Autocrine effects of neuromedin b stimulate the proliferation of rat primary osteoblasts

Neuromedin B (NMB) is a mammalian bombesin-like peptide that regulates exocrine/ endocrine secretion, smooth muscle contraction, body temperature, and the proliferation of some cell types. Here, we show that mRNA encoding Nmb and its receptor (Nmbr) are expressed in rat bone tissue. Immunohistochemical analysis demonstrated thatNMB andNMBR colocalize in osteoblasts, epiphyseal chondrocytes, and proliferative chondrocytes of growth plates frommouse hind limbs. Then, we investigated the effect of NMB on the proliferation of rat primary cultured osteoblasts. Proliferation assays and 5-bromo-2′-deoxyuridine incorporation assays demonstrated that NMB augments the cell number and enhances DNA synthesis in osteoblasts. Pretreatment with the NMBR antagonist BIM23127 inhibited NMB-induced cell proliferation and DNA synthesis. Western blot analysis showed that NMB activates ERK1/2 MAPK signaling in osteoblasts. Pretreatment with the MAPK/ERK kinase inhibitor U0126 attenuatedNMB-induced cell proliferation and DNA synthesis.We also investigated the effects ofmolecules that contribute to osteoblast proliferation and differentiation onNmb expression in osteoblasts. Real-time PCR analysis demonstrated that 17b-estradiol (E2) and transforming growth factor b1 increase and decrease Nmb mRNA expression levels respectively. Finally, proliferation assays revealed that the NMBR antagonist BIM23127 suppresses E2-induced osteoblast proliferation. These results suggest that NMB/NMBR signaling plays an autocrine or paracrine role in osteoblast proliferation and contributes to the regulation of bone formation.