Recruitment of fat cell precursors during high fat diet in C57BL/6J mice is fat depot specific.

OBJECTIVE: The study aims to explore long-term dietary effects on increases in body mass and fat depot enlargement through the recruitment of early in life labeled progenitor cells to the adipolineage. METHODS: Neonate male C57BL/6J (B6) mice were injected intraperitoneally with BrdU. From 4 until 30 weeks of age they were fed either low fat diet (LFD) or high fat diet (HFD). BrdU-labeled cells were analyzed by flow cytometric and immunohistochemical assays after 10 days and 4, 8, 16, and 30 weeks. RESULTS: Mice fed HFD were heavier than mice fed LFD with the most dramatic disparity recorded between week 16 and 30. BrdU-bearing cells showed the decrease in the percentage content of labeled cells in inguinal (iWAT), epididymal (eWAT) and bone marrow (BM) tissues, regardless diets. However, iWAT collected from animals on HFD showed significant increase in labeled-cells at week 16th, which coincides with robust increase in inguinal but not epididymal fat weight between 16 and 30 weeks age. CONCLUSIONS: Cells labeled with BrdU during neonate life of B6 mice persist in fat tissues for long period of time and are recruited to the adipocyte lineage in a favorable (obesogenic) environment in iWAT but not in eWAT.

Insulin receptor-independent upregulation of cellular glucose uptake.

BACKGROUND: Cellular glucose uptake can be enhanced by upregulating Ras signaling in either insulin-dependent or -independent manner. In presence of insulin and intact insulin signaling, Ras has a negligible role in glucose uptake. Conversely, when insulin signaling is impaired in obesity or diabetes, the insulin-independent Ras pathway may be valuable for enhancing glucose disposal. We previously reported that Ad36, a human adenovirus, enhances cellular glucose uptake by upregulating the Ras/Glut4 pathway. Here, we investigated if Ad36-upregulated Ras via the insulin-independent pathway, to enhance glucose uptake. Furthermore, uncontrolled upregulation of Ras is linked with oncogenic cell transformation, if the tumor-suppressor gene p53 is also downregulated. Hence, we determined if upregulation of Ras by Ad36 would induce oncogenic cell transformation. Finally, we determined the relevance of Ad36 to insulin resistance in humans. METHODS: Insulin receptor (IR) was knocked down with small interfering RNA in 3T3-L1 adipocytes, to determine if Ad36 increases the Ras/Glut4 pathway and glucose uptake without IR-signaling. Next, the effects of Ad36 on cell transformation and p53 abundance were determined. Finally, overweight or obese women were screened for seropositivity to Ad36, as an indicator of natural Ad36 infection. Associations of Ad36 infection with adiposity and C-reactive proteins (CRPs)-two key markers of insulin resistance, and with glucose disposal, were determined. RESULTS: Unaffected by IR knock-down, Ad36 significantly increased the Ras pathway, Glut4 translocation and glucose uptake in 3T3-L1 adipocytes. Despite Ras upregulation, Ad36 did not transform 3T3-L1 cells. This may be because Ad36 significantly increased p53 protein in 3T3-L1 cells or mice adipose tissue. Ad36 seropositivity was associated with greater adiposity and CRP levels, yet a significantly higher systemic glucose disposal rate. CONCLUSIONS: Overall, the study offers Ras/Glut4 pathway as an alternate to enhance glucose disposal when insulin signaling is impaired, and, importantly, provides Ad36 as a tool to understand the modulation of that pathway.

Template to improve glycemic control without reducing adiposity or dietary fat.

Drugs that improve chronic hyperglycemia independently of insulin signaling or reduction of adiposity or dietary fat intake may be highly desirable. Ad36, a human adenovirus, promotes glucose uptake in vitro independently of adiposity or proximal insulin signaling. We tested the ability of Ad36 to improve glycemic control in vivo and determined if the natural Ad36 infection in humans is associated with better glycemic control. C57BL/6J mice fed a chow diet or made diabetic with a high-fat (HF) diet were mock infected or infected with Ad36 or adenovirus Ad2 as a control for infection. Postinfection (pi), systemic glycemic control, hepatic lipid content, and cell signaling in tissues pertinent to glucose metabolism were determined. Next, sera of 1,507 adults and children were screened for Ad36 antibodies as an indicator of past natural infection. In chow-fed mice, Ad36 significantly improved glycemic control for 12 wk pi. In HF-fed mice, Ad36 improved glycemic control and hepatic steatosis up to 20 wk pi. In adipose tissue (AT), skeletal muscle (SM), and liver, Ad36 upregulated distal insulin signaling without recruiting the proximal insulin signaling. Cell signaling suggested that Ad36 increases AT and SM glucose uptake and reduces hepatic glucose release. In humans, Ad36 infection predicted better glycemic control and lower hepatic lipid content independently of age, sex, or adiposity. We conclude that Ad36 offers a novel tool to understand the pathways to improve hyperglycemia and hepatic steatosis independently of proximal insulin signaling, and despite a HF diet. This metabolic engineering by Ad36 appears relevant to humans for developing more practical and effective antidiabetic approaches.