The Regulatory Effect of Guanylate Cyclase Activator 1C on Osteoclast Differentiation and Function through the RANKL/RANK/OPG Pathway

This study aimed to investigate the role and mechanism of Guanylate Cyclase Activator 1C (GUCA1C) in osteoclast (OC) differentiation within the context of bone tuberculosis (TB), focusing on the RANKL/RANK/OPG pathway.

RNA sequencing was performed on peripheral blood samples from 10 treatment-naïve patients with isolated skeletal TB, 10 with pulmonary TB, and 10 healthy volunteers. Bioinformatics analyses (GO, KEGG, PPI network) were employed to identify differentially expressed genes (DEGs). In vitro validation was conducted using THP-1-derived macrophages. Cells were transfected with GUCA1C-overexpression or -knockdown lentivirus, followed by osteoclastogenic induction with RANKL and M-CSF. Osteoclast formation and function were assessed by TRAP staining, Western blot (for RANK, RANKL, OPG proteins), and qPCR for key osteoclast markers (NFATc1, TRAP, CTSK, RANK, RANKL, OPG).

Bioinformatics screening identified 210 unique DEGs in the bone TB group. GUCA1C, enriched in the phototransduction pathway, was highlighted as a key candidate. In vitro, GUCA1C overexpression significantly promoted the formation of TRAP-positive multinucleated osteoclasts and upregulated the mRNA and protein levels of RANK, RANKL, and the transcription factor NFATc1 and its downstream effectors (TRAP, CTSK). While both GUCA1C overexpression and knockdown increased OPG expression compared to the control, the knockdown group exhibited higher OPG levels than the overexpression group. Correspondingly, GUCA1C knockdown attenuated the pro-osteoclastic effects observed in the overexpression group.

This study provides the first evidence linking GUCA1C, which encodes the calcium-sensor GCAP3, to bone pathology. We propose that GUCA1C, beyond its known retinal function, may act as a novel calcium-signaling modulator in osteoclast precursors. It appears to preferentially enhance pro-osteoclastic signals (RANKL/RANK) while exerting a comparatively weaker upregulatory effect on the decoy receptor OPG. This differential regulation disrupts the RANKL/RANK/OPG axis balance towards enhanced osteoclastogenesis, potentially contributing to inflammatory bone destruction in bone TB. Thus, GUCA1C represents a potential therapeutic target for mitigating pathological bone loss.

GUCA1C promotes osteoclast differentiation by modulating the RANKL/RANK/OPG signaling axis, identifying it as a potential candidate therapeutic target for bone tuberculosis.