Genome-wide mapping of plasma protein QTLs identifies putatively causal genes and pathways for cardiovascular disease

Identifying genetic variants associated with circulating protein concentrations (protein quantitative trait loci; pQTLs) and integrating them with variants from genome-wide association studies (GWAS) may illuminate the proteome's causal role in disease and bridge a knowledge gap regarding SNP-disease associations. We provide the results of GWAS of 71 high-value cardiovascular disease proteins in 6861 Framingham Heart Study participants and independent external replication. We report the mapping of over 16,000 pQTL variants and their functional relevance. We provide an integrated plasma protein-QTL database. Thirteen proteins harbor pQTL variants that match coronary disease-risk variants from GWAS or test causal for coronary disease by Mendelian randomization. Eight of these proteins predict new-onset cardiovascular disease events in Framingham participants. We demonstrate that identifying pQTLs, integrating them with GWAS results, employing Mendelian randomization, and prospectively testing protein-trait associations holds potential for elucidating causal genes, proteins, and pathways for cardiovascular disease and may identify targets for its prevention and treatment.

[Transition of myocardial ischemia to heart failure]

Myocardial ischemia results in myocardial dysfunction. Recovery may be delayed ("stunning"), or persistent if perfusion remains reduced ("hibernation") and ischemia may go on to necrosis, thus, contributing to chronic heart failure. In addition, myocardium not directly affected by ischemia may undergo adaptive processes like hypertrophy and dilatation, which may result in chronic left heart failure. This process is characterized by hemodynamic, neurohumoral, and progressive morphologic changes of the heart which are closely interrelated. Hemodynamic changes basically consist of an increase in left ventricular filling pressure and a decrease in global ejection fraction, and, in most cases years after myocardial infarction, in an increase in systemic vascular resistance and right atrial pressure. Neurohumoral changes consist of an increase in plasma catecholamines, atrial natriuretic factor and vasopressin, and in an activation of the renin-angiotensin-system. Plasma endothelin-1 was recently reported to be increased in patients with heart failure, and prognosis was related to endothelin levels. Diminished response of vessels to endothelium (EDRF/NO) dependent vasodilatation suggests impairment of vascular endothelium in heart failure. Local changes of cardiac neurohumoral systems could contribute to structural changes of the heart, e.g., systemic activation to hemodynamic changes. Structural changes of the heart are characterized by an increase in volume and thickness of surviving myocardium and an expansion of ischemic and necrotic myocardium. Molecular control of these processes which include various cell types, such as cardiomyocytes and cardiofibroblasts, are currently an issue of intense research and could result in specific therapeutic importance.

Changes of creatine kinase gene expression in rat heart post-myocardial infarction

Creatine kinase (CK) plays a crucial role in cardiac energy transduction. During chronic cardiac stress conditions leading to hypertrophy and/or heart failure, the profile of CK isoenzyme activities changes towards a fetal pattern with increases of BB- and MB-CK and decreases of MM-CK and mito-CK. Changes of myocardial CK gene expression are only indirectly reflected by measurements of CK activities. The purpose of this work was, therefore, to determine myocardial expression of B-, M- and sarcomeric mito-CK genes in an animal model of heart failure where hemodynamic alterations and CK system changes are well defined, that is, in the rat heart post-myocardial infarction. Intact residual left ventricular myocardium was harvested 2 months following infarction (MI; n = 7) or sham operation (sham; n = 6) after in vivo left-ventricular end-diastolic pressure (LVEDP) was recorded. Total CK activity was measured spectrophotometrically, CK isoenzyme distribution with agarose gel electrophoresis. Steady state mRNA levels coding for B-, M- and mito-CK genes were measured with quantitative PCR and were normalized for GAPDH expression. Total CK activity tended to be reduced in MI (5.51 +/- 0.62 IU/mg protein) compared to sham (6.77 +/- 0.24; P = 0.55). CK isoenzyme distribution showed an increase of fetal BB- + MB-CK (MI 22.0 +/- 3.1%, sham 15.1 +/- 1.0%; P < 0.05), no change of MM-CK and a decrease of mito-CK (27.0 +/- 1.5% sham, 20.8 +/- 2.0% MI: P < 0.05). Relative B-CK mRNA levels increased (sham 0.46 +/- 0.06, MI 1.03 +/- 0.09; P < 0.05) and M-CK mRNA levels decreased (sham 1.06 +/- 0.08. MI 0.66 +/- 0.09; P < 0.05) significantly post-MI. The increase of B-CK mRNA (r = 0.72; P = 0.009) and the decrease of M-CK mRNA (r = 0.76; P = 0.003) correlated significantly with in vivo LVEDP. Mito-CK mRNA levels remained unchanged after MI (sham 0.94 +/- 0.16, MI 0.98 +/- 0.09). Intact residual left-ventricular myocardium post-MI is characterized by increased B-CK-mRNA and reduced M-CK-mRNA expression.

Effects of chronic dietary creatine feeding on cardiac energy metabolism and on creatine content in heart, skeletal muscle, brain, liver and kidney

Little is known about the regulation of total creatine concentration in heart, skeletal muscle, brain, liver and kidney in response to increased dietary creatine intake. The phosphorylated fraction of intracellular creatine (phosphocreatine) remain relatively constant, and therefore, higher intracellular creatine levels may increase the energy reserve of the heart [phosphocreatine and phosphoryl transfer via creatine kinase (CK)] and of other organs. To test the effect of supplying exogenous creatine on the myocardial energy reserve and on creatine content of various organs, rats were given chow containing 0 (Untreated), 1, 3, 5, or 7% (of diet weight) creatine for ;40 days. Thereafter, hearts were perfused and left ventricular developed pressure and heart rate were recorded. High-energy phosphate concentrations were determined with 31P-NMR spectroscopy, CK reaction velocity by 31P-magnetization transfer. Total creatine was determined in heart, skeletal muscle, brain, liver, kidney and serum by high-performance liquid chromatography (HPLC). Creatine feeding increased serum creatine by 73% (1% creatine), 142% (3%), 166% (5%) and 202% (7%). In the heart, increased serum creatine levels did not affect mechanical function; ATP, phosphocreatine, inorganic phosphate, CK reaction velocity and total creatine were all unchanged. Total creatine also remained constant in brain and skeletal muscle, while creatine content increased 4.6-fold in the liver and 1.9-fold in the kidney. We conclude that myocardial energy reserve via CK cannot be increased by exogenous creatine treatment.

Regional biochemical remodeling in non-infarcted tissue of rat heart post-myocardial infarction

Changes in the capacities of ATP-synthesizing reactions were analysed in residual non-infarcted myocardium following myocardial infarction. Rats were subjected to left coronary artery ligation (MI; n = 11) or to sham operation (sham; n = 18). Two months later, hearts were excised, rinsed and buffer-perfused isovolumically. In vitro pressure-volume relationships were recorded. After separation into left and right ventricles (LV, RV) and atria (LA, RA), samples were analysed for citrate synthase, glycolytic enzymes (phosphofructokinase, glyceraldehyde-3-phosphate-dehydrogenase, lactate dehydrogenase (LDH) and its isoforms) and the creatine kinase (CK) system [total CK, CK isoenzymes (CKBB, CKMB, CKMM and CKmito) and total creatine]. In residual intact heart, citrate synthase activity and activities of most glycolytic enzymes were unchanged, but LDH activity and anaerobic LDH isoenzymes increased significantly. Total creatine kinae activity (6.5 +/- 0.2 IU/mg protein in sham LV) was decreased by chronic myocardial infarction in LV (5.4 +/- 0.3, with P < 0.05 sham v MI) but not in RV (6.2 +/- 0.2). Significant CK isoenzyme shifts occurred in both ventricles "adult" CKmito (32.5 +/- 1.4% in sham LV) was reduced in LV (22.1 +/- 2.1% with P < 0.05 sham v MI) and in RV (19.2 +/- 2.9%, with P < 0.05 sham v MI), "fetal" CKBB and CKMB increased. Total creatine content was reduced by up to 35% in both ventricles. In sham hearts atria had lower total and mitochondrial CK activity, lower total creatine content and higher CKMB and CKBB activity compared to ventricles; however, myocardial infarction induced changes directionally comparable to the changes observed in ventricles. Thus, 2 months after myocardial infarction changes of the capacities of ATP synthesizing reactions are comparable for all heart chambers, with the exception of total CK activity decreasing only in left ventricular tissue.

Long-term beta-blocker treatment prevents chronic creatine kinase and lactate dehydrogenase system changes in rat hearts after myocardial infarction

OBJECTIVES

We tested the hypothesis that long-term beta-blocker treatment with bisoprolol prevents creatine kinase (CK) and lactate dehydrogenase system changes that occur after chronic myocardial infarction.

BACKGROUND

The mechanism of the beneficial effect of beta-blocker therapy is still unclear.

METHODS

Six groups of rats were studied. Sham operated (sham) and hearts with ligated left anterior descending coronary artery (myocardial infarction) were untreated, treated early (beginning 30 min after infarction) or treated late (beginning 14 days after infarction). After 8 weeks, hearts were isolated and buffer perfused isovolumetrically. With a left ventricular balloon, mechanical function was recorded at an end-diastolic pressure of 10 mm Hg. Biopsy samples of noninfarcted left ventricular tissue were taken. Enzyme activities were measured spectrophotometrically; isoenzymes were separated by agar gel electrophoresis; and total creatine levels were measured with high performance liquid chromatography.

RESULTS

The decrease in left ventricular developed pressure in untreated hearts (120 +/- 9 vs. 104 +/- 5 mm Hg [mean +/- SE], p < 0.05, sham vs. myocardial infarction) after myocardial infarction was prevented by early treatment (118 +/- 9 vs. 113 +/- 4 mm Hg). Late treatment failed to improve mechanical function. Reduction of CK activity occurring in untreated infarcted hearts (6.4 +/- 0.3 vs. 5.1 +/- 0.3 IU/mg protein, p < 0.05, sham vs. myocardial infarction) was prevented by early beta-blocker therapy. The increase in CK isoenzyme BB and MB levels, decrease in mitochondrial CK isoenzyme levels and increase in anaerobic lactate dehydrogenase isoenzyme levels in untreated infarcted hearts did not occur during bisoprolol treatment. The decrease in total creatine levels after myocardial infarction (74.2 +/- 4.9 vs. 54.9 +/- 3.3 nmol/mg protein, p < 0.05, sham vs. myocardial infarction) was prevented by bisoprolol treatment. Early treatment was more effective than late therapy in preventing CK and lactate dehydrogenase system changes. In addition, in sham hearts, a 40% increase of creatine levels above normal levels was detected.

CONCLUSIONS

Bisoprolol prevented changes in CK and lactate dehydrogenase system that occur after myocardial infarction. These observations may be related to the beneficial effects of long-term beta-blocker treatment in patients with chronic myocardial infarction.

Pulmonary granulomas in a patient with pulmonary veno-occlusive disease

A patient with pulmonary veno-occlusive disease is described. Lung biopsy revealed noncaseating granulomas in conjunction with the typical vascular changes of this entity. This concurrence has not been previously described.