Noncoding microdeletion in mouse Hgf disrupts neural crest migration into the stria vascularis, reduces the endocochlear potential and suggests the neuropathology for human nonsyndromic deafness DFNB39

Hepatocyte growth factor (HGF) is a multifunctional protein that signals through the MET receptor. HGF stimulates cell proliferation, cell dispersion, neuronal survival and wound healing. In the inner ear, levels of HGF must be fine-tuned for normal hearing. In mouse, a deficiency of HGF expression limited to the auditory system, or over-expression of HGF, cause neurosensory deafness. In human, noncoding variants in HGF are associated with nonsyndromic deafness DFNB39. However, the mechanism by which these noncoding variants causes deafness was unknown. Here, we reveal the cause of this deafness using a mouse model engineered with a noncoding intronic 10bp deletion (del10) in Hgf, which is located in the 39UTR of a conserved short isoform (Hgf/NK0.5). Mice homozygous for del10 exhibit moderate-to-profound hearing loss at four weeks of age as measured by pure-tone auditory brainstem responses (ABRs). The wild type +80 millivolt endocochlear potential (EP) was significantly reduced in homozygous del10 mice compared to wild type littermates. In normal cochlea, EPs are dependent on ion homeostasis mediated by the stria vascularis (SV). Previous studies showed that developmental incorporation of neural crest cells into the SV depends on signaling from HGF/MET. We show by immunohistochemistry that in del10 homozygotes, neural crest cells fail to infiltrate the developing SV intermediate layer. Phenotyping and RNAseq analyses reveal no other significant abnormalities in other tissues. We conclude that, in the inner ear, the noncoding del10 mutation in Hgf leads to dysfunctional ion homeostasis in the SV and a loss of EP, recapitulating human DFNB39 deafness.