Accumulated ROS Activates HIF-1α-induced Glycolysis And Exerts A Protective Effect On Sensory Hair Cells Against Noise-induced Damage

BackgroundNoise-induced hearing loss(NIHL)is a progressive reduction in hearing ability or even hearing loss caused by noisy environment exposure.NIHL is one of the most important causes of sensorineural hearing loss all over the world,which has always been a significant public health issue globally.Specific damage during NIHL includes hearing threshold elevation and loss of sensory hair cells in the inner ear.The audiological features and cochlear morphology of NIHL are well characterized,but the pathomechanisms of NIHL are complex and not well understood.Although multiple theories have been suggested to explain the occurrence of NIHL,including oxidative stress injury,calcium ion overloading,glutamate-glutamine cycle disorder,inflammatory factor cascade response,genetic susceptibility and other mechanisms,there is no agreement about the exact mechanism.Thus,there is an urgent need for in-depth studies to develop a comprehensive understanding of the pathogenesis of NIHL.Oxidative stress injury is one of the recognized triggers for the pathogenesis of NIHL.Studies have reported that exposure to traumatic noise environment can lead to abnormal accumulation of reactive oxygen species(ROS)in sensory hair cells and may trigger a lethal cascade.However,some studies have also shown that ROS-dependent molecular signals also have a positive effect on the maintenance and survival of cell homeostasis.As a double-edged sword,ROS may play a dual role in the occurrence and development of NIHL,which is worthy of further exploration.As a transcription factor,hypoxia-inducible factor 1α(HIF-1α)can regulate the material and energy metabolism of cells,especially the glycolysis.Studies have shown that there is a crosstalk between HIF-1αand ROS,and that HIF-la also plays a role in preventing hearing loss and protecting sensory hair cells.Based on the above evidence,this study intends to explore whether ROS can regulate the material and energy metabolism of sensory hair cells via HIF-lα,and attempts to excavate the role of overload ROS in the occurrence and development of NIHL,so as to clarify the pathogenesis of NIHL and find possible protective therapeutic targets.MethodsHouse Ear Institute-Organ of Corti 1(HEI-OC1)cells were stimulated with tert-butanol hydroperoxide(t-BHP)to establish an in vitro oxidative stress injury model.To investigate metabolic shifts in ROS overloaded HEI-OC1 cells,in vitro experiments such as mitochondrial content,ATP content,glucose uptake,lactate release,oxygen consumption rate(OCR)and extracellular acidification rate(ECAR),and expressions of glycolytic enzymes were performed.In addition,the expression of HIF-lα in the ROS overloaded HEI-OC1 cell model was detected.The expression of Hif1a gene was inhibited by small interfering RNA(siRNA)to clarify whether the effect of ROS on the energy metabolism in HEI-OC1 cells is mediated by HIF-lα.In present study,an NIHL animal model was established in C57BL/6 mice.To clarify the audiological features of NIHL,the changes of auditory brainstem response(ABR)and distortion product otoacoustic emission(DPOAE)thresholds in animal models were detected before and after noise exposure.Additionally,oxidative stress level,HIF-1α expression,and the expressions of glycolytic enzymes were measured by immunofluorescence in sensory hair cells in NIHL animal models.ResultsIn this study,HEI-OC1 cells were stimulated with 80 μM t-BHP for 4 hours,and an in vitro oxidative stress injury model was established successfully.In t-BHP treated HEI-OC1 cells,we found that ROS overload led to mitochondrial damage,while ATP production did not significantly decrease.Further,we also observed increased glucose uptake,enhanced lactate release,decreased OCR,increased ECAR,and increased expression of glycolytic enzymes in ROS overloaded cell model.HIF-la expression was increased in t-BHP treated HEI-OC1 cells.After inhibiting Hif1α gene expression with siRNA,the metabolic shifts in HEI-OC1 cells caused by ROS overload were partially reversed.In present study,C57BL/6 mice were exposed to noise at a sound pressure level(SPL)of 110 dB for 2 hours each day for two consecutive days,and NIHL animal model was established successfully.The thresholds of the click and tone-pip ABRs were significantly higher than the baseline,and the DPOAE threshold was also significantly increased.The level of oxidative stress and the expression of HIF-1α and glycolytic enzymes were increased in sensory hair cells of mice after noise exposure.DiscussionWe demonstrated that noise trauma led to abnormal accumulation of ROS,which induced HIF-la stabilization in sensory hair cells.HIF-1α as a key regulator of glycolysis,promoted GLUT 1-mediated glucose uptake and upregulated the expression of glycolytic enzymes,which activated glycolysis in the ROS overloaded condition.The accumulation of ROS can damage the mitochondrial structure and function,leading to the damage of mitochondrial respiration capacity.The increased glycolysis can compensate for the insufficient mitochondrial energy supply and maintain the production of intracellular ATP in a compensatory state to ensure cell survival in this situation.Our current study suggests that ROS-mediated upregulation of HIF-1α has a potential protective effect on sensory hair cells by reducing the damage of oxidative stress via remodeling glucose metabolism.This study helps us to understand the role of ROS in NIHL more comprehensively and objectively.