use of an anionic iodinated contrast agent at equilibrium with articular cartilage. In this technique, negatively charged contrast agent molecules distribute themselves inversely with respect to the negatively charged proteoglycans (PGs) within the cartilage tissue (Palmer et al. Proc Natl Acad Sci U S A 103:19255-19260, 2006). This relationship allows for assessment of cartilage degradation, as areas of high X-ray attenuation have been shown to correspond to areas of depleted PGs (Palmer et al. Proc Natl Acad Sci U S A 103:19255-19260, 2006; Xie et al. Osteoarthritis Cartilage 18:65-72, 2010).

Characterization of articular cartilage morphology and composition using microcomputed tomography (microCT) techniques requires the use of contrast agents to enhance X-ray attenuation of the tissue. This chapter describes the use of an anionic iodinated contrast agent at equilibrium with articular cartilage. In this technique, negatively charged contrast agent molecules distribute themselves inversely with respect to the negatively charged proteoglycans (PGs) within the cartilage tissue (Palmer et al. Proc Natl Acad Sci U S A 103:19255-19260, 2006). This relationship allows for assessment of cartilage degradation, as areas of high X-ray attenuation have been shown to correspond to areas of depleted PGs (Palmer et al. Proc Natl Acad Sci U S A 103:19255-19260, 2006; Xie et al. Osteoarthritis Cartilage 18:65-72, 2010).