Proatherosclerotic Effect of the α1-Subunit of Soluble Guanylyl Cyclase by Promoting Smooth Muscle Phenotypic Switching

Abstract

Soluble guanylate cyclase (sGC), a key enzyme of the nitric oxide signaling pathway, is formed as a heterodimer by various isoforms of its α and β subunit. GUCY1A3, encoding the α1 subunit, was identified as a risk gene for coronary artery disease and myocardial infarction, but its specific contribution to atherosclerosis remains unclear. This study sought to decipher the role of Gucy1a3 in atherosclerosis in mice. At age 32 weeks and after 20 weeks of standard or high-fat diet, Gucy1a3(-/-)/Ldlr(-/-) mice exhibited a significant reduction of the atherosclerotic plaque size at the aortic root and the aorta for high-fat diet animals as compared with Ldlr(-/-) control mice. Collagen content in plaques in the aortic root was reduced, suggesting an alteration of smooth muscle cell function. Proliferation and migration were reduced in Gucy1a3(-/-) primary aortic smooth muscle cells (AoSMCs), and proliferation was also reduced in human AoSMCs after inhibition of sGC by 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one. Gucy1a3 deficiency in AoSMCs prevents their phenotypic switching, as indicated by the differential expression of marker proteins. The inherited Gucy1a3(-/-) loss exerts an atheroprotective effect. We suggest that sGC activity promotes the phenotypic switching of smooth muscle cells from a contractile to a synthetic state, fostering the formation of atherosclerosis. Preventing this switch by sGC inhibition may provide a novel target in atherosclerotic disease.

cGMP Signaling and Vascular Smooth Muscle Cell Plasticity

“…While a low concentration (0.5 µM) of the NO donor diethylenetriamine NONOate (DETA-NO) enhanced proliferation via a cGKI-dependent pathway, high concentrations of DETA-NO (100 µM) strongly reduced VSMC growth independent of cGKI. A cGMP-independent, anti-proliferative effect of NO in VSMCs was also observed by other groups [ 50 , 69 ]. In sum, there is strong evidence that low/physiological NO concentrations promote VSMC growth via the cGMP-cGKI axis, whereas high/pathophysiological concentrations of NO inhibit VSMC growth in a cGMP/cGKI-independent manner.…”

“…Studies with cultured VSMCs have linked components of the cGMP signaling pathway to VSMC proliferation and marker protein expression, indicating a role of cGMP in phenotypic switching of VSMCs. In particular, the mechanism and therapeutic relevance of cGMP-regulated VSMC plasticity via the NO-cGMP-cGKI axis has been intensively investigated over the past few decades [ 9 , 13 , 15 , 35 , 50 , 51 , 52 ]. However, it is still debated if stimulation of this cascade inhibits or promotes the growth of VSMCs.…”

Functional Characterization of the GUCY1A3 Coronary Artery Disease Risk Locus

“…Nevertheless, the data uniformly point towards a stronger effect of NO on inhibition of migration and platelet aggregation in GUCY1A3 non-risk allele carriers. Third, a recently published paper suggests that complete knockout of Gucy1a3 in mice may reduce atherosclerotic plaque formation on a proatherogenic background ( Ldlr −/− ) 37 . In contrast to this study, we and others investigated a partial loss of sGC activity and showed experimentally in mice and functionally in human materials that this leads to increased disease risk 10,38–40 .…”

“…In contrast to this study, we and others investigated a partial loss of sGC activity and showed experimentally in mice and functionally in human materials that this leads to increased disease risk 10,38–40 . Thus, in the total Gucy1a3 knockout model compensatory mechanisms affecting NO/cGMP signaling, including a marked compensatory increase of Gucy1a2 expression in Gucy1a3 −/− VSMC 37 , may not have been adequately addressed. Indeed, the total knockout of genes might be more useful to investigate molecular mechanisms rather than complex diseases such as atherosclerosis.…”

Antiinflammatory actions of inorganic nitrate stabilize the atherosclerotic plaque

“…Studies using sGCα1 KO mice crossed with LDLr KO mice have shown surprisingly a decrease in plaque burden compared to LDLr KO alone. The authors suggest that PKG increases smooth muscle proliferation and that this underlies the apparent benefits of deletion of the gene by triggering a switch in smooth muscle cell phenotype (40). Interestingly the authors only consider that such an effect is detrimental; however, of course in the atherosclerotic scenario, a stimulus that is antiinflammatory but at the same time increases smooth muscle content of a plaque would be, in the long term, beneficial in terms of switching a plaque from an unstable to a stable phenotype.…”