Glucagon secretion and islet neuropathy

描述（由申请人提供）：胰高血糖素对胰岛素诱导的低血糖（IIH）的反应在1型糖尿病早期明显受损。我们以前已经证明，这种胰高血糖素反应在很大程度上是由非糖尿病动物和人类介导的。最近，我们在患有1型糖尿病的人类受试者及其动物模型中发现了早期交感性胰岛神经病（eSIN），因此假设eSIN促成了这种胰高血糖素损伤。这项资助的目的是确定1）只有交感神经丢失，2）只有胰岛和3）只有自身免疫性糖尿病的机制。 解释这三个问题的机制是基于发育神经生物学的新兴概念。我们假设，脑源性神经营养因子（BDNF），分泌的B淋巴细胞侵入胰岛在自身免疫性糖尿病的发展，转移平衡的胰岛神经营养因子远离“轴突维护”通过Trk受体向“轴突修剪”通过p75泛神经营养因子受体（NTR），导致选择性损失的胰岛交感神经，从而交感神经α细胞通路的功能障碍。 因此，我们的第一个具体目标是证明BDNF对胰岛交感神经丧失的必要性。我们将通过转基因标记BDNF和化学染色标记的组合定位糖尿病胰岛中的BDNF。我们将通过激光捕获和RT-PCR定量这些胰岛中的BDNF mRNA。我们将通过敲除BDNF基因来证明BDNF的交感神经毒性，从而保留这些神经并防止胰高血糖素对交感神经激活的反应受损。 在我们的第二个具体目标中，我们将通过敲除B淋巴细胞来证明B淋巴细胞的必要性，从而防止胰岛交感神经的丧失和胰高血糖素对交感神经激活的反应受损。 在我们的第三个具体目标中，我们将通过敲除p75 NTR来防止胰岛交感神经的损失，再次保留胰高血糖素对交感神经激活的反应。意义：确定1型糖尿病胰岛交感神经丧失的机制将使我们能够预防或逆转这种丧失。由于交感神经-α细胞通路在IIH期间被激活，并有助于胰高血糖素对IIH的反应，我们预计这种预防可以改善1型糖尿病的胰高血糖素反应。使这种胰高血糖素反应正常化将降低胰岛素诱导的低血糖症的发生率和严重程度，允许对1型糖尿病患者进行更强化的治疗，从而减少导致该疾病长期并发症的慢性高血糖症。

DESCRIPTION (provided by applicant): The glucagon response to insulin-induced hypoglycemia (IIH) is markedly impaired early in type 1 diabetes. We have previously demonstrated that this glucagon response is largely autonomically mediated in nondiabetic animals and humans. More recently we discovered an early sympathetic islet neuropathy (eSIN) in human subjects with type 1 diabetes and animal models thereof and therefore hypothesized that eSIN contributes to this glucagon impairment. The purpose of this grant is to determine the mechanism by which 1) only sympathetic nerves are lost, 2) only from the islets and 3) only in autoimmune diabetes. The mechanism that accounts for all three is based on emerging concepts in developmental neurobiology. We hypothesize that brain derived neurotrophic factor (BDNF), secreted by B-lymphocytes invading the islet during the development of autoimmune diabetes, shifts the balance of islet neurotrophins away from "axonal maintenance" via Trk receptors towards "axonal pruning" via the p75 pan-neurotrophin receptor (NTR), causing a selective loss of islet sympathetic nerves and thereby dysfunction of the sympathetic alpha-cell pathway. Therefore our first Specific Aim is to demonstrate the necessity of BDNF for the loss of islet sympathetic nerves. We will localize BDNF in the diabetic islet by a combination of transgenically tagging BDNF and immunohistochemically staining the tag. We will quantify BDNF mRNA in these islets by laser capturing them and using RT-PCR. We will demonstrate the sympathetic neurotoxicity of BDNF by knocking out the BDNF gene and thereby sparing these nerves and preventing the impairment of the glucagon response to sympathetic nerve activation. In our second Specific Aim we will demonstrate the necessity of B-lymphocytes by knocking them out, thus preventing both the loss of islet sympathetic nerves and the impairment of the glucagon response to sympathetic activation. In our third Specific Aim we will prevent the loss of islet sympathetic nerves by knocking out p75NTR, again preserving the glucagon response to sympathetic nerve activation. Significance: Determining the mechanism for the loss of islet sympathetic nerves in type 1 diabetes will allow us to prevent or reverse that loss. Since the sympathetic-alpha cell pathway is activated during IIH and contributes to the glucagon response to IIH, we expect such prevention to improve this glucagon response in type 1 diabetes. Normalizing this glucagon response will reduce the incidence and severity of insulin induced hypoglycemia, allowing more intensive treatment of patients with type 1 diabetes, thereby reducing the chronic hyperglycemia that causes the long-term complications of this disease.