CAMKK1 couples STIM1-dependent Ca²⁺ signaling to mitochondrial metabolic adaptation during osteoclastogenesis

Excessive osteoclast activation contributes to estrogen deficiency-induced bone loss, but how receptor activator of nuclear factor-κB ligand (RANKL)-induced Ca²⁺ oscillations are coupled to mitochondrial metabolic adaptation remains unclear. Here, we show that calcium/calmodulin-dependent protein kinase kinase 1 (CAMKK1) links osteoclast Ca²⁺ signaling to mitochondrial responses during osteoclastogenesis. CAMKK1 knockdown reduced Ca²⁺ oscillatory activity, mitochondrial Ca²⁺ responses, NFATc1 activation, and osteoclast formation, whereas CAMKK1 overexpression produced the opposite effects. Immunoprecipitation coupled with LC-MS/MS identified stromal interaction molecule 1 (STIM1) as a CAMKK1-associated protein. Reciprocal co-immunoprecipitation and truncation analysis showed that the distal cytosolic region of STIM1 retained CAMKK1 association, while STIM1 depletion attenuated CAMKK1-dependent Ca²⁺ oscillations, mitochondrial Ca²⁺ responses, respiration, and osteoclast differentiation. Forced CAMKK1/STIM1 co-overexpression caused mitochondrial Ca²⁺ accumulation, oxidative stress, membrane-potential disruption, respiratory dysfunction, and apoptosis. CAMKK1/STIM1-dependent signaling was also associated with altered glucose-derived carbon incorporation into tricarboxylic acid cycle metabolites. In vivo, osteoclast-lineage Camkk1 deletion attenuated ovariectomy-induced trabecular bone loss. These findings support a functional role for CAMKK1 in STIM1-dependent Ca²⁺-mitochondrial coupling during osteoclastogenesis and estrogen deficiency-induced bone loss.