SEXUAL DYNAMIC CONTRIBUTION OF DRG MACROPHAGES AND SATELLITE GLIAL CELLS IN VISCERAL PAIN

BACKGROUND: Macrophages and satellite glial cells (SGCs) are two major nonneuronal cell types in dorsal root ganglion (DRG) proximal to sensory neurons to participate in pain development. They are documented to produce proinflammatory factors to facilitate nociception. The precise role of these nonneuronal cells in visceral pain in a sex-dependent fashion has not been characterized. The goal of this study is to use approaches of chemogenetic activation of nociceptors, chemogenetic activation of SGCs, or induction of colitis to induce visceral pain to investigate the interrelationships of sensory neurons-macrophages-SGCs triad in DRG. AIMS: (1) Characterizing the role of macrophages in neuroinflammation by macrophage FAS-induced apoptosis (MAFIA) transgenics; (2) Interrogating SGC activity by hM3Dq-based chemogenetics or conditional gene deletion; and (3) Measuring macrophage subtypes and proinflammatory factors in DRG in colitis. METHODS: MAFIA mice that expressed a suicide gene (FAS) and green fluorescent protein (GFP) under the control of colony-stimulating factor-1 receptor (CSF1R) received AP20187 (AP, 1 mg/kg intraperitoneally (i.p)) treatment to deplete CSF1R⁺ monocytes infiltration. Nav1.8;hM3Dq and proteolipid protein (Plp)1;hM3Dq mice received clozapine N-oxide (CNO, 1 mg/kg, i.p) to activate nociceptive neurons and SGCs, respectively. Inhibition of SGCs was fulfilled by conditional deletion of TrkB.T1. Colitis was induced by intracolonic installation of 2,4,6-Trinitrobenzene sulfonic acid and animals were sacrificed on day 3 based on our time course studies. Macrophage populations were characterized by flow cytometry and immunohistochemistry. Proinflammatory factors were measured by qPCR. RESULTS: Chemogenetic activation of nociceptive neurons or colitis in wildtype mice increased CSF1 production in DRG in both sexes. Colitis also increased CSF1R⁺CD11b⁺ monocytes infiltration of DRG in both sexes with CSF1R⁺GFP⁺ macrophages accumulated around DRG neurons. AP20187 treatment of MAFIA mice with colitis mitigated the population of CD11b⁺ monocyte infiltration in DRG of both sexes, however, only attenuated colitis-induced tumor necrosis factor alpha (TNF-α) upregulation in DRG of female but not male mice. Chemogenetic activation of SGCs did not change the levels of CSF1 in DRG in both sexes, but increased TNFα production in DRG of male mice but not female mice. Genetic inhibition of SGCs attenuated colitis-induced TNFα production in male mice but not female mice. CONCLUSION: Neuroinflammation of DRG manifested by upregulation of TNFα occurs in visceral pain states. CSF1 is produced by DRG neurons but not SGCs in visceral pain. CSF1R⁺CD11b⁺ monocytes have a more pronounced role in female mice than in male mice to drive neuroinflammation. SGCs, on the other hand, have a stronger role in male mice than in female mice to produce TNFα in colitis.