ADAMTS5 deficiency protects against non-alcoholic steatohepatitis in obesity.

BACKGROUND & AIMS: Increased prevalence of obesity is paralleled by an increase in non-alcoholic steatohepatitis (NASH). We previously found that the expression of ADAMTS5 (A Disintegrin And Metalloproteinase with Thrombospondin type 1 motifs; member 5) is enhanced in expanding adipose tissue. However, no information is available on a potential role in liver pathology. We studied the effect of ADAMTS5 deficiency on NASH in mice. METHODS: Wild-type (Adamts5+/+ ) and deficient (Adamts5-/- ) mice were kept on a standard- or high-fat diet (HFD) for 15 weeks. Alternatively, steatohepatitis was induced with methionine/choline-deficient (MCD) diet. RESULTS: HFD feeding resulted in comparable body weights for both genotypes, but Adamts5-/- mice had approximately 40% lower liver weight (P = 0.0004). In the Adamts5-/- mice, the HFD as well as the MCD diet consistently induced less NASH with less fibrosis. The deteriorating effect of ADAMTS5 on the liver during diet-induced obesity may be due, at least in part, to proteolytic cleavage of the matrix components syndecan-1 and versican, thereby enhancing hepatic triglyceride clearance from the circulation. Plasma lipid levels were elevated in obese Adamts5-/- mice. There was no clear effect of ADAMTS5 deficiency on glycaemia or glucose tolerance, whereas insulin sensitivity was somewhat improved. Furthermore, Adamts5-/- mice were protected from hepatic mitochondrial dysfunction, as indicated by increased mitochondrial respiratory chain complex activity, higher ATP levels and higher expression of antioxidant enzymes. CONCLUSIONS: Absence of ADAMTS5 preserves liver integrity in a diet-induced obesity model. Selective targeting of ADAMTS5 could provide a new therapeutic strategy for treatment/prevention of NASH.

Elastin fragmentation in atherosclerotic mice leads to intraplaque neovascularization, plaque rupture, myocardial infarction, stroke, and sudden death.

AIMS: There is a need for animal models of plaque rupture. We previously reported that elastin fragmentation, due to a mutation (C1039G(+/-)) in the fibrillin-1 (Fbn1) gene, promotes atherogenesis and a highly unstable plaque phenotype in apolipoprotein E deficient (ApoE(-/-)) mice on a Western-type diet (WD). Here, we investigated whether plaque rupture occurred in ApoE(-/-)Fbn1(C1039G+/-) mice and was associated with myocardial infarction, stroke, and sudden death. METHODS AND RESULTS: Female ApoE(-/-)Fbn1(C1039G+/-) and ApoE(-/-) mice were fed a WD for up to 35 weeks. Compared to ApoE(-/-) mice, plaques of ApoE(-/-)Fbn1(C1039G+/-) mice showed a threefold increase in necrotic core size, augmented T-cell infiltration, a decreased collagen I content (70 ± 10%), extensive neovascularization, intraplaque haemorrhage, and a significant increase in matrix metalloproteinase-2, -9, -12, and -13 expression or activity. Plaque rupture was observed in 70% of ascending aortas and in 50% of brachiocephalic arteries of ApoE(-/-)Fbn1(C1039G+/-) mice. In ApoE(-/-) mice, plaque rupture was not seen in ascending aortas and only in 10% of brachiocephalic arteries. Seventy percent of ApoE(-/-)Fbn1(C1039G+/-) mice died suddenly, whereas all ApoE(-/-) mice survived. ApoE(-/-)Fbn1(C1039G+/-) mice showed coronary plaques and myocardial infarction (75% of mice). Furthermore, they displayed head tilt, disorientation, and motor disturbances (66% of cases), disturbed cerebral blood flow (73% of cases; MR angiograms) and brain hypoxia (64% of cases), indicative of stroke. CONCLUSIONS: Elastin fragmentation plays a key role in plaque destabilization and rupture. ApoE(-/-)Fbn1(C1039G+/-) mice represent a unique model of acute plaque rupture with human-like complications.

Evaluation of matrix metalloproteinases in atherosclerosis using a novel noninvasive imaging approach.

OBJECTIVE: Despite great advances in our knowledge, atherosclerosis continues to kill more people than any other disease in the Western world. This is because our means of identifying truly vulnerable patients is limited. Prediction of atherosclerotic plaque rupture may be addressed by MRI of activated matrix metalloproteinases (MMPs), a family of enzymes that have been implicated in the vulnerability of plaques prone to rupture. This study evaluated the ability of the novel gadolinium-based MRI contrast agent P947 to target MMPs in atherosclerotic plaques. METHODS AND RESULTS: The affinity of P947 toward activated MMPs was demonstrated in vitro. The affinity and specificity of P947 toward matrix metalloproteinase (MMP)-rich plaques was evaluated both in vivo using ApoE-/- mice and ex vivo in hyperlipidemic rabbits. Gadolinium content quantification and MRI showed a preferential accumulation of P947 in atherosclerotic lesions compared with the nontargeted reference compound, Gd-DOTA. The ex vivo assay on rabbit plaques revealed a higher uptake of P947. Moreover, using human carotid artery endarterectomy specimens, P947 facilitated discrimination between histologically defined MMP-rich and MMP-poor plaques. An in vivo MRI investigation in mice revealed that P947 greatly improved the ability to visualize and delineate atherosclerotic plaques. CONCLUSIONS: P947 may be a useful tool for the detection and characterization of the MMP-rich atherosclerotic plaques.

Does rosiglitazone affect adiposity and cardiac function in genetic diabetic mice?

Rosiglitazone ((RS)-5-[4-(2-[methyl(pyridin-2-yl)amino]ethoxy)benzyl]thiazolidine-2,4-dione, RGZ)-induced adverse drug effects in diabetic patients were not adequately predicted by current preclinical rodent models. Therefore, we have used the Akita mouse with genetic predisposition to diabetes to unravel the underlying molecular mechanisms. The effect of RGZ on adipose tissue and on cardiac function was evaluated in diabetic Akita mice kept on a high fat-high cholesterol diet (HF-HCD) for 4 months. When compared to wild-type (WT) mice with the same C57BL/6J genetic background, Akita mice gained significantly less weight (4.4±1.4 g versus 12±0.97 g for WT; P=0.002) and developed less fat (volume of 3.1±1.2 ml versus 16±2.1 ml for WT; P=0.004), associated with adipocyte hypotrophy. Upon treatment with RGZ (10mg/kg/day), Akita mice showed enhanced weight gain (11±0.70 g; P=0.004 versus untreated Akita mice) and fat volume (7.4±0.63 ml; P<0.05 versus untreated Akita mice), without effects on adipocyte or blood vessel size or on macrophage infiltration in adipose tissues. Akita mice kept on HF-HCD for 4 months with administration of RGZ (30 mg/kg/day) showed increased intraventricular septum thickness and cardiac output, without, however, an effect on fractional shortening or ejection fraction. In conclusion, RGZ promotes adiposity and early signs of hypertrophic cardiomyopathy in the diabetic Akita mouse. Thus, this genetically manipulated model may be suitable to test safety of anti-diabetic drugs.

Impact of clock gene Bmal1 deficiency on nutritionally induced obesity in mice.

To evaluate the hypothesis that the clock gene Bmal1 (brain and muscle arnt like protein-1) plays a role in the development of obesity, 5-week-old male Bmal1-deficient (Bmal1(-/-)) mice and wild-type littermates (Bmal1(+/+)) were kept on a high-fat diet (HFD) for 15 weeks. Despite an initial accelerated weight gain of Bmal1(-/-) mice, body weight and subcutaneous (SC) and gonadal (GON) adipose tissue mass were comparable to Bmal1(+/+) mice at the end of the diet period. Noninvasive magnetic resonance imaging scanning revealed a modest increase in fat content in Bmal1(-/-) mice after 10 weeks of HFD, whereas at the start and the end of the HFD feeding no differences were observed between both genotypes. After 15 weeks of HFD, adipocyte and blood vessel size and density were similar for Bmal1(+/+) and Bmal1(-/-) mice. However, the weight of major organs was significantly reduced in Bmal1(-/-) mice, confirming the premature ageing phenotype. Thus, we hypothesize that an initial accelerated increase in body weight and fat mass of Bmal1(-/-) mice on HFD may have been offset by the effect of premature ageing on organ weight, resulting in comparable weights after 15 weeks of HFD.

Fumagillin reduces adipose tissue formation in murine models of nutritionally induced obesity.

The effect of fumagillin (a methionine aminopeptidase-type 2 (Met-AP2) inhibitor, with antiangiogenic properties) was investigated in murine models of diet-induced obesity. Eleven-week-old male C57Bl/6 mice (group 1) were given fumagillin by oral gavage at a dose of 1 mg/kg/day during 4 weeks while fed a high-fat diet (HFD) (20.1 kJ/g), and control mice (group 2) received solvent and were pair-fed. At the end of the experiment, body weights in group 1 were significantly lower as compared to group 2 (P < 0.0005). The subcutaneous (SC) and gonadal (GON) fat mass was also significantly lower in group 1 (P < 0.005 and P < 0.05, respectively). Adipocytes were smaller in adipose tissues of mice in group 1, associated with higher adipocyte density. Blood vessel density normalized to adipocyte density was lower in group 1 adipose tissues. However, in mice with established obesity monitored to maintain the same body weight and fat mass as controls, short-term fumagillin administration was also associated with adipocyte hypotrophy (P = 0.01) without affecting blood vessel size or density. Thus, treatment with fumagillin impaired diet-induced obesity in mice, associated with adipocyte hypotrophy but without marked effect on adipose tissue angiogenesis.

Blood vessel density in de novo formed adipose tissue is decreased upon overexpression of TIMP-1.

Matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) play a role in the development of obesity by contributing to adipogenesis, angiogenesis, and extracellular matrix degradation. We have evaluated a potential functional role of TIMP-1, which inhibits most MMPs, in in vivo adipogenesis. Therefore, human (h) TIMP-1 was overexpressed by injection in the tail vein of NUDE mice of an adenoviral vector 3 days before injection of 3T3-F442A preadipocytes in the back. After 4 weeks of high-fat diet, the de novo formed fat was analyzed. Overexpression of hTIMP-1 had no effect on de novo formed fat pad mass. However, the blood vessel density of the fat pads from mice overexpressing hTIMP-1 was significantly lower than in controls (587 +/- 11 mm(-2) vs. 806 +/- 20 mm(-2), P < 0.0001) whereas the adipocytes were somewhat larger (1,477 +/- 44 microm(2) vs. 1,285 +/- 32 microm(2), P = 0.03). Thus, in vivo hTIMP-1 overexpression did not significantly affect the extent of de novo adipose tissue formation, but was associated with significantly lower blood vessel density.