Dual-regulation of mitophagy and cytosolic mtDNA-induced inflammation for the treatment of inflammatory bone loss.

Inflammatory osteoporosis, also known as "immunoporosis," is a condition characterized by chronic inflammation and mitochondrial dysfunction, leading to impaired bone regeneration. Mitochondrial DNA (mtDNA) leakage activates the cGAS-STING pathway, triggering excessive inflammatory responses and hindering osteogenesis. Concurrently, defective mitophagy exacerbates mitochondrial damage, perpetuating a cycle of bone loss. This study investigated the role of the mtDNA-cGAS-STING axis in lipopolysaccharide (LPS)-induced bone marrow mesenchymal stem cells (BMSCs) dysfunction and inflammatory bone loss. We exposed BMSCs to LPS and assessed mitochondrial function, mtDNA release, and cGAS-STING activation using RT-qPCR, Western blotting, and immunofluorescence. We then engineered exosomes to co-deliver siRNA targeting STING and PINK1 mRNA, testing their effects on osteogenesis and mitochondrial homeostasis in vitro and in a mouse model of LPS-induced osteoporosis. LPS exposure resulted in mitochondrial damage, mtDNA leakage, and cGAS-STING activation, impairing osteogenic differentiation and increasing inflammatory cytokine expression. While STING inhibition reduced inflammatory signaling, it did not restore mitochondrial function, whereas PINK1 overexpression improved mitophagy and partially suppressed cGAS-STING activation. Dual regulation through siSTING/PINK1@Exo synergistically reduced mitochondrial ROS, restored membrane potential, promoted osteogenic marker expression, and enhanced mineralization in vitro. Dual-regulated exosomes significantly improved trabecular bone microarchitecture, reduced STING expression, and enhanced RUNX2 and OCN expression compared to single treatments in an in vivo model. These results demonstrate that combining mitophagy activation with STING inhibition via engineered exosomes offers a promising therapeutic strategy for inflammatory osteoporosis by addressing both mitochondrial dysfunction and chronic inflammation.