Activity regulates a cell type-specific mitochondrial phenotype in zebrafish lateral line hair cells

Abstract

Hair cells of the inner ear are particularly sensitive to changes in mitochondria, the subcellular organelles necessary for energy production in all eukaryotic cells. There are over thirty mitochondrial deafness genes, and mitochondria are implicated in hair cell death following noise exposure, aminoglycoside antibiotic exposure, as well as in age-related hearing loss. However, little is known about the basic aspects of hair cell mitochondrial biology. Using hair cells from the zebrafish lateral line as a model and serial block-face scanning electron microscopy, we have quantifiably characterized a unique hair cell mitochondrial phenotype that includes (1) a high mitochondrial volume, and (2) specific mitochondrial architecture: multiple small mitochondria apically, and a reticular mitochondrial network basally. This phenotype develops gradually over the lifetime of the hair cell. Disrupting this mitochondrial phenotype with a mutation in opa1 impacts mitochondrial health and function. While hair cell activity is not required for the high mitochondrial volume, it shapes the mitochondrial architecture, with mechanotransduction necessary for all patterning, and synaptic transmission necessary for development of mitochondrial networks. These results demonstrate the high degree to which hair cells regulate their mitochondria for optimal physiology, and provide new insights into mitochondrial deafness.

The Role of Cilia in the Development, Survival, and Regeneration of Hair Cells

“…It is worth noting that decreases in hair cell activity can lead to reduced mitochondrial membrane (Pickett et al, 2018) and changes in mitochondria architecture (McQuate et al, 2023). Hair cells of IFT gene mutants show reduced uptake of the dye FM1-43 (Stawicki et al, 2016; Stawicki et al, 2019).…”

Noise-induced synaptopathy impacts the long and short sensory hair cells differently in the mammalian cochlea

“…This finding is significant since it provides a structural cue for defining the putative ribbon-associated mitochondria (RAM). After the synaptopathic exposure, the overall reduction in spatial correlation between mitochondrial and ribbon gradients (Fig 4B) is presumably not only owing to dramatic ribbon reorganization but also caused by activity-dependent mitochondrial remodeling (McQuate et al, 2023). Given that the ribbon size is tightly regulated by the coupled presynaptic influx and mitochondrial uptake of Ca 2+ (Wong et al, 2019), we attempt to speculate that the altered mitochondrial morphology and basolateral distribution (Fig 4C-E) may hamper the restoration of proper modiolar-pillar ribbon gradient, and thereby contribute to a permanent coding deficit of the IHC.…”

In vivo screening for toxicity-modulating drug interactions identifies antagonism that protects against ototoxicity in zebrafish

“…For calcium testing, zebrafish expressing HC-specific GCaMP targeted to the inner mitochondrial matrix were crossed with fish expressing a HC specific calcium indicator to create double-transgenic embryos (Tg ( myo6b:mitoGCaMP3;myo6b:cytoRGECO ), Table 1 ) with both green fluorescent mitochondrial calcium and red fluorescent cytosolic calcium indicators, then raised as described previously ( McQuate et al, 2023 ). Zebrafish embryos were collected from 2-h spawning periods and raised in Petri dishes in embryo medium (EM: 14.97 mM NaCl, 500 μM KCl, 42 µM Na 2 HPO 4 , 150 µM KH 2 PO 4 , 1 mM CaCl 2 dehydrate, 1 mM MgSO 4 , 0.714 mM NaHCO 3 , pH 7.2) at a density of 60 larvae per 100-mm 2 dish, in a dark 28.5°C incubator until 5 dpf.…”

“…Briefly, zebrafish embryos were collected from 2 h spawning periods, washed with dilute bleach solution (0.005% sodium hypochlorite) by 6 hours post-fertilization to minimize contamination from 1) (Linbo et al, 2009) at a density of 50 larvae per 100-mm 2 dish, in a dark 28.5 °C incubator until 5 dpf, with fluorophore screening performed when relevant alongside dechorionation at 2-4 dpf; fish homozygous and heterozygous for fluorophore expression were both used. For calcium testing, zebrafish expressing HC-specific GCaMP targeted to the inner mitochondrial matrix were crossed with fish expressing a HC specific calcium indicator to create double-transgenic embryos (Tg (myo6b:mitoGCaMP3;myo6b: cytoRGECO), Table 1) with both green fluorescent mitochondrial calcium and red fluorescent cytosolic calcium indicators, then raised as described previously (McQuate et al, 2023). Zebrafish embryos were collected from 2-h spawning periods and raised in Petri dishes in embryo medium (EM: 14.97 mM NaCl, 500 μM KCl, 42 µM Na 2 HPO 4 , 150 µM KH 2 PO 4 , 1 mM CaCl 2 dehydrate, 1 mM MgSO 4 , 0.714 mM NaHCO 3 , pH 7.2) at a density of 60 larvae per 100-mm 2 dish, in a dark 28.5 °C incubator until 5 dpf.…”