Lethal hyperkinetic ventricular arrhythmias and echocardiographic findings in patients with arrhythmogenic right ventricular disease

Posters

Lethal hyperkinetic ventricular arrhythmias and echocardiographic findings in patients with arrhythmogenic right ventricular disease     

Role of genetic analysis in the management of patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a recognized cause of sudden cardiac death, which may be prevented by timely detection and intervention. Clinical diagnosis of ARVC is fraught with difficulties in both index cases and relatives owing to the nonspecific nature of associated features, diverse phenotypic manifestations, and a lack of conspicuous abnormalities in the early, "concealed" phase. During the past 7 years, researchers have isolated causative mutations in several components of the desmosome, shedding light on the molecular mechanisms underlying the disease and offering the promise of genetic testing as a diagnostic tool. Sequence analysis is likely to be the mainstay of genotyping in ARVC because of marked allelic heterogeneity, frequent "private" mutations, and digenicity in a minority, highlighting the importance of comprehensive genetic screening. The main technical obstacle to implementation of genotyping in clinical practice will be the prohibitive costs of performing sequence analysis of a genomic region exceeding 40 kb. Nevertheless, the success rate of genotyping in ARVC is of the order of 40%, and key clinical applications include confirmatory testing of index cases to facilitate interpretation of borderline investigations and cascade screening of families. The latter is particularly attractive in ARVC, because age-related penetrance otherwise demands lifelong clinical reassessment of extended families. A role for genetic analysis in prognostication is more tenuous at present, but increasing identification of individuals with early and familial disease underscores the need for a definitive risk stratification algorithm in this population.     

Sudden cardiac death in the young: a strategy for prevention by targeted evaluation

The annual incidence of sudden cardiac death (SCD) in the general population is estimated as 1 in a 1,000. Since survival rates from out-of-hospital cardiac arrests are poor, primary prevention is key to reducing the burden of SCD in the community. Prominent causes of SCD include ischaemic heart disease, anomalous coronary arteries, and the primary myocardial diseases: hypertrophic cardiomyopathy, dilated cardiomyopathy, and ar rhythmogenic right ventricular cardiomyopathy (ARVC). In 4% of sudden deaths in the 16-64 age group, post-mortem examination fails to identify a cause, yielding a default diagnosis of sudden arrhythmic death syndrome (SADS). The inherited arrhythmia syndromes (long QT, short QT, and Brugada syndromes, and familial catecholaminergic polymorphic ventricular tachycardia) may be implicated in SADS, owing to their propensity for producing ventricular tachyarrhythmia in the structurally normal heart. Monogenic disorders therefore predominate as causes of SCD in the young. The advent of effective therapies for these diseases, particularly implantable cardioverter defibrillators, has prompted calls for universal screening to enable timely diagnosis of occult cardiac disease. Since prospective cardiac assessment of the general population is not feasible, the solution may be to target high-risk subgroups, namely, patients with cardiac symptoms, relatives of SCD victims, and competitive athletes. The recommended preliminary work-up includes a 12-lead ECG, signal-averaged ECG, transthoracic echocardiogram, exercise test, and ambulatory ECG monitoring. Cardiovascular magnetic resonance is a useful adjunct in patients with suspected ARVC or anomalous coronary arteries. Provocative challenge with a sodium challenge blocker may be of value in unmasking the Brugada syndrome. Identification of disease-causing mutations in affected individuals facilitates cascade screening of families.     

Klotho depletion contributes to increased inflammation in kidney of the db/db mouse model of diabetes via RelA (serine)536 phosphorylation

OBJECTIVE

Klotho is an antiaging hormone present in the kidney that extends the lifespan, regulates kidney function, and modulates cellular responses to oxidative stress. We investigated whether Klotho levels and signaling modulate inflammation in diabetic kidneys.

RESEARCH DESIGN AND METHODS

Renal Klotho expression was determined by quantitative real-time PCR and immunoblot analysis. Primary mouse tubular epithelial cells were treated with methylglyoxalated albumin, and Klotho expression and inflammatory cytokines were measured. Nuclear factor (NF)-κB activation was assessed by treating human embryonic kidney (HEK) 293 and HK-2 cells with tumor necrosis factor (TNF)-α in the presence or absence of Klotho, followed by immunoblot analysis to evaluate inhibitor of κB (IκB)α degradation, IκB kinase (IKK) and p38 activation, RelA nuclear translocation, and phosphorylation. A chromatin immunoprecipitation assay was performed to analyze the effects of Klotho signaling on interleukin-8 and monocyte chemoattractant protein-1 promoter recruitment of RelA and RelA serine (Ser)⁵³⁶.

RESULTS

Renal Klotho mRNA and protein were significantly decreased in db/db mice, and a similar decline was observed in the primary cultures of mouse tubule epithelial cells treated with methylglyoxal-modified albumin. The exogenous addition of soluble Klotho or overexpression of membranous Klotho in tissue culture suppressed NF-κB activation and subsequent production of inflammatory cytokines in response to TNF-α stimulation. Klotho specifically inhibited RelA Ser⁵³⁶ phosphorylation as well as promoter DNA binding of this phosphorylated form of RelA without affecting IKK-mediated IκBα degradation, total RelA nuclear translocation, and total RelA DNA binding.

CONCLUSIONS

These findings suggest that Klotho serves as an anti-inflammatory modulator, negatively regulating the production of NF-κB–linked inflammatory proteins via a mechanism that involves phosphorylation of Ser⁵³⁶ in the transactivation domain of RelA.It has long been recognized that diabetes accelerates aging, particularly in the subpopulation of diabetic subjects who are at risk for developing complications (1). Numerous mechanisms have been proposed, including increased production of advanced glycation end products (AGEs), increased oxidative stress, DNA damage, and enhanced inflammation; it is noteworthy that all of these mechanisms have been implicated in the pathogenesis of diabetes complications. Tubular epithelium in the kidneys from type 2 diabetic patients with demonstrated nephropathy display accelerated senescence, characterized by decreased telomere length and an increased expression of senescence markers (2).The recent characterization of the Klotho protein as an antiaging hormone that modulates the expression level of antioxidant enzymes (3,4), as well as its high expression level in the kidney (5–7), suggest that Klotho plays a role in accelerated aging and cellular senescence observed in diabetes. Klotho overexpression extends the mouse lifespan by 20–30% (8). More striking, Klotho-deficient mice exhibit multiple age-related phenotypes and succumb to early, premature death (7,9). Klotho is predominantly expressed in the brain and kidney of normal subjects, and a significant decline in Klotho gene and protein expression has been reported in kidneys of patients with chronic renal failure (10). Klotho expression is significantly suppressed after the induction of renal ischemia-reperfusion injury, whereas Klotho overexpression prevented the development of acute renal failure (11). Also noteworthy, Klotho overexpression suppressed glomerulonephritis-induced accelerated cellular senescence and apoptosis and preserved renal function (12). Despite these observations, the role of Klotho in diabetes remains unexplored, even though accelerated aging is associated with this disease.We investigated potential links between Klotho expression and diabetes-induced inflammation. Our data show that Klotho suppresses nuclear factor (NF)-κB activation and the subsequent production of inflammatory cytokines in response to tumor necrosis factor (TNF)-α stimulation in kidney cells, including primary cultures of mouse tubular epithelium, HK-2, and human embryonic kidney (HEK) 293 cells. We explored potential mechanism(s) for this inhibition and identified a novel and specific site of inhibition. Klotho inhibited p38 kinase and specifically blocked RelA serine (Ser)⁵³⁶ phosphorylation and its subsequent recruitment to NF-κB–dependent promoters of multiple cytokines, without affecting inhibitor of κB (IκB)α degradation or total RelA nuclear translocation and DNA binding. These findings indicate that Klotho serves as an anti-inflammatory modulator, regulating the production of NF-κB–linked inflammatory cytokines, chemokines, and growth factors via a noncanonical NF-κB activation pathway involving RelA phosphorylation in the transactivation domain (13–15). Our observations that Klotho can modulate NF-κB activation and inhibit the production of diabetes-induced inflammatory cytokines suggest that Klotho exerts a renoprotective effect by increasing the resistance to oxidative stress and inhibiting inflammatory cytokine/chemokine cascades induced by NF-κB activation. Our observations further suggest that Klotho is a potential therapeutic target linking oxidative stress to inflammation in type 2 diabetes.     

Arrhythmogenic right ventricular cardiomyopathy: clinical presentation, diagnosis, and management

Arrhythmogenic right ventricular cardiomyopathy, also known as right ventricular dysplasia, is a genetically determined heart muscle disease associated with arrhythmia, heart failure, and sudden death. Autosomal dominant inheritance is typical. The identification of causative mutations in cell adhesion proteins has shed new light on its pathogenesis. Fibrofatty replacement of the myocardium, the hallmark pathologic feature, may be a response to injury caused by myocyte detachment. Sudden death is often the first manifestation in probands, emphasizing the importance of evaluating asymptomatic relatives for the disease. Standardized guidelines facilitate the clinical diagnosis of right ventricular dysplasia. However, familial studies have highlighted the need to broaden the diagnostic criteria, which are highly specific but lack sensitivity for early disease. Modifications have been proposed for the diagnosis of right ventricular dysplasia in relatives. Early right ventricular dysplasia is characterized by a "concealed phase" in which electrocardiographic and imaging abnormalities are often absent, but patients may nonetheless be at risk for arrhythmic events. Detection at this stage remains a clinical challenge, underscoring the potential value of mutation analysis in identifying affected persons. Serial evaluation of patients with suspected right ventricular dysplasia is recommended as clinical features may develop during the follow-up period. The onset of symptoms such as palpitation or syncope may herald an active phase of a previously quiescent disease, during which patients are at increased risk for sudden death. Greater awareness of right ventricular dysplasia among physicians and judicious use of implantable cardioverter-defibrillators may help to prevent unnecessary deaths.