Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC338
The role of clock genes and clock controlled metabolic genes in the developmental priming of fatty liver disease.
K. K. Sihota1, K. D. Bruce1, M. A. Hanson1, C. D. Byrne1, F. R. Cagampang1
1. Institute of Developmental Sciences, University of Southampton Faculty of Medicine, Southampton, United Kingdom.
Sub-optimal nutrition during early development is associated with adult onset of the Metabolic Syndrome (MetS), the hepatic manifestation of which is Non-Alcoholic Fatty Liver Disease (NAFLD). We have previously shown that high fat (HF) exposure during early development primes the development of non-alcoholic steatohepatits (NASH - severe NAFLD) in adulthood through elevated lipogenesis and mitochondrial dysfunction (1). Since both fatty acid and mitochondrial metabolism are regulated by the endogenous molecular “clock” network, we hypothesised that “clock” perturbations could modulate metabolic output and contribute to developmental priming of NASH. Therefore, we investigated whether developmental HF exposure could induce day and night changes in NAD+-dependant, CLOCK/BMAL1 rheostat SIRT1, core clock genes PER2, CLOCK and BMAL1, and downstream lipogenic clock-controlled gene Rev-Erbβ expression in adult offspring. Female mice were fed a HF (45% kcal fat) or control chow (C, 21% kcal fat) diet before and during pregnancy and lactation. Resulting offspring were fed either a C or a HF diet after weaning to generate four offspring groups; HF/HF, HF/C, C/HF, C/C. Livers from 15-week old male offspring were harvested during the day or night. Total RNA was extracted and quantitative PCR was used to determine reference genes that remained stable throughout across time points and dietary exposures. YWHAZ and EIF42A were used to determine relative clock and clock-controlled gene expression. In C/C offspring BMAL1 expression was 13.75 fold higher (p<0.0001) at night. This pattern was maintained in C/HF and HF/C groups. However, in HF/HF daytime BMAL1 expression became elevated (p=0.029), reversing this pattern. PER2 showed a trend towards higher (p=0.1) expression in the HF/HF offspring vs. C/C. Rev-Erbβ was 6.7 fold higher (P=0.003), during the day in C/C, whilst this pattern became diminished (C/HF 3.2 fold, HF/C 1.6 fold, HF/HF 1.2 fold) through prolonged HF exposure. SIRT1 expression was higher in the day in C/C, however this pattern was lost in C/HF and HF/C, and the overall expression was lower (p=0.023) in HF/HF offspring. These results demonstrate that HF diets during early development and in post-weaning life can disrupt hepatic clock and clock-controlled gene expression pattern. Specifically, combined HF exposure during development and adulthood appears to increase expression of BMAL1, which may contribute to the observed deregulation of PER2 and Rev-Erbβ. In addition, we suggest that reduced SIRT1 in the HF/HF offspring may result from mitochondrial impairment via NAD+/NADH levels, and may contribute to BMAL1 elevation, thus providing mechanistic insights into the developmental priming of NASH.
Where applicable, experiments conform with Society ethical requirements