High-mobility group box 1 induces calcineurin-mediated cell hypertrophy in neonatal rat ventricular myocytes

Targeting HMGB1 and Its Interaction with Receptors: Challenges and Future Directions

High mobility group box 1 (HMGB1) is a nonhistone chromatin protein predominantly located in the nucleus. However, under pathological conditions, HMGB1 can translocate from the nucleus to the cytoplasm and subsequently be released into the extracellular space through both active secretion and passive release mechanisms. The distinct cellular locations of HMGB1 facilitate its interaction with various endogenous and exogenous factors, allowing it to perform diverse functions across a range of diseases. This Perspective provides a comprehensive overview of the structure, release mechanisms, and multifaceted roles of HMGB1 in disease contexts. Furthermore, it introduces the development of both small molecule and macromolecule inhibitors targeting HMGB1 and its interaction with receptors. A detailed analysis of the predicted pockets is also presented, aiming to establish a foundation for the future design and development of HMGB1 inhibitors.

Long noncoding RNA AK144717 exacerbates pathological cardiac hypertrophy through modulating the cellular distribution of HMGB1 and subsequent DNA damage response

DNA damage induced by oxidative stress during cardiac hypertrophy activates the ataxia telangiectasia mutated (ATM)-mediated DNA damage response (DDR) signaling, in turn aggravating the pathological cardiomyocyte growth. This study aims to identify the functional associations of long noncoding RNA (lncRNAs) with cardiac hypertrophy and DDR. The altered ventricular lncRNAs in the mice between sham and transverse aortic constriction (TAC) group were identified by microarray analysis, and a novel lncRNA AK144717 was found to gradually upregulate during the development of pathological cardiac hypertrophy induced by TAC surgery or angiotensin II (Ang II) stimulation. Silencing AK144717 had a similar anti-hypertrophic effect to that of ATM inhibitor KU55933 and also suppressed the activated ATM-DDR signaling induced by hypertrophic stimuli. The involvement of AK144717 in DDR and cardiac hypertrophy was closely related to its interaction with HMGB1, as silencing HMGB1 abolished the effects of AK144717 knockdown. The binding of AK144717 to HMGB1 prevented the interaction between HMGB1 and SIRT1, contributing to the increased acetylation and then cytosolic translocation of HMGB1. Overall, our study highlights the role of AK144717 in the hypertrophic response by interacting with HMGB1 and regulating DDR, hinting that AK144717 is a promising therapeutic target for pathological cardiac growth.

Calcium-Regulating Hormonal System and HMGB1 in Cardiomyopathies

BACKGROUND

Calcium ions play a key role in the heart's functional activity. The steadystate levels of calcium are contingent on the calcium regulating hormonal system, impairment of which might result in the development of cardiac pathology. An important role in these processes is also attributed to the specific inflammatory mediator, HMGB1, one of the damage-associated molecular patterns (DAMPs) released by immune cells or cell damage.

OBJECTIVE

This study investigated the cardioprotective potential of the calcium-regulating hormonal system in cardiomyopathies with an emphasis on the possible role of HMGB1.

METHODS

Ca2+ and inorganic phosphate levels were determined in the serum using an electrolyte analyzer and spectrophotometric analyzer correspondingly. The 1-34 fragment of parathyroid hormone (PTH), calcitonin, vitamin D, and HMGB1 were detected using ELISA kits.

RESULTS

The levels of PTH, calcitonin, phosphate, and HMGB1 were found elevated in females suffering from cardiomyopathy. The same tendency was observed in men; however, statistically significant changes were registered only for PTH and phosphate.

CONCLUSION

It can be suggested that among other reasons, the decrease of the left ventricular function in cardiomyopathy patients can be linked to the high HMGB1, whereas the activation of the calciumregulating system as manifested by the elevated PTH aims at restoration of calcium homeostasis and thus have positive, i.e. cardioprotective consequences.

Role of High Mobility Group Box 1 in Cardiovascular Diseases

High Mobility Group Box 1 (HMGB1) is a ubiquitous, highly conserved nuclear and cytosolic protein that has diverse biological roles depending on its cellular location and posttranslational modifications. The HMGB1 is localized in the nucleus but can be translocated to the cytoplasm to modulate the intracellular signaling and eventually secreted outside the cells. It is widely established that HMGB1 plays a key role in inflammation; however, the role of HMGB1 in the cardiovascular diseases is not well understood. In this review, we will discuss the latest reports on the pathophysiological link between HMGB1 and cardiovascular complications, with special emphasis on the inflammation. Thus, the understanding of the role of HMGB1 may provide new insights into developing new HMGB1-based therapies.

Increased Death of Peripheral Blood Mononuclear Cells after TLR4 Inhibition in Sepsis Is Not via TNF/TNF Receptor-Mediated Apoptotic Pathway

Background

Apoptosis is one of the causes of immune depression in sepsis. Pyroptosis also occurs in sepsis. The toll-like receptor (TLR) 4 and receptor for advanced glycation end products (RAGE) have been shown to play important roles in apoptosis and pyroptosis. However, it is still unknown whether TLR4 inhibition decreases apoptosis in sepsis.

Methods

Stimulated peripheral blood mononuclear cells (PBMCs) with or without lipopolysaccharides (LPS) and high-mobility group box 1 (HMGB1) were cultured with or without TLR4 inhibition using monoclonal antibodies from 20 patients with sepsis. Caspase-3, caspase-8, and caspase-9 activities were measured. The expression of B cell lymphoma 2 (Bcl2) and Bcl2-associated X (Bax) was measured. The cell death of PBMCs was detected using a flow cytofluorimeter.

Results

After TLR4 inhibition, Bcl2 to Bax ratio elevated both in LPS and HMGB1-stimulated PBMCs. The activities of caspase-3, caspase-8, and caspase-9 did not change in LPS or HMGB1-stimulated PBMCs. The cell death of LPS and HMGB1-stimulated CD8 lymphocytes and monocytes increased after TLR4 inhibition. The cell death of CD4 lymphocytes was unchanged.

Conclusion

The apoptosis did not decrease, while TLR4 was inhibited. After TLR4 inhibition, there was an unknown mechanism to keep cell death in stimulated PBMCs in patients with sepsis.

AT1 receptor blocker inhibits HMGB1 expression in pressure overload-induced acute cardiac dysfunction by suppressing the MAPK/NF-κB signaling pathway

BACKGROUND

High-mobility group box 1 (HMGB1) expression not only peaks during the early phase of pressure overload (PO), but also serves a role in the pathogenesis of PO-induced cardiac remodeling. Meanwhile, angiotensin II type 1 (AT1) receptor blockers reverse PO-induced cardiac remodeling and repress the secretion of inflammatory factors. However, whether AT1 receptor inhibitors decrease HMGB1 expression in the early stages of PO remains unknown.

MATERIALS AND METHODS

PO mouse models were established using transverse aortic constriction (TAC), in which losartan was administrated. Transthoracic echocardiography was performed 3 days after the operation, and serum and cardiac HMGB1 expression, as well as the expression levels of related proteins were measured.

RESULTS

PO-induced acute cardiac dysfunction was observed 3 days after TAC, and was subsequently slightly, but not significantly relieved by losartan. The expression levels of HMGB1, tumor necrosis factor-α and interleukin-6 in both the serum and myocardium were upregulated in response to TAC, while they were significantly reduced by losartan. Moreover, the phosphorylation of extracellular signal-regulated kinases, p38 mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) in the myocardium were significantly increased under PO, and this was also prevented by losartan.

CONCLUSION

These data suggest that losartan may downregulate the expression of HMGB1 in acute cardiac dysfunction induced by PO by inhibiting the MAPKs/NF-κB signaling pathway, which indicates a novel beneficial role of AT1 receptor antagonists in ameliorating cardiac remodeling under PO.

Recombinant high‑mobility group box 1 induces cardiomyocyte hypertrophy by regulating the 14‑3‑3η, PI3K and nuclear factor of activated T cells signaling pathways

High-mobility group box 1 (HMGB1) is released by necrotic cells and serves an important role in cardiovascular pathology. However, the effects of HMGB1 in cardiomyocyte hypertrophy remain unclear. Therefore, the aim of the present study was to investigate the potential role of HMGB1 in cardiomyocyte hypertrophy and the underlying mechanisms of its action. Neonatal mouse cardiomyocytes (NMCs) were co-cultured with recombinant HMGB1 (rHMGB1). Wortmannin was used to inhibit PI3K activity in cardiomyocytes. Subsequently, atrial natriuretic peptide (ANP), 14-3-3 and phosphorylated-Akt (p-Akt) protein levels were detected using western blot analysis. In addition, nuclear factor of activated T cells 3 (NFAT3) protein levels were measured by western blot analysis and observed in NMCs under a confocal microscope. The results revealed that rHMGB1 increased ANP and p-Akt, and decreased 14-3-3η protein levels. Furthermore, wortmannin abrogated the effects of rHMGB1 on ANP, 14-3-3η and p-Akt protein levels. In addition, rHMGB1 induced nuclear translocation of NFAT3, which was also inhibited by wortmannin pretreatment. The results of this study suggest that rHMGB1 induces cardiac hypertrophy by regulating the 14-3-3η/PI3K/Akt/NFAT3 signaling pathway.

Novel Therapeutic Effects of Pterosin B on Ang II-Induced Cardiomyocyte Hypertrophy

Pathological cardiac hypertrophy is characterized by an abnormal increase in cardiac muscle mass in the left ventricle, resulting in cardiac dysfunction. Although various therapeutic approaches are being continuously developed for heart failure, several studies have suggested natural compounds as novel potential strategies. Considering relevant compounds, we investigated a new role for Pterosin B for which the potential life-affecting biological and therapeutic effects on cardiomyocyte hypertrophy are not fully known. Thus, we investigated whether Pterosin B can regulate cardiomyocyte hypertrophy induced by angiotensin II (Ang II) using H9c2 cells. The antihypertrophic effect of Pterosin B was evaluated, and the results showed that it reduced hypertrophy-related gene expression, cell size, and protein synthesis. In addition, upon Ang II stimulation, Pterosin B attenuated the activation and expression of major receptors, Ang II type 1 receptor and a receptor for advanced glycation end products, by inhibiting the phosphorylation of PKC-ERK-NF-κB pathway signaling molecules. In addition, Pterosin B showed the ability to reduce excessive intracellular reactive oxygen species, critical mediators for cardiac hypertrophy upon Ang II exposure, by regulating the expression levels of NAD(P)H oxidase 2/4. Our results demonstrate the protective role of Pterosin B in cardiomyocyte hypertrophy, suggesting it is a potential therapeutic candidate.

HMGB1 enhances mechanical stress-induced cardiomyocyte hypertrophy in vitro via the RAGE/ERK1/2 signaling pathway

Pressure overload-induced cardiac hypertrophy is associated with a complex spectrum of pathophysiological mechanisms, including the inflammation response. High mobility group box-1 (HMGB1), a pro-inflammatory cytokine, is not only increased in myocardium under pressure overload, but also exacerbates pressure overload-induced cardiac hypertrophy and dysfunction; however, the underlying mechanisms have remained elusive. In the present study, cultured cardiomyocytes were stimulated by mechanical stress and/or HMGB1 for various durations to examine the role of HMGB1 in cardiomyocyte hypertrophy, and to detect the expression of receptor for advanced glycation end products (RAGE), toll-like receptor 4 (TLR-4) and the activation status of mitogen-activated protein kinases (MAPKs) and Janus kinase 2 (JAK2)/STAT3. The results indicated that HMGB1 aggravated mechanical stress-induced cardiomyocyte hypertrophy. Furthermore, mechanical stress and HMGB1 stimulation activated extracellular signal-regulated kinase 1/2 (ERK1/2), P38 and JAK2/STAT3 signaling in cardiomyocytes, but an additive effect of the combined stimuli was only observed on the activation of ERK1/2. In addition, mechanical stress caused a prompt upregulation of the expression of RAGE and TLR-4 in cardiomyocytes, while the activation of ERK1/2 by HMGB1 was inhibited by blockage of RAGE, but not by blockage of TLR-4. In summary, the present results indicated that extracellular HMGB1 enhanced mechanical stress-induced cardiomyocyte hypertrophy in vitro, at least partially via the RAGE/ERK1/2 signaling pathway.

Cardiac Nuclear High-Mobility Group Box 1 Ameliorates Pathological Cardiac Hypertrophy by Inhibiting DNA Damage Response

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HMGB1 is a DNA-binding protein associated with nuclear homeostasis and DNA repair.

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Decreased nuclear HMGB1 expression is observed in human failing hearts, which is associated with cardiomyocyte hypertrophy and fibrosis.

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Cardiac nuclear HMGB1 overexpression ameliorates Ang II–induced pathological cardiac remodeling by inhibiting cardiomyocyte DNA damage and following ataxia telangiectasia mutated activation in mice.

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Ataxia telangiectasia mutated inhibitor treatment provided a cardioprotective effect on Ang II–induced cardiac remodeling in mice.

High-mobility group box 1 (HMGB1) is a deoxyribonucleic acid (DNA)–binding protein associated with DNA repair. Decreased nuclear HMGB1 expression and increased DNA damage response (DDR) were observed in human failing hearts. DNA damage and DDR as well as cardiac remodeling were suppressed in cardiac-specific HMGB1 overexpression transgenic mice after angiotensin II stimulation as compared with wild-type mice. In vitro, inhibition of HMGB1 increased phosphorylation of extracellular signal-related kinase 1/2 and nuclear factor kappa B, which was rescued by DDR inhibitor treatment. DDR inhibitor treatment provided a cardioprotective effect on angiotensin II–induced cardiac remodeling in mice.

The Janus face of HMGB1 in heart disease: a necessary update

High mobility group box 1 (HMGB1) is a ubiquitous nuclear protein involved in transcription regulation, DNA replication and repair and nucleosome assembly. HMGB1 is passively released by necrotic tissues or actively secreted by stressed cells. Extracellular HMGB1 acts as a damage-associated molecular pattern (DAMPs) molecule and gives rise to several redox forms that by binding to different receptors and interactors promote a variety of cellular responses, including tissue inflammation or regeneration. Inhibition of extracellular HMGB1 in experimental models of myocardial ischemia/reperfusion injury, myocarditis, cardiomyopathies induced by mechanical stress, diabetes, bacterial infection or chemotherapeutic drugs reduces inflammation and is protective. In contrast, administration of HMGB1 after myocardial infarction induced by permanent coronary artery ligation ameliorates cardiac performance by promoting tissue regeneration. HMGB1 decreases contractility and induces hypertrophy and apoptosis in cardiomyocytes, stimulates cardiac fibroblast activities, and promotes cardiac stem cell proliferation and differentiation. Interestingly, maintenance of appropriate nuclear HMGB1 levels protects cardiomyocytes from apoptosis by preventing DNA oxidative stress, and mice with HMGB1cardiomyocyte-specific overexpression are partially protected from cardiac damage. Finally, higher levels of circulating HMGB1 are associated to human heart diseases. Hence, during cardiac injury, HMGB1 elicits both harmful and beneficial responses that may in part depend on the generation and stability of the diverse redox forms, whose specific functions in this context remain mostly unexplored. This review summarizes recent findings on HMGB1 biology and heart dysfunctions and discusses the therapeutic potential of modulating its expression, localization, and oxidative-dependent activities.

Simvastatin Protects Heart from Pressure Overload Injury by Inhibiting Excessive Autophagy

Cardiac hypertrophy is an independent predictor of cardiovascular morbidity and mortality. To identify the mechanisms by which simvastatin inhibits cardiac hypertrophy induced by pressure overload, we determined effects of simvastatin on 14-3-3 protein expression and autophagic activity. Simvastatin was administered intragastrically to Sprague-Dawley (SD) rats before abdominal aortic banding (AAB). Neonatal rat cardiomyocytes (NRCs) were treated with simvastatin before angiotensin II (AngII) stimulation. 14-3-3, LC3, and p62 protein levels were determined by western blot. Autophagy was also measured by the double-labeled red fluorescent protein-green fluorescent protein autophagy reporter system. Simvastatin alleviated excessive autophagy, characterized by a high LC3II/LC3I ratio and low level of p62, and blunted cardiac hypertrophy while increasing 14-3-3 protein expression in rats that had undergone AAB. In addition, it increased 14-3-3 expression and inhibited excessive autophagy in NRCs exposed to AngII. Our study demonstrated that simvastatin may inhibit excessive autophagy, increase 14-3-3 expression, and finally exert beneficial effects on cardioprotection against pressure overload.

HMGB1-RAGE Axis Makes No Contribution to Cardiac Remodeling Induced by Pressure-Overload

High-mobility group box1 (HMGB1) exerts effects on inflammation by binding to receptor for advanced glycation end products (RAGE) or Toll-like receptor 4. Considering that inflammation is involved in pressure overload-induced cardiac hypertrophy, we herein attempted to investigate whether HMGB1 plays a role in myocardial hypertrophy in RAGE knockout mice as well as in the growth and apoptosis of cardiomyocytes. The myocardial expression of RAGE was not significantly changed while TLR4 mRNA was upregulated in response to transverse aortic constriction (TAC) for 1 week. The myocardial expression of HMGB1 protein was markedly increased in TAC group when compared to the sham group. Heart weight to body weight ratio (HW/BW) and lung weight to body weight ratio (LW/BW) were evaluated in RAGE knockout (KO) and wild-type (WT) mice 1 week after TAC. Significant larger HW/BW and LW/BW ratios were found in TAC groups than the corresponding sham groups, but no significant difference was found between KO and WT TAC mice. Similar results were also found when TAC duration was extended to 4 weeks. Cultured neonatal rat cardiomyocytes were treated with different concentrations of recombinant HMGB1, then cell viability was determined using MTT and CCK8 assays and cell apoptosis was determined by Hoechst staining and TUNEL assay. The results came out that HMGB1 exerted no influence on viability or apoptosis of cardiomyocytes. Besides, the protein expression levels of Bax and Bcl2 in response to different concentrations of HMGB1 were similar. These findings indicate that HMGB1 neither exerts influence on cardiac remodeling by binding to RAGE nor induces apoptosis of cardiomyocytes under physiological condition.

Extracellular high-mobility group box 1 mediates pressure overload-induced cardiac hypertrophy and heart failure

Inflammation plays a key role in pressure overload-induced cardiac hypertrophy and heart failure, but the mechanisms have not been fully elucidated. High-mobility group box 1 (HMGB1), which is increased in myocardium under pressure overload, may be involved in pressure overload-induced cardiac injury. The objectives of this study are to determine the role of HMGB1 in cardiac hypertrophy and cardiac dysfunction under pressure overload. Pressure overload was imposed on the heart of male wild-type mice by transverse aortic constriction (TAC), while recombinant HMGB1, HMGB1 box A (a competitive antagonist of HMGB1) or PBS was injected into the LV wall. Moreover, cardiac myocytes were cultured and given sustained mechanical stress. Transthoracic echocardiography was performed after the operation and sections for histological analyses were generated from paraffin-embedded hearts. Relevant proteins and genes were detected. Cardiac HMGB1 expression was increased after TAC, which was accompanied by its translocation from nucleus to both cytoplasm and intercellular space. Exogenous HMGB1 aggravated TAC-induced cardiac hypertrophy and cardiac dysfunction, as demonstrated by echocardiographic analyses, histological analyses and foetal cardiac genes detection. Nevertheless, the aforementioned pathological change induced by TAC could partially be reversed by HMGB1 inhibition. Consistent with the in vivo observations, mechanical stress evoked the release and synthesis of HMGB1 in cultured cardiac myocytes. This study indicates that the activated and up-regulated HMGB1 in myocardium, which might partially be derived from cardiac myocytes under pressure overload, may be of crucial importance in pressure overload-induced cardiac hypertrophy and cardiac dysfunction.

Serum apelin is associated with left ventricular hypertrophy in untreated hypertension patients

BACKGROUND

Apelin is an endogenous ligand for the G protein-coupled receptor APJ. The association between apelin and cardiac modeling has been reported. However, if serum apelin affect the left ventricular hypertrophy (LVH) prevalence in hypertensive patients remains unknown.

METHODS

We enrolled 344 untreated hypertensive patients. The presence of LVH was determined by echocardiography. The blood was drawn from these patients and serum apelin level was detected. To study the direct effect of apelin on cardiac hypertrophy, cardiomyocytes were cultured and were transfected with apelin gene. Morphometric analysis and measurement of protein contain per cell were then performed.

RESULTS

We observed a significantly lower serum apelin level in hypertensive patients with LVH compared with those without LVH. Receiver operating characteristic analyses shows that serum apelin level is robust in discriminating patients with LVH from those without. Our in vitro study showed that cellular protein content and cellular size was increased by Ang II treatment, which can be markedly inhibited by the apelin over-expression in cultured cardiomyocytes.

CONCLUSION

Our clinical date established a link between apelin and LVH, suggesting serum apelin may be used as a predicator for LVH prevalence in hypertensive patients. The direct evidence in vitro suggest apelin pathway is involved in the cardiomyocyte adaption to hypertrophic stimuli.

Protective effect of olmesartan against cardiac ischemia/reperfusion injury in spontaneously hypertensive rats

Olmesartan, as a new angiotensin II receptor blocker, has shown beneficial effects on cardiovascular diseases. Nevertheless, the effect of olmesartan on ischemia/reperfusion (I/R) injury in the hypertensive heart has not been investigated. Therefore, the present study aimed to investigate the effect of olmesartan on I/R injury in spontaneously hypertensive rats (SHRs). Experimental groups were designed with a 2×2 factorial design for olmesartan and I/R effects. In the I/R group, the left anterior descending coronary artery (LAD) was ligated for 40 min followed by a 180-min reperfusion. In the sham group, SHRs underwent the same surgical procedure as the I/R group, with the exception that the suture passed under the LAD without being tightened. In the Olm-I/R group, the SHRs received olmesartan (5 mg/kg) for 4 weeks prior to surgery and other procedures were the same as for the I/R group. In the Olm-sham group, the SHRs received olmesartan (5 mg/kg) for 4 weeks prior to surgery and other procedures were the same as for the sham group. Infarct size was measured for the I/R and Olm-I/R groups. Blood pressure (BP), serum creatine kinase (CK), left ventricular mass index (LVMI), high mobility group box 1 (HMGB1) protein expression levels and hypoxia-inducible factor-1α (HIF-1α) mRNA expression levels were measured for all four groups. Olmesartan significantly reduced BP and LVMI in the olmesartan-treated SHRs compared with those in the SHRs that were not treated with olmesartan. HMGB1 and HIF-1α expression levels were significantly decreased in the Olm-sham and Olm-I/R groups compared with those in the sham and I/R groups, respectively. The proportional increase in HIF-1α expression due to I/R was greater in the olmesartan-treated rats than in the untreated rats. Serum CK levels were significantly reduced in the Olm-I/R group compared with those in the I/R group. In conclusion, olmesartan ameliorates left ventricular hypotrophy and protects the heart against I/R injury in addition to lowing BP in SHRs. The protective effect of olmesartan may be partly due to its antioxidative and anti-inflammatory properties.

The association between BMP4 gene polymorphism and its serum level with the incidence of LVH in hypertensive patients

Background

Bone morphogenic proteins 4 (BMP4) is associated with cardiac remodeling under different conditions. However, the role of BMP4 and its gene polymorphism in the incidence of left ventricular hypertrophy (LVH) in hypertensive patients remains unknown.

Methods

A total of 1265 patients diagnosed with essential hypertension (EH) were recruited. Patients were assigned to LVH+ (n = 420) and LVH- (n = 845) groups. serum BMP4 level was measured and two single nucleotide polymorphism (SNPs) polymorphisms, 6007C > T and -5826G > A of BMP4 gene were genotyped. We also inhibited the BMP4 by small interfering RNA (siRNA). The effect of BMP4 on the hypertrophic response in Human Cardiomyocytes AC16 cells was studied.

Results

We found that the 6007C > T polymorphism of the BMP4 gene and the serum BMP4 level were significantly associated with the risk to develop LVH. With TT as reference, multivariate logistic regression analysis showed the 6007CC genotype carriers had a higher susceptibility to LVH incidence (adjusted OR = 2.65, 95% CI: 1.63-4.31, adjusted P < 0.001). Our in vitro study shows that the BMP4 inhibition in cardiomyocyte by si-RNA technique significantly decreased the Ang II induced cardiomyocyte size and protein content per cell, indicating the importance of BMP4 in the cardiomyocyte hypertrophy.

Conclusion

Collectively, our data suggest that both the 6007C > T of the BMP4 gene and the serum BMP4 level may be used as potential marker for LVH incidence among the EH patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0368-x) contains supplementary material, which is available to authorized users.

Role of osteoprotegerin and its gene polymorphisms in the occurrence of left ventricular hypertrophy in essential hypertensive patients

The aim of the study was to investigate the role of osteoprotegerin (OPG) in left ventricular hypertrophy (LVH) development in patients with essential hypertension (EH). A total of 1092 patients diagnosed with EH were recruited. The LVHs were determined and OPG gene polymorphisms were genotyped. Patients with LVH had a significantly higher mean serum OPG level than those without LVH. The 1181CC genotype carriers had significantly lower risk for LVH compared with GC and GG genotype carriers. The serum OPG level and OPG 1181 G>C polymorphism were found to be independent risk factors for the occurrence of LVH in hypertensive patients. In vitro study shows that OPG overexpression upregulates cell surface size, protein synthesis per cell, and hypertrophy- and fibrosis-related proteins in both cardiomyocytes and cardiac fibroblasts, whereas OPG inhibition can abolish the above-mentioned changes. Consistent with the in vitro data, our in vivo study revealed that the OPG administration induced the LVH in hypertensive rats. This study is the first to report the close association between OPG and LVH development in EH patients and the regulatory effect of OPG on cardiomyocytes and cardiac fibroblasts.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Innate immunity and cardiomyocytes in ischemic heart disease

Myocardial ischemia/reperfusion (I/R) is the most common cause of myocardial inflammation, which is primarily a manifestation of the innate immune responses. Innate immunity is activated when pattern recognition receptors (PRRs) respond to molecular patterns common to microbes and to danger signals expressed by injured or infected cells, so called pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). The expression of various PRRs in cardiomyocytes and the release of DAMPs from cardiomyocytes subjected to I/R injury, through active mechanisms as well as passive processes, enable cardiomyocytes to generate innate immune responses. Studies in isolated heart and cardiomyocytes have confirmed the inflammatory and functional effects of cardiac PRRs especially Toll-like receptors in response to I/R-derived DAMPs, such as heat shock proteins. This review addresses the active role of cardiomyocytes in mediating innate inflammatory responses to myocardial I/R. We propose that cardiomyocytes act as innate immune cells in myocardial I/R injury.

Inhibition of high-mobility group box 1 improves myocardial fibrosis and dysfunction in diabetic cardiomyopathy

BACKGROUND

High-mobility group box 1 (HMGB1) is an important mediator of the inflammatory response. Its expression is increased in diabetic cardiomyopathy (DCM), but its role is unclear. We investigated the potential role and mechanism of HMGB1 in diabetes-induced myocardial fibrosis and dysfunction in mice.

METHODS

In vivo, type 1 diabetes was induced by streptozotocin (STZ) in mice. HMGB1 expression was knocked down by lentivirus-mediated short-hairpin RNA (shRNA). Cardiac function was assessed by echocardiography. Total collagen deposition was assessed by Masson's trichrome and Picrosirius red staining. HMGB1, collagen I and III, and transforming growth factor β1 (TGF-β1) expression was quantified by immunostaining and western bolt analysis. In vitro, isolated neonatal cardiac fibroblasts were treated with high glucose (HG) or recombinant HMGB1 (rHMGB1). Pharmacologic (neutralizing anti-HMGB1 antibody) or genetic (shRNA-HMGB1) inhibition of HMGB1 was used to investigate the role of HMGB1 in HG-induced functional changes of cardiac fibroblasts.

RESULTS

In vivo, HMGB1 was diffusely expressed in the myocardium of diabetic mice. HMGB1 silencing ameliorated left ventricular dysfunction and remodeling and decreased collagen deposition in diabetic mice. In vitro, HG induced HMGB1 translocation and secretion in both viable cardiomyocytes and fibroblasts. Administration of rHMGB1 dose-dependently increased the expression of collagens I and III and TGF-β1 in cardiac fibroblasts. HMGB1 inhibition reduced HG-induced collagen production, matrix metalloproteinase (MMP) activities, proliferation, and activated mitogen-activated protein kinase signaling in cardiac fibroblasts.

CONCLUSIONS

HMGB1 inhibition could alleviate cardiac fibrosis and remodeling in diabetic cardiomyopathy. Inhibition of HMGB1 might have therapeutic potential in the treatment of the disease.

Serum osteopontin, but not OPN gene polymorphism, is associated with LVH in essential hypertensive patients

This study aims to investigate the role of osteopontin (OPN) genetic polymorphisms in the occurrence of left ventricular hypertrophy (LVH) in Chinese patients with essential hypertension (EH). A total of 1,092 patients diagnosed with EH were recruited. Three single nucleotide polymorphisms (SNP) on the promoter region of the OPN gene, including -66T/G, -156G/GG, and -443C/T were genotyped. The serum thrombin-cleaved OPN levels were studied. Patients were divided into LVH+ (n = 443) and the LVH- (n = 649) groups. We found that none of the studied SNPs in the OPN gene was associated with the risk and severity of LVH. The SNPs in the OPN gene did not correlate with the serum OPN levels. However, the serum thrombin-cleaved OPN levels were found to be an independent risk factor for LVH in the EH patients. Multivariate logistic regression analysis showed that serum thrombin-cleaved OPN levels were independently associated with the development of LVH (adjusted OR = 2.47, 95 % CI 1.56-4.01, adjusted P < 0.001). In vitro studies showed that the thrombin-cleaved OPN treatment increased the protein content per cell, the cardiomyocyte surface size, and the expression level of atrial natriuretic peptide protein in a dose-dependent manner. The thrombin-cleaved OPN serum level, but not OPN gene polymorphism, is associated with the development of LVH in EH patients.

KEY MESSAGES

Serum OPN is related to LVH incidence in essential hypertension subjects. OPN stimulates cardiomyocyte hypertrophy in vitro. OPN SNPs are not related to LVH incidence.

Role of calcineurin and actin dynamics in regulated secretion of microneme proteins in Plasmodium falciparum merozoites during erythrocyte invasion

Plasmodium falciparum invades host erythrocytes by multiple invasion pathways. The invasion of erythrocytes by P. falciparum merozoites is a complex process that requires multiple interactions between host receptors and parasite ligands. A number of parasite proteins that mediate interaction with host receptors during invasion are localized to membrane-bound apical organelles referred to as micronemes and rhoptries. The timely release of these proteins to the merozoite surface is crucial for receptor engagement and invasion. It has been demonstrated previously that exposure of merozoites to a low potassium (K(+)) ionic environment as found in blood plasma leads to a rise in cytosolic calcium (Ca(2+)), which triggers microneme secretion. The signalling pathways that regulate microneme discharge in response to rise in cytosolic Ca(2+) are not completely understood. Here, we show that a P. falciparum Ca(2+)-dependent protein phosphatase, calcineurin (PfCN), is an essential regulator of Ca(2+)-dependent microneme exocytosis. An increase in PfCN activity was observed in merozoites following exposure to a low K(+) environment. Treatment of merozoites with calcineurin inhibitors such as FK506 and cyclosporin A prior to transfer to a low K(+) environment resulted in inhibition of secretion of microneme protein apical merozoite antigen-1 (PfAMA-1). Inhibition of PfCN was shown to result in reduced dephosphorylation and depolymerization of apical actin, which appears to be criticalfor microneme secretion. PfCN thus serves as an effector of Ca(2+)-dependent microneme exocytosis by regulating depolymerization of apical actin. Inhibitors that target PfCN block microneme exocytosis and limit growth of P. falciparum blood-stage parasites providing a novel approach towards development of new therapeutic strategies against malaria.