Protein kinase mechanisms for chronic pain in sickle cell disease

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 DESCRIPTION (provided by applicant): Our long-term goal is to advance knowledge of the neural mechanisms of chronic pain in SCD and develop an effective pharmacologic treatment. Pain is not only a life-long companion but also a predictor of mortality rate for the 100,000 Americans living with sickle cell disease (SCD), people mainly of African or Latin descent. Though it is now appreciated that SC pain is characterized by chronic pain with episodes of acute pain, the neurobiology of chronic pain is poorly studied, not well characterized, and is refractory to currently available therapies. A potentially fruitful line of investigation to advanc understanding of pain in SCD is the role of cellular signaling mechanisms mediated by serine/threonine protein kinases. Several isoforms of the protein kinase C (PKC) have been implicated in certain chronic pain conditions. We recently reported that PKCδ is a critical cellulr regulator sensitizing nociceptors in chemotherapy-induced peripheral neuropathy.12 The latter was inhibited by treatments with PKCδ inhibitors or PKCδ-siRNA and was absent in PKCδ-null mice. In a mouse sickle cell transgenic model (TOW mice), PKCδ was found to be significantly activated in the spinal regions relevant for pain and its activity (activation or inhibition) correated with the pain behaviors in TOW mice, thought its exact role remains to be defined. In this proposal, we hypothesize that spinal PKCδ is a neuronal mechanism promoting and maintaining the manifestation of chronic pain in SCD. Our strategy is to systematically examine the expression and activity of PKCδ in TOW mice using real-time qPCR, cellular trafficking/translocation, immunohistochemistry, immunoblotting and enzymatic kinetics methods, and correlate changes in PKCδ expression and activity with the on-set and development of chronic pain (Aim 1). To directly test the hypothesis that spinal PKCδ is a molecular mechanism that maintains (Aim 2) and promote (Aim 3) the manifestation of chronic pain in SCD, we will conduct pharmacologic studies by employing complementary approaches to inhibit PKCδ (isoform-specific peptide inhibitors, siRNA knockdown, hematopoietic stem cell transplantation, and mouse gene-deletion). Throughout the study, age/sex matched non-sickle wildtype littermate mice will be used as controls. Although the current proposal is mechanistically driven, it may ultimately lead to pharmacological interventions that target the PKCδ-pathway for pain in SCD. Having recently moved another kinase inhibitor from bench to a Phase I study in the previous funding cycle, our team is uniquely suited for the (current) mechanistic study and (future) translational work that can ultimately benefit patients with SCD.