Heterogeneity of the action potential duration is required for sustained atrial fibrillation

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Abstract

Atrial fibrillation (AF) is the most common cardiac arrhythmia and accounts for substantial morbidity and mortality. Recently, we created a mouse model with spontaneous and sustained AF caused by a mutation in the NaV1.5 channel (F1759A) that enhances persistent Na+ current, thereby enabling the investigation of molecular mechanisms that cause AF and the identification of novel treatment strategies. The mice have regional heterogeneity of action potential duration of the atria similar to observations in patients with AF. In these mice, we found that the initiation and persistence of the rotational reentrant AF arrhythmias, known as spiral waves or rotors, were dependent upon action potential duration heterogeneity. The centers of the rotors were localized to regions of greatest heterogeneity of the action potential duration. Pharmacologically attenuating the action potential duration heterogeneity reduced both spontaneous and pacing-induced AF. Computer-based simulations also demonstrated that the action potential duration heterogeneity is sufficient to generate rotors that manifest as AF. Taken together, these findings suggest that action potential duration heterogeneity in mice and humans is one mechanism by which AF is initiated and that reducing action potential duration heterogeneity can lessen the burden of AF.

Authors

Uma Mahesh R. Avula, Jeffrey Abrams, Alexander Katchman, Sergey Zakharov, Sergey Mironov, Joseph Bayne, Daniel Roybal, Anirudh Gorti, Lin Yang, Vivek Iyer, Marc Waase, Deepak Saluja, Edward J. Ciaccio, Hasan Garan, Andrew R. Marks, Steven O. Marx, Elaine Y. Wan

WIPI1 is a conserved mediator of right ventricular failure

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Abstract

Right ventricular dysfunction is highly prevalent across cardiopulmonary diseases and independently predicts death in both heart failure (HF) and pulmonary hypertension (PH). Progression towards right ventricular failure (RVF) can occur in spite of optimal medical treatment of HF or PH, highlighting current insufficient understanding of RVF molecular pathophysiology. To identify molecular mechanisms that may distinctly underlie RVF, we investigated the cardiac ventricular transcriptome of advanced HF patients, with and without RVF. Using an integrated systems genomic and functional biology approach, we identified an RVF-specific gene module, for which WIPI1 served as a hub and HSPB6 and MAP4 as drivers, and confirmed the ventricular specificity of Wipi1, Hspb6, and Map4 transcriptional changes in adult murine models of pressure overload induced RV- versus LV- failure. We uncovered a shift towards non-canonical autophagy in the failing RV that correlated with RV-specific Wipi1 upregulation. In vitro siRNA silencing of Wipi1 in neonatal rat ventricular myocytes limited non-canonical autophagy and blunted aldosterone-induced mitochondrial superoxide levels. Our findings suggest that Wipi1 regulates mitochondrial oxidative signaling and non-canonical autophagy in cardiac myocytes. Together with our human transcriptomic analysis and corroborating studies in an RVF mouse model, these data render Wipi1 a potential target for RV-directed HF therapy.

Authors

Christos Tzimas, Christoph D. Rau, Petra E. Buergisser, Gaston Jean-Louis Jr., Katherine Lee, Jeffrey Chukwuneke, Wen Dun, Yibin Wang, Emily J. Tsai

Hematopoietic stem cell transplant effectively rescues lymphocyte differentiation and function in DOCK8-deficient patients

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Abstract

Bi-allelic inactivating mutations in DOCK8 cause a combined immunodeficiency characterised by severe pathogen infections, eczema, allergies, malignancy and impaired humoral responses. These clinical features result from functional defects in most lymphocyte lineages. Thus, DOCK8 plays a key role in immune cell function. Hematopoietic stem cell transplantation (HSCT) is curative for DOCK8 deficiency. While previous reports have described clinical outcomes for DOCK8 deficiency following HSCT, the effect on lymphocyte reconstitution and function has not been investigated. Our study determined whether defects in lymphocyte differentiation and function in DOCK8-deficient patients were restored following HSCT. DOCK8-deficient T and B lymphocytes exhibited aberrant activation and effector function in vivo and in vitro. Frequencies of αβ T and MAIT cells were reduced while γδT cells were increased in DOCK8-deficient patients. HSCT improved, abnormal lymphocyte function in DOCK8-deficient patients. Elevated total and allergen-specific IgE in DOCK8-deficient patients decreased over time following HSCT. Our results document the extensive catalogue of cellular defects in DOCK8-deficient patients, and the efficacy of HSCT to correct these defects, concurrent with improvements in clinical phenotypes. Overall, our findings provide mechanisms at a functional cellular level for improvements in clinical features of DOCK8 deficiency post-HSCT, identify biomarkers that correlate with improved clinical outcomes, and inform the general dynamics of immune reconstitution in patients with monogenic immune disorders following HSCT.

Authors

Bethany A. Pillay, Danielle T. Avery, Joanne M. Smart, Theresa Cole, Sharon Choo, Damien Chan, Paul E. Gray, Katie Frith, Richard Mitchell, Tri Giang Phan, Melanie Wong, Dianne E. Campbell, Peter Hsu, John B. Ziegler, Jane Peake, Frank Alvaro, Capucine Picard, Jacinta Bustamante, Benedicte Neven, Andrew J. Cant, Gulbu Uzel, Peter D. Arkwright, Jean-Laurent Casanova, Helen C. Su, Alexandra Freeman, Nirali Shah, Dennis D. Hickstein, Stuart G. Tangye, Cindy S. Ma

Impaired ketogenesis and increased acetyl-CoA oxidation promote hyperglycemia in human fatty liver

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Abstract

Non-alcoholic fatty liver disease (NAFLD) is a highly prevalent, and potentially morbid, disease that affects one-third of the U.S. population. Normal liver safely accommodates lipid excess during fasting or carbohydrate restriction by increasing their oxidation to acetyl-CoA and ketones, yet lipid excess during NAFLD leads to hyperglycemia and, in some, steatohepatitis. To examine potential mechanisms, flux through pathways of hepatic oxidative metabolism and gluconeogenesis were studied using five simultaneous stable isotope tracers in ketotic (24-hour fast) individuals with a wide range of hepatic triglyceride contents (0-52%). Ketogenesis was progressively impaired as hepatic steatosis and glycemia worsened. Conversely, the alternative pathway for acetyl-CoA metabolism, oxidation in the tricarboxylic (TCA) cycle, was upregulated in NAFLD as ketone production diminished and positively correlated with rates of gluconeogenesis and plasma glucose concentrations. Increased respiration and energy generation that occurred in liver when β-oxidation and TCA cycle activity were coupled may explain these findings, inasmuch as oxygen consumption was higher during fatty liver and highly correlated with gluconeogenesis. These findings demonstrate that increased glucose production and hyperglycemia in NAFLD is not a consequence of acetyl-CoA production per se, but how acetyl-CoA is further metabolized in liver.

Authors

Justin A. Fletcher, Stanislaw Deja, Santhosh Satapati, Xiaorong Fu, Shawn C. Burgess, Jeffrey D. Browning

Intra-islet glucagon signaling is critical for maintaining glucose homeostasis

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Abstract

Glucagon, a hormone released from pancreatic alpha-cells, plays a key role in maintaining proper glucose homeostasis and has been implicated in the pathophysiology of diabetes. In vitro studies suggest that intra-islet glucagon can modulate the function of pancreatic beta-cells. However, because of the lack of suitable experimental tools, the in vivo physiological role of this intra-islet cross-talk has remained elusive. To address this issue, we generated a novel mouse model that selectively expressed an inhibitory designer G protein-coupled receptor (Gi DREADD) in α-cells only. Drug-induced activation of this inhibitory designer receptor almost completely shut off glucagon secretion in vivo, resulting in significantly impaired insulin secretion, hyperglycemia, and glucose intolerance. Additional studies with mouse and human islets indicated that intra-islet glucagon stimulates insulin release primarily by activating β-cell GLP-1 receptors. These new findings strongly suggest that intra-islet glucagon signaling is essential for maintaining proper glucose homeostasis in vivo. Our work may pave the way toward the development of novel classes of antidiabetic drugs that act by modulating intra-islet cross-talk between α- and β-cells.

Authors

Lu Zhu, Diptadip Dattaroy, Jonathan Pham, Lingdi Wang, Luiz F. Barella, Yinghong Cui, Kenneth J. Wilkins, Bryan L. Roth, Ute Hochgeschwender, Franz M. Matschinsky, Klaus H. Kaestner, Nicolai M. Doliba, Jürgen Wess

Erythropoietin inhibits SGK1-dependent T_H17 induction and T_H17-dependent kidney disease

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Abstract

IL-17-producing CD4+ cells (TH17) are pathogenically linked to autoimmunity including to autoimmune kidney disease. Erythropoietin’s (EPO) newly recognized immunoregulatory functions and its predominant intra-renal source suggested that EPO physiologically regulates TH17 differentiation, thereby serving as a barrier to the development of autoimmune kidney disease. Using in vitro studies of human and murine cells and in vivo models, we show that EPO ligation of its receptor (EPO-R) on CD4+ T cells directly inhibits TH17 generation and promotes trans-differentiation of TH17 into IL-17-FOXP3+CD4+ T cells. Mechanistically, EPO/EPO-R ligation abrogates upregulation of SGK1 gene expression and blocks p38 activity to prevent SGK1 phosphorylation, thereby inhibiting RORC-mediated transcription of IL-17 and IL-23 receptor genes. In a murine model of TH17-dependent aristolochic acid (ArA)-induced, interstitial kidney disease associated with reduced renal EPO production, we demonstrate that transgenic EPO overexpression or recombinant EPO (rEPO) administration limits TH17 formation and clinical/histological disease expression. EPO/EPO-R ligations on CD4+ T cells abrogate, while absence of T cell-expressed EPO-R augments, TH17 induction and clinical/histological expression of pristane-induced glomerulonephritis (associated with decreased intrarenal EPO). rEPO prevents spontaneous glomerulonephritis and TH17 generation in MRL-lpr mice. Together, our findings indicate that EPO physiologically and therapeutically modulate TH17 cells to limit expression of TH17-associated autoimmune kidney disease.

Authors

Chiara Donadei, Andrea Angeletti, Chiara Cantarelli, Vivette D. D'Agati, Gaetano La Manna, Enrico Fiaccadori, Julian Horwitz, Huabao Xiong, Chiara Guglielmo, Susan Hartzell, Joren C. Madsen, Umberto Maggiore, Peter S. Heeger, Paolo Cravedi

Early alterations in stem-like/resident T cells, innate and myeloid cells in the bone marrow in preneoplastic gammopathy

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Abstract

Preneoplastic lesions carry many of the antigenic targets found in cancer cells but often exhibit prolonged dormancy. Understanding how the host response to premalignancy is maintained and altered during malignant transformation is needed to prevent cancer. In order to understand the immune microenvironment in precursor monoclonal gammopathy of undetermined significance (MGUS) and myeloma, we analyzed bone marrow immune cells from 12 healthy donors and 26 MGUS/myeloma patients by mass cytometry and concurrently profiled transcriptomes of 42,606 single immune cells from these bone marrows. Compared to age-matched healthy donors, memory T cells from both MGUS and myeloma patients exhibit greater terminal-effector differentiation. However, memory T cells in MGUS show greater enrichment of stem-like TCF1/7hi cells. Clusters of T cells with stem-like and tissue-residence genes were also found to be enriched in MGUS by single-cell transcriptome analysis. Early changes in both NK and myeloid cells were also observed in MGUS. Enrichment of stem-like T cells correlated with a distinct genomic profile of myeloid cells and levels of Dickkopf-1 in bone-marrow plasma. These data describe the landscape of changes in both innate and adaptive immunity in premalignancy and suggest that attrition of the bone-marrow-resident T cell compartment due to loss of stem-like cells may underlie loss of immune surveillance in myeloma.

Authors

Jithendra Kini Bailur, Samuel S. McCachren, Deon B. Doxie, Mahesh Shrestha, Katherine E. Pendleton, Ajay K. Nooka, Natalia Neparidze, Terri L. Parker, Noffar Bar, Jonathan L. Kaufman, Craig C. Hofmeister, Lawrence H. Boise, Sagar Lonial, Melissa L. Kemp, Kavita M. Dhodapkar, Madhav V. Dhodapkar

Potassium acts through mTOR to regulate its own secretion

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Abstract

Potassium (K+) secretion by kidney tubule cells is central to electrolyte homeostasis in mammals. In the K+ secretory “principal” cells of the distal nephron, electrogenic Na+ transport by the epithelial sodium channel (ENaC) generates the electrical driving force for K+ transport across the apical membrane. Regulation of this process is attributable in part to aldosterone, which stimulates the gene transcription of the ENaC-regulatory kinase, SGK1. However, a wide range of evidence supports the conclusion that an unidentified aldosterone-independent pathway exists. We show here that in principal cells, K+ itself acts through the type 2 mTOR complex (mTORC2) to activate SGK1, which stimulates ENaC to enhance K+ excretion. The effect depends on changes in K+ concentration on the blood side of the cells, and requires basolateral membrane K+-channel activity. However, it does not depend on changes in aldosterone, or on enhanced distal delivery of Na+ from upstream nephron segments. These data strongly support the idea that K+ is sensed directly by principal cells to stimulate its own secretion by activating the mTORC2-SGK1 signaling module, and stimulate ENaC. We propose that this local effect acts in concert with aldosterone and increased Na+ delivery from upstream nephron segments to sustain K+ homeostasis.

Authors

Mads Vaarby Sørensen, Bidisha Saha, Iben Skov Jensen, Peng Wu, Niklas Ayasse, Catherine E. Gleason, Samuel Levi Svendsen, Wen-Hui Wang, David Pearce

Targeting self and neo-epitopes with a modular self-adjuvanting cancer vaccine

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Abstract

Induction of a potent CD4 and CD8 T-cell response against tumor-specific and tumor-associated antigen is critical for eliminating tumor cells. Recent vaccination strategies have been hampered by an inefficacious and low amplitude immune response. Here we describe a self-adjuvanted chimeric protein vaccine platform to address these challenges, characterized by a multidomain construction incorporating (i) a cell penetrating peptide (CPP) allowing internalization of several multiantigenic Major Histocompatibility Complex (MHC)-restricted peptides within (ii) the multiantigenic domain (Mad) and (iii) a TLR2/4 agonist domain (TLRag). Functionality of the resulting chimeric protein is based on the combined effect of the above-mentioned three different domains for simultaneous activation of antigen presenting cells and antigen cross-presentation, leading to an efficacious multiantigenic and multiallelic cellular immune response. Helper and cytotoxic T-cell responses were observed against model-, neo- and self-antigens, and were highly potent in several murine tumor models. The safety and the immunogenicity of a human vaccine candidate designed for colorectal cancer treatment was demonstrated in a non-human primate model. This newly engineered therapeutic vaccine approach is promising for the treatment of poorly infiltrated tumors that do not respond to currently marketed immunotherapies.

Authors

Elodie Belnoue, Jean-François Mayol, Susanna Carboni, Wilma Di Berardino Besson, Eloise Dupuychaffray, Annika Nelde, Stefan Stevanovic, Marie-Laure Santiago-Raber, Paul R. Walker, Madiha Derouazi

Activation of the calcium sensing receptor attenuates TRPV6-dependent intestinal calcium absorption

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Abstract

Plasma calcium (Ca2+) is maintained by amending the release of parathyroid hormone and through direct effects of the Ca2+ sensing receptor (CaSR) in the renal tubule. Combined, these mechanisms alter intestinal Ca2+ absorption by modulating 1,25-dihydroxy vitamin D3 production, bone resorption, and renal Ca2+ excretion. The CaSR is a therapeutic target in the treatment of secondary hyperparathyroidism and hypocalcemia a common complication of calcimimetic therapy. The CaSR is also expressed in intestinal epithelium, however, a direct role in regulating local intestinal Ca2+ absorption is unknown. Chronic CaSR activation decreased expression of genes involved in Ca2+ absorption. In Ussing chambers, increasing extracellular Ca2+ or basolateral application of the calcimimetic cinacalcet decreased net Ca2+ absorption across intestinal preparations acutely. Conversely, Ca2+ absorption increased with decreasing extracellular Ca2+ concentration. These responses were absent in mice expressing a non-functional TRPV6, TRPV6D541A. Cinacalcet also attenuated Ca2+ fluxes through TRPV6 in Xenopus oocytes when co-expressed with the CaSR. Moreover, the phospholipase C inhibitor, U73122, prevented cinacalcet-mediated inhibition of Ca2+ flux. These results reveal a regulatory pathway whereby activation of the CaSR in the basolateral membrane of the intestine directly attenuates local Ca2+ absorption via TRPV6 to prevent hypercalcemia and help explain how calcimimetics induce hypocalcemia.

Authors

Justin J. Lee, Xiong Liu, Debbie O'Neil, Megan R. Beggs, Petra Weissgerber, Veit Flockerzi, Xing-Zhen Chen, Henrik Dimke, R. Todd Alexander