High-Fat Diet-Induced Adiposity, Adipose Inflammation, Hepatic Steatosis and Hyperinsulinemia in Outbred CD-1 Mice

<div><p>High-fat diet (HFD) has been applied to a variety of inbred mouse strains to induce obesity and obesity related metabolic complications. In this study, we determined HFD induced development of metabolic disorders on outbred female CD-1 mice in a time dependent manner. Compared to mice on regular chow, HFD-fed CD-1 mice gradually gained more fat mass and consequently exhibited accelerated body weight gain, which was associated with adipocyte hypertrophy and up-regulated expression of adipose inflammatory chemokines and cytokines such as <i>Mcp-1</i> and <i>Tnf-α</i>. Increased fat accumulation in white adipose tissue subsequently led to ectopic fat deposition in brown adipose tissue, giving rise to whitening of brown adipose tissue without altering plasma level of triglyceride. Ectopic fat deposition was also observed in the liver, which was associated with elevated expression of key genes involved in hepatic lipid sequestration, including <i>Ppar-γ2</i>, <i>Cd36</i> and <i>Mgat1</i>. Notably, adipose chronic inflammation and ectopic lipid deposition in the liver and brown fat were accompanied by glucose intolerance and insulin resistance, which was correlated with hyperinsulinemia and pancreatic islet hypertrophy. Collectively, these results demonstrate sequentially the events that HFD induces physiological changes leading to metabolic disorders in an outbred mouse model more closely resembling heterogeneity of the human population.</p></div

Gene expression in liver.

<p>(A) Expression level of <i>Ppar-γ2</i>. (B) Expression level of <i>Cd36</i>. (C) Expression level of <i>Mgat1</i>. (D) Expression level of <i>Fgf21</i>. Values represent average ± SD (n = 4). * <i>P</i> < 0.05 compared with mice on chow, ** <i>P</i> < 0.01 compared with mice on chow.</p

HFD impaired glucose homeostasis, which subsequently gave rise to hyperinsulinemia and pancreatic islet hypertrophy.

<p>(A) Profiles of blood glucose concentration as function of time upon intraperitoneal injection of glucose (n = 5). (B) Profiles of glucose concentration (percentage of initial value) as a function of time upon intraperitoneal injection of insulin (n = 5). (C) Blood insulin (n = 4). (D) Representative images of pancreas histological examinations. Values in (A), (B) and (C) represent average ± SD. * <i>P</i> < 0.05 compared with mice on chow, ** <i>P</i> < 0.01 compared with mice on chow.</p

HFD induced hepatic steatosis.

<p>(A) Representative images of liver histological examinations. (B) Liver triglyceride determination. (C) Blood aspartate aminotransferase. (D) Blood alanine aminotransferase. Values in (B), (C) and (D) represent average ± SD (n = 4). ** <i>P</i> < 0.01 compared with mice on chow.</p

HFD caused hypertrophy of white adipocytes.

<p>(A) Lean mass (n = 10). (B) Fat mass (n = 10). (C) Representative images of WAT histological examinations (bar length = 100 μm). (D) Adipocyte diameter (n = 4). Values in (A), (B) and (D) represent average ± SD. ** <i>P</i> < 0.01 compared with mice on chow.</p

Gene expression analysis in WAT.

<p>(A) Expression level of <i>F4/80</i>. (B) Expression level of <i>Cd11b</i>. (C) Expression level of <i>Cd11c</i>. (D) Expression level of <i>Mcp-1</i>. (E) Expression level of <i>Tnf-α</i>. (F) Expression level of <i>Leptin</i>. Values represent average ± SD (n = 4). ** <i>P</i> < 0.01 compared with mice on chow.</p

HFD caused whitening of BAT without significantly changing blood clearance of triglyceride.

<p>(A) Representative images of BAT histological examinations. (B) Measurement of BAT nuclei. (C) Determination of Blood triglyceride. (D) Representative image of lipoprotein electrophoresis (C for chow and H for HFD). Values in (B) and (C) represent average ± SD (n = 4). ** <i>P</i> < 0.01 compared with mice on chow.</p

HFD increased body weight gain in female CD-1 mice.

<p>(A) Growth curve of mice on HFD or chow. (B) Representative images of mice (bar length = 1 cm). (C) Energy intake. Values in (A) and (C) represent average ± SD (n = 10). * <i>P</i> < 0.05 compared with mice on chow, ** <i>P</i> < 0.01 compared with mice on chow.</p

The mRNA level of selected genes in adipose tissue.

<p>(A) The mRNA level of <i>leptin</i> and <i>adiponectin</i> genes. (B) The mRNA level of <i>lxrα</i>, <i>pparα</i>, <i>pparγ</i> and <i>pparδ</i>. (C) The mRNA level of <i>f4/80</i>, <i>cd11c</i> and <i>cd206</i>. (D) The mRNA level of <i>mcp1</i>, <i>tnfα</i>, <i>ifnγ</i> and <i>il1β</i> Values represent average ± SD (n = 4); **<i>p</i><0.01 <i>vs</i> control.</p

Effect of T0901317 (T09), finofibrate (FF) or in combination (T09+ FF) on <b><i>fgf21</i></b><b> gene expression in liver and adipose tissue.</b>

<p>(A) The mRNA level of <i>fgf21</i> in the liver. (B) The mRNA level of <i>fgf21</i> in adipose tissue. Values represent average ± SD (n = 4); **<i>p</i><0.01 <i>vs</i> control; ^##<i>p</i><0.01 <i>vs</i> T0901317-treated animals.</p