The Study On The Mechanism Of Dexamethasone On Noise-induced Inner Ear Microcirculation Disorder

ObjectiveNoise is one of the main causes of deafness.It can lead to mechanical damage to the cochlea tissue,which in turn causes a series of histological,pathological and molecular changes.An epidemiological survey found that about 10%of the world’s people have hearing loss,and half of the population is due to noise exposure.The death of cochlear hair cells and spiral ganglion cells is the main cause of noise-induced deafness.Recent studies have found that noise causes the permeability changes of the blood-labyrinth barrier.The blood-labyrinth barrier(BLB)is located on the outer wall of the cochlea,which is composed of vascular endothelial cells EC,pericytes PC,perivascular macrophage-like melanocytes PVM/M and basement membrane BM.The normal function of BLB plays an important role in maintaining the endocochlear potential EP,ion transportation and liquid balance.Among them,PC is a type of shrinkable cells surrounding the surface of endothelial cells,which is essential for angiogenesis,blood-flow regulation,vascular integrity and tissue fibrosis.At present,it is believed that loud sound noise can damage the pericytes,leading to pericytes migration from the normal attachment sites of endothelial cells,thereby the blood-labyrinth barrier lose its stability and increase permeability.PDGF belongs to the family of vascular endothelial growth factors and is a growth factor for mesenchymal cells and other important intracellular processes.Among them,PDGF-BB combines its receptors to activate downstream signal pathways and regulate the survival,migration,apoptosis,proliferation and differentiation.And PDGF-BB are closely related to the occurrence of malignant tumors,atherosclerosis and fibrosis.Dexamethasone is a synthetic glucocorticoid agonist,which is commonly used in clinical treatment of auditory diseases,such as autoimmune inner ear disease,sudden deafness and Meniere’s disease.It plays an important role in development and regulation of hearing sensitivity in adults,and has a protective effect on noise damage.However,although dexamethasone is used widely,its molecular mechanism for the auditory disorders is not yet known.This study aims to study the role and potential mechanism of dexamethasone in noise-induced hearing loss.Methods1.Adult C57BL/6 mice aged 6-8 weeks were divided into four groups:control group,noise-exposure group,dexamethasone plus noise group and imatinib plus noise group.2.Immunofluorescence staining was applied to observe the distribution of blood vessels in the strial vascular of the control group,the noise-exposure group and the imatinib plus noise group,the morphology of PC and the relationship between them,then calculate the percentage of PC migration and vessel density.3.Western blot were used to detect the protein levels of PDGF-BB in the strial vascular of mice in the control group,the noise-exposure group and the imatinib plus noise group.4.The qRT-PCR were used to detect the RNA levels of PDGF-BB in the strial vascular of mice in the control group,the noise-exposure group and the imatinib plus noise group.5.The auditory brainstem response ABR was used to detect the hearing of mice in the control group,the noise-exposure group and the dexamethasone plus noise group,with the left monaural hearing as the standard.6.Immunofluorescence staining was aimed to observe the distribution of blood vessels in the stria vascular of mice in the control group,noise-exposure group,dexamethasone plus noise group,the morphology of PC and the relationship between them,then calculate the percentage of PC migration and vessel density and vessel density.7.Western blot were used to measure the protein level of PDGF-BB in the control group,the noise-exposure group and the dexamethasone plus noise group.8.The qRT-PCR were used to measure the RNA level of PDGF-BB in the control group,the noise-exposure group and the dexamethasone plus noise group.Results1.Immunofluorescence results illuminated that the shape of PC in the control group was regular,the cell body were flat and the axons were closely attached to the surface of adjacent vessels.Besides,the vessel density was normal.However,the PC in the noise-exposure group show abnormal morphology,and the number of migrated PC were decreased while the vascular density were elevated.The axons of detached PC moved away from the blood vessels and the cell body of the protruded PC appeared as cylinders or protruding triangles.Due to using the inhibitor Imatinib,the percentage of migrated PC was decreased,and the vascular density was significantly elevated.2.Western blot results indicated that the protein level of PDGF-BB in the noise-exposure group was increased apparently in contrast to the control group,while that decreased after Imatinib application.3.The qRT-PCR results indicated that the RNA level of PDGF-BB in the noise-exposure group was increased apparently in contrast to the control group,while that decreased after Imatinib application.4.ABR results showed that compared with the control group,the hearing threshold of mice in the noise-exposure group was significantly increased,while that in the dexamethasone plus noise group was decreased.5.Immunofluorescence results manifested that compared with the control group,pericytes migration in the noise-exposure group was obvious and the vascular density decreased,while that in the dexamethasone plus noise group declined and the vascular density rose.6.Western blot results indicated that the protein level of PDGF-BB in the the noise-exposure group increased evidently in contrast to the control group,while that decreased in the dexamethasone plus noise group.7.The qRT-PCR results indicated that the RNA level of PDGF-BB in the the noise-exposure group increased evidently in contrast to the control group,while that decreased in the dexamethasone plus noise group.ConclusionsNoise-induced hearing loss is closely related to the increased permeability of the blood-labyrinth barrier,and the migration of pericytes plays an important role in this process.Noise increased the expression of PDGF-BB in the stria vascular,and inhibition of PDGF-BB resulted in mitigated pericytes migration,proving that the PDGF-BB/PDGFRβsignaling pathway is associated with the migration of PC in the cochlear caused by noise.Dexamethasone can also reduce the migration of pericytes by controlling PDGF-BB,control vascular edema,restore tissue homeostasis in stria vascularis,and thus have a certain protective effect on hearing.Although there have been so many researches on the mechanism and effect of glucocorticoid on the inner ear,this innovatively proposes a new mechanism of dexamethasone for clinical treatment,providing a idea for the treatment and research of inner ear diseases in the future.