Cochlear Organoids Shed Light on Hair Cell Regeneration for Hearing Loss Treatment
Key findings
- The generation of new hair cells after damage to the cochlea is a potential treatment for deafness
- Mass Eye and Ear researchers previously developed murine cochlear organoids that yield large numbers of hair cells with molecular markers of native cells
- This paper describes comprehensive transcriptional characterization of the organoids in comparison to in vivo cell types
- The organoids mimicked nearly all supporting cell and hair cell subtypes of the in vivo cochlea as well as the utricle, and gene regulatory network modeling identified transcription factors that regulate hair cell development and differentiation
- Higher-throughput screening might identify small molecules and genes that could generate new hair cells after damage to the cochlea
Birds that endure hearing loss can transdifferentiate sensory epithelial progenitor cells and regenerate hair cells in the cochlea. In mammals, by contrast, cochlear progenitor cells can differentiate into hair cells only in the early postnatal period.
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Determining what signals reprogram mammalian cochlear supporting cells into hair cells would be a significant advance toward using hair cell regeneration as a therapy for deafness. The mouse is the usual model for studying hearing. Still, the tiny size of the mouse cochlea, its location, and the relatively small number of hair cells make studies of hair cell regeneration difficult.
In Cell Reports, researchers at Mass Eye and Ear previously published a protocol to expand and differentiate murine Lgr5+ cochlear progenitor cells into 3D organoids that recapitulate developmental pathways. Organoid differentiation yielded large numbers of hair cells with molecular markers of native cells, including markers for inner and outer hair cells.
To allow expanded analyses, the team recently performed a comprehensive transcriptional characterization of the cochlear organoids, in comparison to in vivo cell types, at multiple time points in their differentiation.
Albert Edge, PhD, director of the Tillotson Cell Biology Unit and principal investigator in the Eaton–Peabody Laboratories at Mass Eye and Ear, and colleagues detail the findings in a more recent paper in Cell Reports.
Principal Findings
Transcriptional signatures of maturing hair cells were apparent after 10 days of organoid differentiation. During the course of differentiation, the cells mimicked nearly all subtypes of supporting cells and hair cell subtypes in the neonatal cochlea and utricle.
The researchers then studied how gene activity and chromatin structure changed as Lgr5+ progenitor cells differentiated into hair cells. The data revealed a transcriptional network of genes that control hair cell formation:
- The model identified known regulators of hair cell development, including Atoh1, Pou4f3, and Gfi1
- It predicted roles in postnatal hair cell differentiation for certain genes expressed by hair cells: Sox4, Tceb2, Nr2f1, and Lmo1
- Ddit3, whose loss contributes to hearing loss, was upregulated, had high influence during differentiation, was most active toward the end of the maturation process and acted similarly to Pou4f3, Atoh1, and Lmo1 in activating transcription of genes such as Sox4 and Tceb2
- Other important transcription factors identified in the network were Atf4, a downstream target of Ddit3, and Tcf4, a heterodimerization partner of Atoh1
Conclusions
Because the organoids faithfully represent in vivo cell types and regenerative processes, they hold promise for higher-throughput screening. That future work might identify small molecules and genes that could generate new hair cells after damage to the cochlea.
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