The inhibitory effects of vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide on osteoclast formation are associatedwith upregulation of osteoprotegerin and downregulation of RANKL and RANK

The presence of a network of peptidergic nerve fibers in the skeleton, expr essing several neuropeptides including vasoactive intestinal peptide (VIP), has been demonstrated. This observation, together with our findings in vit ro showing that VIP can regulate the activities of osteoblasts and osteocla sts as well as the recruitment of osteoclasts, has suggested the existence of a neuro-osteogenic interplay in bone metabolism. In the present study th e effects of VIP and pituitary adenylate cyclase-activating polypeptide (PA CAP), two members of the VIP/secretin/glucagon superfamily, on osteoclast f ormation and mRNA expression of three key regulatory proteins involved in o steoclast formation have been investigated. VIP, PACAP-27, and PACAP-38, at concentrations of 10(-6) M, all significantly inhibited formation of tartr ate-resistant acid phosphatase-positive multinuclear cells (TRAP + MNC) in mouse bone marrow cultures stimulated by 1,25(OH)(2)-vitamin D3 (D3; 10-(8) M). By using semiquantitative RT-PCR, it was found that D3 upregulated the mRNA expressions of receptor activator of NF-kappa B ligand (RANKL) and re ceptor activator of NF-kappa B (RANK), whereas the expression of osteoprote gerin (OPG;) was downregulated in mouse bone marrow cultures stimulated by D3 for 7 days. Both VIP and PACAP-38 decreased the stimulatory effects of D 3 on RANKL and RANK expression, whereas the inhibitory effect of D3 on OPG expression was reversed by VIP and PACAP-38. These observations indicate th at the inhibitory effects of VIP and PACAP on osteoclast recruitment are du e to regulation of the expression of key proteins involved in later stages of osteoclast differentiation. (C) 2000 Academic Press.