Neuromedin U directly stimulates growth of cultured rat calvarial osteoblast-like cells acting via the NMU receptor 2 isoform

The neuromedin U (NMU) system is composed of NMU, neuromedin S (NMS) and their receptors NMUR1 and NMUR2. This system is involved in the regulation of energy homeostasis, neuroendocrine functions, immune response, circadian rhythm and spermatogenesis. The present study aimed to investigate the possible role of the NMU system in regulating functions of cultured rat calvarial osteoblast-like (ROB) cells. By using QPCR, high expression of NMU mRNA was found in freshly isolated ROB cells while after 7, 14, and 21 days of culture, expression of the studied gene was very low. In contrast, NMUR2 mRNA expression in freshly isolated ROB cells was negligible and very high in cultured cells. The highest NMUR2 mRNA expression was observed at day 7, and was followed by lower levels at days 14 and 21 of culture. Neither NMS nor NMUR1 mRNA was found in studied cells. Exposure of cultured ROB cells to NMU8 at concentrations 10−6 to 10−10 M had no effect on expression levels of the genes. During the entire culture period, NMU8 did not affect osteocalcin production, but stimulated proliferative activity of ROB cells at days 14 and 21 of culture. Thus, we demonstrated that cultured rat calvarial osteoblast-like cells are provided with NMUR2, the receptor isoform typical for the central nervous system. Acting via this receptor NMU8 stimulates proliferation of cultured cells and has no effect on their differentiated function (osteocalcin secretion).