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Karen W. Ho, Tatiana N. Sidorova, Wendi S. Lambert, David J. Calkins; Age and Elevated Pressure Increase Astrocyte Expression of TRPV1 in Retina and Optic Nerve of the DBA2J Mouse Model of Glaucoma. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2446.
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Astrocytes provide structural and metabolic support to retinal ganglion cells (RGCs) and their axons. Calcium mediates a variety of intracellular events that underlie many aspects of astrocyte function in health and disease. Activation of TRPV1, a member of the transient receptor potential vanilloid (TRPV) family of cation channels, has been shown to increase intracellular Ca2+ in RGCs and retinal microglia in response to glaucomatous stressors. Here we examined the expression and localization of TRPV1 in retinal and optic nerve astrocytes in the DBA/2J mouse model of glaucoma to determine whether TRPV1 could similarly regulate astrocyte activity during disease progression.
We performed fluorescent in situ hybridization and immunocytochemistry to localize TRPV1 mRNA and protein, respectively, in retina and optic nerve harvested from paraformaldehyde-perfused C57 and DBA/2J mice between 3 and 10 months of age. Sense and anti-sense digoxigenin-labeled probes for TRPV1 were transcribed and detected using TSA Plus Fluorescence System in combination with peroxidase -based visualization. Immunolabeling for GFAP to identify astrocytes following in situ hybridization or in combination with TRPV1 was performed to determine the localization and relative amounts of TRPV1 in astrocytes specifically.
TRPV1 protein co-localized with GFAP-labeled astrocyte cell bodies and processes in both the retina and optic nerve. TRPV1 levels increased with age and elevated ocular pressure in DBA/2J mice compared to C57. While TRPV1 mRNA was expressed in astrocytes of the optic nerve, it was absent in retinal astrocytes for both C57 and DBA/2J mice.
Increased expression of TRPV1 in DBA/2J mice with age and elevated pressure could indicate an important role for the channel in regulating astrocyte activity during glaucomatous progression. The absence of TRPV1 mRNA in retinal astrocytes may suggest the presence of another isoform, emphasizing the inherent complexity of TRPV1 function. We have previously shown that TRPV1 activation increases intracellular calcium in RGCs and microglia following exposure to elevated pressure in vitro. Since astrocytes provide vital support to RGCs and their axons, it is important to determine whether TRPV1 also contributes to calcium-initiated cascades in astrocytes and whether this contribution changes in glaucoma.
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