ADAM10 and γ-secretase regulate sensory regeneration in the avian vestibular organs

Abstract

The loss of sensory hair cells from the inner ear is a leading cause of hearing and balance disorders. The mammalian ear has a very limited ability to replace lost hair cells, but the inner ears of non-mammalian vertebrates can spontaneously regenerate hair cells after injury. Prior studies have shown that replacement hair cells are derived from epithelial supporting cells and that the differentiation of new hair cells is regulated by the Notch signaling pathway. The present study examined molecular influences on regeneration in the avian utricle, which has a particularly robust regenerative ability. Chicken utricles were placed in organotypic culture and hair cells were lesioned by application of the ototoxic antibiotic streptomycin. Cultures were then allowed to regenerate in vitro for seven days. Some specimens were treated with small molecule inhibitors of γ-secretase or ADAM10, proteases which are essential for transmission of Notch signaling. As expected, treatment with both inhibitors led to increased numbers of replacement hair cells. However, we also found that inhibition of both proteases resulted in increased regenerative proliferation. Subsequent experiments showed that inhibition of γ-secretase or ADAM10 could also trigger proliferation in undamaged utricles. To better understand these phenomena, we used RNA-Seq profiling to characterize changes in gene expression following γ-secretase inhibition. We observed expression patterns that were consistent with Notch pathway inhibition, but we also found that the utricular sensory epithelium contains numerous γ-secretase substrates that might regulate cell cycle entry and possibly supporting cell-to-hair cell conversion. Together, our data suggest multiple roles for γ-secretase and ADAM10 in vestibular hair cell regeneration.

Regenerating hair cells in vestibular sensory epithelia from humans

“…Studies in birds and mammals have shown that replacement hair cells can be derived from the supporting cells that remain after hair cell loss through inhibition of the Notch-signalling pathway ( Daudet et al, 2009 ; Lin et al, 2011 ; Warchol et al, 2017 ). To test the hypothesis that hair cell regeneration in human inner ear tissue could be induced by inhibition of Notch signalling, we maintained gentamicin treated cultures (N = 7) in TAPI-1 for 18 days.…”

Partial Aminoglycoside Lesions in Vestibular Epithelia Reveal Broad Sensory Dysfunction Associated with Modest Hair Cell Loss and Afferent Calyx Retraction

“…Early investigations of aminoglycoside otopathology in animal models focused upon hair cells as the primary targets ( Wersall and Hawkins, 1962 ; Lindeman, 1969a ; Wersall et al, 1969 ; Watanuki et al, 1972 ). Since then, aminoglycosides have been widely used as research tools to lesion vestibular epithelia in investigations of the cellular and molecular mechanisms of hair cell regeneration ( Weisleder and Rubel, 1992 ; Forge et al, 1993 ; Weisleder and Rubel, 1993 ; Lopez et al, 1999 ; Popper et al, 1999 ; Stone and Rubel, 2000 ; Dickman and Lim, 2004 ; Stone et al, 2004 ; Lyford-Pike et al, 2007 ; Haque et al, 2009 ; Kawamoto et al, 2009 ; Warchol, 2010b ; Burns and Corwin, 2014 ; Warchol et al, 2017 ). Additionally, gentamicin is an agent commonly used in investigations of mammalian vestibular pathophysiology ( Imamura and Adams, 2003a , b ; Hirvonen et al, 2005 ; Hong et al, 2006 ; Day et al, 2007 ; Lue et al, 2009 ; Ding et al, 2010 ; Warchol, 2010a ; Bremer et al, 2014 ; King et al, 2017 ).…”

Aminoglycoside Damage and Hair Cell Regeneration in the Chicken Utricle

“…The molecular mechanisms that trigger the onset of avian hair cell regeneration by either process are unknown. Despite identification of signaling pathways potentially involved in hair cell regeneration (Alvarado et al 2011;Ku et al 2014;Warchol et al 2017), a thorough mechanistic insight of regeneration from the earliest events of initiation, realization, and ultimately termination is not known. Moreover, in vivo experiments to investigate regeneration require repeated systemic injections of ototoxic aminoglycoside to induce reliable hair cell loss throughout the utricle (e.g., Cafaro et al 2007), which makes it difficult to define the precise dosage or onset of injury.…”