Elevated Cyclic Guanosine Monophosphate Research Articles

Effective AAV-mediated gene replacement therapy in retinal organoids modeling AIPL1-associated LCA4

Biallelic variations in the aryl hydrocarbon receptor interacting protein-like 1 (AIPL1) gene cause Leber congenital amaurosis subtype 4 (LCA4), an autosomal recessive early-onset severe retinal dystrophy that leads to the rapid degeneration of retinal photoreceptors and the severe impairment of sight within the first few years of life. Currently, there is no treatment or cure for AIPL1-associated LCA4. In this study, we investigated the potential of adeno-associated virus-mediated AIPL1 gene replacement therapy in two previously validated human retinal organoid (RO) models of LCA4. We report here that photoreceptor-specific AIPL1 gene replacement therapy, currently being tested in a first-in-human application, effectively rescued molecular features of AIPL1-associated LCA4 in these models. Notably, the loss of retinal phosphodiesterase 6 was rescued and elevated cyclic guanosine monophosphate (cGMP) levels were reduced following treatment. Transcriptomic analysis of untreated and AAV-transduced ROs revealed transcriptomic changes in response to elevated cGMP levels and viral infection, respectively. Overall, this study supports AIPL1 gene therapy as a promising therapeutic intervention for LCA4.

Potential contribution of ryanodine receptor 2 upregulation to cGMP/PKG signaling-induced cone degeneration in cyclic nucleotide-gated channel deficiency.

Photoreceptor cyclic nucleotide-gated (CNG) channels regulate Ca2+ influx in rod and cone photoreceptors. Mutations in cone CNG channel subunits CNGA3 and CNGB3 are associated with achromatopsia and cone dystrophies. Mice lacking functional cone CNG channel show endoplasmic reticulum (ER) stress-associated cone degeneration. The elevated cyclic guanosine monophosphate (cGMP)/cGMP-dependent protein kinase (PKG) signaling and upregulation of the ER Ca2+ channel ryanodine receptor 2 (RyR2) have been implicated in cone degeneration. This work investigates the potential contribution of RyR2 to cGMP/PKG signaling-induced ER stress and cone degeneration. We demonstrated that the expression and activity of RyR2 were highly regulated by cGMP/PKG signaling. Depletion of cGMP by deleting retinal guanylate cyclase 1 or inhibition of PKG using chemical inhibitors suppressed the upregulation of RyR2 in CNG channel deficiency. Depletion of cGMP or deletion of Ryr2 equivalently inhibited unfolded protein response/ER stress, activation of the CCAAT-enhancer-binding protein homologous protein, and activation of the cyclic adenosine monophosphate response element-binding protein, leading to early-onset cone protection. In addition, treatment with cGMP significantly enhanced Ryr2 expression in cultured photoreceptor-derived Weri-Rb1 cells. Findings from this work demonstrate the regulation of cGMP/PKG signaling on RyR2 in the retina and support the role of RyR2 upregulation in cGMP/PKG signaling-induced ER stress and photoreceptor degeneration.

Genetic Rescue Reverses Microglial Activation in Preclinical Models of Retinitis Pigmentosa.

Microglia cells (MGCs) play a key role in scavenging pathogens and phagocytosing cellular debris in the central nervous system and retina. Their activation, however, contributes to the progression of multiple degenerative diseases. Given the potential damage created by MGCs, it is important to better understand their mechanism of activation. Here, we explored the role of MGCs in the context of retinitis pigmentosa (RP) by using four independent preclinical mouse models. For therapeutic modeling, tamoxifen-inducible CreER was introduced to explore changes in MGCs when RP progression halted. The phenotypes of the MGCs were observed using live optical coherence tomography, live autofluorescence, and immunohistochemistry. We found that, regardless of genetic background, MGCs were activated in neurodegenerative conditions and migrated beyond the layers where they are typically found to the inner and outer segments, where degeneration was ongoing. Genetic rescue not only halted degeneration but also deactivated MGCs, regardless of whether the intervention occurred at the early, middle, or late stage of the disease. These findings suggest that halting long-term disease progression may be more successful by downregulating MGC activity while co-administering the therapeutic intervention.

Response of soybean nodules to exogenously applied caffeic acid during NaCl-induced salinity

Caffeic acid acts as an antioxidant to scavenge reactive oxygen species, but its influence on plant responses to abiotic stresses is only partially understood. Here, we investigated the influence of exogenously applied caffeic acid on soybean during NaCl-induced salinity. Exogenously applied caffeic acid reduced the deleterious effects of salinity stress on soybean plants and increased nitric oxide content in root nodules and this corresponded with elevated cyclic guanosine monophosphate content in the nodules. Salinity stress reduced nodule legheamoglobin content and nitrogenase activity whereas exogenous application of caffeic acid to NaCl-treated plants reversed these negative effects of NaCl on legheamoglobin content and nitrogenase activity. Hydrogen peroxide (H2O2) and malondialdehyde contents in soybean root nodules from plants exposed to salinity were lower when these plants were supplemented with exogenous caffeic acid than when no caffeic acid was supplemented. We suggest that caffeic acid enhances nitric oxide biosynthesis, which possibly acts to reduce salinity-induced oxidative stress through a mechanism that involves nitric oxide signaling coupled with cyclic guanosine monophosphate-mediated signaling to scavenge reactive oxygen species.The ability of caffeic acid to reduce salinity-induced oxidative stress via regulation of nitric oxide signaling has implications for genetic improvement of crop to enhance their tolerance against salinity. This can be achieved by identifying genes, namely genes encoding p-coumarate 3-hydroxylases, responsible for the biosynthesis of caffeic acid and modulating their expression under salinity. Such improvement would impact positively on food security as it would limit the detrimental effects of salinity of crop productivity.

Effect of sodium-potassium pump inhibitors and membrane-depolarizing agents on sodium nitroprusside-induced relaxation and cyclic guanosine monophosphate accumulation in rat aorta.

The purpose of this study was to investigate the relationship between sodium nitroprusside-induced relaxation, inhibition of the sodium-potassium pump, and cyclic guanosine monophosphate. Exposure of rat thoracic aorta to ouabain, or potassium- or magnesium-free Krebs-Ringer bicarbonate solution, procedures which presumably inhibit the sodium-potassium pump, or to potassium chloride or tetraethylammonium, membrane-depolarizing agents, inhibited relaxation to nitroprusside. These conditions had little or no effect on the elevated cyclic guanosine monophosphate levels at a concentration of nitroprusside (0.1 microM) that relaxed norepinephrine contracted tissues by 80%. However, at a maximum relaxant concentration of nitroprusside (1.0 microM), these conditions decreased the elevation of cyclic guanosine monophosphate. The inhibition of elevated cyclic guanosine monophosphate levels was independent of the endothelium, extracellular calcium, and the cyclic guanosine monophosphate phosphodiesterase inhibitor, M&B 22,948. The inhibitory effects of ouabain and of potassium- and magnesium-free solution on the increased levels of cyclic guanosine monophosphate caused by 1.0 microM nitroprusside were abolished when tissues were incubated without norepinephrine, or with norepinephrine in the presence of the alpha-adrenergic blocker, phentolamine. In contrast, a beta-adrenergic blocker, propranolol, had no effect on the ouabain-induced inhibition of elevated cyclic guanosine monophosphate levels, with norepinephrine present. These results are consistent with the hypothesis that membrane events regulate cyclic guanosine monophosphate synthesis. At nitroprusside concentrations greater than 0.1 microM, the formation of cyclic guanosine monophosphate appears to be coupled to the status of the smooth muscle cell membrane and integrity of the sodium-potassium pump.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between cyclic adenosine monophosphate and cyclic gunaosine monophosphate in guinea pig ventricular myocardium.

The purpose of this study was to examine the mechanisms underlying adrenergic-cholinergic antagonism in ventricular myocardium. Myocardial contractility, cyclic adenosine monophosphate (AMP) levels, and cyclic guanosine monophosphate (GMP) levels were measure in isolated guinea pig ventricles after treatment with various inotropic agents given alone and simultaneously with acetylcholine. Acetylcholine alone markedly elevated cyclic GMP levels but did not substantially change myocardial contractility. However, the same concentration of acetylcholine significantly attenuated the inotropic effect of isoproterenol and histamine, two drugs that may act by increasing myocardial levels of cyclic AMP. The decrease in the inotropic response to isoproterenol did not appear to be due to a decrease in the generation of cyclic AMP, because cyclic AMP levels were similar in hearts receiving isoproterenol alone and those receiving isoproterenol with acetylcholine. Dibutyryl cyclic GMP also antagonized the intropic action of isoproterenol. Acetylcholine did not alter the inotropic effects of ouabain, an agent that increases myocardial contractility without changing cyclic AMP levels. These results suggest that cyclic GMP mediates the antiadrenergic effects of acetylcholine by specifically antagonizing the inotropic actions of cyclic AMP.