Acyloxyacyl Hydrolase Regulates Microglia-Mediated Pelvic Pain Through Toll-Like Receptor-4

Abstract

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a devastating condition of chronic pelvic pain and urinary dysfunction. We have shown that mice deficient for the lipase acyloxyacyl hydrolase (AOAH) develop pelvic allodynia and exhibit symptoms and comorbidities consistent with IC/BPS, as well as gut dysbiosis. Microglia are resident immune cells of the central nervous system (CNS) that respond to changes in the gut microbiome, and studies have linked microglial activation to neuropathic pain. Additionally, microglia express toll-like receptors (TLRs), including TLR4, which are activated by microbial components. We have previously shown that AOAH-deficient mice exhibit increased gut permeability, suggesting a possible mechanism of microglial TLR4 activation via translocation of microbial products across the intestinal barrier to the brain. Here, we assessed the role of AOAH and TLR4 in microglial activation and pelvic pain. AOAH immunoreactivity co-localized with the microglial marker P2YR12 but not astrocytes, suggesting a functional role for AOAH in microglia. Pharmacologic ablation of CNS microglia with PLX5622 resulted in decreased pelvic allodynia in AOAH-deficient mice and resurgence of pelvic pain upon drug washout. Aligned with microglial activation, we observed altered cytokine abundance in AOAH-deficient cortex that was reduced in AOAH/TLR4-deficient cortex. Consistent with our hypothesis of TLR4 activation by gut microbes, we observed microbiome-dependent activation of cultured BV2 microglial cells. Skeletal analyses revealed that AOAH-deficient mice have an activated microglia morphology in brain regions associated with neuropathic pain, independent of TLR4. Compared to AOAH-deficient mice, AOAH/TLR4-deficient mice exhibited decreased pelvic pain and microglial cytokine expression. Together, these findings demonstrate differential roles for AOAH and TLR4 in microglial activation and pelvic pain and thus identify novel therapeutic targets for IC/BPS.