Background/Aim
A link between an impaired intestinal barrier, endotoxemia, and the pathogenesis of metabolic diseases, such as type 2 diabetes mellitus (T2DM), has been proposed. In previous work, we ...have demonstrated that the tight junction (TJ)-mediated intestinal barrier in ileum/colon was marginally changed in prediabetic mice; therefore, it does not seem to mainly contribute to the T2DM onset. In this study, the TJ-mediated epithelial barrier in the duodenum and jejunum was evaluated in mice during the development of type 2 prediabetes.
Methods/Results
HF diet induced prediabetes after 60 days associated with a significant rise in intestinal permeability to the small-sized marker Lucifer yellow in these mice, with no histological signs of mucosal inflammation or rupture of the proximal intestine epithelium. As revealed by immunofluorescence, TJ proteins, such as claudins-1, -2, -3, and ZO-1, showed a significant decrease in junctional content in duodenum and jejunum epithelia, already after 15 days of treatment, suggesting a rearrangement of the TJ structure. However, no significant change in total cell content of these proteins was observed in intestinal epithelium homogenates, as assessed by immunoblotting. Despite the changes in intestinal permeability and TJ structure, the prediabetic mice showed similar LPS, zonulin, and TNF-α levels in plasma or adipose tissue, and in intestinal segments as compared to the controls.
Conclusion
Disruption of the TJ-mediated paracellular barrier in the duodenum and jejunum is an early event in prediabetes development, which occurs in the absence of detectable endotoxemia/inflammation and may contribute to the HF diet-induced increase in intestinal permeability.
Wnt proteins act mainly as paracrine signals regulating cell proliferation and differentiation. The canonical Wnt pathway has recently been associated with pancreas development and the onset of type ...2 diabetes in rodent and human but the underlying mechanisms are still unclear. The aim of this work was threefold: (a) to screen for Wnt expressed by murine pancreas/islet cells, (b) to investigate whether the Wnt gene expression profile can be changed in hyperplastic islets from type 2 prediabetic mice (fed a high‐fat diet), and (c) to verify whether soluble factors (namely Wnts) released by pancreatic islets affect insulin secretion and proliferation of a beta‐cell line in vitro condition. The majority of the Wnt subtypes are expressed by islet cells, such as Wnts 2, 2b, 3, 3a, 4, 5a, 5b, 6, 7a, 7b, 8a, 8b, 9a, 9b, and 11, while in the whole pancreas homogenates were found the same subtypes, except Wnts 3, 6, 7a, and 7b. Among all the Wnts, the Wnts 3a and 5b showed a significantly increased gene expression in hyperplastic islets from prediabetic mice compared with those from control mice. Furthermore, we observed that coculture with hyperplastic or nonhyperplastic islets did not change the secretory function of the mouse insulinoma clone 6 (MIN6) beta cells but induced a significant increase in cell proliferation in this lineage, which was partially blocked by the IWR‐1 and IWP‐2 Wnt inhibitors. In conclusion, we demonstrated that murine pancreas/islet cells can secrete Wnts, and that islet‐released Wnts may participate in the regulation of beta‐cell mass under normal and prediabetic conditions.
We demonstrated that murine islet cells can express a broad range of Wnt ligands, and that islet‐released Wnts may participate in the regulation of beta‐cell mass under normal and prediabetic conditions.
Background
Brazilian berry is a fruit popularly known as “Jaboticaba,” rich in bioactive compounds with antioxidant and anti‐inflammatory properties. Senescence and overweight are increasing ...worldwide and are considered risk factors to prostatic pathogenesis mainly due to oxidative and inflammatory processes induction. Thus, this study aimed to evaluate the effect of two increasing doses of the patented jaboticaba peel extract (PJE) on oxidative‐stress and inflammation in the prostate of aging or high‐fat‐fed aging mice.
Methods
PJE and/or high‐fat diet (HFD) treatments started with 11‐month‐old mice and lasted 60 days. The levels or the immunoexpression of different inflammatory (nuclear factor κB NFκB, CD3+, cyclooxygenase 2 COX‐2, toll‐like receptor 4 TLR4, phosphorylated signal transducers and activators of transcription 3 pSTAT‐3, tumor necrosis factor α TNF‐α, interleukin 6 IL‐6, and IL‐1β) and oxidative‐stress (catalase, superoxide dismutase 2 SOD2, glutathione reductase GSR, reduced glutathione, and glutathione peroxidase 3 GPx3) related molecules were analyzed by western‐blotting, immunohistochemistry, and enzyme‐linked immunosorbent assays.
Results
Both PJE doses reduced the levels of oxidative‐stress‐related molecules (GPx3, GSR, catalase), lipid peroxidation (4‐hydroxynonenal), inflammatory mediators (COX‐2, TNF‐α, and pSTAT‐3) and CD3+ T cells number, which were associated with the maintenance of the glandular morphological integrity in aging and HFD‐fed‐aging mice. Nevertheless, only the high PJE dose reduced the NFκB and TLR4 levels in aging mice; and SOD2, IL‐6, and IL‐1β levels in HFD‐aging mice. Aging itself promoted an oxidative inflammation in the prostate, interfering in the levels of the different oxidative‐stress, lipid peroxidation, and inflammatory mediators evaluated, in association with high incidence of prostate epithelial and stromal damages. The HFD intake intensified aging alterations, showing an unfavorable prostatic microenvironment prone to oxidative and inflammatory damages.
Conclusions
PJE exerted a dose‐dependent effect controlling inflammation and oxidative‐stress in aging and HFD‐fed aging mice prostate. This fact contributed to prostate microenvironment balance recovery, preserving the tissue architecture of this gland. Thus, the PJE emerges as a potential therapy to prevent inflammation and oxidative stress in the prostate.
Osmotic alterations are associated with several human diseases, including diabetic nephropathy. We have previously shown that high glucose, which is a well‐known osmotic agent, induces significant ...disruption of the tight junction (TJ)‐mediated tubular barrier of the Madin–Darby canine kidney (MDCK) cell line. In this study, we investigated the effect of acute (24 h) and chronic (72 h) exposure to increased osmolality (with a 14.5 mM mannitol solution) on TJ‐mediated barrier function in MDCK cells. The treatment with mannitol significantly increased the transepithelial electrical resistance (TEER) and accelerated the TEER recovery after Ca2+ switch assay in comparison with control monolayers. Immunofluorescence and Western blot analyses showed that mannitol treatment induced a significant increase in the tight junctional and cellular content of claudin‐1 (a barrier‐forming claudin) as well as a significant decrease in claudin‐2 (a pore‐forming claudin) junctional and cellular contents. These data suggest that an increased osmolality induces enhancement of the TJ‐mediated barrier of MDCK cells, and that, therefore, the negative effect of high glucose on the epithelial paracellular barrier cannot be attributed to its osmotic actions. In addition, a subtle increase in osmolality may have an impact on kidney function and renal‐related diseases.
Type 2 diabetes mellitus (T2D) is nowadays a worldwide epidemic and has become a major challenge for health systems around the world. It is a multifactorial disorder, characterized by a chronic state ...of hyperglycemia caused by defects in the production as well as in the peripheral action of insulin. This minireview highlights the experimental and clinical evidence that supports the novel idea that intercellular junctions (IJs)-mediated cell–cell contacts play a role in the pathogenesis of T2D. It focuses on IJs repercussion for endocrine pancreas, intestinal barrier, and kidney dysfunctions that contribute to the onset and evolution of this metabolic disorder.
Tissue/cellular actions of butyrate on energy metabolism and intestinal barrier in normal metabolic conditions or prediabetes are still unclear. In this work, we investigated the beneficial effect of ...dietary supplementation with sodium butyrate on energy metabolism, body mass composition, and intestinal epithelial barrier mediated by tight junction (TJ) in chow diet-fed normal and high-fat diet (HF)-fed prediabetic mice, considering the well-known butyrate action as an epigenetic and inflammatory regulator. Butyrate significantly reduced the fat/lean mass ratio, slightly ameliorated dyslipidemia, restored oral glucose tolerance, and increased basal energy expenditure in prediabetic HF-fed mice but had no effect on control animals. Such effects were observed in the absence of significant alterations in the hypothalamic expression of orexigenic and anorexigenic genes and motor activity. Also, butyrate suppressed the whitening effect of HF on brown adipose tissue but did not affect cell bioenergetics in immortalized UCP1-positive adipocytes in vitro. Butyrate reinforced the intestinal epithelial barrier in HF-fed mice and in Caco-2 monolayers, which involved higher trafficking of TJ proteins to the cell-cell contact region of the intestinal epithelia, without affecting TJ gene expression or the acetylation level of histones H3 and H4 in vivo. All metabolic and intestinal effects of butyrate in prediabetic mice occurred in the absence of detectable changes in systemic or local inflammation, or alterations in endotoxemia markers. Butyrate has no effect on chow diet-fed mice but, in the context of HF-induced prediabetes, it prevents metabolic and intestinal dysfunctions independently of its anti-inflammatory and epigenetic actions.
The diet supplementation with sodium butyrate has no metabolic and intestinal effect on chow diet-fed mice but, in the context of high fat (HF) diet-induced prediabetes, it prevents metabolic and intestinal dysfunctions independently of its anti-inflammatory actions. Butyrate reinforces the intestinal epithelial barrier in HF-fed mice and in Caco-2 intestinal cell monolayers exposed to the intestinal luminal content of HF-fed mice treated with butyrate in comparison to those that did not receive this SCFA. The mechanism involves higher trafficking of tight junction (TJ) proteins (such as claudin-1, Cld-1) to the cell-cell contact region of the intestinal epithelium, without affecting TJ gene expression or the acetylation level of histones. Display omitted
Summary
In this study, we investigated the effect of low density lipoprotein receptor (LDLr) deficiency on gap junctional connexin 36 (Cx36) islet content and on the functional and growth response of ...pancreatic beta‐cells in C57BL/6 mice fed a high‐fat (HF) diet. After 60 days on regular or HF diet, the metabolic state and morphometric islet parameters of wild‐type (WT) and LDLr−/− mice were assessed. HF diet‐fed WT animals became obese and hypercholesterolaemic as well as hyperglycaemic, hyperinsulinaemic, glucose intolerant and insulin resistant, characterizing them as prediabetic. Also they showed a significant decrease in beta‐cell secretory response to glucose. Overall, LDLr−/− mice displayed greater susceptibility to HF diet as judged by their marked cholesterolaemia, intolerance to glucose and pronounced decrease in glucose‐stimulated insulin secretion. HF diet induced similarly in WT and LDLr−/− mice, a significant decrease in Cx36 beta‐cell content as revealed by immunoblotting. Prediabetic WT mice displayed marked increase in beta‐cell mass mainly due to beta‐cell hypertrophy/replication. Nevertheless, HF diet‐fed LDLr−/− mice showed no significant changes in beta‐cell mass, but lower islet–duct association (neogenesis) and higher beta‐cell apoptosis index were seen as compared to controls. The higher metabolic susceptibility to HF diet of LDLr−/− mice may be explained by a deficiency in insulin secretory response to glucose associated with lack of compensatory beta‐cell expansion.
Cell-to-cell interactions mediated by intercellular junctions (IJs) are crucial for beta-cell functioning and proper insulin secretion, however, their role in type-2 diabetes is still unclear. This ...work aimed to evaluate the cellular distribution and expression of proteins associated with adherens (AJs) and gap junctions (GJs) in pancreatic islets of C57BL6 mice fed a high-fat (HF) diet. The administration of HF diet for 30 days induced an increase in body weight, post-prandial glycemia, insulinemia, glucose intolerance, and moderate insulin resistance associated with mild perturbations in insulin secretion. The intercellular content of the AJ-associated proteins (namely, E-, N-cadherins, and α-, β-catenins) was significantly higher in islet cells of HF-fed mice. Inversely, the gap junctional content of Cx36 was significantly decreased, as revealed by immunofluorescence, which was paralleled by a reduction in the frequency of calcium oscillations in islets of prediabetic mice. In conclusion, the endocrine pancreas displays significant changes in the content of several junctional proteins at the cell-cell contact region following short-term HF diet administration, indicating that IJs may be involved in the adaptive response of beta cells seen during this state.
We have recently demonstrated by electron microscopy, using lanthanum nitrate as an extracellular tracer, that the intravenous injection of
Phoneutria nigriventer spider venom (PNV) induces ...blood–brain barrier (BBB) breakdown in rat hippocampus. One and nine days after PNV injection, tracer was found in pinocytic vesicles crossing the endothelium and in the interendothelial cleft, suggesting that BBB breakdown had occurred through enhanced transendothelial transport and/or tight-junction opening. In the present work, we investigated the mechanisms by which PNV (850 μg/kg, i.v.) increased the hippocampal microvascular permeability in rats 24 h after the endovenous administration. The expression and phosphorylation of some tight- and adherens junctions-associated proteins in hippocampal homogenate and hippocampal microvessel homogenate were assessed by Western blotting and immunoprecipitation. The microtubule-dependent transcellular transport was also evaluated by quantitative ultrastructural methods in pretreated rats with colchicine (0.5 mg/kg, i.p.), prior to PNV injection. Western blots showed no significant increase in the expression of the tight junction-associated proteins ZO-1 and occludin or in the adherens junction-associated β-catenin after 24 h of PNV administration. Morphological study showed no alterations of the immunolabeling for occludin and ZO-1 in rat brain cryosection following PNV. In addition, no changes were observed in phosphotyrosine content of occludin and β-catenin in PNV-treated rats compared with control animals. However, the disruption of microtubule-dependent transcellular transport by colchicine completely prevented (
p<0.001) PNV-induced leakage of the BBB tracer. These findings indicate that the increased BBB permeability evoked by PNV in rats probably resulted from enhanced microtubule-dependent transendothelial vesicular transport, with no substantial involvement of the paracellular barrier in the time interval studied.
PDF
