HO-1 alleviates neuroinflammation and cystitis-related symptoms in cyclophosphamide-induced cystitis via the SIRT1 pathway

Abstract Background Our previous study suggested that astrocytes and microglia are activated in the spinal dorsal horn (SDH) of interstitial cystitis/bladder pain syndrome (IC/BPS) rats and induce neuroinflammation by secreting proinflammatory cytokines. Heme oxygenase-1 (HO-1) plays a key role in inhibiting neuroinflammatory processes in the central nervous system and can activate silent information regulator 1 (SIRT1), which has an inhibitory effect on neuroinflammation; however, whether HO-1 alleviates neuroinflammation in IC remains unclear. This study aimed to elucidate the role of HO-1 in rat IC models and confirm whether SIRT1 mediates HO-1 function. Methods Rats were administered with cyclophosphamide (CYP) by systemic intraperitoneal injection to develop IC models. Hemin (inducer of HO-1) and Znpp (HO-1 inhibitor) were performed intraperitoneally 1-day prior to each CYP injection. EX-527 was injected intrathecally for 3 consecutive days to selectively inhibit SIRT1. We used the von Frey filament test to measure mechanical withdrawal threshold, and urinary frequency was assessed using urodynamic tests. HO-1, SIRT1, glial fibrillary acidic protein (an astrocyte marker), ionized calcium-binding adapter molecule (a microglia marker), phosphorylated (p)-c-Jun N-terminal kinase (JNK), p-p38, and proinflammatory cytokines [interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α] levels were assessed by western blot, and immunofluorescence was used to identify HO-1 and SIRT1 cellular localization. Results We observed downregulated HO-1 expression in the SDH of rats with CYP-induced cystitis, which was accompanied by neuroinflammation, mechanical allodynia, and urinary frequency. Additionally, HO-1 induction after hemin treatment suppressed glial cell activation and attenuated IL-1β, IL-6, and TNF-α expression by inhibiting activation of the JNK/p38 pathway, ultimately improving IC-related symptoms. Moreover, Znpp administration exacerbated inflammatory responses and pain sensitivity by inhibiting HO-1 activity. Furthermore, HO-1 positively regulated SIRT1 activation and alleviated IC-related symptoms, whereas the therapeutic effect of HO-1 upregulation was significantly impaired by SIRT1 inhibition. Conclusion HO-1 attenuated neuroinflammation, mechanical allodynia, and urinary frequency caused by glial activation in rats with CYP-induced cystitis by activating SIRT1 to inhibit JNK/p38 signaling.