CP-25 ameliorates dysfunction in the M₃R-IP₃R-Ca²⁺-AQP5 signaling pathway by inhibiting ERS in primary Sjögren's...

Primary Sjögren's syndrome (pSS) is an autoimmune disease with incompletely elucidated pathological mechanisms and a current lack of effective therapeutic agents. CP-25, a structurally modified derivative of paeoniflorin, demonstrates significant therapeutic effects in experimental Sjögren's syndrome (ESS) mouse models; however, its underlying mechanism remains elusive. In this study, we constructed an ESS mouse model induced by autoantigen immunization to explore the biological effects of CP-25 on pSS and its potential mechanisms. The study first revealed the overactivation of endoplasmic reticulum stress (ERS) and the impaired function of M₃R-IP₃R-Ca²⁺-AQP5 signaling pathway in human labial gland tissue. Critically, inhibiting ERS (using 4-PBA) was found to directly ameliorate the impaired M₃R-IP₃R-Ca²⁺-AQP5 signaling pathway function, as evidenced by normalized M₃R expression, restored IP₃R and AQP5 levels, and enhanced intracellular Ca²⁺ intensity in IFNα-stimulated HSGECs, resulting in significantly increased salivary flow rate and reduced salivary gland inflammation in vivo. Furthermore, CP-25 exerted its therapeutic effect by upregulating the M₃R-IP₃R-Ca²⁺-AQP5 signaling pathway function, regulating M₃R membrane expression, and critically inhibiting ERS. Crucially, the beneficial effects of CP-25 on both ERS suppression and pathway restoration were demonstrated to be mechanistically dependent on disrupting the pathological interaction between the key ERS chaperone GRP78 and the IP₃R calcium channel. In summary, impaired M₃R-IP₃R-Ca²⁺-AQP5 signaling contributes to pSS pathogenesis. CP-25 treats pSS by restoring this pathway through regulating M₃R membrane expression, inhibiting ERS, reducing apoptosis, and decreasing GRP78-IP₃R co-expression in HSGECs. This study provides experimental support for CP-25's mechanism and potential clinical application in pSS.