Birth weight is nongenetically associated with glucose intolerance in elderly twins, independent of adult obesity

OBJECTIVES

Using a unique twin approach, we examined the extent to which birth weight is determined by genetic and nongenetic factors and whether associations between birth weight and measures of glucose metabolism are of genetic or nongenetic origin.

SETTING/SUBJECTS

An oral glucose tolerance test (OGTT) was performed in a population-based cohort of twins including 138 same-sex monozygotic (MZ) and 214 dizygotic (DZ) twin pairs aged 55-73 years whose birth weight was known. Heritability of birth weight was determined and regression analyses with intra-twin pair differences of birth weight and measures of glucose metabolism, with and without adjustment for adult obesity, were performed.

RESULTS

The heritability of birth weight was estimated to be 38%. We demonstrated significant nongenetic associations between birth weight and measures of glucose homeostasis in MZ twins, with a reduction in fasting plasma glucose, 120 min post-OGTT plasma glucose, fasting plasma insulin and HOMA-IR index of 15.7%, 25.5%, 26.4% and 37.2%, respectively, for every 1 kg increase in birth weight. The nongenetic negative associations between birth weight and measures of glucose intolerance were independent of adult obesity, whereas the nongenetic association between birth weight and insulin resistance persisted, although not as strongly, after adjusting for current body size.

CONCLUSIONS

We demonstrated a genetic component to birth weight in elderly twins. When adjusting for this influence, we found a nongenetic negative association between birth weight and glucose tolerance as well as insulin resistance that was partially independent of adult obesity. This implies that the foetal environment influences glucose homeostasis in elderly twins.

Decreased protein levels of key insulin signalling molecules in adipose tissue from young men with a low birthweight: potential link to increased risk of diabetes?

AIMS/HYPOTHESIS

Individuals with low birthweight are at increased risk of type 2 diabetes mellitus. However, the underlying molecular mechanisms are unknown. Previously we have shown that low birthweight is associated with changes in muscle insulin signalling proteins. Here we determined whether low birthweight is associated with changes in insulin signalling proteins in adipose tissue.

METHODS

Men (age 23 years) with either a low (bottom 10th percentile) (n = 17) or a normal (50th-90th percentile) (n = 17) birthweight were recruited from the Danish Medical Birth Registry and subcutaneous adipose biopsies were taken.

RESULTS

Between the two groups there was no difference in protein level of the insulin receptor, protein kinase C zeta, glycogen synthase kinase-3 (GSK3) alpha, GSK3 beta, protein kinase B alpha and beta, peroxisome proliferative activated receptor gamma coactivator 1 or Src-homology-2-containing protein. However, the levels of GLUT4 (also known as solute carrier family 2 [facilitated glucose transporter], member 4 [SLC2A4]) (52 +/- 10.9% reduction, p < 0.01), p85alpha subunit of phosphoinositide 3-kinase (PI3K) (45 +/- 9% reduction, p < 0.01), p110ss subunit of PI3K (48 +/- 17% reduction, p = 0.06) and IRS1 (59 +/- 24% reduction, p < 0.05) were reduced in men of low birthweight.

CONCLUSIONS/INTERPRETATION

These findings show that low birthweight is associated with reduced levels of adipose insulin signalling proteins, thus providing a potential molecular framework to explain why people with low birthweight are at increased risk of developing type 2 diabetes. These differences precede the development of diabetes and thus may help predict disease risk.

Metabolic aspects of insulin resistance in individuals born small for gestational age

Numerous studies have shown an association between low weight at birth and being born small for gestational age (SGA) on the one hand and risk of developing insulin resistance and type 2 diabetes on the other. Our studies in twins have indicated a non-genetic age-dependent origin of insulin resistance and type 2 diabetes associated with being born SGA. In order to gain insight into the molecular metabolic defects and mechanisms linking SGA with insulin resistance and type 2 diabetes, we performed a series of experiments in young and elderly twins, and, in particular, in young men (aged 19-23 years) with a weight at birth at term in the lowest 10th percentile with no family history of diabetes. The control group included age-matched men with birth weights at term in the upper normal range. While body mass index and waist-to-hip ratios were similar in the individuals born SGA and controls, dual-energy X-ray absorptiometry studies documented a higher degree of abdominal obesity in the men who had a low weight at birth. Using the gold standard hyperinsulinaemic-euglycaemic clamp technique combined with glucose tracers and studies of forearm glucose uptake, we found an impairment of insulin-stimulated glycolytic flux and reduced forearm (muscle) glucose uptake in the face of normal whole-body glucose uptake. In addition, we found a significantly decreased insulin secretion rate during oral glucose ingestion after correction for insulin action (disposition index), a paradoxical enhanced insulin suppression of hepatic glucose production and lower fasting plasma glycerol levels, suggesting impaired lipolysis. Finally, analysis of skeletal muscle biopsies showed reduced muscle expression of several key proteins involved in insulin signalling and glucose transport, including protein kinase C-zeta, the two subunits of phosphoinositol 3-kinase (i.e., p85alpha and p110beta) and the insulin-sensitive glucose transporter, Glut-4, in individuals of low birth weight. In conclusion, being born SGA and of low birth weight is associated with type 2 diabetes in a non-genetic manner, and programming of muscle insulin action and signalling represents an early mechanism responsible for this association.

Plasma cytokine levels in young and elderly twins: genes versus environment and relation to in vivo insulin action

AIMS/HYPOTHESIS

We studied the impact of genetic versus pre- and postnatal environmental factors on the plasma levels of IL6, TNF and the soluble TNF receptor superfamily, member 1A (TNFRSF1A, previously known as TNF receptor type1 [TNFR1]).

MATERIALS AND METHODS

Using the hyperinsulinaemic-euglycaemic clamp, we assessed the association between cytokine levels and both peripheral insulin sensitivity and hepatic glucose production. Fasting plasma IL6, TNF and soluble TNFRSF1A levels were measured using ELISA in 55 young and 43 elderly twin pairs.

RESULTS

Plasma IL6 and TNF were influenced by genetic factors in young and elderly twins respectively, while no significant impact of genetics was found for soluble TNFRSF1A. Significant intra-twin pair correlations between birthweight and both IL6 and soluble TNFRSF1A levels were found. In addition to the effect of birthweight on IL6, age and fat % also significantly influenced IL6 levels, whereas soluble TNFRSF1A levels were significantly influenced by zygosity, age, fat % and sex. Plasma soluble TNFRSF1A was associated with higher plasma NEFA and to some extent with reduced insulin sensitivity. Plasma IL6 was associated positively with basal NEFA. TNF level was not associated with in vivo glucose or fat metabolism after correction for known confounders.

CONCLUSIONS/INTERPRETATION

Plasma IL6 and soluble TNFRSF1A are influenced by the intrauterine environment. We found some evidence of a genetic component for TNF and IL6 in young and elderly twins respectively. Plasma IL6 may influence basal lipolysis, but neither plasma TNF nor IL6 levels are independently associated with hepatic or peripheral insulin action. Nevertheless, plasma soluble TNFRSF1A may play some role in the control of insulin action.

Reversibility of exercise-induced translocation of Na+-K+ pump subunits to the plasma membrane in rat skeletal muscle

Exercise-induced translocation of Na+-K+ pump subunits to the sarcolemmal membrane was studied using sarcolemmal giant vesicles as a membrane purification procedure. The subunit content was quantified by Western blotting or by ouabain labeling. Low-intensity treadmill running increased (P<0.01) the alpha1, alpha2, beta1, and beta2 subunit contents by 19-32% in membranes from oxidative muscle fibers and the alpha1, alpha2, and beta2 contents increased by 13-25% in membranes from glycolytic muscle fibers. Ouabain labeling of membranes from mixed fibers was increased by 29% after exercise. A similar increase in subunit content could be induced by 5 min of fatiguing, high-intensity electrical stimulation of isolated soleus muscles. An increased subunit content was just detectable in vesicles produced 30 min after exercise, and the content was completely back to control levels 3 h after exercise. It is concluded that both low-intensity long-lasting running and short-lasting high-intensity contractions are able to induce a translocation of pump subunits to the sarcolemmal membrane. The post-exercise disappearance of the extra subunits (half-time approximately 20 min) from the membrane demonstrates the reversible nature of the translocation process.