Restriction of spontaneous and prednisolone-induced leptin production to dedifferentiated state in human hip OA chondrocytes: role of Smad1 and β-catenin activation.

The aetiology of OA is not fully understood although several adipokines such as leptin are known mediators of disease progression. Since leptin levels were increased in synovial fluid compared to serum in OA patients, it was suggested that joint cells themselves could produce leptin. However, exact mechanisms underlying leptin production by chondrocytes are poorly understood. Nevertheless, prednisolone, although displaying powerful anti-inflammatory properties has been recently reported to be potent stimulator of leptin and its receptor in OA synovial fibroblasts. Therefore, we investigated, in vitro, spontaneous and prednisolone-induced leptin production in OA chondrocytes, focusing on transforming growth factor-β (TGFβ) and Wnt/β-catenin pathways. We used an in vitro dedifferentiation model, comparing human freshly isolated hip OA chondrocytes cultivated in monolayer during 1 day (type II, COL2A1 +; type X, COL10A1 + and type I collagen, COL1A1 -) or 14 days (COL2A1 -; COL10A1 - and COL1A1+). Leptin expression was not detected in day1 OA chondrocytes whereas day14 OA chondrocytes produced leptin, significantly increased with prednisolone. Activin receptor-like kinase 1 (ALK1)/ALK5 ratio was shifted during dedifferentiation, from high ALK5 and phospho (p)-Smad2 expression at day1 to high ALK1, endoglin and p-Smad1/5 expression at day14. Moreover, inactive glycogen synthase kinase 3 (GSK3) and active β-catenin were only found in dedifferentiated OA chondrocytes. Smad1 and β-catenin but not endoglin stable lentiviral silencing led to a significant decrease in leptin production by dedifferentiated OA chondrocytes. Only dedifferentiated OA chondrocytes produced leptin. Prednisolone markedly enhanced leptin production, which involved Smad1 and β-catenin activation.

Charlier E ，Malaise O ，Zeddou M ，Neuville S ，Cobraiville G ，Deroyer C ，Sanchez C ，Gillet P ，Kurth W ，de Seny D ，Relic B ，Malaise MG ... -  《-》

Increase in ALK1/ALK5 ratio as a cause for elevated MMP-13 expression in osteoarthritis in humans and mice.

Blaney Davidson EN ，Remst DF ，Vitters EL ，van Beuningen HM ，Blom AB ，Goumans MJ ，van den Berg WB ，van der Kraan PM ... -  《-》

ALK1 opposes ALK5/Smad3 signaling and expression of extracellular matrix components in human chondrocytes.

Finnson KW ，Parker WL ，ten Dijke P ，Thorikay M ，Philip A ... -  《-》

TGF-β is a potent inducer of Nerve Growth Factor in articular cartilage via the ALK5-Smad2/3 pathway. Potential role in OA related pain?

Pain is the main problem for patients with osteoarthritis (OA). Pain is linked to inflammation, but in OA a subset of patients suffers from pain without inflammation, indicating an alternative source of pain. Nerve Growth Factor (NGF) inhibition is very efficient in blocking pain during OA, but the source of NGF is unclear. We hypothesize that damaged cartilage in OA releases Transforming Growth Factor-β (TGF-β), which in turn stimulates chondrocytes to produce NGF. Murine and human chondrocyte cell lines, primary bovine and human chondrocytes, and cartilage explants from bovine metacarpal joints and human OA joints were stimulated with TGF-β1 and/or Interleukin-1 (IL-1)β. We analyzed NGF expression on mRNA level with QPCR and stained human OA cartilage for NGF immunohistochemically. Cultures were additionally pre-incubated with inhibitors for TAK1, Smad2/3 or Smad1/5/8 signaling to identify the TGF-β pathway inducing NGF. NGF expression was consistently induced in higher levels by TGF-β than IL-1 in all of our experiments: murine, bovine and human origin, in cell lines, primary chondrocytes and explants cultures. TAK1 inhibition consistently reduced TGF-β-induced NGF whereas it fully blocked IL-1β-induced NGF expression. In contrast, ALK5-Smad2/3 inhibition fully blocked TGF-β-induced NGF expression. Despite the large variation in basal NGF in human OA samples (mRNA and histology), TGF-β exposure led to a consistent high level of NGF induction. We show for the first time that TGF-β induces NGF expression in chondrocytes, in a ALK5-Smad2/3 dependent manner. This reveals a potential alternative non-inflammatory source of pain in OA.

Blaney Davidson EN ，van Caam AP ，Vitters EL ，Bennink MB ，Thijssen E ，van den Berg WB ，Koenders MI ，van Lent PL ，van de Loo FA ，van der Kraan PM ... -  《-》

Age-related alterations in TGF beta signaling as a causal factor of cartilage degeneration in osteoarthritis.

van der Kraan PM 《-》