Khodorova A, Nicol G D, Strichartz G
Pain Research Center, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham & Women's Hospital, Harvard Medical School, Boston, MA, USA.
Neuroscience. 2013 Dec 19;254:312-23. doi: 10.1016/j.neuroscience.2013.09.046. Epub 2013 Oct 1.
Nerve growth factor (NGF) augments the excitability of isolated rat sensory neurons through activation of the p75 neurotrophin receptor (p75(NTR)) and its downstream sphingomyelin signaling cascade, wherein neutral sphingomyelinase(s) (nSMase), ceramide, and the atypical protein-kinase C (aPKC), protein-kinase M zeta (PKMζ), are key mediators. Here we examined these same receptor-pathways in vivo for their role in mechanical hyperalgesia from exogenous NGF. Mechanical sensitivity was tested by the number of paw withdrawals in response to 10 stimuli (PWF=n/10) by a 4-g von Frey hair (VFH, testing "allodynia") and by 10 and 15g VFHs (testing "hyperalgesia"). NGF (500ng/10μL) injected into the male rat's plantar hind paw induced long-lasting ipsilateral mechanical hypersensitivity. Mechano-hypersensitivity, relative to baseline responses and to those of the contralateral paw, developed by 0.5-1.5h and remained elevated at least for 21-24h, Acute intraplantar pre-treatment with nSMase inhibitors, glutathione (GSH) or GW4869, prevented the acute hyperalgesia from NGF (at 1.5h) but not that at 24h. A single injection of N-acetyl sphingosine (C2-ceramide), simulating the ceramide produced by nSMase activity, induced ipsilateral allodynia that persisted for 24h, and transient hyperalgesia that resolved by 2h. Intraplantar injection of hydrolysis-resistant mPro-NGF, selective for the p75(NTR) over the tyrosine kinase (TrkA) receptor, gave very similar results to NGF and was susceptible to the same inhibitors. Hyperalgesia from both NGF and mPro-NGF was prevented by paw pre-injection with blocking antibodies to rat p75(NTR) receptor. Finally, intraplantar (1day before NGF) injection of mPSI, the myristolated pseudosubstrate inhibitor of PKCζ/PKMζ, decreased the hyperalgesia resulting from NGF or C2-ceramide, although scrambled mPSI was ineffective. The findings indicate that mechano-hypersensitivity from peripheral NGF involves the sphingomyelin signaling cascade activated via p75(NTR), and that a peripheral aPKC is essential for this sensitization.
神经生长因子（NGF）通过激活p75神经营养因子受体（p75(NTR)）及其下游的鞘磷脂信号级联反应，增强离体大鼠感觉神经元的兴奋性，其中中性鞘磷脂酶（nSMase）、神经酰胺和非典型蛋白激酶C（aPKC）、蛋白激酶Mζ（PKMζ）是关键介质。在此，我们在体内研究了这些相同的受体途径在外源性NGF诱导的机械性痛觉过敏中的作用。通过4克冯·弗雷毛发（VFH，测试“异常性疼痛”）对10次刺激的爪部撤回次数（PWF=n/10）以及通过10克和15克VFH（测试“痛觉过敏”）来测试机械敏感性。将NGF（500ng/10μL）注射到雄性大鼠的后足底爪部可诱导持久的同侧机械性超敏反应。相对于基线反应和对侧爪部的反应，机械性超敏反应在0.5 - 1.5小时出现，并至少持续升高21 - 24小时。足底急性预处理nSMase抑制剂、谷胱甘肽（GSH）或GW4869可预防NGF引起的急性痛觉过敏（在1.5小时时），但不能预防24小时时的痛觉过敏。单次注射N - 乙酰鞘氨醇（C2 - 神经酰胺），模拟nSMase活性产生的神经酰胺，可诱导持续24小时的同侧异常性疼痛以及在2小时内消退的短暂性痛觉过敏。足底注射对p75(NTR)比对酪氨酸激酶（TrkA）受体具有选择性的抗水解mPro - NGF，得到了与NGF非常相似的结果，并且对相同的抑制剂敏感。预先向爪部注射针对大鼠p75(NTR)受体的阻断抗体可预防NGF和mPro - NGF引起的痛觉过敏。最后，足底注射（在NGF注射前1天）mPSI，即PKCζ/PKMζ的肉豆蔻酰化假底物抑制剂，可减轻NGF或C2 - 神经酰胺引起的痛觉过敏，尽管乱序的mPSI无效。这些发现表明，外周NGF引起的机械性超敏反应涉及通过p75(NTR)激活的鞘磷脂信号级联反应，并且外周aPKC对于这种致敏作用至关重要。
