Abstract
Inflammatory pain presents a significant clinical challenge. AMP-activated protein kinase (AMPK) is recognized for its capacity to alleviate inflammation by inhibiting transcription factors such as nuclear factor kappa B (NF-κB) and signal transducer and activator of transcription (STAT). Our prior research demonstrated that AMPK reduces inflammatory pain by inhibiting NF-κB activation and interleukin-1 beta (IL-1β) expression. However, the role of AMPK in regulating reactive oxygen species (ROS) and inducible nitric oxide synthase (iNOS) by modulating STAT3 phosphorylation in inflammatory pain remains inadequately understood. This study aims to investigate the role of AMPK in modulating STAT3 phosphorylation in the macrophages of inflamed tissues to mitigate inflammatory pain. A Complete Freund's Adjuvant (CFA)-induced inflammatory pain model was established by subcutaneous injection into the plantar surface of the left hindpaw of adult male mice. Behavioral tests of mechanical allodynia and thermal latency were used to determine nociceptive behavior. Immunoblotting quantified p-AMPK and iNOS expression levels. Nuclear translocation of p-STAT3(Ser727) and STAT3 in macrophages was assessed by western blot and immunofluorescence. ROS accumulation and mitochondrial damage in NR8383 macrophages were detected by flow cytometry. Lentivirus infection cells experiment was performed to transfect vectors encoding the STAT3 S727D mutants. Treatment with the AMPK activator AICAR alleviated CFA-induced inflammatory pain, enhanced AMPK phosphorylation, and reduced iNOS expression in inflamed skin tissues. AICAR effectively prevented STAT3 nuclear translocation while promoting the phosphorylation of STAT3 (Ser727) in the cytoplasm. In vitro studies with CFA-stimulated NR8383 macrophages revealed that AICAR increased STAT3(Ser727) phosphorylation, curtailed iNOS expression, and attenuated ROS accumulation and mitochondrial damage. Furthermore, the S727D mutation, which enhances STAT3 phosphorylation, replicated the protective effects of AICAR against CFA-induced oxidative stress and mitochondrial dysfunction. Our study shows that the AMPK acitvation downregulates iNOS expression by inhibiting the STAT3 nuclear translocation and promotes cytoplasmic STAT3(Ser727) phosphorylation, which reduces ROS expression and mitochondrial dysfunction, thereby alleviating inflammatory pain. These findings underscore the therapeutic potential of targeting AMPK and STAT3 pathways in inflammatory pain management.