Citations

Background— In contrast to the wealth of data on isolated systolic hypertension involving the systemic circulation in the elderly, much less is known about age-related change in pulmonary artery systolic pressure (PASP) and its prognostic impact in the general population. We sought to define the relationship between PASP and age, to evaluate which factors influence PASP, and to determine whether PASP is independently predictive of mortality in the community. Methods and Results— A random sample of the Olmsted County, Minn, general population (n=2042) underwent echocardiography and spirometry and was followed up for a median of 9 years. PASP was measured from the tricuspid regurgitation velocity. Left ventricular diastolic pressure was estimated with Doppler echocardiography (E/e′ ratio), and arterial stiffening was assessed from the brachial artery pulse pressure. Among 1413 subjects (69%) with measurable PASP (age, 63±11 years; 43% male), median PASP was 26 mm Hg (25th to 75th percentile, 24 to 30 mm Hg) and increased with age ( r =0.31, P <0.001). Independent predictors of PASP were age, pulse pressure, and mitral E/e′ (all P ≤0.003). Increasing PASP was associated with higher mortality (hazard ratio, 2.73 per 10 mm Hg; P <0.001). In subjects without cardiopulmonary disease (any heart failure, coronary artery disease, hypertension, diabetes mellitus, or chronic obstructive lung disease), the age-adjusted hazard ratio was 2.74 per 10 mm Hg ( P =0.016). Conclusions— We provide the first population-based evidence of age-related increase in pulmonary artery pressure, its association with increasing left heart diastolic pressures and systemic vascular stiffening, and its negative impact on survival. Pulmonary artery pressure may serve as a novel cardiovascular risk factor and potential therapeutic target.

Exercise training elicits a metabolic and cardiovascular response that underlies fitness. The molecular mechanisms that orchestrate this adaptive response and secure the wide-ranging gains of a regimented exercise program are poorly understood. Formed through association of the Kir6.2 pore and the sulfonylurea receptor, the stress-responsive ATP-sensitive K+ channels (KATP channels), with their metabolic-sensing capability and broad tissue expression, are potential candidates for integrating the systemic adaptive response to repetitive exercise. Here, the responses of mice lacking functional Kir6.2-containing KATP channels (Kir6.2-KO) were compared with wild-type controls following a 28-day endurance swimming protocol. While chronic aquatic training resulted in lighter, leaner, and fitter wild-type animals, the Kir6.2-KO manifested less augmentation in exercise capacity and lacked metabolic improvement in body fat composition and glycemic handling with myocellular defects. Moreover, the repetitive stress of swimming unmasked a survival disadvantage in the Kir6.2-KO, associated with pathologic calcium-dependent structural damage in the heart and impaired cardiac performance. Thus, Kir6.2-containing KATP channel activity is required for attainment of the physiologic benefits of exercise training without injury.

Metabolic-sensing ATP-sensitive K+ channels (KATP channels) adjust membrane excitability to match cellular energetic demand. In the heart, KATP channel activity has been linked to homeostatic shortening of the action potential under stress, yet the requirement of channel function in securing cardiac electrical stability is only partially understood. Here, upon catecholamine challenge, disruption of KATP channels, by genetic deletion of the pore-forming Kir6.2 subunit, produced defective cardiac action potential shortening, predisposing the myocardium to early afterdepolarizations. This deficit in repolarization reserve, demonstrated in Kir6.2-knockout hearts, translated into a high risk for induction of triggered activity and ventricular dysrhythmia. Thus, intact KATP channel function is mandatory for adequate repolarization under sympathetic stress providing electrical tolerance against triggered arrhythmia.

Sepsis, the systemic inflammatory response to infection, imposes a high demand for bodily adaptation, with the cardiovascular response a key determinant of outcome. The homeostatic elements that secure cardiac tolerance in the setting of the sepsis syndrome are poorly understood. Here, in a model of acute septic shock induced by endotoxin challenge with Escherichia coli lipopolysaccharide (LPS), knockout of the KCNJ8 gene encoding the vascular Kir6.1 K ATP channel pore predisposed to an early and profound survival disadvantage. The exaggerated susceptibility provoked by disruption of this stress‐responsive sensor of cellular metabolism was linked to progressive deterioration in cardiac activity, ischemic myocardial damage, and contractile dysfunction. Deletion of KCNJ8 blunted the responsiveness of coronary vessels to cytokine‐ or metabolic‐mediated vasodilation necessary to support myocardial perfusion in the wild‐type (WT), creating a deficit in adaptive response in the Kir6.1 knockout. Application of a K ATP channel opener drug improved survival in the endotoxic WT but had no effect in the Kir6.1 knockout. Restoration of the dilatory capacity of coronary vessels was required to rescue the Kir6.1 knockout phenotype and reverse survival disadvantage in lethal endotoxemia. Thus, the Kir6.1containing K ATP channel, by coupling vasoreactivity with metabolic demand, provides a vital feedback element for cardiovascular tolerance in endotoxic shock.—Kane, G. C., Lam, C‐F., O'Cochlain, F., Hodgson, D. M., Reyes, S., Liu, X‐K., Miki, T., Seino, S., Katusic, Z. S., Terzic, A. Gene knockout of the KCNJ8encoded Kir6.1 KATP channel imparts fatal susceptibility to endotoxemia. FASEB J. 20, 2271–2280 (2006)

ABSTRACT Members of the transforming growth factor pβ (TGF‐β) superfamily‐namely, TGF‐β and BMP2—applied to undifferentiated murine embryonic stem cells up‐regulated mRNA of mesodermal (Brachyury) and cardiac specific transcription factors (Nkx2.5, MEF2C). Embryoid bodies generated from stem cells primed with these growth factors demonstrated an increased potential for cardiac differentiation with a significant increase in beating areas and enhanced myofibrillogenesis. In an environment of postmitotic cardiomyocytes, stem cells engineered to express a fluorescent protein under the control of a cardiac promoter differentiated into fluorescent ventricular myocytes beating in synchrony with host cells, a process significantly enhanced by TGF‐β or BMP2. In vitro, disruption of the TGF‐β/BMP signaling pathways by latency‐associated peptide and/or noggin prevented differentiation of stem cells. In fact, only host cells that secrete a TGF‐β family member induced a cardiac phenotype in stem cells. In vivo, transplantation of stem cells into heart also resulted in cardiac differentiation provided that TGF‐β/BMP2 signaling was intact. In infarcted myocardium, grafted stem cells differentiated into functional cardiomyocytes integrated with surrounding tissue, improving contractile performance. Thus, embryonic stem cells are directed to differentiate into cardiomyocytes by signaling mediated through TGF‐β/BMP2, a cardiac paracrine pathway required for therapeutic benefit of stem cell transplantation in diseased heart.—Behfar, A., Zingman, L. V., Hodgson, D. M., Rauzier, J.‐M., Kane, G. C., Terzic, A., Pucéat, M. Stem cell differentiation requires a paracrine pathway in the heart. FASEB J . 16, 1558–1566 (2002)

Reaction to stress requires feedback adaptation of cellular functions to secure a response without distress, but the molecular order of this process is only partially understood. Here, we report a previously unrecognized regulatory element in the general adaptation syndrome. Kir6.2, the ion-conducting subunit of the metabolically responsive ATP-sensitive potassium (K ATP ) channel, was mandatory for optimal adaptation capacity under stress. Genetic deletion of Kir6.2 disrupted K ATP channel-dependent adjustment of membrane excitability and calcium handling, compromising the enhancement of cardiac performance driven by sympathetic stimulation, a key mediator of the adaptation response. In the absence of Kir6.2, vigorous sympathetic challenge caused arrhythmia and sudden death, preventable by calcium-channel blockade. Thus, this vital function identifies a physiological role for K ATP channels in the heart.