Role of Calcium-Sensing Receptor in Mechanotransducer-Channel-Mediated Ca2+ Influx in Hair Cells of Zebrafish Larvae

Abstract

The calcium-sensing receptor (CaSR) is an extracellular Ca2+ sensor that plays a critical role in maintaining Ca2+ homeostasis in several organs, including the parathyroid gland and kidneys. In this study, through in situ hybridization, the expression of CaSR mRNA was found in the neuromasts of zebrafish larvae. Immunohistochemistry further demonstrated that the CaSR protein was present in neuromast hair cell stereocilia and basolateral membranes. Based on the expression and subcellular localization of the CaSR in hair cells, we hypothesized that the CaSR is expressed in zebrafish lateral-line hair cells to regulate mechanotransducer (MET)-channel-mediated Ca2+ entry. Using the scanning ion-selective electrode technique, MET-channel-mediated Ca2+ influx at the stereocilia of hair cells was measured in intact larvae. Ca2+ influx was suppressed after larvae were pretreated with a CaSR activator (R-568) or high-Ca2+ (HCa) medium. Gene knockdown by using morpholino oligonucleotides decreased CaSR expression in hair cells and eliminated the effects of R-568 and HCa on Ca2+ influx. In addition, we found that treatment with R-568 attenuated neomycin-induced hair cell death. This study is the first to demonstrate that the CaSR is involved in mechanotransduction in zebrafish hair cells.

Immunolocalization of calcium sensing and transport proteins in the murine endolymphatic sac indicates calciostatic functions within the inner ear

“…Consistent with the immunolocalization of CaSR in MRCs of the mature murine ES shown here, previous gene expression studies detected CaSR mRNA expression in MRCs of the early postnatal murine ES (Honda et al 2017), in the adult rat ES (Beitz et al 1999), and, moreover, in the adult rat organ of Corti, stria vascularis, Reissner’s membrane, and vestibulum (Beitz et al 1999), as well as in neuromast hair cell stereocilia of zebrafish larvae (Lin et al 2018). The results of the present study indicate that the CaSR protein in the mature murine inner ear is exclusively expressed in the ES or that immunolabeling at other cellular sites was below the detection level.…”

“…In those tissues, CaSR senses changes in Ca 2+ levels in urine and plasma and modulates the activity and expression of Ca 2+ transport proteins to increase renal Ca 2+ reabsorption (Riccardi et al 1998) and the Ca 2+ -mediated release of calciotropic hormones (parathyroid hormone, calcitonin) (Brown and MacLeod 2001), respectively. In the inner ear, the endolymphatic sac (ES), among other epithelial tissues, is a site of CaSR gene expression (Beitz et al 1999; Lin et al 2018) and critically contributes to endolymphatic Ca 2+ homeostasis. This function was first indicated by in vivo animal experiments in which surgical separation of the ES resulted in a nonphysiological increase in [Ca 2+ ] endolymph and endolymphatic hydrops development in the cochlea (Ninoyu and Meyer zum Gottesberge 1986; Salt and DeMott 1994).…”

Focusing on Mechanoregulation Axis in Fibrosis: Sensing, Transduction and Effecting

“…CaSR is a member of the class C GPCR. A study found that CaSR expression in zebrafish lateral-line hair cells regulates mechanotransducer-channel-mediated calcium entry ( Lin et al, 2018 ), suggesting that CaSR is involved in mechanotransduction and could be a potential therapeutic target. In renal ischemia–reperfusion mice, a sustained influx of Orai1+ CD4 T cells with increased IL-17 expression and intracellular calcium concentration was observed.…”

The calcium-sensing receptor (CaSR) regulates zebrafish sensorimotor decision making via a genetically defined cluster of hindbrain neurons

“…In vertebrates, CaSR is expressed in neurons, 33 hair cells, 36 and various glial cell types including astrocytes 30 and oligodendrocytes. 34 To determine the cell type(s) in which CaSR functions to regulate sensorimotor decision making, we utilized a transgenic rescue approach.…”