Heme oxygenase-mediated increases in adiponectin decrease fat content and inflammatory cytokines tumor necrosis factor-alpha and interleukin-6 in Zucker rats and reduce adipogenesis in human mesenchymal stem cells

Role of heme oxygenase-1 in postnatal differentiation of stem cells: a possible cross-talk with microRNAs

SIGNIFICANCE

Heme oxygenase-1 (HO-1) converts heme to biliverdin, carbon monoxide, and ferrous ions, but its cellular functions are far beyond heme metabolism. HO-1 via heme removal and degradation products acts as a cytoprotective, anti-inflammatory, immunomodulatory, and proangiogenic protein, regulating also a cell cycle. Additionally, HO-1 can translocate to nucleus and regulate transcription factors, so it can also act independently of enzymatic function.

RECENT ADVANCES

Recently, a body of evidence has emerged indicating a role for HO-1 in postnatal differentiation of stem and progenitor cells. Maturation of satellite cells, skeletal myoblasts, adipocytes, and osteoclasts is inhibited by HO-1, whereas neurogenic differentiation and formation of cardiomyocytes perhaps can be enhanced. Moreover, HO-1 influences a lineage commitment in pluripotent stem cells and maturation of hematopoietic cells. It may play a role in development of osteoblasts, but descriptions of its exact effects are inconsistent.

CRITICAL ISSUES

In this review we discuss a role of HO-1 in cell differentiation, and possible HO-1-dependent signal transduction pathways. Among the potential mediators, we focused on microRNA (miRNA). These small, noncoding RNAs are critical for cell differentiation. Recently we have found that HO-1 not only influences expression of specific miRNAs but also regulates miRNA processing enzymes.

FUTURE DIRECTIONS

It seems that interplay between HO-1 and miRNAs may be important in regulating fates of stem and progenitor cells and needs further intensive studies.

Up-regulation of heme oxygenase-1 after infarct initiation reduces mortality, infarct size and left ventricular remodeling: experimental evidence and proof of concept

BACKGROUND

Up-regulation of HO-1 by genetic manipulation or pharmacological pre-treatment has been reported to provide benefits in several animal models of myocardial infarction (MI). However, its efficacy following MI initiation (as in clinical reality) remains to be tested. Therefore, this study investigated whether HO-1 over-expression, by cobalt protoporphyrin (CoPP) administered after LAD ligation, is still able to improve functional and structural changes in left ventricle (LV) in a rat model of 4-week MI.

METHODS

A total of 144 adult male Wistar rats were subjected to either left anterior coronary artery ligation or sham-operation. The effect of CoPP treatment (5 mg/kg i.p. at the end of the surgical session and, then, once a week for 4 weeks) was evaluated on the basis of survival, electro- and echocardiography, plasma levels of B-type natriuretic peptide (BNP), endothelin-1 and prostaglandin E2, coronary microvascular reactivity, MI size, LV wall thickness and vascularity. Besides, the expression of HO-1 and connexin-43 in different LV territories was assessed by western blot analysis and immunohistochemistry, respectively.

RESULTS

CoPP induced an increased expression of HO-1 protein with >16 h delay. CoPP treatment significantly reduced mortality, MI size, BNP concentration, ECG alterations, LV dysfunction, microvascular constriction, capillary rarefaction and restored connexin-43 expression as compared to untreated MI. These functional and structural changes were paralleled by increased HO-1 expression in all LV territories. HO activity inhibition by tin-mesoporphyrin abolished the differences between CoPP-treated and untreated MI animals.

CONCLUSIONS

This is the first report demonstrating the putative role of pharmacological induction of HO-1 following coronary occlusion to benefit infarcted and remote territories, leading to better cardiac function in a 4-week MI outcome.

Adipose tissue and its role in organ crosstalk

The discovery of adipokines has revealed adipose tissue as a central node in the interorgan crosstalk network, which mediates the regulation of multiple organs and tissues. Adipose tissue is a true endocrine organ that produces and secretes a wide range of mediators regulating adipose tissue function in an auto-/paracrine manner and important distant targets, such as the liver, skeletal muscle, the pancreas and the cardiovascular system. In metabolic disorders such as obesity, enlargement of adipocytes leads to adipose tissue dysfunction and a shift in the secretory profile with an increased release of pro-inflammatory adipokines. Adipose tissue dysfunction has a central role in the development of insulin resistance, type 2 diabetes, and cardiovascular diseases. Besides the well-acknowledged role of adipokines in metabolic diseases, and the increasing number of adipokines being discovered in the last years, the mechanisms underlying the release of many adipokines from adipose tissue remain largely unknown. To combat metabolic diseases, it is crucial to better understand how adipokines can modulate adipose tissue growth and function. Therefore, we will focus on adipokines with a prominent role in auto-/paracrine crosstalk within the adipose tissue such as RBP4, HO-1, WISP2, SFRPs and chemerin. To depict the endocrine crosstalk between adipose tissue with skeletal muscle, the cardiovascular system and the pancreas, we will report the main findings regarding the direct effects of adiponectin, leptin, DPP4 and visfatin on skeletal muscle insulin resistance, cardiovascular function and β-cell growth and function.

Bilirubin increases insulin sensitivity in leptin-receptor deficient and diet-induced obese mice through suppression of ER stress and chronic inflammation

Obesity-induced endoplasmic reticulum (ER) stress causes chronic inflammation in adipose tissue and steatosis in the liver, and eventually leads to insulin resistance and type 2 diabetes (T2D). The goal of this study was to understand the mechanisms by which administration of bilirubin, a powerful antioxidant, reduces hyperglycemia and ameliorates obesity in leptin-receptor-deficient (db/db) and diet-induced obese (DIO) mouse models. db/db or DIO mice were injected with bilirubin or vehicle ip. Blood glucose and body weight were measured. Activation of insulin-signaling pathways, expression of inflammatory cytokines, and ER stress markers were measured in skeletal muscle, adipose tissue, and liver of mice. Bilirubin administration significantly reduced hyperglycemia and increased insulin sensitivity in db/db mice. Bilirubin treatment increased protein kinase B (PKB/Akt) phosphorylation in skeletal muscle and suppressed expression of ER stress markers, including the 78-kDa glucose-regulated protein (GRP78), CCAAT/enhancer-binding protein (C/EBP) homologous protein, X box binding protein (XBP-1), and activating transcription factor 4 in db/db mice. In DIO mice, bilirubin treatment significantly reduced body weight and increased insulin sensitivity. Moreover, bilirubin suppressed macrophage infiltration and proinflammatory cytokine expression, including TNF-α, IL-1β, and monocyte chemoattractant protein-1, in adipose tissue. In liver and adipose tissue of DIO mice, bilirubin ameliorated hepatic steatosis and reduced expression of GRP78 and C/EBP homologous protein. These results demonstrate that bilirubin administration improves hyperglycemia and obesity by increasing insulin sensitivity in both genetically engineered and DIO mice models. Bilirubin or bilirubin-increasing drugs might be useful as an insulin sensitizer for the treatment of obesity-induced insulin resistance and type 2 diabetes based on its profound anti-ER stress and antiinflammatory properties.

PPARδ binding to heme oxygenase 1 promoter prevents angiotensin II-induced adipocyte dysfunction in Goldblatt hypertensive rats

OBJECTIVE

Renin-angiotensin system (RAS) regulates adipogenic response with adipocyte hypertrophy by increasing oxidative stress. Recent studies have shown the role of peroxisome proliferator-activated receptor-δ (PPARδ) agonist in attenuation of angiotensin II-induced oxidative stress. The aim of this study was to explore a potential mechanistic link between PPARδ and the cytoprotective enzyme heme oxygenase-1 (HO-1) and to elucidate the contribution of HO-1 to the adipocyte regulatory effects of PPARδ agonism in an animal model of enhanced RAS, the Goldblatt 2 kidney 1 clip (2K1C) model.

METHOD

We first established a direct stimulatory effect of the PPARδ agonist (GW 501516) on the HO-1 gene by demonstrating increased luciferase activity in COS-7 cells transfected with a luciferase-HO-1 promoter construct. Sprague-Dawley rats were divided into four groups: sham-operated animals, 2K1C rats and 2K1C rats treated with GW 501516, in the absence or presence of the HO activity inhibitor, stannous mesoporphyrin (SnMP).

RESULTS

2K1C animals had increased visceral adiposity, adipocyte hypertrophy, increased inflammatory cytokines, increased circulatory and adipose tisssue levels of renin and Ang II along with increased adipose tissue gp91 phox expression (P<0.05) when compared with sham-operated animals. Treatment with GW 501516 increased adipose tissue HO-1 and adiponectin levels (P<0.01) along with enhancement of Wnt10b and β-catenin expression. HO-1 induction was accompanied by the decreased expression of Wnt5b, mesoderm specific transcript (mest) and C/EBPα levels and an increased number of small adipocytes (P<0.05). These effects of GW501516 were reversed in 2K1C animals exposed to SnMP (P<0.05).

CONCLUSION

Taken together, our study demonstrates, for the first time, that increased levels of Ang II contribute towards adipose tissue dysregulation, which is abated by PPARδ-mediated upregulation of the heme-HO system. These findings highlight the pivotal role and symbiotic relationship of HO-1, adiponectin and PPARδ in the regulation of metabolic homeostasis in adipose tissues.

Therapeutic roles of heme oxygenase-1 in metabolic diseases: curcumin and resveratrol analogues as possible inducers of heme oxygenase-1

Metabolic diseases, such as insulin resistance, type II diabetes, and obesity, are associated with a low-grade chronic inflammation (inflammatory stress), oxidative stress, and endoplasmic reticulum (ER) stress. Because the integration of these stresses is critical to the pathogenesis of metabolic diseases, agents and cellular molecules that can modulate these stress responses are emerging as potential targets for intervention and treatment of metabolic diseases. It has been recognized that heme oxygenase-1 (HO-1) plays an important role in cellular protection. Because HO-1 can reduce inflammatory stress, oxidative stress, and ER stress, in part by exerting antioxidant, anti-inflammatory, and antiapoptotic effects, HO-1 has been suggested to play important roles in pathogenesis of metabolic diseases. In the present review, we will explore our current understanding of the protective mechanisms of HO-1 in metabolic diseases and present some emerging therapeutic options for HO-1 expression in treating metabolic diseases, together with the therapeutic potential of curcumin and resveratrol analogues that have their ability to induce HO-1 expression.

Taurine attenuates oxidative stress and alleviates cardiac failure in type I diabetic rats

Aim

To investigate cardioprotective effect of taurine in diabetic rats.

Methods

Male Sprague-Dawley rats were assigned randomly into four groups of 15 rats: control group, control + taurine group, streptozotocin (STZ) group, and STZ + taurine group. Rats in STZ and STZ+ taurine groups were treated by a single injection of STZ (70 mg kg^-1, intraperitoneally) dissolved in 0.01 M citrate buffer (pH 4.5) for induction of diabetes, and rats in control and control + taurine groups were treated with the same volume citrate buffer. Taurine was orally administered to rats in control + taurine and STZ + taurine groups daily for 8 weeks. Rats were examined for diabetic cardiomyopathy by left ventricular (LV) hemodynamic analysis. Myocardial oxidative stress was assessed by measuring the activity of superoxide dismutase (SOD) and the level of malondialdehyde (MDA). Myocardial protein kinase B (Akt/PKB) phosphorylation and heme oxygenase-1 (HO-1) protein levels were measured by Western blot in all rats at the end of the study.

Results

In untreated diabetic rats, LV systolic pressure, rate of pressure rise, and rate of pressure fall were decreased, while LV end-diastolic pressure was increased, indicating reduced LV contractility and slowing of LV relaxation. The levels of Akt/PKB phosphorylation and SOD activity were decreased and HO-1 protein expression and MDA content increased. Taurine treatment significantly improved LV systolic and diastolic function, and there were persistent increases in activities of Akt/PKB and SOD, and the level of HO-1 protein.

Conclusion

Taurine treatment ameliorates myocardial function and heart oxidant status, while increasing myocardial Akt/PKB phosphorylation, and HO-1 levels have beneficial effects on diabetic cardiomyopathy.

Increased heme-oxygenase 1 expression in mesenchymal stem cell-derived adipocytes decreases differentiation and lipid accumulation via upregulation of the canonical Wnt signaling cascade

Introduction

Heme oxygenase (HO), a major cytoprotective enzyme, attenuates oxidative stress and obesity. The canonical Wnt signaling cascade plays a pivotal role in the regulation of adipogenesis. The present study examined the interplay between HO-1and the Wnt canonical pathway in the modulation of adipogenesis in mesenchymal stem cell (MSC)-derived adipocytes.

Methods

To verify the role of HO-1 in generating small healthy adipocytes, cobalt protoporphyrin (CoPP), inducer of HO-1, was used during adipocyte differentiation. Lipid accumulation was measured by Oil red O staining and lipid droplet size was measured by BODIPY staining.

Results

During adipogenesis in vitro, differentiating pre-adipocytes display transient increases in the expression of genes involved in canonical Wnt signaling cascade. Increased levels of HO-1 expression and HO activity resulted in elevated levels of β-catenin, pGSK3β, Wnt10b, Pref-1, and shh along with increased levels of adiponectin (P < 0.05). In addition, induction of HO-1 resulted in a reduction in C/EBPα, PPARγ, Peg-1/Mest, aP2, CD36 expression and lipid accumulation (P < 0.05). Suppression of HO-1 gene by siRNA decreased Wnt10b, pGSK3β and β-catenin expression, and increased lipid accumulation. The canonical Wnt responsive genes, IL-8 and SFRP1, were upregulated by CoPP and their expression was decreased by the concurrent administration of tin mesoporphyrin (SnMP), an inhibitor of HO activity. Furthermore, knockdown of Wnt10b gene expression by using siRNA showed increased lipid accumulation, and this effect was not decreased by concurrent treatment with CoPP. Also our results show that blocking the Wnt 10b antagonist, Dickkopf 1 (Dkk-1), by siRNA decreased lipid accumulation and this effect was further enhanced by concurrent administration of CoPP.

Conclusions

This is the first study to demonstrate that HO-1 acts upstream of canonical Wnt signaling cascade and decreases lipogenesis and adipocyte differentiation suggesting that the HO-1 mediated increase in Wnt10b can modulate the adipocyte phenotype by regulating the transcriptional factors that play a role in adipogenesis. This is evidenced by a decrease in lipid accumulation and inflammatory cytokine levels, increased adiponectin levels and elevation of the expression of genes of the canonical Wnt signaling cascade.

Cyclooxygenase-2 dependent metabolism of 20-HETE increases adiposity and adipocyte enlargement in mesenchymal stem cell-derived adipocytes

20-Hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE), a product of the cytochrome P450 (CYP)-catalyzed ω-hydroxylation of arachidonic acid, induces oxidative stress and, in clinical studies, is associated with increased body mass index (BMI) and the metabolic syndrome. This study was designed to examine the effects of exogenous 20-HETE on mesenchymal stem cell (MSC)-derived adipocytes. The expression levels of CYP4A11 and CYP4F2 (major 20-HETE synthases in humans) in MSCs decreased during adipocyte differentiation; however, exogenous administration of 20-HETE (0.1–1 μM) increased adipogenesis in a dose-dependent manner in these cells (P < 0.05). The inability of a 20-HETE analog to reproduce these effects suggested the involvement of a metabolic product of 20-HETE in mediating its pro-adipogenic effects. A cyclooxygenase (COX)-1 selective inhibitor enhanced, whereas a COX-2 selective or a dual COX-1/2 inhibitor attenuated adipogenesis induced by 20-HETE. The COX-derived metabolite of 20-HETE, 20-OH-PGE₂, enhanced adipogenesis and lipid accumulation in MSCs. The pro-adipogenic effects of 20-HETE and 20-OH-PGE₂ resulted in the increased expression of the adipogenic regulators PPARγ and β-catenin in MSC-derived adipocytes. Taken together we show for the first time that 20-HETE-derived COX-2-dependent 20-OH-PGE₂ enhances mature inflamed adipocyte hypertrophy in MSC undergoing adipogenic differentiation.

Topical application of capsaicin reduces visceral adipose fat by affecting adipokine levels in high-fat diet-induced obese mice

OBJECTIVE

Visceral obesity contributes to the development of obesity-related disorders such as diabetes, hyperlipidemia, and fatty liver disease, as well as cardiovascular diseases. In this study, we determined whether topical application of capsaicin can reduce fat accumulation in visceral adipose tissues.

METHODS AND RESULTS

We first observed that topical application of 0.075% capsaicin to male mice fed a high-fat diet significantly reduced weight gain and visceral fat. Fat cells were markedly smaller in the mesenteric and epididymal adipose tissues of mice treated with capsaicin cream. The capsaicin treatment also lowered serum levels of fasting glucose, total cholesterol, and triglycerides. Immunoblot analysis and RT-PCR revealed increased expression of adiponectin and other adipokines including peroxisome proliferator-activated receptor (PPAR) α, PPARγ, visfatin, and adipsin, but reduced expression of tumor necrosis factor-α and IL-6.

CONCLUSIONS

These results indicate that topical application of capsaicin to obese mice limits fat accumulation in adipose tissues and may reduce inflammation and increase insulin sensitivity.

The heme oxygenase 1 inducer (CoPP) protects human cardiac stem cells against apoptosis through activation of the extracellular signal-regulated kinase (ERK)/NRF2 signaling pathway and cytokine release

Intracoronary delivery of c-kit-positive human cardiac stem cells (hCSCs) is a promising approach to repair the infarcted heart, but it is severely limited by the poor survival of donor cells. Cobalt protoporphyrin (CoPP), a well known heme oxygenase 1 inducer, has been used to promote endogenous CO generation and protect against ischemia/reperfusion injury. Therefore, we determined whether preconditioning hCSCs with CoPP promotes CSC survival. c-kit-positive, lineage-negative hCSCs were isolated from human heart biopsies. Lactate dehydrogenase release assays demonstrated that preconditioning CSCs with CoPP markedly enhanced cell survival after oxidative stress induced by H(2)O(2), concomitant with up-regulation of heme oxygenase 1, COX-2, and anti-apoptotic proteins (BCL2, BCL2-A1, and MCL-1) and increased phosphorylation of NRF2. Apoptotic cytometric assays showed that pretreatment of CSCs with CoPP enhanced the cells' resistance to apoptosis induced by oxidative stress. Conversely, knocking down HO-1, COX-2, or NRF2 by shRNA gene silencing abrogated the cytoprotective effects of CoPP. Further, preconditioning CSCs with CoPP led to a global increase in release of cytokines, such as EGF, FGFs, colony-stimulating factors, and chemokine ligand. Conditioned medium from cells pretreated with CoPP conferred naive CSCs remarkable resistance to apoptosis, demonstrating that cytokines released by preconditioned cells play a key role in the anti-apoptotic effects of CoPP. Preconditioning CSCs with CoPP also induced an increase in the phosphorylation of Erk1/2, which are known to modulate multiple pro-survival genes. These results potentially provide a simple and effective strategy to enhance survival of CSCs after transplantation and, therefore, their efficacy in repairing infarcted myocardium.

Heme oxygenase gene targeting to adipocytes attenuates adiposity and vascular dysfunction in mice fed a high-fat diet

We examined the hypothesis that adipocyte dysfunction in mice fed a high-fat (HF) diet can be prevented by lentiviral-mediated and adipocyte specific-targeting delivery of the human heme oxygenase-1 (aP2-HO-1). A bolus intracardial injection of aP2-HO-1 resulted in expression of human HO-1 for up to 9.5 months. Transduction of aP2-HO-1 increased human HO-1 expression in fat tissues without affecting murine HO-1. In mice fed a HF diet, aP2-HO-1 transduction attenuated the increases in body weight, blood glucose, blood pressure, and inflammatory cytokines, as well as the content of both visceral and subcutaneous fat. Transduction of aP2-HO-1 increased the numbers of adipocytes of small cell size (P<0.05), insulin sensitivity (P<0.05), adiponectin levels, as well as vascular relaxation to acetylcholine compared with HF mice administered the aP2-green fluorescent protein. Adipocytes of mice fed a HF diet expressed high levels of peroxisome proliferator activator receptor, aP2, C/EBP, and Wnt5b proteins and displayed marked increases in Peg1/Mesoderm specific transcript (P<0.03). Transduction of aP2-HO-1 lowered the elevated levels of these proteins and increased Sonic hedgehog, Wnt10b, and β-catenin (P<0.05). Inhibition of HO activity by administration of tin mesoporphyrin to HF-fed mice transduced with the aP2-HO-1 reversed the decrease in Peg1/Mesoderm-specific transcript, TNFα, and MCP-1 levels. Collectively, this novel study demonstrates that adipocyte-specific overexpression of HO-1 attenuates HF-mediated adiposity and vascular dysfunction; increases insulin sensitivity; and improves adipocyte function by increasing adiponectin, Shh, and WNT10b, and by decreasing inflammatory cytokines. These effects are reversed by the HO activity inhibitor, stannous mesoporphyrin.

High-fat diet exacerbates renal dysfunction in SHR: reversal by induction of HO-1-adiponectin axis

High-dietary fat intake is a major risk factor for development of metabolic and cardiovascular-renal dysfunction including obesity, coronary artery disease, hypertension, and chronic renal failure. We examined the effect of a high-fat diet on renal function and morphology in spontaneously hypertensive rats (SHR), a phenotype designed to mimic metabolic syndrome. High-fat diet induced increase (P < 0.05) in blood pressure, body weight, and renal lipid deposition in these rats. This increase in body weight was accompanied by elevations (P < 0.05) of blood glucose and low-density lipoprotein (LDL) levels, a decrease (P < 0.05) in adiponectin and increases (P < 0.05) in plasma monocyte chemotactic protein-1 (MCP-1) along with renal macrophage infiltration. These pathophysiological perturbations were attenuated (P < 0.05) by heme oxygenase-1 (HO-1) induction by treatment with cobalt protoporphyrin (CoPP). Further effects of CoPP included increased (P < 0.05) renal expression of adiponectin along with enhancement (P < 0.05) of pAKT, pAMPK, and p-eNOS in SHRs fed a high-fat diet. Prevention of such beneficial effects of CoPP by the concurrent administration of the heme-HO inhibitor stannous mesoporphyrin (SnMP) corroborates the role of HO system in mediating such effects. Taken together, our results demonstrate that high-fat diet induces a metabolic syndrome-like phenotype in hypertensive rats, which is amenable to rescue by increases in HO-1- and adiponectin-dependent pathways.

Endothelial progenitor cell function inversely correlates with long-term glucose control in diabetic patients: association with the attenuation of the heme oxygenase-adiponectin axis

BACKGROUND

Endothelial progenitor cells (EPCs) are attenuated, both in number and functionality, in animal models of chronic cardiovascular and metabolic disorders. This effect has subsequently been linked to the aggravation of long-term morbidity and mortality associated with such disorders. The objective was to examine EPC number and survival in chronic diabetic vs nondiabetic patients in conjunction with the examination of their redox, inflammatory, and antioxidant defense system (Nrf2 genes) status in serum and visceral fat.

METHODS

Visceral adipose tissue from diabetic and nondiabetic patients undergoing coronary artery bypass graft surgery was analyzed for Nrf2-dependent genes. Oxidative stress was evaluated using thiobarbituric acid-reactive substance assay (TBARS). Peripheral blood, collected 1 day prior to surgery, was evaluated for inflammatory cytokines and EPCs.

RESULTS

When compared with controls (P < 0.05), results of the thiobarbituric acid-reactive substance assay were higher in diabetic patients. Although Nrf2-dependent antioxidant proteins (thioredoxin-1 [Trx-1], nicotinamide adenine dinucleotide phosphate [NAD(P)H] quinone oxidoreductase [NQO1], glutathione S-transferase [GST]) were upregulated, heme oxygenase (HO-1) and adiponectin protein expression were lower in the diabetic group (P < 0.05). Serum levels of bilirubin were lower (P < 0.005) while the levels of inflammatory cytokines were higher in diabetic patients (P < 0.05). EPC levels and their colony forming units were significantly lower (P < 0.05) with reduced viability in diabetic patients as compared with nondiabetic patients.

CONCLUSIONS

These results demonstrate for the first time that in diabetic patients, there is an inadequate heme oxygenase-adiponectin axis response, which could compromise the compensatory antioxidant and anti-inflammatory effects consequently contributing toward EPC dysfunction in these patients.

Sensing endoplasmic reticulum stress by protein kinase RNA-like endoplasmic reticulum kinase promotes adaptive mitochondrial DNA biogenesis and cell survival via heme oxygenase-1/carbon monoxide activity

Endoplasmic reticulum (ER) stress activates the adaptive unfolded protein response, allowing cells to recover folding capacity in the organelle. However, the overwhelming response to severe damage results in apoptotic cell death. Because of the physical proximity between ER and mitochondria, a functional interrelationship between these two organelles, including mitochondrial ATP production and apoptosis, has been suggested. The adaptive response to ER stress includes the maintenance of cellular energetics, which eventually determines cell fate. We previously demonstrated that heme oxygenase-1 (HO-1) activity protects cells against ER stress in a protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent pathway. Here, we provide evidence that PERK-mediated induction of HO-1 in murine macrophages, RAW264.7, relays ER stress to mitochondrial DNA (mtDNA) replication and function. ER stress induced by thapsigargin treatments (10-100 nM) resulted in a 2-fold increase in mtDNA contents compared with that in the untreated control. HO-1 activity on ER stress is proven to be critical for mitochondrial integrity because chemical inhibition (zinc protoporphyrin, 5-20 μM) and genetic depletion of HO-1 by small interference RNA transfection suppress the activation of transcription factors for mitochondrial biogenesis. Carbon monoxide (CO), an enzymatic by-product of HO-1 activity is responsible for the function of HO-1. Limited bioavailability of CO by hemoglobin treatment triggers cell death with a concomitant decline in ATP production. Approximately 78.1% of RAW264.7 cells were damaged in the presence of hemoglobin compared with the percentage of injured cells (26.9%) under ER stress alone. Mitochondrial generation of ATP levels significantly declined when CO availability was limited under prolonged ER stress. Taken together, these results suggest that the cellular HO-1/CO system conveys ER stress to cell survival signals from mitochondria via both the activation of transcriptional factors and functional integrity of mtDNA.

Heme oxygenase (HO-1) rescue of adipocyte dysfunction in HO-2 deficient mice via recruitment of epoxyeicosatrienoic acids (EETs) and adiponectin

BACKGROUND/AIMS

HO-1 and EETs are functionally linked and their interactions influence body weight, insulin sensitivity, and serum levels of inflammatory cytokines in metabolic syndrome phenotype of HO-2 null mice. The HO-2 isozyme is essential for regulating physiological levels of ROS. Recent studies have suggested a potential role of EET in modifying adipocyte differentiation through up-regulation of HO-1-adiponectin-AkT signaling in human mesenchymal stem cells (MSCs). Our aim was to examine the consequences of HO deficiency on MSC-derived adipogenesis in vitro using MSC derived from HO-2 null and WT mice in vivo.

METHODS

Four-month-old HO-2 null (HO-2(-/-)) and B6/129SF2/J (WT) mice were divided into three groups (four mice/group): WT, HO-2(-/-), and HO-2(-/-) +CoPP. Adipogenesis was performed on purified MSC-derived adipocytes cultured in adipogenic differentiation media and an EET-agonist was added every 3 days.

RESULTS

HO-2 depletion of MSC adipocytes resulted in increased adipogenesis (p<0.01) and increased levels of inflammatory cytokines including (TNF)-alpha (p<0.05), (MCP)-1 (p<0.05), and (IL-1)-beta (p<0.05). These results were accompanied by decreases in HO-1 (p<0.05) and subsequently EET and HO activity (p<0.05). Up-regulation of HO-1 resulted in decreased MSC-derived adipocyte differentiation, decreased production of TNF-alpha and MCP-1 and increased levels of adiponectin (p<0.05). Cyp2J5 (p<0.05), HO-1 (p<0.05), and adiponectin mRNA levels (p<0.05) were also decreased in visceral adipose tissue isolated from HO-2 null compared to WT mice. EET agonist stimulation of MSC adipocytes derived from HO-2 null mice yielded similar results.

CONCLUSION

Increased levels of EET and HO-1 are essential for protection against the adverse effects of adipocyte hypertrophy and the ensuing metabolic syndrome. These results offer a portal into therapeutic approaches for the prevention of the metabolic syndrome.

Oxidative stress and heme oxygenase-1 regulated human mesenchymal stem cells differentiation

This paper describes the effect of increased expression of HO-1 protein and increased levels of HO activity on differentiation of bone-marrow-derived human MSCs. MSCs are multipotent cells that proliferate and differentiate into many different cell types including adipocytes and osteoblasts. HO, the rate-limiting enzyme in heme catabolism, plays an important role during MSCs differentiation. HO catalyzes the stereospecific degradation of heme to biliverdin, with the concurrent release of iron and carbon monoxide. Upregulation of HO-1 expression and increased HO activity are essential for MSC growth and differentiation to the osteoblast lineage consistent with the role of HO-1 in hematopoietic stem cell differentiation. HO-1 participates in the MSC differentiation process shifting the balance of MSC differentiation in favor of the osteoblast lineage by decreasing PPARγ and increasing osteogenic markers such as alkaline phosphatase and BMP-2. In this paper, we define HO-1 as a target molecule in the modulation of adipogenesis and osteogenesis from MSCs and examine the role of the HO system in diabetes, inflammation, osteoporosis, hypertension, and other pathologies, a burgeoning area of research.

ApoA1: mimetic peptide reverses adipocyte dysfunction in vivo and in vitro via an increase in heme oxygenase (HO-1) and Wnt10b

Insulin resistance is a risk factor in the development of type 2 diabetes and is a major cause of atherosclerosis. Reduction in heme oxygenase (HO-1) has been shown to exacerbate vascular dysfunction and insulin resistance in obese mice and involves a decrease in adiponectin levels. Adiponectin is released from mesenchymal stem cell (MSC)-derived adipocytes, its levels are decreased in type 2 diabetes. We hypothesized that the apoA1 mimetic peptide, L-4F, will target the expression of the HO-1-adiponectin axis and reverse adipocyte dysfunction both in vivo and in vitro. The administration of L-4F [2 mg/Kg/daily (i.p.) for 4-week to 8-week-old obese (ob) mice restored adipocyte function, increased adiponectin release (p < 0.05) and decreased the levels of IL-1 and IL-6 (p < 0.05)]. These perturbations were associated with an increase in insulin sensitivity (p < 0.01 vs. untreated ob mice) and decreased glucose levels (309 + 42 vs. 201 + 8 mg/d after L-4F treatment). Treatment of both mesenchymal stem cell (MSC)-derived adipocytes with L-4F (50 μg/ml) increased adiponectin (p < 0.05), decreased IL-1 and IL-6 (p < 0.05) levels and increased MSC-derived adipocyte cell numbers by 50% in S phase (p < 0.05). MSC-derived adipocytes treated with L-4F increased WNT10b and decreased Peg 1/Mest. Inhibition of HO activity reversed the decrease in the adipogenic response gene, Peg 1/Mest. An increase of HO-1 expression by L-4F increased insulin-receptor phosphorylation. These findings support the hypothesis that L-4F increases early adipocyte markers, HO-1-adiponectin, WNT10b and decreases Peg1/Mest, negative regulators of adipocyte differentiation.

Reciprocal Effects of Oxidative Stress on Heme Oxygenase Expression and Activity Contributes to Reno-Vascular Abnormalities in EC-SOD Knockout Mice

Heme oxygenase (HO) system is one of the key regulators of cellular redox homeostasis which responds to oxidative stress (ROS) via HO-1 induction. However, recent reports have suggested an inhibitory effect of ROS on HO activity. In light of these conflicting reports, this study was designed to evaluate effects of chronic oxidative stress on HO system and its role in contributing towards patho-physiological abnormalities observed in extracellular superoxide dismutase (EC-SOD, SOD3) KO animals. Experiments were performed in WT and EC-SOD((-/-)) mice treated with and without HO inducer, cobalt protoporphyrin (CoPP). EC-SOD((-/-)) mice exhibited oxidative stress, renal histopathological abnormalities, elevated blood pressure, impaired endothelial function, reduced p-eNOS, p-AKT and increased HO-1 expression; although, HO activity was significantly (P < 0.05) attenuated along with attenuation of serum adiponectin and vascular epoxide levels (P < 0.05). CoPP, in EC-SOD((-/-)) mice, enhanced HO activity (P < 0.05) and reversed aforementioned pathophysiological abnormalities along with restoration of vascular EET, p-eNOS, p-AKT and serum adiponectin levels in these animals. Taken together our results implicate a causative role of insufficient activation of heme-HO-adiponectin system in pathophysiological abnormalities observed in animal models of chronic oxidative stress such as EC-SOD((-/-)) mice.

Epoxyeicosatrienoic acids and heme oxygenase-1 interaction attenuates diabetes and metabolic syndrome complications

MSCs are considered to be the natural precursors to adipocyte development through the process of adipogenesis. A link has been established between decreased protective effects of EETs or HO-1 and their interaction in metabolic syndrome. Decreases in HO-1 or EET were associated with an increase in adipocyte stem cell differentiation and increased levels of inflammatory cytokines. EET agonist (AKR-I-27-28) inhibited MSC-derived adipocytes and decreased the levels of inflammatory cytokines. We further describe the role of CYP-epoxygenase expression, HO expression, and circulating cytokine levels in an obese mouse, ob/ob(-/-) mouse model. Ex vivo measurements of EET expression within MSCs derived from ob/ob(-/-) showed decreased levels of EETs that were increased by HO induction. This review demonstrates that suppression of HO and EET systems exist in MSCs prior to the development of adipocyte dysfunction. Further, adipocyte dysfunction can be ameliorated by induction of HO-1 and CYP-epoxygenase, i.e. EET.

Stress in obesity and associated metabolic and cardiovascular disorders

Obesity has significant implications for healthcare, since it is a major risk factor for both type 2 diabetes and the metabolic syndrome. This syndrome is a common and complex disorder combining obesity, dyslipidemia, hypertension, and insulin resistance. It is associated with high atherosclerotic cardiovascular risk, which can only partially be explained by its components. Therefore, to explain how obesity contributes to the development of metabolic and cardiovascular disorders, more and better insight is required into the effects of personal and environmental stress on disease processes. In this paper, we show that obesity is a chronic inflammatory disease, which has many molecular mechanisms in common with atherosclerosis. Furthermore, we focus on the role of oxidative stress associated with obesity in the development of the metabolic syndrome. We discuss how several stress conditions are related to inflammation and oxidative stress in association with obesity and its complications. We also emphasize the relation between stress conditions and the deregulation of epigenetic control mechanisms by means of microRNAs and show how this impairment further contributes to the development of obesity, closing the vicious circle. Finally, we discuss the limitations of current anti-inflammation and antioxidant therapy to treat obesity.

Obesity-related glomerulopathy and podocyte injury: a mini review

Obesity-related glomerulopathy (ORG) is morphologically defined as focal segmental glomerulosclerosis and glomerulomegaly. Podocyte hypertrophy and reduced density are related to proteinuria which in a portion of patients is in the nephrotic range and evolvs towards renal failure. This article reviews the pathogenetic mechanisms of podocyte injury or dysfunction and lists new possible antiproteinuric strategies based on pharmaceutical targeting of the reported pathogenetic mechanisms. The pathogenetic mechnisms discussed include: renin angiotensin system, plasminogen activation inhibitor-1 (PAI-1), lipid metabolism, adiponectin, macrophages and proinflammatory cytokines, oxidative stress. The proposed antiproteinuric strategies include: AT2 receptor blockers; adipokine complement C19 TNF-related protein-1 blocker; selective PAI-1 inhibitor; farnesoid x receptor activation; increase of circulating adiponectin; selective antiinflammatory drugs; more potent antioxidants (Heme oxigenase, NOX4 inhibitors). However, because ORG is a rare disease, the need for a long term pharmaceutical approach in obese proteinuric patients should be carefully evaluated and limited to the cases with progressive loss of renal function.

EET agonist prevents adiposity and vascular dysfunction in rats fed a high fat diet via a decrease in Bach 1 and an increase in HO-1 levels

Recent reports have shown interplay between EETs (epoxides) and the heme oxygenase (HO) system in attenuating adipogenesis in cell culture models; prompting an examination of the effectiveness of EET agonist on obesity and associated cardio-metabolic dysfunction. Patho-physiological effects of an EET agonist (NUDSA) were contrasted in the absence and in the presence of stannous mesoporphyrin (an HO inhibitor) in SD rats fed a high fat (58%, HF) for 16 weeks. Animals on HF diet exhibited enhanced oxidative stress, increased levels of inflammatory cytokines and decreased levels of adiponectin along with reduced vascular and adipose tissue levels of EETs, HO-1; as compared to control rats (11% dietary fat). Treatment with NUDSA not only reversed serum adiponectin and vascular and adipose tissue levels of EETs and HO-1, but also, decreased blood pressure, subcutaneous and visceral fat content and serum TNFα and IL-6 levels in rats on HF diet. Aortic endothelial function, peNOS expression and adipose tissue markers of energy homeostasis i.e. pAMPK, Sirt1 and FAS, impaired in rats fed a HF diet, were restored in animals treated with this EET agonist. That NUDSA enhanced HO-1 expression, was accompanied by increase in p-GSK-3β and pAKT levels along with attenuation of adipose tissue levels of Bach 1--the transcriptional suppresser of HO-1 expression. Prevention of these beneficial effects of NUDSA, in animals on HF diet and concurrently exposed to NUDSA and SnMP, supports the role of EET-HO interaction in mediating such effects. Taken together, our findings suggest that the EETs stimulate HO-1 expression via suppression of Bach 1 and interplay of these two systems affords vascular and metabolic protection in diet induced obesity.

High fat diet enhances cardiac abnormalities in SHR rats: Protective role of heme oxygenase-adiponectin axis

BACKGROUND

High dietary fat intake is a major risk factor for development of cardiovascular and metabolic dysfunction including obesity, cardiomyopathy and hypertension.

METHODS

The present study was designed to examine effect of high fat (HF) diet on cardio-vascular structure and function in spontaneously hypertensive rats (SHR), fed HF diet for 15 weeks, a phenotype designed to mimic metabolic syndrome.

RESULTS

Development of metabolic syndrome like phenotype was confirmed using parameters, including body weight, total cholesterol and blood pressure levels. High fat diet impaired vascular relaxation by acetylcholine and exacerbated cardiac dysfunction in SHRs as evidenced by lower left ventricular function, and higher coronary resistance (CR) as compared to controls (p < 0.05). The histological examination revealed significant myocardial and peri-vascular fibrosis in hearts from SHRs on HF diet. This cardiac dysfunction was associated with increased levels of inflammatory cytokines, COX-2, NOX-2, TxB2 expression and increase in superoxide (O2-) levels in SHR fed a HF diet (p < 0.05). HO-1 induction via cobalt-protoporphyrin (CoPP,3 mg/kg), in HF fed rats, not only improved cardiac performance parameters, but also prevented myocardial and perivascular fibrosis. These effects of CoPP were accompanied by enhanced levels of cardiac adiponectin levels, pAMPK, peNOS and iNOS expression; otherwise significantly attenuated (p < 0.05) in HF fed SHRs. Prevention of such beneficial effects of CoPP by the concurrent administration of the HO inhibitor stannic mesoporphyrin (SnMP) corroborates the role of HO system in mediating such effects.

CONCLUSION

In conclusion, this novel study demonstrates that up-regulation of HO-1 improves cardiac and vascular dysfunction by blunting oxidative stress, COX-2 levels and increasing adiponectin levels in hypertensive rats on HF diet.

Identification and validation of novel adipokines released from primary human adipocytes

Adipose tissue is a major endocrine organ, releasing signaling and mediator proteins, termed adipokines, via which adipose tissue communicates with other organs. Expansion of adipose tissue in obesity alters adipokine secretion, which may contribute to the development of metabolic diseases. Although recent profiling studies have identified numerous adipokines, the amount of overlap from these studies indicates that the adipokinome is still incompletely characterized. Therefore, we conducted a complementary protein profiling on concentrated conditioned medium derived from primary human adipocytes. SDS-PAGE/liquid chromatography-electrospray ionization tandem MS and two-dimensional SDS-PAGE/matrix-assisted laser desorption ionization/time of flight MS identified 347 proteins, 263 of which were predicted to be secreted. Fourty-four proteins were identified as novel adipokines. Furthermore, we validated the regulation and release of selected adipokines in primary human adipocytes and in serum and adipose tissue biopsies from morbidly obese patients and normal-weight controls. Validation experiments conducted for complement factor H, αB-crystallin, cartilage intermediate-layer protein, and heme oxygenase-1 show that the release and expression of these factors in adipocytes is regulated by differentiation and stimuli, which affect insulin sensitivity, as well as by obesity. Heme oxygenase-1 especially reveals to be a novel adipokine of interest. In vivo, circulating levels and adipose tissue expression of heme oxygenase-1 are significantly increased in obese subjects compared with lean controls. Collectively, our profiling study of the human adipokinome expands the list of adipokines and further highlights the pivotal role of adipokines in the regulation of multiple biological processes within adipose tissue and their potential dysregulation in obesity.

Crosstalk between EET and HO-1 downregulates Bach1 and adipogenic marker expression in mesenchymal stem cell derived adipocytes

Epoxygenase activity and synthesis of epoxyeicosatrienoic acids (EETs) have emerged as important modulators of obesity and diabetes. We examined the effect of the EET-agonist 12-(3-hexylureido)dodec-8(2) enoic acid on mesenchymal stem cell (MSC) derived adipocytes proliferation and differentiation. MSCs expressed substantial levels of EETs and inhibition of soluble epoxide hydrolase (sEH) increased the level of EETs and decreased adipogenesis. EET agonist treatment increased HO-1 expression by inhibiting a negative regulator of HO-1 expression, Bach-1. EET treatment also increased βcatenin and pACC levels while decreasing PPARγ C/EBPα and fatty acid synthase levels. These changes were manifested by a decrease in the number of large inflammatory adipocytes, TNFα, IFNγ and IL-1α, but an increase in small adipocytes and in adiponectin levels. In summary, EET agonist treatment inhibits adipogenesis and decreases the levels of inflammatory cytokines suggesting the potential action of EETs as intracellular lipid signaling modulators of adipogenesis and adiponectin.

Insulin-induced oxidative stress up-regulates heme oxygenase-1 via diverse signaling cascades in the C2 skeletal myoblast cell line

Impaired insulin sensitivity (insulin resistance) is a common denominator in many metabolic disorders, exerting pleiotropic effects on skeletal muscle, liver, and adipose tissue function. Heme oxygenase-1 (HOX-1), the rate-limiting enzyme in heme catabolism, has recently been shown to confer an antidiabetic effect while regulating cellular redox-buffering capacity. Therefore, in the present study, we probed into the mechanisms underlying the effect of insulin on HOX-1 in C2 skeletal myoblasts. Hence, insulin was found to suppress C2 myoblasts viability via stimulation of oxidative stress, with HOX-1 counteracting this action. Insulin induced HOX-1 expression in a time- and dose-dependent manner, an effect attenuated by selective inhibitors of ERK1/2 (PD98059), Src (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d] pyrimidine), and c-Jun terminal kinases 1 and 2 (SP600125) pathways. Furthermore, nuclear factor-κB role in insulin-induced HOX-1 up-regulation was verified, with ERK1/2, Src, and c-Jun terminal kinases 1 and 2 mediating p65-nuclear factor-κB subunit phosphorylation. Overall, our novel findings highlight for the first time the transduction mechanisms mediating HOX-1 induction in insulin-treated C2 myoblasts. This effect was established to be cell type specific because insulin failed to promote HOX-1 expression in HepG2 hepatoma cells. Deciphering the signaling networks involved in insulin-stimulated HOX-1 up-regulation is of prominent significance because it may potentially contribute to elucidation of the mechanisms involved in associated metabolic pathologies.

Liver and pancreatic fat content and metabolism in healthy monozygotic twins with discordant physical activity

BACKGROUND & AIMS

Ectopic fat in muscle and liver is linked to obesity and type 2 diabetes. Recently, pancreatic lipid accumulation has also been associated with β-cell dysfunction and reduced insulin production, leading to the development of type 2 diabetes. Physical exercise training has been shown to attenuate β-cell dysfunction in patients, but little is known about its effects on pancreatic and hepatic fat accumulation. In this study, we validated in-vivo proton magnetic resonance spectroscopy ((1)H MRS) in pancreatic fat measurement with biochemical measurements in a pig model. Thereafter, the effects of increased physical activity on the amounts of pancreatic and liver fat were studied in eight monozygotic twin pairs who have discordant physical activity and fitness.

METHODS

Pancreatic fat content was studied in 15 pigs using (1)H MRS and/or biochemical analyses. In addition, liver and pancreatic fat were assessed using (1)H MRS in eight monozygotic male twin pairs with 18% mean difference in VO(2max) between the twin brothers.

RESULTS

Twins with higher physical fitness had 23% less liver fat (1.3±1.3% vs. 2.1±2.6%, p=0.022) but no such difference was observed in the pancreatic fat (8.2±9.3% vs. 9.8±8.5%, respectively, p=0.3). Hepatic fat content was inversely associated with VO(2max). A positive association was found between pancreatic and liver fat contents (β=5.18, p=0.012). Pancreatic fat content was also associated with insulin sensitivity indexes and plasma adiponectin and glutamyltransferase concentrations.

CONCLUSIONS

Pancreatic fat content is associated with insulin resistance and hepatic fat content. An active lifestyle seems to beneficially influence hepatic fat metabolism.

Induction of heme oxygenase-1 protects against nutritional fibrosing steatohepatitis in mice

BACKGROUND

Heme oxygenase-1 (HO-1), an antioxidant defense enzyme, has been shown to protect against oxidant-induced liver injury. However, its role on liver fibrosis remains unclear. This study aims to elucidate the effect and the mechanism of HO-1 in nutritional fibrosing steatohepatitis in mice.

METHODS

Male C57BL/6J mice were fed with a methionine-choline deficient (MCD) diet for eight weeks to induce hepatic fibrosis. HO-1 chemical inducer (hemin), HO-1 chemical inhibitor zinc protoporphyrin IX (ZnPP-IX) and/or adenovirus carrying HO-1 gene (Ad-HO-1) were administered to mice, respectively. Liver injury was assessed by serum ALT, AST levels and histological examination; hepatic lipid peroxides levels were determined; the expression levels of several fibrogenic related genes were assayed by real-time quantitative PCR and Western blot.

RESULTS

MCD feeding mice showed progressive hepatic injury including hepatic steatosis, inflammatory infiltration and fibrosis. Induction of HO-1 by hemin or Ad-HO-1 significantly attenuated the severity of liver injury. This effect was associated with the up-regulation of HO-1, reduction of hepatic lipid peroxides levels, down-regulation of inflammatory factors tumor necrosis factor-alpha, interleukin-6 and suppressor of cytokine signaling-1 as well as the pro-fibrotic genes alpha-smooth muscle actin, transforming growth factor-β1, matrix metallopeptidase-2 and matrix metallopeptidase-9. A contrary effect was observed in mice treated with ZnPP-IX.

CONCLUSIONS

The present study provided the evidence for the protective role of HO-1 in ameliorating MCD diet-induced fibrosing steatohepatitis. Modulation of HO-1 expression might serve as a therapeutic approach for fibrotic steatohepatitis.

Insulin up-regulates heme oxygenase-1 expression in 3T3-L1 adipocytes via PI3-kinase- and PKC-dependent pathways and heme oxygenase-1-associated microRNA downregulation

Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme catabolism, has antioxidant, antiinflammatory, and antiapoptotic effects in many physiological systems. HO-1 activity in obese mice is lower than in controls, and a sustained increase in HO-1 protein levels ameliorates insulin resistance and compensatory hyperinsulinemia. In the present study, we explored the regulatory effect of insulin on HO-1 expression in 3T3-L1 adipocytes and the underlying mechanism. We investigated the time- and dose-effect of insulin on HO-1 expression in 3T3-L1 adipocytes. Using specific inhibitors acting on insulin signaling pathways, we clarified the involvement of insulin downstream signaling molecules in insulin-regulated HO-1 expression. We also investigated the involvement of microRNAs (miRNAs) in insulin-regulated HO-1 expression using microarray and real-time RT-PCR assays. In an in vivo study, we performed insulin/glucose coinfusion in rats to increase circulating insulin levels for 8 h, then measured adipocyte HO-1 expression. Insulin caused a significant increase in HO-1 expression that was time- and dose-dependent, and this effect was blocked by inhibition of phosphatidylinositol 3 (PI3)-kinase activation using LY294002 (50 μM) or of protein kinase C activation using Ro-318220 (2 μM), but not by an Akt inhibitor, triciribine (10 μM). Furthermore, incubation of 3T3-L1 adipocytes with 100 nm insulin resulted in a significant decrease in levels of the miRNAs mir-155, mir-183, and mir-872, and this effect was also blocked by pretreatment with LY294002 or Ro-318220, but not triciribine. An in vivo study in rats showed that 8 h of a hyperinsulinemic euglycemic state resulted in a significant increase in adipocyte HO-1 expression. In conclusion, insulin increases HO-1 protein expression in 3T3-L1 adipocytes via PI3-kinase and protein kinase C-dependent pathways and miRNAs down-regulation.

Lentiviral-human heme oxygenase targeting endothelium improved vascular function in angiotensin II animal model of hypertension

We examined the hypothesis that vascular and renal dysfunction caused by angiotensin II (Ang II) through increased levels of blood pressure, inflammatory cytokines, and oxidative stress in Sprague-Dawley rats can be prevented by lentiviral-mediated delivery of endothelial heme oxygenase (HO)-1. We targeted the vascular endothelium using a lentiviral construct expressing human HO-1 under the control of the endothelium-specific promoter VE-cadherin (VECAD-HO-1) and examined the effect of long-term human HO-1 expression on blood pressure in Ang II-mediated increases in blood pressure and oxidant stress. A bolus injection of VECAD-HO-1 into the renal artery resulted in expression of human HO-1 for up to 6-9 weeks. Sprague-Dawley rats were implanted with Ang II minipumps and treated with lentivirus carrying either the HO-1 or green fluorescent protein. Renal tissue from VECAD-HO-1-transduced rats expresses human HO-1 mRNA and proteins without an effect on endogenous HO-1. Infusion of Ang II increased blood pressure (p < 0.001) but decreased vascular relaxation in response to acetylcholine, endothelial nitric oxide synthase (eNOS) and phosphorylated eNOS (peNOS) levels, and renal and plasma levels of adiponectin (p < 0.05); in contrast, plasma tumor necrosis factor-α and monocyte chemoattractant protein-1 levels increased. Ang II-treated animals had higher levels of superoxide anion and inducible nitric oxide synthase and increased urinary protein and plasma creatinine levels. Lentiviral transduction with the VECAD-HO-1 construct attenuated the increase in blood pressure (p < 0.05), improved vascular relaxation, increased plasma adiponectin, and prevented the elevation in urinary protein and plasma creatinine in Ang II-treated rats. Endothelial-specific expression of HO-1 also reduced oxidative stress and levels of inflammatory cytokines resulting in increased expression of the anti-apoptotic proteins phosphorylated AKT, phosphorylated AMP-activated protein kinase, peNOS, and eNOS. Collectively, these findings demonstrate that endothelial-specific increases in HO-1 expression attenuate Ang II hypertension and the associated vascular dysfunction that is associated with increases in adiponectin and peNOS and reductions in oxidative stress and levels of inflammatory cytokines.

Adipocyte heme oxygenase-1 induction attenuates metabolic syndrome in both male and female obese mice

Increases in visceral fat are associated with increased inflammation, dyslipidemia, insulin resistance, glucose intolerance, and vascular dysfunction. We examined the effect of the potent heme oxygenase (HO)-1 inducer, cobalt protoporphyrin (CoPP), on regulation of adiposity and glucose levels in both female and male obese mice. Both lean and obese mice were administered CoPP intraperitoneally (3 mg/kg once per week) for 6 weeks. Serum levels of adiponectin, tumor necrosis factor α (TNFa), interleukin (IL)-1β and IL-6, and HO-1, PPARγ, pAKT, and pAMPK protein expression in adipocytes and vascular tissue were measured. While female obese mice continued to gain weight at a rate similar to controls, induction of HO-1 slowed the rate of weight gain in male obese mice. HO-1 induction led to lowered blood pressure levels in obese male and female mice similar to that of lean male and female mice. HO-1 induction also produced a significant decrease in the plasma levels of IL-6, TNFα, IL-1β, and fasting glucose of obese females compared to untreated female obese mice. HO-1 induction increased the number and decreased the size of adipocytes of obese animals. HO-1 induction increased adiponectin, pAKT, pAMPK, and PPARγ levels in adipocyte of obese animals. Induction of HO-1 in adipocytes was associated with an increase in adiponectin and a reduction in inflammatory cytokines. These findings offer the possibility of treating not only hypertension, but also other detrimental metabolic consequences of obesity including insulin resistance and dyslipidemia in obese populations by induction of HO-1 in adipocytes.

Epoxyeicosatrienoic acid agonist regulates human mesenchymal stem cell-derived adipocytes through activation of HO-1-pAKT signaling and a decrease in PPARγ

Human mesenchymal stem cells (MSCs) expressed substantial levels of CYP2J2, a major CYP450 involved in epoxyeicosatrienoic acid (EET) formation. MSCs synthesized significant levels of EETs (65.8 ± 5.8 pg/mg protein) and dihydroxyeicosatrienoic acids (DHETs) (15.83 ± 1.62 pg/mg protein), suggesting the presence of soluble epoxide hydrolase (sEH). The addition of an sEH inhibitor to MSC culture decreased adipogenesis. EETs decreased MSC-derived adipocytes in a concentration-dependent manner, 8,9- and 14,15-EET having the maximum reductive effect on adipogenesis. We examined the effect of 12-(3-hexylureido)dodec-8(Z)-enoic acid, an EET agonist, on MSC-derived adipocytes and demonstrated an increased number of healthy small adipocytes, attenuated fatty acid synthase (FAS) levels (P < 0.01), and reduced PPARγ, C/EBPα, FAS, and lipid accumulation (P < 0.05). These effects were accompanied by increased levels of heme oxygenase (HO)-1 and adiponectin (P < 0.05), and increased glucose uptake (P < 0.05). Inhibition of HO activity or AKT by tin mesoporphyrin (SnMP) and LY2940002, respectively, reversed EET-induced inhibition of adipogenesis, suggesting that activation of the HO-1-adiponectin axis underlies EET effect in MSCs. These findings indicate that EETs decrease MSC-derived adipocyte stem cell differentiation by upregulation of HO-1-adiponectin-AKT signaling and play essential roles in the regulation of adipocyte differentiation by inhibiting PPARγ, C/EBPα, and FAS and in stem cell development. These novel observations highlight the seminal role of arachidonic acid metabolism in MSCs and suggest that an EET agonist may have potential therapeutic use in the treatment of dyslipidemia, diabetes, and the metabolic syndrome.

Adiponectin-mediated heme oxygenase-1 induction protects against iron-induced liver injury via a PPARα dependent mechanism

Protective effects of adiponectin (APN; an adipocytokine) were shown against various oxidative challenges; however, its therapeutic implications and the mechanisms underlying hepatic iron overload remain unclear. Herein, we show that the deleterious effects of iron dextran on liver function and iron deposition were significantly reversed by adiponectin gene therapy, which was accompanied by AMP-activated protein kinase (AMPK) phosphorylation and heme oxygenase (HO)-1 induction. Furthermore, AMPK-mediated peroxisome proliferator-activated receptor-α (PPARα) activation by APN was ascribable to HO-1 induction. Additionally, we revealed direct transcriptional regulation of HO-1 by the binding of PPARα to a PPAR-responsive element (PPRE) by various experimental assessments. Interestingly, overexpression of HO-1 in hepatocytes mimicked the protective effect of APN in attenuating iron-mediated injury, whereas it was abolished by SnPP and small interfering HO-1. Furthermore, bilirubin, the end-product of the HO-1 reaction, but not CO, protected hepatocytes from iron dextran-mediated caspase activation. Herein, we demonstrate a novel functional PPRE in the promoter regions of HO-1, and APN-mediated HO-1 induction elicited an antiapoptotic effect and a decrease in iron deposition in hepatocytes subjected to iron challenge.

Prolactin regulatory element-binding protein involved in cAMP-mediated suppression of adiponectin gene

Adiponectin (ApN) has several protective effects against diabetes and atherosclerosis. However, the detailed mechanisms of the regulation of the ApN gene have not yet been clarified. Prolactin regulatory element-binding (PREB) protein has been identified as a factor that regulates insulin gene expression in the pancreas. PREB is located not only in the pancreas but also in adipose tissue; however, its role in adipose tissue is not known. To analyse the effects of PREB on ApN gene transcription, we employed a reporter gene assay and electrophoretic mobility shift assay (EMSA). In the cells expressing or knocking down the PREB, ApN expression was determined. PREB was located mainly in the nuclei of adipose tissue and its cell line, 3T3-L1 cells. The nuclear extract contained ApN promoter-binding activity that was super-shifted by PREB antiserum in EMSA studies. In the 3T3-L1 cells, the co-expression of PREB and the ApN promoter inhibited the activity of the latter. The addition of cAMP to the cells increased PREB expression in a dose-dependent manner. A deletional analysis of the ApN promoter showed that the PREB-responsive cis-element in the ApN promoter mediated the transcriptional effect of PREB, whereas a mutant of this motif in the ApN promoter abrogated the effect of PREB, as well as that of cAMP. Furthermore, cells expressing or knocking down PREB exhibited decreased and increased ApN expression, respectively. These results demonstrate that PREB may contribute to the regulation of ApN gene transcription, in response to cAMP activation in adipocytes.

Role of heme oxygenase in inflammation, insulin-signalling, diabetes and obesity

Diabetes and obesity are chronic conditions associated with elevated oxidative/inflammatory activities with a continuum of tissue insults leading to more severe cardiometabolic and renal complications including myocardial infarction and end-stage-renal damage. A common denominator of these chronic conditions is the enhanced the levels of cytokines like tumour necrosis factor-alpha (TNF-α), interleukin (IL-6), IL-1β and resistin, which in turn activates the c-Jun-N-terminal kinase (JNK) and NF-κB pathways, creating a vicious cycle that exacerbates insulin resistance, type-2 diabetes and related complications. Emerging evidence indicates that heme oxygenase (HO) inducers are endowed with potent anti-diabetic and insulin sensitizing effects besides their ability to suppress immune/inflammatory response. Importantly, the HO system abates inflammation through several mechanisms including the suppression of macrophage-infiltration and abrogation of oxidative/inflammatory transcription factors like NF-κB, JNK and activating protein-1. This review highlights the mechanisms by which the HO system potentiates insulin signalling, with particular emphasis on HO-mediated suppression of oxidative and inflammatory insults. The HO system could be explored in the search for novel remedies against cardiometabolic diseases and their complications.

Overexpression of heme oxygenase-1 increases human osteoblast stem cell differentiation

Human bone marrow mesenchymal stem cells (MSCs) are pleiotrophic cells that differentiate to either adipocytes or osteoblasts as a result of crosstalk by specific signaling pathways including heme oxygenase (HO)-1/-2 expression. We examined the effect of inducers of HO-1 expression and inhibitors of HO activity on MSC differentiation to the osteoblast and following high glucose exposure. MSC cultured in osteogenic medium increased expression of osteonectin, Runt-related transcription factor 2 (RUNX-2), osteocalcin, and alkaline phosphatase. HO-1 expression during differentiation was initially decreased and then followed by a rebound increase after 15 days of culture. Additionally, the effect of HO-1 on osteoblasts appears different to that seen in adipocyte stem cells. On addition of a cobalt compound, the resultant induction of HO-1 decreases adipogenesis. Moreover, glucose (30 mM) inhibited osteoblast differentiation, as evidenced by decreased bone morphogenetic protein (BMP)-2, osteonectin, osteocalcin, and osteoprotegerin (OPG). In contrast, MSC-derived adipocytes were increased by glucose. Increased HO-1 expression increased the levels of osteonectin, OPG, and BMP-2. Inhibition of HO activity prevented the increase in osteonectin and potentiated the decrease of osteocalcin and OPG in cells exposed to high glucose levels. Furthermore, targeting HO-1 expression increased pAMPK and endothelial nitric oxide synthase (eNOS) and restored osteoblastic markers. Our findings suggest that targeting HO-1 gene expression attenuates the hyperglycemia-mediated decrease in MSC-derived osteoblast differentiation. Finally, the mechanism underlying the HO-1-specific cell effect on osteoblasts and adipocytes is yet to be explored. Thus, the targeting of HO-1 gene expression presents a portal to increase osteoblast function and differentiation and attenuate osteoporosis by promoting bone formation.

The anti-inflammatory effects of adiponectin are mediated via a heme oxygenase-1-dependent pathway in rat Kupffer cells

Altered expression and activity of immunomodulatory cytokines plays a major role in the pathogenesis of alcoholic liver disease. Chronic ethanol feeding increases the sensitivity of Kupffer cells, the resident hepatic macrophage, to lipopolysaccharide (LPS), leading to increased tumor necrosis factor alpha (TNF-alpha) expression. This sensitization is normalized by treatment of primary cultures of Kupffer cells with adiponectin, an anti-inflammatory adipokine. Here we tested the hypothesis that adiponectin-mediated suppression of LPS signaling in Kupffer cells is mediated via an interleukin-10 (IL-10)/heme oxygenase-1 (HO-1) pathway after chronic ethanol feeding. Knockdown of IL-10 expression in primary cultures of Kupffer cells with small interfering RNA (siRNA) prevented the inhibitory effect of globular adiponectin (gAcrp) on LPS-stimulated TNF-alpha expression. gAcrp increased IL-10 mRNA and protein expression, as well as expression of the IL-10 inducible gene, HO-1; expression was higher in Kupffer cells from ethanol-fed rats compared with pair-fed controls. Although IL-10 receptor surface expression on Kupffer cells was not affected by ethanol feeding, IL-10-mediated phosphorylation of STAT3 and expression of HO-1 was higher in Kupffer cells after ethanol feeding. Inhibition of HO-1 activity, either by treatment with the HO-1 inhibitor zinc protoporphyrin or by siRNA knockdown of HO-1, prevented the inhibitory effect of gAcrp on LPS-stimulated TNF-alpha expression in Kupffer cells. LPS-stimulated TNF-alpha expression in liver was increased in mice after chronic ethanol exposure. When mice were treated with cobalt protoporphyrin to induce HO-1 expression, ethanol-induced sensitivity to LPS was ameliorated.

CONCLUSION

gAcrp prevents LPS-stimulated TNF-alpha expression in Kupffer cells through the activation of the IL-10/STAT3/HO-1 pathway. Kupffer cells from ethanol-fed rats are highly sensitive to the anti-inflammatory effects of gAcrp; this sensitivity is associated with both increased expression and sensitivity to IL-10.

Mechanical stress promotes odontoblastic differentiation via the heme oxygenase-1 pathway in human dental pulp cell line

AIMS

Although heme oxygenase-1 (HO-1) is involved in osteoblastic differentiation, the HO-1- and odontoblastic differentiation-inducing effects of mechanical stress (MS) have not been clarified in human dental pulp cells (HDPCs). In this study, we examined the effects of MS on the odontoblastic differentiation of immortalized HDPCs and on the primary intracellular signaling pathways, including the HO-1 pathway, implicated in this differentiation.

MAIN METHODS

A Flexercell strain unit was used to generate cyclic tensile strain in HDPCs. Expressions of mRNAs encoding HO-1 and HDPC differentiation markers, such as osteopontin (OPN), bone sialoprotein (BSP), dentin sialophosphoprotein (DSPP), and dentin matrix-protein-1 (DMP-1), were evaluated using the reverse transcription-polymerase chain reaction. Expression of the NF-E2-related transcription factor 2 (Nrf2) protein was analyzed by Western blotting.

KEY FINDINGS

MS significantly increased the expression of HO-1, OPN, BSP, DSPP, and DMP-1 mRNAs in HDPCs. HO-1 silencing and inhibitors of HO-1, p38 MAPK, ERK, phosphoinositide 3-kinase, and nuclear factor-kappaB (NF-kappaB) all attenuated MS-stimulated differentiation. The MS-induced nuclear translocation of Nrf2 was suppressed by inhibitors of PI3K and NF-kappaB.

SIGNIFICANCE

Collectively, these results provide the first evidence that MS stimulates odontoblastic differentiation of HDPCs via modulation of the Nrf2-mediated HO-1 pathway.

Heme oxygenase: the key to renal function regulation

Heme oxygenase (HO) plays a critical role in attenuating the production of reactive oxygen species through its ability to degrade heme in an enzymatic process that leads to the production of equimolar amounts of carbon monoxide and biliverdin/bilirubin and the release of free iron. The present review examines the beneficial role of HO-1 (inducible form of HO) that is achieved by increased expression of this enzyme in renal tissue. The influence of the HO system on renal physiology, obesity, vascular dysfunction, and blood pressure regulation is reviewed, and the clinical potential of increased levels of HO-1 protein, HO activity, and HO-derived end products of heme degradation is discussed relative to renal disease. The use of pharmacological and genetic approaches to investigate the role of the HO system in the kidney is key to the development of therapeutic approaches to prevent the adverse effects that accrue due to an impairment in renal function.

Diabetes impairs the vascular recruitment of normal stem cells by oxidant damage, reversed by increases in pAMPK, heme oxygenase-1, and adiponectin

BACKGROUND

Atherosclerosis progression is accelerated in diabetes mellitus (DM) by either direct endothelial damage or reduced availability and function of endothelial progenitor cells (EPCs). Both alterations are related to increased oxidant damage.

AIM

We examined if DM specifically impairs vascular signaling, thereby reducing the recruitment of normal EPCs, and if increases in antioxidant levels by induction of heme oxygenase-1 (HO-1) can reverse this condition.

METHODS

Control and diabetic rats were treated with the HO-1 inducer cobalt protoporphyrin (CoPP) once a week for 3 weeks. Eight weeks after the development of diabetes, EPCs harvested from the aorta of syngenic inbred normal rats and labeled with technetium-99m-exametazime were infused via the femoral vein to estimate their blood clearance and aortic recruitment. Circulating endothelial cells (CECs) and the aortic expression of thrombomodulin (TM), CD31, and endothelial nitric oxide synthase (eNOS) were used to measure endothelial damage.

RESULTS

DM reduced blood clearance and aortic recruitment of EPCs. Both parameters were returned to control levels by CoPP treatment without affecting EPC kinetics in normal animals. These abnormalities of EPCs in DM were paralleled by reduced serum adiponectin levels, increased numbers of CECs, reduced endothelial expression of phosphorylated eNOS, and reduced levels of TM, CD31, and phosphorylated AMP-activated protein kinase (pAMPK). CoPP treatment restored all of these parameters to normal levels.

CONCLUSION

Type II DM and its related oxidant damage hamper the interaction between the vascular wall and normal EPCs by mechanisms that are, at least partially, reversed by the induction of HO-1 gene expression, adiponectin, and pAMPK levels.

Targeting heme oxygenase: therapeutic implications for diseases of the cardiovascular system

Heme oxygenase (HO) is important in attenuating the overall production of reactive oxygen species through its ability to degrade heme and to produce carbon monoxide, biliverdin/bilirubin, and release of free iron. Excess free heme catalyzes the formation of reactive oxygen species, which leads to endothelial cell (EC) dysfunction as seen in numerous pathologic vascular conditions including systemic hypertension and diabetes, as well as in ischemia/reperfusion injury.The up-regulation of HO-1 can be achieved through the use of pharmaceutical agents such as metalloporphyrins and statins. In addition, atrial natriuretic peptide and nitric oxide donors are important modulators of the heme-HO system, either through induction of HO-1 or the increased biologic activity of its products. Gene therapy and gene transfer, including site- and organ-specific targeted gene transfer have become powerful tools for studying the potential role of the 2 isoforms of HO, HO-1/HO-2, in the treatment of cardiovascular disease, as well as diabetes. HO-1 induction by pharmacological agents or the in vitro gene transfer of human HO-1 into ECs increases cell cycle progression and attenuates angiotensin II, tumor necrosis factor-alpha, and heme-mediated DNA damage; administration in vivo corrects blood pressure elevation after angiotensin II exposure. Delivery of human HO-1 to hyperglycemic rats significantly lowers superoxide levels and prevents EC damage and sloughing of vascular EC into the circulation. In addition, administration of human HO-1 to rats in advance of ischemia/reperfusion injury considerably reduces tissue damage.The ability to up-regulate HO-1 either through pharmacological means or through the use of gene therapy may offer therapeutic strategies for the prevention of cardiovascular disease in the future. This review discusses the implications of HO-1 delivery during the early stages of cardiovascular system injury or in early vascular pathology, and suggests that pharmacological agents that regulate HO activity or HO-1 gene delivery itself may become powerful tools for preventing the onset or progression of various cardiovascular diseases.

Up-regulating the hemeoxygenase system enhances insulin sensitivity and improves glucose metabolism in insulin-resistant diabetes in Goto-Kakizaki rats

Insulin-mediated signal transduction is positively correlated to adiponectin, adenosine monophosphate-activated protein kinase (AMPK), and glucose-transporter-4 (GLUT4) but negatively to oxidative/inflammatory mediators such as nuclear factor-kappaB, activating-protein (AP)-1, AP-2, and c-Jun-N-terminal-kinase. Although hemeoxygenase (HO) suppresses oxidative insults, its effects on insulin-sensitizing agents like AMPK and GLUT4 remains unclear and were investigated using Goto-Kakizaki rats (GK), a nonobese insulin-resistant type-2 diabetic model. HO was induced with hemin or inhibited with chromium mesoporphyrin (CrMP). The application of hemin to GK rats evoked a 3-month antidiabetic effect, whereas the HO-inhibitor, CrMP, exacerbated hyperglycemia and nullified insulin-signaling/glucose metabolism. Interestingly, the antidiabetic was accompanied by a paradoxical increase of insulin alongside the potentiation of insulin-sensitizing agents such as adiponectin, AMPK, and GLUT4 in the gastrocnemius muscle. Furthermore, hemin enhanced mediators/regulators of insulin signaling like cGMP and cAMP and suppressed oxidative insults by up-regulating HO-1, HO activity, superoxide dismutase, catalase, and the total antioxidant capacity in the gastrocnemius muscle. Accordingly, oxidative markers/mediators including nuclear factor-kappaB, AP-1, AP-2, c-Jun-N-terminal-kinase, and 8-isoprostane were abated, whereas CrMP annulled the cytoprotective and antidiabetic effects of hemin. Correspondingly, ip glucose tolerance, insulin tolerance, and homeostasis model assessment insulin resistance analyses revealed improved glucose tolerance, reduced insulin intolerance, enhanced insulin sensitivity, and reduced insulin resistance in hemin-treated GK rats. In contrast, CrMP, abolished the insulin-sensitizing effects and restored and/or exacerbated insulin resistance. Our study unveils a 3-month enduring antidiabetic effect of hemin and unmasks the synergistic interaction among the HO system, adiponectin, AMPK, and GLUT4 that could be explored to enhance insulin signaling and improve glucose metabolism in insulin-resistant diabetes.

Upregulation of the heme oxygenase system ameliorates postprandial and fasting hyperglycemia in type 2 diabetes

In type 2 diabetes (T2D), postprandial and fasting hyperglycemia are important predictors of cardiovascular diseases; however, few drugs are currently available to simultaneously suppress these conditions. Here, we report an enduring antidiabetic effect of the heme oxygenase (HO) inducer hemin on Goto-Kakizaki rats (GK), a nonobese insulin-resistant T2D model. HO breaks down the heme-moiety-generating antioxidants (biliverdin/bilirubin and ferritin) and carbon monoxide, which stimulate insulin secretion. Hemin induces HO-1 to potentiate HO activity and the HO-derived products. Chronically applied hemin (30 mg/kg ip) for a month reduced and maintained fasting glucose at physiological levels for 3 mo. Before therapy, glucose levels were 9.3 +/- 0.3 mmol/l (n = 14). At 1, 2, and 3 mo posttherapy, we recorded 6.7 +/- 0.13, 5.9 +/- 0.2, and 7.2 +/- 0.2 mmol/l, respectively. Hemin was also effective against postprandial hyperglycemia (14.6 +/- 1.1 vs. 7.5 +/- 0.4 mmol/l; n = 14; P < 0.01), and the effect remained sustained for 3 mo after therapy. The reduction of hyperglycemia was accompanied by enhanced HO-1, HO activity, and cGMP of the soleus muscle, alongside increased plasma bilirubin, ferritin, SOD, total antioxidant capacity, and insulin levels, whereas markers/mediators of oxidative stress like urinary-8-isoprostane and soleus muscle nitrotyrosine, NF-kappaB, and activator protein-1 and -2 were abated. Furthermore, inhibitors of insulin signaling including soleus muscle glycogen synthase kinase-3 and JNK were reduced, while the insulin-sensitizing adipokine, adiponectin, alongside AMPK were increased. Correspondingly, hemin improved glucose tolerance, suppressed insulin intolerance, reduced insulin resistance, and overturned the inability of insulin to enhance glucose transporter 4, a protein required for glucose uptake. Hemin also upregulated HO-1/HO activity and cGMP and lowered glucose in euglycemic Sprague-Dawley control rats albeit less intensely, suggesting greater selectivity of the HO system in diabetic conditions. In conclusion, reduced oxidative stress alongside the concomitant and paradoxical enhancement of insulin secretion and insulin-sensitizing pathways may account for the 3-mo-enduring antidiabetic effect. The synergistic interaction among HO, adiponectin, and GLUT4 may be explored against insulin-resistant diabetes.