Abstract 595: Transcriptional Control of Intestinal Cholesterol Absorption, Adipose Energy Expenditure and Lipid Handling by Sortilin

Objective: The sorting receptor Sortilin functions in the regulation of glucose and lipid metabolism. Dysfunctional lipid uptake, storage, and metabolism contribute to several major human diseases including atherosclerosis and obesity. Sortilin associates with cardiovascular disease; however, the role of Sortilin in adipose tissue and lipid metabolism remains unclear.

Approach and Results: Here we show that in the low-density lipoprotein receptor-deficient (Ldlr -/- ) atherosclerosis model, Sortilin deficiency ( Sort1 -/- ) in female mice inhibits intestinal Niemann-Pick type C1-Like 1 (Npc1l1) expression (-60.6 %, p<0.01), reduces body (-17.2 %, p<0.01) and white adipose tissue weight (-35.2 %, p<0.05), and improves brown adipose tissue function partially via transcriptional downregulation of Krüppel-like factor 4 and Liver X receptor (Figure). Female Ldlr -/- Sort1 -/- mice on a high fat/cholesterol diet had elevated plasma Fibroblast growth factor 21 (+89.1 %, p<0.05) and Adiponectin (+37.7 %, p<0.01), an adipokine that when reduced is associated with obesity and cardiovascular disease related factors. Additionally, Sortilin deficiency suppressed cholesterol absorption in both human colon Caco-2 cells (-16.5 %, p<0.05) and mouse ex vivo intestinal tissue (-16.9 %, p<0.05) in a similar manner to treatment with the Npc1l1 inhibitor - ezetimibe.

Conclusions: Together our findings support a novel role of Sortilin in energy regulation and lipid homeostasis in female mice, which may be a potential therapeutic target for obesity and cardiovascular disease.

Abstract 452: Longitudinal Visualization of Calcification Genesis and Growth in vivo : Novel Implications for Plaque Vulnerability

Background: Clinical evidence links arterial calcification and cardiovascular risk. Fibrous cap microcalcifications can promote atherosclerotic plaque failure, and large calcifications can stabilize the plaque. Therefore, calcification morphology can determine cardiovascular morbidity, but temporal patterns of calcific mineral deposition and growth remain unknown.

Results: Apolipoprotein E-deficient ( Apoe-/- ) mice on an atherogenic diet develop plaque calcification. Longitudinal studies were performed using two different fluorescent calcium tracers injected intravenously into Apoe-/- mice: calcein injection following 18 weeks of atherogenic diet (n=7) and alizarin red S injection into the same mice 1 (n=4) or 3 (n=3) weeks later. Imaging green (calcein) and red (alizarin red S) fluorescence provided snapshots of aortic calcification at 18, 19, and 21 weeks. Observations within histological sections revealed green microcalcifications at 18 weeks embedded within alizarin red stained larger calcifications that were formed by 19 weeks (a). These data demonstrate that microcalcifications present at the start of calcification become the core of the larger calcifications that develop over time. Serial histological sections from aortic root to arch (b) were digitally reconstructed into 3D volumes (c) to reveal total calcific burden and localization within the aortic wall (d). Total calcification volume increased at a significant rate of 6.0x10 6 μm 3 per week (R 2 =0.99, p=0.007) and progressed from aortic arch to aortic root over time (p<0.001). Observations closely match calcification morphologies found by micro-computed tomography of human coronary arteries.

Conclusion: Temporal and spatial understanding arterial calcification growth is crucial given the link between mineral morphology and cardiovascular risk, and these techniques provide a method for testing therapeutic approaches to control calcification morphology over time in situ .

Abstract 647: Induction of Cardiovascular Calcification in Non-transgenic Mice via a Single Injection of Pcsk9 Adeno-associated Viral Vector

Background: Studying atherosclerotic calcification in vivo requires mouse models with genetic deletion of low-density lipoprotein receptor (Ldlr) or apolipoprotein E. A previous study showed a rapid induction of atherosclerosis by proprotein convertase subtilisin/kexin type 9 (PCSK9) in mice. Here, we hypothesize that this method is a useful in vivo tool to study cardiovascular calcification in non-genetically modified C57BL/6 mice.

Results: 10 week old C57BL/6 mice received a single tail vein injection of recombinant adeno-associated viral vector (AAV) encoding PCSK9 (rAAV8/D377Y-mPCSK9). Ldlr -/- and saline injected C57BL/6 mice served as controls. Mice consumed a high-fat, high-cholesterol (HF/HC) diet for 15-20 weeks. PCSK9 and total cholesterol serum levels were significantly increased within one week after injection and maintained for 20 weeks (cholesterol: 82 mg/dL to 820 mg/dL, p<0.01; PCSK9: 0.14 μg/ml to 20 μg/ml, p<0.01). Total cholesterol levels remained 20-30% lower than those of of Ldlr -/- mice. Atherosclerotic lesion size was similar between PSCK9 and Ldlr -/- mice. Saline injected mice did not show any lesions. Plaque collagen content was 31.9%±6.6 in PCSK9 mice and 62.9%±16.6 in Ldlr -/- mice at 15 weeks of HF/HC diet (p=0.01). However, by 20 weeks, the PCSK9 mice had 57.9%±18.6 plaque collagen, suggesting a different stage of plaque progression. Fluorescence reflectance imaging of a near infrared calcium tracer in intact arteries detected 0.4%±0.4 aortic calcification in PCSK9 mice and 9.7%±1.6 in Ldlr -/- mice at 15 weeks of HF/HC diet (p=0.01); by 20 weeks, the PCSK9 mice had 5.3%±1.0 aortic calcification. Tissue non-specific alkaline phosphatase activity positive lesion area was 7.9%±4.0 and 8.3%±2.6 in PCSK9 mice and 10.8%±2.5 and 12.7%±1.7in Ldlr -/- mice at 15 and 20 weeks, respectively. Immunofluorescence analysis demonstrated accumulation of CD68 and RUNX2-positive cells in the plaques of PCSK9 mice similar to Ldlr -/- .

Conclusion: While injection of recombinant AAV encoding PCSK9 into C57BL/6 mice induces atherosclerotic calcification with slower sclerotic plaque remodeling compared to Ldlr -/- mice, it may serve as a useful tool to study cardiovascular calcification in mice independent of their genetic background.