Differential distribution of exchange proteins directly activated by cyclic AMP within the adult rat retina

Abstract

The recently discovered exchange protein directly activated by cAMP (Epac), a guanine exchange factor for the G-protein RAP-1, is directly activated by cAMP independently of PKA. While cAMP is known to be an important second messenger in the retina, the presence of Epac has not been investigated in this tissue. The goal of the present study was to determine if the Epac1 and Epac2 genes are present and to characterize their location within the retina. Western blot analysis revealed that Epac1 and Epac2 proteins are expressed within the retina, and the presence of mRNA was demonstrated with the aid of RT-PCR. Additionally, we used immunofluorescence and confocal microscopy to demonstrate that Epac1 and Epac2 have overlapping as well as unique distributions within the retina. Both are present within horizontal cells, rod and cone bipolar cells, cholinergic amacrine cells, retrograde labeled retinal ganglion cells, and Müller cells. Uniquely, Epac2 was expressed by cone photoreceptor inner and outer segments, cell bodies, and synaptic terminals. In contrast, Epac1 was expressed in VGlut1 and CtBP2 positive photoreceptor synaptic terminals. Together, these results provide evidence that Epac1 and Epac2 are differentially expressed within the retina and provide the framework for further functional studies of cAMP pathways within the retina.

Protein Composition of Immunoprecipitated Synaptic Ribbons

“…We observed 3 isoforms (α, β, and δ) of CaM Kinase II, with equimolar amounts of α and β and twice as much of the δ isoform. EPAC2 is expressed in photoreceptors 45 ; it is known to be involved in cAMP mediated vesicle release 46 and is a binding partner of Piccolo 17 and Rim 47 . Piccolo also binds L-TYPE Ca Channels 17 and an Actin-Binding Protein 48 providing a possible link between members in the presynaptic complex.…”

Neuronal Epac1 mediates retinal neurodegeneration in mouse models of ocular hypertension

“…Epac1 is expressed in many retinal cell types (Whitaker and Cooper, 2010). To delineate in which cell type Epac1 expression is responsible for ischemic injury-induced retinal neuron death, we conditionally deleted Epac1 in myeloid/microglia and astrocytes using the Cre-loxP system.…”

“…Epac1 is ubiquitously expressed in tissues and often involved in pathologic conditions such as cardiac hypertrophy, heart failure, pain perception, and obesity, while Epac2 regulates physiological processes including insulin secretion, learning, and memory (Breckler et al, 2011;Okumura et al, 2014;Srivastava et al, 2012;Wang et al, 2013;Yan et al, 2013;Zhang et al, 2009). In the retina, Epac1 is expressed in retinal layers containing neurons (Whitaker and Cooper, 2010), but its pathophysiological role is largely unknown.…”

Epac2-deficiency leads to more severe retinal swelling, glial reactivity and oxidative stress in transient middle cerebral artery occlusion induced ischemic retinopathy

“…Both Epac1 and Epac2 are expressed in the retina [19]. It has been shown that Epacs have a profound role in cognition, loss of Epacs leads to impairment in memory retrieval in a fear conditioning paradigm [34], and it is also noted that in depressed patients, the Epac2 expression but not Epac1 is altered in the cortex [35].…”

“…Epac2 participates in the modulation of neuronal activities, including neurotransmitter release and synaptic plasticity [1517]. Both Epac1 and Epac2 are expressed in the brain [18], and retina [19], which is part of central nervous system (CNS) and can be viewed using non-invasive methods.…”