Adipokinome Signatures in Obese Mouse Models Reflect Adipose Tissue Health and Are Associated with Serum Lipid Composition

Adipocyte and hepatic lipid metabolism govern whole-body metabolic homeostasis, whereas a disbalance of de novo lipogenesis (DNL) in fat and liver might lead to obesity, with severe co-morbidities. Nevertheless, some obese people are metabolically healthy, but the “protective” mechanisms are not yet known in detail. Especially, the adipocyte-derived molecular mediators that indicate adipose functionality are poorly understood. We studied transgenic mice (alb-SREBP-1c) with a “healthy” obese phenotype, and obob mice with hyperphagia-induced “sick” obesity to analyze the impact of the tissue-specific DNL on the secreted proteins, i.e., the adipokinome, of the primary adipose cells by label-free proteomics. Compared to the control mice, adipose DNL is reduced in both obese mouse models. In contrast, the hepatic DNL is reduced in obob but elevated in alb-SREBP-1c mice. To investigate the relationship between lipid metabolism and adipokinomes, we formulated the “liver-to-adipose-tissue DNL” ratio. Knowledge-based analyses of these results revealed adipocyte functionality with proteins, which was involved in tissue remodeling or metabolism in the alb-SREBP-1c mice and in the control mice, but mainly in fibrosis in the obob mice. The adipokinome in “healthy” obesity is similar to that in a normal condition, but it differs from that in “sick” obesity, whereas the serum lipid patterns reflect the “liver-to-adipose-tissue DNL” ratio and are associated with the adipokinome signature.

Abstract 607: Endothelin-1 Increases ß-Actin Expression During Osteochondrogenesis of Aortic Smooth Muscle Cells from Leptin-Deficient ob/ob Mice

β-actin, a highly conserved gene/protein, which is usually not modulated by different stimuli, is routinely used to normalize target gene or protein expression in experimental biology, and so defined endogenous housekeeping gene. However, investigators showed that β-actin expression could change during cellular growth and differentiation. We hypothesized that endothelin 1 (ET-1), a cellular proliferative agonist, increases β-actin expression and stimulates calcification in vascular smooth muscle cells (SMC) from obob mice. Primary aortic SMC passage 4-6 isolated from obese leptin-deficient (obob) and from C57BL/6 (C57) mice were incubated without (Cont) or with ET-1 50nM (ET) for 0-72h. Cell lysates were assessed for β-actin and RUNX2 expression by western blotting and normalized by GAPDH. ObobET SMC increased β-actin expression after 24h, 48h and 72h (1.68±0.06, 1.66±0.05, 1.73±0.06 respectively) vs obobCont (1.01±0.07), p<.05 n=6. However, C57ET did not change β-actin expression (0.91±0.06, 1.04±0.03, 0.99±0.08) after 24h, 48h and 72h respectively vs. C57Cont (0.95 ± 0.04), p=NS n=6. Concomitantly, obobET SMC increased osteochondrogenic differentiation, by modulating RUNX2 (1.23±0.03 vs obobCont 1±0.01, p<.05 n=3) after 48h, which did not occur in C57 (C57ET 1.07±0.07 vs C57Cont 1.02±0.11), p=NS. Furthermore, obobET increased calcification vs obobCont (1.69±0.025 vs 1.03±0.03) after 14 days p<.05, n=3 and C57ET did not calcify (0.97±0.02 vs C57Cont 1±0.05), p=NS. We showed that ET-1 modulates β-actin expression and osteochodrogenenic differentiation only in obob SMC, thus increasing calcification. In conclusion, β-actin is not a consistent endogenous control in ET-1-stimulated SMC from obob mice during osteochondrogenic differentiation.

The development of obesity in preweanling obob mice

1. The body compositions of obob and lean (ob+ and + +) mice at 10, 12, 17 and 28 d of age were investigated using a ‘cold stress’ test to identify the two groups.2. At each of these ages the obob mice were found to contain significantly more fat than the lean. At 10 d 20 % more fat was present and by 17 d the increase was 72 %. The obob mice at 28 d contained nearly three times as much fat as the lean.3. Carcass energy was significantly higher in obob mice at all ages investigated.4. Other changes in body composition found in the 28 d obob mice, i.e. a reduction in total carcass nitrogen and water content, were already established in the 17-d-old mice but differences at 10 and 12 d were not apparent.5. The livers of obob mice were significantly heavier than those from lean control mice at 28 d but no differences were detected at the earlier ages.6. The results are discussed with reference to the early origin of obesity in obob mice.

Hormone-substrate responses to total fasting in lean and obese mice

The hormone-substrate milieu has been investigated in male fasted lean (C57BL/6-+/+) mice and mutant obese mice of the same strain (C57BL/6-obob). The lean mouse, in winter, mobilized insufficient fat (due to inadequate stores) to permit survival beyong 3 days and was unable to achieve any degree of conservation of vital protein stores. By contrast, in summer, the same animals survived 7 days and showed evidence of greater and more sustained fat mobilization and ketosis and the ability to conserve protein. The insulin, glucagon, and insulin/glucagon molar ratios changed in both groups in a direction consistent with conversion to a catabolic state, and hence were probably largely responsible for the mobilization of substrates and stimulation of gluconeogenesis and ketogenesis. The seasonal difference in response is unexplained. The obob mice, generally employed as a model for obesity, hyperglycemia, and hyperinsulinemia showed these features but also adapted to fasting in a fashion permitting prolonged survival during this state. In a fashion analogous to that known to occur in man, these animals developed fall in glycemia, rise in circulating fat-derived substrates, and marked protein conservation. Profound fall in insulinemia was associated with a fall in glucagonemia, the latter from normal levels. Thus the initial markedly "anabolic" insulin/glucagon molar ratio diminished, but nevertheless remained higher than at any time in the lean mice. Pancreatic contents of insulin showed markedly different changes with fasting in obob compared with lean mice. The ability of the obese mouse to adapt to prolonged fasting in a fashion largely analogous to that of man renders it a useful model for the study of metabolism in this state, with the potential of applicability of findings to man.