Search

Atrial fibrillation (AF) is the most common cardiac arrhythmia worldwide; however, the underlying causes of AF initiation are still poorly understood, particularly because currently available models do not allow in distinguishing the initial causes from maladaptive remodeling that induces and perpetuates AF. Lately, the genetic background has been proven to be important in the AF onset. iPSC-derived cardiomyocytes, being patient- and mutation-specific, may help solve this diatribe by showing the initial cell-autonomous changes underlying the development of the disease. Transcription factor paired-like homeodomain 2 (PITX2) has been identified as a key regulator of atrial development/differentiation, and the PITX2 genomic locus has the highest association with paroxysmal AF. PITX2 influences mitochondrial activity, and alterations in either its expression or function have been widely associated with AF. In this work, we investigate the activity of mitochondria in iPSC-derived atrial cardiomyocytes (aCMs) obtained from a young patient (24 years old) with paroxysmal AF, carrying a gain-of-function mutation in PITX2 (rs138163892) and from its isogenic control (CTRL) in which the heterozygous point mutation has been reverted to WT. PITX2 aCMs show a higher mitochondrial content, increased mitochondrial activity, and superoxide production under basal conditions when compared to CTRL aCMs. However, increasing mitochondrial workload by FCCP or p-adrenergic stimulation allows us to unmask mitochondrial defects in PITX2 aCMs, which are incapable of responding efficiently to the higher energy demand, determining ATP deficiency. [ABSTRACT FROM AUTHOR]

The mannose receptor C-type 1 (Mrc1) is a C-type lectin receptor expressed on the immune cells and sinusoidal endothelial cells (ECs) of several tissues, including the bone marrow (BM). Parallel to systemic metabolic alterations and hematopoietic cell proliferation, high-fat diet (HFD) feeding increases the expression of Mrc1 in sinusoidal ECs, thus calling for the investigation of its role in bone marrow cell reprogramming and the metabolic profile during obesity. Mrc1−/− mice and wild-type (WT) littermates were fed an HFD (45% Kcal/diet) for 20 weeks. Weight gain was monitored during the diet regimen and glucose and insulin tolerance were assessed. Extensive flow cytometry profiling, histological, and proteomic analyses were performed. After HFD feeding, Mrc1−/− mice presented impaired medullary hematopoiesis with reduced myeloid progenitors and mature cells in parallel with an increase in BM adipocytes compared to controls. Accordingly, circulating levels of neutrophils and pro-inflammatory monocytes decreased in Mrc1−/− mice together with reduced infiltration of macrophages in the visceral adipose tissue and the liver compared to controls. Liver histological profiling coupled with untargeted proteomic analysis revealed that Mrc1−/− mice presented decreased liver steatosis and the downregulation of proteins belonging to pathways involved in liver dysfunction. This profile was reflected by improved glucose and insulin response and reduced weight gain during HFD feeding in Mrc1−/− mice compared to controls. Our data show that during HFD feeding, mannose receptor deficiency impacts BM and circulating immune cell subsets, which is associated with reduced systemic inflammation and resistance to obesity development. [ABSTRACT FROM AUTHOR]

Rivaroxaban (RVX) was suggested to possess anti-inflammatory and vascular tone modulatory effects. The goal of this study was to investigate whether RVX impacts lipopolysaccharide (LPS)-induced acute vascular inflammatory response. Male rats were treated with 5 mg/kg RVX (oral gavage) followed by 10 mg/kg LPS i.p injection. Circulating levels of IL-6, MCP-1, VCAM-1, and ICAM-1 were measured in plasma 6 and 24 hours after LPS injection, while isolated aorta was used for gene expression analysis, immunohistochemistry, and vascular tone evaluation. RVX pre-treatment significantly reduced LPS mediated increase after 6h and 24h for IL-6 (4.4±2.2 and 2.8±1.7 fold), MCP-1 (1.4±1.5 and 1.3±1.4 fold) VCAM-1 (1.8±2.0 and 1.7±2.1 fold). A similar trend was observed in the aorta for iNOS (5.5±3.3 and 3.3±1.9 folds reduction, P<0.01 and P<0.001, respectively), VCAM-1 (1.3±1.2 and 1.4±1.3 fold reduction, P<0.05), and MCP-1 (3.9±2.2 and 1.9±1.6 fold reduction, P<0.01). Moreover, RVX pre-treatment, improved LPS-induced PE contractile dysfunction in aortic rings (Control vs LPS, Emax reduction = 35.4 and 31.19%, P<0.001; Control vs LPS+RVX, Emax reduction = 10.83 and 11.48%, P>0.05, respectively), resulting in 24.5% and 19.7% change in maximal constriction in LPS and LPS+RVX respectively. These data indicate that RVX pre-treatment attenuates LPS-induced acute vascular inflammation and contractile dysfunction. [ABSTRACT FROM AUTHOR]

Cholesterol homeostasis has a pivotal function in regulating immune cells. Here we show that apolipoprotein E (apoE) deficiency leads to the accumulation of cholesterol in the cell membrane of dendritic cells (DC), resulting in enhanced MHC-II-dependent antigen presentation and CD4+ T-cell activation. Results from WT and apoE KO bone marrow chimera suggest that apoE from cells of hematopoietic origin has immunomodulatory functions, regardless of the onset of hypercholesterolemia. Humans expressing apoE4 isoform (ε4/3-ε4/4) have increased circulating levels of activated T cells compared to those expressing WT apoE3 (ε3/3) or apoE2 isoform (ε2/3-ε2/2). This increase is caused by enhanced antigen-presentation by apoE4-expressing DCs, and is reversed when these DCs are incubated with serum containing WT apoE3. In summary, our study identifies myeloid-produced apoE as a key physiological modulator of DC antigen presentation function, paving the way for further explorations of apoE as a tool to improve the management of immune diseases. Cholesterol homeostasis can modulate immunity via multiple pathways. Here the authors show that apolipoprotein E, an important regulator of cholesterol, produced by myeloid cells can regulate T cell activation by controlling the antigen presentation activity of dendritic cells in both humans and mice. [ABSTRACT FROM AUTHOR]

Aims: Mitochondria are plastic organelles that continuously undergo biogenesis, fusion, fission, and mitophagy to control cellular energy metabolism, calcium homeostasis, hormones, sterols, and bile acids (BAs) synthesis. Here, we evaluated how the impairment of mitochondrial fusion in hepatocytes affects diet-induced liver steatosis and obesity., Methods and Results: Male mice selectively lacking the key protein involved in inner mitochondrial fusion, optic atrophy 1 (OPA1) (OPA1ΔHep) were fed a high fat diet (HFD) for 20 weeks. OPA1ΔHep mice were protected from the development of hepatic steatosis and obesity because of reduced lipid absorption; a profile which was accompanied by increased respiratory exchange ratio in vivo, suggesting a preference for carbohydrates in OPA1ΔHep compared to controls. At the molecular level, this phenotype emerged as a consequence of poor mitochondria-peroxisome- endoplasmic reticulum (ER) tethering in OPA1 deficient hepatocytes, which impaired BAs conjugation and release in the bile, thus impacting lipid absorption from the diet. Concordantly, the liver of subjects with non-alcoholic fatty liver disease (NAFLD) presented an increased expression of OPA1 and of the network of proteins involved in mitochondrial function when compared with controls., Conclusion: Patients with NAFLD present increased expression of proteins involved in mitochondrial fusion in the liver. The selective deficency of OPA1 in hepatocytes protects mice from HFD-induced metabolic dysfunction by reducing BAs secretion and dietary lipids absorption as a consequence of reduced liver mitochondria-peroxisome-ER tethering., Competing Interests: Conflict of interest: This article was handled by consulting editor Francesco Cosentino., (© The Author(s) 2023. Published by Oxford University Press on behalf of the European Society of Cardiology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

A fine balance between uptake, storage, and the use of high energy fuels, like lipids, is crucial in the homeostasis of different metabolic tissues. Nowhere is this balance more important and more precarious than in the heart. This highly energy-demanding muscle normally oxidizes almost all the available substrates to generate energy, with fatty acids being the preferred source under physiological conditions. In patients with cardiomyopathies and heart failure, changes in the main energetic substrate are observed; these hearts often prefer to utilize glucose rather than oxidizing fatty acids. An imbalance between uptake and oxidation of fatty acid can result in cellular lipid accumulation and cytotoxicity. In this review, we will focus on the sources and uptake pathways used to direct fatty acids to cardiomyocytes. We will then discuss the intracellular machinery used to either store or oxidize these lipids and explain how disruptions in homeostasis can lead to mitochondrial dysfunction and heart failure. Moreover, we will also discuss the role of cholesterol accumulation in cardiomyocytes. Our discussion will attempt to weave in vitro experiments and in vivo data from mice and humans and use several human diseases to illustrate metabolism gone haywire as a cause of or accomplice to cardiac dysfunction., Competing Interests: Conflict of interest: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© The Author(s) 2023. Published by Oxford University Press on behalf of the European Society of Cardiology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Aims: Leucocyte telomere length (LTL) shortening is a marker of cellular senescence and associates with increased risk of cardiovascular disease (CVD). A number of cardiovascular risk factors affect LTL, but the correlation between elevated LDL cholesterol (LDL-C) and shorter LTL is debated: in small cohorts including subjects with a clinical diagnosis of familial hypercholesterolaemia (FH). We assessed the relationship between LDL-C and LTL in subjects with genetic familial hypercholesterolaemia (HeFH) compared to those with clinically diagnosed, but not genetically confirmed FH (CD-FH), and normocholesterolaemic subjects., Methods and Results: LTL was measured in mononuclear cells-derived genomic DNA from 206 hypercholesterolaemic subjects (135 HeFH and 71 CD-FH) and 272 controls. HeFH presented shorter LTL vs. controls (1.27 ± 0.07 vs. 1.59 ± 0.04, P = 0.045). In particular, we found shorter LTL in young HeFH as compared to young controls (<35 y) (1.34 ± 0.08 vs. 1.64 ± 0.08, P = 0.019); moreover, LTL was shorter in statin-naïve HeFH subjects as compared to controls (1.23 ± 0.08 vs. 1.58 ± 0.04, P = 0.001). HeFH subjects presented shorter LTL compared to LDL-C matched CD-FH (1.33 ± 0.05 vs. 1.55 ± 0.08, P = 0.029). Shorter LTL was confirmed in leucocytes of LDLR-KO vs. wild-type mice and associated with lower abundance of long-term haematopoietic stem and progenitor cells (LT-HSPCs) in the bone marrow. Accordingly, HeFH subjects presented lower circulating haematopoietic precursors (CD34 + CD45dim cells) vs. CD-FH and controls., Conclusions: We found (i) shorter LTL in genetically determined hypercholesterolaemia, (ii) lower circulating haematopoietic precursors in HeFH subjects, and reduced bone marrow resident LT-HSPCs in LDLR-KO mice. We support early cellular senescence and haematopoietic alterations in subjects with FH., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2020. For permissions, please email: journals.permissions@oup.com.)

Aims: PCSK9 is secreted into the circulation, mainly by the liver, and interacts with low-density lipoprotein receptor (LDLR) homologous and non-homologous receptors, including CD36, thus favouring their intracellular degradation. As PCSK9 deficiency increases the expression of lipids and lipoprotein receptors, thus contributing to cellular lipid accumulation, we investigated whether this could affect heart metabolism and function., Methods and Results: Wild-type (WT), Pcsk9 KO, Liver conditional Pcsk9 KO and Pcsk9/Ldlr double KO male mice were fed for 20 weeks with a standard fat diet and then exercise resistance, muscle strength, and heart characteristics were evaluated. Pcsk9 KO presented reduced running resistance coupled to echocardiographic abnormalities suggestive of heart failure with preserved ejection fraction (HFpEF). Heart mitochondrial activity, following maximal coupled and uncoupled respiration, was reduced in Pcsk9 KO mice compared to WT mice and was coupled to major changes in cardiac metabolism together with increased expression of LDLR and CD36 and with lipid accumulation. A similar phenotype was observed in Pcsk9/Ldlr DKO, thus excluding a contribution for LDLR to cardiac impairment observed in Pcsk9 KO mice. Heart function profiling of the liver selective Pcsk9 KO model further excluded the involvement of circulating PCSK9 in the development of HFpEF, pointing to a possible role locally produced PCSK9. Concordantly, carriers of the R46L loss-of-function variant for PCSK9 presented increased left ventricular mass but similar ejection fraction compared to matched control subjects., Conclusion: PCSK9 deficiency impacts cardiac lipid metabolism in an LDLR independent manner and contributes to the development of HFpEF., (© The Author(s) 2021. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Aims: PCSK9 loss of function genetic variants are associated with lower low-density lipoprotein cholesterol but also with higher plasma glucose levels and increased risk of Type 2 diabetes mellitus. Here, we investigated the molecular mechanisms underlying this association., Methods and Results: Pcsk9 KO, WT, Pcsk9/Ldlr double KO (DKO), Ldlr KO, albumin AlbCre+/Pcsk9LoxP/LoxP (liver-selective Pcsk9 knock-out mice), and AlbCre-/Pcsk9LoxP/LoxP mice were used. GTT, ITT, insulin and C-peptide plasma levels, pancreas morphology, and cholesterol accumulation in pancreatic islets were studied in the different animal models. Glucose clearance was significantly impaired in Pcsk9 KO mice fed with a standard or a high-fat diet for 20 weeks compared with WT animals; insulin sensitivity, however, was not affected. A detailed analysis of pancreas morphology of Pcsk9 KO mice vs. controls revealed larger islets with increased accumulation of cholesteryl esters, paralleled by increased insulin intracellular levels and decreased plasma insulin, and C-peptide levels. This phenotype was completely reverted in Pcsk9/Ldlr DKO mice implying the low-density lipoprotein receptor (LDLR) as the proprotein convertase subtilisin/kexin Type 9 (PCSK9) target responsible for the phenotype observed. Further studies in albumin AlbCre+/Pcsk9LoxP/LoxP mice, which lack detectable circulating PCSK9, also showed a complete recovery of the phenotype, thus indicating that circulating, liver-derived PCSK9, the principal target of monoclonal antibodies, does not impact beta-cell function and insulin secretion., Conclusion: PCSK9 critically controls LDLR expression in pancreas perhaps contributing to the maintenance of a proper physiological balance to limit cholesterol overload in beta cells. This effect is independent of circulating PCSK9 and is probably related to locally produced PCSK9.