Does the early aldosterone-induced SGK1 play a role in early Kaliuresis?

Urinary K <sup>+</sup> potassium excretion rapidly increases after a potassium-rich meal. The early aldosterone-induced sgk1 gene (encoding serum and glucocorticoid-induced kinase 1), activates potassium clearance, but the role of this kinase in the early activation of K <sup>+</sup> secretion has not been clearly defined. Here, we challenged inducible renal-tubule-specific Sgk1 <sup>Pax8</sup> <sup>/</sup> <sup>LC1</sup> knockout mice with an acute high-potassium load (HK:5%K <sup>+</sup> ) and compared the physiological and molecular responses to control mice. We observe that urinary excretion after a K <sup>+</sup> load over the first 3 h is not dependent on SGK1 but is coincident with the rapid dephosphorylation of the Na <sup>+</sup> ,Cl <sup>-</sup> -cotransporter (NCC) to increase distal salt delivery. Molecular analyses indicate that whereas SGK1-mediated phosphorylation of the ubiquitin-protein ligase NEDD4-2 begins to increase by 3h, SGK1-dependent proteolytic activation of ENaC only becomes detectable after 6 h of HK intake. Consistent with SGK1-dependent ENaC activation via inhibition of NEDD4-2-mediated ubiquitylation, Sgk1 <sup>Pax8</sup> <sup>/</sup> <sup>LC1</sup> mice are unable to efficiently inhibit NEDD4-2 or increase ENaC cleavage after 6 h of HK. Nevertheless, no defect in acute K <sup>+</sup> balance was detected in the mutant mice after 6 h of HK. Moreover, we found that Sgk1 <sup>Pax8</sup> <sup>/</sup> <sup>LC1</sup> mice reduce NCC phosphorylation and NCC-mediated salt absorption to a greater extent than control mice after a K <sup>+</sup> load, promoting increased amiloride-sensitive Na <sup>+</sup> -reabsorption via ENaC to maintain adequate kaliuresis. Together, these data indicate that: (a) during the early 3 h of HK intake, K <sup>+</sup> excretion is SGK1-independent even under an extreme K <sup>+</sup> challenge, (b) shortly after, SGK1 inhibits NEDD4-2 and activates ENaC to stimulate K <sup>+</sup> -secretion, (c) SGK1-dependent phosphorylation of NCC occurs, acting more likely as a brake pedal to prevent excessive K <sup>+</sup> loss

Universality behind Basquin's law of fatigue

One of the most important scaling laws of time dependent fracture is Basquin's law of fatigue, namely, that the lifetime of the system increases as a power law with decreasing external load amplitude, $t_f\sim \sigma_0^{-\alpha}$, where the exponent $\alpha$ has a strong material dependence. We show that in spite of the broad scatter of the Basquin exponent $\alpha$, the fatigue fracture of heterogeneous materials exhibits intriguing universal features. Based on stochastic fracture models we propose a generic scaling form for the macroscopic deformation and show that at the fatigue limit the system undergoes a continuous phase transition when changing the external load. On the microlevel, the fatigue fracture proceeds in bursts characterized by universal power law distributions. We demonstrate that in a range of systems, including deformation of asphalt, a realistic model of deformation, and a fiber bundle model, the system dependent details are contained in Basquin's exponent for time to failure, and once this is taken into account, remaining features of failure are universal.Comment: 4 pages in Revtex, 4 figures, accepted by PR

Renal tubular SGK1 deficiency causes impaired K+ excretion via loss of regulation of NEDD4-2/WNK1 and ENaC.

The stimulation of postprandial K(+) clearance involves aldosterone-independent and -dependent mechanisms. In this context, serum- and glucocorticoid-induced kinase (SGK)1, a ubiquitously expressed kinase, is one of the primary aldosterone-induced proteins in the aldosterone-sensitive distal nephron. Germline inactivation of SGK1 suggests that this kinase is fundamental for K(+) excretion under conditions of K(+) load, but the specific role of renal SGK1 remains elusive. To avoid compensatory mechanisms that may occur during nephrogenesis, we used inducible, nephron-specific Sgk1(Pax8/LC1) mice to assess the role of renal tubular SGK1 in K(+) regulation. Under a standard diet, these animals exhibited normal K(+) handling. When challenged by a high-K(+) diet, they developed severe hyperkalemia accompanied by a defect in K(+) excretion. Molecular analysis revealed reduced neural precursor cell expressed developmentally downregulated protein (NEDD)4-2 phosphorylation and total expression. γ-Epithelial Na(+) channel (ENaC) expression and α/γENaC proteolytic processing were also decreased in mutant mice. Moreover, with no lysine kinase (WNK)1, which displayed in control mice punctuate staining in the distal convoluted tubule and diffuse distribution in the connecting tubule/cortical colleting duct, was diffused in the distal convoluted tubule and less expressed in the connecting tubule/collecting duct of Sgk(Pax8/LC1) mice. Moreover, Ste20-related proline/alanine-rich kinase phosphorylation, and Na(+)-Cl(-) cotransporter phosphorylation/apical localization were reduced in mutant mice. Consistent with the altered WNK1 expression, increased renal outer medullary K(+) channel apical localization was observed. In conclusion, our data suggest that renal tubular SGK1 is important in the regulation of K(+) excretion via the control of NEDD4-2, WNK1, and ENaC

A structural biology community assessment of AlphaFold2 applications

Most proteins fold into 3D structures that determine how they function and orchestrate the biological processes of the cell. Recent developments in computational methods for protein structure predictions have reached the accuracy of experimentally determined models. Although this has been independently verified, the implementation of these methods across structural-biology applications remains to be tested. Here, we evaluate the use of AlphaFold2 (AF2) predictions in the study of characteristic structural elements; the impact of missense variants; function and ligand binding site predictions; modeling of interactions; and modeling of experimental structural data. For 11 proteomes, an average of 25% additional residues can be confidently modeled when compared with homology modeling, identifying structural features rarely seen in the Protein Data Bank. AF2-based predictions of protein disorder and complexes surpass dedicated tools, and AF2 models can be used across diverse applications equally well compared with experimentally determined structures, when the confidence metrics are critically considered. In summary, we find that these advances are likely to have a transformative impact in structural biology and broader life-science research

Association between loop diuretic dose changes and outcomes in chronic heart failure: observations from the ESC-EORP Heart Failure Long-Term Registry

[Abstract] Aims. Guidelines recommend down-titration of loop diuretics (LD) once euvolaemia is achieved. In outpatients with heart failure (HF), we investigated LD dose changes in daily cardiology practice, agreement with guideline recommendations, predictors of successful LD down-titration and association between dose changes and outcomes. Methods and results. We included 8130 HF patients from the ESC-EORP Heart Failure Long-Term Registry. Among patients who had dose decreased, successful decrease was defined as the decrease not followed by death, HF hospitalization, New York Heart Association class deterioration, or subsequent increase in LD dose. Mean age was 66±13 years, 71% men, 62% HF with reduced ejection fraction, 19% HF with mid-range ejection fraction, 19% HF with preserved ejection fraction. Median [interquartile range (IQR)] LD dose was 40 (25–80) mg. LD dose was increased in 16%, decreased in 8.3% and unchanged in 76%. Median (IQR) follow-up was 372 (363–419) days. Diuretic dose increase (vs. no change) was associated with HF death [hazard ratio (HR) 1.53, 95% confidence interval (CI) 1.12–2.08; P = 0.008] and nominally with cardiovascular death (HR 1.25, 95% CI 0.96–1.63; P = 0.103). Decrease of diuretic dose (vs. no change) was associated with nominally lower HF (HR 0.59, 95% CI 0.33–1.07; P = 0.083) and cardiovascular mortality (HR 0.62 95% CI 0.38–1.00; P = 0.052). Among patients who had LD dose decreased, systolic blood pressure [odds ratio (OR) 1.11 per 10 mmHg increase, 95% CI 1.01–1.22; P = 0.032], and absence of (i) sleep apnoea (OR 0.24, 95% CI 0.09–0.69; P = 0.008), (ii) peripheral congestion (OR 0.48, 95% CI 0.29–0.80; P = 0.005), and (iii) moderate/severe mitral regurgitation (OR 0.57, 95% CI 0.37–0.87; P = 0.008) were independently associated with successful decrease. Conclusion. Diuretic dose was unchanged in 76% and decreased in 8.3% of outpatients with chronic HF. LD dose increase was associated with worse outcomes, while the LD dose decrease group showed a trend for better outcomes compared with the no-change group. Higher systolic blood pressure, and absence of (i) sleep apnoea, (ii) peripheral congestion, and (iii) moderate/severe mitral regurgitation were independently associated with successful dose decrease

Sex- and age-related differences in the management and outcomes of chronic heart failure: an analysis of patients from the ESC HFA EORP Heart Failure Long-Term Registry

Aims: This study aimed to assess age- and sex-related differences in management and 1-year risk for all-cause mortality and hospitalization in chronic heart failure (HF) patients. Methods and results: Of 16 354 patients included in the European Society of Cardiology Heart Failure Long-Term Registry, 9428 chronic HF patients were analysed [median age: 66 years; 28.5% women; mean left ventricular ejection fraction (LVEF) 37%]. Rates of use of guideline-directed medical therapy (GDMT) were high (angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, beta-blockers and mineralocorticoid receptor antagonists: 85.7%, 88.7% and 58.8%, respectively). Crude GDMT utilization rates were lower in women than in men (all differences: P\ua0 64 0.001), and GDMT use became lower with ageing in both sexes, at baseline and at 1-year follow-up. Sex was not an independent predictor of GDMT prescription; however, age >75 years was a significant predictor of GDMT underutilization. Rates of all-cause mortality were lower in women than in men (7.1% vs. 8.7%; P\ua0=\ua00.015), as were rates of all-cause hospitalization (21.9% vs. 27.3%; P\ua075 years. Conclusions: There was a decline in GDMT use with advanced age in both sexes. Sex was not an independent predictor of GDMT or adverse outcomes. However, age >75 years independently predicted lower GDMT use and higher all-cause mortality in patients with LVEF 6445%

Targeted In Situ Protein Diversification and Intra-organelle Validation in Mammalian Cells

Engineered proteins must be phenotypically selected for function in the appropriate physiological context. Here, we present a versatile approach that allows generating panels of mammalian cells that express diversified heterologous protein libraries in the cytosol or subcellular compartments under stable conditions and in a single-variant-per-cell manner To this end we adapt CRISPR/Cas9 editing technology to diversify targeted stretches of a protein of interest in situ. We demonstrate the utility of the approach by in situ engineering and intra-lysosome specific selection of an extremely pH-resistant long Stokes shift red fluorescent protein variant. Tailoring properties to specific conditions of cellular sub-compartments or organelles of mammalian cells can be an important asset to optimize various proteins, protein-based tools, and biosensors for distinct functions