Activation of mitochondrial DNA-mediated cGAS-STING pathway contributes to chronic postsurgical pain by inducing type I interferons and A1 reactive astrocytes in the spinal cord

Chronic postsurgical pain (CPSP) is increasingly recognized as a public health issue. Recent studies indicated the innate immune pathway of cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) was involved in pain regulation. However, the detailed mechanisms remain unclear. Previous studies found A1 reactive astrocytes in the spinal cord contributed to CPSP. This study aimed to investigate the roles and mechanisms of the cGAS-STING pathway in regulating the generation of A1 reactive astrocytes during CPSP. First, CPSP model was established using skin/muscle incision and retraction (SMIR) in rats. We found that cGAS-STING pathway was activated accompanied with an increase in mitochondrial DNA in the cytosol in the spinal cord following SMIR. Second, a STING inhibitor C-176 was intrathecally administrated. We found that C-176 decreased the expression of type I interferons and A1 reactive astrocytes in the spinal cord, and alleviated mechanical allodynia in SMIR rats. Third, cyclosporin A as a mitochondrial permeability transition pore blocker was intrathecally administrated. We found that cyclosporin A decreased the leakage of mitochondrial DNA and inhibited the activation of cGAS-STING pathway. Compared with C-176, cyclosporin A exhibits similar analgesic effects. The expression of type I interferons and A1 reactive astrocytes in the spinal cord were also down-regulated after intervention with cyclosporin A. Moreover, simultaneous administration of cyclosporin A and C-176 did not show synergistic effects in SMIR rats. Therefore, our study demonstrated that the cGAS-STING pathway activated by the leakage of mitochondrial DNA contributed to chronic postsurgical pain by inducing type I interferons and A1 reactive astrocytes in the spinal cord.