Arrhythmogenic Cardiomyopathy: Molecular Insights for Improved Therapeutic Design

Arrhythmogenic cardiomyopathy (ACM) is an inherited disorder characterized by structural and electrical cardiac abnormalities, including myocardial fibro-fatty replacement. Its pathological ventricular substrate predisposes subjects to an increased risk of sudden cardiac death (SCD). ACM is a notorious cause of SCD in young athletes, and exercise has been documented to accelerate its progression. Although the genetic culprits are not exclusively limited to the intercalated disc, the majority of ACM-linked variants reside within desmosomal genes and are transmitted via Mendelian inheritance patterns; however, penetrance is highly variable. Its natural history features an initial “concealed phase” that results in patients being vulnerable to malignant arrhythmias prior to the onset of structural changes. Lack of effective therapies that target its pathophysiology renders management of patients challenging due to its progressive nature, and has highlighted a critical need to improve our understanding of its underlying mechanistic basis. In vitro and in vivo studies have begun to unravel the molecular consequences associated with disease causing variants, including altered Wnt/β-catenin signaling. Characterization of ACM mouse models has facilitated the evaluation of new therapeutic approaches. Improved molecular insight into the condition promises to usher in novel forms of therapy that will lead to improved care at the clinical bedside.

Download Full-text

The Novel Role of PGC1α in Bone Metabolism

International Journal of Molecular Sciences ◽

10.3390/ijms22094670 ◽

2021 ◽

Vol 22 (9) ◽

pp. 4670

Author(s):

Cinzia Buccoliero ◽

Manuela Dicarlo ◽

Patrizia Pignataro ◽

Francesco Gaccione ◽

Silvia Colucci ◽

...

Keyword(s):

Bone Metabolism ◽

Osteoblastic Differentiation ◽

In Vivo Studies ◽

Peroxisome Proliferator ◽

Sirtuin 3 ◽

Peroxisome Proliferator Activated Receptor ◽

Increased Risk

Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) is a protein that promotes transcription of numerous genes, particularly those responsible for the regulation of mitochondrial biogenesis. Evidence for a key role of PGC1α in bone metabolism is very recent. In vivo studies showed that PGC1α deletion negatively affects cortical thickness, trabecular organization and resistance to flexion, resulting in increased risk of fracture. Furthermore, in a mouse model of bone disease, PGC1α activation stimulates osteoblastic gene expression and inhibits atrogene transcription. PGC1α overexpression positively affects the activity of Sirtuin 3, a mitochondrial nicotinammide adenina dinucleotide (NAD)-dependent deacetylase, on osteoblastic differentiation. In vitro, PGC1α overexpression prevents the reduction of mitochondrial density, membrane potential and alkaline phosphatase activity caused by Sirtuin 3 knockdown in osteoblasts. Moreover, PGC1α influences the commitment of skeletal stem cells towards an osteogenic lineage, while negatively affects marrow adipose tissue accumulation. In this review, we will focus on recent findings about PGC1α action on bone metabolism, in vivo and in vitro, and in pathologies that cause bone loss, such as osteoporosis and type 2 diabetes.

Download Full-text

The ligand specificity of the G-protein-coupled receptor GPR34

Biochemical Journal ◽

10.1042/bj20112090 ◽

2012 ◽

Vol 443 (3) ◽

pp. 841-850 ◽

Cited By ~ 20

Author(s):

Lars Ritscher ◽

Eva Engemaier ◽

Claudia Stäubert ◽

Ines Liebscher ◽

Philipp Schmidt ◽

...

Keyword(s):

Structural Changes ◽

Transmembrane Helix ◽

In Vivo Studies ◽

Ligand Specificity ◽

Functional Specification ◽

Agonistic Activity ◽

Human Orthologue ◽

Lipid Compounds

Lyso-PS (lyso-phosphatidylserine) has been shown to activate the Gi/o-protein-coupled receptor GPR34. Since in vitro and in vivo studies provided controversial results in assigning lyso-PS as the endogenous agonist for GPR34, we investigated the evolutionary conservation of agonist specificity in more detail. Except for some fish GPR34 subtypes, lyso-PS has no or very weak agonistic activity at most vertebrate GPR34 orthologues investigated. Using chimaeras we identified single positions in the second extracellular loop and the transmembrane helix 5 of carp subtype 2a that, if transferred to the human orthologue, enabled lyso-PS to activate the human GPR34. Significant improvement of agonist efficacy by changing only a few positions strongly argues against the hypothesis that nature optimized GPR34 as the receptor for lyso-PS. Phylogenetic analysis revealed several positions in some fish GPR34 orthologues which are under positive selection. These structural changes may indicate functional specification of these orthologues which can explain the species- and subtype-specific pharmacology of lyso-PS. Furthermore, we identified aminoethyl-carbamoyl ATP as an antagonist of carp GPR34, indicating ligand promiscuity with non-lipid compounds. The results of the present study suggest that lyso-PS has only a random agonistic activity at some GPR34 orthologues and the search for the endogenous agonist should consider additional chemical entities.

Download Full-text

2288Oxidized LDL/CD36/PPARg circuitry is a trigger of adipogenesis in arrhythmogenic cardiomyopathy

European Heart Journal ◽

10.1093/eurheartj/ehz748.0133 ◽

2019 ◽

Vol 40 (Supplement_1) ◽

Author(s):

I Stadiotti ◽

E Sommariva ◽

M Casella ◽

V Catto ◽

A Dello Russo ◽

...

Keyword(s):

Oxidative Stress ◽

Lipid Accumulation ◽

Foam Cell ◽

Plasma Cholesterol ◽

Foam Cell Formation ◽

Arrhythmogenic Cardiomyopathy ◽

Knock Out ◽

Fatty Replacement

Abstract Background Arrhythmogenic Cardiomyopathy (ACM) is a genetic condition hallmarked by ventricular fibro-fatty replacement and arrhythmias. Cardiac mesenchymal stromal cells (C-MSC) differentiate into adipocytes in ACM hearts, through the activation of PPARγ, caused by ACM mutations (e.g. PKP2). The clinical phenotype of ACM is variable for poorly understood reasons. The only recognized cofactor is physical exercise, which is known to increases oxidative stress. An accepted marker of exercise-induced oxidative stress is 13HODE, a component of oxLDL and direct activator of PPARγ. In macrophages, during foam cell formation, 13HODE creates a feed-forward loop increasing both PPARγ and the oxLDL receptor CD36, resulting in fat accumulation. Purpose To investigate oxLDL effects on ACM adipogenesis and to dissect the involved pathways. Methods We analyzed plasmas (n=42) and ventricular tissues (n=4) of ACM patients and matched healthy controls (HC). For in vitro experiments, ACM and HC C-MSC (n=10) have been used, while in vivo experiments have been conducted in heterozygous Pkp2 knock-out mice (Pkp2+/−; n=10). Results We observed higher plasma oxLDL in ACM patients compared to HC (ACM 246.70±55.89 vs HC 102.5±17.95ng/ml; p=0.019). oxLDL levels also discriminate between ACM patients with overt phenotype and their unaffected relatives carriers of the same causative mutations (p=0.03). We observed higher oxidative stress (MDA intensity 40.87±11.76 fold; p=0.015) and CD36 levels (14.72±2.10 fold; p=0.0007) in ACM ventricular tissue, compared to HC. In basal conditions, ACM C-MSC showed greater oxidative stress (MDA intensity 8.83±2.78 fold p=0.017) and higher expression of PPARγ (1.47±0.14 fold; p=0.009) compared to HC C-MSC. The adipogenic stimulation led to a parallel increase of CD36 and lipid accumulation, mainly in ACM C-MSC (slopes statistically different p=0.016). OxLDL and 13HODE administration increased lipid accumulation in ACM C-MSC (ORO staining ACM vs ACM+oxLDL p=0.01; ACM vs ACM+13HODE p=0.014). On the contrary, the antioxidant N-Acetylcysteine (NAC) prevented lipid accumulation in ACM C-MSC (ORO staining ACM+13HODE vs ACM+13HODE+NAC p=0.0009). Through CD36 silencing of ACM C-MSC, we obtained a significantly lower lipid accumulation than non-silenced cells (ORO staining 0.35±0.10 fold; p=0.003). Pkp2+/− mice do not spontaneously accumulate adipocytes in the heart, however Pkp2+/− C-MSC are more prone to lipid accumulation in vitro than WT cells (p=0.007). Accordingly, mice have low plasma oxLDL and cardiac oxidative stress. By increasing plasma cholesterol and oxidative stress through high fat diet, we observed fibro-fatty substitution in Pkp2+/− hearts (p=0.046). Figure 1 Conclusions These findings reveal a modulatory role of oxidized lipids in ACM adipogenesis at a cellular, tissue and clinical level, enlightening novel targets for pharmacological strategies to prevent adipogenic substitution and consequent ACM clinical phenotypes. Acknowledgement/Funding Telethon Foundation; Italian Ministry of Health

Download Full-text

Discovery and validation of the nuclear export protein CRM1 (XPO1) as a new target for the treatment of renal cell carcinoma (RCC).

Journal of Clinical Oncology ◽

10.1200/jco.2013.31.6_suppl.411 ◽

2013 ◽

Vol 31 (6_suppl) ◽

pp. 411-411

Author(s):

Hiromi Inoue Wettersten ◽

Michael Kauffman ◽

Sharon Shacham ◽

Yosef Landesman ◽

Joy Yang ◽

...

Keyword(s):

Cell Lines ◽

Nuclear Export ◽

Human Kidney ◽

In Vivo Studies ◽

Tumor Growth Inhibition ◽

Phase I Clinical Trials ◽

New Therapeutic Approaches ◽

Xenograft Mice

411 Background: The currently available targeted therapies for RCC have had limited success, so it is imperative to discover new therapeutic approaches for metastatic RCC. In a search for new such targets, we have identified inhibitors of CRM1 (XPO1, exportin1), the major karyopherin that mediates the export of most tumor suppressor proteins from the nucleus. To expand our initial work on the first generation of CRM1 inhibitors, we now evaluate KPT-330, an orally available Selective Inhibitor of Nuclear Export (SINE), the best tolerated among a series of CRM1 inhibitors that is currently in phase I clinical trials. Methods: The RCC cell lines (Caki-1 and 786-O) and a primary normal human kidney (NHK) cell line were treated with KPT-330, and MTT assays were performed. The cells were subjected to immunofluorescence and immunoblotting for appropriate proteins. Caki-1 xenograft mice were treated with KPT-330 for 15 days, and tumor volume was assessed. Results: KPT-330 selectively attenuated CRM1 levels and caused dose-dependent toxicity (EC50 < 1 µM) through apoptosis in all RCC cells. In untreated RCC cells, p21 was localized in the nucleus, where it likely functions as a cell cycle arrest protein, and in the cytosol, where it functions as an anti-apoptotic protein. However, in NHK cells, p21 was confined to the nucleus. KPT-330 increased p53 and p21 and confined them to the nucleus in both NHK and RCC cells. KPT-330 given orally inhibited RCC growth in xenograft mice (85.3 % inhibition, p < 0.001). Moreover, KPT-330 showed synergism with a Bcl-2 inhibitor ABT-737 in vitro, indicating the potential for combination therapy with a CRM1 inhibitor and Bcl-2 inhibitor. In vivo studies to test the combination of KPT-330 with Bcl-2 inhibitors are ongoing. Conclusions: We introduce a new therapeutic approach for RCC treatment based on the inhibition of the nuclear export of key tumor suppressors. Inhibition of CRM1 causes forced nuclear retention, and thereby activation, of several key p53-pathway proteins, leading to apoptosis in RCC cell lines in vitro and tumor growth inhibition in vivo.

Download Full-text

PF-06869206 is a selective inhibitor of renal Pi transport: evidence from in vitro and in vivo studies

AJP Renal Physiology ◽

10.1152/ajprenal.00146.2020 ◽

2020 ◽

Vol 319 (3) ◽

pp. F541-F551

Author(s):

Linto Thomas ◽

Jianxiang Xue ◽

Viktor N. Tomilin ◽

Oleh M. Pochynyuk ◽

Jessica A. Dominguez Rieg ◽

...

Keyword(s):

Collecting Duct ◽

Inhibitory Effect ◽

In Vivo Studies ◽

Open Probability ◽

Ok Cells ◽

Increased Risk ◽

Dose Dependent Increase ◽

Dose Dependent

Plasma phosphate (Pi) levels are tightly controlled, and elevated plasma Pi levels are associated with an increased risk of cardiovascular complications and death. Two renal transport proteins mediate the majority of Pi reabsorption: Na+-phosphate cotransporters Npt2a and Npt2c, with Npt2a accounting for 70–80% of Pi reabsorption. The aim of the present study was to determine the in vitro effects of a novel Npt2a inhibitor (PF-06869206) in opossum kidney (OK) cells as well as determine its selectivity in vivo in Npt2a knockout (Npt2a−/−) mice. In OK cells, Npt2a inhibitor caused dose-dependent reductions of Na+-dependent Pi uptake (IC50: ~1.4 μmol/L), whereas the unselective Npt2 inhibitor phosphonoformic acid (PFA) resulted in an ~20% stronger inhibition of Pi uptake. The dose-dependent inhibitory effects were present after 24 h of incubation with both low- and high-Pi media. Michaelis-Menten kinetics in OK cells identified an ~2.4-fold higher Km for Pi in response to Npt2a inhibition with no significant change in apparent Vmax. Higher parathyroid hormone concentrations decreased Pi uptake equivalent to the maximal inhibitory effect of Npt2a inhibitor. In vivo, the Npt2a inhibitor induced a dose-dependent increase in urinary Pi excretion in wild-type mice (ED50: ~23 mg/kg), which was completely absent in Npt2a−/− mice, alongside a lack of decrease in plasma Pi. Of note, the Npt2a inhibitor-induced dose-dependent increase in urinary Na+ excretion was still present in Npt2a−/− mice, a response possibly mediated by an off-target acute inhibitory effect of the Npt2a inhibitor on open probability of the epithelial Na+ channel in the cortical collecting duct.

Download Full-text

Pleiotropic Effects of Statins: New Therapeutic Approaches to Chronic, Recurrent Infection by Staphylococcus aureus

Pharmaceutics ◽

10.3390/pharmaceutics13122047 ◽

2021 ◽

Vol 13 (12) ◽

pp. 2047

Author(s):

Melissa D. Evans ◽

Susan A. McDowell

Keyword(s):

Staphylococcus Aureus ◽

Recurrent Infection ◽

Opportunistic Pathogen ◽

Pleiotropic Effects ◽

In Vivo Studies ◽

Therapeutic Approaches ◽

Risk Of Death ◽

New Therapeutic Approaches

An emergent approach to bacterial infection is the use of host rather than bacterial-directed strategies. This approach has the potential to improve efficacy in especially challenging infection settings, including chronic, recurrent infection due to intracellular pathogens. For nearly two decades, the pleiotropic effects of statin drugs have been examined for therapeutic usefulness beyond the treatment of hypercholesterolemia. Interest originated after retrospective studies reported decreases in the risk of death due to bacteremia or sepsis for those on a statin regimen. Although subsequent clinical trials have yielded mixed results and earlier findings have been questioned for biased study design, in vitro and in vivo studies have provided clear evidence of protective mechanisms that include immunomodulatory effects and the inhibition of host cell invasion. Ultimately, the benefits of statins in an infection setting appear to require attention to the underlying host response and to the timing of the dosage. From this examination of statin efficacy, additional novel host-directed strategies may produce adjunctive therapeutic approaches for the treatment of infection where traditional antimicrobial therapy continues to yield poor outcomes. This review focuses on the opportunistic pathogen, Staphylococcus aureus, as a proof of principle in examining the promise and limitations of statins in recalcitrant infection.

Download Full-text

Biologic Studies of Chimeras of Highly and Moderately Virulent Molecular Clones of Simian Immunodeficiency Virus SIVsmPBj Suggest a Critical Role for Envelope in Acute AIDS Virus Pathogenesis

Journal of Virology ◽

10.1128/jvi.75.14.6645-6659.2001 ◽

2001 ◽

Vol 75 (14) ◽

pp. 6645-6659 ◽

Cited By ~ 7

Author(s):

Malcolm Haddrick ◽

Charles R. Brown ◽

Ronald Plishka ◽

Alicia Buckler-White ◽

Vanessa M. Hirsch ◽

...

Keyword(s):

Marked Reduction ◽

Mononuclear Cells ◽

Critical Role ◽

In Vivo Studies ◽

Peripheral Blood Mononuclear ◽

Related Clone ◽

Virion Envelope ◽

Mechanistic Basis

ABSTRACT Previous studies identified three molecular clones of the acutely pathogenic SIVsmPBj strain that varied in terms of relative in vivo pathogenicity. One clone, SIVsmPBj6.6, reproducibly induced a rapidly fatal disease in pigtailed macaques. In contrast, a highly related clone (SIVsmPBj6.9) was only minimally pathogenic in macaques. PBj6.6 and PBj6.9 shared a tyrosine substitution at position 17 in the Nef protein that is a major determinant of virulence but differed at one residue in Vpx (C89R), three residues within the envelope (D119G, R871G, G872R), and a single residue in Nef (F252L). SIVsmPBj6.9 was less efficient in inducing proliferation of resting macaque peripheral blood mononuclear cells in vitro than SIVsmPBj6.6 and exhibited a marked reduction in infectivity relative to SIVsmPBj6.6. Chimeric viruses for each of these variable residues were constructed, and their biologic properties were compared to those of the parental strains. Differences in Vpx and Nef did not alter the basic biologic phenotype of the chimeras. However, the D119G substitution in the envelope of SIVsmPBj6.9 was associated with a marked reduction in the infectivity of this virus relative to SIVsmPBj6.6. An associated processing defect in gp160 of SIVsmPBj6.9 and chimeras expressing the D119G substitution suggests that a reduction in virion envelope incorporation is the mechanistic basis for reduced virion infectivity. In vivo studies revealed that substitution of the PBj6.9 amino acid into PBj6.6 (D119) abrogated the pathogenicity of this previously pathogenic virus. Introduction of the PBj6.9 G119, however, did not confer full virulence to the parental PBj6.9 virus, implicating one or all of the other four substitutions in the virulence of SIVsmPBj6.6.

Download Full-text

Inflammation in the Pathogenesis of Arrhythmogenic Cardiomyopathy: Secondary Event or Active Driver?

Frontiers in Cardiovascular Medicine ◽

10.3389/fcvm.2021.784715 ◽

2021 ◽

Vol 8 ◽

Author(s):

Viviana Meraviglia ◽

Mireia Alcalde ◽

Oscar Campuzano ◽

Milena Bellin

Keyword(s):

Inflammatory Cell ◽

Current Knowledge ◽

Myocardial Damage ◽

Secondary Response ◽

Arrhythmogenic Cardiomyopathy ◽

Primary Event ◽

Fatty Replacement ◽

Inherited Cardiac Disease

Arrhythmogenic cardiomyopathy (ACM) is a rare inherited cardiac disease characterized by arrhythmia and progressive fibro-fatty replacement of the myocardium, which leads to heart failure and sudden cardiac death. Inflammation contributes to disease progression, and it is characterized by inflammatory cell infiltrates in the damaged myocardium and inflammatory mediators in the blood of ACM patients. However, the molecular basis of inflammatory process in ACM remains under investigated and it is unclear whether inflammation is a primary event leading to arrhythmia and myocardial damage or it is a secondary response triggered by cardiomyocyte death. Here, we provide an overview of the proposed players and triggers involved in inflammation in ACM, focusing on those studied using in vivo and in vitro models. Deepening current knowledge of inflammation-related mechanisms in ACM could help identifying novel therapeutic perspectives, such as anti-inflammatory therapy.

Download Full-text