Soluble Adenylyl Cyclase Activity Is Necessary for Retinal Ganglion Cell Survival and Axon Growth

Abstract

Cyclic adenosine monophosphate (cAMP) is a critical second messenger mediating activity-dependent neuronal survival and neurite growth. We investigated the expression and function of the soluble adenylyl cyclase (sAC, ADCY10) in central nervous system (CNS) retinal ganglion cells (RGCs). We found sAC protein expressed in multiple RGC compartments including the nucleus, cytoplasm and axons. sAC activation increased cAMP above the level seen with transmembrane adenylate cyclase (tmAC) activation. Electrical activity and bicarbonate, both physiologic sAC activators, significantly increased survival and axon growth, whereas pharmacologic or siRNA-mediated sAC inhibition dramatically decreased RGC survival and axon growth in vitro, and survival in vivo. Conversely, RGC survival and axon growth was unaltered in RGCs from AC1/AC8 double knockout mice or after specifically inhibiting tmACs. These data identify a novel sAC-mediated cAMP signaling pathway regulating RGC survival and axon growth, and suggest new neuroprotective or regenerative strategies based on sAC modulation.

Exchange Protein Directly Activated by cAMP (epac): A Multidomain cAMP Mediator in the Regulation of Diverse Biological Functions

“…Subsequent studies show that, depending on the duration of signaling, Epac converts cAMP from a proliferative into a differentiation signal (Kiermayer et al, 2005). In retinal ganglion cells, Epac links, both in vitro and in vivo, ganglion cell survival and axon growth to PKA and soluble AC (Corredor et al, 2012). As Epac regulates the phosphorylation of PKB/Akt in primary cortical neurons (Nijholt et al, 2008), this Epac signaling route probably supports neuronal survival.…”

“…In murine primary cortical neurons and HT-4 cells, Epac2 enhances PKB/Akt phosphorylation through Rap1 complexed to AKAP79/ 150 (Nijholt et al, 2008). In addition, Epac promotes neuronal survival and neurite growth through a nuclear complex composed of PKA and sAC (Corredor et al, 2012), suggesting that distinct cAMP microdomains maintained by sAC profoundly alter the signaling properties of Epac. The ability of Epac2 to promote remodeling of spiny synapses requires a distinct complex composed of neuroligin-3/PSD95/Rap complex (Woolfrey et al, 2009).…”

“…The complex protein-protein/protein-lipid interactions of Epac are linked to the existence of cAMP-sensing multiprotein complexes maintained by the AKAP family members, mAKAP, AKAP5, and AKAP9 Nijholt et al, 2008;Sehrawat et al, 2011). Together with the potential link to cAMP microdomains maintained by sAC (Corredor et al, 2012), such complexes generate compartmentalized cAMP signaling and lead to celltype specific functions of Epac. As AKAP are also the molecular interaction partner of PKA, AKAP-bearing complexes are the most logical explanation for biologic responses driven by both PKA and Epac.…”

Established and potential physiological roles of bicarbonate-sensing soluble adenylyl cyclase (sAC) in aquatic animals

“…These functions include epithelial ion and fluid transport, sperm flagellar movement, gene expression, development and cell differentiation, ciliary beating in airways and oxidative phosphorylation in mitochondria (reviewed in Tresguerres et al, 2010a;Tresguerres et al, 2011). At the time of writing, sAC has additionally been shown to regulate the metabolic coupling between neurons and astrocytes (Choi et al, 2012), intraocular pressure (Lee et al, 2011), survival of retinal ganglion cells and axon growth (Corredor et al, 2012), aromatase gene expression and estradiol production (Chen et al, 2012a), pathologic activation of proteases in pancreatic acinar cells…”

Pharmacological Distinction between Soluble and Transmembrane Adenylyl Cyclases

“…Therefore, we sought to identify a structurally unrelated sAC-selective inhibitor that can be used to complement KH7 and ddAdo. The catechol estrogens 2-CE and 4-CE inhibit pure sAC protein with low micromolar EC 50 s (Steegborn et al, 2005), and although they were shown to inhibit specific tmAC isoforms in vitro, they have been used as sAC-selective inhibitors in a number of physiologic systems (Pastor-Soler et al, 2003;Wu et al, 2006;Choi et al, 2012;Corredor et al, 2012;Di Benedetto et al, 2013). We used our two cell lines, sAC-overexpressing 4-4 cells and sAC KO MEFs, to definitively explore their utility in cell-based assays.…”