Molecular Roles of Cdk5 in Neuronal Functions and Pain Signaling

Cdk 5调节疼痛信号传导： 我们最近报道了Cdk 5在疼痛信号传导中的新作用。我们以前报道，Cdk 5和p35的表达，以及Cdk 5激酶活性，增加在背根神经节（DRG）和脊髓（SC）外周炎症后。在小鼠后爪注射角叉菜胶诱导的炎症增加了伤害性神经元中Cdk 5/p35的mRNA和蛋白水平，随后增加了Cdk 5激酶活性。此外，我们发现Cdk 5活性升高使瞬时受体电位香草酸1（TRPV 1）磷酸化，TRPV 1是调节激动剂诱导的神经元钙内流的关键受体。此外，我们发现炎症通过TNF-α激活早期生长反应1（Egr-1）和p35表达触发Cdk 5活性增加。这些发现表明Cdk 5在疼痛信号传导的分子机制中起着重要作用。 Cdk 5和TGF-β通路之间的串扰影响伤害性信号传导： 我们早期对TGF-β 1-/-小鼠表型特征的研究证实了TGF-β 1是炎症的关键调节因子。TGF-β 1-/-小鼠发展为快速消耗综合征，并在3-4周龄时死亡。这些小鼠表现出过度的炎症反应，淋巴细胞和巨噬细胞大量浸润到许多器官中，主要是心脏、肺和唾液腺。TGF-β 1通常以低水平存在于健康的成年CNS细胞中，但其水平在损伤后迅速上调，并诱导几种损伤相关基因的表达。TGF-β 1也被认为可以促进神经元的存活，尽管其机制尚不清楚。TGF-β 1也与阿尔茨海默病的病理学有关。TGF-β 1在星形胶质细胞中的过度表达可导致细胞外基质成分在脑中过度沉积，从而导致神经系统疾病。最近的研究表明，TGF-β 1可能参与神经病理性疼痛和炎性疼痛，然而，其参与疼痛信号传导的分子机制仍然很不清楚。因此，我们研究的主要目的是探索Cdk 5和TGF-β信号通路之间可能的串扰，以及这种串扰对炎症诱导的疼痛的影响。 我们的研究表明，在TGF-β 1-/-小鼠的神经组织中，Cdk 5、p35和p39的蛋白水平降低，导致Cdk 5活性降低。此外，TGF-β 1-/-小鼠显示TG和DRG中Cdk 5介导的TRPV 1磷酸化减少，伴随着对有害热刺激的行为反应减弱。这与PKC-δ（一种已知的p35调节因子）活性降低有关。最重要的是，我们发现TGF-β R1 f/f; SNS-Cre小鼠还显示出沿着痛觉减退的DRG中Cdk 5表达降低。此外，TGF-β 1治疗大鼠神经母细胞瘤B104细胞增加Cdk 5活性，而SB-431542，TGF-β 1信号传导抑制剂治疗，降低Cdk 5活性。在DRG原代培养物中，TGF-β 1处理增强辣椒素诱导的Ca+2内流。这些发现表明TGF-β和Cdk 5通路之间的主动串扰调节炎症诱导的疼痛信号传导。

Cdk5 regulates pain signaling: We have recently reported a novel role of Cdk5 in pain signaling. We previously reported that expression of Cdk5 and p35, as well as Cdk5 kinase activity, was increased in the dorsal root ganglia (DRG) and the spinal cord (SC) after peripheral inflammation. Inflammation induced by carrageenan injection in the hind paws of mice increased the mRNA and protein levels of Cdk5/p35 in nociceptive neurons, with a subsequent increase in Cdk5 kinase activity. Furthermore, we identified that the elevated Cdk5 activity phosphorylates transient receptor potential vanilloid 1 (TRPV1), a key receptor that modulates agonist-induced calcium influx in neurons. Additionally, we found that inflammation triggers an increase in Cdk5 activity through activation of early growth response 1 (Egr-1) and p35 expression by TNF-alpha. These findings suggest that Cdk5 plays an important role in the molecular mechanisms involved in pain signaling. Crosstalk between Cdk5 and TGF-beta pathways affects nociceptive signaling: Our earlier studies on the characterization of the TGF-beta1-/- mouse phenotype confirmed TGF-beta1 as a key regulator of inflammation. TGF-beta1-/- mice develop a rapid wasting syndrome and die by 3-4 weeks of age. These mice display an excessive inflammatory response with massive infiltration of lymphocytes and macrophages into many organs, principally the heart, lungs, and salivary glands. TGF-beta1 is normally present at low levels in healthy adult CNS cells, but its level is rapidly up-regulated following injury and induces expression of several injury-related genes. TGF-beta1 is also known to promote the survival of neurons, although the mechanism is still not clear. TGF-beta1 has also been implicated in the pathology of Alzheimer's disease. TGF-beta1 over-expression in astrocytes can lead to excessive deposition of extracellular matrix components in the brain, resulting in neurological disease. Recent reports indicate that TGF-beta1 may participate in neuropathic and inflammatory pain; however, the molecular mechanisms underlying its involvement in pain signaling are still far from clear. Therefore, the main objective of our study was to explore possible crosstalk between Cdk5 and TGF-beta signaling pathways, and the influence of this crosstalk on inflammation-induced pain. Our studies revealed that the protein levels of Cdk5, p35, and p39 are reduced in the nervous tissues of TGF-beta1-/- mice, resulting in decreased Cdk5 activity. Moreover, TGF-beta1-/- mice showed decreased Cdk5-mediated phosphorylation of TRPV1 in the TG and DRG, with concomitant attenuated behavioral responses to noxious thermal stimulation. This was associated with decreased activity of PKC-delta, a known regulator of p35. Most importantly, we found that TGF-betaR1f/f; SNS-Cre mice also displayed decreased Cdk5 expression in DRGs along with hypoalgesia. In addition, TGF-beta1 treatment of rat neuroblastoma B104 cells increased Cdk5 activity, whereas treatment with SB-431542, an inhibitor of TGF-beta1 signaling, decreased Cdk5 activity. Treatment with TGF-beta1 potentiated capsaicin-induced Ca+2 influx in DRG primary cultures. These findings indicate that active crosstalk between TGF-beta and Cdk5 pathways regulate inflammation-induced pain signaling.