The National Institutes of Health’s National Institute of Neurological Disorders and Stroke has awarded Duke Anesthesiology’s Andrea Nackley, PhD, a $2,623,436, five-year grant for her project, titled “Defining the Role of Peripheral Adrb3 in Chronic Pain and Inflammation.”
Functional pain syndromes affect more than 100 million people, yet remain ineffectively treated because the causes are largely unknown. Accumulating evidence suggests that these syndromes are due, in large part, to low activity of catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines. An estimated 66 percent of patients with functional pain syndromes, such as fibromyalgia, possess variants in the COMT gene that lead to low activity of the COMT enzyme. Individuals with the ‘low COMT activity’ genotype report greater pain at baseline and enhanced pain following stressful events that potentiate catecholamine release from sympathetic nerves.
Consistent with clinical syndromes, Nackley’s Translational Pain Research Laboratory has shown that pharmacologic inhibition of COMT in rodents produces pain at multiple body sites and enhances pain following repeated stress. In subsequent studies, they demonstrated that COMT-dependent pain is initiated by peripheral adrenergic receptor beta-3 (Adrb3) through the release of pro-inflammatory cytokines in local tissues. The pain is maintained by subsequent increases in pro-inflammatory cytokines in spinal tissues and activation of mitogen activated protein kinases (MAPKs) in the cell bodies and central terminals of pain-sensing nociceptors. Together, this data reveals that heightened catecholamine tone leads to chronic pain via peripheral Adrb3 and its downstream effectors. However, the cell types that express Adrb3 and mediate pain still need to be identified and the molecular mechanisms determined.
Nackley hypothesizes that activation of Adrb3 on adipocytes (fat cells that surround peripheral nociceptor and sympathetic nerve terminals) drives chronic COMT-dependent pain via increases in cytokines and MAPKs that promote inflammation and nociceptor activation. Further, she hypothesizes that stress-induced catecholamine release amplifies the effects of Adrb3 signaling on inflammation and pain. Preliminary data reveal that COMT-dependent increases in pro-inflammatory cytokines are mediated by Adrb3 located on adipocytes. Additional data reveal that sustained activation of Adrb3 leads to decreased levels of miR-133a, a microRNA expressed in adipocytes that is able to block MAPK signaling. Nackley’s new study will extend this work to directly determine 1) Adrb3 and miR-133a expression patterns in adipose vs other peripheral tissues over time and their relationship to COMT-dependent functional pain, 2) the role of peripheral Adrb3 and miR-133a in mediating COMT-dependent inflammation and neuroinflammation, 3) the role of peripheral Adrb3 and miR-133a in mediating COMT-dependent increases in the activity of mechosensitive and thermosensitive nociceptors, and 4) how these molecular and behavioral phenotypes are influenced by stress.
“Conventional therapies, such as opioids and antidepressants, have poor efficacy for managing chronic pain as well as adverse central side-effects, including altered mental states, addiction, and life-threatening respiratory depression,” says Nackley, associate professor in anesthesiology and faculty in the department’s Center for Translational Pain Medicine. “Results from this study will advance our knowledge about the mechanisms whereby peripheral Adrb3 drives chronic pain and elucidate new targets for the development of peripherally-restricted therapies with improved specificity and side-effect profiles for the treatment of functional pain syndromes.”