Expression of canonical transient receptor potential channel (TRPC) 1-7 in the mouse inner ear

Immunohistochemistry Reveals TRPC Channels in the Human Hearing Organ-A Novel CT-Guided Approach to the Cochlea

TRPC channels are critical players in cochlear hair cells and sensory neurons, as demonstrated in animal experiments. However, evidence for TRPC expression in the human cochlea is still lacking. This reflects the logistic and practical difficulties in obtaining human cochleae. The purpose of this study was to detect TRPC6, TRPC5 and TRPC3 in the human cochlea. Temporal bone pairs were excised from ten body donors, and the inner ear was first assessed based on computed tomography scans. Decalcification was then performed using 20% EDTA solutions. Immunohistochemistry with knockout-tested antibodies followed. The organ of Corti, the stria vascularis, the spiral lamina, spiral ganglion neurons and cochlear nerves were specifically stained. This unique report of TRPC channels in the human cochlea supports the hypothesis of the potentially critical role of TRPC channels in human cochlear health and disease which has been suggested in previous rodent experiments.

Differential immunostaining patterns of transient receptor potential (TRP) ion channels in the rat nodose ganglion

Vagal afferents regulate numerous physiological functions including arterial blood pressure, heart rate, breathing, and nociception. Cell bodies of vagal afferents reside in the inferior vagal (nodose) ganglia and their stimulation by various means is being considered as a way to regulate cardiorespiratory responses and control pain sensations. Stimulation of the nodose by exposure to infrared light is recently being considered as a precise way to elicit responses. These responses would likely involve the activity of temperature-sensitive membrane-bound channels. While papers have been published to track the expression of these transient receptor potential ion channels (TRPs), further studies are warranted to determine the in situ expression of the endogenous TRP proteins in the nodose ganglia to fully understand their pattern of expression, subcellular locations, and functions in this animal model. TRP ion channels are a superfamily of Na+ /Ca2+ -channels whose members are temperature- and/or mechano-sensitive and therefore represent a potential set of proteins that will be activated directly or indirectly by infrared light. Here, we report the spatial localization of six TRP channels, TRPV1, TRPV4, TRPM3, TRPM8, TRPA1, and TRPC1, from nodose ganglia taken from juvenile male Sprague-Dawley rats. The channels were detected using immunohistology with fluorescent tags on cryosections and imaged using confocal microscopy. All six TRP channels were detected with different levels of intensity in neuronal cell bodies and some were also detected in axonal fibers and blood vessels. The TRP receptors differed in their prevalence, in their patterns of expression, and in subcellular expression/localization. More specifically, TRPV1, TRPV4, TRPA1, TRPM8, TRPC1, and TRPM3 were found in vagal afferent cell bodies with a wide range of immunostaining intensity from neuron to neuron. Immunostaining for TRPV1, TRPV4, and TRPA1 appeared as fine particles scattered throughout the cytoplasm of the cell body. Intense TRPV1 immunostaining was also evident in a subset of axonal fibers. TRPM8 and TRPC1 were expressed in courser particles suggesting different subcellular compartments than for TRPV1. The localization of TRPM3 differed markedly from the other TRP channels with an immunostaining pattern that was localized to the periphery of a subset of cell bodies, whereas a scattering or no immunostaining was detected within the bulk of the cytoplasm. TRPV4 and TRPC1 were also expressed on the walls of blood vessels. The finding that all six TRP channels (representing four subfamilies) were present in the nodose ganglia provides the basis for studies designed to understand the roles of these channels in sensory transmission within vagal afferent fibers and in the responses elicited by exposure of nodose ganglia to infrared light and other stimuli. Depending on the location and functionality of the TRP channels, they may regulate the flux of Na+ /Ca2+ -across the membranes of cell bodies and axons of sensory afferents, efferent (motor) fibers coursing through the ganglia, and in vascular smooth muscle.

The Role of the Reactive Oxygen Species Scavenger Agent, Astaxanthin, in the Protection of Cisplatin-Treated Patients Against Hearing Loss

Emerging evidence of significant hearing loss occurring shortly after cisplatin administration in cancer patients has stimulated research into the causes and treatment of this side effect. Although the aetiology of cisplatin-induced hearing loss (CIHL) remains unknown, an increasing body of research suggests that it is associated with excessive generation of intracellular reactive oxygen species (ROS) in the cochlea. Astaxanthin, a xanthophyll carotenoid, has powerful anti-oxidant, anti-inflammatory, and anti-apoptotic properties based on its unique cell membrane function, diverse biological activities, and ability to permeate the blood-brain barrier. In this review, we summarize the role of ROS in CIHL and the effect of astaxanthin on inhibiting ROS production. We focus on investigating the mechanism of action of astaxanthin in suppressing excessive production of ROS.

TRPC1 is required for survival and proliferation of cochlear spiral ganglion stem/progenitor cells

OBJECTIVE

The present studies were designed to test the hypothesis that canonical transient receptor potential channel 1 (TRPC1) is required for the proliferation of cochlear spiral ganglion stem/progenitor cells (SPCs).

METHODS AND MATERIALS

TRPC1 were detected and evaluated in postnatal day 1 CBA/CaJ mice pups derived-cochlear spiral ganglion SPCs by reverse transcription-polymerase chain reaction, Western blot, immunocytochemistry, and calcium imaging. The cell viability and proliferation of the spiral ganglion SPCs following si-RNA mediated knockdown of TRPC1 or addition of TRPC channel blocker SKF9635 were compared to controls.

RESULTS

In spiral ganglion SPCs, TRPC1 was found to be the most abundantly expressed TRPC subunit and shown to contribute to store-operated calcium entry. Silencing of TRPC1 or addition of TRPC channel blockers significantly decreased the rate of cell proliferation.

CONCLUSION

The results suggest that TRPC1 might serve as an essential molecule in regulating the proliferation of spiral ganglion SPCs.

The contribution of TRPC1, TRPC3, TRPC5 and TRPC6 to touch and hearing

•

The contribution of multiple TRPC channels on mechanosensory function is demonstrated.

•

We observe a critical role for TRPC channels in touch sensation.

•

TRPC channels contribute to cutaneous and auditory mechanosensation in a combinatorial manner, but have no direct role in cochlear mechanotransduction.

Transient receptor potential channels have diverse roles in mechanosensation. Evidence is accumulating that members of the canonical subfamily of TRP channels (TRPC) are involved in touch and hearing. Characteristic features of TRP channels include their high structural homology and their propensity to form heteromeric complexes which suggests potential functional redundancy. We previously showed that TRPC3 and TRPC6 double knockout animals have deficits in light touch and hearing whilst single knockouts were apparently normal. We have extended these studies to analyse deficits in global quadruple TRPC1, 3, 5 and 6 null mutant mice. We examined both touch and hearing in behavioural and electrophysiological assays, and provide evidence that the quadruple knockout mice have larger deficits than the TRPC3 TRPC6 double knockouts. Mechano-electrical transducer currents of cochlear outer hair cells were however normal. This suggests that TRPC1, TRPC3, TRPC5 and TRPC6 channels contribute to cutaneous and auditory mechanosensation in a combinatorial manner, but have no direct role in cochlear mechanotransduction.

TRPC3 and TRPC6 are essential for normal mechanotransduction in subsets of sensory neurons and cochlear hair cells

Transient receptor potential (TRP) channels TRPC3 and TRPC6 are expressed in both sensory neurons and cochlear hair cells. Deletion of TRPC3 or TRPC6 in mice caused no behavioural phenotype, although loss of TRPC3 caused a shift of rapidly adapting (RA) mechanosensitive currents to intermediate-adapting currents in dorsal root ganglion sensory neurons. Deletion of both TRPC3 and TRPC6 caused deficits in light touch and silenced half of small-diameter sensory neurons expressing mechanically activated RA currents. Double TRPC3/TRPC6 knock-out mice also showed hearing impairment, vestibular deficits and defective auditory brain stem responses to high-frequency sounds. Basal, but not apical, cochlear outer hair cells lost more than 75 per cent of their responses to mechanical stimulation. FM1-43-sensitive mechanically gated currents were induced when TRPC3 and TRPC6 were co-expressed in sensory neuron cell lines. TRPC3 and TRPC6 are thus required for the normal function of cells involved in touch and hearing, and are potential components of mechanotransducing complexes.

Cisplatin-induced ototoxicity: transporters playing a role in cisplatin toxicity

Cisplatin is a potent antineoplastic agent widely used for a variety of cancer types. Unfortunately, its use leads to dose limiting side effects such as ototoxicity. Up to 93% of patients receiving cisplatin chemotherapy will develop progressive and irreversible sensorineural hearing loss which leads to a decreased quality of life in cancer survivors. No treatment is currently available for cisplatin-induced ototoxicity. It appears that cisplatin causes apoptosis by binding DNA, activating the inflammatory cascade as well as generating oxidative stress in the cell. Various studies have aimed to assess the potential protective effects of compounds such as antioxidants, anti-inflammatories, caspase inhibitors, anti-apoptotic agents and calcium channel blockers against the toxicity caused by cisplatin in the inner ear with variable degrees of protection. Nevertheless, the pathophysiology of cisplatin-induced ototoxicity remains unclear. This review summarizes all of the known transporters that could play a role in cisplatin influx, leading to cisplatin-induced ototoxicity. The following were evaluated: copper transporters, organic cation transporters, the transient receptor potential channel family, calcium channels, multidrug resistance associated proteins, mechanotransduction channels and chloride channels.

Intratympanic dexamethasone up-regulates Fkbp5 in the cochleae of mice in vivo

CONCLUSIONS

Quantitative, real-time RT-PCR demonstrated that intratympanic dexamethasone significantly up-regulates the expression of Fkbp5 in cochleae of mice in vivo. The immunohistochemistry results showed fundamentally ubiquitous expression of Fkbp5 in cochlear structures, with relatively strong expression in type 4 fibrocytes and weak signal in the inner hair cells. These data indicate that dexamethasone regulates gene expression at the level of transcription in vivo and that this process is basically ubiquitous in the cochlea.

OBJECTIVES

To demonstrate that intratympanically applied dexamethasone up-regulates Fkbp5 in the cochlea in vivo.

METHODS

Dexamethasone or control saline were intratympanically applied to adult C57/BL6 mice and dexamethasone-dependent changes in the levels of Fkbp5 expression in the cochlea were analyzed using quantitative real-time RT-PCR. The expression pattern of Fkbp5 in cochlea was investigated by immunohistochemistry in mice that were administered dexamethasone and in controls.

RESULTS

Quantitative real-time RT-PCR demonstrated significant increases of Fkbp5 expression levels in cochleae of dexamethasone-treated mice as compared with controls at 12 h after application (244.8 ± 155.5, n = 5 vs 100.0 ± 3.0, n = 6, p < 0.01). Immunohistochemistry showed fundamentally ubiquitous expression of Fkbp5 in cochlear structures, with some strongly positive fibrocytes in the spiral ligaments and weak immunoreactivity in the inner hair cells. Distribution of Fkbp5 signaling was not different between the dexamethasone-treated group and controls.

Purinergic signaling in cochleovestibular hair cells and afferent neurons

Purinergic signaling in the mammalian cochleovestibular hair cells and afferent neurons is reviewed. The scope includes P2 and P1 receptors in the inner hair cells (IHCs) of the cochlea, the type I spiral ganglion neurons (SGNs) that convey auditory signals from IHCs, the vestibular hair cells (VHCs) in the vestibular end organs (macula in the otolith organs and crista in the semicircular canals), and the vestibular ganglion neurons (VGNs) that transmit postural and rotatory information from VHCs. Various subtypes of P2X ionotropic receptors are expressed in IHCs as well as P2Y metabotropic receptors that mobilize intracellular calcium. Their functional roles still remain speculative, but adenosine 5'-triphosphate (ATP) could regulate the spontaneous activity of the hair cells during development and the receptor potentials of mature hair cells during sound stimulation. In SGNs, P2Y metabotropic receptors activate a nonspecific cation conductance that is permeable to large cations as NMDG(+) and TEA(+). Remarkably, this depolarizing nonspecific conductance in SGNs can also be activated by other metabotropic processes evoked by acetylcholine and tachykinin. The molecular nature and the role of this depolarizing channel are unknown, but its electrophysiological properties suggest that it could lie within the transient receptor potential channel family and could regulate the firing properties of the afferent neurons. Studies on the vestibular partition (VHC and VGN) are sparse but have also shown the expression of P2X and P2Y receptors. There is still little evidence of functional P1 (adenosine) receptors in the afferent system of the inner ear.