Conditioning the Cochlea to Facilitate Survival and Integration of Exogenous Cells into the Auditory Epithelium

Abstract

The mammalian auditory epithelium (AE) cannot replace supporting cells and hair cells once they are lost. Therefore, sensorineural hearing loss associated with missing cells is permanent. This inability to regenerate critical cell types makes the AE a potential target for cell replacement therapies such as stem cell transplantation. Inserting stem cells into the AE of deaf ears is a complicated task due to the hostile, high potassium environment of the scala media in the cochlea, and the robust junctional complexes between cells in the AE that resist stem cell integration. Here, we evaluate whether temporarily reducing potassium levels in the scala media and disrupting the junctions in the AE make the cochlear environment more receptive and facilitate survival and integration of transplanted cells. We used sodium caprate to transiently disrupt the AE junctions, replaced endolymph with perilymph, and blocked stria vascularis pumps with furosemide. We determined that these three steps facilitated survival of HeLa cells in the scala media for at least 7 days and that some of the implanted cells formed a junctional contact with native AE cells. The data suggest that manipulation of the cochlear environment facilitates survival and integration of exogenously transplanted HeLa cells in the scala media.

Survival of human embryonic stem cells implanted in the guinea pig auditory epithelium

“…Placing cells in a culture dish filled with artificial endolymph, which is potassium-rich, leads to their prompt demise13. At present, we can only speculate on the reasons for the rapid death of cells in endolymph-like fluids or in the endolymph of the scala media.…”

“…Sodium caprate has been shown to transiently disrupt the junctional complexes of epithelial cells1326. To enhance adhesion of the hESCs to the endogenous cells or facilitate insertion into the tissue, we added sodium caprate to the conditioning protocol.…”

“…Consequently, it is necessary to inject the cells directly into the scala media, the fluid-filled lumen within the cochlear duct epithelium. However, the high concentration of potassium of the endolymph11 in scala media quickly kills the transplanted cells1213. The two-fold task is therefore to generate conditions that will allow transplanted cells to survive in the endolymph, and then to integrate these cells into the auditory epithelium, an epithelial sheet with especially robust apical junctions14151617.…”

“…To promote cell survival and integration, endolymph can be transiently “conditioned” to decrease the potassium concentration and open cell-cell junctions in the auditory epithelium. Using this conditioning method, we showed that HeLa cells injected into scala media could survive for at least one week13.…”

Severe streptomycin ototoxicity in the mouse utricle leads to a flat epithelium but the peripheral neural degeneration is delayed

“…The slow degeneration of neural components may benefit the re-innervation of new HCs. Feasibility for implanting exogenous cells has been demonstrated for the auditory FE (Lee et al, 2017; Park et al, 2014) and might also be developed for the vestibular organs. It may still be necessary to follow stem cell transplantation with protocols for inducing the transdifferentiation of exogenous cells into vestibular HCs and SCs.…”