Summary Growth hormone significantly impacts lifespan in mammals. Mouse longevity is extended when growth hormone (GH) signaling is interrupted but markedly shortened with high plasma hormone levels. Methionine metabolism is enhanced in growth hormone deficiency, e.g. Ames dwarf, but suppressed in GH transgenic mice. Methionine intake affects also lifespan, thus, GH mutant mice and respective wild type littermates were fed 0.16%, 0.43% or 1.3% methionine to evaluate the interaction between hormone status and methionine. All wild type and GH transgenic mice lived longer when fed 0.16% methionine but not when fed higher levels. In contrast, animals without growth hormone signaling due to hormone deficiency or resistance, did not respond to altered levels of methionine in terms of lifespan, body weight or food consumption. Taken together, our results suggest that the presence of growth hormone is necessary to sense dietary methionine changes thus, strongly linking growth and lifespan to amino acid availability.

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BackgroundExtending mammalian health span and life span has been achieved under a variety of dietary restriction protocols. Reducing the intake of a specific amino acid has also been shown to extend health and longevity. We recently reported that methionine (MET) restriction is not effective in life span extension in growth hormone (GH) signaling mutants. To better understand the apparent necessity of GH in the ‘sensing’ of altered dietary MET, the current study was designed to evaluate MET and glutathione (GSH) metabolism (as well as other pathways) in long-living GH-deficient Ames dwarf and wild-type mice following 8 weeks of restricted (0.16%), low (0.43%), or enriched (1.3%) dietary MET consumption. Metabolite expression was examined in liver tissue, while gene and protein expression were evaluated in liver, kidney, and muscle tissues.ResultsBody weight was maintained in dwarf mice on the MET diets, while wild-type mice on higher levels of MET gained weight. Liver MET levels were similar in Ames mice, while several MET pathway enzymes were elevated regardless of dietary MET intake. Transsulfuration enzymes were also elevated in Ames mice but differences in cysteine levels were not different between genotypes. Dwarf mice maintained higher levels of GSH on MET restriction compared to wild-type mice, while genotype and diet effects were also detected in thioredoxin and glutaredoxin. MET restriction increased transmethylation in both genotypes as indicated by increased S-adenosylmethionine (SAM), betaine, and dimethylglycine. Diet did not impact levels of glycolytic components, but dwarf mice exhibited higher levels of key members of this pathway. Coenzyme A and measures of fatty acid oxidation were elevated in dwarf mice and unaffected by diet.ConclusionsThis component analysis between Ames and wild-type mice suggests that the life span differences observed may result from the atypical MET metabolism and downstream effects on multiple systems. The overall lack of responsiveness to the different diets is well reflected across many metabolic pathways in dwarf mice indicating the importance of GH signaling in the ability to discriminate dietary amino acid levels.Electronic supplementary materialThe online version of this article (doi:10.1186/2046-2395-3-10) contains supplementary material, which is available to authorized users.

Methyltransferase expression and DNA methylation are linked to aging and age-related disease. We utilized 3-, 12-, and 24-month-old Ames dwarf and their wild-type siblings to examine the genotype and age-related differences in the expression of methyltransferase enzymes related to DNA methylation in the liver, glycine-N-methyltransferase and DNA methyltransferase (DNMT). We found that DNMT proteins and transcripts are differentially expressed in dwarf mice compared with wild-type siblings that can be attributed to age and/or genotype. However, DNMT1 protein expression is drastically reduced compared with wild-type controls at every age. DNMT3a protein levels coincide with differences observed in DNMT activity. Growth hormone appears to modulate expression of DNMT1 and 3a in dwarf liver tissue and primary hepatocytes. Therefore, growth hormone may contribute to age-related processes, DNA methylation, and, ultimately, longevity.

Polycystic ovary syndrome (PCOS) is associated with abnormalities of insulin action and insulin secretion. Ethinyl oestradiol/cyproterone acetate is a common agent used to treat the symptoms of PCOS, but its effects on insulin action and insulin pulsatility have not been examined. We investigated the relationship between insulin action and insulin secretion in 11 patients with PCOS, at diagnosis and after 3 months of treatment with ethinyl oestradiol/cyproterone acetate, and in 13 controls. Insulin action was assessed using the euglycaemic hyperinsulinaemic clamp (2 mU/kg/min for 2 h). Insulin pulsatility was examined over 90 min by 2 min sampling. Short-term insulin pulses were identified using PULSAR. Treatment with ethinyl oestradiol/cyproterone acetate resulted in significant reductions in testosterone (3.3+/-0.7 vs. 1.9+/-0.2 nmol/l, p<0.05), free androgen index (10.2+/-0.7 vs. 1.2+/-0.2, p<0.05) and LH/FSH ratio (2.6+/-0.5 vs. 1.0+/-0.2, p<0.05). During hyperinsulinaemic clamps, the glucose infusion rate (GIR) required to maintain euglycaemia was lower in PCOS compared to controls (33.6+/-2.7 vs. 45.1+/-3.5 micromol/kg/min, p<0.05) but similar in PCOS before and after treatment (33.6+/-2.8 vs. 33.6+/-2.7 micromol/kg/min, p=0.9). Numbers of pulses identified in PCOS and controls were similar and unaltered by ethinyl oestradiol/cyproterone acetate. There was no correlation between GIR and frequency of insulin pulses in PCOS before or after treatment (r=0.2, p=0.6; post r=-0.5, p=0.1) unlike controls (r=-0.6, p=0.04). Despite considerable improvement in androgen profile, treatment with ethinyl oestradiol/cyproterone acetate did not alter insulin action in PCOS, and this insulin resistance does not appear to be determined by insulin pulse frequency.