Les laminopathies : lipodystrophies, insulino-résistance, syndromes de vieillissement accéléré… et les autres

Microarray analysis of hepatic gene expression identifies new genes involved in steatotic liver

Trans-10, cis-12-conjugated linoleic acid (CLA)-enriched diets promote fatty liver in mice, while cis-9, trans-11-CLA ameliorates this effect, suggesting regulation of multiple genes. To test this hypothesis, apoE-deficient mice were fed a Western-type diet enriched with linoleic acid isomers, and their hepatic gene expression was analyzed with DNA microarrays. To provide an initial screening of candidate genes, only 12 with remarkably modified expression between both CLA isomers were considered and confirmed by quantitative RT-PCR. Additionally mRNA expression of 15 genes involved in lipid metabolism was also studied. Ten genes (Fsp27, Aqp4, Cd36, Ly6d, Scd1, Hsd3b5, Syt1, Cyp7b1, and Tff3) showed significant associations among their expressions and the degree of hepatic steatosis. Their involvement was also analyzed in other models of steatosis. In hyperhomocysteinemic mice lacking Cbs gene, only Fsp27, Cd36, Scd1, Syt1, and Hsd3b5 hepatic expressions were associated with steatosis. In apoE-deficient mice consuming olive-enriched diet displaying reduction of the fatty liver, only Fsp27 and Syt1 expressions were found associated. Using this strategy, we have shown that expression of these genes is highly associated with hepatic steatosis in a genetic disease such as Cbs deficiency and in two common situations such as Western diets containing CLA isomers or a Mediterranean-type diet. Conclusion: The results highlight new processes involved in lipid handling in liver and will help to understand the complex human pathology providing new proteins and new strategies to cope with hepatic steatosis.

Squalene in a sex-dependent manner modulates atherosclerotic lesion which correlates with hepatic fat content in apoE-knockout male mice

BACKGROUND

Squalene is an intermediate of cholesterol biosynthesis which can be obtained from the diet where it is abundant, for example, in olive oil. The effect of this isoprenoid on the development of atherosclerosis was investigated on apoE-knockout mice.

METHODS AND RESULTS

Two groups of animals, separated according to sex, were fed on standard chow diet: the control group receiving only vehicle and the second group an aqueous solution of squalene to provide a dose of 1g/kg/day in male and female mice. This treatment was maintained for 10 weeks. At the end of this period, plasma lipid parameters, oxidative stress markers and hepatic fat were measured as well as cross-sectional lesion area of aortic root in both groups. Data showed that in males squalene feeding reduced atherosclerotic lesion area independently of plasma lipids and activation of circulating monocytes. In contrast, squalene intake did not decrease lesion area in females, despite reducing plasma cholesterol and triglycerides, isoprostane and percentage of Mac-1 expressing white cells. In males, atherosclerotic lesion area was positively and significantly associated with hepatic fat content and the plasma triglycerides were also strongly associated with liver weight.

CONCLUSIONS

These results indicate that administration of squalene modulates lesion development in a gender specific manner, and that accumulation of hepatic fat by liver is highly correlated with lesion progression in males. Hence, squalene administration could be used as a safe alternative to correct hepatic steatosis and atherosclerosis particularly in males.

Adipocyte death, adipose tissue remodeling, and obesity complications

OBJECTIVE

We sought to determine the role of adipocyte death in obesity-induced adipose tissue (AT) inflammation and obesity complications.

RESEARCH DESIGN AND METHODS

Male C57BL/6 mice were fed a high-fat diet for 20 weeks to induce obesity. Every 4 weeks, insulin resistance was assessed by intraperitoneal insulin tolerance tests, and epididymal (eAT) and inguinal subcutaneous AT (iAT) and livers were harvested for histological, immunohistochemical, and gene expression analyses.

RESULTS

Frequency of adipocyte death in eAT increased from <0.1% at baseline to 16% at week 12, coincident with increases in 1) depot weight; 2) AT macrophages (ATM Phi s) expressing F4/80 and CD11c; 3) mRNA for tumor necrosis factor (TNF)-alpha, monocyte chemotactic protein (MCP)-1, and interleukin (IL)-10; and 4) insulin resistance. ATM Phi s in crown-like structures surrounding dead adipocytes expressed TNF-alpha and IL-6 proteins. Adipocyte number began to decline at week 12. At week 16, adipocyte death reached approximately 80%, coincident with maximal expression of CD11c and inflammatory genes, loss (40%) of eAT mass, widespread collagen deposition, and accelerated hepatic macrosteatosis. By week 20, adipocyte number was restored with small adipocytes, coincident with reduced adipocyte death (fourfold), CD11c and MCP-1 gene expression (twofold), and insulin resistance (35%). eAT weight did not increase at week 20 and was inversely correlated with liver weight after week 12 (r = -0. 85, P < 0.001). In iAT, adipocyte death was first detected at week 12 and remained <or=3%.

CONCLUSIONS

These results implicate depot-selective adipocyte death and M Phi-mediated AT remodeling in inflammatory and metabolic complications of murine obesity.

Les syndromes lipodystrophiques : des adipopathies congénitales ou acquises

Lipodystrophic syndromes regroup a heterogeneous group of genetic or acquired diseases. Lipodystrophy, an altered development and/or repartition of body fat, is associated with alterations of lipid and glucose metabolism with insulin resistance. Genetic forms, rare, can be generalized and recessive resulting from mutations in the seipin or AGPAT2 gene. Partial lipodystrophies are dominant and observed in patients mutated in the gene encoding PPAR-gamma or lamin A/C, a gene seen also mutated in patients with syndromes of premature aging. Acquired forms are common and regroup the highly prevalent Metabolic Syndrome, hypercorticism together with lipodystrophy related to antiretroviral treatment of HIV-infected patients.

Les lipodystrophies secondaires aux traitements antirétroviraux de l’infection par le VIH

HIV infection requires the continuous administration of antiretroviral molecules. Individual molecules belonging to the two main classes, protease inhibitors (PIs) and nucleoside analogues inhibitors of the viral reverse transcriptase (NRTIs) have been shown to be involved in deleterious side effects collectively called the lipodystrophy syndrome. This syndrome associates altered body fat repartition (peripheral lipoatrophy and visceral fat hypertrophy) and metabolic alterations (dyslipidemia, insulin resistance and diabetes). The pathophysiology of these alterations is complex but different studies argue for adipose tissue being a target of some PIs and NRTIs acting through different mechanisms. NRTIs are able to induce mitochondrial dysfonction and to modify adipocyte phenotype and adipose tissue pattern of secretion of cytokines (TNFalpha, IL-6) and other adipokines (adiponectin, leptin) probably through the production of reactive oxygen species. Some PIs also act on adipocyte, alter its differentiation and insulin sensitivity and also the pattern of secretion of adipokines by adipose tissue. These hypotheses could explain the loss of adipose tissue, while the mechanisms of visceral fat hypertrophy remain speculative. Since some adipokines and the free fatty acids released by adipocytes play a major role in the control of liver and muscles insulin sensitivity, these alterations are probably involved in the metabolic alterations seen in the patients. In addition, lipodystrophic adipose tissue could be involved in the increased lesions of atherogenesis and steatohepatitis presented by these patients. The treatment of lipodystrophy remains difficult and, at present, privileges the switch of the more deleterious drugs towards new molecules less aggressive for adipose tissue.