Caveolin-1 and Altered Neuregulinism in Diabetic Neuropathy

描述(申请人提供)：糖尿病周围神经病变(DPN)的病因很复杂，涉及神经元和雪旺细胞(SCs)的变性。尽管许多注意力集中在生长因子信号如何改变对神经元功能障碍的影响上，但在我们对高血糖如何影响神经营养因子的理解上仍有很大差距。神经调节蛋白-1(NRG1)是一种神经胶质营养生长因子，通过激活发育中的干细胞中的Erb B受体酪氨酸激酶，促进细胞存活、有丝分裂和髓鞘形成。相反，与DPN的病因相关的是，有髓干细胞中Erb B2的病理性激活可导致脱髓鞘和周围神经病的发生。我们的广泛假设是，糖尿病引起“改变的中性粒细胞增多症”，导致SC变性和DPN的进展。为了支持这一假设，我们提供了糖尿病刺激周围神经Erb B2活性的证据，并且这与Erb B2的负性调节因子小窝蛋白-1(Cav-1)的下调有关。利用有髓干细胞/感觉神经元共培养，我们证明了高血糖降低Cav-1水平并增强NRG1诱导的脱髓鞘。Cav-1基因敲除的糖尿病小鼠出现机械性痛觉减退的速度比野生型小鼠更快，因此Cav-1基因敲除小鼠体内有髓轴突的变性可能与Cav-1的作用有关。类似地，我们使用一种新型的SC特异性条件转基因小鼠来证明Erb B2的活性足以导致运动神经传导速度减慢并诱导机械性痛觉减退，该转基因小鼠可以上调结构性活性的Erb B2对多西环素的反应。因此，我们的目标是整合动物和细胞模型的发现，从机制上了解Erb B2的病理激活如何影响干细胞，并导致DPN感觉功能障碍的发生。我们的目标是：1)使用野生型和Cav-1基因缺失小鼠的有髓SC/感觉神经元外植体，确定Cav-1在高血糖条件下增强NRG1退变效应的机制；2)利用Cav-1基因缺失的小鼠，确定Cav-1在促进Erb B2激活和DPN发生中的必要性/充分性；3)确定糖尿病对糖尿病神经NRG表达的影响，并利用新型Erb B2条件转基因小鼠确定Erb B2在导致感觉障碍方面的充分性。这项工作将为理解NRGs在调节DPN中的轴突-神经胶质相互作用中的作用提供一个新的范式。公共卫生相关性：糖尿病周围神经病变(DPN)是由腿部和手臂传递感觉的神经退化引起的。雪旺细胞(Schwann cell，SCs)是一种特殊的细胞，与许多神经密切相关，在DPN中也经历着深刻的变化。我们的假设是，长期的高血糖应激改变了干细胞对被称为神经调节蛋白的生长因子的反应。在成人有髓神经中，神经调节蛋白可诱导脱髓鞘，从而导致DPN。利用有髓神经的细胞培养模型，我们发现葡萄糖增加了神经调节蛋白的退变效应。因此，本研究的目的是确定糖尿病是否影响糖尿病小鼠神经中神经调节素的表达和活性，并确定神经调节素诱导神经变性的分子事件。这些研究的预期结果是，我们将确定可能增强生长因子在治疗DPN中的治疗效果的分子相互作用。

DESCRIPTION (provided by applicant): The etiology of diabetic peripheral neuropathy (DPN) is complex and involves the degeneration of both neurons and Schwann cells (SCs). Although much attention has focused on how altered growth factor signaling contributes to neuronal dysfunction, a significant gap exists in our understanding of how hyper-glycemia affects gliotrophic factors. Neuregulin-1 (NRG1) is a gliotrophic growth factor that promotes cell survival, mitogenesis and myelination by activating Erb B receptor tyrosine kinases in developing SCs. In contrast, and relevant to the etiology of DPN, pathologic activation of Erb B2 in myelinated SCs can induce demyelination and the onset of peripheral neuropathies. Our broad hypothesis is that diabetes induces an "altered neuregulinism" that contributes to SC degeneration and the progression of DPN. In support of this hypothesis, we provide evidence that diabetes stimulates Erb B2 activity in peripheral nerve and that this correlates with the downregulation of a negative regulator of Erb B2, caveolin-1 (Cav-1). Using myelinated SC/sensory neuron co-cultures, we demonstrate that hyperglycemia decreases Cav-1 levels and enhances NRG1-induced demyelination. Cav-1 may contribute to the degeneration of myelinated axons in vivo as the rate of onset of a mechanical hypoalgesia was faster in diabetic Cav-1 knockout versus wild type mice. Similarly, we show that Erb B2 activity is sufficient to cause a decrease in motor nerve conduction velocity and induce a mechanical hypoalgesia using a novel SC-specific conditional transgenic mouse that upregulates a constitutively-active Erb B2 in response to doxycycline. Thus, our goal is to integrate findings from animal and cellular models to gain mechanistic insight into how pathologic activation of Erb B2 affects SCs and contributes to the onset of sensory dysfunctions in DPN. Our objectives are to: 1) determine the mechanism by which Cav- 1 enhances the degenerative effects of NRG1 under hyperglycemic conditions using myelinated SC/sensory neuron explants from wild type and Cav-1 null mice, 2) determine the necessity/sufficiency of Cav-1 in contributing to Erb B2 activation and the onset of DPN using Cav-1 null mice and 3) determine the effect of diabetes on NRG expression in diabetic nerve and ascertain the sufficiency of Erb B2 in contributing to sensory deficits using novel Erb B2 conditional transgenic mice. This work will provide a new paradigm toward understanding the effect of NRGs in modulating axo-glial interactions in DPN. PUBLIC HEALTH RELEVANCE: Diabetic peripheral neuropathy (DPN) results from the degeneration of nerves that transmit sensations from the legs and arms. Schwann cells (SCs) are specialized cells that closely associate with many nerves and also undergo profound changes in DPN. Our hypothesis is that prolonged hyperglycemic stress alters the response of SCs to growth factors called neuregulins. In adult myelinated nerve, neuregulins can induce demyelination, which contributes to DPN. Using a cell culture model of myelinated nerve, we have identified that glucose increases the degenerative effects of neuregulins. Thus, the objectives of this research are to determine if diabetes affects the expression and activity of neuregulins in diabetic nerve from mice and to identify the molecular events by which neuregulins may induce nerve degeneration. The expected outcome of these studies is that we will identify molecular interactions that may enhance the therapeutic benefit of growth factors in the treatment of DPN.