PPAR Inhibition of Spinal Pain Transmission

描述（由申请人提供）：过氧化物酶体增殖物激活受体γ (PPAR 3)被认为是噻唑啉二酮（TZD）类抗糖尿病药物的关键靶点。我们的初步结果描述了PPAR 3 mRNA和蛋白在背角的存在。此外，我们证明，鞘内给药罗格列酮（一种TZD）和15d-PGJ2（一种内源性PPAR 3配体）以剂量依赖和PPAR 3依赖的方式，以及全身给药吡格列酮（一种经fda批准的血脑屏障配体），可以迅速减轻与炎症或神经损伤相关的机械和热过敏。该提议的中心假设是，背角中PPAR3的配体依赖性激活减少了损伤诱导的脊髓神经元和神经胶质的激活，从而抑制了炎症和神经性疼痛的行为迹象。本应用的目的是确定PPAR介导的炎症性或神经性疼痛抑制的机制，重点是吡格列酮。我们研究项目的长期目标是利用PPAR信号的治疗潜力来减轻人类的慢性疼痛。AIM 1将检验PPAR 3激动剂减少异位性疼痛和痛觉过敏的假设。我们将使用药理学药物和神经系统特异性PPAR 3缺失突变体来确定脊髓中PPAR 3信号在慢性疼痛的诱导和维持中的作用。首先，我们将确定单次鞘内或全身给药吡格列酮和15d-PGJ2是否能减少炎症和神经性疼痛的行为体征。我们预测它们的镇痛作用将被PPAR 3拮抗剂阻断。其次，我们将确定在组织或神经损伤之前或之后开始慢性鞘内或口服PPAR 3激动剂是否可以减少炎症和神经性疼痛的行为体征。第三，我们预测抗异动作用不会发生在神经元特异性PPAR 3敲低的小鼠身上。AIM 2将验证PPAR 3配体减少背角神经元和小胶质细胞损伤诱导激活的假设。体感刺激损伤大鼠可诱导背角浅层中直接早期基因c-fos的表达。我们预测鞘内吡格列酮将减少炎症和神经损伤诱导的Fos免疫反应神经元的表达，以及OX-42的表达，OX-42是小胶质细胞激活的标志。AIM 3将检验内源性PPAR 3系统强直抑制异位性疼痛的假设。首先，我们将确定PPAR3表达是否发生在疼痛时激活的神经元和/或胶质细胞中。其次，在Aims 1-2的扩展中，我们将确定受体拮抗剂和基因缺失是否会增加异位性疼痛和神经元/神经胶质激活。如果是肯定的，那么我们将确定PPAR3信号传导元件是否与异常性疼痛共同变化。在神经损伤或持续炎症后的不同时间，我们将评估：行为和A) PPAR 3 mRNA和蛋白；B)磷酸化PPAR 3；C) 15d-PGJ2水平的LC/MS/MS。慢性疼痛管理是一项重大的科学和卫生保健挑战，因为目前的镇痛药物很少能在没有严重副作用的情况下提供足够的疗效。我们认为过氧化物酶体增殖物激活受体γ (PPAR 3)的配体，如罗格列酮和吡格列酮，代表了一类新的镇痛/抗异动化合物。这些概念上的创新实验是重要和及时的，因为TZDs在商业上可用于糖尿病，并在中枢神经退行性疾病的临床试验中。因此，证实我们的假设可能会导致快速转化为慢性疼痛的临床治疗。

DESCRIPTION (provided by applicant): Peroxisome proliferator-activated receptor gamma (PPAR 3) is well-characterized as a key target of the thiazolinedione (TZD) class of anti-diabetic drugs. Our preliminary results describe the existence of PPAR 3 mRNA and protein in the dorsal horn. Furthermore, we demonstrate that the mechanical and thermal hypersensitivity associated with inflammation or nerve injury was rapidly reduced by intrathecal administration of rosiglitazone (a TZD) and 15d-PGJ2 (an endogenous PPAR 3 ligand) in a dose- and PPAR 3-dependent manner, and by systemic administration of pioglitazone, a BBB-permeant, FDA-approved ligand. The central hypothesis of this proposal is that ligand-dependent activation of PPAR3 in the dorsal horn decreases injury- induced activation of spinal neurons and glia that then dampens behavioral signs of inflammatory and neuropathic pain. The objective of the present application is to identify the mechanisms underlying PPAR- mediated inhibition of inflammatory or neuropathic pain, with a focus on pioglitazone. The long-term goal of our research program is to harness the therapeutic potential of PPAR signaling to alleviate chronic pain in humans. AIM 1 will test the hypothesis that PPAR 3 agonists reduce allodynia and hyperalgesia. We will use pharmacological agents and nervous system-specific PPAR 3 deletion mutants to determine the contribution of PPAR 3 signaling in the spinal cord to the induction and maintenance of chronic pain. First, we will determine whether single intrathecal or systemic administration of pioglitazone and 15d-PGJ2 reduces behavioral signs of inflammatory and neuropathic pain. We predict that their analgesic actions will be blocked with PPAR 3 antagonists. Second, we will determine whether chronic intrathecal or oral administration of PPAR 3 agonists, begun before or after tissue or nerve injury, reduces behavioral signs of inflammatory and neuropathic pain. Third, we predict that anti-allodynic actions will not occur in mice with neuron-specific PPAR 3 knockdown. AIM 2 will test the hypothesis that PPAR 3 ligands reduce injury-induced activation of neurons and microglia in the dorsal horn. Somatosensory stimulation of injured rats induces the expression of the immediate early gene, c-fos, in the superficial laminae of the dorsal horn. We predict that intrathecal pioglitazone will reduce inflammation- and nerve injury-induced expression of Fos immunoreactive neurons, as well as the expression of OX-42, a marker of microglia activation. AIM 3 will test the hypothesis that endogenous PPAR 3 systems tonically inhibit allodynia. First, we will determine if PPAR3 expression occurs in neurons and/or glia that are activated during pain. Second, in an extension of Aims 1-2, we will determine whether receptor antagonists and genetic deletion increase allodynia and neuronal/glial activation. If affirmative, then we will determine whether the PPAR3 signaling elements co- vary with allodynia. At various times after nerve injury or persistent inflammation, we will evaluate: behavior and A) PPAR 3 mRNA and protein; B) phosphorylated PPAR 3; and C) 15d-PGJ2 levels with LC/MS/MS. PUBLIC HEALTH RELEVANCE Chronic pain management is a major scientific and health care challenge, as current analgesic drugs rarely provide sufficient efficacy in the absence of serious side effects. We propose that ligands for peroxisome proliferator-activated receptor gamma (PPAR 3), such as rosiglitazone and pioglitazone, represent a novel class of analgesic / anti-allodynic compounds. These conceptually innovative experiments are important and timely because TZDs are commercially available for diabetes and are in clinical trials for CNS neurodegenerative diseases. Thus, confirmation of our hypothesis could lead to rapid translation to the clinical treatment of chronic pain.