Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease

Pendrin-null mice develop severe hypokalemia following dietary Na⁺ and K⁺ restriction: role of ENaC.

Pendrin is an intercalated cell Cl <sup>-</sup> /[Formula: see text] exchanger thought to participate in K <sup>+</sup> -sparing NaCl absorption. However, its role in K <sup>+</sup> homeostasis has not been clearly defined. We hypothesized that pendrin-null mice will develop hypokalemia with dietary K <sup>+</sup> restriction. We further hypothesized that pendrin knockout (KO) mice mitigate urinary K <sup>+</sup> loss by downregulating the epithelial Na <sup>+</sup> channel (ENaC). Thus, we examined the role of ENaC in Na <sup>+</sup> and K <sup>+</sup> balance in pendrin KO and wild-type mice following dietary K <sup>+</sup> restriction. To do so, we examined the relationship between Na <sup>+</sup> and K <sup>+</sup> balance and ENaC subunit abundance in K <sup>+</sup> -restricted pendrin-null and wild-type mice that were NaCl restricted or replete. Following a NaCl-replete, K <sup>+</sup> -restricted diet, K <sup>+</sup> balance and serum K <sup>+</sup> were similar in both groups. However, following a Na <sup>+</sup> , K <sup>+</sup> , and Cl <sup>-</sup> -deficient diet, pendrin KO mice developed hypokalemia from increased K <sup>+</sup> excretion. The fall in serum K <sup>+</sup> observed in K <sup>+</sup> -restricted pendrin KO mice was enhanced with ENaC stimulation but eliminated with ENaC inhibition. The fall in serum K <sup>+</sup> observed in K <sup>+</sup> -restricted pendrin KO mice was enhanced with ENaC stimulation but eliminated with ENaC inhibition. However, reducing ENaC activity also reduced blood pressure and increased apparent intravascular volume contraction, since KO mice had lower serum Na <sup>+</sup> , higher blood urea nitrogen and hemoglobin, greater weight loss, greater metabolic alkalosis, and greater NaCl excretion. We conclude that dietary Na <sup>+</sup> and K <sup>+</sup> restriction induces hypokalemia in pendrin KO mice. Pendrin-null mice limit renal K <sup>+</sup> loss by downregulating ENaC. However, this ENaC downregulation occurs at the expense of intravascular volume.NEW & NOTEWORTHY Pendrin is an apical Cl <sup>-</sup> /[Formula: see text] exchanger that provides renal K <sup>+</sup> -sparing NaCl absorption. The pendrin-null kidney has an inability to fully conserve K <sup>+</sup> and limits renal K <sup>+</sup> loss by downregulating the epithelial Na <sup>+</sup> channel (ENaC). However, with Na <sup>+</sup> restriction, the need to reduce ENaC for K <sup>+</sup> balance conflicts with the need to stimulate ENaC for intravascular volume. Therefore, NaCl restriction stimulates ENaC less in pendrin-null mice than in wild-type mice, which mitigates their kaliuresis and hypokalemia but exacerbates volume contraction

The Role of Intercalated Cell Nedd4-2 in BP Regulation, Ion Transport, and Transporter Expression.

BackgroundNedd4-2 is an E3 ubiquitin-protein ligase that associates with transport proteins, causing their ubiquitylation, and then internalization and degradation. Previous research has suggested a correlation between Nedd4-2 and BP. In this study, we explored the effect of intercalated cell (IC) Nedd4-2 gene ablation on IC transporter abundance and function and on BP.Methods We generated IC Nedd4-2 knockout mice using Cre-lox technology and produced global pendrin/Nedd4-2 null mice by breeding global Nedd4-2 null (Nedd4-2 <sup>-/-</sup> ) mice with global pendrin null (Slc26a4 <sup>-/-</sup> ) mice. Mice ate a diet with 1%-4% NaCl; BP was measured by tail cuff and radiotelemetry. We measured transepithelial transport of Cl <sup>-</sup> and total CO <sub>2</sub> and transepithelial voltage in cortical collecting ducts perfused in vitro Transporter abundance was detected with immunoblots, immunohistochemistry, and immunogold cytochemistry.Results IC Nedd4-2 gene ablation markedly increased electroneutral Cl <sup>-</sup> /HCO <sub>3</sub> <sup>-</sup> exchange in the cortical collecting duct, although benzamil-, thiazide-, and bafilomycin-sensitive ion flux changed very little. IC Nedd4-2 gene ablation did not increase the abundance of type B IC transporters, such as AE4 (Slc4a9), H <sup>+</sup> -ATPase, barttin, or the Na <sup>+</sup> -dependent Cl <sup>-</sup> /HCO <sub>3</sub> <sup>-</sup> exchanger (Slc4a8). However, IC Nedd4-2 gene ablation increased CIC-5 total protein abundance, apical plasma membrane pendrin abundance, and the ratio of pendrin expression on the apical membrane to the cytoplasm. IC Nedd4-2 gene ablation increased BP by approximately 10 mm Hg. Moreover, pendrin gene ablation eliminated the increase in BP observed in global Nedd4-2 knockout mice.Conclusions IC Nedd4-2 regulates Cl <sup>-</sup> /HCO <sub>3</sub> <sup>-</sup> exchange in ICs., Nedd4-2 gene ablation increases BP in part through its action in these cells