Endothelial Cells Induced Progenitors Into Brown Fat to Reduce Atherosclerosis.

BACKGROUND: Insulin resistance (IR) can increase atherosclerotic and cardiovascular risk by inducing endothelial dysfunction, decreasing nitric oxide (NO) production, and accelerating arterial inflammation. The aim is to determine the mechanism by which insulin action and NO production in endothelial cells can improve systemic bioenergetics and decrease atherosclerosis via differentiation of perivascular progenitor cells (PPCs) into brown adipocytes (BAT). METHODS: Studies used various endothelial transgenic and deletion mutant ApoE-/- mice of insulin receptors, eNOS (endothelial NO synthase) and ETBR (endothelin receptor type B) receptors for assessments of atherosclerosis. Cells were isolated from perivascular fat and micro-vessels for studies on differentiation and signaling mechanisms in responses to NO, insulin, and lipokines from BAT. RESULTS: Enhancing insulin's actions on endothelial cells and NO production in ECIRS1 transgenic mice reduced body weight and increased systemic energy expenditure and BAT mass and activity by inducing differentiation of PPCs into beige/BAT even with high-fat diet. However, positive changes in bioenergetics, BAT differentiation from PPCs and weight loss were inhibited by N(gamma)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of eNOS, in ECIRS1 mice and eNOSKO mice. The mechanism mediating NO's action on PPC differentiation into BAT was identified as the activation of solubilized guanylate cyclase/PKGIα (cGMP protein-dependent kinase Iα)/GSK3ß (glycogen synthase kinase 3ß) pathways. Plasma lipidomics from ECIRS1 mice with NO-induced increased BAT mass revealed elevated 12,13-diHOME production. Infusion of 12,13-diHOME improved endothelial dysfunction and decreased atherosclerosis, whereas its reduction had opposite effects in ApoE-/-mice. CONCLUSIONS: Activation of eNOS and endothelial cells by insulin enhanced the differentiation of PPC to BAT and its lipokines and improved systemic bioenergetics and atherosclerosis, suggesting that endothelial dysfunction is a major contributor of energy disequilibrium in obesity.

CLINICAL CHARACTERIZATION OF AQUEOUS AND VITREOUS RETINOL-BINDING PROTEIN 3 CONCENTRATIONS IN RELATION TO DIABETIC RETINOPATHY SEVERITY, RETINAL STRUCTURES, AND SYSTEMIC COMPLICATIONS.

PURPOSE: To evaluate Retinol-Binding Protein 3 (RBP3) from photoreceptors in aqueous and its association with vitreous concentrations, diabetic retinopathy (DR) severity, retinal layer thickness, and clinical characteristics in people with diabetes. METHODS: RBP3 concentration was measured by custom-developed enzyme-linked immunosorbent assay in aqueous and correlated with vitreous concentrations in patients from the 50-Year Medalist study and Beetham Eye Institute at Joslin Diabetes Center. RESULTS: Aqueous RBP3 concentration (N = 131) was elevated in eyes with no to mild DR (mean ± SD 0.7 nM ± 0.2) and decreased in eyes with moderate to severe DR (0.65 nM ± 0.3) and proliferative DR (0.5 nM ± 0.2, P < 0.001) compared to eyes without diabetes. Aqueous and vitreous RBP3 concentrations correlated with each other (r = 0.34, P = 0.001) and between fellow eyes (P < 0.0001). History of retinal surgery did not affect aqueous RBP3 concentrations, but cataract surgery affected both vitreous and aqueous levels. Elevated aqueous RBP3 concentration associated with increased thickness of the outer nuclear layer (P = 0.004) and correlated with hemoglobin A1c, whereas vitreous RBP3 concentrations correlated with diabetic systemic complications. CONCLUSION: These findings suggest that aqueous RBP3 concentration may be an important endogenous clinical retinal protective factor, a biomarker for DR severity, and a promising VEGF-independent clinical intervention target in DR.

Endothelial Cell Insulin Signaling Regulates CXCR4 (C-X-C Motif Chemokine Receptor 4) and Limits Leukocyte Adhesion to Endothelium.

BACKGROUND: An activated, proinflammatory endothelium is a key feature in the development of complications of obesity and type 2 diabetes and can be caused by insulin resistance in endothelial cells. METHODS: We analyzed primary human endothelial cells by RNA sequencing to discover novel insulin-regulated genes and used endothelial cell culture and animal models to characterize signaling through CXCR4 (C-X-C motif chemokine receptor 4) in endothelial cells. RESULTS: CXCR4 was one of the genes most potently regulated by insulin, and this was mediated by PI3K (phosphatidylinositol 3-kinase), likely through FoxO1, which bound to the CXCR4 promoter. CXCR4 mRNA in CD31+ cells was 77% higher in mice with diet-induced obesity compared with lean controls and 37% higher in db/db mice than db/+ controls, consistent with upregulation of CXCR4 in endothelial cell insulin resistance. SDF-1 (stromal cell-derived factor-1)-the ligand for CXCR4-increased leukocyte adhesion to cultured endothelial cells. This effect was lost after deletion of CXCR4 by gene editing while 80% of the increase was prevented by treatment of endothelial cells with insulin. In vivo microscopy of mesenteric venules showed an increase in leukocyte rolling after intravenous injection of SDF-1, but most of this response was prevented in transgenic mice with endothelial overexpression of IRS-1 (insulin receptor substrate-1). CONCLUSIONS: Endothelial cell insulin signaling limits leukocyte/endothelial cell interaction induced by SDF-1 through downregulation of CXCR4. Improving insulin signaling in endothelial cells or inhibiting endothelial CXCR4 may reduce immune cell recruitment to the vascular wall or tissue parenchyma in insulin resistance and thereby help prevent several vascular complications.

Association of Coding Variants in Hydroxysteroid 17-beta Dehydrogenase 14 (HSD17B14) with Reduced Progression to End Stage Kidney Disease in Type 1 Diabetes.

BACKGROUND: Rare variants in gene coding regions likely have a greater impact on disease-related phenotypes than common variants through disruption of their encoded protein. We searched for rare variants associated with onset of ESKD in individuals with type 1 diabetes at advanced kidney disease stage. METHODS: Gene-based exome array analyses of 15,449 genes in five large incidence cohorts of individuals with type 1 diabetes and proteinuria were analyzed for survival time to ESKD, testing the top gene in a sixth cohort (n=2372/1115 events all cohorts) and replicating in two retrospective case-control studies (n=1072 cases, 752 controls). Deep resequencing of the top associated gene in five cohorts confirmed the findings. We performed immunohistochemistry and gene expression experiments in human control and diseased cells, and in mouse ischemia reperfusion and aristolochic acid nephropathy models. RESULTS: Protein coding variants in the hydroxysteroid 17-ß dehydrogenase 14 gene (HSD17B14), predicted to affect protein structure, had a net protective effect against development of ESKD at exome-wide significance (n=4196; P value=3.3 × 10-7). The HSD17B14 gene and encoded enzyme were robustly expressed in healthy human kidney, maximally in proximal tubular cells. Paradoxically, gene and protein expression were attenuated in human diabetic proximal tubules and in mouse kidney injury models. Expressed HSD17B14 gene and protein levels remained low without recovery after 21 days in a murine ischemic reperfusion injury model. Decreased gene expression was found in other CKD-associated renal pathologies. CONCLUSIONS: HSD17B14 gene is mechanistically involved in diabetic kidney disease. The encoded sex steroid enzyme is a druggable target, potentially opening a new avenue for therapeutic development.

Regulation of Macrophage Apoptosis and Atherosclerosis by Lipid-Induced PKCδ Isoform Activation.

RATIONALE: Activation of monocytes/macrophages by hyperlipidemia associated with diabetes mellitus and obesity contributes to the development of atherosclerosis. PKCδ (protein kinase C δ) expression and activity in monocytes were increased by hyperlipidemia and diabetes mellitus with unknown consequences to atherosclerosis. OBJECTIVE: To investigate the effect of PKCδ activation in macrophages on the severity of atherosclerosis. METHODS AND RESULTS: PKCδ expression and activity were increased in Zucker diabetic rats. Mice with selective deletion of PKCδ in macrophages were generated by breeding PKCδ flox/flox mice with LyzM-Cre and ApoE-/- mice (MPKCδKO/ApoE-/- mice) and studied in atherogenic (AD) and high-fat diet (HFD). Mice fed AD and HFD exhibited hyperlipidemia, but only HFD-fed mice had insulin resistance and mild diabetes mellitus. Surprisingly, MPKCδKO/ApoE-/- mice exhibited accelerated aortic atherosclerotic lesions by 2-fold versus ApoE-/- mice on AD or HFD. Splenomegaly was observed in MPKCδKO/ApoE-/- mice on AD and HFD but not on regular chow. Both the AD or HFD increased macrophage number in aortic plaques and spleen by 1.7- and 2-fold, respectively, in MPKCδKO/ApoE-/- versus ApoE-/- mice because of decreased apoptosis (62%) and increased proliferation (1.9-fold), and not because of uptake, with parallel increased expressions of inflammatory cytokines. Mechanisms for the increased macrophages in MPKCδKO/ApoE-/- were associated with elevated phosphorylation levels of prosurvival cell-signaling proteins, Akt and FoxO3a, with reduction of proapoptotic protein Bim associated with PKCδ induced inhibition of P85/PI3K. CONCLUSIONS: Accelerated development of atherosclerosis induced by insulin resistance and hyperlipidemia may be partially limited by PKCδ isoform activation in the monocytes, which decreased its number and inflammatory responses in the arterial wall.

Exogenous Insulin Infusion Can Decrease Atherosclerosis in Diabetic Rodents by Improving Lipids, Inflammation, and Endothelial Function.

OBJECTIVE: The objective of this study is to evaluate whether exogenously induced hyperinsulinemia may increase the development of atherosclerosis. APPROACH AND RESULTS: Hyperinsulinemia, induced by exogenous insulin implantation in high-fat fed (60% fat HFD) apolipoprotein E-deficient mice (ApoE-/-) mice, exhibited insulin resistance, hyperglycemia, and hyperinsulinemia. Atherosclerosis was measured by the accumulation of fat, macrophage, and extracellular matrix in the aorta. After 8 weeks on HFD, ApoE-/- mice were subcutaneously implanted with control (sham) or insulin pellet, and phlorizin, a sodium glucose cotransporters inhibitor (1/2)inhibitor, for additional 8 weeks. Intraperitoneal glucose tolerance test showed that plasma glucose levels were lower and insulin and IGF-1 (insulin-like growth factor-1) levels were 5.3- and 3.3-fold higher, respectively, in insulin-implanted compared with sham-treated ApoE-/- mice. Plasma triglyceride, cholesterol, and lipoprotein levels were decreased in mice with insulin implant, in parallel with increased lipoprotein lipase activities. Atherosclerotic plaque by en face and complexity staining showed significant reductions of fat deposits and expressions of vascular adhesion molecule-1, tumor necrosis factor-α, interleukin 6, and macrophages in arterial wall while exhibiting increased activation of pAKT and endothelial nitric oxide synthase (P<0.05) comparing insulin-implanted versus sham HFD ApoE-/- mice. No differences were observed in atherosclerotic plaques between phlorizin-treated and sham HFD ApoE-/- mice, except phlorizin significantly lowered plasma glucose and glycated hemoglobin levels while increased glucosuria. Endothelial function was improved only by insulin treatment through endothelial nitric oxide synthase/nitric oxide activations and reduced proinflammatory (M1) and increased anti-inflammatory (M2) macrophages, which were inhibited by endothelial nitric oxide synthase inhibitor. CONCLUSIONS: Exogenous insulin decreased atherosclerosis by lowering inflammatory cytokines, macrophages, and plasma lipids in HFD-induced hyperlipidemia, insulin resistant and mildly diabetic ApoE-/- mice.

Meta-genome-wide association studies identify a locus on chromosome 1 and multiple variants in the MHC region for serum C-peptide in type 1 diabetes.

AIMS/HYPOTHESIS: The aim of this study was to identify genetic variants associated with beta cell function in type 1 diabetes, as measured by serum C-peptide levels, through meta-genome-wide association studies (meta-GWAS). METHODS: We performed a meta-GWAS to combine the results from five studies in type 1 diabetes with cross-sectionally measured stimulated, fasting or random C-peptide levels, including 3479 European participants. The p values across studies were combined, taking into account sample size and direction of effect. We also performed separate meta-GWAS for stimulated (n = 1303), fasting (n = 2019) and random (n = 1497) C-peptide levels. RESULTS: In the meta-GWAS for stimulated/fasting/random C-peptide levels, a SNP on chromosome 1, rs559047 (Chr1:238753916, T>A, minor allele frequency [MAF] 0.24-0.26), was associated with C-peptide (p = 4.13 × 10-8), meeting the genome-wide significance threshold (p < 5 × 10-8). In the same meta-GWAS, a locus in the MHC region (rs9260151) was close to the genome-wide significance threshold (Chr6:29911030, C>T, MAF 0.07-0.10, p = 8.43 × 10-8). In the stimulated C-peptide meta-GWAS, rs61211515 (Chr6:30100975, T/-, MAF 0.17-0.19) in the MHC region was associated with stimulated C-peptide (ß [SE] = - 0.39 [0.07], p = 9.72 × 10-8). rs61211515 was also associated with the rate of stimulated C-peptide decline over time in a subset of individuals (n = 258) with annual repeated measures for up to 6 years (p = 0.02). In the meta-GWAS of random C-peptide, another MHC region, SNP rs3135002 (Chr6:32668439, C>A, MAF 0.02-0.06), was associated with C-peptide (p = 3.49 × 10-8). Conditional analyses suggested that the three identified variants in the MHC region were independent of each other. rs9260151 and rs3135002 have been associated with type 1 diabetes, whereas rs559047 and rs61211515 have not been associated with a risk of developing type 1 diabetes. CONCLUSIONS/INTERPRETATION: We identified a locus on chromosome 1 and multiple variants in the MHC region, at least some of which were distinct from type 1 diabetes risk loci, that were associated with C-peptide, suggesting partly non-overlapping mechanisms for the development and progression of type 1 diabetes. These associations need to be validated in independent populations. Further investigations could provide insights into mechanisms of beta cell loss and opportunities to preserve beta cell function.

SHP-1 activation inhibits vascular smooth muscle cell proliferation and intimal hyperplasia in a rodent model of insulin resistance and diabetes.

AIMS/HYPOTHESIS: Accelerated migration and proliferation of vascular smooth muscle cells (VSMCs) enhances arterial restenosis after angioplasty in insulin resistance and diabetes. Elevation of Src homology 2-containing protein tyrosine phosphatase 1 (SHP-1) induces apoptosis in the microvasculature. However, the role of SHP-1 in intimal hyperplasia and restenosis has not been clarified in insulin resistance and diabetes. METHODS: We used a femoral artery wire injury mouse model, rodent models with insulin resistance and diabetes, and patients with type 2 diabetes. Further, we modulated SHP-1 expression using a transgenic mouse that overexpresses SHP-1 in VSMCs (Shp-1-Tg). SHP-1 agonists were also employed to study the molecular mechanisms underlying the regulation of SHP-1 by oxidised lipids. RESULTS: Mice fed a high-fat diet (HFD) exhibited increased femoral artery intimal hyperplasia and decreased arterial SHP-1 expression compared with mice fed a regular diet. Arterial SHP-1 expression was also decreased in Zucker fatty rats, Zucker diabetic fatty rats and in patients with type 2 diabetes. In primary cultured VSMCs, oxidised LDL suppressed SHP-1 expression by activating Mek-1 (also known as Map2k1) and increased DNA methylation of the Shp-1 promoter. VSMCs from Shp-1-Tg mice exhibited impaired platelet-derived growth factor (PDGF)-stimulated tyrosine phosphorylation with a concomitant decrease in PDGF-stimulated VSMC proliferation and migration. Similarly, HFD-fed Shp-1-Tg mice and mice treated with the SHP-1 inducer, Icariside II, were protected from the development of intimal hyperplasia following wire injury. CONCLUSIONS/INTERPRETATION: Suppression of SHP-1 by oxidised lipids may contribute to the excessive VSMC proliferation, inflammatory cytokine production and intimal hyperplasia observed in arteries from diabetes and insulin resistance. Augmenting SHP-1 levels is a potential therapeutic strategy to maintain stent patency in patients with insulin resistance and diabetes.

Beta 2-adrenergic receptor agonists are novel regulators of macrophage activation in diabetic renal and cardiovascular complications.

Macrophage activation is increased in diabetes and correlated with the onset and progression of vascular complications. To identify drugs that could inhibit macrophage activation, we developed a cell-based assay and screened a 1,040 compound library for anti-inflammatory effects. Beta2-adrenergic receptor (ß2AR) agonists were identified as the most potent inhibitors of phorbol myristate acetate-induced tumor necrosis factor-α production in rat bone marrow macrophages. In peripheral blood mononuclear cells isolated from streptozotocin-induced diabetic rats, ß2AR agonists inhibited diabetes-induced tumor necrosis factor-α production, which was prevented by co-treatment with a selective ß2AR blocker. To clarify the underlying mechanisms, THP-1 cells and bone marrow macrophages were exposed to high glucose. High glucose reduced ß-arrestin2, a negative regulator of NF-κB activation, and its interaction with IκBα. This subsequently enhanced phosphorylation of IκBα and activation of NF-κB. The ß2AR agonists enhanced ß-arrestin2 and its interaction with IκBα, leading to downregulation of NF-κB. A siRNA specific for ß-arrestin2 reversed ß2AR agonist-mediated inhibition of NF-κB activation and inflammatory cytokine production. Treatment of Zucker diabetic fatty rats with a ß2AR agonist for 12 weeks attenuated monocyte activation as well as pro-inflammatory and pro-fibrotic responses in the kidneys and heart. Thus, ß2AR agonists might have protective effects against diabetic renal and cardiovascular complications.

High density lipoprotein modulates osteocalcin expression in circulating monocytes: a potential protective mechanism for cardiovascular disease in type 1 diabetes.

BACKGROUND: Cardiovascular disease (CVD) is a major cause of mortality in type 1 diabetes (T1D). A pro-calcific drift of circulating monocytes has been linked to vascular calcification and is marked by the surface expression of osteocalcin (OCN). We studied OCN+ monocytes in a unique population with ≥50 years of T1D, the 50-Year Joslin Medalists (J50M). METHODS: CD45 bright/CD14+/OCN+ cells in the circulating mononuclear blood cell fraction were quantified by flow cytometry and reported as percentage of CD45 bright cells. Mechanisms were studied by inducing OCN expression in human monocytes in vitro. RESULTS: Subjects without history of CVD (n = 16) showed lower levels of OCN+ monocytes than subjects with CVD (n = 14) (13.1 ± 8.4% vs 19.9 ± 6.4%, p = 0.02). OCN+ monocytes level was inversely related to total high density lipoprotein (HDL) cholesterol levels (r = -0.424, p = 0.02), large (r = -0.413, p = 0.02) and intermediate (r = -0.445, p = 0.01) HDL sub-fractions, but not to small HDL. In vitro, incubation with OxLDL significantly increased the number of OCN+ monocytes (p < 0.01). This action of OxLDL was significantly reduced by the addition of HDL in a concentration dependent manner (p < 0.001). Inhibition of the scavenger receptor B1 reduced the effects of both OxLDL and HDL (p < 0.05). CONCLUSIONS: Low OCN+ monocytes levels are associated with lack of CVD in people with long duration T1D. A possible mechanism for the increased OCN+ monocytes could be the elevated levels of oxidized lipids due to diabetes which may be inhibited by HDL. These findings suggest that circulating OCN+ monocytes could be a marker for vascular disease in diabetic patients and possibly modified by HDL elevation.

Induction of vascular insulin resistance and endothelin-1 expression and acceleration of atherosclerosis by the overexpression of protein kinase C-ß isoform in the endothelium.

RATIONALE: Loss of insulin action in the endothelium can cause endothelial dysfunction and atherosclerosis. Hyperglycemia and elevated fatty acids induced by diabetes mellitus can activate protein kinase C-ß isoforms and selectively inhibit insulin signaling via phosphatidylinositol 3-kinase/Akt pathway to inhibit the activation of endothelial nitric oxide synthase and metabolic actions. OBJECTIVE: To demonstrate that overexpressing protein kinase C-ß2 isoform in endothelial cells can cause selective insulin resistance and exacerbate atherosclerosis in the aorta. METHODS AND RESULTS: Protein kinase C-ß2 isoform was overexpressed in endothelial cells using a promoter of vascular endothelial cell cadherin. These mice were cross-bred with apoE-/- mice [Tg (Prkcb)apoE-/-]. On a Western diet, Tg(Prkcb)apoE-/- and apoE-/- mice did not differ in systemic insulin sensitivity, glucose tolerance, plasma lipid, or blood pressure. Insulin action in endothelial cells and femoral artery from Tg(Prkcb)apoE-/- mice was impaired by ≈40% with respect to Akt/endothelial nitric oxide synthase activation, and leukocyte-endothelial cell binding increased in cultured lung endothelial cells from Tg(Prkcb)apoE-/- mice compared with that from apoE-/- mice. Basal and angiotensin-stimulated big endothelin-1 levels were elevated in Tg(Prkcb)apoE-/- mice compared with apoE-/- mice. The severity of atherosclerosis in the aorta from Tg(Prkcb)apoE-/- mice increased by ≈70% as measured by en face fat staining and plaque content of the number of smooth muscle cells, macrophages, and extracellular matrix. CONCLUSIONS: Specific protein kinase C-ß2 activation in the endothelial cells caused dysfunction and accelerated atherosclerosis because of loss of insulin-stimulated Akt/endothelial nitric oxide synthase activation and angiotensin-induced increases in endothelin-1 expression.

Insulin receptors in vascular smooth muscle cells regulate plaque stability of atherosclerosis.

AIMS: Increased prevalence of acute myocardial infarction related to diabetes and insulin resistance is associated with elevated risk for unstable atherosclerotic plaques, which are characterized by reduced vascular smooth muscle cells (VSMC) and extracellular matrix (ECM) and increased inflammation. Thus, insulin resistance may reduce plaque stability as deleting insulin receptors (IR) in VSMC decreased their proliferation and enhanced apoptosis. METHODS AND RESULTS: Direct effects of insulin on VSMC to alter plaque composition were studied using mice with double knockout of ApoE and IR genes in VSMC with SMIRKO/ApoE-/- and Myh11-CreERT2EYFP+/ApoE-/- and Myh11-CreERT2EYFP+IRKO/ApoE-/- mice, which were also used for lineage tracing studies. Compared to ApoE-/- mice, SMIRKO/ApoE-/-- mice exhibited more atherosclerotic plaques, which contained less VSMC and collagen, but increased levels of VSMC apoptosis and necrotic areas. Lineage tracing studies showed that Icam1+ Vcam1+ VSMC was inflammatory VSMC, which increased in aortas of Myh11-CreERT2EYFP+IRKO/ApoE-/- mice compared to control mice. Isolated VSMC lacking IR expressed higher inflammatory cytokines than cells with IR. Cell based studies indicated that insulin's anti-apoptotic and pro-proliferative effects in VSMC were mediated via activation of IR/Akt pathway, which were decreased in VSMC from SMIRKO or high fat diet (HFD) mice. Analysis of IR targets that regulated inflammatory cytokines in VSMC showed that thrombospondin 1 (Thbs1) and Mmp2 were consistently increased with loss of IR. Insulin inhibited Thbs1 expression, but not Mmp2, by p-Akt/p-FoxO1 pathways in VSMC from ApoE-/- mice, which was impaired in cells from SMIRKO/ApoE-/-- mice. Thbs1 further induced Icam1 and Mmp2 expressions in VSMC. CONCLUSIONS: Insulin via IR has significant actions in VSMC to decrease inflammation, apoptosis and ECM turnover via the activation of Akt and FoxO1 pathways. Inhibition of insulin actions and related pathways related to insulin resistance and diabetes may contribute to the formation of unstable atherosclerotic plaques.

Hepatic insulin resistance is sufficient to produce dyslipidemia and susceptibility to atherosclerosis.

Insulin resistance plays a central role in the development of the metabolic syndrome, but how it relates to cardiovascular disease remains controversial. Liver insulin receptor knockout (LIRKO) mice have pure hepatic insulin resistance. On a standard chow diet, LIRKO mice have a proatherogenic lipoprotein profile with reduced high-density lipoprotein (HDL) cholesterol and very low-density lipoprotein (VLDL) particles that are markedly enriched in cholesterol. This is due to increased secretion and decreased clearance of apolipoprotein B-containing lipoproteins, coupled with decreased triglyceride secretion secondary to increased expression of Pgc-1 beta (Ppargc-1b), which promotes VLDL secretion, but decreased expression of Srebp-1c (Srebf1), Srebp-2 (Srebf2), and their targets, the lipogenic enzymes and the LDL receptor. Within 12 weeks on an atherogenic diet, LIRKO mice show marked hypercholesterolemia, and 100% of LIRKO mice, but 0% of controls, develop severe atherosclerosis. Thus, insulin resistance at the level of the liver is sufficient to produce the dyslipidemia and increased risk of atherosclerosis associated with the metabolic syndrome.

Inhibition of insulin signaling in endothelial cells by protein kinase C-induced phosphorylation of p85 subunit of phosphatidylinositol 3-kinase (PI3K).

The regulation of endothelial function by insulin is consistently abnormal in insulin-resistant states and diabetes. Protein kinase C (PKC) activation has been reported to inhibit insulin signaling selectively in endothelial cells via the insulin receptor substrate/PI3K/Akt pathway to reduce the activation of endothelial nitric-oxide synthase (eNOS). In this study, it was observed that PKC activation differentially inhibited insulin receptor substrate 1/2 (IRS1/2) signaling of insulin's activation of PI3K/eNOS by decreasing only tyrosine phosphorylation of IRS2. In addition, PKC activation, by general activator and specifically by angiotensin II, increased the phosphorylation of p85/PI3K, which decreases its association with IRS1 and activation. Thr-86 of p85/PI3K was identified to be phosphorylated by PKC activation and confirmed to affect IRS1-mediated activation of Akt/eNOS by insulin and VEGF using a deletion mutant of the Thr-86 region of p85/PI3K. Thus, PKC and angiotensin-induced phosphorylation of Thr-86 of p85/PI3K may partially inhibit the activation of PI3K/eNOS by multiple cytokines and contribute to endothelial dysfunction in metabolic disorders.

Glomerular VEGF resistance induced by PKCδ/SHP-1 activation and contribution to diabetic nephropathy.

This study characterizes the effect of glucose-induced activation of protein kinase Cδ (PKCδ) and Src homology-2 domain-containing phosphatase-1 (SHP-1) expression on vascular endothelial growth factor (VEGF) actions in glomerular podocytes in cultures and in glomeruli of diabetic rodents. Elevation of glucose levels induced PKCδ and p38 mitogen-activated protein kinase (p38 MAPK) to increase SHP-1 expression, increased podocyte apoptosis, and inhibited VEGF activation in podocytes and glomerular endothelial cells. The adverse effects of high glucose levels can be negated by molecular inhibitors of PKCδ, p38MAPK, and SHP-1 and only partially reduced by antioxidants and nuclear factor-κB (NF-κB) inhibitor. Increased PKCδ activation and SHP-1 expression correlated with loss of VEGF signaling and podocyte numbers in the glomeruli of diabetic rats and mice. In contrast, diabetic PKCδ-knockout (Prkcd(-/-)) mice did not exhibit activation of p38 MAPK and SHP-1 or inhibition of VEGF signaling in renal glomeruli. Functionally, diabetic Prkcd(-/-) mice had decreased expressions of TGFß, VEGF, and extracellular matrix and less albuminuria than diabetic Prkcd(+/+) mice. Hyperglycemia and diabetes can cause glomerular podocyte apoptosis and endothelial dysfunction partly due to increased PKCδ/p38 MAPK activation and the expression of SHP-1 to cause VEGF resistance, independent of NF-κB activation.

Hyperinsulinemia does not change atherosclerosis development in apolipoprotein E null mice.

OBJECTIVE: To determine the contribution of hyperinsulinemia to atherosclerosis development. METHODS AND RESULTS: Apolipoprotein E (Apoe) null mice that had knockout of a single allele of the insulin receptor (Insr) gene were compared with littermate Apoe null mice with intact insulin receptors. Plasma insulin levels in Insr haploinsufficient/Apoe null mice were 50% higher in the fasting state and up to 69% higher during a glucose tolerance test, but glucose tolerance was not different in the 2 groups. C-peptide levels, insulin sensitivity, and postreceptor insulin signaling in muscle, liver, fat, and aorta were not different between groups, whereas disappearance in plasma of an injected insulin analog was delayed in Insr haploinsufficient/Apoe null mice, indicating that impaired insulin clearance was the primary cause of hyperinsulinemia. No differences were observed in plasma lipids or blood pressure. Despite the hyperinsulinemia, atherosclerotic lesion size was not different between the 2 groups at time points up to 52 weeks of age when measured as en face lesion area in the aorta, cross-sectional plaque area in the aortic sinus, and cholesterol abundance in the brachiocephalic artery. CONCLUSIONS: Hyperinsulinemia, without substantial vascular or whole-body insulin resistance and without changes in plasma lipids or blood pressure, does not change susceptibility to atherosclerosis.

Dysregulation of CXCL1 Expression and Neutrophil Recruitment in Insulin Resistance and Diabetes-Related Periodontitis in Male Mice.

Insulin resistance and hyperglycemia are risk factors for periodontitis and poor wound healing in diabetes, which have been associated with selective loss of insulin activation of the PI3K/Akt pathway in the gingiva. This study showed that insulin resistance in the mouse gingiva due to selective deletion of smooth muscle and fibroblast insulin receptor (SMIRKO mice) or systemic metabolic changes induced by a high-fat diet (HFD) in HFD-fed mice exacerbated periodontitis-induced alveolar bone loss, preceded by delayed neutrophil and monocyte recruitment and impaired bacterial clearance compared with their respective controls. The immunocytokines, CXCL1, CXCL2, MCP-1, TNFα, IL-1ß, and IL-17A, exhibited delayed maximal expression in the gingiva of male SMIRKO and HFD-fed mice compared with controls. Targeted overexpression of CXCL1 in the gingiva by adenovirus normalized neutrophil and monocyte recruitment and prevented bone loss in both mouse models of insulin resistance. Mechanistically, insulin enhanced bacterial lipopolysaccharide-induced CXCL1 production in mouse and human gingival fibroblasts (GFs), via Akt pathway and NF-κB activation, which were reduced in GFs from SMIRKO and HFD-fed mice. These results provided the first report that insulin signaling can enhance endotoxin-induced CXCL1 expression to modulate neutrophil recruitment, suggesting CXCL1 as a new therapeutic direction for periodontitis or wound healing in diabetes. ARTICLE HIGHLIGHTS: The mechanism for the increased risks for periodontitis in the gingival tissues due to insulin resistance and diabetes is unclear. We investigated how insulin action in gingival fibroblasts modulates the progression of periodontitis in resistance and diabetes. Insulin upregulated the lipopolysaccharide-induced neutrophil chemoattractant, CXCL1, production in gingival fibroblasts via insulin receptors and Akt activation. Enhancing CXCL1 expression in the gingiva normalized diabetes and insulin resistance-induced delays in neutrophils recruitment and periodontitis. Targeting dysregulation of CXCL1 in fibroblasts is potentially therapeutic for periodontitis and may also improve wound healing in insulin resistance and diabetes.

Transforming growth factor beta-1 and incidence of heart failure in older adults: the Cardiovascular Health Study.

CONTEXT: Transforming growth factor-beta1 (TGF-B1) is a highly pleiotropic cytokine whose functions include a central role in the induction of fibrosis. OBJECTIVE: To investigate the hypothesis that elevated plasma levels of TGF-B1 are positively associated with incident heart failure (HF). PARTICIPANTS AND METHODS: The hypotheses were tested using a two-phase case-control study design, ancillary to the Cardiovascular Health Study - a longitudinal, population-based cohort study. Cases were defined as having an incident HF event after their 1992-1993 exam and controls were free of HF at follow-up. TGF-B1 was measured using plasma collected in 1992-1993 and data from 89 cases and 128 controls were used for analysis. The association between TGF-B1 and risk of HF was evaluated using the weighted likelihood method, and odds ratios (OR) for risk of HF were calculated for TGF-B1 as a continuous linear variable and across quartiles of TGF-B1. RESULTS: The OR for HF was 1.88 (95% confidence intervals [CI] 1.26-2.81) for each nanogram increase in TGF-B1, and the OR for the highest quartile (compared to the lowest) of TGF-B1 was 5.79 (95% CI 1.65-20.34), after adjustment for age, sex, C-reactive protein, platelet count and digoxin use. Further adjustment with other covariates did not change the results. CONCLUSIONS: Higher levels of plasma TGF-B1 were associated with an increased risk of incident heart failure among older adults. However, further study is needed in larger samples to confirm these findings.

Activation of protein kinase C isoforms and its impact on diabetic complications.

Both cardio- and microvascular complications adversely affect the life quality of patients with diabetes and have been the leading cause of mortality and morbidity in this population. Cardiovascular pathologies of diabetes have an effect on microvenules, arteries, and myocardium. It is believed that hyperglycemia is one of the most important metabolic factors in the development of both micro- and macrovascular complications in diabetic patients. Several prominent hypotheses exist to explain the adverse effect of hyperglycemia. One of them is the chronic activation by hyperglycemia of protein kinase (PK)C, a family of enzymes that are involved in controlling the function of other proteins. PKC has been associated with vascular alterations such as increases in permeability, contractility, extracellular matrix synthesis, cell growth and apoptosis, angiogenesis, leukocyte adhesion, and cytokine activation and inhibition. These perturbations in vascular cell homeostasis caused by different PKC isoforms (PKC-alpha, -beta1/2, and PKC-delta) are linked to the development of pathologies affecting large vessel (atherosclerosis, cardiomyopathy) and small vessel (retinopathy, nephropathy and neuropathy) complications. Clinical trials using a PKC-beta isoform inhibitor have been conducted, with some positive results for diabetic nonproliferative retinopathy, nephropathy, and endothelial dysfunction. This article reviews present understanding of how PKC isoforms cause vascular dysfunctions and pathologies in diabetes.