Evidence of transcriptional and post-transcriptional regulation of hepatic gene and protein expression changes during the development of diet-induced obesity

Kim YJ1, Do GM1, Kwon EY1, Cho YY1, Shin SK1, Park HJ1, Kim E1, Jung UJ2,Yun JW3, McGregor RA2, Choi MS2

1Department of Food Science and Nutrition, Kyungpook National University, Daegu, Republic of Korea,2Center for Food and Nutritional Genomics, Kyungpook National University, Daegu, Republic of Korea,

3Department of Biotechnology, Daegu University, Daegu, Republic of Korea

IntroductionTo aid the development of new anti-obesitytherapies we need to understand how can-didate obesity genes and proteins are regu-lated. We examined time-dependent hepaticmRNA and protein expression profiles fromhigh-fat diet fed mice for evidence of tran-scriptional or post-transcriptional regulation.

Materials & MethodsC57BL/6J mice were fed a high-fat diet for24 weeks. Liver microarray data from 8 time-points (2, 4, 6, 8, 12, 16, 20, 24 weeks) wasused from Do et al. (2011) Mol Nutr Food Res.55:S173-85. In addition, liver protein profilesbased on 2-Dimensional gel electrophoresis(2-DE) and protein mass fingerprinting (PMF)were obtained from the same mice (2, 4,8, 16, 20, 24 weeks). Data was interpolatedin R/Bioconductor, then the correlation andtimecourse of mRNA and protein changeswere examined. We restricted the analysisto 60 differentially expressed proteins identi-fied by 2-DE gel (out of ~400 proteins). Weused TargetScan to find putative miRNA bind-ing sites in the 3'UTR of genes with divergentmRNA:protein profiles.

ResultsThe overall correlation between mRNA andprotein expression changes (based on time-course mRNA:protein data) was very lowR2=0.13 (Fig.1.). Proteins appeared to beboth transcriptionally and post-transcription-ally regulated during the development of di-et-induced obesity.

Fig. 1. Overall correlation between mRNA and pro-tein expression changes during the developmentof diet-induced obesity over 24 weeks. Based onmRNA:protein data from 8 timepoints. HFD=High-fat diet, ND=Normal Diet.

The heatmap highlights the marked discor-dance between the magnitude of changesin mRNA (left panel) and protein expression(right panel) at multiple timepoints during thedevelopment of diet-induced obesity over 24weeks (Fig. 2).

Fig. 2. Heatmap of mRNA (left panel) and protein(right panel) changes during the development ofdiet-induced obesity. Based on microarray and 2Dgels of the same biological liver specimens.

Fig. 3. Divergent changes in transcription andtranslation of PON1, HSPA9 and CAT during the de-velopment of diet-induced obesity.

When we examined the individual timecourseof mRNA and protein expression changes ofseveral genes including PON1, HSPA9 andCAT during the development of diet-inducedobesity,there was evidence of divergent mR-NA and protein changes, indicating other reg-ulatory factors must also determine proteinchanges during the development of diet-in-duced obesity ( Fig. 3.)

Table 1. Conserved miRNA binding sites in 3'UTRof selected genes with divergent protein changesduring the development of diet-induced obesitybased on TargetScan.

Next we examined whether there were anypredicted miRNA binding sites in the 3'UTRof three genes with discordant mRNA:proteinprofiles. Based on TargetScan the 3'UTR ofPON1 harbours a putative miR-26a bindingsite, the 3'UTR of HSPA9 harbours a putativemiR-217 binding site and CAT harbours a pu-tative miR-30 binding site (Table 1). However,these remain to be experimentally validated.

ConclusionsThese findings indicate both transcription-al and post-transcriptional regulation under-lies the development of diet-induced obesi-ty. It would be worthwhile in future studies toexamine whether post-transcriptional regula-tors such as microRNAs are altered duringthe development of diet-induced obesity.

AcknowledgementsThis work was supported by the Nation-al Research Foundation of Korea (No.2011-0000920).