Microalgal extract from Pseudocalidococcus azoricus KCTC AG61299 as a potential inhibitor of osteoclast formation for osteoporosis therapy

Osteoporosis, a prevalent metabolic bone disorder, results from excessive osteoclast activity and subsequent bone resorption. Natural compounds derived from microorganisms have demonstrated potential in modulating osteoclastogenesis. In this study, we investigated the anti-osteoclastogenic effects of Pseudocalidococcus azoricus KCTC AG61299, a newly characterized freshwater cyanobacterial strain. Whole-genome sequencing and bioinformatics analyses identified putative biosynthetic gene clusters related to secondary metabolite biosynthesis. The KCTC AG61299 extract significantly inhibited RANKL-induced osteoclast differentiation in bone marrow-derived macrophages (BMMs) at concentrations of 1 and 10 μg/mL ( p < 0.001) without exhibiting cytotoxicity. Furthermore, KCTC AG61299 extracts suppressed RANKL-induced F-actin ring formation in BMMs. Mechanistic studies revealed that the extracts significantly reduced the mRNA expression of osteoclast-specific genes, including NFATc1, c-Fos, TRAP, CTSK, DC-STAMP, and V-ATPase-d2 at multiple differentiation stages ( p < 0.001). At the protein level, KCTC AG61299 suppressed NFATc1 and c-Fos expression and markedly inhibited RANKL-induced activation of the MAPK (ERK, JNK, and p38) and Akt/GSK3β signaling pathways, while exerting only minor effects on NF-κB signaling. These findings suggest that KCTC AG61299 represents a novel microbial resource for developing natural compound-based interventions for osteoporosis management. • Pseudocalidococcus azoricus KCTC AG61299 extract significantly inhibits RANKL-induced osteoclast differentiation in bone marrow-derived macrophages without cytotoxicity. • The cyanobacterial extract disrupts F-actin ring formation and suppresses key osteoclast-related transcription factors NFATc1 and c-Fos expression. • KCTC AG61299 extract attenuates osteoclastogenesis through inhibition of MAPK and Akt signaling pathways rather than NF-κB pathway. • Genome mining reveals biosynthetic gene clusters for terpenoids and polyketides, supporting the strain's potential for bioactive metabolite production. • This study establishes freshwater cyanobacteria as a novel source of natural anti-resorptive compounds for osteoporosis therapy development.