Wu Yuan-Bo, Li Hong-Qi, Ren Ming-Shan, Li Wen-Ting, Lv Xin-Yi, Wang Li
Department of Neurology, Provincial Hospital Affiliated to Anhui Medical University, HeFei 230001, China.
Cell Physiol Biochem. 2013;32(2):367-79. doi: 10.1159/000354444. Epub 2013 Aug 15.
BACKGROUND/AIMS: Peripheral neuropathy is a frequent and severe diabetic complication characterized by progressive loss of peripheral nerve axons and manifested by pain and eventually complete loss of sensation. Effective therapy for diabetic peripheral neuropathy (DPN) is still lacking due to our limited understanding of the mechanisms for nerve injury.
Here we tested the roles of endoplasmic reticulum (ER) stress and the ER stress-activated pro-apoptotic protein CHOP and anti-apoptotic protein ORP150 in DPN in a rat model of high-fat/streptozotocin diabetes and in cultured Schwann cells (SCs).
No significant DPN was seen in the early stage of diabetes (4 weeks following verification of diabetes). However, after prolonged diabetes (16 weeks following verification of diabetes), DPN was severely developed as reflected by slowed motor and sensory nerve conduction velocity, blunted thermal nociception, and decreased intraepidermal nerve fiber profiles in the hindpaw. Meanwhile, while it was not noticed in sciatic nerves of early diabetes, ER stress in prolonged diabetic rats was indicated by robust increases in H2O2 production and expression of the ER chaperon glucose-regulated protein 78 (GRP78). ORP150 expression was substantially upregulated, accompanied by mild increase in CHOP expression, resulting in a low CHOP/ORP150 ratio, in early diabetes. In contrast, with prolonged diabetes, CHOP expression exceeded ORP150 expression, resulting in an increased CHOP/ORP150 ratio. In vivo knockdown of ORP150 induced DPN in early diabetes and exacerbated the DPN after prolonged diabetes, whereas knockdown of CHOP ameliorated DPN in rats with prolonged diabetic. On the other hand, in vitro knockdown of ORP150 promoted high glucose-induced SC apoptosis, whereas knockdown of CHOP protected SCs from apoptosis.
Taken together, we have provided evidence for the critical role of ER stress in the development of DN and also uncovered CHOP/ORP150 ratio as an important mechanism for determining neuronal apoptosis during ER stress. In the early stage of diabetes, CHOP/ORP150 ratio was relatively low favoring neuronal cell survival, whereas after prolonged diabetes, CHOP/ORP150 ratio increased resulting in apoptotic cell death leading to accelerated DPN.
背景/目的：周围神经病变是一种常见且严重的糖尿病并发症，其特征为周围神经轴突逐渐丧失，表现为疼痛，最终感觉完全丧失。由于我们对神经损伤机制的理解有限，目前仍缺乏针对糖尿病周围神经病变（DPN）的有效治疗方法。
在此，我们在高脂/链脲佐菌素诱导的糖尿病大鼠模型和培养的雪旺细胞（SCs）中，检测了内质网（ER）应激以及ER应激激活的促凋亡蛋白CHOP和抗凋亡蛋白ORP150在DPN中的作用。
在糖尿病早期（糖尿病确诊后4周）未观察到明显的DPN。然而，在糖尿病病程延长后（糖尿病确诊后16周），DPN严重发展，表现为运动和感觉神经传导速度减慢、热痛觉迟钝以及后爪表皮内神经纤维数量减少。同时，虽然在糖尿病早期的坐骨神经中未观察到，但在病程延长的糖尿病大鼠中，H2O2生成以及ER伴侣葡萄糖调节蛋白78（GRP78）的表达显著增加，提示存在ER应激。在糖尿病早期，ORP150表达大幅上调，同时CHOP表达轻度增加，导致CHOP/ORP150比值较低。相反，随着糖尿病病程延长，CHOP表达超过ORP150表达，导致CHOP/ORP150比值升高。在体内敲低ORP150在糖尿病早期诱导DPN，并在病程延长后加重DPN，而敲低CHOP则改善了病程延长的糖尿病大鼠的DPN。另一方面，在体外敲低ORP150促进了高糖诱导的SCs凋亡，而敲低CHOP则保护SCs免于凋亡。
综上所述，我们提供了证据表明ER应激在DPN发展中起关键作用，并且还揭示了CHOP/ORP150比值是决定ER应激期间神经元凋亡的重要机制。在糖尿病早期，CHOP/ORP150比值相对较低，有利于神经元细胞存活，而在糖尿病病程延长后，CHOP/ORP150比值升高，导致凋亡性细胞死亡，从而加速DPN的发展。
