Insulin Signaling in Arteries Prevents Smooth Muscle Apoptosis

HIV viral protein R induces loss of DCT1-type renal tubules

Hyponatremia and salt wasting is a common occurance in patients with HIV/AIDS, however, the understanding of its contributing factors is limited. HIV viral protein R (Vpr) contributes to HIV-associated nephropathy. To investigate the effects of Vpr on the expression level of the Slc12a3 gene, encoding the Na-Cl cotransporter, which is responsible for sodium reabsorption in distal nephron segments, we performed single-nucleus RNA sequencing of kidney cortices from three wild-type (WT) and three Vpr-transgenic (Vpr Tg) mice. The results showed that the percentage of distal convoluted tubule (DCT) cells was significantly lower in Vpr Tg mice compared with WT mice (P < 0.05), and that in Vpr Tg mice, Slc12a3 expression was not different in DCT cell cluster. The Pvalb+ DCT1 subcluster had fewer cells in Vpr Tg mice compared with WT (P < 0.01). Immunohistochemistry demonstrated fewer Slc12a3+ Pvalb+ DCT1 segments in Vpr Tg mice. Differential gene expression analysis comparing Vpr Tg and WT in the DCT cluster showed Ier3, an inhibitor of apoptosis, to be the most downregulated gene. These observations demonstrate that the salt-wasting effect of Vpr in Vpr Tg mice is mediated by loss of Slc12a3+ Pvalb+ DCT1 segments via apoptosis dysregulation.

Insulin's actions on vascular tissues: Physiological effects and pathophysiological contributions to vascular complications of diabetes

Background

Insulin has been demonstrated to exert direct and indirect effects on vascular tissues. Its actions in vascular cells are mediated by two major pathways: the insulin receptor substrate 1/2-phosphoinositide-3 kinase/Akt (IRS1/2/PI3K/Akt) pathway and the Src/mitogen-activated protein kinase (MAPK) pathway, both of which contribute to the expression and distribution of metabolites, hormones, and cytokines.

Scope of review

In this review, we summarize the current understanding of insulin's physiological and pathophysiological actions and associated signaling pathways in vascular cells, mainly in endothelial cells (EC) and vascular smooth muscle cells (VSMC), and how these processes lead to selective insulin resistance. We also describe insulin's potential new signaling and biological effects derived from animal studies and cultured capillary and arterial EC, VSMC, and pericytes. We will not provide a detailed discussion of insulin's effects on the myocardium, insulin's structure, or its signaling pathways' various steps, since other articles in this issue discuss these areas in depth.

Major conclusions

Insulin mediates many important functions on vascular cells via its receptors and signaling cascades. Its direct actions on EC and VSMC are important for transporting and communicating nutrients, cytokines, hormones, and other signaling molecules. These vascular actions are also important for regulating systemic fuel metabolism and energetics. Inhibiting or enhancing these pathways leads to selective insulin resistance, exacerbating the development of endothelial dysfunction, atherosclerosis, restenosis, poor wound healing, and even myocardial dysfunction. Targeted therapies to improve selective insulin resistance in EC and VSMC are thus needed to specifically mitigate these pathological processes.

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Insulin's actions in vascular cells have a significant influence on systemic metabolism.

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Insulin exerts its vascular effects through its receptors and signaling cascades.

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Inhibition or enhancement of different insulin signaling leads to selective insulin resistance.

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Loss of insulin's actions causes endothelial dysfunction and vascular complications in diabetes.

Effects of insulin on the proliferation and global gene expression profile of A7r5 cells

Insulin contributes to atherosclerosis, but the potential mechanisms are kept unclear. In this study, insulin promoted proliferation of A7r5 cells. Microarray analysis indicated that insulin significantly changed 812 probe sets of genes, including 405 upregulated and 407 downregulated ones (fold change ≥ 1.5 or ≤ - 1.5; p < 0.05). Gene ontology analysis showed that the differentially expressed genes were involved in a number of processes, including the regulation of cell proliferation/migration/cycle, apoptotic process, oxidative stress, inflammatory response, mitogen-activated protein kinase (MAPK) activity, lipid metabolic process and extracellular matrix organization. Moreover, Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that the genes were involved in biosynthesis of amino acids, fatty acid metabolism, glycolysis/gluconeogenesis, metabolic pathways, regulation of autophagy, cell cycle and apoptosis, as well as the PI3K-Akt, MAPK, mTOR and NF-κB signaling pathways. Additionally, insulin enhanced phosphorylation of MAPK kinase 1/2 and Akt, suggesting activation of the MAPK and PI3K-Akt signaling pathways. Inhibition of ERK1/2 reduced insulin-induced proliferation. This study revealed the proliferative effects of insulin and displayed global gene expression profile of A7r5 cells stimulated by insulin, suggesting new insight into the molecular pathogenesis of insulin promoting atherosclerosis.

Insulin augments serotonin-induced contraction via activation of the IR/PI3K/PDK1 pathway in the rat carotid artery

Hyperinsulinemia associated with type 2 diabetes may contribute to the development of vascular diseases. Although we recently reported that enhanced contractile responses to serotonin (5-hydroxytryptamine, 5-HT) are observed in the arteries of type 2 diabetes models, the causative factors and detailed signaling pathways involved remain unclear. The purpose of this study was to investigate whether high insulin would be an amplifier of 5-HT-induced contraction in rat carotid arteries and whether the contraction involves phosphoinositide 3-kinase (PI3K)/3-phosphoinositide-dependent protein kinase 1 (PDK1) signaling, an insulin-mediated signaling pathway. In rat carotid arteries organ-cultured with insulin (for 24 h), (1) the contractile responses to 5-HT were significantly greater (vs. vehicle), (2) the insulin-induced enhancement of 5-HT-induced contractions was largely suppressed by inhibitors of the insulin receptor (IR) (GSK1838705A), PI3K (LY294002), and PDK1 (GSK2334470), and (3) the levels of phosphorylated forms of both PDK1 and myosin phosphatase target subunit 1 (MYPT1) were greater upon 5-HT stimulation. In addition, in rat carotid arteries organ-cultured with an activator of PDK1 (PS48), the 5-HT-induced contraction was greater, and this was suppressed by PDK1 inhibition but not PI3K inhibition. In addition, MYPT1 and PDK1 phosphorylation upon 5-HT stimulation was enhanced (vs. vehicle). These results suggest that high insulin levels amplify 5-HT-induced contraction. Moreover, the present results indicated the direct linkage between IR/PI3K/PDK1 activation and 5-HT-induced contraction in rat carotid arteries for the first time.

Effects of Nigella sativa L. seed oil on intima-media thickness and Bax and Caspase 3 expression in diabetic rat aorta

OBJECTIVE

Hyperglycaemia is an important risk factor for the development and progression of the macrovascular and microvascular complications that occur in diabetes. The expression of apoptotic markers in the aortic medial layer of diabetic rats and the effects of N. sativa L. seed oil on the expression of these markers were investigated in this study.

METHODS

Four-month-old adult female Wistar rats (n=21) were divided into 3 groups: Group 1, control; Group 2, diabetes and Group 3, diabetes+N. sativa L. seed oil. Group 3 received 0.2 mg/kg/day N. sativa L. seed (black cumin) oil intraperitoneally 6 days per week for 30 days. At the end of the experiment, abdominal and thoracic aortas of all animals were collected and fixed in 10% formalin solution. Then, 5-μm-thick sections were stained with Verhoeff-Van Gieson stain to evaluate Bax and Caspase 3 expression. Tunica intima-media thickness was measured using the stained sections.

RESULTS

There were no significant differences in abdominal or thoracic aortic intima-media thickness among the 3 groups. However, there were significant differences in Bax and Caspase 3 expression in the tunica media of the thoracic and abdominal aortas between Group 1 and Group 2 (p<0.05) and between Group 2 and Group 3 (p<0.05) evaluated with the Kruskal-Wallis and Mann-Whitney U tests.

CONCLUSION

It is understood that N. sativa L. seed oil is effective against diabetes. N. sativa L. seed oil is a plant material and has value for further investigation to develop diabetes treatment strategies for preventing apoptosis in vascular structures.

New Insights into Hyperglycemia-induced Molecular Changes in Microvascular Cells

Hyperglycemia is the most prevalent characteristic of diabetes and plays a central role in mediating adverse effects on vascular cells during the progression of diabetic vascular complications. In diabetic microangiopathy, hyperglycemia induces biochemical and molecular changes in microvascular cells that ultimately progress to retinal, renal, and neural complications and extends to other complications, including advanced periodontal disease. In this review, we describe changes involving basement membrane thickening, tissue remodeling, gap junctions, inflammation, cytokines, and transcription factors, and their effects on the pathogenesis of diabetic microvascular complications. The majority of the changes described relate to retinal microangiopathy, since ultrastructural, structural, and biochemical alterations have been well-characterized in this tissue.

Matrix Metalloproteinase-2, -9, and Tissue Inhibitor of Metalloproteinase-1 in Patients with Hypertension

There are conflicting data in the literature regarding the expression pattern of the vascular matrix metalloproteinase (MMP) system and their inhibitors (TIMPs) in human hypertension. The authors hypothesized that MMP-2, MMP-9, and TIMP-1 would be abnormal in hypertension, reflecting alterations in extracellular matrix (ECM) turnover. The authors measured plasma levels and activities of MMP-2, MMP-9, and TIMP-1 in 44 hypertensive patients and 44 controls. MMP-2 levels and activity were significantly higher in hypertensive group (p < .0001). Significant increase was also observed for MMP-9 level and activity (p < .0001) and for TIMP-1 (p < .0001) in hypertensive patients. Plasma levels and activities of MMP-2, MMP-9, and TIMP-1 are increased in hypertensive patients, which may reflect abnormal ECM metabolism.

Arterial smooth muscle cells dysfunction in hyperglycaemia and hyperglycaemia associated with hyperlipidaemia: from causes to effects

Given the important role of smooth muscle cells in arterial wall dysfunction in diabetes, as well as in diabetes associated with accelerated atherosclerosis, we provide a brief review of the recent achievements in identification of signalling molecules underlying their altered cellular responses, and examine the consequences of these pathological insults on smooth muscle cells properties. The original results emerging from the Golden Syrian hamster model (rendered diabetic or simultaneously hyperlipidaemic-diabetic) and from human aortic smooth muscle cells cultured in 25 mM glucose (to mimic diabetic condition) or sera of obese type 2 diabetic patients (to mimic the metabolic syndrome condition) are presented in this context. We conclude this review with several open issues disclosed by the most recent literature that deserve essential attention for targeting the translational medicine.

The macrophage at the crossroads of insulin resistance and atherosclerosis

The macrophage has emerged as an important player in the pathogenesis of both atherosclerosis and insulin resistance. Cross-talk between inflammatory macrophages and adipocytes may be involved in insulin resistance in peripheral tissues. Defective insulin signaling in cells of the arterial wall including macrophages may promote the development of atherosclerosis. Insulin resistant macrophages are more susceptible to endoplasmic reticulum stress and apoptosis in response to various stimuli such as nutrient deprivation, free cholesterol loading, and oxidized LDL. Increased apoptosis of insulin resistant macrophages and impaired phagocytic clearance of apoptotic cells by insulin resistant macrophages in atherosclerotic lesions may lead to enhanced postapoptotic necrosis, larger lipid-rich cores, increased inflammation, and more complex vulnerable plaques.

Metalloproteinase-2 and -9 in diabetic and nondiabetic subjects during acute coronary syndromes

The authors hypothesized that matrix metalloproteinase (MMP)-2, -9, and tissue inhibitor metalloproteinase (TIMP)-1, -2 would be abnormal in acute coronary syndromes (ACSs). MMP-2, -9, and TIMP-1, -2 plasma levels were measured in diabetic patients with ACSs compared to nondiabetic patients with ACSs. A total of 46 diabetic and 78 nondiabetic patients with ACSs were enrolled. The following parameters were measured: body mass index (BMI), glycosylated hemoglobin (HbA1c), fasting plasma glucose (FPG), fasting plasma insulin (FPI), homeostasis model assessment index (HOMA index), systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (Tg), lipoprotein(a) [Lp(a)], plasminogen activator inhibitor-1 (PAI-1), homocysteine (Hct), fibrinogen (Fg), high-sensitivity C-reactive protein (hs-CRP), and plasma levels of MMP-2, MMP-9, TIMP-1, and TIMP-2. Significant HbA1c, FPG, FPI, HOMA index, DBP, Tg, Hct, and Fg increases were present in the diabetic group with ACSs, whereas hs-CRP was lower in these patients compared to nondiabetic patients with ACSs. MMP-9, TIMP-1, and TIMP-2 plasma levels were higher in diabetic patients with ACSs compared to nondiabetic patients with ACSs. MMP-9, TIMP-1, and TIMP-2 plasma levels were increased in diabetic patients with ACSs, which may reflect abnormal extracellular matrix metabolism in diabetes during acute event.

Mechanical stress-initiated signal transduction in vascular smooth muscle cells in vitro and in vivo

Increasing evidence has been demonstrated that hypertension-initiated abnormal biomechanical stress is strongly associated with cardio-/cerebrovascular diseases e.g. atherosclerosis, stroke, and heart failure, which is main cause of morbidity and mortality. How the cells in the cardiovascular system sense and transduce the extracellular physical stimuli into intracellular biochemical signals is a crucial issue for understanding the mechanisms of the disease development. Recently, collecting data derived from our and other laboratories showed that many kinds of molecules in the cells such as receptors, ion channels, caveolin, G proteins, cell cytoskeleton, kinases and transcriptional factors could serve as mechanoceptors directly or indirectly in response to mechanical stimulation implying that the activation of mechanoceptors represents a non-specific manner. The sensed signals can be further sorted and/or modulated by processing of the molecules both on the cell surface and by the network of intracellular signaling pathways resulting in a sophisticated and dynamic set of cues that enable cardiovascular cell responses. The present review will summarise the data on mechanotransduction in vascular smooth muscle cells and formulate a new hypothesis, i.e. a non-specific activation of mechanoceptors followed by a variety of signal cascade activation. The hypothesis could provide us some clues for exploring new therapeutic targets for the disturbed mechanical stress-initiated diseases such as hypertension and atherosclerosis.

Autocrine anti-apoptotic and proliferative effects of insulin in pancreatic beta-cells

Insulin and glucose inhibited apoptosis in the MIN6 insulin-secreting cell line. The protective effect of 25 mM glucose was prevented by an anti-insulin antibody and this antibody-induced increase in apoptosis was reversed by the presence of excess insulin. Glucose stimulated MIN6 cell proliferation and this was inhibited by blockade of insulin secretion, by an anti-insulin antibody and by phosphatidylinositol-3 kinase (PI-3K) inhibition. Furthermore, MIN6 cell proliferation was stimulated by depolarising concentrations of KCl and by insulin itself. These data indicate that insulin secreted by beta-cells in response to elevated glucose exerts autocrine effects to protect against apoptosis and stimulate proliferation, and suggest that the insulin signalling cascade, through the PI-3K pathway, may be an effective means of maintaining beta-cell mass in diabetes.