At the end of the NUTRIX program, we have demonstrated that nutritional deficiencies during pregancy in rodents altered the development of the progeny’s insulin-producing beta cells, the mechanisms being different following the kind of malnutrition used. The lasting sequelae of early malnutrition were visible in such long-term consequences as glucose intolerance, reduced insulin secretion and growth but could be prevented by early intervention. In addition, by comparing the consequences of early growth retardation induced by depletion of nutritional or genetic elements, we shown that lasting consequences were due to the nutritional intrauterine environment and not to genetic factors. The study on human had allowed to underline nutritional components involved in foetal growth and explore the role of glucocoirticoids in the development of the pancreas.
Although we have not yet reached the ultimate aim of formulating nutritional recommendations to pregnant and nursing mothers to improve long-term quality of life and to propose preventive and therapeutic nutritional supplements, our research in the scope of Nutrix has made an important contribution to our understanding of the determining impact of early malnutrition on development and programming of degenerative disease. Human data have provided important insight into the relative importance of different nutriments on foetal development. Our research has also identified some key targets of malnutrition and shown that irrespective of the type of malnutrition and the thereby affected mechanisms, similar long-term consequences can be observed. Fine-tuning of our present findings should lead to the identification of primary and central mechanisms implicated in the programming.
Maternal general food restriction
In the GFR model (WP1), the plasma and islet amino acids level were almost normal. However, we demonstrated a high glucocorticoid plasma level that alters the generation of pancreatic endocrine cells and favours the development of the exocrine pancreas rather than that of the endocrine tissue. This was revealed by changes in the expression of genes specifically involved in the pancreatic development.
Beta cell mass is reduced in GFR due to alteration in the differentiation of the pancreas
GFR favours the development of the exocrine tissue at the detriment of the endocrine tissue
Glucocorticoids favour exocrine cell differentiation but repress beta-cell differentiation
Dexamethasone treatment of pancreatic buds decreased the number of cells expressing both Pdx-1 (green nuclei) and insulin (red cytoplasm) but increased the differentiation into acinar cells (amylase-positive cell area, brown).
Maternal protein restriction: Beta cell mass is reduced in PR due to less mutiplication and more death of the beta cells
By contrast to the maternal general food restriction, maternal PR (WP2) that reduces also the beta cell mass, was associated with a normal glucocorticoid level but with alteration in the plasma amino acid levels. PR altered islet endocrine pancreas development by decreasing the cell multiplication and islet vascularisation. It rendered the beta cell more prone to be destroyed as it is observed in type 1 diabetes. These alterations remained at adulthood even if a normal diet was given from weaning.
Maternal folate restriction (FR)
Maternal Folate Restriction (WP3) had long-term effect on the growth and the metabolism of the offspring. This was manifested by low body weight of the offspring and reduced fasting plasma insulin and triglyceride concentrations at 3 months of age. These effects resembled the long-term effects of maternal protein and iron restriction as previously reported. Thus when the foetus is experiencing malnutrition, it appears that whatever the type of malnutrition, it will adapt in a similar way, but with differing modalities, the development of the organ mastering metabolism, the endocrine pancreas. Although the glucose tolerance and blood pressure were normal at all ages, minor detrimental effects on longevity were observed as the maternal folate restricted offspring showed earlier death as compared to the control animals.
Genetic growth restriction (GGR)
The relative importance of nutritional and factors genetic factors in foetal programming was evaluated by comparing genetic growth restriction models with the nutritional models (WP4). Transgenic mice in which the Insulin Growth Factor-2 gene was made permanently deficient (20% of the wildtype) featured a smaller body weight at weaning that was maintained later, but associated to a normal glucose tolerance. These animals had significantly lower systolic blood pressure compared to the wildtype. If the IGF-2 deficiency was limited to the placenta and thus to the gestational period, pups underwent catch-up growth after birth and had a normal glucose tolerance or blood pressure later in life. Comparing the lasting effect of the early growth restriction induced by genetic or nutritional manipulation, revealed that long-term consequences such as reduced longevity, glucose intolerance, or blood pressure were due to the nutritional intrauterine environment and not due to genetic factors.
Nutritional regulation genes
The programming by maternal malnutrition of insulin-targeted cells (adipocytes and hepatocytes) was analysed by using in vitro culture systems (WP5). We have shown that the proliferation and differentiation of adipocyte precursors was not affected by the maternal diet. We propose that the propensity to develop obesity which is suspected in the progeny of malnourished animals would result from programming of the neuro-hormonal regulation such as the control of appetite or more generally of the hormonal context, and not from a programmed alteration in the fat tissue itself. In contrast to adipocyte, the hepatocyte proliferation was reduced. However, there was no significant gene programming due to the maternal diet. This was confirmed by the absence of effect of the maternal diet on DNA methylation or in the expression of specific proteins involved in the control of cell multiplication. So, observation of the alteration later in life appeared to be also the consequence of the programming of the hormonal system to which participate insulin, glucocorticoids and the insulin-like growth factor axis.
Human pancreas development
Epidemiological analysis in human
Our epidemiological and nutrition study (WP7) performed on 100.000 pregnant women has now allowed us to examine how dietary factors in pregnancy relate to various pregnancy outcomes, including birth weight. When associations between birth weight and specific food were searched, positive correlations were found with milk, fish and sweets. A negative correlation was found with snacks and no correlation was found with fruits and vegetables. The underlying factors behind these correlations are now being explored by an extensive programme of analyses.
Prevention/intervention by taurine
We have highlighted the importance to have adequate taurine plasma level to avoid abnormal development of the endocrine pancreas and its lasting consequences. Taurine is an sulphur amino acid that does not participate to protein synthesis, but was shown to be very important during development. Indeed, most of the alterations induced by the maternal PR diet were restored by the simple supplementation of the PR diet of the dams with taurine during gestation and lactation.