Prolonged insulin treatment sensitizes apoptosis pathways in pancreatic β cells

Insulin resistance results from impaired insulin signaling in target tissues that leads to increased levels of insulin required to control plasma glucose levels. The cycle of hyperglycemia and hyperinsulinemia eventually leads to pancreatic cell deterioration and death by a mechanism that is yet unclear. Insulin induces ROS formation in several cell types. Furthermore, death of pancreatic cells induced by oxidative stress could be potentiated by insulin. Here, we investigated the mechanism underlying this phenomenon. Experiments were done on pancreatic cell lines (Min-6, RINm, INS-1), isolated mouse and human islets, and on cell lines derived from nonpancreatic sources. Insulin (100nM) for 24h selectively increased the production of ROS in pancreatic cells and isolated pancreatic islets, but only slightly affected the expression of antioxidant enzymes. This was accompanied by a time- and dose-dependent decrease in cellular reducing power of pancreatic cells induced by insulin and altered expression of several ER stress response elements including a significant increase in Trb3 and a slight increase in iNos The effect on iNos did not increase NO levels. Insulin also potentiated the decrease in cellular reducing power induced by H2O2 but not cytokines. Insulin decreased the expression of MCL-1, an antiapoptotic protein of the BCL family, and induced a modest yet significant increase in caspase 3/7 activity. In accord with these findings, inhibition of caspase activity eliminated the ability of insulin to increase cell death. We conclude that prolonged elevated levels of insulin may prime apoptosis and cell death-inducing mechanisms as a result of oxidative stress in pancreatic cells.

Insulin increases H2O2-induced pancreatic beta cell death

Insulin resistance results, in part, from impaired insulin signaling in insulin target tissues. Consequently, increased levels of insulin are necessary to control plasma glucose levels. The effects of elevated insulin levels on pancreatic beta (β) cell function, however, are unclear. In this study, we investigated the possibility that insulin may influence survival of pancreatic β cells. Studies were conducted on RINm, RINm5F and Min-6 pancreatic β-cells. Cell death was induced by treatment with H(2)O(2), and was estimated by measurements of LDH levels, viability assay (Cell-Titer Blue), propidium iodide staining and FACS analysis, and mitochondrial membrane potential (JC-1). In addition, levels of cleaved caspase-3 and caspase activity were determined. Treatment with H(2)O(2) increased cell death; this effect was increased by simultaneous treatment of cells with insulin. Insulin treatment alone caused a slight increase in cell death. Inhibition of caspase-3 reduced the effect of insulin to increase H(2)O(2)-induced cell death. Insulin increased ROS production by pancreatic β cells and increased the effect of H(2)O(2). These effects were increased by inhibition of IR signaling, indicative of an effect independent of the IR cascade. We conclude that elevated levels of insulin may act to exacerbate cell death induced by H(2)O(2) and, perhaps, other inducers of apoptosis.

Assembled catalog of immune-related genes from allogeneic challenged corals that unveils the participation of vWF-like transcript

While reef-building corals portray highly complex and specific allorecognition responses, still, no available synthesis on historecognition at the molecular level exists for this group of organisms. Here, we present the first subtractive library of expressed sequence tags (ESTs) from allogeneic challenged coral (Stylophora pistillata) colonies revealing the differential expression of a wide range of immune-related genes. 1760 unique ESTs were clustered and assembled into 230 contigs and 1530 singlets with 28% that showed homology (E-value < or =0.005) to known database sequences, of which 16% (n=80) homologues were identified as immune-relevant genes, encoding for stress proteins, pattern recognition receptors and complement proteins, proteases, cell adhesion proteins, cytokine related proteins, programmed cell death and proteasome-associated proteins. Transcripts that were subjected to quantitative RT-PCR, further supported the library data. In situ hybridization analyses elucidated specific and enhanced expressions of von Willebrand factor-like transcript during S. pistillata allogeneic rejection. Availability of such genome-wide expression tools may lead to significant advances in the research of coral historecognition and comparative immunology.

Physical exercise increases the expression of TNFα and GLUT 1 in muscle tissue of diabetes prone Psammomys obesus

INTRODUCTION

Tumor necrosis factor-alpha (TNFalpha) is a major mediator of insulin resistance. On the other hand, it has been suggested that TNFalpha may facilitate glucose uptake through GLUT 1 expression. We recently found that physical exercise prevented the progression to type 2 diabetes mellitus in diabetes prone Psammomys obesus (sand rat).

AIM

The aim of the present study was to characterize the influence of physical exercise on the expression of TNFalpha, its receptor R1 and GLUT 1 in muscle tissue of this animal model.

METHODS

Animals were assigned for 4 weeks to four groups: high-energy diet (HC), high-energy diet and exercise (HE), low-energy diet (LC), low-energy diet and exercise (LE). TNFalpha, R1 and GLUT 1 expression were analyzed using Western blot technique.

RESULTS

None of the animals in the HE group became diabetic while all the animals in the HC group became diabetic. TNFalpha, its receptor (R1) and GLUT 1 expressions were significantly higher in the two exercising groups (LE and HE) and significantly lower in the HC group compared to the control LC group.

CONCLUSIONS

Physical exercise augments the expression of TNFalpha, its receptor R1 and the glucose transporter GLUT 1 in muscle tissue. We suggest that this mechanism may improve glucose uptake through pathways parallel and unrelated to insulin signaling that may include MAPK and/or NO. These biochemical processes contribute to the beneficial effects of physical exercise on the prevention of type 2 diabetes mellitus.