Cardiovascular consequences of KATP overactivity in Cantu syndrome

Abstract

Cantu syndrome (CS) is characterized by multiple vascular and cardiac abnormalities including vascular dilation and tortuosity, systemic hypotension, and cardiomegaly. The disorder is caused by gain-of-function (GOF) mutations in genes encoding pore-forming (Kir6.1, KCNJ8) and accessory (SUR2, ABCC9) ATP-sensitive potassium (KATP) channel subunits. However, there is little understanding of the link between molecular dysfunction and the complex pathophysiology observed, and there is no known treatment, in large part due to the lack of appropriate preclinical disease models in which to test therapies. Notably, expression of Kir6.1 and SUR2 does not fully overlap, and the relative contribution of KATP GOF in various cardiovascular tissues remains to be elucidated. To investigate pathophysiologic mechanisms in CS we have used CRISPR/Cas9 engineering to introduce CS-associated SUR2[A478V] and Kir6.1[V65M] mutations to the equivalent endogenous loci in mice. Mirroring human CS, both of these animals exhibit low systemic blood pressure and dilated, compliant blood vessels, as well dramatic cardiac enlargement, the effects being more severe in V65M animals than in A478V animals. In both animals, whole-cell patch-clamp recordings reveal enhanced basal KATP conductance in vascular smooth muscle, explaining vasodilation and lower blood pressure, and demonstrating a cardinal role for smooth muscle KATP dysfunction in CS etiology. Echocardiography confirms in situ cardiac enlargement and increased cardiac output in both animals. Patch-clamp recordings reveal reduced ATP sensitivity of ventricular myocyte KATP channels in A478V, but normal ATP sensitivity in V65M, suggesting that cardiac remodeling occurs secondary to KATP overactivity outside of the heart. These SUR2[A478V] and Kir6.1[V65M] animals thus reiterate the key cardiovascular features seen in human CS. They establish the molecular basis of the pathophysiological consequences of reduced smooth muscle excitability resulting from SUR2/Kir6.1-dependent KATP GOF, and provide a validated animal model in which to examine potential therapeutic approaches to treating CS.

Glibenclamide treatment in a Cantú syndrome patient with a pathogenic ABCC9 gain‐of‐function variant: Initial experience

“…In addition to polyhydramnios in utero, our patient exhibited typical CS features in the neonatal period, including PDA, marked edema, pulmonary hypertension, and evidence of an enlarged right ventricle. Since Kir6.1 and SUR2 subunits are the primary components of K ATP channels in smooth muscles, and overactivity of these channels causes smooth muscle relaxation (Huang et al, ; Nelson & Quayle, ), persistence of the PDA may be explained as a consequence of maintained vessel dilation following birth. Reduced lymphatic smooth muscle tone could also underlie edema, and reduced airway smooth muscle contractility may affect breathing.…”

“…Patients also exhibit a variety of cardiovascular, lymphatic, and fluid balance complications (Grange et al, ; Nichols, Singh, & Grange, ). Although the underlying cellular and tissue mechanisms of CS are complex and incompletely understood (Huang et al, ), the molecular basis is now clear: CS results from gain‐of‐function variants in the ABCC9 and KCNJ8 genes, which encode the regulatory ABCC9 (SUR2) sulfonylurea receptor and pore‐forming KCNJ8 (Kir6.1) subunits, respectively, of ATP‐sensitive potassium (K ATP ) channels (Brownstein et al, ; Cooper et al, ; Harakalova et al, ; van Bon et al, ). The realization that CS results from gain‐of‐function of SUR2‐dependent K ATP channels raises the possibility that sulfonylurea drugs such as glibenclamide, which are potent and specific inhibitors of K ATP channel activity (Nichols, ), may be appropriate therapy, as indeed they have proven to be for neonatal diabetes resulting from gain‐of‐function mutations in SUR1‐dependent K ATP channels (Bowman et al, ; Pearson et al, ).…”

Cantu syndrome: A longitudinal review of vascular findings in three individuals

“…It is important to note, however, that the patient previously reported with TAA repair had a different missense variant (p.T1202M) in ABCC9, and one of the previously reported patients with aortic root dilation had a KCNJ8 variant (Brownstein et al, 2013;Hiraki et al, 2014). In line with the prior mouse models of Cantu syndrome demonstrating vasodilation (Huang et al, 2018), there are now multiple patients with different pathogenic variants identified with vessel dilation. The true clinical significance of this vascular involvement including risk for arterial dissection will need to be further characterized to inform appropriate screening protocols.…”

“…Functional studies have shown that variants in both genes result in the gain of K ATP channel activity (Cooper et al, 2014;Cooper, Sala-Rabanal, Lee, & Nichols, 2015;Harakalova et al, 2012;Li et al, 2013;McClenaghan et al, 2018). In vascular smooth muscle, this can result in reduced contractility and compliant, chronically dilated vessels, leading to hypotension (Huang et al, 2018;Li et al, 2013). This, in turn, has been proposed to cause the cardiac enlargement with increased cardiac output observed in many individuals with Cantu syndrome (Huang et al, 2018;Levin et al, 2016).…”

“…Arteriovenous malformations and collateral vessels have been rarely reported (Brownstein et al, 2013;Czeschik et al, 2013;Leon Guerrero et al, 2016;Scurr et al, 2011), and it has been hypothesized that collateral vessels may develop as a secondary consequence of persistent hypotension (Leon Guerrero et al, 2016). Recently, mouse models of Cantu syndrome recapitulating pathogenic variants in KCNJ8 and ABCC9 confirmed the association of arterial dilation with a demonstration of enlargement of the thoracic aorta and carotid arteries (Huang et al, 2018).…”