Cyclooxygenase-2, not microsomal prostaglandin E synthase-1, is the mechanism for interleukin-1ß-induced prostaglandin E2 production and inhibition of insulin secretion in pancreatic islets.

Arachidonic acid is converted to prostaglandin E(2) (PGE(2)) by a sequential enzymatic reaction performed by two isoenzyme groups, cyclooxygenases (COX-1 and COX-2) and terminal prostaglandin E synthases (cPGES, mPGES-1, and mPGES-2). mPGES-1 is widely considered to be the final enzyme regulating COX-2-dependent PGE(2) synthesis. These generalizations have been based in most part on experiments utilizing gene expression analyses of cell lines and tumor tissue. To assess the relevance of these generalizations to a native mammalian tissue, we used isolated human and rodent pancreatic islets to examine interleukin (IL)-1ß-induced PGE(2) production, because PGE(2) has been shown to mediate IL-1ß inhibition of islet function. Rat islets constitutively expressed mRNAs of COX-1, COX-2, cPGES, and mPGES-1. As expected, IL-1ß increased mRNA levels for COX-2 and mPGES-1, but not for COX-1 or cPGES. Basal protein levels of COX-1, cPGES, and mPGES-2 were readily detected in whole cell extracts but were not regulated by IL-1ß. IL-1ß increased protein levels of COX-2, but unexpectedly mPGES-1 protein levels were low and unaffected. In microsomal extracts, mPGES-1 protein was barely detectable in rat islets but clearly present in human islets; however, in neither case did IL-1ß increase mPGES-1 protein levels. To further assess the importance of mPGES-1 to IL-1ß regulation of an islet physiologic response, glucose-stimulated insulin secretion was examined in isolated islets of WT and mPGES-1-deficient mice. IL-1ß inhibited glucose-stimulated insulin secretion equally in both WT and mPGES-1(-/-) islets, indicating that COX-2, not mPGES-1, mediates IL-1ß-induced PGE(2) production and subsequent inhibition of insulin secretion.

Myeloid Cell Prostaglandin E2 Receptor EP4 Modulates Cytokine Production but Not Atherogenesis in a Mouse Model of Type 1 Diabetes.

Type 1 diabetes mellitus (T1DM) is associated with cardiovascular complications induced by atherosclerosis. Prostaglandin E2 (PGE2) is often raised in states of inflammation, including diabetes, and regulates inflammatory processes. In myeloid cells, a key cell type in atherosclerosis, PGE2 acts predominately through its Prostaglandin E Receptor 4 (EP4; Ptger4) to modulate inflammation. The effect of PGE2-mediated EP4 signaling specifically in myeloid cells on atherosclerosis in the presence and absence of diabetes is unknown. Because diabetes promotes atherosclerosis through increased arterial myeloid cell accumulation, we generated a myeloid cell-targeted EP4-deficient mouse model (EP4M-/-) of T1DM-accelerated atherogenesis to investigate the relationship between myeloid cell EP4, inflammatory phenotypes of myeloid cells, and atherogenesis. Diabetic mice exhibited elevated plasma PGE metabolite levels and elevated Ptger4 mRNA in macrophages, as compared with non-diabetic littermates. PGE2 increased Il6, Il1b, Il23 and Ccr7 mRNA while reducing Tnfa mRNA through EP4 in isolated myeloid cells. Consistently, the stimulatory effect of diabetes on peritoneal macrophage Il6 was mediated by PGE2-EP4, while PGE2-EP4 suppressed the effect of diabetes on Tnfa in these cells. In addition, diabetes exerted effects independent of myeloid cell EP4, including a reduction in macrophage Ccr7 levels and increased early atherogenesis characterized by relative lesional macrophage accumulation. These studies suggest that this mouse model of T1DM is associated with increased myeloid cell PGE2-EP4 signaling, which is required for the stimulatory effect of diabetes on IL-6, markedly blunts the effect of diabetes on TNF-α and does not modulate diabetes-accelerated atherogenesis.

Ebselen treatment prevents islet apoptosis, maintains intranuclear Pdx-1 and MafA levels, and preserves ß-cell mass and function in ZDF rats.

We reported earlier that ß-cell-specific overexpression of glutathione peroxidase (GPx)-1 significantly ameliorated hyperglycemia in diabetic db/db mice and prevented glucotoxicity-induced deterioration of ß-cell mass and function. We have now ascertained whether early treatment of Zucker diabetic fatty (ZDF) rats with ebselen, an oral GPx mimetic, will prevent ß-cell deterioration. No other antihyperglycemic treatment was given. Ebselen ameliorated fasting hyperglycemia, sustained nonfasting insulin levels, lowered nonfasting glucose levels, and lowered HbA1c levels with no effects on body weight. Ebselen doubled ß-cell mass, prevented apoptosis, prevented expression of oxidative stress markers, and enhanced intranuclear localization of pancreatic and duodenal homeobox (Pdx)-1 and v-maf musculoaponeurotic fibrosarcoma oncogene family, protein A (MafA), two critical insulin transcription factors. Minimal ß-cell replication was observed in both groups. These findings indicate that prevention of oxidative stress is the mechanism whereby ebselen prevents apoptosis and preserves intranuclear Pdx-1 and MafA, which, in turn, is a likely explanation for the beneficial effects of ebselen on ß-cell mass and function. Since ebselen is an oral antioxidant currently used in clinical trials, it is a novel therapeutic candidate to ameliorate fasting hyperglycemia and further deterioration of ß-cell mass and function in humans undergoing the onset of type 2 diabetes.

Stamp2 controls macrophage inflammation through nicotinamide adenine dinucleotide phosphate homeostasis and protects against atherosclerosis.

The six-transmembrane protein Stamp2 plays an important role in metabolically triggered inflammation and insulin action. We report that Stamp2 is expressed in human and mouse macrophages, is regulated upon differentiation or activation, acts as an anti-inflammatory protein, and regulates foam cell formation. Absence of Stamp2 results in significant increases in cellular NADPH levels, and both NADPH homeostasis and the exaggerated inflammatory response of Stamp2(-/-) macrophages are rescued by exogenous wild-type but not by a reductase-deficient Stamp2 molecule. Chemical and genetic suppression of NADPH production in Stamp2(-/-) macrophages reverts the heightened inflammatory response. Stamp2 is detected in mouse and human atherosclerotic plaques, and its deficiency promotes atherosclerosis in mice. Furthermore, bone marrow transplantation experiments demonstrated that Stamp2 in myeloid cells is sufficient to protect against atherosclerosis. Our data reveal a role of Stamp2 in controlling intermediary metabolites to regulate inflammatory responses in macrophages and in progression of atherosclerosis.

The role of JNK proteins in metabolism.

The stress-activated c-Jun amino-terminal kinase (JNK) plays a pivotal role in metabolic conditions such as obesity, insulin resistance, and type 2 diabetes. Intricate tissue-specific tweaking of JNK activity in preclinical models of metabolic diseases reveals a complex interplay among local and systemic effects on carbohydrate and lipid metabolism. Synthesis of these entangled effects illustrates that for JNK inhibitors to have therapeutic impact, they must function in multiple cell types to modulate JNK activity.

A predominant role for parenchymal c-Jun amino terminal kinase (JNK) in the regulation of systemic insulin sensitivity.

It has been established that c-Jun N-terminal kinase 1 (JNK1) is essential to the pathogenesis of insulin resistance and type 2 diabetes. Although JNK influences inflammatory signaling pathways, it remains unclear whether its activity in macrophages contributes to adipose tissue inflammation and ultimately to the regulation of systemic metabolism. To address whether the action of this critical inflammatory kinase in bone marrow-derived elements regulates inflammatory responses in obesity and is sufficient and necessary for the deterioration of insulin sensitivity, we performed bone marrow transplantation studies with wild type and JNK1-deficient mice. These studies illustrated that JNK1-deficiency in the bone marrow-derived elements (BMDE) was insufficient to impact macrophage infiltration or insulin sensitivity despite modest changes in the inflammatory profile of adipose tissue. Only when the parenchymal elements lacked JNK1 could we demonstrate a significant increase in systemic insulin sensitivity. These data indicate that while the JNK1 activity in BMDE is involved in metabolic regulation and adipose milieu, it is epistatic to JNK1 activity in the parenchymal tissue for regulation of metabolic homeostasis.