Spontaneous hair cell regeneration in the mouse utricle following gentamicin ototoxicity

Abstract

Whereas most epithelial tissues turn-over and regenerate after a traumatic lesion, this restorative ability is diminished in the sensory epithelia of the inner ear; it is absent in the cochlea and exists only in a limited capacity in the vestibular epithelium. The extent of regeneration in vestibular hair cells has been characterized for several mammalian species including guinea pig, rat, and chinchilla, but not yet in mouse. As the fundamental model species for investigating hereditary disease, the mouse can be studied using a wide variety of genetic and molecular tools. To design a mouse model for vestibular hair cell regeneration research, an aminoglycoside-induced method of complete hair cell elimination was developed in our lab and applied to the murine utricle. Loss of utricular hair cells was observed using scanning electron microscopy, and corroborated by a loss of fluorescent signal in utricles from transgenic mice with GFP-positive hair cells. Regenerative capability was characterized at several time points up to six months following insult. Using scanning electron microscopy, we observed that as early as two weeks after insult, a few immature hair cells, demonstrating the characteristic immature morphology indicative of regeneration, could be seen in the utricle. As time progressed, larger numbers of immature hair cells could be seen along with some mature cells resembling surface morphology of type II hair cells. By six months post-lesion, numerous regenerated hair cells were present in the utricle, however, neither their number nor their appearance was normal. A BrdU assay suggested that at least some of the regeneration of mouse vestibular hair cells involved mitosis. Our results demonstrate that the vestibular sensory epithelium in mice can spontaneously regenerate, elucidate the time course of this process, and identify involvement of mitosis in some cases. These data establish a road map of the murine vestibular regenerative process, which can be used for elucidating the molecular events that govern this process.

Hair Cell Generation by Notch Inhibition in the Adult Mammalian Cristae

“…Since it is currently unknown how many new hair cells would be required to noticeably restore function in a damaged crista, the stimulation of hair cell regeneration by DAPT treatment that we have demonstrated may have some therapeutic relevance (Kopke et al 2001). Though very promising, the number of hair cells generated here is likely insufficient to fully repair a damaged organ, which is also true of all other mammalian vestibular regeneration to date Warchol et al 1993;Rubel et al 1995;Tanyeri et al 1995;Li and Forge 1997;Lopez et al 2003;Kawamoto et al 2009;Lin et al 2011;Golub et al 2012;Jung et al 2013). In order to overcome these limitations on mammalian regeneration, we ultimately need a better understanding of the factors and pathways that mediate hair cell regeneration.…”

Over Half the Hair Cells in the Mouse Utricle First Appear After Birth, with Significant Numbers Originating from Early Postnatal Mitotic Production in Peripheral and Striolar Growth Zones

“…In contrast, regenerative responses in mammalian ears are limited and appear largely ineffective Warchol et al 1993;Brigande and Heller 2009;Kawamoto et al 2009). Consistent with this, early investigations in rodents reported that the production of hair cells and supporting cells peaks during the second half of embryogenesis and declines precipitously before birth (Ruben 1967; Sans and Chat 1982; Lee et al 2006).…”

Notch inhibition induces mitotically generated hair cells in mammalian cochleae via activating the Wnt pathway

“…In nonmammalian vertebrates, HCs are regenerated in both auditory and vestibular systems after HC loss, leading to functional recovery of hearing and balance function (1)(2)(3). In mammals, limited spontaneous HC regeneration occurs in the vestibular system (4)(5)(6)(7)(8). In the adult mammalian vestibular sensory epithelium, inner ear stem cells were isolated with the capacity to differentiate into HCs and other inner ear cell types (9).…”