Overexpression of tissue-nonspecific alkaline phosphatase (TNAP) in endothelial cells accelerates coronary artery disease in a mouse model of familial hypercholesterolemia

Abstract

ObjectiveOverexpression of tissue-nonspecific alkaline phosphatase (TNAP) in endothelium leads to arterial calcification in mice. The purpose of this study was to examine the effect of elevated endothelial TNAP on coronary atherosclerosis. In addition, we aimed to examine endogenous TNAP activity in human myocardium.Approach and resultsA vascular pattern of TNAP activity was observed in human non-failing, ischemic, and idiopathic dilated hearts (5 per group); no differences were noted between groups in this study. Endothelial overexpression of TNAP was achieved in mice harboring a homozygous recessive mutation in the low density lipoprotein receptor (whc allele) utilizing a Tie2-cre recombinase (WHC-eTNAP mice). WHC-eTNAP developed significant coronary artery calcification at baseline compared WHC controls (4312 vs 0μm2 alizarin red area, p<0.001). Eight weeks after induction of atherosclerosis, lipid deposition in the coronary arteries of WHC-eTNAP was increased compared to WHC controls (121633 vs 9330μm2 oil red O area, p<0.05). Coronary lesions in WHC-eTNAP mice exhibited intimal thickening, calcifications, foam cells, and necrotic cores. This was accompanied by the reduction in body weight and left ventricular ejection fraction (19.5 vs. 23.6g, p<0.01; 35% vs. 47%, p<0.05). In a placebo-controlled experiment under atherogenic conditions, pharmacological inhibition of TNAP in WHC-eTNAP mice by a specific inhibitor SBI-425 (30mg*kg-1*d-1, for 5 weeks) reduced coronary calcium (78838 vs.144622μm2) and lipids (30754 vs. 77317μm2); improved body weight (22.4 vs.18.8g) and ejection fraction (59 vs. 47%). The effects of SBI-425 were significant in the direct comparisons with placebo but disappeared after TNAP-negative placebo-treated group was included in the models as healthy controls.ConclusionsEndogenous TNAP activity is present in human cardiac tissues. TNAP overexpression in vascular endothelium in mice leads to an unusual course of coronary atherosclerosis, in which calcification precedes lipid deposition. The prevalence and significance of this mechanism in human atherosclerosis requires further investigations.

TNAP limits TGF-β-dependent cardiac and skeletal muscle fibrosis by inactivating SMAD2/3 transcription factors

“…Sheen et al demonstrated that the induced expression of TNAP in vascular smooth muscle cells is sufficient to cause medial vascular calcification (Sheen et al, 2015). Similarly Romanelli and colleagues showed that TNAP overexpression in vascular endothelium in mice leads to arterial calcification and subsequent coronary atherosclerosis (Romanelli et al, 2017). These studies described the effects of sustained TNAP overexpression, but the role of TNAP under physiological levels of expression has not been addressed.…”

“…It is involved in bone mineralization and mutations in the TNAP gene have been associated with hypophosphatasia, a rare inherited disorder, characterized by defective bone mineralization (Mornet et al, 2001). Recently TNAP has been associated with vascular calcification (Romanelli et al, 2017;Sheen et al, 2015) and cardiac fibro-calcification (Herencia et al, 2015). Its role in fibrosis and in the context of TGF-β signaling has not been addressed.…”

Research update for articles published in EJCI in 2017

“…Since its publication, additional evidence has gathered that elevated ALP activity in patients with CAD is associated with increased risk of mortality in prospective cohort studies and patients with acute coronary syndromes or acute ischaemic stroke . Other studies have reported an association between ALP and atherosclerotic risk . A recent study in a mouse model of familial hypercholesterolaemia showed that overexpression of tissue‐nonspecific ALP in endothelial cells accelerates coronary atherosclerosis through an interaction between primary intimal calcification in the form of subendothelial nodules and hypercholesterolaemia increasing lipid deposition into atherosclerotic lesions .…”

“…24 Other studies have reported an association between ALP and atherosclerotic risk. 25,26 A recent study in a mouse model of familial hypercholesterolaemia showed that overexpression of tissue-nonspecific ALP in endothelial cells accelerates coronary atherosclerosis through an interaction between primary intimal calcification in the form of subendothelial nodules and hypercholesterolaemia increasing lipid deposition into atherosclerotic lesions. 26 In subjects free of clinical cardiovascular disease, elevated ALP levels were positively and independently associated with coronary artery calciuma surrogate of coronary atherosclerosis.…”

TNAP limits TGF-β-dependent cardiac and skeletal muscle fibrosis by inactivating the SMAD2/3 transcription factors

“…It is involved in bone mineralization and mutations in the TNAPencoding gene have been associated with hypophosphatasia, a rare inherited disorder, characterized by defective bone mineralization (Mornet et al, 2001). Recently TNAP has been associated with vascular calcification (Romanelli et al, 2017;Sheen et al, 2015) and cardiac fibro-calcification (Herencia et al, 2015). Its role in fibrosis and in the context of TGF-β signalling has not been addressed.…”