gms | German Medical Science

Objectives: Osteoarthritis (OA) is a degenerative joint disease, which is closely associated with age. OA causes cartilage loss and structural damage in all joint tissues, with inflammatory mediators playing a critical role. Moreover, cartilage is a tissue with only minimal intrinsic regenerative capacity. Theα-melanocyte-stimulating hormone (α-MSH) is a melanocortin (MC) peptide, which mediates its effects via MC receptors (MCR). Beyond pigment induction, α-MSH has several anti-inflammatory and chondro-protective effects dampening inflammatory and presumably age-related processes. Abrogated MC1R signalling lead to a more severe OA-pathology in a murine surgical OA model. The underlying molecular mechanisms as signalling pathways and intracellular effectors are mostly unknown yet. Therefore, the aim of this study was to analyse the effect of α-MSH on senescent human OA chondrocytes.

Methods: Chondrocytes and synovial fluid (SF) were obtained from OA and non-OA patients. Chondrocytes, cultivated in 2D monolayers, were incubated withα-MSH and treated with doxorubicin, to induce a senescent phenotype. Induction of senescence was verified by senescence-associated β-galactosidase (SA-β-Gal) activity, caspase 3/7 activity, mitochondrial membrane potential (JC-1 assay) and senescence-marker expression. The expression and secretion of pro-inflammatory cytokines, Matrix metalloproteinases (MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, MMP-13) and complement markers were analysed in SF, cell lysates and supernatants by qPCR, Western Blot and Multiplex-ELISA. OA chondrocytes were genotyped for MC1R loss-of-function polymorphisms.

Results and conclusion: We induced SA-β-Gal expression in all doxorubicin-treated human chondrocytes and did not observe any changes in apoptosis rate. We detected an increase in CDK-inhibitors p16 and p21, as well as increased catabolic markers IL-6, MMP-3, MMP-13, complement components C3 and complement factor B (CFB). Senescent OA chondrocytes incubated with α-MSH showed a decreased inflammatory expression pattern in cell supernatants. α-MSH as well as C3a levels were age-dependently altered in SF between OA patients. Different MC1R polymorphisms were detected in OA samples.

These in vitro data indicated an anti-inflammatory and possibly anti-ageing effect ofα-MSH on senescence-induced human osteoarthritic chondrocytes. A correlation between the effect of α-MSH and genetic MC1R variations on OA chondrocyte metabolism needs to be further investigated.