Early low protein diet increases foetal and adult islet sensitivity to cytokines : protective role of taurine

Epidemiological studies have suggested that malnutrition during development, which leads to offspring growth retardation, might be at the origin of syndrome X later in life. This syndrome includes hypertension, obesity and the propensity to type-2 diabetes. In animal model, it was demonstrated in our laboratory that early protein deficiency (8%; LP vs. 20%; C) alters foetal pancreas development. Indeed, the mass of endocrine pancreas and its vascularisation were reduced. Islet cells featured a higher apoptotic rate, this has prompted us to emit the hypothesis of possible early "programming" of susceptibility to molecules involved in type-1 diabetes following protein deficiency in early life. Therefore, we first investigated the effect of early LP diet on the sensitivity of foetal islet cells to NO. and IL1-â. We found that foetal islets from rats fed on LP diet during gestation were more sensitive to these toxic molecules than control islets. Thereafter, we verified the long-lasting effect of LP diet on islet cells sensitivity to cytokines, when this diet was kept during gestation and lactation (recuperated group, R). Adult islets of the R group remained more sensitive to cytokines despite refeeding a normal diet after weaning. Thus, a permanent alteration in susceptibility of beta cell appeared programmed in foetal life. LP diet has been reported to decrease the level of plasma taurine in dams and their foetuses. Since this amino acid is considered to feature antioxidant properties, we verified the effect of taurine either added in vitro or in vivo to the drinking water (2.5%) of the mother on the sensitivity of foetal and adult islets to cytokines. When taurine was added to the culture medium of foetal and adult islets it provided an important protective effect against cytokines-induced apoptosis. In vivo, it lowered the sensitivity of foetal islets of control group to IL1-â but not to NO. donor. In islets of LP group, the cytotoxic response to IL1-â was suppressed and that to NO. donor was decreased. Taurine supplementation in vivo during early life decreased the susceptibility of adult islets of the R group to cytokines. Whereas, it increased the sensitivity of the controls. On the other hand, when an oral glucose tolerance test (OGTT) was performed at this age, the administration of taurine in early life restored the insulinaemia in R group, while it remained blunted with the absence of treatment by the amino acid. Together these findings emphasize that a normal level of taurine during early life is important for an appropriate function and resistance to aggression in the endocrine pancreas. Some mechanisms by which taurine could exert its protection on beta cell were also investigated in this work. We showed first that the beneficial effect of taurine must be attributed to its sulphonic group, since analogous amino acids, like methionine and b-alanine, were less effective. Second, in an acellular system, taurine appears to react with ONOO- but not with NO.. Finally, in a cellular system, we used rat insulonoma cell line (RINm5F), which was also protected by taurine treatment towards cytokines injury. In this system, we found that the anti-apoptotic effect of taurine does not appear to be related to changes in HSP70 expression, but a decrease in NO. production could be involved. In conclusion, our study demonstrated that LP diet during development increased the sensitivity of beta cell to cytokines suggesting a possible link between foetal "programming" and type-1 diabetes later in life. Moreover, the beneficial effect of taurine was demonstrated in foetal and adult islet cells underlining the important role of normal taurine level during endocrine pancreas development.Doctorat en sciences (sciences biologiques) (BIOL 3)--UCL, 200

Intrauterine low protein diet increases fetal beta-cell sensitivity to NO and IL-1 beta: the protective role of taurine.

We have demonstrated earlier that a low-protein (8% protein) diet during gestation alters fetal beta-cell development. Here, we investigated the effect of a low-protein diet as compared with a control (20% protein) diet, during gestation, on the sensitivity of fetal beta-cells against nitric oxide (NO) or interleukin-1 beta (IL-1 beta), and assessed the protective effect of taurine in vitro and in vivo. Neoformed islets from control fetuses or fetuses of dams fed a low-protein diet (LP group) were incubated with taurine, methionine or beta-alanine and then exposed to sodium nitropruside (SNP), a NO donor, or to IL-1 beta. To understand the effect of taurine in vivo, LP or control pregnant rats received 2.5% of taurine in the drinking water. Mortality and rate of apoptosis were quantified by confocal microscopy. Without treatment, rate of apoptosis was greater in LP group islets than in control islets (1.38+/-0.18% compared with 0.66+/-0.21% respectively, P<0.05). Addition of SNP 100 microM showed an augmentation in cell death, which was greater in the LP than in the control group (17.88+/-0.69% compared with 11.89+/-0.44% respectively, P<0.01). LP islets were more sensitive than control islets to IL-1 beta. Taurine was protective against SNP and IL-1 beta in both the groups, methionine provided a less protective effect than taurine, and pretreatment with beta-alanine had no protective effect. Taurine supplementation of the maternal diet reduced the rate of apoptosis induced by IL-1 beta in control islets and suppressed that induced by IL-1 beta in LP islets. Our findings indicate that a low-protein diet during gestation augments the sensitivity of fetal islet cells to NO and IL-1 beta. However, through in vitro and in vivo experiments our studies indicate that such effects can be rescued using amino acids such as taurine

Inhibition of Histone Deacetylases Induces Bovine Leukemia Virus Expression In Vitro and In Vivo

Packaging into nucleosomes results in a global transcriptional repression as a consequence of exclusion of sequence-specific factors. This inhibition can be relieved by using inhibitors of histone deacetylases, acetylation being a major characteristic of transcriptionally active chromatin. Paradoxically, the expression of only ∼2% of the total cellular genes is modulated by histone hyperacetylation. To unravel the potential role of this transcriptional control on BLV expression, we tested the effect of two highly specific inhibitors of deacetylases, trichostatin A (TSA) and trapoxin (TPX). Our results demonstrate that treatment with TSA efficiently enhanced long terminal repeat-directed gene expression of integrated reporter constructs in heterologous D17 stable cell lines. To further examine the biological relevance of these observations made in vitro, we analyzed ex vivo-isolated peripheral blood mononuclear cells (PBMCs) from bovine leukemia virus (BLV)-infected sheep. TSA deacetylase inhibitor induced a drastic increase in viral expression at levels comparable to those induced by treatment with phorbol-12-myristate 13-acetate and ionomycin, the most efficient activators of BLV expression known to date. TSA acted directly on BLV-infected B lymphocytes to increase viral expression and does not seem to require T-cell cooperation. Inhibition of deacetylation after treatment with TSA or TPX also significantly increased viral expression in PBMCs from cattle, the natural host for BLV. Together, our results show that BLV gene expression is, like that of a very small fraction of cellular genes, also regulated by deacetylation

Taurine supplementation to a low protein diet during foetal and early postnatal life restores a normal proliferation and apoptosis of rat pancreatic islets.

AIMS/HYPOTHESIS: In our previous studies a low protein diet (8% vs 20%) given during foetal and early postnatal life induced abnormal development of the endocrine pancreas; beta-cell mass and islet-cell proliferation were reduced while apoptosis was increased. Taurine, an important amino acid for development was also reduced in maternal and foetal plasma of protein deficient animals. In this study we aim to evaluate the role of taurine in the alterations observed in rats after a low protein diet. METHODS: Four groups of rats were given either a control, a low protein, or control and low protein diets with 2.5% taurine in the drinking water. Diets were given to gestating and lactating mothers and to their pups until day 30. Beta and endocrine cell masses were analysed as well as DNA synthesis and apoptosis after taurine supplementation in foetuses and pups. We also investigated insulin like growth factor-II (IGF-II), inducible nitric oxide synthase (iNOS), and Fas by immunohistochemistry. RESULTS: In foetuses and neonates nourished with a low protein diet, taurine supplementation restored normal DNA synthesis and apoptosis. This led to adequate beta and endocrine cell mass in pups. In islet cells, immunoreactivity was increased for IGF-II, reduced for Fas and unchanged for iNOS after taurine supplementation. CONCLUSION/INTERPRETATION: Taurine supplementation to a low protein diet in foetal and early postnatal life prevents the abnormal development of the endocrine pancreas. The mechanisms by which taurine acts on DNA synthesis and apoptosis rate of endocrine cells involve IGF-II, Fas regulation but not iNOS

Glucose-induced mixed [Ca2+]c oscillations in mouse beta-cells are controlled by the membrane potential and the SERCA3 Ca2+-ATPase of the endoplasmic reticulum

Stimulatory concentrations of glucose induce two patterns of cytosolic Ca2+ concentration ([Ca2+]c) oscillations in mouse islets: simple or mixed. In the mixed pattern, rapid oscillations are superimposed on slow ones. In the present study, we examined the role of the membrane potential in the mixed pattern and the impact of this pattern on insulin release. Simultaneous measurement of [Ca2+]c and insulin release from single islets revealed that mixed [Ca2+]c oscillations triggered synchronous oscillations of insulin secretion. Simultaneous recordings of membrane potential in a single beta-cell within an islet and of [Ca2+]c in the whole islet demonstrated that the mixed pattern resulted from compound bursting (i.e., clusters of membrane potential oscillations separated by prolonged silent intervals) that was synchronized in most beta-cells of the islet. Each slow [Ca2+]c increase during mixed oscillations was due to a progressive summation of rapid oscillations. Digital image analysis confirmed the good synchrony between subregions of an islet. By contrast, islets from sarco(endo)plasmic reticulum Ca2+-ATPase isoform 3 (SERCA3)-knockout mice did not display typical mixed [Ca2+]c oscillations in response to glucose. This results from a lack of progressive summation of rapid oscillations and from altered spontaneous electrical activity, i.e., lack of compound bursting, and membrane potential oscillations characterized by lower-frequency but larger-depolarization phases than observed in SERCA3+/+ beta-cells. We conclude that glucose-induced mixed [Ca2+]c oscillations result from compound bursting in all beta-cells of the islet. Disruption of SERCA3 abolishes mixed [Ca2+]c oscillations and augments beta-cell depolarization. This latter observation indicates that the endoplasmic reticulum participates in the control of the beta-cell membrane potential during glucose stimulation