Proliferation of vascular smooth muscle cells (VSMCs) greatly contributes to vascular remodeling in hypertension.This study is to determine the roles and mechanisms of miR-135a-5p intervention in attenuating VSMC proliferation and vascular remodeling in spontaneously hypertensive rats (SHRs).MiR-135a-5p level was raised,while fibronectin type Ⅲ domain-containing 5 (FNDC5) mRNA and protein expressions were reduced in VSMCs of SHRs compared with those of Wistar-Kyoto rats (WKYs).Enhanced VSMC proliferation in SHRs was inhibited by miR-135a-5p knockdown or miR-135a-5p inhibitor,but exacerbated by miR-135a-5p mimic.VSMCs of SHRs showed reduced myofilaments,increased or even damaged mitochondria,increased and dilated endoplasmic reticulum,which were attenuated by miR-135a-5p inhibitor.Dual-luciferase reporter assay shows that FNDC5 was a target gene of miR-135a-5p.Knockdown or inhibition of miR-135a-5p prevented the FNDC5 downregulation in VSMCs of SHRs,while miR-135a-5p mimic inhibited FNDC5 expressions in VSMCs of both WKYs and SHRs.FNDC5 knockdown had no significant effects on VSMC proliferation of WKYs,but aggravated VSMC proliferation of SHRs.Exogenous FNDC5 or FNDC5 overexpression attenuated VSMC proliferation of SHRs,and prevented miR-135a-5p mimic-induced enhancement of VSMC proliferation of SHR.MiR-135a-5p knockdown in SHRs attenuated hypertension,normalized FNDC5 expressions and inhibited vascular smooth muscle proliferation,and alleviated vascular remodeling.These results indicate that miR-135a-5p promotes while FNDC5 inhibits VSMC proliferation in SHRs.Silencing of miR-135a-5p attenuates VSMC proliferation and vascular remodeling in SHRs via disinhibition of FNDC5 transcription.Either inhibition of miR-135a-5p or upregulation of FNDC5 may be a therapeutically strategy in attenuating vascular remodeling and hypertension.