Inner ear organoids: progress and outlook, with a focus on the vascularization

Construction of organ of Corti organoid to study the effects of berberine sulfate on damaged auditory cells

Sensorineural hearing loss (SNHL) is mainly caused by injury or loss of hair cells (HCs) and associated spiral ganglion neurons (SGNs) in the inner ear. At present, there is still no effective treatment for SNHL in clinic. Recently, advances in organoid bring a promising prospect for research and treatment of SNHL. Meanwhile, three-dimensional (3D) printing provides a tremendous opportunity to construct versatile organoids for tissue engineering and regenerative medicine. In this study, gelatin (Gel), sodium alginate (SA), and polyvinyl alcohol (PVA) were used to fabricate biomimetic scaffold through 3D printing. The organ of Corti derived from neonatal mice inner ear was seeded on the PVA/Gel/SA scaffold to construct organ of Corti organoid. Then, the organ of Corti organoid was used to study the potential protective effects of berberine sulfate on neomycin-juried auditory HCs and SGNs. The results showed that the PVA/Gel/SA biomimetic 3D scaffolds had good cytocompatibilities and mechanical properties. The constructed organoid could maintain organ of Corti activity well in vitro. In addition, the injury intervention results showed that berberine sulfate could significantly inhibit neomycin-induced HC and SGN damage. This study suggests that the fabricated organoid is highly biomimetic to the organ of Corti, which may provide an effective model for drug development, cell and gene therapy for SNHL.

Blood-Labyrinth Barrier in Health and Diseases: Effect of Hormetic Nutrients

Significance: The stria vascularis, located in the inner ear, consists of three layers, one of which is the blood-labyrinth barrier (BLB). It is formed by endothelial cells, sealed together to prevent the passage of toxic substances from the blood to the inner ear, by pericytes and perivascular-resident macrophage-like melanocyte. Recent Advances: There are various causes that lead to hearing loss, and among these are noise-induced and autoimmune hearing loss, ear disorders related to ototoxic medication, Ménière's disease, and age-related hearing loss. For all of these, major therapeutic interventions include drug-loaded nanoparticles, via intratympanic or intracochlear delivery. Critical Issues: Since many pathologies associated with hearing loss are characterized by a weakening of the BLB, in this review, the molecular mechanisms underlying the response to damage of BLB cellular components have been discussed. In addition, insight into the role of hormetic nutrients against hearing loss pathology is proposed. Future Directions: BLB cellular components of neurovascular cochlear unit play important physiological roles, owing to their impermeable function against all ototoxic substances that can induce damage. Studies are needed to investigate the cross talk occurring between these cellular components to exploit their possible role as novel targets for therapeutic interventions that may unravel future path based on the use of hormetic nutrients. Antioxid. Redox Signal. 40, 542-563.

Graphene Hybrid Inner Ear Organoid with Enhanced Maturity

Inner ear organoids (IEOs) are 3D structures grown in vitro, which can mimic the complex cellular structure and function of the inner ear. IEOs are potential solutions to problems related to inner ear development, disease modeling, and drug delivery. However, current approaches in generating IEOs using chemical factors have a few limitations, resulting in unpredictable outcomes. In this study, we propose the use of nanomaterial-based approaches, specifically by using graphene oxide (GO). GO's unique properties promote cell-extracellular matrix interactions and cell-cell gap junctions, thereby enhancing hair cell formation, which is an essential part of IEO development. We also investigated the potential applications for drug testing. Our findings suggest that GO is a promising candidate for enhancing the functionality of IEOs and advancing our understanding of the problems underlying inner ear development. The use of nanomaterial-based approaches may provide a more reliable and effective method for building better IEOs in the future.

Emerging organoid models to study the epididymis in male reproductive toxicology

The importance of the epididymis on sperm maturation and consequently male fertility has been well documented. The pseudostratified epithelium of the epididymis is comprised of multiple cell types, including principal cells, which are the most abundant, and basal cells. The role of basal cells has been unclear and has been a source of discussion in the literature. However, the recent demonstration that these cells are multipotent or adult stem cells has opened new areas of research in epididymal biology. One such avenue is to understand the regulation of these stem cells, and to exploit their properties to develop tools for toxicological studies to elucidate the effects of chemicals on cell differentiation and epididymal function in vitro. Studies in both rat and mouse have shown that purified single epididymal basal cells cultured under 3D conditions can proliferate and differentiate to form organoids, or mini organs. Furthermore, these epididymal basal stem cells can self-renew and differentiate into other epididymal cell types. It is known that during epididymal development, basal cells are derived from undifferentiated columnar cells, which have been reported to share common properties to stem cells. Like basal cells, these undifferentiated columnar cells can also form organoids under 3D culture conditions and can differentiate into basal, principal and clear cells. Organoids derived from either basal cells or columnar cells offer unique models for toxicology studies and represent an exciting and emerging approach to understand the epididymis.