IGF-1/SLC25A33 Maintains Blood-Labyrinth Barrier Integrity by Suppressing TGF-β/Smad2-Mediated Pericyte Activation in Age-Related Hearing Loss.

Abstract

Age-related hearing loss (ARHL) is a prevalent sensory disorder in the elderly, yet the molecular mechanisms underlying cochlear aging remain incompletely understood. While insulin-like growth factor 1 (IGF-1) has been implicated in ARHL, its role in the stria vascularis, particularly in pericyte-mediated blood-labyrinth barrier (BLB) regulation, is poorly defined. We performed transcriptomic analysis of FACS-purified pericytes from young and aged mouse stria vascularis. Functional studies were conducted using primary pericyte cultures, lentiviral gene modulation, and AAV-mediated in vivo delivery. Auditory function was assessed by auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE). Molecular changes were evaluated via qPCR, western blot, immunofluorescence, flow cytometry, and transmission electron microscopy (TEM). Transcriptomics revealed significant downregulation of Igf1 and Slc25a33 in aged pericytes, with enrichment of the TGF-β signaling pathway. IGF-1 deficiency suppressed SLC25A33 expression in vitro, leading to mitochondrial ROS (mtROS) accumulation, activation of TGF-β/Smad2 signaling, and pericyte phenotypic switching, characterized by increased α-SMA and decreased E-cadherin. In vivo, suppression of IGF-1 or SLC25A33 activated TGF-β/Smad2 signaling in the stria vascularis, disrupted BLB ultrastructure, and exacerbated hearing loss. Conversely, exogenous IGF-1 or SLC25A33 overexpression attenuated these effects and partially restored auditory function. Our findings identify a novel IGF-1/SLC25A33-TGF-β/Smad2 axis that regulates pericyte activation and BLB integrity in the aging cochlea. This pathway provides mechanistic insight into ARHL pathogenesis and highlights a potential therapeutic target for preserving hearing in older adults.