ACTH Induced Vascular Smooth Muscle Cell Proliferation In High Cyclic Stretch During Hypertension

The abnormally increased mechanical strain exerted on the arterial wall in hypertension,especially the cyclic strain,is considered to play a significant role in modulating VSMC proliferation and pathological mechanism of vascular remodeling.However,the cellular mechanotransduction involving in the vascular remodeling is so complicated that the mechanobiological mechanism of vascular remodeling remains to be elucidated.Our previous serial studiesshowed that vascular neuropeptide Adrenocorticotropic hormone(ACTH)is highly expressed in vascular tissue of hypertensive rats,which suggests that ACTH is a mechanically sensitive molecule that may parcitipate in vascular remodeling in hypertension.However,the role of ACTH in modulating blood vessel cell function,especially its biomechanical role in vascular remodeling,is still unknown.In the first part,the relationship between ACTH of blood vessel and vascular remodeling in vivo was studied by using two hypertensive rat models.The blood vessel parameters closely related to vascular remodeling,including rat tail arterial pressure,vessel wall component,wall thickness,inner diameter,and opening angle,were detected after the hypertensive rat model was successfully replicated.The expressions of ACTH and its specific receptor melanocortin2-repeptor(MC2R)in blood vessel were tested by immunofluorescence and Real time qPCR.The results show that,compared with control groups,the opening angel decreased in carotid artery while increased in thoracic aorta.Both the vessel wall thickness and lumen diameter of thoracic aorta and carotid artery increased significantly in hypertensive groups.With the expression of collagen I decreasing and collagen III increasing,the ratio of collagen I and collagen III went an apparent decline significantly.The expression level of ACTH and MC2 R was significantly higher in thoracic aortic of hypertensive groups than that of control animals.These results indicate that ACTH plays a role in the vascular remodeling of thoracic aortic and carotid artery induced by hypertension.In the second part,the function and mechanism of ACTH in the vascular remodeling induced by hypertension in vitro was investigated and thus the role of ACTH,MC2 R in VSMC proliferation induced by abnormally high cyclic strain was firstly explored.To probe into the effect of abnormally increased cyclic strain on ACTH and MC2 R mRNA level,VSMCs isolated from Sprague Dawley(SD)rat arota were exposed to 0% static control,5% physiological cyclic stretch and 15% hypertensive pathological cyclic stretch at 1.25 Hz for 1 h,3 h,6h,12 h,24 h respectively.Real time qPCR was then used to detect the mRNA expression level of ACTH in VSMCs.Brdu ELISA was used to test VSMCs proliferation after incubation with different concentrations of ACTH and the protein expressions level of p-STAT3(705),p-STAT3(727),p-ERK in VSMCs were detected by WB after stimulated by ACTH(1000 nM).Combined immunofluorescence and laser scanning confocal microscopy(LSCM),the expression and distribution of ACTH and MC2 R in VSMCs were detected.The data indicated that the ACTH and MC2 R mRNA levels in VSMCs were regulated by 15% cyclic strain in a time-dependent manner,with significant up-regulation at 6 h & 12 h and a peak at 12 h.The immunofluorescence result showed that ACTH expression level in VSMCs was enhanced by ACTH stimulation while MC2 R expression did not change markedly in stimulated groups.Besides,the fluorescentsignal of ACTH was detected mainly in the nucleus while MC2 R mainly located in the cytoplasm,especially around the nuclear membrane.Compared with control groups,the proliferation of VSMCs was prompted and the activations p-ERK,p-STAT3(727),p-STAT3(705)induced by ACTH stimulation were an immediate and short term effect(15 min & 30 min &1 h).In summary,the increased expression of ACTH,MC2 R induced by high cyclic strain may modulate the VSMC proliferation through p-ERK,p-STAT3(727),p-STAT3(705)pathway,and result in vascular remodeling finally.The study shed new light on the molecular mechanism of vascular remodeling,thus may contribute to the pathogenesis mechanism of hypertension and other cardiovascular diseases.