Dexamethasone protects organ of corti explants against tumor necrosis factor-alpha-induced loss of auditory hair cells and alters the expression levels of apoptosis-related genes

Christine T Dinh, S. Haake, S. Chen, K. Hoang, E. Nong, Adrien Eshraghi, T. J. Balkany, Thomas R Van De Water

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Abstract

Objective: Determine the molecular mechanism(s) behind tumor necrosis factor-alpha (TNFα)-induced loss of auditory hair cells and the ability of dexamethasone base (DXMb) to protect against TNFα ototoxicity. Methods: Hair cell counts: Three-day-old rat organ of Corti explants were cultured under three different conditions: 1) untreated-control; 2) TNFα (2 μg/ml); and 3) TNFα (2 μg/ml)+DXMb (70 μg/ml) for 4 days, fixed, and stained with FITC-phalloidin. Hair cells were counted in the basal and middle turns. Gene expression: total RNA was extracted from the three different groups of explants at 0, 12, 24 and 48 h. Using quantitative real-time RT-PCR, mRNAs were transcribed into cDNAs and amplification was performed using primers for rat ß-actin (housekeeping gene), TNFR1, Bcl-2, Bax, and Bcl-xl. Results: DXMb protected explant hair cells from TNFα-induced loss. Bax gene expression was greater in TNFα-exposed explants compared with TNFα+DXMb-treated explants at 48 h (P=0.023), confirmed by the increase in the Bax/Bcl-2 ratio at 48 h (P<0.001). These results correlated with increased TNFR1 expression at 24 h (P=0.038). DXMb otoprotection in TNFα-exposed cultures was accompanied by an up-regulation of Bcl-xl at both the 24 (P<0.001) and 48 h time points (P=0.030) and up-regulation of Bcl-2 expression at 24 h (P=0.018). DXMb treatment also prevented increases in the expression levels of Bax, TNFR1, and the Bax/Bcl-2 ratio that occurred in untreated TNFα-exposed explants. Conclusions: TNFα's ototoxicity may be mediated through an up-regulation of Bax and TNFR1 expression as well as an increase in the Bax/Bcl-2 ratio. DXMb protects the organ of Corti against TNFα ototoxicity by up-regulating Bcl-2 and Bcl-xl expression and by inhibiting TNFα-induced increases in Bax, TNFR1, and the Bax/Bcl-2 ratio. These results support the use of local dexamethasone treatment to conserve hearing following a trauma.

Original languageEnglish
Pages (from-to)405-413
Number of pages9
JournalNeuroscience
Volume157
Issue number2
DOIs
StatePublished - Nov 19 2008

Fingerprint

Auditory Hair Cells
Organ of Corti
Dexamethasone
Tumor Necrosis Factor-alpha
Apoptosis
Receptors, Tumor Necrosis Factor, Type I
Genes
Up-Regulation
Gene Expression
Phalloidine
Fluorescein-5-isothiocyanate
Essential Genes
Hearing

Keywords

  • cell survival
  • cochlea
  • corticosteroids
  • nuclear factor kappa B
  • pro-inflammatory cytokine
  • trauma-induced hair cell loss

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Dexamethasone protects organ of corti explants against tumor necrosis factor-alpha-induced loss of auditory hair cells and alters the expression levels of apoptosis-related genes. / Dinh, Christine T; Haake, S.; Chen, S.; Hoang, K.; Nong, E.; Eshraghi, Adrien; Balkany, T. J.; Van De Water, Thomas R.

In: Neuroscience, Vol. 157, No. 2, 19.11.2008, p. 405-413.

Research output: Contribution to journalArticle

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abstract = "Objective: Determine the molecular mechanism(s) behind tumor necrosis factor-alpha (TNFα)-induced loss of auditory hair cells and the ability of dexamethasone base (DXMb) to protect against TNFα ototoxicity. Methods: Hair cell counts: Three-day-old rat organ of Corti explants were cultured under three different conditions: 1) untreated-control; 2) TNFα (2 μg/ml); and 3) TNFα (2 μg/ml)+DXMb (70 μg/ml) for 4 days, fixed, and stained with FITC-phalloidin. Hair cells were counted in the basal and middle turns. Gene expression: total RNA was extracted from the three different groups of explants at 0, 12, 24 and 48 h. Using quantitative real-time RT-PCR, mRNAs were transcribed into cDNAs and amplification was performed using primers for rat {\ss}-actin (housekeeping gene), TNFR1, Bcl-2, Bax, and Bcl-xl. Results: DXMb protected explant hair cells from TNFα-induced loss. Bax gene expression was greater in TNFα-exposed explants compared with TNFα+DXMb-treated explants at 48 h (P=0.023), confirmed by the increase in the Bax/Bcl-2 ratio at 48 h (P<0.001). These results correlated with increased TNFR1 expression at 24 h (P=0.038). DXMb otoprotection in TNFα-exposed cultures was accompanied by an up-regulation of Bcl-xl at both the 24 (P<0.001) and 48 h time points (P=0.030) and up-regulation of Bcl-2 expression at 24 h (P=0.018). DXMb treatment also prevented increases in the expression levels of Bax, TNFR1, and the Bax/Bcl-2 ratio that occurred in untreated TNFα-exposed explants. Conclusions: TNFα's ototoxicity may be mediated through an up-regulation of Bax and TNFR1 expression as well as an increase in the Bax/Bcl-2 ratio. DXMb protects the organ of Corti against TNFα ototoxicity by up-regulating Bcl-2 and Bcl-xl expression and by inhibiting TNFα-induced increases in Bax, TNFR1, and the Bax/Bcl-2 ratio. These results support the use of local dexamethasone treatment to conserve hearing following a trauma.",
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author = "Dinh, {Christine T} and S. Haake and S. Chen and K. Hoang and E. Nong and Adrien Eshraghi and Balkany, {T. J.} and {Van De Water}, {Thomas R}",
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T1 - Dexamethasone protects organ of corti explants against tumor necrosis factor-alpha-induced loss of auditory hair cells and alters the expression levels of apoptosis-related genes

AU - Dinh, Christine T

AU - Haake, S.

AU - Chen, S.

AU - Hoang, K.

AU - Nong, E.

AU - Eshraghi, Adrien

AU - Balkany, T. J.

AU - Van De Water, Thomas R

PY - 2008/11/19

Y1 - 2008/11/19

N2 - Objective: Determine the molecular mechanism(s) behind tumor necrosis factor-alpha (TNFα)-induced loss of auditory hair cells and the ability of dexamethasone base (DXMb) to protect against TNFα ototoxicity. Methods: Hair cell counts: Three-day-old rat organ of Corti explants were cultured under three different conditions: 1) untreated-control; 2) TNFα (2 μg/ml); and 3) TNFα (2 μg/ml)+DXMb (70 μg/ml) for 4 days, fixed, and stained with FITC-phalloidin. Hair cells were counted in the basal and middle turns. Gene expression: total RNA was extracted from the three different groups of explants at 0, 12, 24 and 48 h. Using quantitative real-time RT-PCR, mRNAs were transcribed into cDNAs and amplification was performed using primers for rat ß-actin (housekeeping gene), TNFR1, Bcl-2, Bax, and Bcl-xl. Results: DXMb protected explant hair cells from TNFα-induced loss. Bax gene expression was greater in TNFα-exposed explants compared with TNFα+DXMb-treated explants at 48 h (P=0.023), confirmed by the increase in the Bax/Bcl-2 ratio at 48 h (P<0.001). These results correlated with increased TNFR1 expression at 24 h (P=0.038). DXMb otoprotection in TNFα-exposed cultures was accompanied by an up-regulation of Bcl-xl at both the 24 (P<0.001) and 48 h time points (P=0.030) and up-regulation of Bcl-2 expression at 24 h (P=0.018). DXMb treatment also prevented increases in the expression levels of Bax, TNFR1, and the Bax/Bcl-2 ratio that occurred in untreated TNFα-exposed explants. Conclusions: TNFα's ototoxicity may be mediated through an up-regulation of Bax and TNFR1 expression as well as an increase in the Bax/Bcl-2 ratio. DXMb protects the organ of Corti against TNFα ototoxicity by up-regulating Bcl-2 and Bcl-xl expression and by inhibiting TNFα-induced increases in Bax, TNFR1, and the Bax/Bcl-2 ratio. These results support the use of local dexamethasone treatment to conserve hearing following a trauma.

AB - Objective: Determine the molecular mechanism(s) behind tumor necrosis factor-alpha (TNFα)-induced loss of auditory hair cells and the ability of dexamethasone base (DXMb) to protect against TNFα ototoxicity. Methods: Hair cell counts: Three-day-old rat organ of Corti explants were cultured under three different conditions: 1) untreated-control; 2) TNFα (2 μg/ml); and 3) TNFα (2 μg/ml)+DXMb (70 μg/ml) for 4 days, fixed, and stained with FITC-phalloidin. Hair cells were counted in the basal and middle turns. Gene expression: total RNA was extracted from the three different groups of explants at 0, 12, 24 and 48 h. Using quantitative real-time RT-PCR, mRNAs were transcribed into cDNAs and amplification was performed using primers for rat ß-actin (housekeeping gene), TNFR1, Bcl-2, Bax, and Bcl-xl. Results: DXMb protected explant hair cells from TNFα-induced loss. Bax gene expression was greater in TNFα-exposed explants compared with TNFα+DXMb-treated explants at 48 h (P=0.023), confirmed by the increase in the Bax/Bcl-2 ratio at 48 h (P<0.001). These results correlated with increased TNFR1 expression at 24 h (P=0.038). DXMb otoprotection in TNFα-exposed cultures was accompanied by an up-regulation of Bcl-xl at both the 24 (P<0.001) and 48 h time points (P=0.030) and up-regulation of Bcl-2 expression at 24 h (P=0.018). DXMb treatment also prevented increases in the expression levels of Bax, TNFR1, and the Bax/Bcl-2 ratio that occurred in untreated TNFα-exposed explants. Conclusions: TNFα's ototoxicity may be mediated through an up-regulation of Bax and TNFR1 expression as well as an increase in the Bax/Bcl-2 ratio. DXMb protects the organ of Corti against TNFα ototoxicity by up-regulating Bcl-2 and Bcl-xl expression and by inhibiting TNFα-induced increases in Bax, TNFR1, and the Bax/Bcl-2 ratio. These results support the use of local dexamethasone treatment to conserve hearing following a trauma.

KW - cell survival

KW - cochlea

KW - corticosteroids

KW - nuclear factor kappa B

KW - pro-inflammatory cytokine

KW - trauma-induced hair cell loss

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