Effect of vocal fold injury on laryngeal muscle dysfunction

ABSTRACT Voice disorders affect millions of Americans at substantive economic cost. Decisions regarding treatment are often primarily based on dichotomous thinking: mucosal injury versus muscle dysfunction. However, laryngeal muscle dysfunction often accompanies laryngeal mucosal pathologies and may be both causative and reactive. This proposal is an innovative combination of in vivo and in vitro methodologies to investigate the effect of both transient and persistent vocal fold mucosal injury on the underlying function, structure, and mechanistic response of the thyroarytenoid muscle, the primary muscle of the vocal fold. The long-term goal of this research is to provide mechanistic insight regarding the complex interactions between the mucosal and muscular vocal fold layers, thereby contributing to a shift in clinical schema and classification of voice disorders, but more importantly, lead to the development of novel, targeted therapeutic strategies for the millions of patients with voice-related disability. The central hypothesis of this work is injury to the vocal folds elicits complex interactions between the vocal fold mucosa and underlying muscle, which consequently results in altered laryngeal muscle structure and function. The proposed research has two specific aims. Aim 1 is to determine functional, structural, and mechanistic laryngeal muscle responses to vocal fold injury in an established in vivo rodent model. Two depths of vocal fold injuries, shallow injury of the mucosa only or deep injury of the mucosa and underlying muscle, will be created in male and female rats to determine the time course of vocal fold injury on a) muscle function via analysis of ultrasonic vocalization acoustic complexity, b) mechanistic response of the muscle via proteomic analysis, and c) changes in specific protein levels identified in the big-data proteomic interrogation. Injury depths will be confirmed via muscle histology. Aim 2 is to characterize and quantify signaling between fibroblasts and myoblasts as well as inflammatory cells from the vocal folds in vitro under basal and stimulated (e.g., injured) conditions. In vitro experimentation will examine the effects of fibrotic and inflammatory mediators on fibroblasts from the vocal fold lamina propria and myoblasts from intrinsic laryngeal muscle to interrogate unique interactions between the two cell types via co-culture and conditioned media experiments. These data will provide critical mechanistic and translational insight regarding the cycle of dysphonia and provide potential targets for pharmacological interventions. The proposed research is significant because this foundational mechanistic insight will optimize treatments for millions of patients with voice-related disability. The proposal is conceptually innovative, proposes novel, cutting-edge methodologies, and coalesces expertise across multiple laboratories and specialties.