Profound defects in pupillary responses to light in TRPM-channel null mice: a role for TRPM channels in non-image-forming photoreception.
ABSTRACT TRPM1 is a spontaneously active non-selective cation channel that has recently been shown to play an important role in the depolarizing light responses of ON bipolar cells. Consistent with this role, mutations in the TRPM1 gene have been identified as a principal cause of congenital stationary night blindness. However, previous microarray studies have shown that Trpm1 and Trpm3 are acutely regulated by light in the eyes of mice lacking rods and cones (rd/rd cl), a finding consistent with a role in non-image-forming photoreception. In this study we show that pupillary light responses are significantly attenuated in both Trpm1(-/-) and Trpm3(-/-) animals. Trpm1(-/-) mice exhibit a profound deficit in the pupillary response that is far in excess of that observed in mice lacking rods and cones (rd/rd cl) or melanopsin, and cannot be explained by defects in bipolar cell function alone. Immunolocalization studies suggest that TRPM1 is expressed in ON bipolar cells and also a subset of cells in the ganglion cell layer, including melanopsin-expressing photosensitive retinal ganglion cells (pRGCs). We conclude that, in addition to its role in bipolar cell signalling, TRPM1 is involved in non-image-forming responses to light and may perform a functional role within pRGCs. By contrast, TRPM3(-/-) mice display a more subtle pupillary phenotype with attenuated responses under bright light and dim light conditions. Expression of TRPM3 is detected in Muller cells and the ciliary body but is absent from pRGCs, and thus our data support an indirect role for TRPM3 in pupillary light responses.
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ABSTRACT: Understanding the normal aging process will help us determine the mechanisms of how age-related diseases are caused and progress. A/J inbred mice have been shown to exhibit accelerated aging phenotypes in the retina including increased inflammation and photoreceptor cell degeneration, which resemble human aging symptoms. C57BL/6J (B6) inbred mice are less susceptible for these abnormalities, indicating the existence of genetic factor(s) that affect their severity. In this study, we determined that another age-dependent phenotype, ectopic synapse formation, is also accelerated in the A/J retina compared to the B6 retina. Through genetic mapping utilizing recombinant inbred strains, we identified quantitative trait loci (QTLs) on chromosome 7 and 19, which contribute to abnormal retinal synapses as well as other age-dependent phenotypes. Using consomic single chromosome substitution lines where a single chromosome is from A/J and the rest of the genome is B6, we investigated the individual effect of each QTL on retinal aging phenotypes. We observed that both QTLs independently contribute to abnormal retinal synapses, reduction in the number of cone cells, and an up-regulation of retinal stress marker, glial fibrillary acidic protein (GFAP). Mice with a single chromosome substitution on chromosome 19 also exhibited an increase in inflammatory cells, which is characteristic of aging and age-related macular degeneration. Thus, we identified QTLs that are independently capable of affecting the severity and progression of age-dependent retinal abnormalities in mice.Mammalian Genome 10/2014; 26(1-2). DOI:10.1007/s00335-014-9546-7 · 2.88 Impact Factor
Article: TRPM3 Expression in Mouse Retina[Show abstract] [Hide abstract]
ABSTRACT: Transient receptor potential (TRP) channels constitute a large family of cation permeable ion channels that serve crucial functions in sensory systems by transducing environmental changes into cellular voltage and calcium signals. Within the retina, two closely related members of the melastatin TRP family, TRPM1 and TRPM3, are highly expressed. TRPM1 has been shown to be required for the depolarizing response to light of ON-bipolar cells, but the role of TRPM3 in the retina is unknown. Immunohistochemical staining of mouse retina with an antibody directed against the C-terminus of TRPM3 labeled the inner plexiform layer (IPL) and a subset of cells in the ganglion cell layer. Within the IPL, TRPM3 immunofluorescence was markedly stronger in the OFF sublamina than in the ON sublamina. Electroretinogram recordings showed that the scotopic and photopic a- and b-waves of TRPM3-/- mice are normal indicating that TRPM3 does not play a major role in visual processing in the outer retina. TRPM3 activity was measured by calcium imaging and patch-clamp recording of immunopurified retinal ganglion cells. Application of the TRPM3 agonist, pregnenolone sulfate (PS), stimulated increases in intracellular calcium in ~40% of cells from wild type and TRPM1‑/‑ mice, and the PS-stimulated increases in calcium were blocked by co-application of mefenamic acid, a TRPM3 antagonist. No PS-stimulated changes in fluorescence were observed in ganglion cells from TRPM3-/- mice. Similarly, PS-stimulated currents that could be blocked by mefenamic acid were recorded from wild type retinal ganglion cells but were absent in ganglion cells from TRPM3-/- mice.PLoS ONE 02/2015; 10(2):e0117615. DOI:10.1371/journal.pone.0117615 · 3.53 Impact Factor
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ABSTRACT: A subset of mammalian retinal ganglion cells expresses an opsin photopigment (melanopsin, Opn4) and is intrinsically photosensitive. The human retina contains melanopsin, but the literature lacks a direct investigation of its spectral sensitivity or G-protein selectivity. Here, we address this deficit by studying physiological responses driven by human melanopsin under heterologous expression in HEK293 cells. Luminescent reporters for common second messenger systems revealed that light induces a high amplitude increase in intracellular calcium and a modest reduction in cAMP in cells expressing human melanopsin, implying that this pigment is able to drive responses via both Gq and Gi/o class G-proteins. Melanopsins from mouse and amphioxus had a similar profile of G-protein coupling in HEK293 cells, but chicken Opn4m and Opn4x pigments exhibited some Gs activity in addition to a strong Gq/11 response. An action spectrum for the calcium response in cells expressing human melanopsin had the predicted form for an opsin : vitamin A1 pigment and peaked at 479 nm. The G-protein selectivity and spectral sensitivity of human melanopsin is similar to that previously described for rodents, supporting the utility of such laboratory animals for developing methods of manipulating this system using light or pharmacological agents.Proceedings of the Royal Society B: Biological Sciences 03/2013; 280(1759):20122987. DOI:10.1098/rspb.2012.2987 · 5.29 Impact Factor