Riociguat Suppresses Osteoclastogenesis and Ovariectomy-Induced Bone Loss by Attenuating MAPK Signaling and PPARγ–PGC-1β Coupling

Background Postmenopausal osteoporosis is driven in part by excessive osteoclast-mediated bone resorption. We investigated whether the soluble guanylate cyclase stimulator riociguat regulates osteoclastogenesis and protects against estrogen-deficiency-induced bone loss. Methods Riociguat was evaluated in RANKL-stimulated bone marrow-derived macrophages and ovariectomized mice using viability, differentiation, cytoskeletal, resorption, immunoblotting, immunofluorescence, micro-computed tomography, and histomorphometric assays. Computational target prioritization, public single-cell transcriptomic reanalysis, co-immunoprecipitation, rosiglitazone interaction experiments, molecular docking, and molecular dynamics simulations were used to examine MAPK- and PPARγ–PGC-1β-associated responses. Group comparisons used analysis of variance or nonparametric alternatives as appropriate. Results Riociguat inhibited osteoclast formation without detectable cytotoxicity, disrupted F-actin-ring organization, reduced resorption-pit formation, and lowered the abundance of CTSK, integrin β3, c-Fos, and NFATc1. Riociguat attenuated RANKL-induced phosphorylation of JNK, ERK, and p38 and reduced PPARγ–PGC-1β association. Rosiglitazone partially counteracted several cellular and biochemical effects associated with riociguat treatment. Structural simulations associated modelled riociguat occupancy of the PPARγ ligand-binding pocket with reduced energetic favorability of a PPARγ–PGC-1β interface. In ovariectomized mice, riociguat preserved trabecular microarchitecture and reduced histological indices of osteoclast activity. Conclusions Riociguat suppressed osteoclastogenesis and preserved trabecular bone in an ovariectomy model. The data support involvement of early MAPK attenuation and reduced PPARγ–PGC-1β coupling, while direct target engagement, pathway necessity, and canonical sGC–cGMP–PKG dependence remain to be established.