Physiological testosterone levels enhance chondrogenic extracellular matrix synthesis by male intervertebral disc cells in vitro, but not by mesenchymal stem cells

Background contextTestosterone (T) is a hormone and regulator involved in the processes of development of the organism (ie, promoting development of bone and muscle mass). Although T effects on the mesenchyme-derived muscle, bone, and adipose tissues are well studied, T effects on intervertebral disc (IVD) have not been reported.PurposeThe aim was to test the following hypothesis: if a physiological concentration of T (∼30 nM) can improve in vitro chondrogenesis of human IVD cells and mesenchymal stem cells (MSCs).Study design/settingHuman IVD cells and MSCs were differentiated to chondrogenic lineage on gelatin scaffolds for 4 weeks, in the presence or absence of T.MethodsChondrogenesis was assessed by cell viability, by measuring gene expression with quantitative polymerase chain reaction and extracellular matrix (ECM) accumulation with immunoblotting, immunohistochemical, and biochemical methods.ResultsSupplementation of T to chondrogenic culture did not affect viability. In male IVD cells, T had a beneficial impact on chondrogenesis, particularly in nucleus pulposus cells, demonstrated by an increased expression of aggrecan, collagen type I, and especially collagen type II. Conversely, T had no effects on chondrogenesis of female IVD cells or MSCs from both genders. A gene expression array of transforming growth factor β/bone morphogenetic protein signaling cascade showed that in male IVD cells, T promoted a stable general but nonsignificant increase in gene expression. Furthermore, aromatase inhibitor anastrazole repressed the effect of T on ECM expression by IVD cells. The results suggest that T increased ECM accumulation in male IVD cells in combination with its conversion to estradiol by the enzyme aromatase.ConclusionsWe demonstrated that T effectively enhances in vitro chondrogenesis in male IVD cells, rising the interest in the possible role of sex hormones in IVD degeneration. Nevertheless, T does not affect chondrogenic differentiation of female IVD cells and MSCs from both genders.