Altered calcium-handling produces reentry-promoting action potential alternans in atrial fibrillation-remodeled hearts

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Abstract

Atrial fibrillation (AF) alters atrial-cardiomyocyte (ACM) Ca2+-handling, promoting ectopic-beat formation. Here, we examined the effects of AF-associated remodeling on Ca2+-related action-potential (AP) dynamics and consequences for AF-susceptibility. AF was maintained electrically (x1 week) in dogs by right-atrial (RA) tachypacing. ACMs isolated from AF-dogs showed increased Ca2+-release refractoriness, spontaneous Ca2+-spark frequency and cycle-length (CL) threshold for Ca2+ and APD alternans versus controls. Similarly, AF increased the in-situ CL-threshold for Ca2+/APD-alternans and spatial dispersion in Ca2+-release recovery kinetics, leading to spatially-discordant alternans associated with reentrant rotor formation and susceptibility to AF induction/maintenance. The clinically-available agent dantrolene reduced Ca2+-leak and CL-threshold for Ca2+/APD-alternans in both ACMs and AF-dog RA, while suppressing AF-susceptibility; caffeine increased Ca2+-leak, CL-threshold for Ca2+/APD-alternans in control-dog ACMs and RA-tissues. In vivo, the atrial repolarization alternans CL-threshold was increased in AF vs control, as was AF-vulnerability. Intravenous dantrolene restored repolarization alternans-threshold and reduced AF-vulnerability. Immunoblots showed significantly reduced expression of total and phosphorylated ryanodine-receptors and calsequestrin in AF, along with unchanged phospholamban/SERCA expression. Thus, in addition to promoting spontaneous ectopy, AF-induced Ca2+-handling abnormalities favor AF-occurrence by enhancing vulnerability to repolarization-alternans, thereby promoting the initiation and maintenance of reentrant activity; the clinically-available compound dantrolene provides a lead-molecule to target this mechanism.

Authors

Tao Liu, Feng Xiong, Xiao-yan Qi, Jiening Xiao, Louis Villeneuve, Issam Abu-Taha, Dobromir Dobrev, Congxin Huang, Stanley Nattel

Intercalated cell BKα subunit is required for flow-induced K+ secretion

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Abstract

BK channels are expressed in intercalated (ICs) and principal (PCs) cells in the cortical collecting duct (CCD) of the mammalian kidney and have been proposed to be responsible for flow-induced K+ secretion (FIKS) and K+ adaptation. To examine the IC-specific role of BK channels, we generated a mouse with targeted disruption of the pore-forming BK alpha subunit (BKα) in ICs (IC-BKα-KO). Whole cell charybdotoxin (ChTX)-sensitive K+ currents were readily detected in control ICs, but largely absent in ICs of IC-BKα-KO mice. When placed on a high K+ (HK) diet for 13 days, blood [K+] was significantly greater in IC-BKα-KO mice vs. controls in males only, although urinary K+ excretion rates following isotonic volume expansion were similar in males and females. FIKS was present in microperfused CCDs isolated from controls, but was absent in IC-BKα-KO CCDs of both sexes. Also, flow-stimulated ENaC-mediated Na+ absorption was greater in CCDs from female IC-BKα-KO mice than in CCDs from males. Our results confirm a critical role of IC BK channels in FIKS. Sex contributes to the capacity for adaptation to a HK diet in IC-BKα-KO mice.

Authors

Rolando Carrisoza-Gaytan, Evan C. Ray, Daniel Flores, Allison L. Marciszyn, Peng Wu, Leah Liu, Arohan R. Subramanya, WenHui Wang, Shaohu Sheng, Lubika J. Nkashama, Jingxin Chen, Edwin K. Jackson, Stephanie M. Mutchler, Szilvia Heja, Donald E. Kohan, Lisa M. Satlin, Thomas R. Kleyman

Metabolic reprogramming augments potency of human pSTAT3-inhibited iTregs to suppress alloreactivity

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Abstract

Immune suppressive donor regulatory T cells (Tregs) can prevent graft-versus-host disease (GVHD) or solid organ allograft rejection. We previously demonstrated inhibiting STAT3 phosphorylation (pSTAT3) augments FOXP3 expression, stabilizing induced Tregs (iTregs). Here we report human pSTAT3-inhibited iTregs prevent human skin graft rejection and xenogeneic GVHD yet spare donor anti-leukemia immunity. pSTAT3-inhibited iTregs express increased levels of skin-homing CLA antigen, immune suppressive GARP and PD-1, and IL-9 that supports tolerizing mast cells. Further, pSTAT3-inhibited iTregs significantly reduce alloreactive conventional T cells, Th1, and Th17 cells implicated in GVHD and tissue rejection, and impair infiltration by pathogenic Th2 cells. Mechanistically, pSTAT3 inhibition of iTregs provokes a shift in metabolism from oxidative phosphorylation (OxPhos) to glycolysis and reduced electron transport chain activity. Strikingly, co-treatment with coenzyme Q10 (coQ10) restores OxPhos in pSTAT3-inhibited iTregs and augments their suppressive potency. These findings support the rationale for clinically testing the safety and efficacy of metabolically tuned, human pSTAT3-inhibited iTregs to control alloreactive T cells.

Authors

Kelly Walton, Mario R. Fernandez, Elizabeth M. Sagatys, Jordan Reff, Jongphil Kim, Marie Catherine Lee, John Kiluk, Jane Yuet Ching Hui, David McKenna, Meghan Hupp, Colleen Forster, Michael A. Linden, Nicholas J. Lawrence, Harshani R. Lawrence, Joseph Pidala, Steven Z. Pavletic, Bruce R. Blazar, Said M. Sebti, John L. Cleveland, Claudio Anasetti, Brian C. Betts

A role for TNFalpha in alveolar macrophage damange-associated molecular pattern release

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Abstract

Chronic beryllium disease (CBD) is a metal hypersensitivity/autoimmune disease in which damage-associated molecular patterns (DAMPs) promote a break in T cell tolerance and expansion of Be2+/self-peptide reactive CD4+ T cells. In this study, we investigated the mechanism of cell death induced by beryllium particles (Be) in alveolar macrophages (AMΦs) and its impact on DAMP release. We found that phagocytosis of Be led to AM cell death independently of caspase, RIP1K, RIP3K or ROS activity. Prior to cell death, Be-exposed AMΦs secreted TNFalpha that boosted intracellular stores of IL-1alpha followed by caspase 8-dependent fragmentation of DNA. IL-1alpha and nucleosomal DNA were subsequently released from AMΦs upon loss of plasma membrane integrity. In contrast, necrotic AMs released only unfragmented DNA and necroptotic AMΦs released only IL-1alpha. In mice exposed to Be, TNFalpha promoted release of both DAMPs and was required for the mobilization of immunogenic DCs, expansion of Be-reactive CD4+ T cells and pulmonary inflammation in a mouse model of CBD. Thus, early autocrine effects of particle-induced TNFalpha on AMs led to a break in peripheral tolerance. This novel mechanism may underlie the known relationship between fine particle inhalation, TNFalpha and loss of peripheral tolerance in T cell-mediated autoimmune disease and hypersensitivities.

Authors

Morgan K. Collins, Abigail M. Shotland, Morgan F. Wade, Shaikh M. Atif, Denay J.K. Richards, Manolo Torres-Llompart, Douglas G. Mack, Allison K. Martin, Andrew P. Fontenot, Amy S. McKee

CX₃CR1^-CD8⁺ T cells are critical in antitumor efficacy, but functionally suppressed in the tumor microenvironment

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Abstract

While blockade of PD-1/PD-L1 immune checkpoint revolutionized cancer treatment, how it works on tumor-infiltrating CD8+ T cells recognizing the same antigen at various differentiation stages remains elusive. Here, we found that the chemokine receptor CX3CR1 identified three distinct differentiation states of intratumoral CD8+ T-cell subsets. Adoptively transferred antigen-specific CX3CR1neg CD8+ T cells generated phenotypically and functionally distinct CX3CR1int and CX3CR1hi subsets in the periphery. Notably, expression of co-inhibitory receptors and Tcf1 inversely correlated with the degree of T-cell differentiation defined by CX3CR1. Despite significantly lower expression of co-inhibitory receptors and potent cytolytic activity, in vivo depletion of the CX3CR1hi subset did not alter the antitumor efficacy of adoptively transferred CD8+ T cells. Furthermore, differentiated CX3CR1int and CX3CR1hi subsets were impaired in their ability to undergo proliferation upon re-stimulation, and had no impact on established tumors upon second adoptive transfer compared with the CX3CR1neg subset that remained effective. Accordingly, anti-PD-L1 therapy preferentially rescued proliferation and cytokine production of the CX3CR1neg subset, and significantly enhanced antitumor efficacy of adoptively transferred CD8+ T cells. These findings provide a better understanding of the phenotypic and functional heterogeneity of tumor-infiltrating CD8+ T cells, and can be exploited to develop more effective immunotherapy.

Authors

Takayoshi Yamauchi, Toshifumi Hoki, Takaaki Oba, Hidehito Saito, Kristopher Attwood, Michael S. Sabel, Alfred E. Chang, Kunle Odunsi, Fumito Ito

Glucose in the hypothalamic paraventricular nucleus regulates GLP-1 release

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Abstract

Glucokinase (GK) is highly expressed in the hypothalamic paraventricular nucleus (PVN); however its role is currently unknown. We found that glucokinase in the PVN acts as part of a glucose sensing mechanism within the PVN that regulates glucose homeostasis by controlling glucagon like peptide 1 (GLP-1) release. GLP-1 is released from enteroendocrine L-cells in response to oral glucose. Here we identify a brain mechanism critical to the release of GLP-1 in response to oral glucose. We show that increasing expression of GK or injection of glucose into the PVN increases GLP-1 release in response to oral glucose. On the contrary decreasing expression of GK or injection of non-metabolisable glucose into the PVN prevents GLP-1 release. Our results demonstrate that glucosensitive GK neurones in the PVN, are critical to the response to oral glucose and subsequent release of GLP-1.

Authors

Yue Ma, Risheka Ratnasabapathy, Ivan De Backer, Chioma Izzi-Engbeaya, Marie-Sophie Nguyen-Tu, Joyceline Cuenco, Ben Jones, Christopher D. John, Brian Y. H. Lam, Guy A. Rutter, Giles Yeo, Waljit Dhillo, James Gardiner

CIC is a critical regulator of neuronal differentiation

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Abstract

Capicua (CIC), a member of the high mobility group (HMG)-box superfamily of transcriptional repressors, is frequently mutated in human oligodendrogliomas. But its function in brain development and tumorigenesis remains poorly understood. Here, we report that brain-specific deletion of Cic compromises developmental transition of neuroblast to immature neurons in mouse hippocampus and compromises normal neuronal differentiation. Combined gene expression and ChIP-seq analyses identified VGF as an important CIC-repressed transcriptional surrogate involved in neuronal lineage regulation. Aberrant VGF expression promotes neural progenitor cell proliferation by suppressing their differentiation. Mechanistically, we demonstrated that CIC represses VGF expression by tethering SIN3-HDAC to form a transcriptional corepressor complex. Mass spectrometry analysis of CIC-interacting proteins further identified BRG1 containing mSWI/SNF complex whose function is necessary for transcriptional repression by CIC. Together, this study uncovers a novel regulatory pathway of CIC-dependent neuronal differentiation and may implicate these molecular mechanisms in CIC-dependent brain tumorigenesis.

Authors

Inah Hwang, Heng Pan, Jun Yao, Olivier Elemento, Hongwu Zheng, Jihye Paik

MT1-MMP deficiency leads to defective ependymal cell maturation, impaired ciliogenesis and hydrocephalus

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Abstract

Hydrocephalus is characterized by abnormal accumulation of cerebrospinal fluid (CSF) in the ventricular cavity. The circulation of CSF in brain ventricles is controlled by the coordinated beating of motile cilia at the surface of ependymal cells (ECs). Here we show that MT1-MMP is highly expressed in olfactory bulb, rostral migratory stream, and ventricular system. Mice deficient for Membrane type-1-MMP (MT1-MMP) develop typical phenotypes observed in hydrocephalus such as dome-shaped skull, dilated ventricles, corpus callosum agenesis and astrocyte hypertrophy during the first two weeks of postnatal development. MT1-MMP deficient mice exhibits reduced and disorganized motile cilia with the impaired maturation of ECs, leading to abnormal CSF flow. Consistent with the defects in motile cilia morphogenesis, the expressions of pro-multiciliogenic genes are significantly decreased with a concomitant hyper-activation of Notch signaling in the wall of lateral ventricles in Mmp14-/- brains. Inhibition of Notch signaling by γ-secretase inhibitor restores ciliogenesis in Mmp14-/- ECs. Taken together, these data suggest that MT1-MMP is required for ciliogenesis and ependymal cell maturation by suppressing Notch signaling during early brain development. Our findings implicate that MT1-MMP is critical for early brain development and loss of MT1-MMP activity gives rise to hydrocephalus.

Authors

Zhixin Jiang, Jin Zhou, Xin Qin, Huiling Zheng, Bo Gao, Xin-guang Liu, Guoxiang Jin, Zhongjun Zhou

Control of PTH secretion by the TRPC1 ion channel

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Abstract

Familial Hypocalciuric Hypercalcemia (FHH) is a genetic condition associated with hypocalciuria, hypercalcemia and in some cases inappropriately high levels of circulating parathyroid hormone (PTH). FHH is associated with inactivating mutations in CaSR encoding the Ca2+ sensing receptor (CaSR), a G protein coupled receptor (GPCR) and GNA11 encoding G protein subunit alpha 11 (Gα11), implicating defective GPCR signaling as the root pathophysiology for FHH. However, the downstream mechanism by which CaSR activation inhibits PTH production/secretion is incompletely understood. Here, we show that mice lacking the transient receptor potential canonical channel 1 (TRPC1) develop chronic hypercalcemia, hypocalciuria, and elevated PTH levels mimicking human FHH. Ex vivo and in vitro studies reveal that TRPC1 serves a necessary and sufficient mediator to suppress PTH secretion from parathyroid glands (PTG) downstream of CaSR in response to high extracellular Ca2+ concentration. Gα11 physically interacts with both the N- and C-termini of TRPC1 and enhances CaSR-induced TRPC1 activity in transfected cells. These data identify TRPC1-mediated Ca2+ signaling as an essential component of the cellular apparatus controlling PTH secretion in the PTG downstream of CaSR.

Authors

Marta Onopiuk, Bonnie Eby, Vasyl Nesin, Peter Ngo, Megan Lerner, Caroline M. Gorvin, Victoria J. Stokes, Rajesh V. Thakker, Maria Luisa Brandi, Wenhan Chang, Mary Beth Humphrey, Leonidas Tsiokas, Kai Lau

Ribonuclease 1 attenuates septic cardiomyopathy and cardiac apoptosis in a murine model of polymicrobial sepsis

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Abstract

Septic cardiomyopathy is a life-threatening organ dysfunction caused by sepsis. Ribonuclease 1 (RNase 1) belongs to a group of host-defense peptides that specifically cleave extracellular RNA (eRNA). The activity of RNase1 is inhibited by ribonuclease-inhibitor 1 (RNH1). The role of RNase 1 in septic cardiomyopathy and associated cardiac apoptosis, however, is completely unknown. Here, we showed that sepsis resulted in a significant increase in RNH1 and eRNA serum levels compared to those of healthy subjects (p < 0.05). Treatment with RNase 1 resulted in a significant decrease of apoptosis, induced by the intrinsic pathway, and TNF expression in murine cardiomyocytes exposed to either necrotic cardiomyocytes or serum of septic patients for 16 h (p < 0.05). Furthermore, treatment of septic mice with RNase 1 resulted in a reduction in cardiac apoptosis, TNF expression and septic cardiomyopathy (p < 0.05). These data demonstrate that eRNA plays a crucial role in the pathophysiology of the organ (cardiac) dysfunction in sepsis and RNase and RNH1 may be new therapeutic targets/strategies to reduce the cardiac injury and dysfunction caused by sepsis.

Authors

Elisabeth Zechendorf, Caroline E O'Riordan, Lara Stiehler, Natalie Wischmeyer, Fausto Chiazza, Debora Collotta, Bernd Denecke, Sabrina Ernst, Gerhard Müller-Newen, Sina M. Coldewey, Bianka Wissuwa, Massimo Collino, Tim-Philipp Simon, Tobias Schuerholz, Christian Stoppe, Gernot Marx, Christoph Thiemermann, Lukas Martin