Establishment and Validation of a Novel Animal Model of Fibromyalgia

Fibromyalgia (FM) is a chronic debilitating pain condition that affects about four million people in the U.S. alone. Current treatment of FM focuses on symptomatic management because the etiology of FM remains poorly understood. It is pivotal to develop and validate new animal models to provide a preclinical platform to evaluate novel therapeutics and conduct in-depth mechanistic investigations. There is significant heterogeneity in FM etiologies, among which deranged gut homeostasis has been strongly implicated. Intestinal alkaline phosphatase (IAP), a gut brush border enzyme, is a critical regulator of gut homeostasis. IAP deficiency alters gut bacterial composition, increases gut permeability, and induces persistent low-grade systemic inflammation. We recently observed that mice with IAP deficiency [IAP knockout (KO)] demonstrate a robust FM-like phenotype and gut- derived pathophysiological changes: a) hypersensitivity to mechanical, thermal, and cold stimulation; b) spontaneous pain behavior; c) fatigue-, anxiety-, and depression-like behaviors; d) signs of deranged gut homeostasis; e) brain neuroinflammation; f) altered skeletal muscle characteristics; and g) improvement of FM- like behavior with the gabapentinoid or IAP treatment. We have also detected decreased IAP activity in fecal samples of FM patients. Accordingly, we propose a novel animal model of FM in IAP KO mice predicated on the important role of deranged gut homeostasis in the FM pathophysiology. In the R61 phase, reliability and reproducibility of behavior-phenotyping of IAP KO mice will be established. In the R33 phase, face, construct and predictive validity will be assessed. In Aim 1 (R61), we will expand our existing IAP KO mice colonies to obtain sex- and age-matched male and female IAP KO mice and WT (wild type) littermates. Fifteen behavioral tests in eight domains will be standardized to evaluate behavioral readouts using composite weighted Z-scores as a primary outcome measure. Reliability of behavioral tests will be assessed by a test-retest procedure in the same cohort of age- and sex-matched IAP KO mice and WT mice by two testers blinded to the genotype. Reproducibility of the behavioral phenotype will be assessed by two independent research groups using IAP KO mice and WT mice raised in two independent animal facilities. In Aim 2 (R33), we will compare behavioral readouts in IAP KO mice with a) clinical FM symptoms and b) epidemiological FM features (female vs. male; prevailing ages) to assess the face validity. Construct validity will be examined by comparing biochemical and histological profiles of IAP KO mice with the pathophysiological features identified in FM patients. In Aim 3 (R33), we will assess the predictive validity of this mouse model using FDA-approved FM treatment or exogenous IAP supplementation. Reduced opioid responsiveness, a clinical finding in FM patients, also will be examined. We anticipate that this preclinical FM model would be instrumental in developing innovative FM biomarkers and therapeutics. This mouse model also lends itself to investigating the molecular mechanisms of FM when combined with leading-edge technologies including genetic tools.