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Hypertrophic Differentiation (hypertrophic + differentiation)
Selected AbstractsInactivation of Pten in Osteo-Chondroprogenitor Cells Leads to Epiphyseal Growth Plate Abnormalities and Skeletal Overgrowth,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 8 2007Alice Fiona Ford-Hutchinson Abstract To study the role of the Pten tumor suppressor in skeletogenesis, we generated mice lacking this key phosphatidylinositol 3,-kinase pathway regulator in their osteo-chondroprogenitors. A phenotype of growth plate dysfunction and skeletal overgrowth was observed. Introduction: Skeletogenesis is a complex process relying on a variety of ligands that activate a range of intracellular signal transduction pathways. Although many of these stimuli are known to activate phosphatidylinositol 3,-kinase (PI3K), the function of this pathway during cartilage development remains nebulous. To study the role of PI3K during skeletogenesis, we used mice deficient in a negative regulator of PI3K signaling, the tumor suppressor, Pten. Materials and Methods:Pten gene deletion in osteo-chondrodroprogenitors was obtained by interbreeding mice with loxP-flanked Pten exons with mice expressing the Cre recombinase under the control of the type II collagen gene promoter (Ptenflox/flox:Col2a1Cre mice). Phenotypic analyses included microcomputed tomography and immunohistochemistry techniques. Results: ,CT revealed that Ptenflox/flox:Col2a1Cre mice exhibited both increased skeletal size, particularly of vertebrae, and massive trabeculation accompanied by increased cortical thickness. Primary spongiosa development and perichondrial bone collar formation were prominent in Ptenflox/flox:Col2a1Cre mice, and long bone growth plates were disorganized and showed both matrix overproduction and evidence of accelerated hypertrophic differentiation (indicated by an altered pattern of type X collagen and alkaline phosphatase expression). Consistent with increased PI3K signaling, Pten-deficient chondrocytes showed increased phospho-PKB/Akt and phospho-S6 immunostaining, reflective of increased mTOR and PDK1 activity. Interestingly, no significant change in growth plate proliferation was seen in Pten-deficient mice, and growth plate fusion was found at 6 months. Conclusions: By virtue of its ability to modulate a key signal transduction pathway responsible for integrating multiple stimuli, Pten represents an important regulator of both skeletal size and bone architecture. [source] Regulation of embryonic endochondral ossification by Smurf2JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 5 2008Qiuqian Wu Abstract Smurf2 is an E3 ubiquitin ligase that targets TGF-, receptor activated Smad2 and Smad3 for the proteasome in primary articular chondrocytes, thus stimulating their hypertrophic differentiation. Comparatively, how Smurf2 functions in growth plate chondrocytes in a developing long bone is an open question. In this study, we measured the mRNA levels of endogenous Smurf2 and type X collagen in chick growth plate at different embryonic stages to monitor the correlation between the level of Smurf2 expression and chondrocyte maturational stage. We found that high levels of Smurf2 were associated with the differentiative and proliferative stages, while Smurf2 levels were thereafter decreased as the chondrocytes matured toward hypertrophy. In addition, we injected Smurf2 -RCAS into chick wing buds at HH stage 20,23 and examined how the ectopic overexpression of Smurf2 in condensing chondrogenic mesenchyme affects the subsequent process of chondrocyte maturation and ossification during embryonic development. Histological analysis showed that overexpression of Smurf2 in a developing wing bud accelerated chondrocyte maturation and endochondral ossification, which may result from a decrease in TGF-, signaling in the infected chondrocytes with Smurf2 -RCAS. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:704,712, 2008 [source] ERK-1/2 and p38 in the regulation of hypertrophic changes of normal articular cartilage chondrocytes induced by osteoarthritic subchondral osteoblastsARTHRITIS & RHEUMATISM, Issue 5 2010Indira Prasadam Objective Previous studies have shown the influence of subchondral bone osteoblasts (SBOs) on phenotypical changes of articular cartilage chondrocytes (ACCs) during the development of osteoarthritis (OA). The molecular mechanisms involved during this process remain elusive, in particular, the signal transduction pathways. The aim of this study was to investigate the in vitro effects of OA SBOs on the phenotypical changes in normal ACCs and to unveil the potential involvement of MAPK signaling pathways during this process. Methods Normal and arthritic cartilage and bone samples were collected for isolation of ACCs and SBOs. Direct and indirect coculture models were applied to study chondrocyte hypertrophy under the influence of OA SBOs. MAPKs in the regulation of the cell,cell interactions were monitored by phosphorylated antibodies and relevant inhibitors. Results OA SBOs led to increased hypertrophic gene expression and matrix calcification in ACCs by means of both direct and indirect cell,cell interactions. In this study, we demonstrated for the first time that OA SBOs suppressed p38 phosphorylation and induced ERK-1/2 signal phosphorylation in cocultured ACCs. The ERK-1/2 pathway inhibitor PD98059 significantly attenuated the hypertrophic changes induced by conditioned medium from OA SBOs, and the p38 inhibitor SB203580 resulted in the up-regulation of hypertrophic genes in ACCs. Conclusion The findings of this study suggest that the pathologic interaction of OA SBOs and ACCs is mediated via the activation of ERK-1/2 phosphorylation and deactivation of p38 phosphorylation, resulting in hypertrophic differentiation of ACCs. [source] Akt1 in murine chondrocytes controls cartilage calcification during endochondral ossification under physiologic and pathologic conditionsARTHRITIS & RHEUMATISM, Issue 3 2010Atsushi Fukai Objective To examine the role of the phosphoinositide-dependent serine/threonine protein kinase Akt1 in chondrocytes during endochondral ossification. Methods Skeletal phenotypes of homozygous Akt1-deficient (Akt1,/,) mice and their wild-type littermates were compared in radiologic and histologic analyses. An experimental osteoarthritis (OA) model was created by surgically inducing instability in the knee joints of mice. For functional analyses, we used primary costal and articular chondrocytes from neonatal mice and mouse chondrogenic ATDC5 cells with retroviral overexpression of constitutively active Akt1 or small interfering RNA (siRNA) for Akt1. Results Among the Akt isoforms (Akt1, Akt2, and Akt3), Akt1 was the most highly expressed in chondrocytes, and the total level of Akt protein was decreased in Akt1,/, chondrocytes, indicating a dominant role of Akt1. Akt1,/, mice exhibited dwarfism with normal proliferative and hypertrophic zones but suppressed cartilage calcification in the growth plate compared with their wild-type littermates. In mice with surgically induced OA, calcified osteophyte formation, but not cartilage degradation, was prevented in the Akt1,/, joints. Calcification was significantly suppressed in cultures of Akt1,/, chondrocytes or ATDC5 cells overexpressing siRNA for Akt1 and was enhanced in ATDC5 cells overexpressing constitutively active Akt1. Neither proliferation nor hypertrophic differentiation was affected by the gain or loss of function of Akt1. The expression of ANK and nucleotide pyrophosphatase/phosphodiesterase 1, which accumulate pyrophosphate, a crucial calcification inhibitor, was enhanced by Akt1 deficiency or siRNA for Akt1 and was suppressed by constitutively active Akt1. Conclusion Our findings indicate that Akt1 in chondrocytes controls cartilage calcification by inhibiting pyrophosphate during endochondral ossification in skeletal growth and during osteophyte formation in OA. [source] Interleukin-1, and tumor necrosis factor , inhibit chondrogenesis by human mesenchymal stem cells through NF-,B,dependent pathways,ARTHRITIS & RHEUMATISM, Issue 3 2009N. Wehling Objective The differentiation of mesenchymal stem cells (MSCs) into chondrocytes provides an attractive basis for the repair and regeneration of articular cartilage. Under clinical conditions, chondrogenesis will often need to occur in the presence of mediators of inflammation produced in response to injury or disease. The purpose of this study was to examine the effects of 2 important inflammatory cytokines, interleukin-1, (IL-1,) and tumor necrosis factor , (TNF,), on the chondrogenic behavior of human MSCs. Methods Aggregate cultures of MSCs recovered from the femoral intermedullary canal were used. Chondrogenesis was assessed by the expression of relevant transcripts by quantitative reverse transcription,polymerase chain reaction analysis and examination of aggregates by histologic and immunohistochemical analyses. The possible involvement of NF-,B in mediating the effects of IL-1, was examined by delivering a luciferase reporter construct and a dominant-negative inhibitor of NF-,B (suppressor-repressor form of I,B [srI,B]) with adenovirus vectors. Results Both IL-1, and TNF, inhibited chondrogenesis in a dose-dependent manner. This was associated with a marked activation of NF-,B. Delivery of srI,B abrogated the activation of NF-,B and rescued the chondrogenic response. Although expression of type X collagen followed this pattern, other markers of hypertrophic differentiation responded differently. Matrix metalloproteinase 13 was induced by IL-1, in a NF-,B,dependent manner. Alkaline phosphatase activity, in contrast, was inhibited by IL-1, regardless of srI,B delivery. Conclusion Cell-based repair of lesions in articular cartilage will be compromised in inflamed joints. Strategies for enabling repair under these conditions include the use of specific antagonists of individual pyrogens, such as IL-1, and TNF,, or the targeting of important intracellular mediators, such as NF-,B. [source] | ||||||||||