To Explore The Role And Mechanism Of Kalirin7 In The Medial Prefrontal Cortex In Depression

Depression,a recurrent and severe psychiatric disorder,is predicted to be the first leading cause of illness by 2030,but the underlying mechanisms are still not entirely clear.Neuroplasticity theory is a prevalent hypothesis of many theories of depression,and it is well documented that the dysregulation of neural plasticity is associated with depression.The hypothesis believes that abnormality in the morphology and number of neurons that causes neurological circuit dysfunction in the brain leads to depression symptoms.The medial prefrontal cortex(mPFC),as a cognitive and emotional relevant information processing center,is an important brain region in various neural circuits.The mPFC is one of the most sensitive brain regions to stress.Brain-imaging studies report the decreased volume of PFC is accompanied by neuronal atrophy and reduced spine synapses,which is consistent with the findings in postmortem MDD.In rodent study,chronic stress-induced depression-like behaviors also causes a decrease in expression of synapse-related genes and reduction of dendritic spines in pyramidal neurons of the mPFC.Optogenetics studies found that light-stimulated mPFC induced depression-like behaviors in rodents.Therefore,mPFC is a very important brain region in the onset of depression,but the current researches mainly focus on how depression affects the neuroplasticity of mPFC,and the effects of mPFC neuroplasticity on depression still need to be explored.Kalirin7,a Rho guanine nucleotide exchange factor(Rho GEF),plays a critical role in regulating the formation of dendritic spines and maintenance of synaptic plasticity.In rodent studies,CUMS-induced depression-like behaviors caused a decrease in dendritic spine density in the hippocampus and orbitofrontal Cortex,and accompanied by a decrease in Kalirin7 expression.But the role of Kalirin7 in depression remains unknown.These studies generated our hypothesis that Kal7 in the mPFC plays a key role in CUMS-induced depression-like behaviors.The aim of his study was to investigate the effect of Kalirin-7 in the mPFC on depressive-like behaviors induced by chronic unpredictable mild stress(CUMS).Adult male SD rats were divided into two groups,control and CUMS.After 21-day CUMS exposure,I performed the behavior tests including sucrose preference test,open field test,tail suspension test and novelty suppressed feeding test to evaluate the depression-like behaviors.Western blot was used to examine the Kalirin7 level in the mPFC.Then the recombined AAV encoding Kal-shRNA was used to decrease the Kalirin7 protein level.Adult male SD rats were divided into two groups,AAV-Scr-shRNA and AAV-Kal-shRNA.AAV-Scr-shRNA and AAV-Kal-shRNA were stereotaxically delivered to the bilateral mPFC,respectively.After 21-day AAV expression,several behavior tests were performed to measure the depression-like and anxiety-like behaviors and cognitive behaviors.Gene Gun was used to analyses the dendritic spine morphology and density.Western blot was used to examine the levels of the synaptic protein and glutamate receptors level in the mPFCThe results showed:1.CUMS induced depression-like behaviors in rats.Compared with the control group,the body weight and sucrose preference were decreased,and rearing times and time spent in the center of the open field was decreased in the CUMS group.The Kalirin7 protein level of the mPFC was reduced significantly after CUMS exposure.2.Kal7 knockdown in the mPFC induced depression-and anxiety-like behaviors but did not affect the cognitive behaviors.Compared with the Scr-shRNA group,the sucrose preference was decreased,immobility time in the tail suspension test was increased,the rearing times and time spent in the center of the open field were decreased,and the time spent in the open arms in the elevated plus maze test was decreased in the Kal-shRNA group.3.The gene gun labeling results showed that reduced Kal7 protein levels decreased the dendritic spine density and altered the spine morphology.The dendritic spine density was decreased significantly in the Kal-shRNA group,and mushroom spine density was decreased but stubby spine density was increased.4.Western blot results showed that the expression of Drebrin,PSD95,GluN1,GluN2B,and GluAl in the mPFC decreased significantly,while the levels of GAD65 and GluA2 did not change obviously in the Kal-shRNA group compared with the Scr-shRNA groupAll these results showed that CUMS-induced depression-like behaviors were accompanied by a decrease in Kal7 protein level in the mPFC in rats.The shRNA-mediated reduction of the endogenous Kal7 expression in the mPFC induced depression-like behaviors,and caused a decrease in the dendritic spine density especially the proportion of mature mushroom spines,which were accompanied by a decrease in the level of GluN1,GluN2B and GluAl,PSD95 and Drebrin.Taken together,Kalirin7 regulates the depression-like behaviors through regulating the dendritic spines specially the excitatory synapse structure and function.My present study suggests a critical role of Kal7 in the development of stress models-induced depression-like behaviors and a possible role in depression.