Inherited depression of arterial lipoamide dehydrogenase activity associated with susceptibility to atherosclerosis in pigeons

PRKAA1/AMPKα1-driven glycolysis in endothelial cells exposed to disturbed flow protects against atherosclerosis

Increased aerobic glycolysis in endothelial cells of atheroprone areas of blood vessels has been hypothesized to drive increased inflammation and lesion burden but direct links remain to be established. Here we show that endothelial cells exposed to disturbed flow in vivo and in vitro exhibit increased levels of protein kinase AMP-activated (PRKA)/AMP-activated protein kinases (AMPKs). Selective deletion of endothelial Prkaa1, coding for protein kinase AMP-activated catalytic subunit alpha1, reduces glycolysis, compromises endothelial cell proliferation, and accelerates the formation of atherosclerotic lesions in hyperlipidemic mice. Rescue of the impaired glycolysis in Prkaa1-deficient endothelial cells through Slc2a1 overexpression enhances endothelial cell viability and integrity of the endothelial cell barrier, and reverses susceptibility to atherosclerosis. In human endothelial cells, PRKAA1 is upregulated by disturbed flow, and silencing PRKAA1 reduces glycolysis and endothelial viability. Collectively, these results suggest that increased glycolysis in the endothelium of atheroprone arteries is a protective mechanism.

The effect of combined deendothelialization and hypercholesterolemia on some arterial lysosomal and glycolytic enzymes and lactate in rabbits

In eight New Zealand white male rabbits the abdominal aorta and one iliofemoral artery was balloon deendothelialized (group A). After 2 weeks they were kept for 6 weeks on a high cholesterol diet together with eight unoperated rabbits (group B). Eight more rabbits were kept on a commercial diet only (group C). The degree of atherosclerosis was much higher in the deendothelialized Group A vessels than in the uninjured group B vessels. The activity of lactate dehydrogenase and of the rate-limiting glycolytic pyruvate kinase was significantly increased and the activity of lipoamide dehydrogenase decreased in the group A aortas. In the iliofemoral arteries a similar but statistically insignificant tendency was detected. There was no significant difference, however, in aortic lactate between the three groups. Thus, local hypoxia did not significantly contribute to the high degree of atherosclerosis in the group A animals in spite of the enzyme activity differences. Previous experience of the authors, using arterial microcathode pO2 measurements, indicates that following deendothelialization an adaptive proliferation of nutrient vessels and increased arterial oxygenation takes place. The average activity of the lysosomal N-acetyl-beta-glucosaminidase was five times and that of beta-glucuronidase, seven times higher in the Group A than Group B aortas; in the iliofemoral arteries the differences were even larger. The huge elevation of these hydrolases, which are involved in glycosaminoglycan catabolism, provides indirect indication that accumulation of glycosaminoglycans and possibly their ability to form complexes with apoB-containing lipoproteins played a major role in the much increased degree of atherosclerotic lesions in the Group A rabbits.

Oxygen tension within the arterial wall: relationship to altered bioenergetic metabolism and lipid accumulation

Oxygen tension (pO2) was measured in upper thoracic arteries and in muscular foci at the celiac bifurcation from atherosclerosis-susceptible White Carneau and atherosclerosis-resistant Show Racer pigeons at 6, 12, and 24 weeks of age. At each site the pO2 was measured within adventitial (outer), medial (middle), and subendothelial (inner) zones with polarographic oxygen microelectrodes while the animals were under dissociative anesthesia. The atherosclerosis-resistant Show Racer pigeons exhibited no significant age or site differences in pO2 levels. The medial pO2 was approximately 25 mm Hg, while the adventitial and subendothelial zones had pO2 levels of approximately 30 mm Hg. The pO2 profiles through the various zones of the arterial wall of 6-week-old atherosclerosis-susceptible White Carneau pigeons were similar to those of the Show Racers. However, significantly lower oxygen tension was found in the subendothelial zone from 12- and 24-week White Carneau celiac bifurcations (27 and 21 mm Hg) than in corresponding zones in Show Racer sites. Also, the medial zone in 24-week White Carneau celiac foci exhibited a significantly lower pO2 (20 mm Hg) than the medial zone of younger White Carneau. When correlated with previously described biochemical and morphological changes in White Carneau pigeons, the findings presented herein indicate that focal decreases in oxygen availability within arterial tissue occur after the onset of spontaneous atherogenesis, and probably result from decreased diffusion of oxygen into the arterial wall.

Histochromatographical determination of cholesteryl ester composition in the human atherosclerotic aorta

In 14 human aortas, the cholesteryl ester (CE) composition of fatty spots was investigated histochromatographically. By a special method the intracellular lipid (foam cells) lying in the inner intima could be separated from the extracellular lipid found in the depth of the intima in many cases. The fatty acid pattern of CE of the intracellular lipid differed from that of the extracellular lipid by a relative increase in monoenoic acids (M) and trienoic acids (Tr) as well as by a relative decrease in linoleic acid (D), tetraenoic acids (Ar), and saturated fatty acids (S). In every case, the sum of the polyunsaturated fatty acids (PU) of CE (with 2 to 6 double bonds) was lower in the intracellular than in the extracellular lipid (highest difference: 23,2%, lowest difference: 5,7%). High differences of the PU-values between intra- and extracellular CE were associated with high or low D-values and with low values for Tr, Ar, and HU (high unsaturated fatty acids with more than 4 double bonds) of intracellular CE. Low differences of the PU-values between intra- and extracellular CE were accompanied with high D-values and medium or high values for Tr, Ar, and HU of intracellular CE. The results suggest that the cholesteryl esters in the intracellular lipid lose polyunsaturated fatty acids by the processes of hydrolysis and reesterification which are possibly used for other metabolic processes.

Metabolic intermediates, enzymes and lysosomal activity in aortas of spontaneously hypertensive rats

Metabolic intermediate levels, glycolytic and Krebs cycle enzyme activities and lysosomal acid hydrolase activities were measured in aortas of spontaneously hypertensive (SHR) versus normotensive (WKY) rats. In the hypertensive aortas the level of lactate, the ratio of lactate to glucose and of lactate to malate was higher in the SHR than WKY aortas. In the hypertensive aortas the obvious shift of metabolism toward higher rate of glycolysis was associated with decreased activity of malate dehydrogenase and espically of lipoamide dehydrogenase. The latter is an essential compoenent of the alpha-ketoglutarate and pyruvate dehydrogenase enzyme complexes and it appears that these complexes are among the sites of arterialmetavolism which are primarily altered by the elevated blood pressure, resulting in increased production of lactate. The activity of the marker lysosomal enzyme N-acetyl-beta-glucosaminidase was unequivocally elevated in the hypertensive aortas. The activity of beta-glucuronidase exhibited incogruous differences between the SHR and WKY aortas and the activity of aortic acid phosphatase did not differ in the two rat strains. The results are discussed in relation to arterial injury, permeability, and atherogenesis.

Elevation of arterial phosphorfuctokinase activity associated with susceptibility to atherosclerosis in pigeons

The activity of phosphofructokinase (PFK, 2.7.1.11) was measured in arteries of very young (5-8 week old) pigeons known to differ in susceptibility to atherosclerosis. The activity of the arterial enzyme was significantly higher in the atherosclerosis-susceptible White Carneau (WC) pigeons than in the resistant Show Racers (SR). The difference was significant whether enzyme activity was calculated on the basis of extract protein, DNA content or fat-free dry weight. In the White Carneau arteries the activity of the enzyme was higher in the female than the male pigeons. PFK is a key regulatory enzyme of glycolysis and is subject to fine control adjustments. A low ATP/ADP ratio and a fall in citrate concentration, as for example, induced by hypoxia, are meditors of a feedback mechanism leading to a rise in PFK activity and enhancement of glycolysis for energy production. This mechanism appears to be the cause of the higher PFK activity in the WC arteries, because related studies indicate impaired Krebs cycle activity in these vessels. It is suggested that the increased dependence of the WC arteries on glycolysis facilitates the development of atherosclerosis in this pigeon strain and that the mechanism is similar to the mechanism by which tissue hypoxia causes lipid accumulation and connective tissue alterations in the arterial wall.