Defining the In Vivo Role of mTORC1 in Thyrocytes by Studying the TSC2 Conditional Knockout Mouse Model.

Background: The thyroid gland is susceptible to abnormal epithelial cell growth, often resulting in thyroid dysfunction. The serine-threonine protein kinase mechanistic target of rapamycin (mTOR) regulates cellular metabolism, proliferation, and growth through two different protein complexes, mTORC1 and mTORC2. The PI3K-Akt-mTORC1 pathway's overactivity is well associated with heightened aggressiveness in thyroid cancer, but recent studies indicate the involvement of mTORC2 as well. Methods: To elucidate mTORC1's role in thyrocytes, we developed a novel mouse model with mTORC1 gain of function in thyrocytes by deleting tuberous sclerosis complex 2 (TSC2), an intracellular inhibitor of mTORC1. Results: The resulting TPO-TSC2KO mice exhibited a 70-80% reduction in TSC2 levels, leading to a sixfold increase in mTORC1 activity. Thyroid glands of both male and female TPO-TSC2KO mice displayed rapid enlargement and continued growth throughout life, with larger follicles and increased colloid and epithelium areas. We observed elevated thyrocyte proliferation as indicated by Ki67 staining and elevated cyclin D3 expression in the TPO-TSC2KO mice. mTORC1 activation resulted in a progressive downregulation of key genes involved in thyroid hormone biosynthesis, including thyroglobulin (Tg), thyroid peroxidase (Tpo), and sodium-iodide symporter (Nis), while Tff1, Pax8, and Mct8 mRNA levels remained unaffected. NIS protein expression was also diminished in TPO-TSC2KO mice. Treatment with the mTORC1 inhibitor rapamycin prevented thyroid mass expansion and restored the gene expression alterations in TPO-TSC2KO mice. Although total thyroxine (T4), total triiodothyronine (T3), and TSH plasma levels were normal at 2 months of age, a slight decrease in T4 and an increase in TSH levels were observed at 6 and 12 months of age while T3 remained similar in TPO-TSC2KO compared with littermate control mice. Conclusions: Our thyrocyte-specific mouse model reveals that mTORC1 activation inhibits thyroid hormone (TH) biosynthesis, suppresses thyrocyte gene expression, and promotes growth and proliferation.

Interesterified palm oil promotes insulin resistance and altered insulin secretion and signaling in Swiss mice.

Interesterified fats have been used to replace trans-fat in ultra-processed foods. However, their metabolic effects are not completely understood. Hence, this study aimed to investigate the effects related to glucose homeostasis in response to interesterified palm oil or refined palm oil intake. Four-week-old male Swiss mice were randomly divided into four experimental groups and fed the following diets for 8 weeks: a normocaloric and normolipidic diet containing refined palm oil (PO group) or interesterified palm oil (IPO group); a hypercaloric and high-fat diet containing refined PO (POHF group) or interesterified PO (IPOHF group). Metabolic parameters related to body mass, adiposity and food consumption showed no significant differences. As for glucose homeostasis parameters, interesterified palm oil diets (IPO and IPOHF) resulted in higher glucose intolerance than unmodified palm oil diets (PO and POHF). Euglycemic-hyperinsulinemic clamp assessment showed a higher endogenous glucose production in the IPO group compared with the PO group. Moreover, the IPO group showed significantly lower p-AKT protein content (in the muscle and liver tissues) when compared with the PO group. Analysis of glucose-stimulated static insulin secretion (11.1 mmol/L glucose) in isolated pancreatic islets showed a higher insulin secretion in animals fed interesterified fat diets (IPO and IPOHF) than in those fed with palm oil (PO and POHF). Interesterified palm oil, including in normolipidic diets, can impair insulin signaling in peripheral tissues and increase insulin secretion by ß-cells, characterizing insulin resistance in mice.

Sleeve Gastrectomy-Induced Weight Loss Increases Insulin Clearance in Obese Mice.

Sleeve gastrectomy (SG) successfully recovers metabolic homeostasis in obese humans and rodents while also resulting in the normalization of insulin sensitivity and insulinemia. Reduced insulin levels have been attributed to lower insulin secretion and increased insulin clearance in individuals submitted to SG. Insulin degradation mainly occurs in the liver in a process controlled, at least in part, by the insulin-degrading enzyme (IDE). However, research has yet to explore whether liver IDE expression or activity is altered after SG surgery. In this study, C57BL/6 mice were fed a chow (CTL) or high-fat diet (HFD) for 10 weeks. Afterward, the HFD mice were randomly assigned to two groups: sham-surgical (HFD-SHAM) and SG-surgical (HFD-SG). Here, we confirmed that SG improves glucose-insulin homeostasis in obese mice. Additionally, SG reduced insulinemia by reducing insulin secretion, assessed by the analysis of plasmatic C-peptide content, and increasing insulin clearance, which was evaluated through the calculation of the plasmatic C-peptide:insulin ratio. Although no changes in hepatic IDE activity were observed, IDE expression was higher in the liver of HFD-SG compared with HFD-SHAM mice. These results indicate that SG may be helpful to counteract obesity-induced hyperinsulinemia by increasing insulin clearance, likely through enhanced liver IDE expression.

Amino acid restriction alters survival mechanisms in pancreatic beta cells: possible role of the PI3K/Akt pathway.

BACKGROUND AND AIMS: Malnutrition in the early stages of life may lead to changes in the glycemic metabolism during adulthood, such as pancreatic beta cells dysfunction and failure. Therefore, this study aimed to evaluate the effects of an in vitro amino acid restriction model on the function and viability of pancreatic beta cells. METHODS: Insulin-producing cells (INS-1E) were maintained in control or amino acid restricted culture medium containing 1 × or 0.25 × of amino acids, respectively, for 48 h. RESULTS: Amino acid restricted group showed lower insulin secretion and insulin gene expression, reduced mitochondrial oxygen consumption rate and reactive oxygen species production. Besides, amino acid restricted group also showed higher levels of endoplasmic reticulum stress and apoptosis markers and enhanced Akt phosphorylation. However, even with higher levels of apoptosis markers, amino acid restricted group did not show higher levels of cell death unless the PI3K/Akt pathway was inhibited. CONCLUSION: Amino acid restricted beta cell viability seems to be dependent on the PI3K/Akt pathway.

Early protein restriction increases intra-islet GLP-1 production and pancreatic ß-cell proliferation mediated by the ß-catenin pathway.

PURPOSE: In the present study, we investigated whether intra-islet GLP-1 production and its modulation have a role in apoptosis, proliferation or neogenesis that is compromised by protein restriction during the foetal and suckling periods. METHODS: Exendin-4, a GLP-1 receptor agonist (treated groups), or saline (non-treated groups) was intraperitoneally administered for 15 days from 75 to 90 days of age in female adult rats consisting of offspring born to and suckled by mothers fed a control diet (control groups) and who had the same diet until 90 days of age or offspring born to and suckled by mothers fed a low-protein diet and who were fed the control diet after weaning until 90 days of age (protein-restricted group). RESULTS: The ß-cell mass was lower in the protein-restricted groups than in the control groups. Exendin-4 increased ß-cell mass, regardless of the mother's protein intake. The colocalization of GLP-1/glucagon was higher in the protein-restricted rats than in control rats in both the exendin-4-treated and non-treated groups. The frequency of cleaved caspase-3-labelled cells was higher in the non-treated protein-restricted group than in the non-treated control group and was similar in the treated protein-restricted and treated control groups. Regardless of treatment with exendin-4, Ki67-labelled cell frequency and ß-catenin/DAPI colocalization were elevated in the protein-restricted groups. Exendin-4 increased the area of endocrine cell clusters and ß-catenin/DAPI and FoxO1/DAPI colocalization regardless of the mother's protein intake. CONCLUSIONS: Protein restriction in early life increased intra-islet GLP-1 production and ß-cell proliferation, possibly mediated by the ß-catenin pathway.

Duodeno-jejunal bypass restores ß-cell hypersecretion and islet hypertrophy in western diet obese rats.

PURPOSE: Duodeno-jejunal bypass (DJB) operation improves glucose homeostasis in morbid obesity, independently of weight loss or reductions in adiposity, through mechanisms not yet fully elucidated. Herein, we evaluated the effects of DJB upon glucose homeostasis, endocrine pancreatic morphology, and ß-cell responsiveness to potentiating agents of cholinergic and cAMP pathways, in western diet (WD) obese rats, at 2 months after operation. METHODS: From 8 to 18 weeks of age male Wistar rats fed on a WD. After this period, a sham (WD Sham group) or DJB (WD DJB) operations were performed. At 2 months after operation glucose homeostasis was verified. RESULTS: Body weight was similar between WD DJB and WD Sham rats, but WD DJB rats showed a decrease in Lee index, retroperitoneal and perigonadal fat pads. Also, WD DJB rats displayed reduced fasting glycemia and insulinemia, and increased insulin-induced Akt activation in the gastrocnemius. Islets from WD DJB rats secreted less amounts of insulin, in response to activators of the cholinergic (carbachol and phorbol 12-myristate 13-acetate) and cAMP (forskolin and 3-isobutyl-1-methyl-xantine) pathways. Islets of WD DJB rats had higher sintaxin-1 protein content than WD Sham, but without modification in muscarinic-3 receptor, protein kinase (PK)-Cα, and (PK)-Aα protein amounts. In addition, islets of WD DJB animals showed reduction in islets and ß-cell masses. CONCLUSION: DJB surgery improves fasting glycemia and insulin action in skeletal muscle. Better endocrine pancreatic morphofunction was associated, at least in part, with the regulation of the cholinergic and cAMP pathways, and improvements in syntaxin-1 islet protein content induced by DJB.

Bile acid TUDCA improves insulin clearance by increasing the expression of insulin-degrading enzyme in the liver of obese mice.

Disruption of insulin secretion and clearance both contribute to obesity-induced hyperinsulinemia, though reduced insulin clearance seems to be the main factor. The liver is the major site for insulin degradation, a process mainly coordinated by the insulin-degrading enzyme (IDE). The beneficial effects of taurine conjugated bile acid (TUDCA) on insulin secretion as well as insulin sensitivity have been recently described. However, the possible role of TUDCA in insulin clearance had not yet been explored. Here, we demonstrated that 15 days treatment with TUDCA reestablished plasma insulin to physiological concentrations in high fat diet (HFD) mice, a phenomenon associated with increased insulin clearance and liver IDE expression. TUDCA also increased IDE expression in human hepatic cell line HepG2. This effect was not observed in the presence of an inhibitor of the hepatic membrane bile acid receptor, S1PR2, nor when its downstream proteins were inhibited, including IR, PI3K and Akt. These results indicate that treatment with TUDCA may be helpful to counteract obesity-induced hyperinsulinemia through increasing insulin clearance, likely through enhanced liver IDE expression in a mechanism dependent on S1PR2-Insulin pathway activation.

Taurine supplementation regulates Iκ-Bα protein expression in adipose tissue and serum IL-4 and TNF-α concentrations in MSG obesity.

PURPOSE: Obesity is usually associated with low-grade inflammation, which impairs insulin action. The amino acid, taurine (TAU), regulates glucose homeostasis and lipid metabolism and presents anti-inflammatory actions. Here, we evaluated whether inflammatory markers are altered in the serum and retroperitoneal adipose tissue of monosodium glutamate (MSG) obese rats, supplemented or not with TAU. METHODS: Male Wistar rats received subcutaneous injections of MSG (4 mg/kg body weight/day, MSG group) or hypertonic saline (CTL) during the first 5 days of life. From 21 to 120 days of age, half of each of the MSG and CTL groups received 2.5 % TAU in their drinking water (CTAU and MTAU). RESULTS: At 120 days of age, MSG rats were obese and hyperinsulinemic. TAU supplementation reduced fat deposition without affecting insulinemia in MTAU rats. MSG rats presented increased pIκ-Bα/Iκ-Bα protein expression in the retroperitoneal adipose tissue. TAU supplementation decreased the ratio of pIκ-Bα/Iκ-Bα protein, possibly contributing to the increased Iκ-Bα content in MTAU adipose tissue. Furthermore, MSG obesity or supplementation did not alter TNF-α, IL-1ß or IL-6 content in adipose tissue. In contrast, MSG rats presented lower serum TNF-α, IL-4 and IL-10 concentrations, and these alterations were prevented by TAU treatment. CONCLUSION: MSG obesity in rats was not associated with alterations in pro-inflammatory markers in retroperitoneal fat stores; however, reductions in the serum concentrations of anti-inflammatory cytokines and of TNF-α were observed. TAU treatment decreased adiposity, and this effect was associated with the normalization of circulating TNF-α and IL-4 concentrations in MTAU rats.

Vagotomy diminishes obesity in cafeteria rats by decreasing cholinergic potentiation of insulin release.

Herein, we investigated whether subdiaphragmatic vagotomy has benefits on obesity, body glucose homeostasis, and insulin secretion in cafeteria (CAF)-obese rats. Wistar rats were fed a standard or CAF diet for 12 weeks. Subsequently, CAF rats were randomly submitted to truncal vagotomy (CAF Vag) or sham operation (CAF Sham). CAF Sham rats were hyperphagic, obese, and presented metabolic disturbances, including hyperinsulinemia, glucose intolerance, insulin resistance, hyperglycemia, and hypertriglyceridemia. Twelve weeks after vagotomy, CAF Vag rats presented reductions in body weight and perigonadal fat stores. Vagotomy did not modify glucose tolerance but normalized fed glycemia, insulinemia, and insulin sensitivity. Isolated islets from CAF Sham rats secreted more insulin in response to the cholinergic agent, carbachol, and when intracellular cyclic adenine monophosphate (cAMP) is enhanced by forskolin or 3-isobutyl-1-methylxanthine. Vagotomy decreased glucose-induced insulin release due to a reduction in the cholinergic action on ß-cells. This effect also normalized islet secretion in response to cAMP. Therefore, vagotomy in rats fed on a CAF-style diet effectively decreases adiposity and restores insulin sensitivity. These effects were mainly associated with the lack of cholinergic action on the endocrine pancreas, which decreases insulinemia and may gradually reduce fat storage and improve insulin sensitivity.

The bile acid TUDCA increases glucose-induced insulin secretion via the cAMP/PKA pathway in pancreatic beta cells.

OBJECTIVE: While bile acids are important for the digestion process, they also act as signaling molecules in many tissues, including the endocrine pancreas, which expresses specific bile acid receptors that regulate several cell functions. In this study, we investigated the effects of the conjugated bile acid TUDCA on glucose-stimulated insulin secretion (GSIS) from pancreatic ß-cells. METHODS: Pancreatic islets were isolated from 90-day-old male mice. Insulin secretion was measured by radioimmunoassay, protein phosphorylation by western blot, Ca(2+) signals by fluorescence microscopy and ATP-dependent K(+) (KATP) channels by electrophysiology. RESULTS: TUDCA dose-dependently increased GSIS in fresh islets at stimulatory glucose concentrations but remained without effect at low glucose levels. This effect was not associated with changes in glucose metabolism, Ca(2+) signals or KATP channel activity; however, it was lost in the presence of a cAMP competitor or a PKA inhibitor. Additionally, PKA and CREB phosphorylation were observed after 1-hour incubation with TUDCA. The potentiation of GSIS was blunted by the Gα stimulatory, G protein subunit-specific inhibitor NF449 and mimicked by the specific TGR5 agonist INT-777, pointing to the involvement of the bile acid G protein-coupled receptor TGR5. CONCLUSION: Our data indicate that TUDCA potentiates GSIS through the cAMP/PKA pathway.

Insulin replacement restores the vesicular secretory apparatus in the diabetic rat lacrimal gland / Reposição de insulina restaura o mecanismo secretório da glândula lacrimal de ratos diabéticos

ABSTRACT Purpose: In the lacrimal gland (LG) acinar cells, signaling regulates the release of secretory vesicles through specific Rab and SNARE exocytotic proteins. In diabetes mellitus (DM), the LGs are dysfunctional. The aim of this work was to determine if secretory apparatus changes were associated with any effects on the secretory vesicles (SV) in diabetic rats as well as the expression levels of constituent Rab and members of the SNARE family, and if insulin supplementation reversed those changes. Methods: DM was induced in male Wistar rats with an intravenous dose of streptozotocin (60 mg/kg). One of the two diabetic groups was then treated every other day with insulin (1 IU). A third control group was injected with vehicle. After 10 weeks, Western blotting and RT-PCR were used to compared the Rab and SNARE secretory factor levels in the LGs. Transmission electron microscopy evaluated acinar cell SV density and integrity. Results: In the diabetes mellitus group, there were fewer and enlarged SV. The Rab 27b, Rab 3d, and syntaxin-1 protein expression declined in the rats with diabetes mellitus. Insulin treatment restored the SV density and the Rab 27b and syntaxin expression to their control protein levels, whereas the Vamp 2 mRNA expression increased above the control levels. Conclusions: Diabetes mellitus LG changes were associated with the declines in protein expression levels that were involved in supporting exocytosis and vesicular formation. They were partially reversed by insulin replacement therapy. These findings may help to improve therapeutic management of dry eye in diabetes mellitus. .

RESUMO Objetivo: Células acinares da glândula lacrimal (GL) sinalizam a regulação da liberação através de vesículas secretórias específicas Rab proteínas exocitóticas SNARE. No diabetes mellitus (DM), as glândulas lacrimais são disfuncionais. O objetivo deste trabalho foi determinar se em ratos diabéticos, alterações dos aparatos secretórios estão associados a efeitos sobre vesículas secretoras (VS) e sobre os níveis de expressão do constituinte Rab, bem como membros da família SNARE, e se a suplementação de insulina reverte as alterações. Métodos: DM foi induzido em ratos Wistar machos com uma dose intravenosa de estreptozotocina (60 mg/kg). Um dos dois grupos diabéticos foi então tratado a cada dois dias com insulina (1 UI). Um terceiro grupo controle foi injetado com o veículo. Após 10 semanas, western blot e RT-PCR comparou níveis de fatores secretórios de Rab e SNARE na glândula lacrimal. Microscopia eletrônica de transmissão (MET) avaliaram a densidade e integridade de VS de célula acinar. Resultados: No grupo diabetes mellitus , houve poucas e alargadas VS. Rab27b, Rab 3d e Sintaxina-1 diminuiu a expressão da proteína em ratos com Diabetes Mellitus. O tratamento com insulina restaurou a densidade das VS e expressão de Rab 27b e Sintaxina para seus níveis de proteína controle, enquanto a expressão de Vamp 2 RNAm aumentou em relação aos controles. Conclusões: Alterações na glândula lacrimal de diabetes mellitus estão associadas a reduções nos níveis de expressão de proteínas envolvidas no apoio a exocitose e formação vesicular. Eles são, em parte, revertida por terapia de reposição de insulina. Estes resultados podem ajudar a melhorar a conduta terapêutica do olho seco no diabetes mellitus. .

Low-protein diet disrupts the crosstalk between the PKA and PKC signaling pathways in isolated pancreatic islets.

Protein restriction in the early stages of life can result in several changes in pancreatic function. These alterations include documented reductions in insulin secretion and in cytoplasmic calcium concentration [Ca(2+)]i. However, the mechanisms underlying these changes have not been completely elucidated and may result, in part, from alterations in signaling pathways that potentiate insulin secretion in the presence of glucose. Our findings suggest that protein restriction disrupts the insulin secretory synergism between Cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA) and Ca(2+)-dependent protein kinase C (PKC) in isolated islets. Western blot analysis demonstrated reduced levels of both phospho-cAMP response element-binding protein (phospho-CREB) at Ser-133 and substrates phosphorylated by PKCs (Phospho-(Ser) PKC substrate), suggesting that PKA and PKC activity was impaired in islets from rats fed a low-protein diet (LP). cAMP levels and global Ca(2+) entry were also reduced in LP islets. In summary, our findings showed that protein restriction altered the crosstalk between PKA and PKC signaling pathways, resulting in the alteration of secretory synergism in isolated islets.

A low-protein diet during pregnancy prevents modifications in intercellular communication proteins in rat islets

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Impaired muscarinic type 3 (M3) receptor/PKC and PKA pathways in islets from MSG-obese rats.

Monosodium glutamate-obese rats are glucose intolerant and insulin resistant. Their pancreatic islets secrete more insulin at increasing glucose concentrations, despite the possible imbalance in the autonomic nervous system of these rats. Here, we investigate the involvement of the cholinergic/protein kinase (PK)-C and PKA pathways in MSG ß-cell function. Male newborn Wistar rats received a subcutaneous injection of MSG (4 g/kg body weight (BW)) or hyperosmotic saline solution during the first 5 days of life. At 90 days of life, plasma parameters, islet static insulin secretion and protein expression were analyzed. Monosodium glutamate rats presented lower body weight and decreased nasoanal length, but had higher body fat depots, glucose intolerance, hyperinsulinemia and hypertrigliceridemia. Their pancreatic islets secreted more insulin in the presence of increasing glucose concentrations with no modifications in the islet-protein content of the glucose-sensing proteins: the glucose transporter (GLUT)-2 and glycokinase. However, MSG islets presented a lower secretory capacity at 40 mM K(+) (P < 0.05). The MSG group also released less insulin in response to 100 µM carbachol, 10 µM forskolin and 1 mM 3-isobutyl-1-methyl-xantine (P < 0.05, P < 0.0001 and P < 0.01). These effects may be associated with a the decrease of 46 % in the acetylcholine muscarinic type 3 (M3) receptor, and a reduction of 64 % in PKCα and 36 % in PKAα protein expressions in MSG islets. Our data suggest that MSG islets, whilst showing a compensatory increase in glucose-induced insulin release, demonstrate decreased islet M3/PKC and adenylate cyclase/PKA activation, possibly predisposing these prediabetic rodents to the early development of ß-cell dysfunction.

Protein restriction in early life is associated with changes in insulin sensitivity and pancreatic ß-cell function during pregnancy.

Malnutrition in early life impairs glucose-stimulated insulin secretion in adulthood. Conversely, pregnancy is associated with a significant increase in glucose-stimulated insulin secretion under conditions of normoglycaemia. A failure in ß-cell adaptive changes may contribute to the onset of diabetes. Thus, glucose homeostasis and ß-cell function were evaluated in control-fed pregnant (CP) and non-pregnant (CNP) or protein-restricted pregnant (LPP) and non-pregnant (LPNP) rats, from fetal to adult life, and in protein-restricted rats that were recovered after weaning (RP and RNP). The typical insulin resistance of pregnancy was not observed in the RP rats, nor did pregnancy increase the insulin content/islet in the LPP group. The glucose dose-response curves from pregnant rats were shifted to the left in relation to the non-pregnant rats, except in the recovered group. Glucose utilisation but not oxidation in islets from the RP and LPP groups was reduced at a concentration of 8.3 mm-glucose compared with islets from the CP group. Cyclic AMP content and the potentiation of glucose-stimulated insulin secretion by isobutylmethylxanthine at a concentration of 2.8 mm-glucose indicated increased adenylyl cyclase 3 activity but reduced protein kinase A-α activity in islets from the RP and LPP rats. Protein kinase C (PKC)-α but not phospholipase C (PLC)-ß1 expression was reduced in islets from the RP group. Phorbol-12-myristate 13-acetate produced a less potent stimulation of glucose-stimulated insulin secretion in the RP group. Thus, the alterations exhibited by islets from the LPP group appeared to be due to reduced islet mass and/or insulin biosynthesis. In the RP group the loss of the adaptive capacity apparently resulted from uncoupling between glucose metabolism and the amplifying signals of the secretory process, as well as a severe attenuation of the PLC/PKC pathway.

Decreased ß-cell insulin secretory function in aged rats due to impaired Ca(2+) handling.

Ageing is associated with an increased impairment in glucose homeostasis and an increased incidence of type 2 diabetes. In this study, we evaluated ß-cell function and its implications for glucose homeostasis in 24-month-old female Wistar rats. Aged rats showed lower plasma glucose levels in the fed and fasting states compared with control rats. In addition, insulinaemia in the fed state was reduced in the older rats. Insulin receptor ß (IRß) expression was lower in the livers of the aged animals, whereas IRß and Akt(1/2/3) protein expressions were higher in the muscles. These effects may contribute to the normal glucose tolerance observed in older rodents. Isolated islets from aged rats secreted less insulin in response to 8.3 and 16.7 mm glucose. Accordingly, this group presented a lower [Ca(2+)](i) in the presence of glucose and a depolarizing stimulus (30 mm K(+)). In addition, islets from aged rats showed reduced insulin secretion in response to 100 µm carbachol (CCh), 10 nm phorbol 12-myristate 13-acetate and 10 µm forskolin. The expressions of protein kinase C, protein kinase A and exocytotic proteins, such as syntaxin 1 and synaptosomal-associated protein 25 kDa (SNAP-25), were similar in islets from aged and control rats. In conclusion, our evidence suggests that the increased incidence of type 2 diabetes with age may be due to a progressive decline in ß-cell secretory capacity due to disruption of Ca(2+) handling. Furthermore, the expression of proteins of the insulin transduction cascade showed an adaptive profile, with a compensatory increase in IRß and Akt(1/2/3) in gastrocnemius muscles, which may maintain normal glucose homeostasis in 24-month-old rats.

Taurine supplementation prevents morpho-physiological alterations in high-fat diet mice pancreatic ß-cells.

Taurine (Tau) is involved in beta (ß)-cell function and insulin action regulation. Here, we verified the possible preventive effect of Tau in high-fat diet (HFD)-induced obesity and glucose intolerance and in the disruption of pancreatic ß-cell morpho-physiology. Weaning Swiss mice were distributed into four groups: mice fed on HFD diet (36 % of saturated fat, HFD group); HTAU, mice fed on HFD diet and supplemented with 5 % Tau; control (CTL); and CTAU. After 19 weeks of diet and Tau treatments, glucose tolerance, insulin sensitivity and islet morpho-physiology were evaluated. HFD mice presented higher body weight and fat depots, and were hyperglycemic, hyperinsulinemic, glucose intolerant and insulin resistant. Their pancreatic islets secreted high levels of insulin in the presence of increasing glucose concentrations and 30 mM K(+). Tau supplementation improved glucose tolerance and insulin sensitivity with a higher ratio of Akt phosphorylated (pAkt) related to Akt total protein content (pAkt/Akt) following insulin administration in the liver without altering body weight and fat deposition in HTAU mice. Isolated islets from HTAU mice released insulin similarly to CTL islets. HFD intake induced islet hypertrophy, increased ß-cell/islet area and islet and ß-cell mass content in the pancreas. Tau prevented islet and ß-cell/islet area, and islet and ß-cell mass alterations induced by HFD. The total insulin content in HFD islets was higher than that of CTL islets, and was not altered in HTAU islets. In conclusion, for the first time, we showed that Tau enhances liver Akt activation and prevents ß-cell compensatory morpho-functional adaptations induced by HFD.

Lower expression of PKAα impairs insulin secretion in islets isolated from low-density lipoprotein receptor (LDLR(-/-)) knockout mice.

Hypercholesterolemic low-density lipoprotein receptor knockout mice (LDLR(-/-)) show normal whole-body insulin sensitivity, but impaired glucose tolerance due to a reduced insulin secretion in response to glucose. Here, we investigate the possible mechanisms involved in such a defect in isolated LDLR(-/-) mice islets. Low-fat chow-fed female and male mice aged 20 weeks, LDLR(-/-) mice, and wild-type (WT) mice were used in this study. Static insulin secretion, cytoplasmatic Ca(2+) analysis, and protein expression were measured in islets isolated from LDLR(-/-) and WT mice. At basal (2.8 mmol/L) and stimulatory (11.1 mmol/L) glucose concentrations, the insulin secretion rates induced by depolarizing agents such as KCl, L-arginine, and tolbutamide were significantly reduced in LDLR(-/-) when compared with control (WT) islets. In addition, KCl-induced Ca(2+) influx at 2.8 mmol/L glucose was lower in LDLR(-/-) islets, suggesting a defect downstream of the substrate metabolism step of the insulin secretion pathway. Insulin secretion induced by the protein kinase A (PKA) activators forskolin and 3-isobutyl-1-methyl-xanthine, in the presence of 11.1 mmol/L glucose, was lower in LDLR(-/-) islets and was normalized in the presence of the protein kinase C pathway activators carbachol and phorbol 12-myristate 13-acetate. Western blotting analysis showed that phospholipase Cß(2) expression was increased and PKAα was decreased in LDLR(-/-) compared with WT islets. Results indicate that the lower insulin secretion observed in islets from LDLR(-/-) mice at postprandial levels of glucose can be explained, at least in part, by the reduced expression of PKAα in these islets.