Saturated fatty acids like palmitate contribute to muscle atrophy in a number of conditions (e.g., type II diabetes) by altering insulin signaling. Akt is a key modulator of protein balance that inhibits the FoxO transcription factors (e.g., FoxO3) which selectively induce the expression of atrophy-inducing genes (atrogenes) in the ubiquitin-proteasome and autophagy-lysosome systems. Conversely, omega-3 polyunsaturated fatty acids have beneficial effects on insulin signaling and may preserve muscle mass. In an earlier report, the omega-3 fatty acid docosahexaenoic acid (DHA) protected myotubes from palmitate-induced atrophy; the mechanisms underlying the alterations in protein metabolism were not identified. This study investigated whether DHA prevents a palmitate-induced increase in proteolysis by restoring Akt/FoxO signaling. Palmitate increased the rate of protein degradation, while cotreatment with DHA prevented the response. Palmitate reduced the activation state of Akt and increased nuclear FoxO3 protein while decreasing its cytosolic level. Palmitate also increased the messenger RNAs (mRNAs) of two FoxO3 atrogene targets, the E3 ubiquitin ligase atrogin-1/MAFbx and the autophagy mediator Bnip3. DHA attenuated the effects of palmitate on Akt activation, FoxO3 localization and atrogene mRNAs. DHA, alone or in combination with palmitate and decreased the ratio of LC3B-II:LC3B-I protein as well as the rate of autophagosome formation, as indicated by reduced LC3B-II protein in the presence of 10 mmol/L methylamine, suggesting an independent effect of DHA on the macroautophagy pathway. These data indicate that palmitate induces myotube atrophy, at least in part, by activating multiple proteolytic systems and that DHA counters the catabolic effects of palmitate by restoring Akt/FoxO signaling.
by
Maria Chavez-Canales;
Juan Pablo Arroyo;
Benjamin Ko;
Norma Vazquez;
Rocio Bautista;
Maria Castaneda-Bueno;
Norma A. Bobadilla;
Robert S. Hoover Jr;
Gerardo Gamba
Objectives: Insulin is recognized to increase renal salt reabsorption in the distal nephron and hyperinsulinemic states have been shown to be associated with increased expression of the renal NaCl cotransporter (NCC). However, the effect of insulin on NCC functional activity has not been reported.
Methods: Using a heterologous expression system of Xenopus laevis oocytes, a mouse distal convoluted cell line, mDCT15 cells, endogenously expressing NCC, and an ex-vivo kidney perfusion technique, we assessed the effect of insulin on the activity and phosphorylation of NCC. The signaling pathway involved was analyzed.
Results: In Xenopus oocytes insulin increases the activity of NCC together with its phosphorylation at threonine residue 58. Activation of NCC by insulin was also observed in mDCT15 cells. Additionally, insulin increased the NCC phosphorylation in kidney under the ex-vivo perfusion technique. In oocytes and mDCT15 cells, insulin effect on NCC was prevented with inhibitors of phosphatidylinositol 3-kinase (PI3K), mTORC2, and AKT1 kinases, but not by inhibitors of MAP or mTORC1 kinases, suggesting that PI3K-mTORC2-AKT1 is the intracellular pathway required. Additionally, activation of NCC by insulin was not affected by wild-type or mutant versions of with no lysine kinase 1, with no lysine kinase 4, or serum glucocorticoid kinase 1, but it was no longer observed in the presence of wild-type or the dominant negative, catalytically inactive with no lysine kinase 3, implicating this kinase in the process.
Conclusion: Insulin induces activation and phosphorylation of NCC. This effect could play an important role in arterial hypertension associated with hyperinsulinemic states, such as obesity, metabolic syndrome, or type 2 diabetes mellitus.
The thiazide-sensitive sodium chloride cotransporter (NCC) and the epithelial sodium channel (ENaC) are two of the most important determinants of salt balance and thus systemic blood pressure. Abnormalities in either result in profound changes in blood pressure. There is one segment of the nephron where these two sodium transporters are coexpressed, the second part of the distal convoluted tubule. This is a key part of the aldosterone-sensitive distal nephron, the final regulator of salt handling in the kidney. Aldosterone is the key hormonal regulator for both of these proteins. Despite these shared regulators and coexpression in a key nephron segment, associations between these proteins have not been investigated. After confirming apical localization of these proteins, we demonstrated the presence of functional transport proteins and native association by blue native PAGE. Extensive coimmunoprecipitation experiments demonstrated a consistent interaction of NCC with α-And γ-ENaC. Mammalian two-hybrid studies demonstrated direct binding of NCC to ENaC subunits. Fluorescence resonance energy transfer and immunogold EM studies confirmed that these transport proteins are within appropriate proximity for direct binding. Additionally, we demonstrate that there are functional consequences of this interaction, with inhibition of NCC affecting the function of ENaC. This novel finding of an association between ENaC and NCC could alter our understanding of salt transport in the distal tubule.
miR-155 was synthesized and loaded into exosomes in increased infiltration of macrophages in a uremic heart. The released exosomal fusion with the plasma membrane leads to the release of miR-155 into the cytosol and translational repression of forkhead transcription factors of the O class (FoxO3a) in cardiomyocytes. Finally, macrophage-derived miR-155–containing exosomes promoted cardiomyocyte pyroptosis and uremic cardiomyopathy changes (cardiac hypertrophy and fibrosis) by directly targeting FoxO3a in uremic mice.
Background: Urea, the end product of protein metabolism, has been considered to have negligible toxicity for a long time. Our previous study showed a depression phenotype in urea transporter (UT) B knockout mice, which suggests that abnormal urea metabolism may cause depression. The purpose of this study was to determine if urea accumulation in brain is a key factor causing depression using clinical data and animal models.
Methods: A meta-analysis was used to identify the relationship between depression and chronic diseases. Functional Magnetic Resonance Imaging (fMRI) brain scans and common biochemical indexes were compared between the patients and healthy controls. We used behavioural tests, electrophysiology, and molecular profiling techniques to investigate the functional role and molecular basis in mouse models.
Findings: After performing a meta-analysis, we targeted the relevance between chronic kidney disease (CKD) and depression. In a CKD mouse model and a patient cohort, depression was induced by impairing the medial prefrontal cortex. The enlarged cohort suggested that urea was responsible for depression. In mice, urea was sufficient to induce depression, interrupt long-term potentiation (LTP) and cause loss of synapses in several models. The mTORC1-S6K pathway inhibition was necessary for the effect of urea. Lastly, we identified that the hydrolysate of urea, cyanate, was also involved in this pathophysiology.
Interpretation: These data indicate that urea accumulation in brain is an independent factor causing depression, bypassing the psychosocial stress. Urea or cyanate carbamylates mTOR to inhibit the mTORC1-S6K dependent dendritic protein synthesis, inducing impairment of synaptic plasticity in mPFC and depression-like behaviour. CKD patients may be able to attenuate depression only by strict management of blood urea.
Aim: Protein kinase Cα (PKCα) is a critical regulator of multiple cell signaling pathways including gene transcription, posttranslation modifications and activation/inhibition of many signaling kinases. In regards to the control of blood pressure, PKCα causes increased vascular smooth muscle contractility, while reducing cardiac contractility. In addition, PKCα has been shown to modulate nephron ion transport. However, the role of PKCα in modulating mean arterial pressure (MAP) has not been investigated. In this study, we used a whole animal PKCα knock out (PKC KO) to test the hypothesis that global PKCα deficiency would reduce MAP, by a reduction in vascular contractility. Methods: Radiotelemetry measurements of ambulatory blood pressure (day/night) were obtained for 18 h/day during both normal chow and high-salt (4%) diet feedings. PKCα mice had a reduced MAP, as compared with control, which was not normalized with high-salt diet (14 days). Metabolic cage studies were performed to determine urinary sodium excretion. Results: PKC KO mice had a significantly lower diastolic, systolic and MAP as compared with control. No significant differences in urinary sodium excretion were observed between the PKC KO and control mice, whether fed normal chow or high-salt diet. Western blot analysis showed a compensatory increase in renal sodium chloride cotransporter expression. Both aorta and mesenteric vessels were removed for vascular reactivity studies. Aorta and mesenteric arteries from PKC KO mice had a reduced receptor-independent relaxation response, as compared with vessels from control. Vessels from PKC KO mice exhibited a decrease in maximal contraction, compared with controls. Conclusion: Together, these data suggest that global deletion of PKCα results in reduced MAP due to decreased vascular contractility.
Background: Both dialysis facilities and hospitals are accountable for 30-day hospital readmissions among U.S. hemodialysis patients. We examined the association of post-hospitalization processes of care at hemodialysis facilities with pulmonary edema-related and other readmissions. Methods: In a retrospective cohort comprised of electronic medical record (EMR) data linked with national registry data, we identified unique patient index admissions (n = 1056; 2/1/10-7/31/15) that were followed by ≥3 in-center hemodialysis sessions within 10 days, among patients treated at 19 Southeastern dialysis facilities. Indicators of processes of care were defined as present vs. absent in the dialysis facility EMR. Readmissions were defined as admissions within 30 days of the index discharge; pulmonary edema-related vs. other readmissions defined by discharge codes for pulmonary edema, fluid overload, and/or congestive heart failure. Multinomial logistic regression to estimate odds ratios (ORs) for pulmonary edema-related and other vs. no readmissions. Results: Overall, 17.7% of patients were readmitted, and 8.0% had pulmonary edema-related readmissions (44.9% of all readmissions). Documentation of the index admission (OR = 2.03, 95% CI 1.07-3.85), congestive heart failure (OR = 1.87, 95% CI 1.07-3.27), and home medications stopped (OR = 1.81, 95% CI 1.08-3.05) or changed (OR = 1.69, 95% CI 1.06-2.70) in the EMR post-hospitalization were all associated with higher risk of pulmonary edema-related vs. no readmission; lower post-dialysis weight (by ≥0.5 kg) after vs. before hospitalization was associated with 40% lower risk (OR = 0.60, 95% CI 0.37-0.96). Conclusions: Our results suggest that some interventions performed at the dialysis facility in the post-hospitalization period may be associated with reduced readmission risk, while others may provide a potential existing means of identifying patients at higher risk for readmissions, to whom such interventions could be efficiently targeted.
Background/Aims: Patients on chronic hemodialysis have a high prevalence of heart disease and poor self-reported physical function. The association between structural heart disease and self-reported physical function in patients on hemodialysis is unknown.
Methods: We studied the association between elevated pulmonary artery systolic pressure (PASP) and self-reported physical function in ESRD in 253 patients in the USRDS ACTIVE/ADIPOSE study between 2009 and 2011. We used multivariate linear regression with PASP obtained from clinical echocardiogram reports as the primary predictor and the Physical Function (PF) subscale of the SF-36 as the primary outcome. To determine whether associations between PASP and PF were driven by fluid overload or left ventricular hypertrophy, we assessed whether PASP was associated with bioimpedance spectroscopy (BIS)-derived extracellular water (ECW) and with left ventricular posterior wall thickness.
Results: In a multivariable model, each 10 mm Hg higher PASP was associated with a 3.32-point lower PF score (95% CI -5.95, -0.68). In a multivariable model that included BIS estimates, both left ventricular posterior wall thickness (LVPW, per 5 mm) and ECW were associated with a higher PASP (LVPW 4.21 mm Hg, 95% 0.38-8.04; ECW 1.12 mm Hg per liter, 95% CI 0.07-2.18). Higher LVPW and ECW were independently associated with a lower PF score.
Conclusion: Left ventricular hypertrophy and elevated pulmonary pressure are associated with worse self-reported physical function in patients on hemodialysis. The role of chronic volume overload on PASP and PF score should be evaluated in a prospective manner.
Background:
Although older adults with predialysis chronic kidney disease are at higher risk for falls, the prognostic significance of a serious fall injury prior to dialysis initiation has not been well described in the end-stage renal disease population.
Methods:
We examined the association between a serious fall injury in the year prior to starting hemodialysis and adverse health outcomes in the year following dialysis initiation using a retrospective cohort study of U.S. Medicare beneficiaries . 67 years old who initiated dialysis in 2010.2012. Serious fall injuries were defined using diagnostic codes for falls plus an injury (fracture, joint dislocation, or head injury). Health outcomes, defined as time-to-event variables within the first year of dialysis, included four outcomes: a subsequent serious fall injury, hospital admission, post-acute skilled nursing facility (SNF) utilization, and mortality.
Results:
Among this cohort of 81,653 initiating hemodialysis, 2,958 (3.6%) patients had a serious fall injury in the year prior to hemodialysis initiation. In the first year of dialysis, 7.6% had a subsequent serious fall injury, 67.6% a hospitalization, 30.7% a SNF claim, and 26.1% died. Those with versus without a serious fall injury in the year prior to hemodialysis initiation were at higher risk (hazard ratio, 95% confidence interval) for a subsequent serious fall injury (2.65, 2.41.2.91), hospitalization (1.11, 1.06.1.16), SNF claim (1.40, 1.30.1.50), and death (1.14, 1.06.1.22).
Conclusions:
For older adults initiating dialysis, a history of a serious fall injury may provide prognostic information to support decision making and establish expectations for life after dialysis initiation.
Regulation of the epithelial sodium channel (ENaC), which regulates fluid homeostasis and blood pressure, is complex and remains incompletely understood. The TIP peptide, a mimic of the lectin-like domain of TNF, activates ENaC by binding to glycosylated residues in the extracellular loop of ENaC-α as well as to a hitherto uncharacterized internal site. Molecular docking studies suggested three residues, Val 567 , Glu 568 , and Glu 571 , located at the interface between the second transmembrane and C-terminal domains of ENaC-α, as a critical site for binding of the TIP peptide. We generated Ala replacement mutants in this region of ENaC-α and examined its interaction with TIP peptide (3M, V567A/E568A/E571A; 2M, V567A/E568A; and 1M, E571A). 3M and 2M ENaC-α but not 1M ENaC-α, displayed significantly reduced binding capacity to TIP peptide and to TNF. When overexpressed in H441 cells,3M mutant ENaC-α formed functional channels with similar gating and density characteristics as the WT subunit and efficiently associated with the β and γ subunits in the plasma membrane. We subsequently assayed for increased open probability time and membrane expression, both of which define ENaC activity, following addition of TIP peptide. TIP peptide increased open probability time in H441 cells overexpressing wild type and 1M ENaC-α channels, but not 3M or 2M ENaC-α channels. On the other hand, TIP peptide-mediated reduction in ENaC ubiquitination was similar in cells overexpressing either WT or 3M ENaC-α subunits. In summary, this study has identified a novel site in ENaC-α that is crucial for activation of the open probability of the channel, but not membrane expression, by the lectin-like domain of TNF.