IUGR With Catch-up Growth Programs An Insulin-resistant Phenotype Through DNA Methylation Of PGC-1Alpha In Rats

Part ⅠThe DNA methylation and transcription of PGC-la in IUGR rats with catch-up growthBackground and Objective:IUGR followed by postnatal accelerated growth (CG-IUGR) is associated with long-term adverse metabolic consequences, and an involvement of epigenetic deregulation has been implicated. PGC-1αa is a key orchestrator in energy homeostasis. We aimed to investigate the alterations in DNA methylation level in promoter of PGC-la, the transcriptional activity of PGC-la and the core body temperature as well as the spontaneous activity in CG-IUGR rats.Methods:A CG-IUGR rat model was established using maternal gestational nutritional restriction followed by infantile overnutrition achieved by reducing the litter size on postnatal day1. The8-week rats were sacrificed, and the RNA, DNA were extracted. After bisulfite treated, DNA sequence of PGC-1α promoter was amplified, thereafter, DNA methylation was determined by Pyrosequencing. The mRNA expression was assessed by real-time PCR. Core body temperature was measured rectally by a digital probe thermometer, and spontaneous physical activity was recorded in locomotion cages by using AniLab Software.Results:Compared with control (appropriate for gestational age, AGA group), IUGR pups had lower weights and lower BMI at birth, and caught up with the AGA pups prior to the3rd postnatal week. Adult CG-IUGR rats showed increase in weight, BMI and DNA methylation of specific CpG sites in PGC-1α, and decrease in transcriptional activity of PGC-1α(p<0.05). The core body temperature and spontaneous physical activity were comparable between the two groups (p>0.05). Conclusions:IUGR followed by catch-up growth may induce the alterations in DNA methylation and transcriptional activity of PGC-1α, which provide a potential mechanism linking early-life nutrition insult to adult insulin-resistant phenotype. Part ⅡThe mitochondrial content and the transcriptional activity of PGC-la-responsive genes in IUGR rats with catch-up growthObjective:We aimed to investigate the alterations in mitochondrial content, the transcriptional activity of PGC-1α-responsive genes involved in fatty acid oxidation as well as oxidative phosphorylation, the tissue triglyceride and the fasting insulin level, and the post-transcriptional alteration of the canonical components of insulin signaling pathway including PI3K and phosphorylated-Akt2in liver and muscle of IUGR rats with catch-up growth (CG-IUGR).Methods:A CG-IUGR rat model was established using maternal gestational nutritional restriction followed by infantile overnutrition achieved by reducing the litter size on postnatal day1. The8-week rats were sacrificed, and the RNA, DNA and protein were extracted. The mRNA expression of PGC-la-responsive genes involved in fatty acid oxidation as well as oxidative phosphorylation and the mitochondrial content of liver and muscle were assessed by real-time PCR. The protein levels of the canonical components of insulin signaling pathway including PI3K and phosphorylated-Akt2in liver and muscle was determined using Western blot. Fasting plasma insulin was measured using an ELISA kit. Triglyceride content was determined using a colorimetric assay.Results:Compared with control, adult CG-IUGR rats had decreased mitochondrial content (mtDNA/nDNA), the transcriptional activity of PGC-1α-responsive genes involved in fatty acid oxidation (including PPAR-a in muscle and CD36as well as PPAR-y in liver) as well as oxidative phosphorylation (including Cycs, Sdhd and Atp5b in liver as well as Sdhd and Uqcrc1in muscle), impaired insulin signaling in liver and muscle tissue, as well as increased fasting insulin and liver triglyceride levels(p<0.05). Moreover, the fasting insulin concentrations were positively correlated with the methylation levels of CpG sites-787and-803of PGC-la promoter in liver and muscle (p<0.05).Conclusions:The alterations in DNA methylation and transcriptional activity of PGC-1α may program an insulin-resistant phenotype through mediating the reduction of mitochondrial content, the transcriptional activity of PGC-1α-responsive genes involved in fatty acid oxidation as well as oxidative phosphorylation, and the increment of hepatic TG accumulation in CG-IUGR rats, providing a potential mechanism linking early-life nutrition insult to long term adverse metabolic consequence.