We recently found that the metabolic sensor AMP-activated kinase (AMPK) inhibits the epithelial Na ؉ channel (ENaC) through decreased plasma membrane ENaC expression, an effect requiring the presence of a binding motif in the cytoplasmic tail of the ␤-ENaC subunit for the ubiquitin ligase Nedd4-2. To further examine the role of Nedd4-2 in the regulation of ENaC by AMPK, we studied the effects of AMPK activation on ENaC currents in Xenopus oocytes co-expressing ENaC and wild-type (WT) or mutant forms of Nedd4-2. ENaC inhibition by AMPK was preserved in oocytes expressing WT Nedd4-2 but blocked in oocytes expressing either a dominant-negative (DN) or constitutively active (CA) Nedd4-2 mutant, suggesting that AMPK-dependent modulation of Nedd4-2 function is involved. Similar experiments utilizing WT or mutant forms of the serum-and glucocorticoid-regulated kinase (SGK1), modulators of protein kinase A (PKA), or extracellular-regulated kinase (ERK) did not affect ENaC inhibition by AMPK, suggesting that these pathways known to modulate the Nedd4-2-ENaC interaction are not responsible. AMPK-dependent phosphorylation of Nedd4-2 expressed in HEK-293 cells occurred both in vitro and in vivo, suggesting a potential mechanism for modulation of Nedd4-2 and thus cellular ENaC activity. Moreover, cellular AMPK activation significantly enhanced the interaction of the ␤-ENaC subunit with Nedd4-2, as measured by co-immunoprecipitation assays in HEK-293 cells. In summary, these results suggest a novel mechanism for ENaC regulation in which AMPK promotes ENaC-Nedd4-2 interaction, thereby inhibiting ENaC by increasing Nedd4-2-dependent ENaC retrieval from the plasma membrane. AMPK-dependent ENaC inhibition may limit cellular Na ؉ loading under conditions of metabolic stress when AMPK becomes activated.The epithelial Na ϩ channel (ENaC) 2 is an apical Na ϩ channel expressed in a variety of salt-reabsorbing epithelial tissues, including the kidney, lung, exocrine gland ducts, and colon (1). This channel plays a major role in the regulation of total body salt and volume homeostasis, blood pressure, and airway surface liquid clearance. ENaC is comprised of three structurally similar ␣-, ␤-, and ␥-subunits, whose full-length forms are ϳ90 -95 kDa in size. Each subunit has two presumed transmembrane domains, a large extracellular loop, and cytoplasmic N and C termini (1). ENaC expressed in oocytes has a presumed ␣ 2 ␤ 1 ␥ 1 stoichiometry (2, 3), although alternate subunit stoichiometries have been proposed (4, 5). ENaC can be identified by its sensitivity to the diuretic amiloride, its ohmic currentvoltage relationship, and its high selectivity for conductance of Na ϩ and Li ϩ over K ϩ (1). ENaC is regulated by the actions of several hormones, including aldosterone, vasopressin, and insulin, as well as various non-hormonal mechanisms. Cellular mechanisms that control ENaC activity include the regulation of channel synthesis, intracellular trafficking, membrane insertion and retrieval, and single channel properties (1). In addition, rece...

Background: Short-term follow-up of COVID-19 patients reveals pulmonary dysfunction, myocardial damage and severe psychological distress. Little is known of the burden of these sequelae, and there are no clear recommendations for follow-up of COVID-19 patients. In this multi-disciplinary evaluation, cardiopulmonary function and psychological impairment after hospitalization for COVID-19 are mapped. Methods: We evaluated patients at our outpatient clinic 6 weeks after discharge. Cardiopulmonary function was measured by echocardiography, 24-hours ECG monitoring and pulmonary function testing. Psychological adjustment was measured using questionnaires and semi-structured clinical interviews. A comparison was made between patients admitted to the general ward and Intensive care unit (ICU), and between patients with a high versus low functional status. Findings: Eighty-one patients were included of whom 34 (41%) had been admitted to the ICU. New York Heart Association class II-III was present in 62% of the patients. Left ventricular function was normal in 78% of patients. ICU patients had a lower diffusion capacity (mean difference 12,5% P = 0.01), lower forced expiratory volume in one second and forced vital capacity (mean difference 14.9%; P<0.001; 15.4%; P<0.001; respectively). Risk of depression, anxiety and PTSD were 17%, 5% and 10% respectively and similar for both ICU and non-ICU patients. Interpretation: Overall, most patients suffered from functional limitations. Dyspnea on exertion was most frequently reported, possibly related to decreased DLCOc. This could be caused by pulmonary fibrosis, which should be investigated in long-term follow-up. In addition, mechanical ventilation, deconditioning, or pulmonary embolism may play an important role.

Our results indicate that functional connectivity in several brain networks, particularly the homeostatic and cognitive control network and the reward network, was different between obese and lean subjects. In the fasting state, obesity appears to be associated with stronger functional connectivity between brain areas involved in cognitive control, motivation, and reward, whereas these connections are largely unaffected by food intake in obese compared with lean subjects.

Background During the first wave of the COVID-19 pandemic older patients had an increased risk of hospitalisation and death. Reports on the association of frailty with poor outcome have been conflicting. Objective The aim of the present study was to investigate the independent association between frailty and in-hospital mortality in older hospitalised COVID-19 patients in the Netherlands. Methods This was a multi-centre retrospective cohort study in 15 hospitals in the Netherlands, including all patients aged ≥70 years, who were hospitalised with clinically confirmed COVID-19 between February and May 2020. Data were collected on demographics, co-morbidity, disease severity and Clinical Frailty Scale (CFS). Primary outcome was in-hospital mortality. Results A total of 1,376 patients were included (median age 78 years (IQR 74–84), 60% male). In total, 499 (38%) patients died during hospital admission. Parameters indicating presence of frailty (CFS 6–9) were associated with more co-morbidities, shorter symptom duration upon presentation (median 4 vs. 7 days), lower oxygen demand and lower levels of CRP. In multivariable analyses, the CFS was independently associated with in-hospital mortality: compared to patients with CFS 1–3, patients with CFS 4–5 had a two times higher risk (odds ratio (OR) 2.0 (95%CI 1.3–3.0) and patients with CFS 6–9 had a three times higher risk of in-hospital mortality (OR 2.8 (95%CI 1.8–4.3)). Conclusions The in-hospital mortality of older hospitalised COVID-19 patients in the Netherlands was 38%. Frailty was independently associated with higher in-hospital mortality, even though COVID-19 patients with frailty presented earlier to the hospital with less severe symptoms.

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