Leptin Promoted CGRP Expression By ERK/MAPK Pathway, Thereby Attenuating Cerebral Ischemia Injury

Cerebral stroke is the major leading cause of death and disability, and it is estimated that it is responsible for nearly 50% of the patients hospitalized for acute neurological disorders. Stroke is usually characterized by ischemia/reperfusion (I/R) of cerebral blood vessels, resulting in decreased blood flow and neurocyte damage. Therefore, improving blood flow and neurocyte function are keys to protecting the brain from ischemia/reperfusion injury.Leptin has been identified as an ob gene-expression protein, mainly secreted by adipose tissue, with roles of inhibiting food intake, modulating weight balance, and regulating energy metabolism. Previous studies showed that leptin could protect the cerebral ischemia tissues from injury; however, the identity of the signaling molecules downstream of leptin that protect against cerebral ischemic injury remains unclear. Calcitonin gene-related peptide (CGRP) is known to play an important role in the control of intracranial blood flow and protection of neurons. It has been reported that CGRPs-37 administration torats with CIP (Caerulein-Induced Pancreatitis) that were pretreated with leptin resulted in the partial reversal of pancreato protective effect of leptin. This study demonstrates that CGRP is involved in the protective effects of leptin on the caerulein-overstimulated pancreas. However, whether and how peripherally-administered leptin could attenuate the collateral vessels around the ischemic region and protect I/R injury by inducing CGRP expression in this injury has not been reported. Here we used an in vivo I/R model and in vitro H/R model to explore the mechanism of leptin neuroprotection and the relationship between the leptin and CGRP in vitro.Part I The neuroprotection of leptin on mouse cerebral ischemia-reperfusion injury and the role of CGRP in leptin-mediated neuroprotection; Part II How leptin regulats CGRP in neuroprotection. The results are as follows:Part I:(1) Mouse models of transient focal cerebral ischemia/reperfusion were established by cerebral ischemia/reperfusion injury in mouse; leptin decreased Neurological defect; leptin improved mouse regional cerebral blood flow; leptin reduced infarct volume; leptin reduced neuronal apoptosis; it suggestd that leptin has a protective effect on mouse cerebral ischemia/reperfusion injury.(2) After cerebral ischemia/reperfusion, the CGRP expression in ischemic penumbral region was significant reduced, which was increased after leptin treatment; it suggested that CGRP might be involved in leptin-mediated protection against cerebral ischemia/reperfusion injury.(3) The role of primary neurons was aim to explore the neuroprotection of leptin on neurons and the relationship with CGRP. leptin could increased the cell viability; CGRPs-37 reversed the beneficial effects of leptin administration on the neurons; it suggested leptin improved neuron survival rate through CGRP.(4) CGRP expression was significantly increased in the leptin treatment group; leptin increased bcl-2 mRNA levels, decreased caspase-3 mRNA level; CGRP8-37 reversed the beneficial effects of leptin.Part II:(1) OB-Rb mRNA expression was significant increased in SH-SY5Y cells after H/R injury.(2) Compared to the H/R group that was not incubated with leptin, the expression of CGRP in both the leptin-low group and the leptin group was significantly greater in a leptin concentration-dependent manner. However, the effects of increased CGRP expression were inhibited by treatment with Nanobody.(3) Leptin could enhance the level of CGRP in culture, ERK inhibitor U0126 blocked this effect.(4) Organotypic slice belongs to the level of organization, it can better simulate the influence between cells and it is more closer to the state in vivo. Leptin could enhance CGRP expression, ERK inhibitor U0126 blocked this effect.(5) The same with cell level, leptin significantly promoted CGRP expression, which was abolished by ERK inhibitor U0126; it suggested that Leptin may promote CGRP expression by ERK activaion.In summary, this study shows that:(1) Lepitn could promote CGRP expression. This increase appeared to occur in a leptin concentration-dependent manner;(2) The effects of increased CGRP expression were inhibited by treatment with Nanobody.(3)The apoptosis effect of leptin was abolished by CGRP inhibitor CGRP8-37(4) After hypxia/reoxygenation injury, ERK activation was inhibited, which was promoted by leptin treatment.(5) The effect of leptin on increasing CGRP expression was inhibited by ERK inhibitor UO126.