Role of the planar cell polarity pathway in regulating ectopic hair cell-like cells induced by Math1 and testosterone treatment

Hair-Shaft Growth in Gelfoam® Histoculture of Skin and Isolated Hair Follicles

Human scalp skin with abundant hair follicles in various stages of the hair growth cycle was histocultured for up to 40 days on Gelfoam^® at the air/liquid interface. The anagen hair follicles within the histoculture scalp skin produced growing hair shafts. Hair follicles could continue their cycle in histoculture; for example, apparent spontaneous catagen induction was observed both histologically and by the actual regression of the hair follicle. In addition, vellus follicles were shown to be viable at day 40 after initiation of culture. Follicle keratinocytes continued to incorporate [³H]thymidine for up to several weeks after shaft elongation had ceased. Intensive hair growth was observed in the pieces of shaved mouse skin histocultured on Gelfoam^®. Isolated human and mouse hair follicles also produced growing hair shafts. By day 63 in histoculture of mouse hair follicles, the number of hair follicle-associated pluripotent (HAP) stem cells increased significantly and the follicles were intact. Gelfoam^® histoculture of skin demonstrated that the hair follicle cells are the most sensitive to doxorubicin which prevented hair growth, thereby mimicking chemotherapy-induced alopecia in Gelfoam^® histoculture.

Afferent synaptogenesis between ectopic hair-cell-like cells and neurites of spiral ganglion induced by Atoh1 in mammals in vitro

Newly formed ectopic hair-cell-like cells (EHCLCs) induced by overexpression of atonal homolog 1 (Atoh1) in vitro were found to possess features of endogenous hair cells (HCs) in previous reports and in the present study. However, limited information is available regarding whether EHCLCs and native spiral ganglion neurons (SGNs) form afferent synapses, which are important for the restoration of hearing. In the current study, we focused on the afferent synaptogenesis between EHCLCs and SGN-derived dendrites. Cochlear explants of auditory epithelia with native SGNs retained were cultured in vitro, and human adenovirus serotype 5 (Ad5) vectors encoding Atoh1 were used to overexpress Atoh1 and induce EHCLCs. We observed that the neurites of the original SGNs extended toward the lesser epithelial ridge (LER) and innervated the EHCLCs. Immunohistochemical analyses revealed the expression of presynaptic ribbon C-terminal-binding protein 2 (CtBP2) and postsynaptic density protein (PSD)-95 in the nerve endings of SGN-derived neurons adjacent to EHCLCs. PSD-95 was located directly opposite CtBP2-positive puncta in the terminals of branches of SGNs, demonstrating that the neurites of SGNs formed afferent-like synaptic connections with EHCLCs. However, the expression of glutamate receptor type 2 (GluR2) could not be detected in the terminals of branches of SGNs surrounding EHCLCs. In addition, we found that the presynaptic ribbon (CtBP2) formation in EHCLCs preceded neural innervation. Furthermore, CtBP2-positive puncta increased and then decreased in EHCLCs, similar to the changes observed in endogenous HCs in terms of their number and distribution. Our finding of the generation of cochlear afferent synapses between EHCLCs and original SGNs will lay the foundation for regenerative approaches to restoring hearing after hair cell loss.