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.

Nutritional regulation of proteases involved in fetal rat insulin secretion and islet cell proliferation.

Epidemiological studies have indicated that malnutrition during early life may programme chronic degenerative disease in adulthood. In an animal model of fetal malnutrition, rats received an isoenergetic, low-protein (LP) diet during gestation. This reduced fetal beta-cell proliferation and insulin secretion. Supplementation during gestation with taurine prevented these alterations. Since proteases are involved in secretion and proliferation, we investigated which proteases were associated with these alterations and their restoration in fetal LP islets. Insulin secretion and proliferation of fetal control and LP islets exposed to different protease modulators were measured. Lactacystin and calpain inhibitor I, but not isovaleryl-L-carnitine, raised insulin secretion in control islets, indicating that proteasome and cysteinyl cathepsin(s), but not mu-calpain, are involved in fetal insulin secretion. Insulin secretion from LP islets responded normally to lactacystin but was insensitive to calpain inhibitor I, indicating a loss of cysteinyl cathepsin activity. Taurine supplementation prevented this by restoring the response to calpain inhibitor I. Control islet cell proliferation was reduced by calpain inhibitor I and raised by isovaleryl-L-carnitine, indicating an involvement of calpain. Calpain activity appeared to be lost in LP islets and not restored by taurine. Most modifications in the mRNA expression of cysteinyl cathepsins, calpains and calpastatin due to maternal protein restriction were consistent with reduced protease activity and were restored by taurine. Thus, maternal protein restriction affected cysteinyl cathepsins and the calpain-calpastatin system. Taurine normalised fetal LP insulin secretion by protecting cysteinyl cathepsin(s), but the restoration of LP islet cell proliferation by taurine did not implicate calpains.

Antihyperglycemic and blood pressure-reducing effects of stevioside in the diabetic Goto-Kakizaki rat.

Stevioside, a glycoside present in the leaves of the plant, Stevia rebaudiana Bertoni (SrB), has acute insulinotropic effects in vitro. Its potential antihyperglycemic and blood pressure-lowering effects were examined in a long-term study in the type 2 diabetic Goto-Kakizaki (GK) rat. Rats were fed 0.025 g x kg(-1) x d(-1) of stevioside (purity > 99.6%) for 6 weeks. An intra-arterial catheter was inserted into the rats after 5 weeks, and conscious rats were subjected to arterial glucose tolerance test (2.0 g x kg(-1)) during week 6. Stevioside had an antihyperglycemic effect (incremental area under the glucose response curve [IAUC]): 985 +/- 20 (stevioside) versus 1,575 +/- 21 (control) mmol/L x 180 minutes, (P <.05), it enhanced the first-phase insulin response (IAUC: 343 +/- 33 [stevioside] v 136 +/- 24 [control] microU/mL insulin x 30 minutes, P <.05) and concomitantly suppressed the glucagon levels (total AUC: 2,026 +/- 234 [stevioside] v 3,535 +/- 282 [control] pg/mL x 180 minutes, P <.05). In addition, stevioside caused a pronounced suppression of both the systolic (135 +/- 2 v 153 +/- 5 mm Hg; P <.001) and the diastolic blood pressure (74 +/- 1 v 83 +/- 1 mm Hg; P <.001). Bolus injections of stevioside (0.025 g x kg(-1)) did not induce hypoglycemia. Stevioside augmented the insulin content in the beta-cell line, INS-1. Stevioside may increase the insulin secretion, in part, by induction of genes involved in glycolysis. It may also improve the nutrient-sensing mechanisms, increase cytosolic long-chain fatty acyl-coenzyme A (CoA), and downregulate phosphodiesterase 1 (PDE1) estimated by the microarray gene chip technology. In conclusion, stevioside enjoys a dual positive effect by acting as an antihyperglycemic and a blood pressure-lowering substance; effects that may have therapeutic potential in the treatment of type 2 diabetes and the metabolic syndrome.

Cloning of glucocorticoid receptor and mineralocorticoid receptor cDNA and gene expression in the central nervous system of the tree shrew (Tupaia belangeri).

The glucocorticoid (GR) and the mineralocorticoid (MR) receptor mediate corticosteroid actions in the mammalian brain. Here, we report the sequence and distribution of both receptor subtype mRNAs in the central nervous system of the tree shrew Tupaia belangeri, a non-rodent mammal, phylogenetically located between insectivores and primates. The specific glucocorticoid and mineralocorticoid receptor cDNAs were cloned, employing polymerase chain reaction (PCR) based methods. The GR cDNA and MR cDNA encode the 776-amino acid (aa) and 977-aa receptor, respectively. Comparisons of both GR and MR with corresponding cDNA-sequences of other species revealed the highest homology to the human equivalents (GR: 90%, MR: 89% nucleotide sequence identity of the coding regions). The localization of GR and MR mRNA in tree shrew brain was investigated by in situ hybridization using 35S-labeled riboprobes. The GR mRNA is widely distributed throughout all observed brain areas, with high signal intensities in the dentate gyrus, piriform cortex, cerebellum, anterior pituitary, subfornical organ and pineal gland. Whereas, moderate expression of GR mRNA was noted in region CA1 of the hippocampus, region CA3 displayed only low signal intensity. MR mRNA hybridization is mainly restricted to the strongly labeled hippocampal formation, but in contrast to the localization pattern found in rat, higher signal intensities are detected in field CA1 than in CA3. These data indicate that both GR and MR mRNAs are highly expressed in tree shrew brain with a species-specific expression pattern.