Increased susceptibility to streptozotocin and impeded regeneration capacity of beta-cells in adult offspring of malnourished rats

BACKGROUND

Epidemiological studies related poor maternal nutrition and subsequent growth retardation in the progeny to the development of diabetes later in life. Low-protein diet during gestation altered the beta-cell development of the rat progeny by decreasing beta-cell proliferation and increasing their sensitivity to nitric oxide and cytokines in the foetus. This disturbed maternal environment had long-lasting consequences because the higher beta-cell vulnerability was maintained at adulthood.

AIM

The aim of this study was to determine whether early malnutrition influences the vulnerability and the regeneration capacity of beta-cells after streptozotocin (STZ) damage at adulthood.

METHODS

Gestating rats were fed either a control or a low-protein diet until weaning. Adult female offspring received injections of Freund's adjuvant weekly for 5 weeks followed 24 h later by STZ. Half of the cohort was killed at d34, whereas the other half was maintained until d48 to analyse the regeneration capacity of the beta-cells.

RESULTS

Although control and low-protein rats had equivalent pancreatic insulin content and beta-cell volume density at d34, hyperglycaemia appeared earlier and was more dramatic in low-protein rats than in control rats. STZ treatment increased beta-cell proliferation similarly in both groups. At d48, apoptotic rate was higher in the low-protein group. Regeneration appeared in control, but not in the low-protein rats, where beta-cell aggregates/surface area and Reg1-positive area were decreased compared to control.

CONCLUSION

Maternal malnutrition programmes a more vulnerable endocrine pancreas in the progeny which is unable to regenerate after injury, therefore predisposing it to develop glucose intolerance and diabetes later in life.

Implication of nitric oxide in the increased islet-cells vulnerability of adult progeny from protein-restricted mothers and its prevention by taurine

An increased vulnerability of adult beta-cells seems to be programmed in early life as adult islets from the progeny of dams fed a low-protein diet exhibited an increased apoptotic rate after cytokine stimulation. This was prevented by maternal taurine supplementation. Here, we investigated the mechanisms implicated in such an increased vulnerability and how taurine exerts its protective role. Throughout gestation and lactation, Wistar rats were fed a 20% (control (C group)) or an isocaloric 8% protein diet (recovery (R group)) supplemented or not with taurine (control+taurine and recovery+taurine groups respectively). Offspring received a 20% protein diet after weaning. Islets from 3-month-old females were isolated and cultured for 48 h before being incubated with or without cytokines for 24 h. In unstimulated islets, apoptotic rate and NO(.) secretion were higher in R than in C. Both GADD153 mRNA and protein were increased, whereas mRNA of mitochondrial gene ATPase6 was downregulated in R group compared with C. In the RT group, taurine prevented apoptosis and restored a normal NO(.) production in GADD153 as well as ATPase6 mRNA expression. After cytokines-induction, apoptosis and NO(.) secretion were still increased in R compared with C but both parameters were normalized in the RT group. In conclusion, a maternal low-protein diet programmes a different pattern of gene expression in islet-cells of adult progeny. Higher NO(.) production by these islets could be an important factor in the subsequent cell death. The prevention of these events by maternal taurine supplementation emphasizes the importance of taurine during endocrine pancreas development.

The intrauterine metabolic environment modulates the gene expression pattern in fetal rat islets: prevention by maternal taurine supplementation

AIMS/HYPOTHESIS

Events during fetal life may in critical time windows programme tissue development leading to organ dysfunction with potentially harmful consequences in adulthood such as diabetes. In rats, the beta cell mass of progeny from dams fed with a low-protein (LP) diet during gestation is decreased at birth and metabolic perturbation lasts through adulthood even though a normal diet is given after birth or after weaning. Maternal and fetal plasma taurine levels are suboptimal. Maternal taurine supplementation prevents these induced abnormalities. In this study, we aimed to reveal changes in gene expression in fetal islets affected by the LP diet and how taurine may prevent these changes.

METHODS

Pregnant Wistar rats were fed an LP diet (8% [wt/wt] protein) supplemented or not with taurine in the drinking water or a control diet (20% [wt/wt] protein). At 21.5 days of gestation, fetal pancreases were removed, digested and cultured for 7 days. Neoformed islets were collected and transcriptome analysis was performed.

RESULTS

Maternal LP diet significantly changed the expression of more than 10% of the genes. Tricarboxylic acid cycle and ATP production were highly targeted, but so too were cell proliferation and defence. Maternal taurine supplementation normalised the expression of all altered genes.

CONCLUSIONS/INTERPRETATION

Development of the beta cells and particularly their respiration is modulated by the intrauterine environment, which may epigenetically modify expression of the genome and programme the beta cell towards a pre-diabetic phenotype. This mis-programming by maternal LP diet was prevented by early taurine intervention.

Intrauterine programming of the endocrine pancreas

Epidemiological studies have revealed strong relationships between poor foetal growth and subsequent development of the metabolic syndrome. Persisting effects of early malnutrition become translated into pathology, thereby determine chronic risk for developing glucose intolerance and diabetes. These epidemiological observations identify the phenomena of foetal programming without explaining the underlying mechanisms that establish the causal link. Animal models have been established and studies have demonstrated that reduction in the availability of nutrients during foetal development programs the endocrine pancreas and insulin-sensitive tissues. Whatever the type of foetal malnutrition, whether there are not enough calories or protein in food or after placental deficiency, malnourished pups are born with a defect in their beta-cell population that will never completely recover, and insulin-sensitive tissues will be definitively altered. Despite the similar endpoint, different cellular and physiological mechanisms are proposed. Hormones operative during foetal life like insulin itself, insulin-like growth factors and glucocorticoids, as well as specific molecules like taurine, or islet vascularization were implicated as possible factors amplifying the defect. The molecular mechanisms responsible for intrauterine programming of the beta cells are still elusive, but two hypotheses recently emerged: the first one implies programming of mitochondria and the second, epigenetic regulation.

Non-esterified fatty acids are deleterious for human pancreatic islet function at physiological glucose concentration

AIMS/HYPOTHESIS

Whether excess glucose (glucotoxicity) and excess non-esterified fatty acids (lipotoxicity) act synergistically or separately to alter beta-cell function on Type 2 diabetes remains controversial. We examined the influence of non-esterified fatty acids, with or without concomitant increased glucose concentrations, on human islet function and on the expression of genes involved in lipid metabolism.

METHODS

Human islets isolated from non-diabetic and non-obese donors were cultured with 5.5, 16 or 30 mmol/l glucose, and when appropriate with 1 or 2 mmol/l non-esterified fatty acids. After 48 h, glucose-stimulated insulin secretion, insulin content, triglyceride content and expression of different genes were evaluated.

RESULTS

Non-esterified fatty acids decreased glucose-stimulated insulin secretion, insulin content and increased triglyceride content of human isolated islets, independently from the deleterious effect of glucose. Increased glucose concentrations also decreased glucose-stimulated insulin secretion and insulin content, but had no influence on triglyceride content. Glucose-stimulated insulin secretion of islets appeared to be significantly correlated with their triglyceride content. Glucose and non-esterified fatty acids modified the gene expression of carnitine palmitoyltransferase-I, acetyl-CoA carboxylase, acyl-CoA oxidase and uncoupling protein 2.

CONCLUSION/INTERPRETATION

In our model of isolated human islets, increased glucose and non-esterified fatty acids separately reproduced the two major beta-cell alterations observed in vivo, i.e. loss of glucose-stimulated insulin secretion and reduction in islet insulin content. Our results also suggest that this deleterious effect was, at least in part, mediated by modifications in lipid metabolism gene expression.

Hepatocyte nuclear factor 4 alpha isoforms originated from the P1 promoter are expressed in human pancreatic beta-cells and exhibit stronger transcriptional potentials than P2 promoter-driven isoforms

The nuclear receptor hepatocyte nuclear factor (HNF) 4 alpha is involved in a transcriptional network and plays an important role in pancreatic beta-cells. Mutations in the HNF4 alpha gene are correlated with maturity-onset diabetes of the young 1. HNF4 alpha isoforms result from both alternative splicing and alternate usage of promoters P1 and P2. It has recently been reported that HNF4 alpha transcription is driven almost exclusively by the P2 promoter in pancreatic islets. We observed that transcripts from both P1 and P2 promoters were expressed in human pancreatic beta-cells and in the pancreatic beta-cell lines RIN m5F and HIT-T15. Expression of HNF4 alpha proteins originating from the P1 promoter was confirmed by immunodetection. Due to the presence of the activation function module AF-1, HNF4 alpha isoforms originating from the P1 promoter exhibit stronger transcriptional activities and recruit coactivators more efficiently than isoforms driven by the P2 promoter. Conversely, activities of isoforms produced by both promoters were similarly repressed by the corepressor small heterodimer partner. These behaviors were observed on the promoter of HNF1 alpha that is required for beta-cell function. Our results highlight that expression of P1 promoter-driven isoforms is important in the control of pancreatic beta-cell function.