Molecular Mechanisms Of Deafness Induced By Mitochondrial TRNAPhe593T>C Mutations Associated With Maternally Inherited Nonsyndromic Deafness

Deafness is a major global public health problems,affecting 360 million persons worldwide.Mitochondrial dysfunction has been potentially implicated in both syndromic and non-syndromic deafness.We found a Dongxiang Chinese pedigree subjected with maternally transmittted nonsyndromic deafness carrying the m.593T>C mutation in the t RNAPhe gene.Five of 9 matrilineal relatives exhibited sensorineural hearing impairment.In the mutant lymphoblastoid cell lines,44% reduction in steady state of t RNAPhe and 35% decrease in t RNAPhe mt DNA-encoded polypeptides were observed;the basal OCR,or ATP-linked OCR,maximal OCR were correlated with mitochondrial protein synthesis rate;39% drop in mitochondrial ATP production was observed.These results provide the first evidence that the t RNAPhe mutation might be associated with deafness in minority ethnic people.Then Using cytoplasmic hybrid(cybrids)constructed by transferring mitochondria from lymphoblastoid cell lines derived from III-11 into mt DNA less(p0206)cells.We showed 20% decrease in the steady-state level of t RNAPhe in mutant cybrids cells,compared with the control cybrids cells.The failure in t RNAPhe metabolism was responsible for the variable reductions in mt DNA encoded polypeptides in mutant cells,ranging from 21% to 68%,with the average of 40% reduction,as compared with those of control cells.The impaired mitochondrial translation caused defects in stability of mitochondrial respiratory chain complexes and mitochondrial oxidative phosphorylation capacity in mutant cells.The complexe I and complexe III activity in mutant cell lines were 55 and 47%,relative to the control cell lines.As a result,the respiratory deficiency reduced mitochondrial ATP production 40% drop ATP production in cybrid carrying the m.593T>C mutation.Furthermore,the deficient activities of respiratory chain complexes I,III caused by t RNA mutations altered mitochondrial membrane potentials with 18% reduction,also 30% increase the ROS production.In summary,this study elaborated the molecular mechanism of m.593T>C mutation causing mitochondrial dysfunction,the results may offer the new insights into the knowledge of pathophysiology of maternally inherited deafness.