The following two studies have received funding through the National Institutes of Health Program Announcements on Chronic Overlapping Pain Conditions.
Title: GCAMP6 MICE FOR DETERMINATION OF MECHANISMS OF CHRONIC MUSCLE ACHE, PAIN AND FATIGUE
Project Leader: Dr. Alan R. Light, University of Utah
DESCRIPTION (provided by applicant): GCAMP6 mice for determination of mechanisms of chronic muscle ache, pain and fatigue. Muscle pain and muscle fatigue are symptoms in many chronic diseases including Fibromyalgia, Chronic Fatigue Syndrome, Myofacial Pain, Chronic Tension Headache, and Temporomandibular Disorder. Many more patients have degraded quality of life because of short term myalgia and fatigue that sometimes remits with treatment, or for unknown reasons, becomes chronic. Our long term goal is to determine the fundamental mechanisms that signal intense muscle pain, ache and fatigue to sensory and motor systems. We have previously used discoveries in mouse models to prove that combinations of protons, lactate, and ATP are necessary and sufficient to activate muscle sensory neurons. In translational studies in human subjects we showed that combination of these three metabolites activated the sensations of muscle ache and fatigue in human subjects. Here we propose to create a transgenic mouse that will make it possible, for the first time, to image the activity of sensory neurons that signal pain and fatigue in functioning skeletal muscle. This will allow us to establish the molecular and cellular mechanisms of the sensory signaling pathways for cognitive sensations of muscle pain and muscle fatigue. It will also make it possible to directly observe the mechanisms of several controversial phenomena in muscle pain including trigger points, the pulsating nature of muscle ache and chronic and migraine headache, lymphatic disease association with muscle fatigue and muscle pain, and sympathetic activation enhancement of muscle pain. The specific aims for this proposal are: 1) Create mice that have endogenous calcium sensors with promoters that allow expression in Group III/IV muscle innervating sensory neurons. 2) Use these mice to record III/IV afferents responses to low and high metabolites using anesthetized in vivo preparations. This will allow comparisons with the digit muscle recordings collected from teased muscle nerve fibers previously, and dorsal root ganglion neurons recorded with calcium imaging. With this method we will also determine the location and structures that physiologically identified Group III/IV receptor endings innervate (both nociceptors and ergoreceptors of all types e.g., mechanoreceptor and metaboreceptor).
Title: CIRCULATING MICRORNAS AND TLR8 ACTIVATION IN CHRONIC PAIN
Project Leader: Dr. Asma Khan, University of North Carolina at Chapel Hill
DESCRIPTION (provided by applicant): MicroRNAs (miRs) regulate the molecular pathways linked to pain, inflammation, and immune response. Aberrant miR expression is seen in a variety of conditions including acute and chronic pain, inflammation, neurodegeneration, cancer, and others. Acute and chronic pain affects over 100 million US adults, and a large subpopulation of chronic pain patients suffer from >1 pain condition. Recent studies indicate that extracellular miRs (including those in serum-derived exosomes) act as physiologic ligands for rodent toll-like receptor 7 (TLR7; TLR8 in humans). The long-term goal is to better understand the role of extracellular miRs in acute and chronic pain. Pain associated with inflammation of the tooth pulp (pulpitis) is used here as a model of a single acute pain condition. Pain in patients diagnosed with ≥3 of the following conditions – temporomandibular disorder (TMD), episodic migraine (EM), vulvar vestibulitis syndrome (VVS), fibromyalgia (FM), and irritable bowel syndrome (IBS) – is used as a model of chronic overlapping pain conditions. The objective of this project is to examine whether serum-derived exosomal miRs contribute to chronic overlapping pain conditions. The central hypothesis is that serum-derived exosomal miRs bind TLR8 and activate NFKB, resulting in the release of pro-pain cytokines. This hypothesis has been formulated on the basis of preliminary data produced in our laboratory. Using pulpitis as a model of acute pain, we show that miRs are differentially expressed in inflamed pulps as compared to normal pulps. Using blood samples of chronic pain patients we show that the miR profile in the blood of patients with chronic pain conditions differs from that o pain-free controls, and that the miR profiles of patients with >1 chronic pain condition differs from those with a single pain condition. Our pilot data also suggest that experimental muscle pain sensitivity and affective pain is correlated with miR expression. These preliminary studies lead us to propose the novel hypothesis that serum-derived exosomal miRs bind TLR8 and activate NFKB, resulting in the release of pro-pain cytokines. Specific Aim 1 examines the miR profile in serum-derived exosomes and affected (local) tissues of three groups of patients (n=150) (50 with symptomatic pulpitis; 50 with asymptomatic pulpitis; and 50 pain-free controls). Specific Aim 2 compares the miR profile in serum-derived exosomes of patients diagnosed with ≥3 chronic pain conditions (TMD, EM, VVS, FM, IBS) (n=100) with that of pain-free controls (n=100). Specific Aim 3 explores whether miRs differentially expressed in pain patients bind TLR8 and induce NFKB activation and the release of pro-pain cytokines. This proposal is innovative because it is the first to examine the role of exosomal miRs in overlapping pain conditions. The proposed research is significant because it is the first step in a continuum of research that is expected to lead to the development of miR-based biomarkers and pharmacologic strategies that will result in better diagnosis and management of chronic overlapping pain conditions.