Ultrastructural Characterization of Stem Cell-Derived Replacement Vestibular Hair Cells Within Ototoxin-Damaged Rat Utricle Explants

Maturation of type I and type II rat vestibular hair cells in vivo and in vitro

Vestibular sensory epithelia contain type I and type II sensory hair cells (HCI and HCII). Recent studies have revealed molecular markers for the identification of these cells, but the precise composition of each vestibular epithelium (saccule, utricle, lateral crista, anterior crista, posterior crista) and their postnatal maturation have not been described in detail. Moreover, in vitro methods to study this maturation are not well developed. We obtained total HCI and HCII counts in adult rats and studied the maturation of the epithelia from birth (P0) to postnatal day 28 (P28). Adult vestibular epithelia hair cells were found to comprise ∼65% HCI expressing osteopontin and PMCA2, ∼30% HCII expressing calretinin, and ∼4% HCII expressing SOX2 but neither osteopontin nor calretinin. At birth, immature HCs express both osteopontin and calretinin. P28 epithelia showed an almost adult-like composition but still contained 1.3% of immature HCs. In addition, we obtained free-floating 3D cultures of the epithelia at P1, which formed a fluid-filled cyst, and studied their survival and maturation in vitro up to day 28 (28 DIV). These cultures showed good HC resiliency and maturation. Using an enriched medium for the initial 4 days, a HCI/calretinin+-HCII ratio close to the in vivo ratio was obtained. These cultures are suitable to study HC maturation and mature HCs in pharmacological, toxicological and molecular research.

A Regenerative Medicine Approach to the Treatment of Hearing, Balance, and Olfactory Disorders: What Is in the Future for Otolaryngology?

Regenerative medicine is being applied to many fields of medicine and is now starting to be considered and developed for application to treat hearing, balance, olfaction, and voice disorders. This special issue of the Anatomical Record with a series of over 20 papers covers many aspects of gene and stem cell therapies as they are developed for clinical applications in both in vitro and in vivo laboratory studies. These studies cover a wide range of approaches from gene editing in zebrafish with the latest technology (i.e., CRISPR/Cas9) to the isolation of human inner ear progenitor cells, to tracking transplanted human umbilical cord stem cells in mini pigs, to the in vitro building of graft tissues to repair tracheal defects with adipose tissue-derived stem cells. Anat Rec, 303:385-389, 2020. © 2019 American Association for Anatomy.