Activation of CHK1 in Supporting Cells Indirectly Promotes Hair Cell Survival

Abstract

The sensory hair cells of the inner ear are exquisitely sensitive to ototoxic insults. Loss of hair cells after exposure to ototoxic agents causes hearing loss. Chemotherapeutic agents such as cisplatin causes hair cell loss. Cisplatin forms DNA mono-adducts as well as intra- and inter-strand DNA crosslinks. DNA cisplatin adducts are repaired through the DNA damage response. The decision between cell survival and cell death following DNA damage rests on factors that are involved in determining damage tolerance, cell survival and apoptosis. Cisplatin damage on hair cells has been the main focus of many ototoxic studies, yet the effect of cisplatin on supporting cells has been largely ignored. In this study, the effects of DNA damage response in cochlear supporting cells were interrogated. Supporting cells play a major role in the development, maintenance and oto-protection of hair cells. Loss of supporting cells may indirectly affect hair cell survival or maintenance. Activation of the Phosphoinositide 3-Kinase (PI3K) signaling was previously shown to promote hair cell survival. To test whether activating PI3K signaling promotes supporting cell survival after cisplatin damage, cochlear explants from the neural subset (NS) Cre Pten conditional knockout mice were employed. Deletion of Phosphatase and Tensin Homolog (PTEN) activates PI3K signaling in multiple cell types within the cochlea. Supporting cells lacking PTEN showed increased cell survival after cisplatin damage. Supporting cells lacking PTEN also showed increased phosphorylation of Checkpoint Kinase 1 (CHK1) levels after cisplatin damage. Nearest neighbor analysis showed increased numbers of supporting cells with activated PI3K signaling in close proximity to surviving hair cells in cisplatin damaged cochleae. We propose that increased PI3K signaling promotes supporting cell survival through phosphorylation of CHK1 and increased survival of supporting cells indirectly increases hair cell survival after cisplatin damage.

ERBB2 is a Key Mediator in Hearing Restoration in Noise-Deafened Young Adult Mice

“…Under this interpretation, our work extends these findings in several important ways. First, we prove that activation in supporting cells alone is sufficient to promote hair cell survival, as the previous studies used either pharmacological inhibitors, deleted PTEN in both supporting cells and hair cells, or both (57,58). Second, our work indicates that the induction of CA-ERBB2, and/or its potential effector PI3K, can rescue adult hair cells from a noise-induced death.…”

PI3K and Inhibitor of Apoptosis Proteins Modulate Gentamicin- Induced Hair Cell Death in the Zebrafish Lateral Line

“…Our data do not allow us to determine the cell type(s) specifically responsible for PI3K-dependent protection. The effect could be cell-autonomous and confined to hair cells, but previous studies demonstrate that supporting cells are critical for hair cell survival in the undamaged ear and play an important role in hair cell responses to ototoxic damage ( Haddon et al, 1998 ; May et al, 2013 ; Jadali et al, 2017 ). PI3K signaling is dependent on an extracellular ligand binding to a membrane-bound receptor to initiate the intracellular cascade (reviewed in Gamper and Powerll, 2012 ; Cunningham and Ruggero, 2013 ).…”

Mutations in TOP2B cause autosomal‐dominant hereditary hearing loss via inhibition of the PI3K‐Akt signalling pathway

“…Hair cell survival is challenged by the addition of gentamicin to hair cell cultures; however, activation of PI3K-Akt signalling could reduce the hair cell loss induced by gentamicin to prevent hearing loss [28]. Upon treatment with cisplatin in mice, more supporting cells of Pten-cKO mouse cochleae were observed compared with controls, demonstrating that activation of PI3K-Akt signalling not only promotes hair cell survival but also promotes the survival of supporting cells [13]. Upon treatment with cisplatin in mice, more supporting cells of Pten-cKO mouse cochleae were observed compared with controls, demonstrating that activation of PI3K-Akt signalling not only promotes hair cell survival but also promotes the survival of supporting cells [13].…”

“…Activation of PI3K-Akt signalling can protect hair cells from TNFa-induced cell death to prevent hearing loss [29]. Upon treatment with cisplatin in mice, more supporting cells of Pten-cKO mouse cochleae were observed compared with controls, demonstrating that activation of PI3K-Akt signalling not only promotes hair cell survival but also promotes the survival of supporting cells [13]. The PI3K-Akt signalling pathway plays an important role in the survival and neurite extension of spiral ganglion neurons as well [30].…”

“…5A). In particular, the PI3K-Akt pathway is the only one out of 10 pathways that has a strong correlation with hearing development [13]. The expression level of akt was assessed by RT-qPCR and western blotting, which revealed that its expression in both mRNA and protein was reduced in 48 hpf morphants (Fig.…”