Background The role of fat–bone interactions in the pathogenesis of osteoporosis is poorly understood. An inverse relationship between bone marrow adipose tissue and bone mineral density during ageing and in osteoporosis is well documented. Adipokines (eg, visfatin, resistin and leptin) are adipocyte-derived factors with immunomodulatory properties and they might influence the differentiation of bone marrow-derived mesenchymal stem cells (MSC) into osteoblasts and adipocytes. The aim was to analyse the presence of adipokines in the bone marrow cavity and their effects on MSC differentiation.
Methods Spongiosa from femoral heads containing bone marrow were collected (hip replacement of osteoarthritis patients or after osteoporotic femoral neck fracture). MSC were cultured in adipogenic and osteogenic media with/without adipokines. For the transfer and differentiation of MSC on cancellous bone, bone fragments were purified and sterilised. mRNA expression of adipokines, bone marker genes, TIMPs and MMPs of stimulated MSC and of bone samples were evaluated by real time PCR. Matrix mineralization was investigated using Alizarin red S staining. Proinflammatory factors were measured by ELISA.
Results Visfatin and leptin level were increased in osteoporotic bone vs. non-osteoporotic bone (n=14). Visfatin induced the secretion of proinflammatory factors (IL-6, IL-8, MCP-1) during both, osteogenic and adipogenic differentiation but not leptin or resistin. Visfatin markedly increased mineralization during osteogenic differentiation, whereas the Coll.1-expression was significantly downregulated (eg, d21: −4.6-fold). In contrast to resistin and leptin visfatin also reduced the expression of MMP2, MMP13, RunX2, TIMP1 and TIMP2 (eg, d21: −2.4-fold/−3.18 fold/−5.85 fold/−3.2 fold/−4.3 fold respectively) in osteogenic differentiated cells. In contrast to osteogenesis, visfatin significantly increased MMP13 expression (eg, d21: 104-fold) during adipogenic differentiation under standard cell culture conditions, however visfatin induced MMP13-Expression was markedly reduced during differentiation on purified autologous cancellous bone.
Conclusion Visfatin and leptin were elevated in osteoporotic bone tissue. Visfatin-mediated increase of matrix mineralization and reduction of Coll.1 expression could enhance bone fragility and contribute to the pathogenesis of osteoporosis. Visfatin might impair bone remodelling at the adipose tissue/bone interface through enhancing secretion of proinflammatory factors and dysregulated MMP- and TIMP-expression during MSC-differentiation.