HCMV immediate-early protein IE2 induces neurotoxicity and hearing loss by disrupting TSC2-mTOR signaling and metabolic homeostasis

Sensorineural hearing loss (SNHL) caused by human cytomegalovirus (HCMV) infection involves alterations in both the central auditory pathways and cochlear structures. Immediate early (IE) proteins are critical for HCMV pathogenicity and have been associated with neurodevelopmental disorders; however, their contribution to HCMV-associated SNHL remains unclear. Here, we generated transgenic mouse models expressing HCMV IE1 and IE2 protein to investigate their effects on auditory function and cochlear pathology. Auditory brainstem response (ABR) measurements revealed that expression of IE2, but not IE1, led to significantly elevated ABR thresholds and impaired auditory processing. IE2-transgenic mice exhibited synaptic loss, hair cell degeneration, and neuronal atrophy in auditory regions. scRNA-seq analysis indicated broad activation of inflammatory pathways and cytokines within the cochlea, along with disruptions in mitochondrial and metabolic pathways, suggesting that IE2 may contribute to hearing loss through mitochondrial impairment and inflammation. Transmission electron microscopy of cochlear tissues showed severe morphological abnormalities and a marked reduction in mitochondrial number in spiral ganglion neurons (SGNs). Further mechanistic investigation demonstrated that IE2 interacts with TSC2, leading to hyperactivation of mTOR signaling, metabolic dysregulation, and mitochondrial dysfunction. Importantly, administration of mTOR inhibitors substantially alleviated IE2-induced auditory deficits, hair cell degeneration, and neuronal atrophy. These findings identify IE2 through TSC2-mTOR-mediated mitochondrial dysfunction, metabolic reprogramming, and neuroinflammation leading to SNHL. Our study reveals a previously unrecognized mechanism linking IE2 protein expression to auditory neurodegeneration and suggests mTOR modulation as a potential therapeutic strategy for congenital HCMV infection and associated hearing loss.