Background/Purpose:  

Leptin, mainly produced by the adipose tissue including fat neighboring the joint, is considered as pro-inflammatory in osteoarthritis (OA). Normal cartilage does not express leptin, while OA cartilage is a potential producer. We recently showed that joint derived-cells such as synovial fibroblasts (SF), but also bone marrow mesenchymal stem cells, were able to spontaneously produce leptin in vitro, strongly enhanced by glucocorticoids (prednisolone and dexamethasone) involving the ALK-1/Smad1/5 pathway as inducer and the ALK-5/Smad2 pathway as inhibitor. In this work, we have tested isolated human chondrocytes (CH) for leptin, leptin receptor (Ob-R) and balance ALK-5/Smad2 – ALK-1/Smad1/5, during dedifferentiation process. Secondly, we have studied if the glucocorticoid prednisolone and the mineralocorticoid aldosterone were able to induce leptin and Ob-R expression as well as the involvement of the glucocorticoid receptor (GR) or/and mineralocorticoid  receptor (MR). 

Methods:

Humain CH were obtained during joint replacement. To detect surface antigens, cells were immunolabelled with the following anti-human antibodies: CD90–APC, CD105–PE, CD73–PE and analysed on a FACS-CANTO with the CellQuest software. Cells were stimulated with prednisolone, aldosterone, mifepristone (GR inhibitor), spironolactone and epleronone (MR inhibitors) or TGF-β1. Leptin was determined by ELISA, while Ob-R expression, Smad1/5 phosphorylation, Smad2 phosphorylation, ALK-1 and ALK-5 were determined by Western blot.

Results:

1. Primary (PCH) and dedifferentiated (DCH) chondrocytes were similarly positive for CD90 (98.5% ± 1.5 and 99.4% ± 0.3, respectively) and CD73 (84.9% ± 24 and 98.9 ± 0.2, respectively), whereas DCH significantly increased their CD105 (endoglin) expression (33.7% ± 21 and 68.6% ± 17.8, P=0,004). 2. PCH did not produce leptin nor expressed Ob-R. Opposite, DCH significantly expressed leptin and Ob-R. Both leptin and Ob-R expressions were markedly induced by prednisolone. TGF-β1 significantly downregulated prednisolone-induced leptin and Ob-R. With chondrocyte dedifferenciation, ALK-5/Smad2 phosphorylation was progressively decreasing, while ALK-1/Smad1/5 phosphorylation was increasing. 3. Aldosterone, as prednisolone, significantly induced leptin and Ob-R expression in DCH, both stimulations significantly downregulated with the GR inhibitor mifepristone, but not with MR inhibitors spironolactone and eplerenone.

Conclusion:  

1. PCH expressed low levels of CD105 endoglin, exhibited an ALK-5/Smad2 phosphorylation and did not produce leptin nor Ob-R 2. On the contrary, DCH significantly increased their capacity to express CD105 endoglin, exhibited an ALK-1/Smad1/5 phosphorylation, and spontaneously produced leptin and Ob-R. 2. Leptin and Ob-R expressions were inhibited by TGF-β1, but markedly increased by the glucocorticoid prednisolone and the mineralocorticoid aldosterone. 4. Prednisolone and aldosterone increased leptin and Ob-R expressions through GR but not MR stimulation.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/human-chondrocyte-dedifferentiation-is-accompagnied-by-cd105-endoglin-expression-alk-1smad15-phosphorylation-and-leptin-production-stimulation-by-prednisolone-and-aldosterone-through-the-gl/