Activation of apoptotic pathways in the absence of cell death in an inner-ear immortomouse cell line

Abstract

Aminoglycoside antibiotics and cisplatin (CDDP) are the major ototoxins of clinical medicine due to their capacity to cause significant, as well as permanent hearing loss by targeting the mammalian sensory cells. Understanding the pathogenesis of damage is the first step in designing effective prevention of drug-induced hearing loss. In-vitro systems greatly enhance the efficiency of biochemical and molecular investigations through ease of access and manipulation. HEI-OC1, an inner ear cell line derived from the immortomouse, expresses markers for auditory sensory cells and, therefore, is a potential tool to study the ototoxic mechanisms of drugs like aminoglycoside antibiotics and CDDP. HEI-OC1 cells (and also HeLa cells) efficiently take up fluorescently tagged gentamicin and respond to drug treatment with changes in cell death and survival signaling pathways. Within hours, the C-jun N-terminal kinase pathway and the transcription factor AP-1 were activated and at later times, the “executioner caspase”, caspase-3. These responses were robust and elicited by both gentamicin and kanamycin. However, despite the initiation of apoptotic pathways and transient changes in nuclear morphology, cell death was not observed following aminoglycoside treatment, while administration of CDDP lead to significant cell death as determined by flow cytometric measurements; β-galactosidase analysis ruled out senescence in gentamicin-treated cells. The ability to withstand treatment with aminoglycosides but not with CDDP suggests that this cell line might be helpful in providing some insight into the differential actions of the two ototoxic drugs.

Loss of aminoglycoside sensitivity in HEI-OC1 cells?

“…In a recent issue of Hearing Research, Fu-Quan Chen and colleagues, a group with a strong expertise in ototoxicity, report the lack of cell death despite moderate but significant induction of apoptotic signaling following 1 mM gentamicin treatment of HEI-OC1 cells (Chen et al, 2012). We were able to replicate their published findings using their culture conditions.…”

Evaluation of Apoptotic Markers in HEI-OC1 Cells Treated with Gentamicin with and without the Mitochondria-Targeted Antioxidant Mitoquinone

“…Because MitoQ attenuated gentamicin-induced upregulation of the Bak gene but not its product, the Bak protein, and the proapoptotic properties are associated with the protein, not the gene, this may explain why MitoQ did not ameliorate the gentamicin-induced apoptosis in the present study using the Annexin V assay. This finding could also be attributed to the observation that a high dose of gentamicin (2 mM) was used to induce significant cell death in HEI-OC1 cells in the present study, which reflects the ability of HEI-OC1 cells to withstand treatment with AGs (20). In addition, HEI-OC1 cells have also been shown to avoid cell death after gentamicin treatment despite activation of the apoptotic pathways (20).…”

“…This finding could also be attributed to the observation that a high dose of gentamicin (2 mM) was used to induce significant cell death in HEI-OC1 cells in the present study, which reflects the ability of HEI-OC1 cells to withstand treatment with AGs (20). In addition, HEI-OC1 cells have also been shown to avoid cell death after gentamicin treatment despite activation of the apoptotic pathways (20).…”

Response to Cederroth

“…Christopher R. Cederroth's report is a thoughtful extension of our study (Chen et al, 2012) and a valuable scientific contribution in its own right. We are gratified by the author's statement "We were able to replicate their published findings using their culture conditions".…”

“…

Response to CederrothChristopher R. Cederroth's report is a thoughtful extension of our study (Chen et al, 2012) and a valuable scientific contribution in its own right. We are gratified by the author's statement "We were able to replicate their published findings using their culture conditions".

Cederroth's study confirms our central finding that cell death markers can be induced by aminoglycosides in the HEI-OC1 cell line without subsequent cell death.

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