Noise induces Ca2+ signaling waves and Chop/S-Xbp1 expression in the hearing cochlea
Yesai Park, Jiang Li, Noura Ismail Mohamad, Ian R. Matthews, Peu Santra, Elliott H. Sherr, Dylan K. Chan
Yesai Park, Jiang Li, Noura Ismail Mohamad, Ian R. Matthews, Peu Santra, Elliott H. Sherr, Dylan K. Chan
View: Text | PDF
Research Article Otology

Noise induces Ca2+ signaling waves and Chop/S-Xbp1 expression in the hearing cochlea

Abstract

Exposure to loud noise is a common cause of acquired hearing loss. Disruption of subcellular calcium homeostasis and downstream stress pathways in the endoplasmic reticulum and mitochondria, including the unfolded protein response (UPR), have been implicated in the pathophysiology of noise-induced hearing loss. However, studies on the association between calcium homeostasis and stress pathways have been limited due to limited ability to measure calcium dynamics in mature-hearing, noise-exposed mice. We used a genetically encoded calcium indicator mouse model in which GCaMP6f is expressed specifically in hair cells or supporting cells under control of Myo15Cre or Sox2Cre, respectively. We performed live calcium imaging and UPR gene expression analysis in 8-week-old mice exposed to levels of noise that cause cochlear synaptopathy (98 db sound pressure level [SPL]) or permanent hearing loss (106 dB SPL). UPR activation occurred immediately after noise exposure, and the pattern of UPR activation was dependent on noise level, with the proapoptotic pathway upregulated only after 106 dB noise exposure. Spontaneous calcium transients in hair cells and intercellular calcium waves in supporting cells, which are present in neonatal cochleae, were quiescent in mature-hearing cochleae but reactivated upon noise exposure. Noise exposure of 106 dB was associated with more persistent and expansive intercellular Ca2+ signaling wave activity. These findings demonstrate a strong and dose-dependent association between noise exposure, UPR activation, and changes in calcium homeostasis in hair cells and supporting cells, suggesting that targeting these pathways may be effective to develop treatments for noise-induced hearing loss.

Authors

Yesai Park, Jiang Li, Noura Ismail Mohamad, Ian R. Matthews, Peu Santra, Elliott H. Sherr, Dylan K. Chan

×

Figure 4

Ca2+ activity in neonatal cochlear hair cells.

Options: View larger image (or click on image) Download as PowerPoint
Ca2+ activity in neonatal cochlear hair cells. (A) Live imaging of Myo15...
(A) Live imaging of Myo15Cre-GCaMP6f neonatal cochlea. No spontaneous Ca2+ activity was seen in hair cells of the neonatal cochlea. However, application of 1 μm ATP (applied after the leftmost panel) induced an increase in cytosolic Ca2+ with subsequent return to baseline in both inner hair cells (IHCs) and outer hair cells (OHCs). Time interval between successive images was 8 seconds. Scale bar: 20 μm. Representative video also shown in Supplemental Video 2. (B and C) ATP-induced Ca2+ peaks. In an individual cochlear IHC (B), bath application of 1 μm ATP (arrow) induced an increase in Ca2+ in the presence of vehicle (VEH, black), thapsigargin (TG, red), and vanadate (VN, blue), with prolonged onset and decay time with TG and prolonged elevation with no return to baseline in the presence of VN. An OHC (C) was also responsive to ATP; however, TG and VN had minimal effects on return to baseline. For both B and C, peak height was normalized to maximum amplitude of the initial ATP-induced peak. (D–G) Change in Ca2+ after drug treatment. Treatment with TG (red) and VN (blue) induced initial increases in Ca2+, as seen in mean fluorescence tracings across IHC (D) and OHC regions (E) immediately after drug treatment (arrow). Comparison of steady-state Ca2+ levels after drug treatment (F and G) showed that TG induced a significant persistent increase in Ca2+ in OHCs (G) but not IHCs (F), where VN increased steady-state Ca2+ in both IHCs and OHCs. (F and G) Tukey plots (box: first quartile/median/third quartile; whiskers: 10th and 90th percentile; dots: individual points outside the whiskers) representing all cells measured in individual cochleae under the indicated conditions. Groups were compared with 2-way ANOVA to detect treatment or cochlea-specific differences in fluorescence. P values indicate treatment effect for the indicated drug compared with control. Sample sizes tested enabled detection of effect size > 3.07× SD with 80% power. AU, arbitrary units.