Osteoprotective effects of the neuropeptide VIP: insights from triple cultures of human osteocytes, osteoblasts, and osteoclasts

Abstract

Bone remodelling is a dynamic process of osteoblastic bone formation and osteoclastic bone resorption, regulated by local, paracrine and endocrine factors, in which osteocytes act as orchestrators of bone homeostasis. Among these regulatory factors, the neuropeptide VIP (vasoactive intestinal peptide) has demonstrated osteoprotective effects by inhibiting osteoclastogenesis and promoting osteoblast differentiation. However, its potential role in osteocyte biology remains unexplored. In this study, we investigated the effect of VIP on the differentiation of primary human osteocytes. We describe for the first time the expression of VIP and its receptors during in vitro osteocyte differentiation. Our results show that VIP promotes osteocytogenesis, accompanied by a reduction in the RANKL/OPG ratio, thereby supporting its role as an anti-osteoclastogenic factor. To better mimic the complexity of bone tissue, we performed triple co-cultures of osteoblasts and simultaneously differentiating osteocytes and osteoclasts, in the presence or absence of VIP. Our results confirmed that VIP supports the osteoblast-to-osteocyte transition and promotes an osteoprotective phenotype, characterized by a reduced RANKL/OPG ratio and decreased SOST expression. The downregulation of sclerostin may attenuate osteocyte-mediated inhibitory signalling toward osteoblasts and, in turn, contribute to the reduction of the osteoblastic RANKL/OPG ratio. Collectively, our findings reinforce the anti-osteoclastogenic actions of VIP, supporting its role as a potential osteoprotective factor.