Endocrine Abstracts

Introduction: In rodents, dietary choline deficiency (CDD) results in macrovesicular hepatic steatosis and insulin sensitisation whereas methionine and choline deficient (MCDD) diets result in inflammatory fibrotic steatohepatitis with hepatic insulin resistance. The methyl donors choline and methionine are essential components of one-carbon metabolism. Our hypothesis was that methyl donor deficiency in mice would affect the expression of key genes in pathways of hepatic lipid biosynthesis, lipid disposal and insulin signal transduction.

Methods: Male C57BL/6 mice (n=10/group) were maintained on CDD, MCDD or control diet for 4 weeks. Hepatic triglyceride content was quantified by colorimetric analysis and histology analysed by light microscopy. Liver transcript profile was examined using the Illumina Mouseref-6 platform (n=4/group) and expression changes validated using quantitative PCR.

Results: Hepatic triglyceride levels were increased in CDD and MCDD (P<0.05) compared to controls. Histologically, CDD mice exhibited hepatic steatosis with mild inflammatory infiltrate whereas MCDD mice demonstrated steatosis, inflammatory infiltrate and periportal fibrosis. Mediators of de novo lipogenesis were transcriptionally suppressed in CDD and MCDD (Srebf1, ACSL1, ChREBP, ACACA, FASn, and SCD1; P<0.001). Pathways of triglyceride synthesis, mitochondrial and peroxisomal β oxidation were largely unaffected. Expression of ER associated mediators of triglyceride hydrolysis and VLDL assembly (PNPLA3 and the carboxylesterase enzymes: CES1d, CES1f, CES1g, and CES3b) were strikingly suppressed in MCDD mice (P<0.001), with a subgroup (Ced1d and PNPLA3) also suppressed in CDD (P<0.05). Two key mediators of insulin signal transduction (IRS2 and PDK1) were down-regulated in MCDD (P<0.05).

Conclusions: Hepatic steatosis in methyl donor deficiency may be promoted by down-regulation of CES enzymes required for TG hydrolysis and VLDL assembly. MCDD associated hepatic insulin resistance may be further exacerbated by IRS2 and pdk1 suppression.