TRPV1: Contribution to Retinal Ganglion Cell Apoptosis and Increased Intracellular Ca²⁺with Exposure to Hydrostatic Pressure

Abstract

Purpose Elevated hydrostatic pressure induces retinal ganglion cell (RGC) apoptosis in culture. The authors investigated whether the transient receptor potential vanilloid 1 (TRPV1) channel, which contributes to pressure sensing and Ca2+-dependent cell death in other systems, also contributes to pressure-induced RGC death and whether this contribution involves Ca2+. Methods trpv1 mRNA expression in RGCs was probed with the use of PCR and TRPV1 protein localization through immunocytochemistry. Subunit-specific antagonism (iodo-resiniferatoxin) and agonism (capsaicin) were used to probe how TRPV1 activation affects the survival of isolated RGCs at ambient and elevated hydrostatic pressure (+70 mm Hg). Finally, for RGCs under pressure, the authors tested whether EGTA chelation of Ca2+ improves survival and whether, with the Ca2+ dye Fluo-4 AM, TRPV1 contributes to increased intracellular Ca2+. Results RGCs express trpv1 mRNA, with robust TRPV1 protein localization to the cell body and axon. For isolated RGCs under pressure, TRPV1 antagonism increased cell density and reduced apoptosis to ambient levels (P ≤ 0.05), whereas for RGCs at ambient pressure, TRPV1 agonism reduced density and increased apoptosis to levels for elevated pressure (P ≤ 0.01). Chelation of extracellular Ca2+ reduced RGC apoptosis at elevated pressure by nearly twofold (P ≤ 0.01). Exposure to elevated hydrostatic pressure induced a fourfold increase in RGC intracellular Ca2+ that was reduced by half with TRPV1 antagonism. Finally, in the DBA/2 mouse model of glaucoma, levels of TRPV1 in RGCs increased with elevated IOP. Conclusions RGC apoptosis induced by elevated hydrostatic pressure arises substantially through TRPV1, likely through the influx of extracellular Ca2+.

Distal axonopathy with structural persistence in glaucomatous neurodegeneration

“…3). Thus, sensitivity to IOP is an added stressor to other age-related factors (35). A small number of younger DBA/2 (3-5 mo) had transport deficits without IOP elevation (Fig.…”

“…An important hypothesis in glaucoma posits trophic deprivation proximally at the optic nerve head along with loss of axonal integrity (5)(6)(7)(8)43). Myriad somatic and dendritic factors are also likely to contribute, including intrinsic pressure sensitivity and synapse elimination (35,44). Importantly, transport loss at distal sites is predegenerative in that much of the structure of the retinal projection remains intact for a period afterward.…”

“…Labeling of the retina in whole-mount preparations, sections of optic nerve, and brain was performed as previously described (35). We used antibodies against detyrosinated α-tubulin (monoclonal, 1:200; Millipore) and phosphorylated heavy-chain neurofilament (SMI31, 1:1,000; Sternberger Monoclonal) (8,15) to visualize RGCs; myelin basic protein (SMI99, 1:1,000; Sternberger Monoclonal) to delineate the optic nerve head; ERRβ (polyclonal, 1:500; Sigma) (29) to label the RGC SC projection; hyperphosphorylated heavy-chain neurofilament (SMI34, 1:1.000; Sternberger Monoclonal) (15) to highlight axonal dystrophies; and VGluT2 (polyclonal, 1:500; Synaptic Systems) (32) to visualize RGC axon terminals in the SC.…”

Analysis of laser-induced heating in optical neuronal guidance

“…It has been shown that chemical guidance of growth cones is mediated by an asymmetric influx of calcium ions Ca 2+ ) and the neuronal transient receptor potential (TRP) channels appear to be the key sensors and mediators in the process (Wang and Poo, 2005;Talavera et al, 2008;Li et al, 2005;Sappington et al, 2009). It is know that TRP channels can be activated by depolarization of the cell using chemical guidance factors or by an increase in temperature (Talavera et al, 2008;Caterina et al, 1997) and highly localized heating (Huang et al, 2010), and there is strong evidence in general that depolarization of the neuronal membrane is highly sensitive to small variations in thermodynamic variables like temperature and pressure (Wunderlich et al, 2009;Blicher et al, 2009;Andersen et al, 2009;Wodzinska et al, 2009).…”

Pseudoexfoliative glaucoma and molecular genetic characteristics of vitamin D metabolism

“…Учитывая известные механизмы патоге-неза глаукомы и ПЭС, витамин D, в условиях его дефицита, может оказывать влияние на скорость и степень обновления внеклеточного матрикса, прогрессию апоптоза ганглиозных клеток сетчат-ки, а также на состояние эндотелия и базальных мембран сосудов и структур, имеющих отноше-ние как к гидродинамике глаза, так и к продукции псевдоэксфолиативного материала, приводя к на-рушениям, выявляемым при ПЭС/ПЭГ [10,18,21,30].…”