Lymphatic contractile dysfunction in mouse models of Cantú Syndrome with KATP channel gain-of-function

Abstract

Cantú Syndrome (CS) is an autosomal dominant disorder caused by gain-of-function (GoF) mutations in the Kir6.1 and SUR2 subunits of KATP channels. KATP overactivity results in a chronic reduction in arterial tone and hypotension, leading to other systemic cardiovascular complications. However, the underlying mechanism of lymphedema, developed by > 50% of CS patients, is unknown. We investigated whether lymphatic contractile dysfunction occurs in mice expressing CS mutations in Kir6.1 (Kir6.1[V65M]) or SUR2 (SUR2[A478V], SUR2[R1154Q]). Pressure myograph tests of contractile function of popliteal lymphatic vessels over the physiological pressure range revealed significantly impaired contractile strength and reduced frequency of spontaneous contractions at all pressures in heterozygous Kir6.1[V65M] vessels, compared to control littermates. Contractile dysfunction of intact popliteal lymphatics in vivo was confirmed using near-infrared fluorescence microscopy. Homozygous SUR2[A478V] vessels exhibited profound contractile dysfunction ex vivo, but heterozygous SUR2[A478V] vessels showed essentially normal contractile function. However, further investigation of vessels from all three GoF mouse strains revealed significant disruption in contraction wave entrainment, decreased conduction speed and distance, multiple pacemaker sites, and reversing wave direction. Tests of 2-valve lymphatic vessels forced to pump against an adverse pressure gradient revealed that all CS-associated genotypes were essentially incapable of pumping under an imposed outflow load. Our results show that varying degrees of lymphatic contractile dysfunction occur in proportion to the degree of molecular GoF in Kir6.1 or SUR2. This is the first example of lymphatic contractile dysfunction caused by a smooth muscle ion channel mutation and potentially explains the susceptibility of CS patients to lymphedema.

A dual-clock-driven model of lymphatic muscle cell pacemaking to emulate knock-out of Ano1 or IP3R

“…A prominent example of the former is the loss of contractile ability in lymphatic beds that have been irradiated during cancer treatment. The latter is exemplified by Cantú syndrome, which Davis et al (2023) have shown in a mouse model stems from a gain-of-function mutation in one particular ion channel in the LMC pacemaker. The resulting loss of pumping capability leads to lymphoedema in >50% of Cantú syndrome patients.…”

Lymphatic muscle cells are unique cells that undergo aging induced changes

“…LMCs are known to express Kcnj8 (ATP sensitive potassium channel Kir6.1) across multiple species and Kcnj11 (protein Kir6.2) is expressed in some LMC populations (Davis et al, 2022). Cantú syndrome, which has a lymphedema phenotype, can be caused by mutations in the genes Kcnj8 or ABCC9 (Davis et al, 2023a). We observed the expression of Kcnj8, Kcnj11, Abcc8, and Abcc9 genes in a small subset of LMCs (Figure S5D).…”

ERG K + channels mediate a major component of action potential repolarization in lymphatic muscle

“…Contraction waves in the lymphatic muscle layer are normally entrained across one or more lymphangions and the degree of entrainment is a critical determinant of the peak internal pressure developed in lymphatic systole 6 . If KCNH2 mutations result in reduced LMC excitability, they will impair contraction wave entrainment 43 and could compromise effective pumping. This consequence of reduced ERG channel activity is predicted to become particularly evident when lymph is transported against an adverse pressure gradient, as we have documented in other contexts 6, 44 .…”