Deranged Gut Homeostasis and the Pathogenesis of Fibromyalgia

About This Grant

Fibromyalgia (FM) is a chronic debilitating painful condition, affects millions of people in the U.S. alone, and is often refractory to the current treatment. The etiology of FM is multifactorial in which deranged gut homeostasis has been strongly implicated. Up to 70% of FM patients exhibit signs of deranged gut homeostasis, highlighting a key gastrointestinal component in the pathogenesis of FM. To date, the molecular link between deranged gut homeostasis and FM is poorly understood. The gut brush border enzyme intestinal alkaline phosphatase (IAP), encoded by Akp3 gene in mice and Alpi gene in humans, is a critical regulator of gut homeostasis. We and others have reported that knockout of Akp3 (Akp3-/-, IAP deficiency) in mice disrupts gut homeostasis with increased gut and systemic inflammation markers. Our preliminary data demonstrate that a) Akp3-/- mice recapitulated FM- like phenotypes including i) hypersensitivity to mechanical and thermal stimulation, ii) spontaneous pain behavior, and iii) FM-related comorbid behaviors including depression and anxiety; b) administration of exogenous recombinant IAP reversed IAP deficiency and improved FM-like phenotypes in Akp3-/- mice; c) macrophages and transient receptor potential vanilloid 1 (TrpV1) expression were increased in the dorsal root ganglion (DRG) of Akp3-/- mice; and d) IAP levels were reduced in stool samples of FM patients as compared to healthy subjects. These findings suggest that IAP could be a key molecule link between deranged gut homeostasis and the pathogenesis of FM. We propose that deficiency of Akp3-encoded IAP would lead to FM-like phenotypes through macrophage-mediated sensitization of TrpV1 positive (TrpV1+) nociceptors in the DRG. In Aim 1, we will test the hypothesis that IAP deficiency induces macrophage infiltration into the DRG and FM-like phenotypes. We will examine i) macrophage infiltration into the DRG using flow cytometry, immunostaining, and two-photon imaging with an innovative in vivo DRG window technique to correlate with FM-like phenotypes; ii) the effect of reversing IAP deficiency with exogenous recombinant IAP on macrophage infiltration into the DRG and FM-like phenotypes; and iii) the relationship between IAP deficiency-induced deranged gut homeostasis and DRG macrophage infiltration. In Aim 2, we will test the hypothesis that macrophage infiltration into the DRG plays a critical role in FM-like phenotypes. Genetic and pharmacological approaches will be used to i) deplete systemic vs. DRG macrophages; ii) inhibit monocyte/macrophage trafficking; and iii) suppress inflammatory macrophages. In Aim 3, we will test the hypothesis that TrpV1+ nociceptors in the DRG are sensitized via macrophage- nociceptor interactions in mice with FM-like phenotypes. We will i) inhibit TrpV1 genetically (TrpV1DTR) or pharmacologically and ii) examine a macrophage-mediated signaling in sensitization of TrpV1+ nociceptors using an innovative DRG calcium imaging platform, TrpV1::ChR2 mice, and patch clamp recording. This project will provide insights into a novel molecular mechanism of FM pathogenesis and help transform the current treatment limited to managing FM symptoms to mechanism-based therapy for FM patients with deranged gut homeostasis.