gms | German Medical Science

Background: Osteoporosis (OP) is the most common age-related disorder characterized by bone loss and correlates with increased bone marrow adiposity due to an imbalance between osteogenic and adipogenic differentiation potential of bone marrow mesenchymal stem cells (MSC). Adipocyte-derived factors - adipokines - are differentially expressed in bone tissue (Tsiklauri et al., Osteoarthritis Cartilage 2018). Moreover, visfatin levels were significantly elevated in OP bone. Thus, we analyzed the impact of visfatin during adipogenic differentiation of MSC in standard culture vs. culture on spongiosa and possible signaling pathways involved in visfatin-mediated effects in course of adipogenesis.

Methods: MSC were isolated from spongiosa of femoral heads after hip replacement surgery. Adipogenic MSC differentiation was performed with/without visfatin and inhibitors of visfatin (Apo866) as well as p38-MAPK (SB203580) or ERK1/2 (SCH772984). For the transfer and differentiation of MSC on cancellous bone, bone fragments were purified and sterilized. Gene expression was evaluated by Realtime PCR. Protein production was analyzed by ELISA.

Results: Stimulation with visfatin induced the secretion of proinflammatory factors during adipogenesis in standard cell culture as well as on cancellous bone. However, visfatin-induced cytokine release was markedly reduced during differentiation on spongiosa (e.g. 14d IL6, x-fold: standard culture 151±110, spongiosa 40±30, n=7). Visfatin also significantly upregulated MMP13 mRNA as well as protein expression at 7d, 14d and 21d after induction of adipogenesis in standard cell culture as well as on spongiosa, but cancellous bone significantly reduced visfatin-mediated MMP13 expression (e.g. 21d, x-fold,: standard culture 81±89, spongiosa 13±21, n=7). The visfatin inhibitor Apo866 inhibited the visfatin-induced cytokine release, however, the MMP13 expression was not influenced during adipogenesis in culture (n=8). In contrast to Apo866, the p38-MAPK inhibitor did not reduce cytokine release during adipogenesis. Costimulation with ERK1/2-inhibitor suppressed the visfatin-induced secretion of proinflammatory cytokines as well as of MMP13.

Conclusion: Visfatin-mediated increase of MMPs and proinflammatory cytokines during adipogenic differentiation might influence bone turnover at the adipose tissue/bone interface. Our results support the idea that the extracellular matrix attenuates visfatin-mediated matrix-degrading effects during adipogenesis. The observed visfatin-mediated effects most likely depend on the NAMP activity of visfatin inhibited by APO866 as well as ERK-signaling.