The Role Of RPTN Protein In The Emotional And Social Behavior Of Mice And Its Mechanism

RPTN(Repetin)is a precursor protein related to the formation of keratinocyte membrane,which widely exists in epithelial tissue and plays a role in the formation of skin barrier.PRTN belongs to the S100 protein family,which includes S100A4,S100A5,S100A10 and S100A13.These proteins are found in the human prefrontal cortex and hippocampus.P11 protein(S100A10)interacts with serotonin receptors in the prefrontal cortex and participates in the regulation of depressive behavior.In recent years,it has been found that RPTN is expressed in the nervous system of mouse and human,with high levels in the hippocampus,prefrontal cortex and locus coeruleus.The decreased levels of RPTN in the prefrontal cortex and hippocampus were accompanied by depression-like behaviors in mice induced by chronic unpredictic mild stress(CUMS).These results suggest that RPTN plays a role in depression.Prefrontal cortex and hippocampus are the key brain regions on mood circuit which regulaes cognitive and social behaviors.RPTN is highly expressed in these two brain regions,but it is unknown whether RPTN regulates social behaviors.The aim of this study was to study the role of RPTN in emotional and social behaviors and the underlying mechanism.Firstly,immune-fluorescence staining was used to determine where RPTN are expressed in the rodent brain.Western Blot was used to determine RPTN expression in the hippocampus during postnatal development.Secondly,RPTNKO/KO mice and RPTNWT/WT mice were selected as experimental animals.Behavioral tests were used to determine the differences of behaviors between KO and WT mice,such as depression-like behaviors,anxiety-like behaviors,social behaviors and so on.Western Blot was used to compare the differences in the levels of glutamate receptor and synaptic proteins in the prefrontal cortex and hippocampus between KO and WT mice.Golgi staining was used to analyze the dendritic spine density in KO and WT mice.Last aim was to compare the diference indepression-like behaviors induced by CUMS between KO and WT mice.Results:1.RPTN is expressed in the pyramidal neurons and intemeurons of the mouse in hippocampus and prefrontal cortex.Highest level of RPTN was observed in the prefrontal cortex on the 14th day after birth.2.Western Blot showed that the RPTN protein in the hippocampus of KO mice was not detected compared with Wt mice.3.In behavioral tests,KO mice did not show significant difference in sucrose preference index,immobility time in both forced swimming and tail-suspension test compared with WT mice.However,KO mice showed social proximity disorder in the social approach test of three-chamber test,cognitive impairment in new object recognition test and high stereotyped behavior in marble burying test.4.Western Blot showed the levels of GluA1,GluA2,GluN1,PSD95 and SYP in the prefrontal cortex of KO mice were significantly decreased compared with WT.But no significant difference was observed in the levels of GluN2B and Kalirin-7 between KO and WT.The levels of GluA1,GluA2,GluN1 and GluN2B in the hippocampus of KO mice were significantly increased compared with WT.But no significant difference was observed in Kalirin-7,SYP and PSD95 between KO and WT.5.Golgi staining showed the dendritic spine density in the pyramidal neurons of the hippocampal CA3 apical dendrites in KO mice was significantly higher than that of WT.6.CUMS induced depression-like behaviors in both KO-control group and WT-control groups.Compared with WT-CUMS group,the sucrose preference index of KO-CUMS group was significantly decreased,the immobility time in both of forced swimming and tail suspension tests was significantly increased in KO-CUMS group.Sucrose preference index in KO-CUMS group was significantly lower than WT-CUMS group in the 7th day after the onset of CUMS.These results showed that the highest level of RPTN is detected at the 14th postnatal day,the critical time of dendritic spine formation and synaptogenesis.RPTN is expressed mainly in the cell soma and dendrites of pyramidal neurons and intermediate neurons in the hippocampus.RPTN knockout mice did not exhibit depreson-like and anxiety-like behaviors,but showed typical autism related behaviors.RPTN knockout mice is more sensitive to CUMS than WT,which was accompanied by alterations in the levels of glutamate receptors and synaptic proteins in the prefrontal cortex and hippocampus,as well as increase in dendritic spine density in the hippocampus.These results suggested that RPTN regulate emotional and social behaviors in mice through glutamate receptors,synaptic proteins and dendritic spines.However,interactions among RPTN,glutamate receptors and synaptic proteins are not clear,so to understand the mechanism through which RPTN regulates emotional and social behaviors needs further study.