Objective
Long bones develop through the strictly regulated process of endochondral ossification within the growth plate, resulting in the replacement of cartilage by bone. Defects in this process result in skeletal abnormalities and can predispose to disease such as osteoarthritis (OA). Studies suggest that activation of the transcription factor peroxisome proliferator activated receptor gamma (PPARγ) is a therapeutic target for OA. In order to devise PPARγ-related therapies in OA and related diseases, it is critical to identify its role in cartilage biology. Therefore, we determined the in vivo role of PPARγ in endochondral ossification and cartilage development using cartilage-specific PPARγ knockout (KO) mice.
Methods
Cartilage-specific PPARγ KO mice were generated using LoxP/Cre system. Histomorphometric and immunohistochemical analysis was performed to account for ossification patterns, chondrocyte proliferation, differentiation, hypertrophy, skeletal organization, bone density and calcium deposition. Real-Time PCR and western blotting was performed to determine the expression of key markers involved in endochondral ossification.
Results
PPARγ KO mice exhibited reduced body length, weight, length of long bones, skeletal growth, cellularity, bone density, calcium deposition and trabecular bone thickness, abnormal growth plate organization, loss of columnar organization, shorter hypertrophic zones, and delayed primary and secondary ossification. Immunohistochemistry for Sox9, BrdU, p57, collagen X and PECAM revealed reduction in chondrocyte differentiation and proliferation, and hypertrophy and vascularisation in growth plates of mutant mice. Isolated chondrocytes and cartilage explants from mutant mice showed aberrant expression of ECM markers including aggrecan, collagen II and MMP-13.
Conclusion
PPARγ is required for normal endochondral ossification and cartilage development in vivo.
IntroductionMicrosomal prostaglandin E2 synthase-1 (mPGES-1) is an inducible enzyme that acts downstream of cyclooxygenase (COX) to specifically catalyze the conversion of prostaglandin (PG) H2 to PGE2. mPGES-1 plays a key role in inflammation, pain and arthritis; however, the role of mPGES-1 in fibrogenesis is largely unknown. Herein, we examine the role of mPGES-1 in a mouse model of skin scleroderma using mice deficient in mPGES-1.MethodsWild type (WT) and mPGES-1 null mice were subjected to the bleomycin model of cutaneous skin scleroderma. mPGES-1 expressions in scleroderma fibroblasts and in fibroblasts derived from bleomycin-exposed mice were assessed by Western blot analysis. Degree of fibrosis, dermal thickness, inflammation, collagen content and the number of α-smooth muscle actin (α-SMA)-positive cells were determined by histological analyses. The quantity of the collagen-specific amino acid hydroxyproline was also measured.ResultsCompared to normal skin fibroblasts, mPGES-1 protein expression was elevated in systemic sclerosis (SSc) fibroblasts and in bleomycin-exposed mice. Compared to WT mice, mPGES-1-null mice were resistant to bleomycin-induced inflammation, cutaneous thickening, collagen production and myofibroblast formation.ConclusionsmPGES-1 expression is required for bleomycin-induced skin fibrogenesis. Inhibition of mPGES-1 may be a viable method to alleviate the development of cutaneous sclerosis and is a potential therapeutic target to control the onset of fibrogenesis.
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