ApoC2 deficiency elicits severe hypertriglyceridemia and spontaneous atherosclerosis: A rodent model rescued from neonatal death.

RATIONALE: ApoC2 is an important activator for lipoprotein lipase-mediated hydrolysis of triglyceride-rich plasma lipoproteins. ApoC2-deficient patients display severe hypertriglyceridemia (sHTG) and recurrent acute pancreatitis. However, due to embryonic lethality in ApoC2 deleted mouse extensive understanding of ApoC2 function is limited in mammalian species. OBJECTIVE: We sought to generate an animal model with ApoC2 deficiency in a rodent with some human-like features and then study the precise effects of ApoC2 on lipid and glucose homeostasis. METHODS AND RESULTS: Using CRISPR/Cas9, we deleted Apoc2 gene from golden Syrian hamster and the homozygous (-/-) pups can be born in matured term but exhibited neonatal lethality. By continuous iv administration of normal hamster serum the ApoC2-/- pups could survive till weaning and displayed severe HTG in adulthood on chow diet. A single iv injection of AAV-hApoC2 at birth can also rescue the neonatal death of ApoC2-/- pups. Adult ApoC2-/-hamsters exhibited a unique phenotype of sHTG with hypoglycemia, hypoinsulinemia and spontaneous atherosclerosis. The sHTG in ApoC2-/- adult hamsters could not be corrected by various lipid-lowering medications, but partially ameliorated by medium chain triglyceride diet and completely corrected by AAV-hApoC2. CONCLUSIONS: Our study provides a novel ApoC2-deleted mammalian model with severe hypertriglyceridemia that was fully characterized and highlights a potential therapeutic approach for the treatment of ApoC2 deficient patients.

Hypertriglyceridemia and atherosclerosis.

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death and it has been confirmed that increased low density lipoprotein cholesterol (LDL-C) is an independent risk factor for atherosclerosis. Recently, the increasing evidence has showed that hypertriglyceridemia is associated with incremental ASCVD risk. But the proatherogenic mechanism of triglyceride (TG) remains unclear. Therefore, this article focuses on the clinical studies and proatherogenic mechanism related to hypertriglyceridemia, in order to provide reference for the prevention and treatment of ASCVD.

17ß-estradiol lowers triglycerides in adipocytes via estrogen receptor α and it may be attenuated by inflammation.

BACKGROUND: Estrogen was reported to protect against obesity, however the mechanism remains unclear. We aimed to investigate the impact of 17ß-estradiol (17ß-E2) on triglyceride metabolism in adipocytes with or without lipopolysacchride (LPS) stimulating, providing novel potential mechanism for estrogen action. METHODS: 3T3-L1 adipocytes were cultured and differentiated into mature adipocytes in vitro. The differentiated 3T3-L1 cells were divided into six groups: (i) control group, treated with 0.1% DMSO alone; (ii) 17ß-E2 group, treated with 1, 0.1, or 0.001 µM 17ß-E2 for 48 h; (iii) 17ß-E2 plus MPP group, pre-treated with 10 µM MPP (a selective ERα receptor inhibitor) for 1 h, then incubated with 1 µM 17ß-E2 for 48 h; (iv) 17ß-E2 plus PHTPP group, pre-treated with 10 µM PHTPP (a selective ERß receptor inhibitor), then incubated with 1 µM 17ß-E2 for 48 h; (v) LPS group, pre-treated with 100 ng/mL LPS for 24 h, then cells were washed by PBS for 3 times and incubated with 0.1% DMSO alone for 48 h; (vi) 17ß-E2 plus LPS group, pre-treated with 100 ng/mL LPS for 24 h, then cells were washed by PBS for 3 times and incubated with 1 µM 17ß-E2 for 48 h. The levels of triglyceride and adipose triglyceride lipase (ATGL) in differentiated 3T3-L1 cells and the concentrations of interleukin-6 (IL-6) in culture medium were measured. RESULTS: Comparing with control group, 1 µM and 0.1 µM 17ß-E2 decreased the intracellular TG levels by about 20% and 10% respectively (all P < 0.05). The triglyceride-lowing effect of 17ß-E2 in differentiated 3T3-L1 cells was abolished by ERα antagonist MPP but not ERß antagonist PHTPP. Comparing with control group, the IL-6 levels were significantly higher in the culture medium of the cultured differentiated 3T3-L1 cells in LPS group and 17ß-E2 + LPS group (all P < 0.05). And, the IL-6 levels were similar in LPS group and 17ß-E2 + LPS group (P > 0.05). There was no significant difference in the triglyceride contents of differentiated 3T3-L1 cells among control group, LPS group and 17ß-E2 + LPS group (all P > 0.05). ATGL expression in 17ß-E2 group was significantly higher than control group (P < 0.05), which was abolished by ERα antagonist MPP or LPS. CONCLUSIONS: 17ß-E2 increased ATGL expression and lowered triglycerides in adipocytes but not in LPS stimulated adipocytes via estrogen ERα.

Combined use of metformin and atorvastatin attenuates atherosclerosis in rabbits fed a high-cholesterol diet.

Statins are widely used to reduce cardiovascular risk. Unfortunately, some patients still experience cardiovascular events though prescribed with high-intensity statins. Metformin, an anti-diabetic drug, was reported to possess anti-atherosclerotic effects. Therefore, the experiments were designed to evaluate whether combined use of metformin and atorvastatin can achieve additional benefits. In rabbits fed a high-cholesterol diet, we evaluated the effects of the combination therapy on atherosclerotic plaques, lipid profiles, blood glucose levels, liver and kidney functions. Effects of combination therapy on cholesterol efflux and the expression of related transporters were studied in vitro. Our results showed that the combination therapy induced a more significant decrease in atherosclerotic lesion area than atorvastatin without additional lipid-lowering effect. The combination therapy significantly increased the percentage of large high-density lipoprotein subfraction. The intravenous glucose tolerance test showed that atorvastatin-treated rabbits had an increased area under the curve for time-dependent glucose levels after a bolus injection of glucose, which was completely reversed by metformin treatment. In cultured macrophages, co-treatment with metformin and atorvastatin promoted cholesterol efflux and up-regulated expression of ATP-binding cassette transporters A1 and G1. Taken together, our results suggest that atorvastatin/metformin combination therapy may achieve additional anti-atherosclerotic benefits likely through increasing cholesterol efflux in macrophages.

Estrogen lowers triglyceride via regulating hepatic APOA5 expression.

Estrogen had been found to be negatively associated with serum triglyceride (TG) levels. Apolipoprotein A5 (APOA5), a novel member of apolipoprotein family, was reported to have a strong ability to decrease serum concentrations of TG. Clinical data found concentrations of APOA5 were higher in woman than that in men, and the negative relationship between APOA5 and TG levels was more significant in woman. These suggests APOA5 may involve in estrogen actions. Therefore, we hypothesize estrogen up-regulates serum concentrations of APOA5 and subsequently decreases serum TG levels. We will design the following experiments to test this hypothesis. (1) We will treat wild and APOA5-defeted ovariectomized hamster with or without estrogen to examine if estrogen could up-regulate concentrations of APOA5 and decrease TG levels. (2) We will treat HepG2 cells with estrogen and investigate the possible mechanisms.