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Monika Lakk, Grace E.F. Hoffmann, Derek Young, Sarah N. Redmon, David Krizaj; Mechanical strain regulates apoptotic pathways in retinal ganglion cells through activation of the polymodal TRPV4 channel. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3713.
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© ARVO (1962-2015); The Authors (2016-present)
Mechanical deformations of the eye can lead to neuronal damage, inflammation and may contribute to optic neuropathies. The molecular mechanisms that transduce strain into dysfunction of retinal ganglion cells (RGCs) remain to be identified but are likely to involve activation of specialized mechanosensors and downstream activation of proapoptotic signaling cascades. Our goals are to identify and characterize the molecular mechanisms that drive strain-dependent plasticity in the pathophysiology of RGCs.
The experiments used C57BL/6, TRPV1-/- and TRPV4-/- mouse retinas. Intraocular pressure in a subset of eyes was elevated through injection of polystyrene microbeads. RGCs were isolated by immunopanning (I). I-RGCs were plated onto silicon membranes and exposed to cyclic biaxial strains (0.5 Hz; 1 – 15%) in the presence/absence of putative mechanosensitive ion channel inhibitors. Immunolabeling, Ca-imaging and qRT-PCR were utilized to determine the strain-dependent changes in transcripts, protein, calcium dynamics and RGC survival.
Mechanical strain had profound, dose- and time-dependent effects on transcript levels of putative mechanosensitive channels from TRP, Piezo and K2P families. Stretch-evoked responses were reduced or absent in cells exposed to selective blockers or from TRP channel KO mice. Stretch induced changes in expression/trafficking of key proapoptotic proteins (calpains, caspases, annexin-V). While TRPV4 showed spatial and functional overlap with TRPV1 in a subset of RGCs, stretch-induced RGC signaling and apoptosis was independent of TRPV1 channels. Instead, the fraction of caspase-3 positive cells increased in a TRPV4-dependent manner for both I-RGCs isolated from control retinas, and for glaucomatous retinas exposed to chronic ocular hypertension. RGCs responded to increased radial stretch with dose-dependent elevations in [Ca2+]i that were suppressed by TRP channel antagonists and mimicked by TRP agonists.
We found that the expression of putative mechano-activated ion channels in RGCs is regulated by IOP and mechanical strain. Mechanical stress regulates proapoptotic pathways that have been previously linked to neurodegeneration in glaucoma. These effects required the activation of TRPV4 but not TRPV1 channels, identifying TRPV4 as a potential target for neuroprotection in the mammalian retina.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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