Identification of P2Y Receptor Subtypes in Human Müller Glial Cells by Physiology, Single Cell RT-PCR, and Immunohistochemistry

PURPOSE

Retinal Müller glial cells are known to express metabotropic P2Y receptors. The present study was conducted to identify certain subtypes of P2Y receptors in human Müller cells.

METHODS

The patch-clamp technique was used to measure increases of Ca(2+)-dependent K+ currents mediated by the activation of P2Y receptors in freshly isolated human Müller cells. Several P2 agonists were used. Subsequently, the cells were harvested into the patch pipette and a single cell RT-PCR was performed. Moreover, retinal tissue from organ donors was used for immunohistochemistry.

RESULTS

The electrophysiological data were consistent with the expression of P2Y1, P2Y2, P2Y4, and P2Y6 receptor subtypes. RT-PCR revealed that mRNA for all these subtypes was present in Müller cells. However, the incidence of P2Y2 receptor mRNA was significantly lower than that of the other subtypes. Immunoreactivity for all four subtypes was found in retinal tissue, partly colocalized with immunoreactivity for vimentin.

CONCLUSIONS

The presented data obtained by different techniques revealed that human Müller cells express P2Y1, P2Y2, P2Y4, and P2Y6 receptors. The specific roles of these receptor subtypes in retinal physiology and/or pathophysiology remain to be investigated in future studies.

OPA1, the disease gene for autosomal dominant optic atrophy, is specifically expressed in ganglion cells and intrinsic neurons of the retina

PURPOSE

Autosomal dominant optic atrophy is a hereditary disorder characterized by progressive loss of vision and caused by mutations in a dynamin-related gene, OPA1, which translates into a protein with a mitochondrial leader sequence. In this study the OPA1 gene and its protein were localized in the rat and mouse retina, and its rat orthologue, rOpa1, was identified.

METHODS

The rOpa1 cDNA was isolated by using reverse transcribed cDNA from total RNA obtained from a rat retinal ganglion cell line. The spatial and temporal expression patterns of OPA1 and its gene product were investigated by RNA in situ hybridization and immunohistochemistry in mouse and rat retinas. To characterize further the OPA1-positive neurons, retinal ganglion cells were retrogradely labeled by an immunogold fluorescent tracer or double labeled with OPA1 and choline acetyltransferase or calbindin antibodies.

RESULTS

Protein sequence alignment revealed a 96% identity between rat and human OPA1 mRNA. OPA1 expression was found as early as postnatal day 3 in the developing rodent retina. In the mature retina, the OPA1 gene and its protein were found not only in retinal ganglion cells, but also in starburst amacrine cells and horizontal cells, both of which are involved in lateral signal processing within the retina. However, OPA1 was absent from mitochondria rich nerve fibers and photoreceptor indicating a specific role for OPA1 in signal processing rather than in the requirement of mitochondrial energy supply in the retina.

CONCLUSIONS

The data suggest an important and specific function of the OPA1 protein, not only in the optic nerve forming ganglion cells but also in the intrinsic signal processing of the inner retina.

Expression of P2Y1, P2Y2, P2Y4, and P2Y6 receptor subtypes in the rat retina

PURPOSE

To elucidate the expression pattern of different types of metabotropic P2Y receptors in the adult rat retina.

METHODS

Qualitative RT-PCR was used to investigate the expression profile of different P2Y receptor subtypes (P2Y1, P2Y2, P2Y4, and P2Y6), and in situ hybridization studies were performed to show their cellular localization within the retina. Immunohistochemical staining was used to detect the corresponding P2Y proteins (P2Y1, P2Y2, and P2Y4) and their cellular localization. Southern blot analysis and sequencing verified the identity of the P2Y PCR products.

RESULTS

RT-PCR revealed the presence of P2Y1, -2, -4, and -6 mRNA in the neural retina and the retinal pigment epithelium (RPE) and choroid. In situ hybridization showed labeling in the retinal ganglion cell layer for all four P2Y receptor subtypes, although the intensity varied. In addition, staining for P2Y1, -4, and -6 mRNA was shown in the inner nuclear layer, but was absent for the P2Y2 receptor subtype. Immunohistochemistry showed intense staining for P2Y1, -2, and -4 in the ganglion cell layer and the outer plexiform layer. There was also a specific subtype staining in the inner plexiform layer (P2Y2, -4), the inner (P2Y1, -4) and outer (P2Y1) nuclear layers and the inner segments of the photoreceptors (P2Y1, -2). discussion. The data suggest that extracellular nucleotides may play complex roles as autocrine-paracrine mediators and may have neuromodulatory effects in the retina through metabotropic P2Y receptors.

Distribution of metabotropic P2Y receptors in the rat retina: a single-cell RT-PCR study

P2Y receptors are metabotropic G-protein linked purinergic receptors, which are especially widespread in the central nervous system. The purpose of the present study was to determine the distribution patterns of P2Y receptors in distinct retinal cell types in the adult retina. Retinal ganglion cells (RGC), bipolar cells (BPC) and Muller cells (MC) of adult pigmented rats were analyzed for their expression of P2Y-receptor subtypes P2Y1, P2Y2, P2Y4, and P2Y6 by single-cell reverse transcription polymerase chain reaction (SC-RT-PCR). SC-RT-PCR resulted in a positive amplification signal for all P2Y-receptor subtype mRNAs in all cell types examined. However, subtype distribution differed among the different cell types. The percentage of cells expressing a distinct P2Y subtype was: (a) for RGCs: 80% with P2Y1, 100% with P2Y2, 30% with P2Y4 and 50% with P2Y6, (b) for BPCs: 60% with P2Y1, 40% with P2Y2, 20% with P2Y4 and 80% with P2Y6, and (c) for MCs: 60% with P2Y1, 80% with P2Y2, 60% with P2Y4 and 100% with P2Y6. Our data show that different subtypes of P2Y receptors (P2Y1, P2Y2, P2Y4 and P2Y6) are expressed in various retinal cells and indicate that extracellular purines and pyrimidines act on RGCs, BPCs and MCs via different P2Y receptors.

Isolation of the mouse nyctalopin gene nyx and expression studies in mouse and rat retina

PURPOSE

It has been shown recently that mutations in NYX (nyctalopin on chromosome X), encoding a novel protein associated with the leucine-rich repeat (LRR) protein superfamily, are responsible for the complete form of X-linked congenital stationary night blindness (CSNB1). This study describes the isolation and molecular characterization of the mouse orthologue Nyx and its expression pattern in the retina.

METHODS

Nyx was isolated by conventional DNA library screening and polymerase chain reaction (PCR)-based approaches. Gene expression in different mouse tissues was studied by RT-PCR. Subsequently, the expression pattern of Nyx and its gene product in mouse and rat retinas was investigated by RNA in situ hybridization and immunohistochemistry with Nyx-specific antibodies.

RESULTS

The Nyx gene encodes a protein of 476 amino acids that contain 11 consecutive LRR motifs flanked by amino- and carboxyl-terminal cysteine-rich LRRs. At the amino acid level, Nyx is highly homologous to its human orthologue (86% identity). The gene is expressed in the eye but also, at lower levels, in brain, lung, spleen, and testis. Nyx expression was found during all stages of postnatal retinal development and was confined to cells of the inner nuclear layer and the ganglion cell layer in adult mouse and rat retinas.

CONCLUSIONS

These data suggest an important function of the Nyx protein in the inner retina and provide evidence that CSNB1 is based on a defect in the inner retinal circuitry.

Electrophysiological alterations and upregulation of ATP receptors in retinal glial Müller cells from rats infected with the Borna disease virus

Infection with the neurotropic Borna disease virus (BDV) causes an immune-mediated neurological disease in a broad range of species. In addition to encephalitis, BDV-infected Lewis rats develop a retinitis histologically characterized by the loss of most retinal neurons. By contrast, the dominating retinal macroglia, the Müller cells, do not degenerate. It is known from several models of neurodegeneration that glial cells may survive but undergo significant alterations of their physiological parameters. This prompted us to study the electrophysiology and ATP-induced changes of intracellular Ca(2+)-concentration ([Ca(2+)](i)) in Müller cells from BDV-infected rat retinae. Freshly isolated cells were used for whole-cell patch-clamp recordings. Whereas neither zero current potentials nor membrane resistances showed significant alterations, the membrane capacitance increased in cells from BDV-infected rats during survival times of up to 8 months. This process was accompanied by a decrease in K(+) current densities. Müller cells from BDV-infected rats were characterized by expression of a prominent fast-inactivating A-type K(+) current which was rarely found in control cells. Moreover, the number of cells displaying Na(+) currents was slightly increased after BDV-infection. ATP evoked increases in [Ca(2+)](i) in Müller cells within retinal wholemounts of both control and BDV-infected animals. However, the number of ATP-responding isolated cells increased from 24% (age-matched controls) to 78% (cells from animals > or =18 weeks after infection). We conclude that in BDV-induced retinopathy, reactive rat Müller cells change their physiological parameters but these changes are different from those in Müller cells during proliferative vitreoretinopathy in man and rabbit.