Causal relationship between occlusive lesions of the coronary artery and myocardial fibrosis in arteriosclerotic rabbits--differences between cholesterol-fed and heritable hyperlipidemic rabbits

The insulin-like growth factor binding protein-microfibrillar associated protein-sterol regulatory element binding protein axis regulates fibroblast-myofibroblast transition and cardiac fibrosis

BACKGROUND AND PURPOSE

Excessive fibrogenesis is associated with adverse cardiac remodelling and heart failure. The myofibroblast, primarily derived from resident fibroblast, is the effector cell type in cardiac fibrosis. Megakaryocytic leukaemia 1 (MKL1) is considered the master regulator of fibroblast-myofibroblast transition (FMyT). The underlying transcriptional mechanism is not completely understood. Our goal was to identify novel transcriptional targets of MKL1 that might regulate FMyT and contribute to cardiac fibrosis.

EXPERIMENTAL APPROACH

RNA sequencing (RNA-seq) performed in primary cardiac fibroblasts identified insulin-like growth factor binding protein 5 (IGFBP5) as one of the genes most significantly up-regulated by constitutively active (CA) MKL1 over-expression. IGFBP5 expression was detected in heart failure tissues using RT-qPCR and western blots.

KEY RESULTS

Once activated, IGFBP5 translocated to the nucleus to elicit a pro-FMyT transcriptional programme. Consistently, IGFBP5 knockdown blocked FMyT in vitro and dampened cardiac fibrosis in mice. Of interest, IGFBP5 interacted with nuclear factor of activated T-cell 4 (NFAT4) to stimulate the transcription of microfibril-associated protein 5 (MFAP5). MFAP5 contributed to FMyT and cardiac fibrosis by enabling sterol response element binding protein 2 (SREBP2)-dependent cholesterol synthesis.

CONCLUSIONS AND IMPLICATIONS

Our data unveil a previously unrecognized transcriptional cascade, initiated by IGFBP5, that promotes FMyT and cardiac fibrosis. Screening for small-molecule compounds that target this axis could yield potential therapeutics against adverse cardiac remodelling.

Carotid atherosclerosis is associated with left ventricular diastolic function

BACKGROUND

It has been reported that carotid intima-media thickness (IMT) correlates with the risk of stroke or cardiovascular disease. The purpose of this study was to analyze the relationships between echocardiographic findings and carotid atherosclerosis.

METHODS

A total of 234 patients (62 ± 15 years) were referred for echocardiography to evaluate the left ventricular (LV) function. The LV ejection fraction, the ratio of the peak velocity of early rapid filling and the peak velocity of atrial filling (E/A), and the peak early diastolic mitral annular velocity (e') were obtained by echocardiography. The maximum IMT (Max-IMT) and plaque score (PS) were measured by carotid ultrasonography within 1 month of the echocardiographic examination.

RESULTS

The mean values of Max-IMT and carotid PS were 2.41 ± 1.23 mm and 8.5 ± 6.3, respectively. The decreased mean E/A (0.94 ± 0.39) and mitral e' (5.5 ± 1.9 cm/s) indicated LV diastolic dysfunction. A good correlation was observed between Max-IMT and PS (r = 0.83, p < 0.0001). It was shown that 2.8 mm of Max-IMT was equivalent to 10.1 of carotid PS, which indicated severe carotid atherosclerosis. In multiple logistic stepwise regression analysis, among the echocardiographic parameters, only e' was independently associated with severe carotid atherosclerosis (Max-IMT ≥ 2.8 mm or PS ≥ 10.1).

CONCLUSIONS

The present study demonstrated that decreased early diastolic mitral annular velocity relates to the parameter reflecting carotid atherosclerosis. Therefore, the presence of severe carotid atherosclerosis may affect LV diastolic dysfunction.

A novel computer-based method for the measurement of the lipid “load” in the coronary vessels of rabbits

INTRODUCTION

This study reports the development of a new, accurate and reproducible method which combines histological and computer techniques for the determination of fatty load in cholesterol-fed rabbits.

METHODS

New Zealand male rabbits were randomly divided into three groups. The animals in group 1 (control) received neither cholesterol nor drugs. Those in group 2 received a 2% cholesterol diet for 30 days, followed by a normal diet for 45 days. In addition during the latter period (day 31 to day 75) animals received 200 g of chopped carrots each morning. The rabbits in group 3 followed the same dietary regime as those in group 2 except that 8.36 mg of simvastatin and 1.76 g cholestyramine were mixed with their carrots. On the 76th day, the animals were sacrificed and their blood and hearts were collected. Histological sections (15 microm thick) of hearts were cut at 90 degrees to the long axis using a motorized freezing microtome. Every tenth section was mounted on a glass slide and stained with Oil Red O. A total of hundred slides prepared from each heart were scanned into a computer and the area stained by Oil Red O was measured, giving a measure of the total fatty "load" in each heart.

RESULTS

There was a highly significant increase in the coronary fatty deposits in the hearts of the animals fed with cholesterol rich diet (group 2) as compared to the control rabbits in group 1. Treatment of rabbits with simvastatin plus cholestyramine (group 3) significantly reduced the coronary lipids load.

DISCUSSION

The combination of histological and computer-based techniques used in this study provides an accurate and reproducible method for the quantitation of fatty deposits in rabbit coronary vessels. This report is based on the measurement of coronary lipid depositions rather than aortic lesions. It also overcomes the shortcoming of the majority of the earlier published methods which are generally limited to the measurement of fatty plaques in only few major coronary vessels, totally neglecting the many small distributive vessels which are often responsible for cardiac ischemic disease.

Hypercholesterolemia-Induced Long-Term Increase of Macrophages in the Myocardium of New Zealand White Rabbits

The effect of hypercholesterolemia on the number, immunological phenotype and oxidative stress-dependent processes of macrophages (MPhi) and dendritic cells (DC) was studied in New Zealand White rabbits. The left ventricular myocardium was immunohistochemically analyzed in group I (control), which was on standard chow, and groups II and III, which both received a 0.5% cholesterol-enriched diet for 96 days, but thereafter, only group III was fed standard chow for 4 months. In the myocardial interstitium of group I, (1) significantly less RAM-11-immunoreactive (ir) MPhi than S-100-ir DC were found; (2) both, MPhi and DC, were similar major histocompatibility complex (MHC) class II molecules LN3-, ISCR3-, and 2.06-ir; (3) all MPhi and most DC were manganese superoxide dismutase (MnSOD)-ir and homing receptor CD44-ir. In group II, only MPhi increased about 10-fold in the myocardium in parallel to the about 40-fold increase of the serum cholesterol levels. In group III, the elevated serum cholesterol levels significantly decreased (about 90%), while the MPhi still remained significantly increased (about 8-fold). The cellular immunoreactivities of MHC class II molecules, as well as MnSOD and CD44 did not change in groups II and III in comparison to group I. We suggest that mainly the MPhi, which increase within the myocardium of rabbits after elevation of serum cholesterol levels and remain significantly increased for a long time after decrease of the blood lipid levels, might initiate or aggravate eventual complications such as coronary atherosclerosis and myocardial fibrosis.

Arteriosclerosis in the influx and intravisceral arteries of the liver, kidney and lung of WHHL rabbits

We performed a histopathological investigation on arteriosclerotic development in the influx and intravisceral arteries of the liver, kidney and lung of male WHHL rabbits. In the influx arteries of these organs, we observed severe atherosclerotic vascular lesions with high-grade luminal stenosis. In the intravisceral arteries of the liver and kidney, no arteriosclerotic lesions were observed. However, in the intrapulmonary arteries, we recognized severe atherosclerotic vascular changes with high-grade stenosis or total obstruction of the lumen in some middle to large sized pulmonary arteries. These observations indicate that the development of arteriosclerosis in parenchymatous organs differs, and that some organs are predisposed to arteriosclerosis formation.

Distribution and prevalence of inducible nitric oxide synthase in atherosclerotic vessels of long-term cholesterol-fed rabbits

The expression of inducible nitric oxide synthase (iNOS) as well as its functional activity has recently been reported in atherosclerotic lesions. The aim of the present study was to evaluate the expression of iNOS in various arteries of rabbits fed a long-term but low-level cholesterol-enriched diet which promotes different types of atherosclerotic lesions resembling human diseased vessels. No iNOS expression was revealed in arteries from control rabbits and in fatty streaks found in carotid and femoral arteries from hypercholesterolemic rabbits. In transitional lesions from the thoracic and abdominal aortas, the coronary and pulmonary arteries, a punctiform iNOS staining was detected in the intima. When lesions were more advanced, iNOS expression was found more intense and diffuse and localized in the subendothelial layer as well as in the media. Smooth muscle cell accumulation in intimal layers of the arteries is a marker of the degree of evolution of the atherosclerotic lesion; since we found a correlation between the smooth muscle cell infiltration in the intima and the iNOS expression in the intima and the subendothelial layer, our results suggest a link between the severity of the lesion and the iNOS expression.

Oral administration of NO synthase inhibitor failed to promote arteriosclerotic lesions in the aorta and the coronary arteries of rabbits fed cholesterol

We examined whether or not the oral administration of L-nitroarginine methylester (L-NAME), an inhibitor of nitric oxide (NO) synthase, promotes cholesterol-induced arteriosclerosis in the aorta and the coronary artery. Thirty-six male Japanese white rabbits were fed 0.5% cholesterol-containing laboratory chow and randomly assigned to the following three groups: (1) water, (2) 80 microg/ml L-NAME and (3) 400 microg/ml L-NAME in drinking water. The rabbits were fed a 0.5% cholesterol-containing diet for 8 months. During the 8-month period, the concentration of total cholesterol and L-nitroarginine in the serum and the mean blood pressure were measured. The concentration of NO3 in the serum was also measured. After sacrifice, the aortic surface involvement (AI%), the ratio of the thickened intima to the media and the contents of the total cholesterol of the aorta, the maximum % stenosis of the subepicardial large coronary artery, the % frequency of the nearly completely occlusive distal small coronary artery and the area of the myocardial fibrosis were all measured. We found no statistical difference among the three groups regarding the degree of arteriosclerotic lesions of the aorta and of the large coronary artery, and the area of myocardial fibrosis, as well as the serum cholesterol exposure index (the area under the curve of the serum total cholesterol concentration) and the mean blood pressure. However, the serum concentration of L-nitroarginine was approximately 50 and 200 microM/l in groups 2 and 3, respectively. The concentration of NO3 in the serum in group 1 was significantly higher than that in groups 2 and 3. We thus conclude, that the oral administration of L-NAME in the rabbits fed a cholesterol-containing diet for 8 months failed to promote arteriosclerotic lesions in the aorta and the coronary artery, even though the serum concentration of L-nitroarginine increased sufficiently to inhibit NO synthase in the arterial endothelium and the NO3 concentration in the serum decreased in the rabbits given L-NAME.