SS-31 inhibits mtDNA–cGAS–STING signaling to improve POCD by activating mitophagy in aged mice

Neuroinflammation is crucial in the development of postoperative cognitive dysfunction (POCD), and microglial activation is an active participant in this process. SS-31, a mitochondrion-targeted antioxidant, is widely regarded as a potential drug for neurodegenerative diseases and inflammatory diseases. In this study, we sought to explore whether SS-31 plays a neuroprotective role and the underlying mechanism.

Internal fixation of tibial fracture was performed in 18-month-old mice to induce surgery-associated neurocognitive dysfunction. LPS was administrated to BV2 cells to induce neuroinflammation. Neurobehavioral deficits, hippocampal injury, protein expression, mitophagy level and cell state were evaluated after treatment with SS-31, PHB2 siRNA and an STING agonist.

Our study revealed that SS-31 interacted with PHB2 to activate mitophagy and improve neural damage in surgically aged mice, which was attributed to the reduced cGAS–STING pathway and M1 microglial polarization by decreased release of mitochondrial DNA (mtDNA) but not nuclear DNA (nDNA). In vitro, knockdown of PHB2 and an STING agonist abolished the protective effect of SS-31.

SS-31 conferred neuroprotection against POCD by promoting PHB2-mediated mitophagy activation to inhibit mtDNA release, which in turn suppressed the cGAS–STING pathway and M1 microglial polarization.