A Novel Role of Cytosolic Protein Synthesis Inhibition in Aminoglycoside Ototoxicity

Abstract

Ototoxicity is a main dose-limiting factor in the clinical application of aminoglycoside antibiotics. Despite longstanding research efforts, our understanding of the mechanisms underlying aminoglycoside ototoxicity remains limited. Here we report the discovery of a novel stress pathway that contributes to aminoglycoside-induced hair cell degeneration. Modifying the recently developed bioorthogonal noncanonical amino acid tagging (BONCAT) method, we used click-chemistry to study the role of protein synthesis activity in aminoglycoside-induced hair cell stress. We demonstrate that aminoglycosides inhibit protein synthesis in hair cells and activate a signaling pathway similar to ribotoxic stress response, contributing to hair cell degeneration. The ability of a particular aminoglycoside to inhibit protein synthesis and to activate the c-Jun N-terminal kinase (JNK) pathway correlated well with its ototoxic potential. Finally, we report that a FDA-approved drug known to inhibit ribotoxic stress response also prevents JNK activation and improves hair cell survival, opening up novel strategies to prevent and treat aminoglycoside ototoxicity.

Designer aminoglycosides prevent cochlear hair cell loss and hearing loss

“…In particular, work on apramycin, a structurally unique aminoglycoside used in veterinary medicine, suggests that its differential antiribosomal activities against eukaryotic cells versus bacteria contribute to its low ototoxic potential. Moreover, recent work suggests that aminoglycosides induce hair cell toxicity by causing ribotoxic stress and in turn inhibit cytoplasmic protein synthesis (46). While our data support the conclusion that decreased drug entry via MET channels underlies diminished aminoglycoside ototoxicity, we did not determine whether sisomicin and sisomicin derivatives differentially bind eukaryotic and bacterial ribosomes, induce ribotoxic stress, or inhibit protein synthesis in hair cells.…”

Exome sequencing and CRISPR/Cas genome editing identify mutations of ZAK as a cause of limb defects in humans and mice

“…In addition to limb defects, all patients in family 1 had bilateral sensorineural hearing impairment (Supplemental Fig. 2), consistent with Zak expression in hair cells of the mouse cochlea (Francis et al 2013). We refer to this distinct phenotype as "split-foot malformation with mesoaxial polydactyly" (SFMMP).…”

Designer Aminoglycosides That Selectively Inhibit Cytoplasmic Rather than Mitochondrial Ribosomes Show Decreased Ototoxicity

“…In contrast, the most recent work by Francis et al (13) suggests that AGs ototoxicity correlates closely with cytoplasmic protein synthesis inhibition. Using the bioorthogonal noncanonical amino acid tagging method, this group investigated the role of cytoplasmic protein synthesis inhibition in hair cells and demonstrated that the ability of a particular AG to block cytoplasmic protein synthesis and to activate the JNK pathway correlates with its ototoxic potential.…”

“…One model suggests that AGs exert their ototoxicity by inhibiting mitochondrial protein synthesis, followed by mitochondrial dysfunction caused by oxidative stress, which ultimately leads to cell death (11,12). In contrast, an alternative model considers cytoplasmic protein synthesis inhibition as a potential trigger of a cellular pathway, similar to ribotoxic stress response, leading to hair cell apoptosis (13). Although in principle the inhibition of either the mitochondrial or cytoplasmic protein synthesis can contribute to ototoxicity, it needs to be determined which mechanism operates or predominates in vivo.…”