Nitric oxide regulation of cGMP production in osteoclasts

Bone resorption by osteoclasts is modified by agents that affect cyclic gua nosine monophosphate (cGMP), but their relative physiological roles, and wh at components of the process are present in osteoclasts or require accessor y cells such as osteoblasts, are unclear. We studied cGMP regulation in avi an osteoclasts, and in particular the roles of nitric oxide and natriuretic peptides, to clarify the mechanisms involved. C-type natriuretic peptide d rives a membrane guanylate cyclase, and increased cGMP production in mixed bone cells. However, C-type natriuretic peptide did not increase cGMP in pu rified osteoclasts. By contrast, osteoclasts did produce cGMP in response t o nitric oxide (NO) generators, sodium nitroprusside or 1-hydroxy-2-oxo-3,3 -bis(3-aminoethyl)-1-triazene. These findings indicate that C-type natriure tic peptide and NO modulate cGMP in different types of bone cells. The acti vity of the osteoclast centers on HCl secretion that dissolves bone mineral , and both NO generators and hydrolysis-resistant cGMP analogues reduced bo ne degradation, while cGMP antagonists increased activity. NO synthase agon ists did not affect activity, arguing against autocrine NO production. Oste oclasts express NO-activated guanylate cyclase and cGMP-dependent protein k inase (C-kinase). G-kinase reduced membrane HCl transport activity in a con centration-dependent manner, and phosphorylated a 60-kD osteoclast membrane protein, which immunoprecipitation showed is not an H+-ATPase subunit. We conclude that cGMP is a negative regulator of osteoclast activity, cGMP is produced in response to NO made by other cells, but not in response to C-ty pe natriuretic peptide. C-kinase modulates osteoclast membrane HCl transpor t via intermediate protein(s) and may mediate cGMP effects in osteoclasts. (C) 1999 Wiley-Liss, Inc.