The extracellular matrix (ECM) plays a major role in the pathophysiology of painful connective tissue diseases characterized by inflammation and tissue injury, such as arthritis and dermatitis. High molecular weight hyaluronan (HMWH), the major non-protein component of the ECM, is metabolized to low molecular weight hyaluronans (LMWH) in these clinical conditions. In preliminary studies we have shown that LMWH sensitizes synovial and cutaneous nociceptors, and produces articular and cutaneous mechanical hyperalgesia. In contrast, HMWH is currently used in the treatment of pain in patients with arthritis and other connective tissue diseases, and while current dogma teaches that the analgesic properties of HMWH are due to its viscoelastic properties, we propose the novel hypothesis that both HMWH-induced analgesia/anti-hyperalgesia, and LMWH-induced mechanical hyperalgesia are both generated by their action at the cognate hyaluronan (HA) receptor, CD44, in the plasma membrane of pain sensory neurons (nociceptors). To test this hypothesis, we will: 1) comprehensively study the pro- and anti-nociceptive properties of these two size classes of HA to establish the properties of LMWH that induce pain (hyperalgesia) and HMWH that induce analgesia (anti-hyperalgesia); 2) use in vitro patch-clamp electrophysiology to establish that HA acts directly on nociceptors to sensitize (LMWH) or reverse sensitization (HMWH) of nociceptor excitability, and determine the nociceptor populations upon which HAs act to produce their effects and the ion channels in each population whose function is modulated by HA; 3) confirm the role of the cognate hyaluronan receptor, CD44 and its downstream second messenger signaling pathways, in LMWH hyperalgesia and HMWH analgesia, and that the CD44 is in nociceptors; and, 4) use preclinical models of inflammatory, neuropathic and stress-induced pain to demonstrate that nociceptor CD44 is involved in the pain in with these syndromes, and that HMWH can be used as an anti-hyperalgesia/analgesia therapeutic modality. The proposed experiments will provide insight into the role of an important element of the ECM in diverse pain syndromes, and a rationale for developing new, more effective forms of HMWH to treat pain.
Once thought to only serve a structural role as a matrix to support cells, the extracellular matrix (ECM), which is present in all tissues, is now known to have important functional roles in cell signaling. High molecular weight hyaluronan (HMWH) is an ECM molecule used to treat osteoarthritis pain, and other pain conditions; we hypothesize that HMWH reduces pain by acting at receptors on pain sensory neurons (nociceptors), and, importantly, in diseased tissue in which HMWH is metabolized to produce small fragments ? low molecular weight hyaluronan (LMWH) ? that can activate nociceptors, thereby producing hyperalgesia (tenderness) and pain. In this grant application we propose to evaluate the role of HMWH and LMWH and their receptors on the function of pain sensing neurons, and in preclinical models of pain conditions, in order to understand the role of hyaluronan in pain, thereby providing guidance for the more rational design of new hyaluronan molecules to improve their analgesic profile.