Transgenic expression of matrix metalloproteinase-2 induces coronary artery ectasia

Abstract

Coronary artery ectasia (CAE) is generally diagnosed in patients undergoing arteriography for presumptive atherosclerotic coronary artery disease. CAE is commonly considered as a variant of atherosclerotic disease; however, recent studies suggest that CAE is the result of a systemic vascular disorder. There is increasing evidence that aneurysmal vascular disease is a systemic disorder characterized by enhanced expression of pro-inflammatory cytokines and increased synthesis of enzymes capable of degrading elastin and other components of the vascular wall. Matrix metalloproteinase-2 degrades a number of extracellular substrates, including elastin and has been shown to play a critical role in the development of abdominal aortic aneurysms. This study characterizes the development of CAE in a unique murine transgenic model with cardiac-specific expression of active MMP-2. Transgenic mice were engineered to express an active form of MMP-2 under control of the α-myosin heavy chain promoter. Coronary artery diameters were quantified, along with studies of arterial structure, elastin integrity and vascular expression of the MMP-2 transgene. Latex casts quantified total coronary artery volumes and arterial branching. Mid-ventricular coronary luminal areas were increased in the MMP-2 transgenics, coupled with foci of aneurysmal dilation, ectasia and perivascular fibrosis. There was no evidence for atherogenesis. Coronary vascular elastin integrity was compromised and coupled with inflammatory cell infiltration. Latex casts of the coronary arteries displayed ectasia with fusiform dilatation. The MMP-2 transgenic closely replicates human CAE and supports a critical and initiating role for this enzyme in the pathogenesis of this disorder.

Figure 1

Masson trichrome stain of mid-ventricular coronary artery cross sections from wild-type (WT) and MMP-2 transgenic (MMP2 TG) mice at 8 months. (a) Cross section of WT coronary artery showing normal diameter, minimal branching and normal amounts of perivascular fibrosis. (b) Cross section of MMP-2 transgenic showing coronary artery dilatation, multiple primary and secondary branching arteries and large amounts of perivascular fibrosis (×200).

Figure 2

Luminal areas of coronary and femoral arteries of WT and MMP-2 TG mice (a) Coronary artery luminal areas of WT and MMP-2 TG mice at 4 months of age. There is a trend for increased coronary artery luminal diameters in the MMP-2 TG mice, but does not reach statistical significance. (b) Coronary artery luminal areas of WT and MMP-2 TG mice at 8 months of age: there is a significant increase in coronary artery luminal diameters (approximately 60%) in the MMP-2 TG mice. (c) Femoral artery luminal diameters of WT and MMP-2 TG mice at 8 months of age. There is no significant difference in the luminal areas between the two study groups.

Figure 3

Immunohistochemical detection of c-myc-tagged MMP-2 transgene expression in coronary arteries of WT and MMP-2 TG mice at 4 and 8 months. (a) There is no detectable expression of the c-myc epitope in the WT heart and coronary arteries. (b) Dark brown staining for the c-myc epitope is widely present within the cardiomyocytes in 4-month-old hearts, whereas the cellular components of the coronary artery are not stained. (c) Prominent staining for the transgenic c-myc epitope tag is evident within the perivascular adventitia (arrow) of 8-month-old mice, whereas transgene expression is patchy in the cardiomyocytes due to age-dependent silencing. (d) Medial staining for the transgenic c-myc epitope is evident in this dilated coronary artery from an 8-month-old mouse. (a–c × 200; d × 400).

Figure 4

Verhoeff’s elastin stain of mid-ventricular coronary artery cross sections at 8 months of age. (a) WT control with intact internal elastic lamina (arrow). (b) MMP-2 TG: The internal elastic lamina is fragmented and disrupted (arrows). (a, b × 300, inset ×500).

Figure 5

Characterization of coronary artery ectasia in MMP-2 TG mice. (a) Longitudinal section of a mid-ventricular coronary artery from an 8-month-old transgenic mice, demonstrating massive, localized arterial dilatation with ectasia. (b) Severely ectatic coronary artery with perivascular cellular infiltrates. (c) Focus of medial disruption (black arrow) immediately adjacent to proliferating vascular smooth muscle cell (blue arrow). (d) Focus of profound perivascular inflammatory cell infiltrate (black arrow) extending through the vascular media layer (blue arrow). (Masson trichrome stain; a × 50; b × 100; c, d × 400).

Figure 6

Latex casts of WT and MMP-2 TG coronary arterial trees from 8-month-old mice. (a) WT coronary arterial tree. (b) TG coronary arterial tree with a diffuse increase in diameter along with increased arterial branching and ectasia (black arrow). (c) Extensive fusiform dilatation of the left anterior descending coronary artery (white arrow). (a–c: ×10).

Figure 7

Quantification of coronary arterial vasculature branching and volumes of latex casts from 8-month-old mice. (a) Primary and secondary branches extending from the left main coronary artery (LMCA). There is a significant increase in the extent of primary and secondary arterial branching in the MMP-2 TG mice. (b) Total coronary arterial volumes as determined by quantitative densitometry of digitized images of the coronary artery latex casts. There is a significant, greater than two-fold increase in total coronary artery volumes in the MMP-2 TG mice.