Characterization Of Expression Levels Of Genes Involved In Adipogenesis And Inflammation In Congenic Mice Carrying Obesity and Hyperlipidemia QTL on Chromosome 1

Abstract

Obesity is an international health crisis and is considered the leading cause of preventable death. The development of obesity is likely due to interactions of susceptibility genes with obesity‐promoting environments such as high fat diets (HFD). These interactions lead to an expansion of adipose tissue, through an increase in adipocyte size and/or number. Adipose tissue inflammation is a well‐recognized characteristic of obesity. Previously, we identified quantitative trait loci (QTL) linked to obesity and hyperlipidemia on mouse chromosome (Chr) 1 in an intercross of obese and diabetic TALLYHO/Jng (TH) mice with C57BL/6 (B6) mice. Subsequently, we established a congenic mouse strain carrying the Chr1 QTL, 128 Mb in size, derived from TH on a B6 background (B6.TH‐Chr1–128Mb). The congenic mice were found to be more susceptible to diet‐induced obesity and hyperlipidemia than their B6 counterparts. The purpose of this study was to characterize the congenic mice by examining mRNA and protein levels of adipocyte differentiation and inflammation markers in white adipose tissue and liver. B6.TH‐Chr1–128Mb congenic and B6 mice were weaned onto chow and HFD and maintained until 16 weeks of age. Total RNA was isolated from adipose tissue and reverse‐transcribed with SUPERSCRIPT RT using oligo dT as primer to synthesize first‐strand cDNA. mRNA levels of peroxisome proliferator‐activated receptor gamma (Pparg), CCAAT/enhancer binding protein beta (Cebpb), preadipocyte factor 1 (Pref‐1), and Interleukin 6 (Il‐6) genes were measured by real‐time quantitative RT‐PCR. For protein levels, adipose tissue and liver were lysed in RIPA buffer and lysates subjected to SDA‐PAGE and Western blotting. Blots were probed with specific antibodies against PPARG and IL‐6, and detection of immunoreactive bands performed using enhanced chemiluminescence. Data analysis was conducted by ANOVA with GraphPad Prism 7. Congenic mice had a 2‐fold increase in gene expression level of Pparg, a major regulator of adipogenesis and lipogenesis, in adipose tissue compared to B6 mice on chow. HFD significantly increased the gene expression level of Pparg in both B6 and congenic mice, with greater degree in congenic mice. This trend was also the case for the protein expression level of PPARG in adipose tissue, as well as in liver, but it did not reach statistical significance. There were no significant differences in gene expression levels of Pref‐1, the most upstream repressor to adipocyte differentiation, and Cebpb, a major transcription factor during an early stage of adipogenesis, in adipose tissue between congenic and B6 mice for either diet. The gene expression level of Il‐6, a proinflammatory marker, was increased by HFD in both congenic and B6 mice, without genotype difference. A similar trend was also shown in IL‐6 protein levels in adipose tissue, as well as in liver, but it did not reach statistical significance. Collectively, we demonstrated that gene expression levels of Pparg were significantly upregulated in adipose tissue of B6.TH‐Chr1–128Mb congenic mice on chow and HFD.Support or Funding InformationThis work was supported by NASA WVSGC Graduate Fellowship to JKP and in part by NIH/NIDDK Grant R01DK077202 and institutional start‐up funding from Marshall University to JHK.