Zusammenfassung
Background and Objectives: Mesenchymal,Trial stem cells (MSCs) become hypertrophic in long term despite chondrogenic ditterentiation following the pathway of growth plate chondrocytes. This terminal differentiation leads to phenotypically unstable cartilage and was mirrored in vitro by addition of hypertrophy inducing medium. We investigated how intrinsic TGF-beta signaling is altered in ...
Zusammenfassung
Background and Objectives: Mesenchymal,Trial stem cells (MSCs) become hypertrophic in long term despite chondrogenic ditterentiation following the pathway of growth plate chondrocytes. This terminal differentiation leads to phenotypically unstable cartilage and was mirrored in vitro by addition of hypertrophy inducing medium. We investigated how intrinsic TGF-beta signaling is altered in pro-hypertrophic conditions. Methods and Results: Human hone marrow derived MSC were chondrogenically differentiated in 3D culture. At day 14 medium conditions were changed to I. pro-hypertrophic by addition of T3 and withdrawal of TGF-beta and dexamethasone 2. pro-hypertrophic by addition of BMP 4 and withdrawal of TGF-beta and dexamethasone and 3. kept n prochondrogenic medium conditions. All groups were treated with and without TGF beta-type-1-receptor inhibitor SB431542 from day 14 on. Aggregates were harvested for histo- and immunohistological analysis at d14 and d28, for gene expression analysis (rt-PCR) on dl, d3, d7, d14, d17, d21 and d28 and for Western blot analysis on d21 and d28. Induction of hypertrophy was achieved in the pro-hypertrophic groups while expression of TGF beta-type-I- and 2-receptor and Sox 9 were significantly downregulatcd compared to pro-chondrogcnic conditions. Western blotting showed reduced phosphorylation of Smad 2 and 3 in hypertrophic samples, reduced TGF-beta-1 receptor proteins and reduced SOX 9. Addition of SB431542 did not initiate hypertrophy under pro-chondrogenic conditions, but was capable of enhancing hypertrophy when applied simultaneously with BMP-4. Conclusions: Our results suggest that the enhancement of hypertrophy in this model is a result of both activation of pro-hypertrophic BMP signaling and reduction of anti-hypertrophic TGF beta signaling.
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