Impact of type 1 diabetes on cardiac fibroblast activation: enhanced cell cycle progression and reduced myofibroblast content in diabetic myocardium

LPS differentially affects expression of CD14 and CCR2 in monocyte subsets of Post-STEMI patients with hyperglycemia

AIMS

Following ST-segment elevation myocardial infarction (STEMI), recruitment and activation of monocytes [classical (CD14⁺⁺CD16^-CCR2⁺⁺), intermediate (CD14⁺⁺CD16⁺CCR2⁺), non-classical (CD14^LowCD16⁺⁺CCR2^Low)] are needed for myocardial wound healing. Monocyte surface receptor CC chemokine receptor type 2 (CCR2) is responsible for monocyte chemotaxis to sites of inflammation and the lipopolysaccharide (LPS)-binding protein co-receptor, CD14, is involved in pro-inflammatory monocyte activation. The purpose of this investigation was to determine the effects of ex-vivo LPS activation on monocyte subset CD14 and CCR2 expression in post-STEMI individuals with normal and elevated random blood glucose.

METHODS

Post-STEMI subjects were identified as normal random glucose (NG, <98 mg/dL, n = 13) or impaired random glucose (IG, ≥98 mg/dL, n = 26) and monocytes were analyzed for non-activated and LPS-activated (1 µg/mL for 4 h) CCR2 and CD14 expression.

RESULTS

Non-activated intermediate monocytes from IG showed decreased CD14 expression when compared to NG, which was maintained following LPS-activation. The NG group showed a larger absolute reduction in classical CCR2 expression, leading to a significant difference between NG and IG following LPS-activation.

CONCLUSION

Results suggest a heightened response to pro-inflammatory activation in IG following STEMI, which may impair or delay post-STEMI myocardial healing, and thus increase the incidence of chronic heart failure. NIH 1R34HL121402.

Reverse remodelling in diabetic cardiomyopathy: the role of extracellular matrix

Diabetic patients are prone to suffer from cardiovascular disease, specifically from ischemic heart disease and diabetic cardiomyopathy, which have a huge impact on morbidity and mortality worldwide. Cardiac fibrosis due to alteration of the extracellular matrix (ECM) remodelling is often observed in diabetes and myocardial fibrosis is an important part of cardiac remodeling that leads to heart failure and death. At single-cell level, the ECM govern, metabolism, motility, orientation and proliferation. However, in pathological condition such as diabetes, changes in ECM lead to fibrosis and subsequently cardiac stiffness and cardiomyocytes dysfunction. Anti-diabetic drugs, particularly sodium-glucose cotransporter-2 (SGLT2) inhibitors have anti-fibrotic effects, and may promote ECM reverse remodelling. In this mini-review, the mechanisms and the role of ECM remodelling and reverse remodelling as a potential therapeutic targets for diabetic cardiomyopathy are discussed.

Protein O-GlcNAcylation in the heart

O-GlcNAcylation is a ubiquitous post-translational modification that is extremely labile and plays a significant role in physiology, including the heart. Sustained activation of cardiac O-GlcNAcylation is frequently associated with alterations in cellular metabolism, leading to detrimental effects on cardiovascular function. This is particularly true during conditions such as diabetes, hypertension, cardiac remodelling, heart failure and arrhythmogenesis. Paradoxically, transient elevation of cardiac protein O-GlcNAcylation can also exert beneficial effects in the heart. There is compelling evidence to suggest that a complex interaction between O-GlcNAcylation and phosphorylation also exists in the heart. Beyond direct functional consequences on cardiomyocytes, O-GlcNAcylation also acts indirectly by altering the function of transcription factors that affect downstream signalling. This review focuses on the potential cardioprotective role of protein O-GlcNAcylation during ischaemia-reperfusion injury, the deleterious consequences of chronically elevated O-GlcNAc levels, the interplay between O-GlcNAcylation and phosphorylation in the cardiomyocytes and the effects of O-GlcNAcylation on other major non-myocyte cell types in the heart.

The Diabetic Cardiac Fibroblast: Mechanisms Underlying Phenotype and Function

Diabetic cardiomyopathy involves remodeling of the heart in response to diabetes that includes microvascular damage, cardiomyocyte hypertrophy, and cardiac fibrosis. Cardiac fibrosis is a major contributor to diastolic dysfunction that can ultimately result in heart failure with preserved ejection fraction. Cardiac fibroblasts are the final effector cell in the process of cardiac fibrosis. This review article aims to describe the cardiac fibroblast phenotype in response to high-glucose conditions that mimic the diabetic state, as well as to explain the pathways underlying this phenotype. As such, this review focuses on studies conducted on isolated cardiac fibroblasts. We also describe molecules that appear to oppose the pro-fibrotic actions of high glucose on cardiac fibroblasts. This represents a major gap in knowledge in the field that needs to be addressed.

Trimetazidine inhibits cardiac fibrosis by reducing reactive oxygen species and downregulating connective tissue growth factor in streptozotocin-induced diabetic rats

Diabetes may affect myocardial fibrosis through oxidative stress. Trimetazidine (TMZ) is an anti-anginal agent. The present study aimed to determine the modulatory effect of TMZ on reactive oxygen species (ROS) and connective tissue growth factor (CTGF) expression and to evaluate the potential of TMZ to improve diastolic function in streptozotocin (STZ)-induced diabetic rats. After treating STZ-induced diabetic rats with TMZ for 16 weeks, a decrease in malondialdehyde levels, cardiac collagen volume fraction, left ventricular (LV) end-diastolic pressure and protein expression of collagen-I (Col I), Col III and CTGF compared with those in diabetic control rats was observed. In vitro, TMZ inhibited Col I, Col III and CTGF protein expression in cardiac fibroblasts treated with high glucose and decreased intracellular ROS generation and hydroxyproline content in the cell culture medium of cardiac fibroblasts. TMZ markedly improved cardiac fibrosis and diastolic function in diabetic rats. This effect was associated with a reduction in ROS production and CTGF expression in cardiac fibroblasts. The present study suggests that TMZ may be beneficial for protecting the hearts of diabetic patients.

Hyperglycemia induces vascular smooth muscle cell dedifferentiation by suppressing insulin receptor substrate-1-mediated p53/KLF4 complex stabilization

Hyperglycemia and insulin resistance accelerate atherosclerosis by an unclear mechanism. The two factors down-regulate insulin receptor substrate-1 (IRS-1), an intermediary of the insulin/IGF-I signaling system. We previously reported that IRS-1 down-regulation leads to vascular smooth muscle cell (VSMC) dedifferentiation and that IRS-1 deletion from VSMCs in normoglycemic mice replicates this response. However, we did not determine IRS-1's role in mediating differentiation. Here, we sought to define the mechanism by which IRS-1 maintains VSMC differentiation. High glucose or IRS-1 knockdown decreased p53 levels by enhancing MDM2 proto-oncogene (MDM2)-mediated ubiquitination, resulting in decreased binding of p53 to Krüppel-like factor 4 (KLF4). Exposure to nutlin-3, which dissociates MDM2/p53, decreased p53 ubiquitination and enhanced the p53/KLF4 association and differentiation marker protein expression. IRS-1 overexpression in high glucose inhibited the MDM2/p53 association, leading to increased p53 and p53/KLF4 levels, thereby increasing differentiation. Nutlin-3 treatment of diabetic or Irs1 ^-/- mice enhanced p53/KLF4 and the expression of p21, smooth muscle protein 22 (SM22), and myocardin and inhibited aortic VSMC proliferation. Injecting normoglycemic mice with a peptide disrupting the IRS-1/p53 association reduced p53, p53/KLF4, and differentiation. Analyzing atherosclerotic lesions in hypercholesterolemic, diabetic pigs, we found that p53, IRS-1, SM22, myocardin, and KLF4/p53 levels are significantly decreased compared with their expression in nondiabetic pigs. We conclude that IRS-1 is critical for maintaining VSMC differentiation. Hyperglycemia- or insulin resistance-induced IRS-1 down-regulation decreases the p53/KLF4 association and enhances dedifferentiation and proliferation. Our results suggest that enhancing IRS-1-dependent p53 stabilization could attenuate the progression of atherosclerotic lesions in hyperglycemia and insulin-resistance states.

Argatroban Attenuates Diabetic Cardiomyopathy in Rats by Reducing Fibrosis, Inflammation, Apoptosis, and Protease-Activated Receptor Expression

PURPOSE

Chronic diabetes is associated with cardiovascular dysfunctions. Diabetic cardiomyopathy (DCM) is one of the serious cardiovascular complications associated with diabetes. Despite significant efforts in understanding the pathophysiology of DCM, management of DCM is not adequate due to its complex pathophysiology. Recently, involvement of protease-activated receptors (PARs) has been postulated in cardiovascular diseases. These receptors are activated by thrombin, trypsin, or other serine proteases. Expression of PAR has been shown to be increased in cardiac diseases such as myocardial infarction, viral myocarditis, and pulmonary arterial hypertension. However, the role of PAR in DCM has not been elucidated yet. Therefore, in the present study, we have investigated the role of PAR in the condition of DCM using a pharmacological approach. We used argatroban, a direct thrombin inhibitor for targeting PAR.

METHODS

Type-2 diabetes mellitus (T2DM) was induced by high-fat feeding along with low dose streptozotocin (STZ 35 mg/kg, i.p. single dose) in male Sprague-Dawley rats. After 16 weeks of diabetes induction, animals were treated with argatroban at 0.3 and 1 mg/kg dose daily for 4 weeks. After 20 weeks, ventricular functions were measured using ventricular catheterization. Cardiac histology, TUNEL staining, and immunoblotting were performed to evaluate cardiac fibrosis, DNA fragmentation, and expression level of different proteins, respectively.

RESULTS

T2DM was associated with cardiac structural and functional disturbances as evidenced from impaired cardiac functional parameters and increased fibrosis. There was a significant increase in PAR expression after 20 weeks of diabetes induction. Four weeks argatroban treatment ameliorated metabolic alterations (reduced plasma glucose and cholesterol), ventricular dysfunctions (improved systolic and diastolic functions), cardiac fibrosis (reduced percentage area of collagen in picro-sirius red staining), and apoptosis (reduced TUNEL positive nuclei). Reduced expression of PAR1 and PAR4 in the argatroban-treated group indicates a response towards inhibition of thrombin. In addition, AKT (Ser-473), GSK-3β (Ser-9), p-65 NFĸB phosphorylation, TGF-β, COX-2, and caspase-3 expression were reduced significantly along with an increase in SERCA expression in argatroban-treated diabetic rats which indicated the anti-fibrotic, anti-inflammatory, and anti-apoptotic potential of argatroban in DCM.

CONCLUSION

This study suggests the ameliorative effects of argatroban in diabetic cardiomyopathy by improving ventricular functions and reducing fibrosis, inflammation, apoptosis, and PAR expression.

Periodontal-induced chronic inflammation triggers macrophage secretion of Ccl12 to inhibit fibroblast-mediated cardiac wound healing

Chronic inflammatory diseases, such as periodontal disease, associate with adverse wound healing in response to myocardial infarction (MI). The goal of this study was to elucidate the molecular basis for impaired cardiac wound healing in the setting of periodontal-induced chronic inflammation. Causal network analysis of 168 inflammatory and extracellular matrix genes revealed that chronic inflammation induced by a subseptic dose of Porphyromonas gingivalis lipopolysaccharide (LPS) exacerbated infarct expression of the proinflammatory cytokine Ccl12. Ccl12 prevented initiation of the reparative response by prolonging inflammation and inhibiting fibroblast conversion to myofibroblasts, resulting in diminished scar formation. Macrophage secretion of Ccl12 directly impaired fibronectin and collagen deposition and indirectly stimulated collagen degradation through upregulation of matrix metalloproteinase-2. In post-MI patients, circulating LPS levels strongly associated with the Ccl12 homologue monocyte chemotactic protein 1 (MCP-1). Patients with LPS levels ≥ 1 endotoxin units (EU)/ml (subseptic endotoxemia) at the time of hospitalization had increased end diastolic and systolic dimensions compared with post-MI patients with < 1 EU/ml, indicating that low yet pathological concentrations of circulating LPS adversely impact post-MI left ventricle (LV) remodeling by increasing MCP-1. Our study provides the first evidence to our knowledge that chronic inflammation inhibits reparative fibroblast activation and generates an unfavorable cardiac-healing environment through Ccl12-dependent mechanisms.

MicroRNA-9 inhibits high glucose-induced proliferation, differentiation and collagen accumulation of cardiac fibroblasts by down-regulation of TGFBR2

To investigate the effects of miR-9 on high glucose (HG)-induced cardiac fibrosis in human cardiac fibroblasts (HCFs), and to establish the mechanism underlying these effects. HCFs were transfected with miR-9 inhibitor or mimic, and then treated with normal or HG. Cell viability and proliferation were detected by using the Cell Counting Kit-8 (CCK-8) assay and Brdu-ELISA assay. Cell differentiation and collagen accumulation of HCFs were detected by qRT-PCR and Western blot assays respectively. The mRNA and protein expressions of transforming growth factor-β receptor type II (TGFBR2) were determined by qRT-PCR and Western blotting. Up-regulation of miR-9 dramatically improved HG-induced increases in cell proliferation, differentiation and collagen accumulation of HCFs. Moreover, bioinformatics analysis predicted that the TGFBR2 was a potential target gene of miR-9 Luciferase reporter assay demonstrated that miR-9 could directly target TGFBR2. Inhibition of TGFBR2 had the similar effect as miR-9 overexpression. Down-regulation of TGFBR2 in HCFs transfected with miR-9 inhibitor partially reversed the protective effect of miR-9 overexpression on HG-induced cardiac fibrosis in HCFs. Up-regulation of miR-9 ameliorates HG-induced proliferation, differentiation and collagen accumulation of HCFs by down-regulation of TGFBR2. These results provide further evidence for protective effect of miR-9 overexpression on HG-induced cardiac fibrosis.

Investigating inherent functional differences between human cardiac fibroblasts cultured from nondiabetic and Type 2 diabetic donors

INTRODUCTION

Type 2 diabetes mellitus (T2DM) promotes adverse myocardial remodeling and increased risk of heart failure; effects that can occur independently of hypertension or coronary artery disease. As cardiac fibroblasts (CFs) are key effectors of myocardial remodeling, we investigated whether inherent phenotypic differences exist in CF derived from T2DM donors compared with cells from nondiabetic (ND) donors.

METHODS

Cell morphology (cell area), proliferation (cell counting over 7-day period), insulin signaling [phospho-Akt and phospho-extracellular signal-regulated kinase (ERK) Western blotting], and mRNA expression of key remodeling genes [real-time reverse transcription-polymerase chain reaction (RT-PCR)] were compared in CF cultured from atrial tissue from 14 ND and 12 T2DM donors undergoing elective coronary artery bypass surgery.

RESULTS

The major finding was that Type I collagen (COL1A1) mRNA levels were significantly elevated by twofold in cells derived from T2DM donors compared with those from ND donors; changes reflected at the protein level. T2DM cells had similar proliferation rates but a greater variation in cell size and a trend towards increased cell area compared with ND cells. Insulin-induced Akt and ERK phosphorylation were similar in the two cohorts of cells.

CONCLUSION

CF from T2DM individuals possess an inherent profibrotic phenotype that may help to explain the augmented cardiac fibrosis observed in diabetic patients.

MINI SUMMARY

We investigated whether inherent phenotypic differences exist between CF cultured from donors with or without Type 2 diabetes. Cell morphology, proliferation, insulin signaling, and gene expression were compared between multiple cell populations. The major finding was that Type I collagen levels were elevated in fibroblasts from diabetic donors, which may help explain the augmented cardiac fibrosis observed with diabetes.

Hyperglycemia enhances function and differentiation of adult rat cardiac fibroblasts

Diabetes is an independent risk factor for cardiovascular disease that can eventually cause cardiomyopathy and heart failure. Cardiac fibroblasts (CF) are the critical mediators of physiological and pathological cardiac remodeling; however, the effects of hyperglycemia on cardiac fibroblast function and differentiation is not well known. Here, we performed a comprehensive investigation on the effects of hyperglycemia on cardiac fibroblasts and show that hyperglycemia enhances cardiac fibroblast function and differentiation. We found that high glucose treatment increased collagen I, III, and VI gene expression in rat adult cardiac fibroblasts. Interestingly, hyperglycemia increased CF migration and proliferation that is augmented by collagen I and III. Surprisingly, we found that short term hyperglycemia transiently inhibited ERK1/2 activation but increased AKT phosphorylation. Finally, high glucose treatment increased spontaneous differentiation of cardiac fibroblasts to myofibroblasts with increasing passage compared with low glucose. Taken together, these findings suggest that hyperglycemia induces cardiac fibrosis by modulating collagen expression, migration, proliferation, and differentiation of cardiac fibroblasts.

TRPV4 channels mediate cardiac fibroblast differentiation by integrating mechanical and soluble signals

The phenotypic switch underlying the differentiation of cardiac fibroblasts into hypersecretory myofibroblasts is critical for cardiac remodeling following myocardial infarction. Myofibroblasts facilitate wound repair in the myocardium by secreting and organizing extracellular matrix (ECM) during the wound healing process. However, the molecular mechanisms involved in myofibroblast differentiation are not well known. TGF-β has been shown to promote differentiation and this, combined with the robust mechanical environment in the heart, lead us to hypothesize that the mechanotransduction and TGF-β signaling pathways play active roles in the differentiation of cardiac fibroblasts to myofibroblasts. Here, we show that the mechanosensitve ion channel TRPV4 is required for TGF-β1-induced differentiation of cardiac fibroblasts into myofibroblasts. We found that the TRPV4-specific antagonist AB159908 and siRNA knockdown of TRPV4 significantly inhibited TGFβ1-induced differentiation as measured by incorporation of α-SMA into stress fibers. Further, we found that TGF-β1-induced myofibroblast differentiation was dependent on ECM stiffness, a response that was attenuated by TRPV4 blockade. Finally, TGF-β1 treated fibroblasts exhibited enhanced TRPV4 expression and TRPV4-mediated calcium influx compared to untreated controls. Taken together these results suggest for the first time that the mechanosensitive ion channel, TRPV4, regulates cardiac fibroblast differentiation to myofibroblasts by integrating signals from TGF-β1 and mechanical factors.

Anti-fibrotic cardio protective efficacy of aminoguanidine against streptozotocin induced cardiac fibrosis and high glucose induced collagen up regulation in cardiac fibroblasts

This study mainly focuses on cardio protective anti-fibrotic activity of aminoguanidine against streptozotocin induced cardiac fibrosis and high glucose induced collagen accumulation in cardiac fibroblasts. Dysregulation of matrix metalloproteinase especially 2 and 9 were considered to be responsible for the abnormal collagen deposition, which resulting improper cardiac contractile function in diabetic mice. Mice received a single dose of streptozotocin (100 mg/kg) through tail vein to induce diabetes. Normal and diabetic mice received aminoguanidine orally (100 mg/kg/day) throughout the study period of 8 weeks. Cardiac fibroblasts cultured and exposed to high glucose, aminoguanidine and both for 48 h. Collagen quantitatively estimated in both in vivo and in vitro models. Altered structural changes were studied using the Masson tri-chrome staining, TEM images of cardiac sections. Increased collagen and metalloproteinase activities were confirmed using gelatin zymography, western blotting and gene expression studies. The exact mechanism responsible for high glucose induced collagen up regulation in diabetic heart was incompletely understood. From this above in vivo and in vitro results, we conclude that, the cardio protective anti fibrotic activity of amino guanidine was mainly attributed by exhibiting the inhibitory efficacy against streptozotocin and high glucose induced collagen accumulation probably by inhibiting high glucose altered metalloproteinase-2 and -9 activities.

Diabetes-induced alterations in the extracellular matrix and their impact on myocardial function

Diabetes is an increasing public health problem that is expected to escalate in the future due to the growing incidence of obesity in the western world. While this disease is well known for its devastating effects on the kidneys and vascular system, diabetic individuals can develop cardiac dysfunction, termed diabetic cardiomyopathy, in the absence of other cardiovascular risk factors such as hypertension or atherosclerosis. While much effort has gone into understanding the effects of elevated glucose or altered insulin sensitivity on cellular components within the heart, significant changes in the cardiac extracellular matrix (ECM) have also been noted. In this review article we highlight what is currently known regarding the effects diabetes has on both the expression and chemical modification of proteins within the ECM and how the fibrotic response often observed as a consequence of this disease can contribute to reduced cardiac function.

Micro-ultrasound for preclinical imaging

Over the past decade, non-invasive preclinical imaging has emerged as an important tool to facilitate biomedical discovery. Not only have the markets for these tools accelerated, but the numbers of peer-reviewed papers in which imaging end points and biomarkers have been used have grown dramatically. High frequency 'micro-ultrasound' has steadily evolved in the post-genomic era as a rapid, comparatively inexpensive imaging tool for studying normal development and models of human disease in small animals. One of the fundamental barriers to this development was the technological hurdle associated with high-frequency array transducers. Recently, new approaches have enabled the upper limits of linear and phased arrays to be pushed from about 20 to over 50 MHz enabling a broad range of new applications. The innovations leading to the new transducer technology and scanner architecture are reviewed. Applications of preclinical micro-ultrasound are explored for developmental biology, cancer, and cardiovascular disease. With respect to the future, the latest developments in high-frequency ultrasound imaging are described.