Objective To investigate the effect of exosomal miR-146a-5p expression on gray matter volume in patients with major depressive disorder(MDD).Methods A total of 113 MDD patients(MDD group)and 107 healthy controls(HC)(HC group)were selected.Peripheral blood was collected and exosomes were isolated to quantify miR-146a-5p expression.Brain high-resolution T1 WI images of MDD and HC were obtained via MR,and gray matter volume was computed via SPM12 software.The interaction effect of"Depression×miR-146a-5p expression"on gray matter volume was analyzed using SPM's Flexible factorial design,and the between-group difference was assessed by extracting the mean value,thus to analyze whether MDD-related gray matter volume abnormalities were dependent on miR-146a-5p expression.Results Exosomal miR-146a-5p expression was significantly elevated in MDD group compared to HC group.Voxel-based factorial analysis revealed a relationship between high miR-146a-5p expression in MDD group and reduced gray matter volume in the anterior and posterior cingulate cortices(independent voxel threshold P＜0.001,AlphaSim corrected),and a significantly reduced gray matter volume as compared with HC group was detected in the two regions.Conclusion The exosomal miR-146a-5p is overexpressed in patients with MDD and may be associated with specific cortical atrophy in patients with MDD.