Lack of osteopontin improves cardiac function in streptozotocin-induced diabetic mice

Myocardial fibrosis from the perspective of the extracellular matrix: Mechanisms to clinical impact

Fibrosis is defined by the excessive accumulation of extracellular matrix (ECM) and constitutes a central pathophysiological process that underlies tissue dysfunction, across organs, in multiple chronic diseases and during aging. Myocardial fibrosis is a key contributor to dysfunction and failure in numerous diseases of the heart and is a strong predictor of poor clinical outcome and mortality. The excess structural and matricellular ECM proteins deposited by cardiac fibroblasts, is found between cardiomyocytes (interstitial fibrosis), in focal areas where cardiomyocytes have died (replacement fibrosis), and around vessels (perivascular fibrosis). Although myocardial fibrosis has important clinical prognostic value, access to cardiac tissue biopsies for histological evaluation is limited. Despite challenges with sensitivity and specificity, cardiac magnetic resonance imaging (CMR) is the most applicable diagnostic tool in the clinic, and the scientific community is currently actively searching for blood biomarkers reflecting myocardial fibrosis, to complement the imaging techniques. The lack of mechanistic insights into specific pro- and anti-fibrotic molecular pathways has hampered the development of effective treatments to prevent or reverse myocardial fibrosis. Development and implementation of anti-fibrotic therapies is expected to improve patient outcomes and is an urgent medical need. Here, we discuss the importance of the ECM in the heart, the central role of fibrosis in heart disease, and mechanistic pathways likely to impact clinical practice with regards to diagnostics of myocardial fibrosis, risk stratification of patients, and anti-fibrotic therapy.

Expression of Osteopontin and Gremlin 1 Proteins in Cardiomyocytes in Ischemic Heart Failure

A relevant role of osteopontin (OPN) and gremlin 1 (Grem1) in regulating cardiac tissue remodeling and formation of heart failure (HF) are documented, with the changes of OPN and Grem1 levels in blood plasma due to acute ischemia, ischemic heart disease-induced advanced HF or dilatative cardiomyopathy being the primary focus in most of these studies. However, knowledge on the early OPN and Grem1 proteins expression changes within cardiomyocytes during remodeling due to chronic ischemia remains insufficient. The aim of this study was to determine the OPN and Grem1 proteins expression changes in human cardiomyocytes at different stages of ischemic HF. A semi-quantitative immunohistochemical analysis was performed in 105 myocardial tissue samples obtained from the left cardiac ventricles. Increased OPN immunostaining intensity was already detected in the stage A HF group, compared to the control group (p < 0.001), and continued to increase in the stage B HF (p < 0.001), achieving the peak of immunostaining in the stages C/D HF group (p < 0.001). Similar data of Grem1 immunostaining intensity changes in cardiomyocytes were documented. Significantly positive correlations were detected between OPN, Grem1 expression in cardiomyocytes and their diameter as well as the length, in addition to positive correlation between OPN and Grem1 expression changes within cardiomyocytes. These novel findings suggest that OPN and Grem1 contribute significantly to reorganization of cellular geometry from the earliest stage of cardiomyocyte remodeling, providing new insights into the ischemic HF pathogenesis.

Osteopontin/SPP1: a potential mediator between immune cells and vascular calcification

Vascular calcification (VC) is considered a common pathological process in various vascular diseases. Accumulating studies have confirmed that VC is involved in the inflammatory response in heart disease, and SPP1+ macrophages play an important role in this process. In VC, studies have focused on the physiological and pathological functions of macrophages, such as pro-inflammatory or anti-inflammatory cytokines and pro-fibrotic vesicles. Additionally, macrophages and activated lymphocytes highly express SPP1 in atherosclerotic plaques, which promote the formation of fatty streaks and plaque development, and SPP1 is also involved in the calcification process of atherosclerotic plaques that results in heart failure, but the crosstalk between SPP1-mediated immune cells and VC has not been adequately addressed. In this review, we summarize the regulatory effect of SPP1 on VC in T cells, macrophages, and dendritic cells in different organs' VC, which could be a potential therapeutic target for VC.

Clinical and Molecular Implications of Osteopontin in Heart Failure

The matricellular protein osteopontin modulates cell-matrix interactions during tissue injury and healing. A complex multidomain structure of osteopontin enables it not only to bind diverse cell receptors but also to interact with various partners, including other extracellular matrix proteins, cytokines, and growth factors. Numerous studies have implicated osteopontin in the development and progression of myocardial remodeling in diverse cardiac diseases. Osteopontin influences myocardial remodeling by regulating extracellular matrix production, the activity of matrix metalloproteinases and various growth factors, inflammatory cell recruitment, myofibroblast differentiation, cardiomyocyte apoptosis, and myocardial vascularization. The exploitation of osteopontin loss- and gain-of-function approaches in rodent models provided an opportunity for assessment of the cell- and disease-specific contribution of osteopontin to myocardial remodeling. In this review, we summarize the recent knowledge on osteopontin regulation and its impact on various cardiac diseases, as well as delineate complex disease- and cell-specific roles of osteopontin in cardiac pathologies. We also discuss the current progress of therapeutics targeting osteopontin that may facilitate the development of a novel strategy for heart failure treatment.

T Cell Immunosenescence in Aging, Obesity, and Cardiovascular Disease

Although advances in preventive medicine have greatly improved prognosis, cardiovascular disease (CVD) remains the leading cause of death worldwide. This clearly indicates that there remain residual cardiovascular risks that have not been targeted by conventional therapies. The results of multiple animal studies and clinical trials clearly indicate that inflammation is the most important residual risk and a potential target for CVD prevention. The immune cell network is intricately regulated to maintain homeostasis. Ageing associated changes to the immune system occurs in both innate and adaptive immune cells, however T cells are most susceptible to this process. T-cell changes due to thymic degeneration and homeostatic proliferation, metabolic abnormalities, telomere length shortening, and epigenetic changes associated with aging and obesity may not only reduce normal immune function, but also induce inflammatory tendencies, a process referred to as immunosenescence. Since the disruption of biological homeostasis by T cell immunosenescence is closely related to the development and progression of CVD via inflammation, senescent T cells are attracting attention as a new therapeutic target. In this review, we discuss the relationship between CVD and T cell immunosenescence associated with aging and obesity.

Fibrosis of the diabetic heart: Clinical significance, molecular mechanisms, and therapeutic opportunities

In patients with diabetes, myocardial fibrosis may contribute to the pathogenesis of heart failure and arrhythmogenesis, increasing ventricular stiffness and delaying conduction. Diabetic myocardial fibrosis involves effects of hyperglycemia, lipotoxicity and insulin resistance on cardiac fibroblasts, directly resulting in increased matrix secretion, and activation of paracrine signaling in cardiomyocytes, immune and vascular cells, that release fibroblast-activating mediators. Neurohumoral pathways, cytokines, growth factors, oxidative stress, advanced glycation end-products (AGEs), and matricellular proteins have been implicated in diabetic fibrosis; however, the molecular links between the metabolic perturbations and activation of a fibrogenic program remain poorly understood. Although existing therapies using glucose- and lipid-lowering agents and neurohumoral inhibition may act in part by attenuating myocardial collagen deposition, specific therapies targeting the fibrotic response are lacking. This review manuscript discusses the clinical significance, molecular mechanisms and cell biology of diabetic cardiac fibrosis and proposes therapeutic targets that may attenuate the fibrotic response, preventing heart failure progression.

Osteopontin in Cardiovascular Diseases

Unprecedented advances in secondary prevention have greatly improved the prognosis of cardiovascular diseases (CVDs); however, CVDs remain a leading cause of death globally. These findings suggest the need to reconsider cardiovascular risk and optimal medical therapy. Numerous studies have shown that inflammation, pro-thrombotic factors, and gene mutations are focused not only on cardiovascular residual risk but also as the next therapeutic target for CVDs. Furthermore, recent clinical trials, such as the Canakinumab Anti-inflammatory Thrombosis Outcomes Study trial, showed the possibility of anti-inflammatory therapy for patients with CVDs. Osteopontin (OPN) is a matricellular protein that mediates diverse biological functions and is involved in a number of pathological states in CVDs. OPN has a two-faced phenotype that is dependent on the pathological state. Acute increases in OPN have protective roles, including wound healing, neovascularization, and amelioration of vascular calcification. By contrast, chronic increases in OPN predict poor prognosis of a major adverse cardiovascular event independent of conventional cardiovascular risk factors. Thus, OPN can be a therapeutic target for CVDs but is not clinically available. In this review, we discuss the role of OPN in the development of CVDs and its potential as a therapeutic target.

Osteopontin: A Promising Therapeutic Target in Cardiac Fibrosis

Osteopontin (OPN) is recognized for its significant roles in both physiological and pathological processes. Initially, OPN was recognized as a cytokine with pro-inflammatory actions. More recently, OPN has emerged as a matricellular protein of the extracellular matrix (ECM). OPN is also known to be a substrate for proteolytic cleavage by several proteases that form an integral part of the ECM. In the adult heart under physiological conditions, basal levels of OPN are expressed. Increased expression of OPN has been correlated with the progression of cardiac remodeling and fibrosis to heart failure and the severity of the condition. The intricate process by which OPN mediates its effects include the coordination of intracellular signals necessary for the differentiation of fibroblasts into myofibroblasts, promoting angiogenesis, wound healing, and tissue regeneration. In this review, we discuss the role of OPN in contributing to the development of cardiac fibrosis and its suitability as a therapeutic target.

The Extracellular Matrix in Ischemic and Nonischemic Heart Failure

The ECM (extracellular matrix) network plays a crucial role in cardiac homeostasis, not only by providing structural support, but also by facilitating force transmission, and by transducing key signals to cardiomyocytes, vascular cells, and interstitial cells. Changes in the profile and biochemistry of the ECM may be critically implicated in the pathogenesis of both heart failure with reduced ejection fraction and heart failure with preserved ejection fraction. The patterns of molecular and biochemical ECM alterations in failing hearts are dependent on the type of underlying injury. Pressure overload triggers early activation of a matrix-synthetic program in cardiac fibroblasts, inducing myofibroblast conversion, and stimulating synthesis of both structural and matricellular ECM proteins. Expansion of the cardiac ECM may increase myocardial stiffness promoting diastolic dysfunction. Cardiomyocytes, vascular cells and immune cells, activated through mechanosensitive pathways or neurohumoral mediators may play a critical role in fibroblast activation through secretion of cytokines and growth factors. Sustained pressure overload leads to dilative remodeling and systolic dysfunction that may be mediated by changes in the interstitial protease/antiprotease balance. On the other hand, ischemic injury causes dynamic changes in the cardiac ECM that contribute to regulation of inflammation and repair and may mediate adverse cardiac remodeling. In other pathophysiologic conditions, such as volume overload, diabetes mellitus, and obesity, the cell biological effectors mediating ECM remodeling are poorly understood and the molecular links between the primary insult and the changes in the matrix environment are unknown. This review article discusses the role of ECM macromolecules in heart failure, focusing on both structural ECM proteins (such as fibrillar and nonfibrillar collagens), and specialized injury-associated matrix macromolecules (such as fibronectin and matricellular proteins). Understanding the role of the ECM in heart failure may identify therapeutic targets to reduce geometric remodeling, to attenuate cardiomyocyte dysfunction, and even to promote myocardial regeneration.

Concomitant Obesity and Metabolic Syndrome Add to the Atrial Arrhythmogenic Phenotype in Male Hypertensive Rats

Background

Besides hypertension, obesity and the metabolic syndrome have recently emerged as risk factors for atrial fibrillation. This study sought to delineate the development of an arrhythmogenic substrate for atrial fibrillation in hypertension with and without concomitant obesity and metabolic syndrome.

Methods and Results

We compared obese spontaneously hypertensive rats (SHR‐obese, n=7–10) with lean hypertensive controls (SHR‐lean, n=7–10) and normotensive rats (n=7–10). Left atrial emptying function (MRI) and electrophysiological parameters were characterized before the hearts were harvested for histological and biochemical analyses. At the age of 38 weeks, SHR‐obese, but not SHR‐lean, showed increased body weight and impaired glucose tolerance together with dyslipidemia compared with normotensive rats. Mean blood pressure was similarly increased in SHR‐lean and SHR‐obese when compared with normotensive rats (178±9 and 180±8 mm Hg [not significant] versus 118±5 mm Hg, P<0.01 for both), but left ventricular end‐diastolic pressure was more increased in SHR‐obese than in SHR‐lean. Impairment of left atrial emptying function, increase in total atrial activation time, and conduction heterogeneity, as well as prolongation of inducible atrial fibrillation durations, were more pronounced in SHR‐obese as compared with SHR‐lean. Histological and biochemical examinations revealed enhanced triglycerides and more pronounced fibrosis in the left atrium of SHR‐obese. Besides increased expression of profibrotic markers in SHR‐lean and SHR‐obese, the profibrotic extracellular matrix protein osteopontin was highly upregulated only in SHR‐obese.

Conclusions

In addition to hypertension alone, concomitant obesity and metabolic syndrome add to the atrial arrhythmogenic phenotype by impaired left atrial emptying function, local conduction abnormalities, interstitial atrial fibrosis formation, and increased propensity for atrial fibrillation.

Osteopontin-stimulated apoptosis in cardiac myocytes involves oxidative stress and mitochondrial death pathway: role of a pro-apoptotic protein BIK

Increased osteopontin (OPN) expression in the heart, specifically in myocytes, associates with increased myocyte apoptosis and myocardial dysfunction. Recently, we provided evidence that OPN interacts with CD44 receptor, and induces myocyte apoptosis via the involvement of endoplasmic reticulum stress and mitochondrial death pathways. Here we tested the hypothesis that OPN induces oxidative stress in myocytes and the heart via the involvement of mitochondria and NADPH oxidase-4 (NOX-4). Treatment of adult rat ventricular myocytes (ARVMs) with OPN (20 nM) increased oxidative stress as analyzed by protein carbonylation, and intracellular reactive oxygen species (ROS) levels as analyzed by ROS detection kit and dichlorohydrofluorescein diacetate staining. Pretreatment with NAC (antioxidant), apocynin (NOX inhibitor), MnTBAP (superoxide dismutase mimetic), and mitochondrial KATP channel blockers (glibenclamide and 5-hydroxydecanoate) decreased OPN-stimulated ROS production, cytosolic cytochrome c levels, and apoptosis. OPN increased NOX-4 expression, while decreasing SOD-2 expression. OPN decreased mitochondrial membrane potential as measured by JC-1 staining, and induced mitochondrial abnormalities including swelling and reorganization of cristae as observed using transmission electron microscopy. OPN increased expression of BIK, a pro-apoptotic protein involved in reorganization of mitochondrial cristae. Expression of dominant-negative BIK decreased OPN-stimulated apoptosis. In vivo, OPN expression in cardiac myocyte-specific manner associated with increased protein carbonylation, and expression of NOX-4 and BIK. Thus, OPN induces oxidative stress via the involvement of mitochondria and NOX-4. It may affect mitochondrial morphology and integrity, at least in part, via the involvement of BIK.

Targeting osteopontin, the silent partner of Na+/H+ exchanger isoform 1 in cardiac remodeling

Cardiac hypertrophy (CH), characterized by the enlargement of cardiomyocytes, fibrosis and apoptosis, contributes to cardiac remodeling, which if left unresolved results in heart failure. Understanding the signaling pathways underlying CH is necessary to identify potential therapeutic targets. The Na(+) /H(+) -exchanger isoform I (NHE1), a ubiquitously expressed glycoprotein and cardiac specific isoform, regulates intracellular pH. Recent studies have demonstrated that enhanced expression/activity of NHE1 contributes to cardiac remodeling and CH. Inhibition of NHE1 in both in vitro and in vivo models have suggested that inhibition of NHE1 protects against hypertrophy. However, clinical trials using NHE1 inhibitors have proven to be unsuccessful, suggesting that additional factors maybe contributing to cardiac remodeling. Recent studies have indicated that the upregulation of NHE1 is associated with enhanced levels of osteopontin (OPN) in the setting of CH. OPN has been demonstrated to be upregulated in left ventricular hypertrophy, dilated cardiomyopathy and in diabetic cardiomyopathy. The cellular interplay between OPN and NHE1 in the setting of CH remains unknown. This review focuses on the role of NHE1 and OPN in cardiac remodeling and emphasizes the signaling pathways implicating OPN in the NHE1-induced hypertrophic response.

SVVYGLR motif of the thrombin-cleaved N-terminal osteopontin fragment enhances the synthesis of collagen type III in myocardial fibrosis

Osteopontin (OPN) is involved in various physiological processes such as inflammatory and wound healing. However, little is known about the effects of OPN on these tissues. OPN is cleaved by thrombin, and cleavage of the N-terminal fragment exposes a SVVYGLR sequence on its C-terminus. In this study, we examined the effects of the thrombin-cleaved OPN fragments on fibroblasts and myocardial fibrosis, particularly the role of the SVVYGLR sequence. The recombinant thrombin-cleaved OPN fragments (N-terminal fragment [N-OPN], C-terminal fragment [C-OPN], and the N-terminal fragment lacking the SVVYGLR sequence [ΔSV N-OPN]) were added to fibroblasts, and the cellular motility, signal activity, and production of collagen were evaluated. A sustained-release gel containing an OPN fragment or SVVYGLR peptide was transplanted into a rat model of ischemic cardiomyopathy and the quantities and ratio of collagen type I (COL I) and type III (COL III) were estimated. N-OPN significantly promoted fibroblast migration. Smad signal activity, expression of smooth muscle actin (SMA), and the production of COL III were enhanced by N-OPN and SVVYGLR peptide. Conversely, ΔSV N-OPN and C-OPN had no effect. In vivo, the expression level of N-OPN was associated with COL III distribution, and the COL III/COL I ratio was significantly increased by the sustained-release gel containing N-OPN or SVVYGLR peptide. The cardiac function was also significantly improved by the N-OPN- or SVVYGLR peptide-released gel treatment. The N-terminal fragment of thrombin-cleaved OPN-induced Smad signal activation, SMA expression, and COL III production, and its SVVYGLR sequence influences this function.

Osteopontin: At the cross-roads of myocyte survival and myocardial function

Heart failure represents a major cause of morbidity and mortality in Western society. Cardiac myocyte loss due to apoptosis plays a significant role in the progression of heart failure. The extracellular matrix (ECM) maintains the structural integrity of the heart and allows the transmission of electrical and mechanical signals during cardiac contraction and relaxation. Matricellular proteins, a class of non-structural ECM proteins, play a significant role in ECM homeostasis and intracellular signaling via their interactions with cell surface receptors, structural proteins, and/or soluble extracellular factors such as growth factors and cytokines. Osteopontin (OPN), also called cytokine Eta-1, is a member of the matricellular protein family. The normal heart expresses low levels of OPN. However, OPN expression increases markedly under a variety of pathophysiological conditions of the heart. Many human and transgenic mouse studies provide evidence that increased OPN expression, specifically in myocytes, is associated with increased myocyte apoptosis and myocardial dysfunction. This review summarizes OPN expression in the heart, and its role in myocyte apoptosis and myocardial function.

Cardioprotective effects of osteopontin-1 during development of murine ischemic cardiomyopathy

Repetitive brief ischemia and reperfusion (I/R) is associated with ventricular dysfunction in pathogenesis of murine ischemic cardiomyopathy and human hibernating myocardium. We investigated the role of matricellular protein osteopontin-1 (OPN) in murine model of repetitive I/R. One 15-min LAD-occlusion followed by reperfusion was performed daily over 3, 5, and 7 consecutive days in C57/Bl6 wildtype- (WT-) and OPN^−/−-mice (n = 8/group). After echocardiography hearts were processed for histological and mRNA-studies. Cardiac fibroblasts were isolated, cultured, and stimulated with TGF-β1. WT-mice showed an early, strong, and cardiomyocyte-specific osteopontin-expression leading to interstitial macrophage infiltration and consecutive fibrosis after 7 days I/R in absence of myocardial infarction. In contrast, OPN^−/−-mice showed small, nontransmural infarctions after 3 days I/R associated with significantly worse ventricular dysfunction. OPN^−/−-mice had different expression of myocardial contractile elements and antioxidative mediators and a lower expression of chemokines during I/R. OPN^−/−-mice showed predominant collagen deposition in macrophage-rich small infarctions. We found lower induction of tenascin-C, MMP-9, MMP-12, and TIMP-1, whereas MMP-13-expression was higher in OPN^−/−-mice. Cultured OPN^−/−-myofibroblasts confirmed these findings. In conclusion, osteopontin seems to modulate expression of contractile elements, antioxidative mediators, and inflammatory response and subsequently remodel in order to protect cardiomyocytes in murine ischemic cardiomyopathy.

Osteopontin stimulates apoptosis in adult cardiac myocytes via the involvement of CD44 receptors, mitochondrial death pathway, and endoplasmic reticulum stress

Increased osteopontin (OPN) expression associates with increased myocyte apoptosis and myocardial dysfunction. The objective of this study was to identify the receptor for OPN and get insight into the mechanism by which OPN induces cardiac myocyte apoptosis. Adult rat ventricular myocytes (ARVMs) and transgenic mice expressing OPN in a myocyte-specific manner were used for in vitro and in vivo studies. Treatment with purified OPN (20 nM) protein or adenoviral-mediated OPN expression induced apoptosis in ARVMs. OPN co-immunoprecipitated with CD44 receptors, not with β1 or β3 integrins. Proximity ligation assay confirmed interaction of OPN with CD44 receptors. Neutralizing anti-CD44 antibodies inhibited OPN-stimulated apoptosis. OPN activated JNKs and increased expression of Bax and levels of cytosolic cytochrome c, suggesting involvement of mitochondrial death pathway. OPN increased endoplasmic reticulum (ER) stress, as evidenced by increased expression of Gadd153 and activation of caspase-12. Inhibition of JNKs using SP600125 or ER stress using salubrinal or caspase-12 inhibitor significantly reduced OPN-stimulated apoptosis. Expression of OPN in adult mouse heart in myocyte-specific manner associated with decreased left ventricular function and increased myocyte apoptosis. In the heart, OPN expression increased JNKs and caspase-12 activities, and expression of Bax and Gadd153. Thus, OPN, acting via CD44 receptors, induces apoptosis in myocytes via the involvement of mitochondrial death pathway and ER stress.

Atorvastatin inhibits hyperglycemia-induced expression of osteopontin in the diabetic rat kidney via the p38 MAPK pathway

Osteopontin (OPN), a large phosphoglycoprotein adhesion molecule, which is up-regulated in the kidneys of humans and mice with diabetes, has emerged as a potentially key pathophysiological contributor in diabetic nephropathy. Here, we investigated the role of OPN in kidney injury caused by diabetic nephropathy and the effect of atorvastatin on the expression of OPN and on diabetic nephropathy. Diabetes was induced with streptozotocin in rats, and atorvastatin (5 mg/kg) was orally administered once a day for 8 weeks. We analyzed the expression and regulation of OPN in the kidneys of streptozotocin-induced diabetic Sprague-Dawley albino rats by immunohistochemistry and western blot analysis. The expression of OPN was increased in diabetic rat kidney, and atorvastatin inhibited this process. Atorvastatin also decreased the expression and phosphorylation of p38. In vitro, atorvastatin inhibited the high glucose-induced OPN expression in Madin-Darby canine kidney epithelial cells through the p38 MAPK signaling pathway. These results suggested that atorvastatin reduced the expression of OPN through inhibition of the p38 MAPK pathway. The expression of OPN was associated with kidney injury. These molecules may represent therapeutic targets for the prevention of acute kidney injury induced by diabetes.

Alterations in lung gene expression in streptozotocin-induced diabetic rats

BACKGROUND

Diabetes profoundly affects gene expression in organs such as heart, skeletal muscle, kidney and liver, with areas of perturbation including carbohydrate and lipid metabolism, oxidative stress, and protein ubiquitination. Type 1 diabetes impairs lung function, but whether gene expression alterations in the lung parallel those of other tissue types is largely unexplored.

METHODS

Lung from a rat model of diabetes mellitus induced by streptozotocin was subjected to gene expression microarray analysis.

RESULTS

Glucose levels were 67 and 260 mg/dl (p < 0.001) in control and diabetic rats, respectively. There were 46 genes with at least ± 1.5-fold significantly altered expression (19 increases, 27 decreases). Gene ontology groups with significant over-representation among genes with altered expression included apoptosis, response to stress (p = 0.03), regulation of protein kinase activity (p = 0.04), ion transporter activity (p = 0.01) and collagen (p = 0.01). All genes assigned to the apoptosis and response to stress groups had increased expression whereas all genes assigned to the collagen group had decreased expression. In contrast, the protein kinase activity and ion transporter activity groups had genes with both increased and decreased expression.

CONCLUSIONS

Gene expression in the lung is affected by type 1 diabetes in several specific areas, including apoptosis. However, the lung is resistant to changes in gene expression related to lipid and carbohydrate metabolism and oxidative stress that occur in other tissue types such as heart, skeletal muscle and kidney.

Deep sequence analysis of gene expression identifies osteopontin as a downstream effector of integrin-linked kinase (ILK) in cardiac-specific ILK knockout mice

BACKGROUND

Integrin-linked kinase (ILK) is a serine/threonine kinase that has been linked to human and experimental heart failure, but its role in the heart is not fully understood.

METHODS AND RESULTS

To define the role of cardiomyocyte ILK, we generated cardiac-specific ILK knockout mice using α-myosin heavy chain-driven Cre expression. Cardiac-specific ILK knockout mice spontaneously developed lethal dilated cardiomyopathy and heart failure with an early increase in apoptosis, fibrosis, and cardiac inflammation. To identify downstream effectors, we used deep sequence analysis of gene expression to compare comprehensive transcriptional profiles of cardiac-specific ILK knockout and wild-type hearts from 10-day-old mice before the development of cardiac dysfunction. Approximately 2×10(6) cDNA clones from each genotype were sequenced, corresponding to 33 274 independent transcripts. A total of 93 genes were altered, using nominal thresholds of >1.4-fold change and P<0.001. The most highly upregulated gene was osteopontin (47-fold increase; P=9.6×10(-45)), an inflammatory chemokine implicated in heart failure pathophysiology. ILK also regulated osteopontin expression in cardiomyocytes in vitro. Importantly, blocking antibodies to osteopontin mitigated but did not fully rescue the functional decline in cardiac-specific ILK knockout mice.

CONCLUSIONS

Cardiomyocyte-specific ILK deletion leads to a lethal cardiomyopathy characterized by cardiomyocyte death, fibrosis, and inflammation. Comprehensive profiling identifies ILK-dependent transcriptional effects and implicates osteopontin as a contributor to these phenotypes.

Plant polyphenols in the treatment of age-associated diseases: revealing the pleiotropic effects of icariin by network analysis

Polyphenols are a broad class of compounds. Some are ingested in substantial quantities from nutritional sources, more are produced by medicinal plants, and some of them are taken as drugs. It is becoming clear, that a single polyphenol is impacting several cellular pathways. Thus, a network approach is becoming feasible, describing the interaction of a single polyphenol with cellular networks. Here we have selected icariin to draw a prototypic network of icariin activities. Icariin appears to be a promising drug to treat major age-related diseases, like neurodegeneration, memory and depressive disorders, chronic inflammation, diabetes, and osteoporosis. It interacts with several relevant pathways, like PDE, TGF-ß, MAPK, PPAR, NOS, IGF, Sirtuin, and others. Such networks will be useful to future comparative studies of complex effects of polyphenols.

Fish oil selectively improves heart function in a mouse model of lipid-induced cardiomyopathy

Fish oil (FO) supplementation may improve cardiac function in some patients with heart failure, especially those with diabetes. To determine why this occurs, we studied the effects of FO in mice with heart failure either due to transgenic expression of the lipid uptake protein acyl CoA synthetase 1 (ACS1) or overexpression of the transcription factor peroxisomal proliferator-activated receptor (PPAR) γ via the cardiac-specific myosin heavy chain (MHC) promoter. ACS1 mice and control littermates were fed 3 diets containing low-dose or high-dose FO or nonpurified diet (NPD) for 6 weeks. MHC-PPARγ mice were fed low-dose FO or NPD. Compared with control mice fed with NPD, ACS1, and MHC-PPARγ, mice fed with NPD had reduced cardiac function and survival with cardiac fibrosis. In contrast, ACS1 mice fed with high-dose FO had better cardiac function, survival, and less myocardial fibrosis. FO increased eicosapentaenoic and docosahexaenoic acids and reduced saturated fatty acids in cardiac diacylglycerols. This was associated with reduced protein kinase C alpha and beta activation. In contrast, low-dose FO reduced MHC-PPARγ mice survival with no change in protein kinase C activation or cardiac function. Thus, dietary FO reverses fibrosis and improves cardiac function and survival of ACS1 mice but does not benefit all forms of lipid-mediated cardiomyopathy.

Advanced glycation end-products enhance calcification in cultured rat dental pulp cells

INTRODUCTION

Amorphous calcification frequently appears in dental pulp tissues of diabetic patients; however, its pathologic process has not been fully elucidated. We previously found that pulp stones and thickened predentin occurred more frequently in diabetic rats. Recent findings demonstrated that accumulation of advanced glycation end-products (AGE) might be involved in vascular calcification complicated with diabetes. The aim of this study was to determine the effect of AGE on calcified nodule formation by rat dental pulp cells in culture.

METHODS

Rat dental pulp cells and gingival fibroblasts were independently cultured with 50 and 100 μg/mL AGE. Alkaline phosphatase activity and calcified nodule formation were measured. Expressions of receptor for AGE, osteopontin (OPN), and osteocalcin (OCN) mRNA were determined by quantitative real-time polymerase chain reaction. Protein levels of OPN and OCN secreted in culture medium were quantified by enzyme-linked immunosorbent assay.

RESULTS

AGE (50 and 100 μg/mL) markedly increased both alkaline phosphatase activity and calcified nodule formation in dental pulp cells (P < .01), whereas it did not affect those in gingival fibroblasts. Real-time polymerase chain reaction analysis revealed that AGE increased mRNA expressions of receptor for AGE, OPN, and OCN in dental pulp cells (P < .05). Enzyme-linked immunosorbent assay analysis revealed that the protein levels of OPN and OCN produced by dental pulp cells were higher in AGE-treated than in untreated cells (P < .05).

CONCLUSIONS

AGE enhanced the calcification potentials of rat dental pulp cells, suggesting that it may stimulate pathologic calcification of diabetic dental pulp tissues.

Activation of myocardial phosphoinositide-3-kinase p110α ameliorates cardiac dysfunction and improves survival in polymicrobial sepsis

Phosphoinositide-3-kinase (PI3K)/Akt dependent signaling has been shown to improve outcome in sepsis/septic shock. There is also ample evidence that PI3K/Akt dependent signaling plays a crucial role in maintaining normal cardiac function. We hypothesized that PI3K/Akt signaling may ameliorate septic shock by attenuating sepsis-induced cardiac dysfunction. Cardiac function and survival were evaluated in transgenic mice with cardiac myocyte specific expression of constitutively active PI3K isoform, p110α (caPI3K Tg). caPI3K Tg and wild type (WT) mice were subjected to cecal ligation/puncture (CLP) induced sepsis. Wild type CLP mice showed dramatic cardiac dysfunction at 6 hrs. Septic cardiomyopathy was significantly attenuated in caPI3K CLP mice. The time to 100% mortality was 46 hrs in WT CLP mice. In contrast, 80% of the caPI3K mice survived at 46 hrs after CLP (p<0.01) and 50% survived >30 days (p<0.01). Cardiac caPI3K expression prevented expression of an inflammatory phenotype in CLP sepsis. Organ neutrophil infiltration and lung apoptosis were also effectively inhibited by cardiac PI3k p110α expression. Cardiac high mobility group box–1 (HMGB-1) translocation was also inhibited by caPI3K p110α expression. We conclude that cardiac specific activation of PI3k/Akt dependent signaling can significantly modify the morbidity and mortality associated with sepsis. Our data also indicate that myocardial function/dysfunction plays a prominent role in the pathogenesis of sepsis and that maintenance of cardiac function during sepsis is essential. Finally, these data suggest that modulation of the PI3K/p110α signaling pathway may be beneficial in the prevention and/or management of septic cardiomyopathy and septic shock.

Matricellular proteins: new molecular targets to prevent heart failure

Matricellular proteins are highly expressed in reparative responses to pressure and volume overload, ischemia, oxidative stress after myocardial injury, and modulate the inflammatory and fibrotic process in ventricular remodeling, which leads to cardiac dysfunction and eventually overt heart failure. Generally, matricellular proteins loosen strong adhesion of cardiomyocytes to extracellular matrix, which would help cells to move for rearrangement and allow inflammatory cells and capillary vessels to spread during tissue remodeling. Among matricellular proteins, osteopontin (OPN) and tenascin-C (TN-C) are de-adhesion proteins and upregulate the expression and activity of matrix metalloproteinases. These matricellular proteins could be key molecules to diagnose cardiac remodeling and also might be targets for the prevention of adverse ventricular remodeling. This review provides an overview of the role of matricellular proteins such as OPN and TN-C in cardiac function and remodeling, as determined by both in basic and in clinical studies.

Sildenafil decreased cardiac cell apoptosis in diabetic mice: reduction of oxidative stress as a possible mechanism

Oxidative stress plays a dominant role in the pathogenesis of cardiac cell apoptosis in diabetic patients. Sildenafil has been demonstrated to have antioxidant effects. In this study, the effects of sildenafil on diabetes-induced cardiac cell apoptosis and the antioxidant status of diabetic mouse hearts were investigated. Diabetic mice showed lower body weight gains and heart weights compared with control mice, and sildenafil treatment did not increase these parameters in diabetic mice. Although apoptotic rates, caspase-3 enzyme activity, and malondialdehyde levels were significantly higher in diabetic mouse hearts than in controls, they were reduced in diabetic mice after sildenafil treatment. At the end of the first week, we observed no significant differences in antioxidant enzyme activities (CAT, GSH-Px, and SOD) in diabetic and control groups, whereas at the end of the second week of sildenafil treatment, antioxidant enzyme activities were higher in the diabetic group. In conclusion, our study indicated that sildenafil was beneficial to hearts of diabetic mice by reducing cardiac cell apoptosis, partially because of its antioxidant effects in the heart.

Transcriptomic analysis of patients with tetralogy of Fallot reveals the effect of chronic hypoxia on myocardial gene expression

OBJECTIVES

In cyanotic patients undergoing repair of heart defects, chronic hypoxia is thought to lead to greater susceptibility to ischemia and reoxygenation injury. We sought to find an explanation to such a hypothesis by investigating the cardiac gene expression in patients with tetralogy of Fallot undergoing cardiac surgery.

METHODS

The myocardial gene profile was investigated in right ventricular biopsy specimens obtained from 20 patients with a diagnosis of cyanotic (n = 11) or acyanotic (n = 9) tetralogy of Fallot undergoing surgical repair. Oligonucleotide microarray analyses were performed on the samples, and the array results were validated with Western blotting and enzyme-linked immunosorbent assay.

RESULTS

Data revealed 795 differentially expressed genes in cyanotic versus acyanotic hearts, with 198 upregulated and 597 downregulated. Growth/morphogenesis, remodeling, and apoptosis emerged as dominant functional themes for the upregulated genes and included the apoptotic gene TRAIL (tumor necrosis factor-related apoptosis-inducing ligand), the remodeling factor OPN (osteopontin), and the mitochondrial function gene COX11 (cytochrome-c oxidase 11). In contrast, transcription, mitogen-activated protein kinase signaling, and contractile machinery were the dominant functional classes for the downregulated genes, which included the calcium-handling gene NCX1 (sodium-calcium exchanger). Protein levels of COX11, NCX1, OPN, and LYZ (lysozyme) in the myocardium followed the same pattern obtained by means of transcriptomics. The TRAIL level did not change in myocardium but increased in circulating blood of cyanotic patients, suggesting the myocardium as a possible source. Additionally, our data showed increased protein expression of apoptosis markers in cyanotic myocardium.

CONCLUSIONS

Chronic hypoxia in cyanotic children with tetralogy of Fallot induced the expression of genes associated with apoptosis and remodeling and reduced the expression of genes associated with myocardium contractility and function.

Efficacy of olmesartan and nifedipine on recurrent hypoxia-induced left ventricular remodeling in diabetic mice

AIMS

Recurrent hypoxia due to sleep apnea syndrome is implicated in cardiovascular events, especially in diabetic patients, but the underlying mechanisms remain controversial. We previously reported that angiotensin II receptor blockers can improve hypoxia-induced left ventricular remodeling. The aim of this study was to examine the effect on left ventricular remodeling of adding a calcium channel blocker to angiotensin II receptor blocker therapy in diabetic mice exposed to recurrent hypoxia.

MAIN METHODS

Male db/db mice (8-week-old) and age-matched control db/+ mice were fed a Western diet and subjected to recurrent hypoxia (oxygen at 10+/-0.5% for 8h daily during the daytime) or normoxia for 3weeks. Hypoxic db/db mice were treated with the vehicle, olmesartan (3mg/kg/day), nifedipine (10mg/kg/day), or both drugs.

KEY FINDINGS

Recurrent hypoxia caused hypertrophy of cardiomyocytes, interstitial fibrosis, and a significant increase in expression of the oxidative stress marker 4-hydroxy-2-nonenal (4-HNE) in the left ventricular myocardium. Treatment with olmesartan, nifedipine, or both drugs had no effect on systolic blood pressure, and each treatment achieved similar suppression of 4-HNE expression. Olmesartan and the combination with olmesartan and nifedipine significantly prevented cardiomyocyte hypertrophy more than treatment with nifedipine alone. On the other hand, olmesartan combined with nifedipine significantly reduced cytokine expression, superoxide production and matrix metalloproteinase (MMP)-9 activity, and significantly suppressed interstitial fibrosis in the left ventricular myocardium.

SIGNIFICANCE

The combination with olmesartan and nifedipine, as well as a monotherapy with olmesartan, exerts preferable cardioprotection in diabetic mice exposed to recurrent hypoxia.

Osteopontin: role in extracellular matrix deposition and myocardial remodeling post-MI

Remodeling after myocardial infarction (MI) associates with left ventricular (LV) dilation, decreased cardiac function and increased mortality. The dynamic synthesis and breakdown of extracellular matrix (ECM) proteins play a significant role in myocardial remodeling post-MI. Expression of osteopontin (OPN) increases in the heart post-MI. Evidence has been provided that lack of OPN induces LV dilation which associates with decreased collagen synthesis and deposition. Inhibition of matrix metalloproteinases, key players in ECM remodeling process post-MI, increased ECM deposition (fibrosis) and improved LV function in mice lacking OPN after MI. This review summarizes--1) signaling pathways leading to increased expression of OPN in the heart; 2) the alterations in the structure and function of the heart post-MI in mice lacking OPN; and 3) mechanisms involved in OPN-mediated ECM remodeling post-MI.

High glucose promotes retinal endothelial cell migration through activation of Src, PI3K/Akt1/eNOS, and ERKs

Hyperglycemia impacts retinal vascular function and promotes the development and progression of diabetic retinopathy, which ultimately results in growth of new blood vessels and loss of vision. How high glucose affects retinal endothelial cell (EC) properties requires further investigation. Here we determined the impact of high glucose on mouse retinal EC function in vitro. High glucose significantly enhanced the migration of retinal EC without impacting their proliferation, apoptosis, adhesion, and capillary morphogenesis. The enhanced migration of retinal EC under high glucose was reversed in the presence of the antioxidant N-acetylcysteine, suggesting increased oxidative stress under high-glucose conditions. Retinal EC under high-glucose conditions also expressed increased levels of fibronectin, osteopontin, and alpha(v)beta(3)-integrin, and reduced levels of thrombospondin-1. These changes were concomitant with sustained activation of the downstream prosurvival and promigratory signaling pathways, including Src kinase, phosphatidylinositol 3-kinase/Akt1/endothelial nitric oxide synthase, and ERKs. The sustained activation of these signaling pathways was essential for enhanced migration of retinal EC under high-glucose conditions. Together, our results indicate the exposure of retinal EC to high glucose promotes a promigratory phenotype. Thus alterations in the proangiogenic properties of retinal EC during diabetes may contribute to the development and pathogenesis of diabetic retinopathy.

Differential roles of cardiomyocyte and macrophage peroxisome proliferator-activated receptor gamma in cardiac fibrosis

OBJECTIVE

Cardiac fibrosis is an important component of diabetic cardiomyopathy. Peroxisome proliferator-activated receptor gamma (PPARgamma) ligands repress proinflammatory gene expression, including that of osteopontin, a known contributor to the development of myocardial fibrosis. We thus investigated the hypothesis that PPARgamma ligands could attenuate cardiac fibrosis.

RESEARCH DESIGN AND METHODS

Wild-type cardiomyocyte- and macrophage-specific PPARgamma(-/-) mice were infused with angiotensin II (AngII) to promote cardiac fibrosis and treated with the PPARgamma ligand pioglitazone to determine the roles of cardiomyocyte and macrophage PPARgamma in cardiac fibrosis.

RESULTS

Cardiomyocyte-specific PPARgamma(-/-) mice (cPPARgamma(-/-)) developed spontaneous cardiac hypertrophy with increased ventricular osteopontin expression and macrophage content, which were exacerbated by AngII infusion. Pioglitazone attenuated AngII-induced fibrosis, macrophage accumulation, and osteopontin expression in both wild-type and cPPARgamma(-/-) mice but induced hypertrophy in a PPARgamma-dependent manner. We pursued two mechanisms to explain the antifibrotic cardiomyocyte-PPARgamma-independent effects of pioglitazone: increased adiponectin expression and attenuation of proinflammatory macrophage activity. Adenovirus-expressed adiponectin had no effect on cardiac fibrosis and the PPARgamma ligand pioglitazone did not attenuate AngII-induced cardiac fibrosis, osteopontin expression, or macrophage accumulation in monocyte-specific PPARgamma(-/-) mice.

CONCLUSIONS

We arrived at the following conclusions: 1) both cardiomyocyte-specific PPARgamma deficiency and activation promote cardiac hypertrophy, 2) both cardiomyocyte and monocyte PPARgamma regulate cardiac macrophage infiltration, 3) inflammation is a key mediator of AngII-induced cardiac fibrosis, 4) macrophage PPARgamma activation prevents myocardial macrophage accumulation, and 5) PPARgamma ligands attenuate AngII-induced cardiac fibrosis by inhibiting myocardial macrophage infiltration. These observations have important implications for potential interventions to prevent cardiac fibrosis.

Mouse models for studies of cardiovascular complications of type 1 diabetes

Mouse models represent a powerful tool for investigating the underlying mechanisms of disease. Type 1 diabetes results in a markedly increased risk of cardiovascular disease. The cardiovascular complications are manifested primarily as ischemic heart disease caused by accelerated atherosclerosis, but also as cardiomyopathy, defined as ventricular dysfunction in the absence of clear ischemic heart disease. Several mouse models are now available to study atherosclerosis and cardiomyopathy associated with type 1 diabetes. For studies of diabetes-accelerated atherosclerosis, these models include low-density lipoprotein (LDL) receptor-deficient and apolipoprotein E-deficient mice in which diabetes is induced by streptozotocin or viral infection. In these mouse models, type 1 diabetes can be induced without marked changes in plasma lipid levels, thereby mimicking the accelerated atherosclerosis seen in patients with type 1 diabetes. However, mouse models that exhibit thrombotic events and myocardial infarctions as a result of diabetes still need to be developed. Conversely, cardiomyopathy associated with diabetes has now been extensively evaluated in streptozotocin-treated C57BL/6 mice, and in transgenic mice expressing calmodulin under a beta-cell-specific promoter. These mouse models have given significant insight into the molecular mechanisms causing cardiomyopathy, and indicate that increased oxidative stress contributes to diabetes-associated cardiomyopathy. In this review, we will discuss the available mouse models for studies of cardiovascular complications of type 1 diabetes, the potential mechanisms underlying these complications, and the need for new and improved mouse models.