RESUMO
Human apolipoprotein A-I (hApoA-I) overexpression improves high-density lipoprotein (HDL) function and the metabolic complications of obesity. We used a mouse model of diabesity, the db/db mouse, to examine the effects of hApoA-I on the two main functional properties of HDL, i.e., macrophage-specific reverse cholesterol transport (m-RCT) in vivo and the antioxidant potential, as well as the phenotypic features of obesity. HApoA-I transgenic (hA-I) mice were bred with nonobese control (db/+) mice to generate hApoA-I-overexpressing db/+ offspring, which were subsequently bred to obtain hA-I-db/db mice. Overexpression of hApoA-I significantly increased weight gain and the incidence of fatty liver in db/db mice. Weight gain was mainly explained by the increased caloric intake of hA-I-db/db mice (>1.2-fold). Overexpression of hApoA-I also produced a mixed type of dyslipidemia in db/db mice. Despite these deleterious effects, the overexpression of hApoA-I partially restored m-RCT in db/db mice to levels similar to nonobese control mice. Moreover, HDL from hA-I-db/db mice also enhanced the protection against low-density lipoprotein (LDL) oxidation compared with HDL from db/db mice. In conclusion, overexpression of hApoA-I in db/db mice enhanced two main anti-atherogenic HDL properties while exacerbating weight gain and the fatty liver phenotype. These adverse metabolic side-effects were also observed in obese mice subjected to long-term HDL-based therapies in independent studies and might raise concerns regarding the use of hApoA-I-mediated therapy in obese humans.
Assuntos
Apolipoproteína A-I/genética , Colesterol/metabolismo , Diabetes Mellitus/genética , Diabetes Mellitus/metabolismo , Expressão Gênica , Macrófagos/metabolismo , Animais , Transporte Biológico , Peso Corporal , Modelos Animais de Doenças , Fígado Gorduroso/genética , Fígado Gorduroso/metabolismo , Fígado Gorduroso/patologia , Perfilação da Expressão Gênica , Humanos , CamundongosRESUMO
Diabesity and fatty liver have been associated with low levels of high-density lipoprotein cholesterol, and thus could impair macrophage-specific reverse cholesterol transport (m-RCT). Liver X receptor (LXR) plays a critical role in m-RCT. Abcg5/g8 sterol transporters, which are involved in cholesterol trafficking into bile, as well as other LXR targets, could be compromised in the livers of obese individuals. We aimed to determine m-RCT dynamics in a mouse model of diabesity, the db/db mice. These obese mice displayed a significant retention of macrophage-derived cholesterol in the liver and reduced fecal cholesterol elimination compared with nonobese mice. This was associated with a significant downregulation of the hepatic LXR targets, including Abcg5/g8. Pharmacologic induction of LXR promoted the delivery of total tracer output into feces in db/db mice, partly due to increased liver and small intestine Abcg5/Abcg8 gene expression. Notably, a favorable upregulation of the hepatic levels of ABCG5/G8 and NR1H3 was also observed postoperatively in morbidly obese patients, suggesting a similar LXR impairment in these patients. In conclusion, our data show that downregulation of the LXR axis impairs cholesterol transfer from macrophages to feces in db/db mice, whereas the induction of the LXR axis partly restores impaired m-RCT by elevating the liver and small intestine expressions of Abcg5/g8.
Assuntos
Colesterol/metabolismo , Diabetes Mellitus/genética , Diabetes Mellitus/metabolismo , Receptores X do Fígado/metabolismo , Macrófagos/metabolismo , Membro 5 da Subfamília G de Transportadores de Cassetes de Ligação de ATP/genética , Membro 5 da Subfamília G de Transportadores de Cassetes de Ligação de ATP/metabolismo , Membro 8 da Subfamília G de Transportadores de Cassetes de Ligação de ATP/genética , Membro 8 da Subfamília G de Transportadores de Cassetes de Ligação de ATP/metabolismo , Animais , Transporte Biológico , Lipoproteínas/genética , Lipoproteínas/metabolismo , Receptores X do Fígado/genética , Masculino , Camundongos , Obesidade , Transdução de Sinais , Regulação para CimaRESUMO
The aim of this work is to present basic information on the lipoprotein physiology. The protein fraction of lipoproteins consists of several apolipoproteins and enzymes whose functions are lipid transport and metabolism. Classification of lipoproteins is based on their density. Chylomicrons, VLDL, IDL, LDL and HDL can be isolated by ultracentrifugation. Both chylomicrons- and VLDL-triglycerides are transported from the intestine and liver, respectively, to the peripheral tissues. The metabolism of VLDL originates IDL and LDL. LDL is the main transporter of cholesterol to extrahepatic tissues. HDL mobilizes cholesterol from peripheral tissues to the liver where it is secreted to bile as free cholesterol or bile salts, a process termed reverse cholesterol transport. Lipoprotein metabolism can be regulated by nuclear receptors that regulate the expression of genes involved in triglyceride and apolipoprotein metabolism.