scholarly journals Modulation of cardiac Na+,K+-ATPase cell surface abundance by simulated ischemia-reperfusion and ouabain preconditioning

2013 ◽  
Vol 304 (1) ◽  
pp. H94-H103 ◽  
Author(s):  
Aude Belliard ◽  
Yoann Sottejeau ◽  
Qiming Duan ◽  
Jessa L. Karabin ◽  
Sandrine V. Pierre
Keyword(s):  
Cell Surface ◽  
Atpase Activity ◽  
Ion Transport ◽  
Cell Viability ◽  
Ischemia Reperfusion ◽  
Resistant Mutant ◽  
Surface Expression ◽  
Live Cells ◽  
Mutant Form ◽  
Dependent Manner

Na+,K+-ATPase and cell survival were investigated in a cellular model of ischemia-reperfusion (I/R)-induced injury and protection by ouabain-induced preconditioning (OPC). Rat neonatal cardiac myocytes were subjected to 30 min of substrate and coverslip-induced ischemia followed by 30 min of simulated reperfusion. This significantly compromised cell viability as documented by lactate dehydrogenase release and Annexin V/propidium iodide staining. Total Na+,K+-ATPase α1- and α3-polypeptide expression remained unchanged, but cell surface biotinylation and immunostaining studies revealed that α1-cell surface abundance was significantly decreased. Na+,K+-ATPase-activity in crude homogenates and 86Rb+ transport in live cells were both significantly decreased by about 30% after I/R. OPC, induced by a 4-min exposure to 10 μM ouabain that ended 8 min before the beginning of ischemia, increased cell viability in a PKCε-dependent manner. This was comparable with the protective effect of OPC previously reported in intact heart preparations. OPC prevented I/R-induced decrease of Na+,K+-ATPase activity and surface expression. This model also revealed that Na+,K+-ATPase-mediated 86Rb+ uptake was not restored to control levels in the OPC group, suggesting that the increased viability was not conferred by an increased Na+,K+-ATPase-mediated ion transport capacity at the cell membrane. Consistent with this observation, transient expression of an internalization-resistant mutant form of Na+,K+-ATPase α1 known to have increased surface abundance without increased ion transport activity successfully reduced I/R-induced cell death. These results suggest that maintenance of Na+,K+-ATPase cell surface abundance is critical to myocyte survival after an ischemic attack and plays a role in OPC-induced protection. They further suggest that the protection conferred by increased surface expression of Na+,K+-ATPase may be independent of ion transport.

scholarly journals Regulation of the Expression, Oligomerisation and Signaling of the Inhibitory Receptor CLEC12A by Cysteine Residues in the Stalk Region

2021 ◽  
Vol 22 (19) ◽  
pp. 10207
Author(s):  
Julien Vitry ◽  
Guillaume Paré ◽  
Andréa Murru ◽  
Xavier Charest-Morin ◽  
Halim Maaroufi ◽  
...  
Keyword(s):  
Cell Surface ◽  
Cell Activation ◽  
Secretory Pathway ◽  
Surface Expression ◽  
Site Directed Mutagenesis ◽  
Cell Surface Expression ◽  
Dependent Manner ◽  
Inhibitory Receptor ◽  
Lectin Receptors ◽  
Stalk Domain

CLEC12A is a myeloid inhibitory receptor that negatively regulates inflammation in mouse models of autoimmune and autoinflammatory arthritis. Reduced CLEC12A expression enhances myeloid cell activation and inflammation in CLEC12A knock-out mice with collagen antibody-induced or gout-like arthritis. Similarly to other C-type lectin receptors, CLEC12A harbours a stalk domain between its ligand binding and transmembrane domains. While it is presumed that the cysteines in the stalk domain have multimerisation properties, their role in CLEC12A expression and/or signaling remain unknown. We thus used site-directed mutagenesis to determine whether the stalk domain cysteines play a role in CLEC12A expression, internalisation, oligomerisation, and/or signaling. Mutation of C118 blocks CLEC12A transport through the secretory pathway diminishing its cell-surface expression. In contrast, mutating C130 does not affect CLEC12A cell-surface expression but increases its oligomerisation, inducing ligand-independent phosphorylation of the receptor. Moreover, we provide evidence that CLEC12A dimerisation is regulated in a redox-dependent manner. We also show that antibody-induced CLEC12A cross-linking induces flotillin oligomerisation in insoluble membrane domains in which CLEC12A signals. Taken together, these data indicate that the stalk cysteines in CLEC12A differentially modulate this inhibitory receptor’s expression, oligomerisation and signaling, suggestive of the regulation of CLEC12A in a redox-dependent manner during inflammation.

scholarly journals Dectin-1-Mediated Production of Pro-Inflammatory Cytokines Induced by Yeast β-Glucans in Bovine Monocytes

2021 ◽  
Vol 12 ◽  
Author(s):  
Ana R. V. Pedro ◽  
Tânia Lima ◽  
Ricardo Fróis-Martins ◽  
Bárbara Leal ◽  
Isabel C. Ramos ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Surface ◽  
Inflammatory Cytokines ◽  
Surface Expression ◽  
Cell Surface Receptor ◽  
Dependent Manner ◽  
Feed Supplements ◽  
Surface Receptor ◽  
Dose Dependent ◽  
Pro Inflammatory Cytokines

Yeast-derived products containing β-glucans have long been used as feed supplements in domesticated animals in an attempt to increase immunity. β-glucans are mainly recognized by the cell surface receptor CLEC7A, also designated Dectin-1. Although the immune mechanisms elicited through Dectin-1 activation have been studied in detail in mice and humans, they are poorly understood in other species. Here, we evaluated the response of bovine monocytes to soluble and particulate purified β-glucans, and also to Zymosan. Our results show that particulate, but not soluble β-glucans, can upregulate the surface expression of costimulatory molecules CD80 and CD86 on bovine monocytes. In addition, stimulated cells increased production of IL-8 and of TNF, IL1B, and IL6 mRNA expression, in a dose-dependent manner, which correlated positively with CLEC7A gene expression. Production of IL-8 and TNF expression decreased significantly after CLEC7A knockdown using two different pairs of siRNAs. Overall, we demonstrated here that bovine monocytes respond to particulate β-glucans, through Dectin-1, by increasing the expression of pro-inflammatory cytokines. Our data support further studies in cattle on the induction of trained immunity using dietary β-glucans.

Succinate alters respiration, membrane potential, and intracellular K+ in proximal tubule

1988 ◽  
Vol 255 (6) ◽  
pp. F1170-F1177 ◽  
Author(s):  
S. R. Gullans ◽  
B. C. Kone ◽  
M. J. Avison ◽  
G. Giebisch
Keyword(s):  
Membrane Potential ◽  
Atpase Activity ◽  
Ion Transport ◽  
Proximal Tubule ◽  
Basolateral Membrane ◽  
Coupling Efficiency ◽  
Atp Synthesis ◽  
Dependent Manner ◽  
Kinetic Evaluation ◽  
Apparent Increase

Succinate, a dicarboxylic acid, is an intermediate in the Krebs cycle that is transported and metabolized by the renal proximal tubule. It is also known to increase proximal tubule transport of phosphate and glucose but not fluid by unknown mechanisms. In the present study, succinate increased proximal tubule respiration in a dose-dependent manner, and a kinetic evaluation indicated that two separate processes were activated. A lower-affinity (Km = 0.9 mM), higher-capacity stimulation (Vmax increase of 49%) was attributed to a decrease in the mitochondrial coupling efficiency. A higher-affinity process (Km = 0.012 mM) was related to an apparent increase in ATP synthesis. The apparent increase in ATP synthesis was not associated with a change in Na+-K+-ATPase activity, however, but rather indicated a 49% increase in ion transport-independent ATP utilization. Basolateral membrane potential hyperpolarized by -7 mV in the presence of succinate, and this was related to an increase in the K+ transference number. Finally, 1 and 5 mM succinate promoted a net cellular uptake of K+, leading to an 11% increase in intracellular K+, which was not the result of an increase in Na+-K+-ATPase activity. Thus the cellular entry and metabolism of succinate promotes multiple changes in ion transport without altering Na+-K+-ATPase activity.

scholarly journals Intracellular Na+ Controls Cell Surface Expression of Na,K-ATPase via a cAMP-independent PKA Pathway in Mammalian Kidney Collecting Duct Cells

2003 ◽  
Vol 14 (7) ◽  
pp. 2677-2688 ◽  
Author(s):  
Manlio Vinciguerra ◽  
Georges Deschênes ◽  
Udo Hasler ◽  
David Mordasini ◽  
Martine Rousselot ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Cell Surface ◽  
Atpase Activity ◽  
Collecting Duct ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Cortical Collecting Duct ◽  
Mammalian Kidney ◽  
Duct Cells ◽  
Collecting Duct Cells

In the mammalian kidney the fine control of Na+ reabsorption takes place in collecting duct principal cells where basolateral Na,K-ATPase provides the driving force for vectorial Na+ transport. In the cortical collecting duct (CCD), a rise in intracellular Na+ concentration ([Na+]i) was shown to increase Na,K-ATPase activity and the number of ouabain binding sites, but the mechanism responsible for this event has not yet been elucidated. A rise in [Na+]i caused by incubation with the Na+ ionophore nystatin, increased Na,K-ATPase activity and cell surface expression to the same extent in isolated rat CCD. In cultured mouse mpkCCDcl4 collecting duct cells, increasing [Na+]i either by cell membrane permeabilization with amphotericin B or nystatin, or by incubating cells in a K+-free medium, also increased Na,K-ATPase cell surface expression. The [Na+]i-dependent increase in Na,K-ATPase cell-surface expression was prevented by PKA inhibitors H89 and PKI. Moreover, the effects of [Na+]i and cAMP were not additive. However, [Na+]i-dependent activation of PKA was not associated with an increase in cellular cAMP but was prevented by inhibiting the proteasome. These findings suggest that Na,K-ATPase may be recruited to the cell membrane following an increase in [Na+]i through cAMP-independent PKA activation that is itself dependent on proteasomal activity.

scholarly journals All-Trans Retinoic Acid Enhances Bacterial Flagellin-Stimulated Proinflammatory Responses in Human Monocyte THP-1 Cells by Upregulating CD14

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Thi Xoan Hoang ◽  
Jong Hyeok Jung ◽  
Jae Young Kim
Keyword(s):  
Retinoic Acid ◽  
Cell Surface ◽  
Human Monocyte ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Dependent Manner ◽  
Atra Treatment ◽  
Trans Retinoic Acid ◽  
All Trans Retinoic Acid ◽  
Proinflammatory Responses

All-trans retinoic acid (ATRA), an active form of vitamin A, exerts immunomodulatory functions. In this study, we examined the immune potentiating effect of ATRA on bacterial flagellin-induced NF-κB activation and proinflammatory cytokine production in human monocytic cell line THP-1. ATRA treatment significantly enhanced the flagellin-induced NF-κB/AP-1 activity in THP-1 via the RAR/RXR pathway. Similarly, ATRA enhanced the expression and production of TNF-α and IL-1β in THP-1 cells upon flagellin challenge. The cell surface expression of toll-like receptor 5 (TLR5), which is the receptor for bacterial flagellin, was significantly reduced by ATRA in a concentration- and time-dependent manner. To determine the mechanisms underlying the ATRA-enhanced immune response against bacterial flagellin despite the reduced cell surface expression of TLR5 in ATRA-treated THP-1, we examined the cell surface expression of CD14, which has been proposed to be a TLR co-receptor that enhances the response to microbial components. The cell surface expression of CD14 was significantly enhanced by ATRA treatment, especially in the presence of flagellin. Anti-CD14 antibody treatment prior to ATRA and flagellin treatments completely abolished ATRA-enhanced TNF-α and IL-1β production. Our results suggest that ATRA enhances flagellin-stimulated proinflammatory responses in human monocyte THP-1 cells by upregulating CD14 in a RAR/RXR-dependent manner.

CD39/NTPDase1 Variants Identified in Human Neutrophils Regulate Antithrombotic Activity.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 3088-3088 ◽  
Author(s):  
Kim E. Olson ◽  
Dianne Pulte ◽  
Marinus Johan Broekman ◽  
Ashley E. Olson ◽  
Joan Drosopoulos ◽  
...  
Keyword(s):  
Cell Surface ◽  
Atpase Activity ◽  
Western Blot ◽  
Transmembrane Domain ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Human Neutrophils ◽  
Platelet Activity ◽  
Total Rna ◽  
Cos Cells

Abstract Blood-borne cellular elements expressing ectonucleotidase activity have been shown to regulate platelet activation and recruitment in response to agonists. In particular, exposure of a platelet releasate to isolated neutrophils (PMN) results in loss of its platelet activating activity in a subsequent assay (Valles et al, J Clin Invest1993, 92:1357–1365). Whereas expression of CD39 on vascular endothelial cells has been well characterized, expression on leukocytes has been less well studied. Freshly prepared lymphocyte and PMN cell populations were evaluated for both cell surface expression of CD39 and ectonucleotidase activity. FACS analysis showed that 98% of PMN were positive for CD39 compared to only 20% of lymphocytes. In addition, neutrophils stained more intensely, indicating the presence of a higher quantity of cell surface-expressed CD39. Interestingly, neutrophils exhibited only 1/3 of the ATPase and 1/2 of the ADPase activities of the same number of lymphocytes, although the latter are thought to have greater antithrombotic capacity. RT-PCR products from total RNA isolated from lymphocytes and PMN were sequenced. This revealed alternately spliced CD39 mRNA species present in PMN at levels equal to that of CD39 mRNA. In contrast, lymphocytes, which showed much higher levels of CD39 mRNA, expressed these variants at much lower levels. RACE analyses of cDNAs generated from total RNA demonstrated two CD39 gene-derived mRNAs. Each was comprised of an alternate 3′ segment lacking the C-terminal transmembrane domain, and distinguished by an internal deletion. Myc- and Flag-tagged constructs expressed in COS cells resulted in cell surface expression of the respectively tagged variants (immunocytochemistry, western blot analyses of plasma membrane preparations). Membrane preparations assayed for enzyme activity revealed no apyrase activity for either molecule expressed alone or together. Co-transfection of CD39 with equal amounts of either construct singly or in combination resulted in a 30-50% decrease in ATPase activity compared to CD39 alone. Similarly, CD39 co-expressed with either construct alone lost 75–90% of its ADPase activity. Unexpectedly, co-transfection of CD39 with both variants together resulted in a 20–40% increase in ADPase activity. Glutaraldehyde cross-linking of membrane preparations from triply transfected COS cells followed by immunoprecipitation and western blot analyses demonstrated the presence of all three species in higher order complexes. Thus, both variants can simultaneously associate with CD39, generating hetero-multimers with altered substrate preference and catalytic efficiency compared to CD39 tetramers. These observations add to our understanding of the regulation of ectonucleotidase activity at the cell surface. The balanced expression of CD39 and its two identified variants may underlie the anti-platelet activity of neutrophils previously reported. The finding that association of CD39 with either construct alone results in near complete loss of ADPase activity with only partial diminution of ATPase activity suggests a possible etiology for a pro-thrombotic phenotype.

Erlotinib Antagonizes Efflux Via ABC Transporters and Decreases P-Gp Cell Surface Expression by Inhibiting SRC Kinase and mTOR Pathways in Acute Myeloid Leukemia (AML)

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 2564-2564 ◽  
Author(s):  
Elodie Lainey ◽  
Marie Sebert ◽  
Cyrielle Bouteloup ◽  
Carole Leroy ◽  
Sylvain Thepot ◽  
...  
Keyword(s):  
Cell Surface ◽  
Protein Expression ◽  
Atpase Activity ◽  
Abc Transporters ◽  
Ex Vivo ◽  
Synergistic Effects ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Drug Efflux ◽  
Hoechst 33342

Abstract Abstract 2564 Background: Erlotinib (Erlo) was originally developed as an epidermal growth factor receptor inhibitor, yet it also exerts antileukemic “off-target” effects, in vitro and in vivo in MDS and AML (Boehrer et al., Blood, 2008). In a preliminary pre-clinical study, we observed that Erlo increased chemosensitivity to current AML drugs in different AML cell lines and in ex vivo AML patient cells (n=3) (ASH 2010, 2163). Those first results suggested an implication of ABC-transporters in the potentiation of apoptosis. Here, we bring direct evidence for Erlo's ability to hinder efflux pumps and to decrease their expression on AML cells. Methods: Drug efflux via ABC-transporters (substrate: mitoxantrone-MTZ or doxorubicin-Dox), and specific efflux via P-gp (substrates: DioC23 and Rho-123), MRP (s: Calcein and CDCFDA) and BCRP (s: Hoechst 33342) were quantified by FACS following incubation with 10mM Erlo. Intracellular VP-16) content was quantified by Rapid Resolution Liquid Chromatography (RRLC). Biochemical inhibitors of the respective ABC-transporters (CSA (1μM), verapamil (Vera-10μM), MK571 (10μM), KO143 (500nM) served as positive controls. To assess chemosensitivity, 10mM Erlo was combined to AraC (100nM), Dox (100nM), or VP-16 (1mM) and apoptosis over-time (24, 48, 72h) quantified by DioC3(6)/PI staining. Assessment of sensitivity to the drug combinations listed above were carried out in KG-1 cells, and its more immature variant KG-1a and in ex vivo CD34+ marrow cells from AML patients (AML post MDS n=5, de novo AML n=5). P-gp's ATPase activity was quantified with the luminescence-based Pgp-Gloä Assay System. Surface expression of P-gp was determined by FACS analysis and total protein expression of MRP, BCRP and P-gp by immunoblot analysis. Functional relevance of signaling pathways was tested using the SRC inhibitor PP2 (10μM) and the mTOR inhibitor Rapamicin (10nM). Results: We found that I) Erlo inhibited efflux via P-gp, MRP and BCRP as demonstrated by increased intracellular retention of DioC23/Rho-123, Calcein/CDCFDA and Hoechst 33342, respectively, andby its ability to retain MTX (300nM) and Dox (200nM) intracellularly II) Inhibition of drug efflux was higher in KG-1 than in KG-1a cellss, in agreement with a lower expression of P-gp and BCRP on KG-1a as compared to KG-1 cells; III) Quantification of VP-16 by RRLC after incubation with or without Erlo showed the ability of Erlo to increase intracellular VP-16 contents by approximately 60%; IV) Erlo increased ATPase activity in a dose-dependant manner, supporting the notion that Erlo is a competitive inhibitor of P-gp; IV) Erlo combined to VP-16 induced synergistic effects on apoptosis in KG-1 cells, and to a lesser extent in KG-1a (48h KG-1: Erlo 20%, VP-16 38%, Erlo+VP16 78%, KG-1a 48h: Erlo 10%, VP-16: 12%, Erlo+VP16: 35%); V) 48h of incubation with Erlo reduced cell surface expression of P-gp in KG-1 cells by 50%, whereas total P-gp protein expression remained unchanged, suggesting that Erlo interferes exclusively with the protein form expressed on the cell surface, VI) Decrease of P-gp cell surface expression was recapitulated upon incubation with PP2 (10μM) or Rapamicin (10nM); VII) the combination of Erlo+VP-16 in 10 AML-patient samples induced synergistic effects on apoptosis in 5 of them and additive effects in 3 of them. Conclusions: We here confirm that Erlo increases sensitivity towards chemotherapeutic agents subjected to drug efflux via ABC-transporters and delineate the molecular pathways conveying these effects. Disclosures: Fenaux: Celgene: Honoraria, Research Funding.

scholarly journals A mammalian homolog of the zebrafish transmembrane protein 2 (TMEM2) is the long-sought-after cell-surface hyaluronidase

2017 ◽  
Vol 292 (18) ◽  
pp. 7304-7313 ◽  
Author(s):  
Hayato Yamamoto ◽  
Yuki Tobisawa ◽  
Toshihiro Inubushi ◽  
Fumitoshi Irie ◽  
Chikara Ohyama ◽  
...  
Keyword(s):  
Cell Surface ◽  
Dermatan Sulfate ◽  
Transmembrane Protein ◽  
Live Cells ◽  
Dependent Manner ◽  
Cellular Functions ◽  
Ph Optimum ◽  
Hyaluronidase Activity ◽  
A Cell ◽  
Intermediate Size

Hyaluronan (HA) is an extremely large polysaccharide (glycosaminoglycan) involved in many cellular functions. HA catabolism is thought to involve the initial cleavage of extracellular high-molecular-weight (HMW) HA into intermediate-size HA by an extracellular or cell-surface hyaluronidase, internalization of intermediate-size HA, and complete degradation into monosaccharides in lysosomes. Despite considerable research, the identity of the hyaluronidase responsible for the initial HA cleavage in the extracellular space remains elusive. HYAL1 and HYAL2 have properties more consistent with lysosomal hyaluronidases, whereas CEMIP/KIAA1199, a recently identified HA-binding molecule that has HA-degrading activity, requires the participation of the clathrin-coated pit pathway of live cells for HA degradation. Here we show that transmembrane protein 2 (TMEM2), a mammalian homolog of a protein playing a role in zebrafish endocardial cushion development, is a cell-surface hyaluronidase. Live immunostaining and surface biotinylation assays confirmed that mouse TMEM2 is expressed on the cell surface in a type II transmembrane topology. TMEM2 degraded HMW-HA into ∼5-kDa fragments but did not cleave chondroitin sulfate or dermatan sulfate, indicating its specificity to HA. The hyaluronidase activity of TMEM2 was Ca2+-dependent; the enzyme's pH optimum is around 6–7, and unlike CEMIP/KIAA1199, TMEM2 does not require the participation of live cells for its hyaluronidase activity. Moreover, TMEM2-expressing cells could eliminate HA immobilized on a glass surface in a contact-dependent manner. Together, these data suggest that TMEM2 is the long-sought-after hyaluronidase that cleaves extracellular HMW-HA into intermediate-size fragments before internalization and degradation in the lysosome.

scholarly journals Distinct Cell Surface Expression Patterns of N-Glycosylation Site Mutants of AMPA-Type Glutamate Receptor under the Homo-Oligomeric Expression Conditions

2020 ◽  
Vol 21 (14) ◽  
pp. 5101
Author(s):  
Jyoji Morise ◽  
Saki Yamamoto ◽  
Ryosuke Midorikawa ◽  
Kogo Takamiya ◽  
Motohiro Nonaka ◽  
...  
Keyword(s):  
Cell Surface ◽  
Glutamate Receptor ◽  
Expression Patterns ◽  
Surface Expression ◽  
Glycosylation Site ◽  
Synaptic Activity ◽  
Cell Surface Expression ◽  
Dependent Manner ◽  
Distinct Cell

The AMPA-type glutamate receptor (AMPAR) is a homotetrameric or heterotetrameric ion channel composed of various combinations of four subunits (GluA1–4), and its abundance in the synapse determines the strength of synaptic activity. The formation of oligomers in the endoplasmatic reticulum (ER) is crucial for AMPAR subunits’ ER-exit and translocation to the cell membrane. Although N-glycosylation on different AMPAR subunits has been shown to regulate the ER-exit of hetero-oligomers, its role in the ER-exit of homo-oligomers remains unclear. In this study, we investigated the role of N-glycans at GluA1N63/N363 and GluA2N370 in ER-exit under the homo-oligomeric expression conditions, whose mutants are known to show low cell surface expressions. In contrast to the N-glycosylation site mutant GluA1N63Q, the cell surface expression levels of GluA1N363Q and GluA2N370Q increased in a time-dependent manner. Unlike wild-type (WT) GluA1, GluA2WT rescued surface GluA2N370Q expression. Additionally, the expression of GluA1N63Q reduced the cell surface expression level of GluA1WT. In conclusion, our findings suggest that these N-glycans have distinct roles in the ER-exit of GluA1 and GluA2 homo-oligomers; N-glycan at GluA1N63 is a prerequisite for GluA1 ER-exit, whereas N-glycans at GluA1N363 and GluA2N370 control the ER-exit rate.

Abstract 379: Inhibition of Bcl-x Phosphorylation Prevents Cardiomyocyte Death, Cardiac Remodeling and Heart Failure After Myocardial Infarction

2015 ◽  
Vol 117 (suppl_1) ◽  
Author(s):  
Michinari Nakamura ◽  
Peiyong Zhai ◽  
Dominic D Re ◽  
Junichi Sadoshima
Keyword(s):  
Myocardial Infarction ◽  
Heart Failure ◽  
Cardiac Remodeling ◽  
Ischemia Reperfusion ◽  
Resistant Mutant ◽  
Cardiac Contraction ◽  
Dependent Manner ◽  
Infarct Area

Cardiac remodeling promotes heart failure (HF). Cardiomyocyte (CM) death is one of the mechanisms to develop cardiac remodeling. We recently reported that Mst1 phosphorylates Bcl-xL at Ser14, which promotes apoptosis by inducing dissociation of Bcl-xL from Bax and consequent activation of Bax in CMs. Its phosphorylation is increased in response to ischemia-reperfusion (IR) in an Mst1-dependent manner. However, the functional significance of endogenous Bcl-xL phosphorylation remains unclear in vivo. To address this question, knock-in (KI) mice with alanine mutation at Ser14 in Bcl-x were generated. At baseline, cardiac function was similar between wild-type (WT) and heterozygous KI (HKI) mice (EF 76% and 79%, respectively). HKI mice exhibited smaller % infarct area (30%) than WT (43%) (p=0.016) upon IR, suggesting that phosphorylation of endogenous Bcl-xL at Ser14 plays an essential role in mediating IR injury. In order to test the role of Bcl-xL phosphorylation in the development of HF, HKI and WT mice were subjected to permanent ligation of LAD for 4 weeks. During progression of cardiac remodeling, Mst1 was activated in both WT and HKI mice. Phosphorylation of Bcl-xL and Bcl-xS, an alternative transcriptional variant of Bcl-x, both at Ser14, were increased in WT mice, which were abrogated in HKI mice. The infarct area evaluated with TTC staining at Day 1 was similar in WT and HKI mice (59.1% and 61.2%, p=0.65). Four weeks after myocardial infarction (MI), WT mice exhibited lower cardiac contraction (EF 46.5%) and higher LVEDP (10.8mmHg) than those in HKI mice (EF 68.9% and LVEDP 7.0mmHg) (both p<0.05). Scar area and TUNEL-positive CMs were greater in WT (49.0% and 1.6%, respectively) than in HKI mice (29.2% and 0.4%, respectively) (both p<0.05). Cleaved caspase 3 and 9 were significantly increased (3.2- and 5.7-fold, respectively) in WT but not in HKI mice. In vitro experiments with overexpression of phospho-mimicking mutant (Bcl-xS-S14D) showed 13% reduction in cell viability compared with that of phospho-resistant mutant (Bcl-xS-S14A) (p=0.01%). Our results suggest that phosphorylation of Bcl-xL and Bcl-xS at Ser14 contributes to CM death in response to IR and chronic MI in vivo, thereby promoting cardiac remodeling and HF.

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