Expression of HGF and Met During Development and After Nerve Injury in Muscles of the Rat Larynx.

OBJECTIVES: Injury to the recurrent laryngeal nerve results in robust but synkinetic nerve regrowth, highlighting the need to better characterize neurotrophic factors guiding correct primary innervation. Hepatocyte growth factor (HGF) is a chemoattractant that confers neuronal survival through its receptor Met. This study examined HGF and Met within the developing rat intrinsic laryngeal muscles (ILMs) using RNAScope and associated gene expression during development and after injury using RNASeq. METHODS: HGF and Met RNA expression were quantified as puncta/cell using QuPath within the posterior cricoarytenoid (PCA), lateral thyroarytenoid (LTA), and medial thyroarytenoid (MTA) of rat embryos. RNA was extracted from PCA, LTA, and MTA during development and following nerve injury in adults, and RNASeq was performed. Bioinformatic analysis was conducted for HGF-associated genes. One- and two-way ANOVA analyses and post hoc Tukey's tests were performed in R. RESULTS: HGF puncta/cell varied significantly throughout development by age (p = 0.007) and ILM (p = 0.0257), with expression decreasing with age in both the PCA and LTA (p = 0.042 and p = 0.048). Met increased with age within the PCA (p = 0.002) and MTA (p = 0.011), and decreased in the LTA (p = 0.0095). RNASeq demonstrated significant up- and downregulation of several associated proteins along the HGF-Met pathway and variation in Met/HGF expression post-injury, primarily in the PCA. CONCLUSIONS: HGF and Met were expressed in the developing rat ILMs with temporal variation at key points in primary innervation, with post-injury upregulation in the PCA. These findings suggest a role for the HGF-Met signaling pathway in primary laryngeal innervation with potential dysregulation after nerve injury. LEVEL OF EVIDENCE: N/A.