Increasing evidence suggests a critical role for mitochondrial aldehyde dehydrogenase 2 (ALDH2) in protection against cardiac injuries; however, the downstream cytosolic actions of this enzyme are largely undefined.
Enzymatic proteolysis by calpains, Ca(2+)-dependent intracellular cysteine proteases, has been implicated in pathological processes such as cellular degeneration or death. Here, we investigated the role of calpain activation in the hearts subjected to myocardial infarction. We produced myocardial infarction in Cast(-/-) mice deficient for calpastatin, the specific endogenous inhibitory protein for calpains, and Cast(+/+) mice. The activity of cardiac calpains in Cast(+/+) mice was not elevated within 1 day but showed a gradual elevation after 7 days following myocardial infarction, which was further pronounced in Cast(-/-) mice. Although the prevalence of cardiomyocyte death was indistinguishable between Cast(-/-) and Cast(+/+) mice, Cast(-/-) mice exhibited profound contractile dysfunction and chamber dilatation and showed a significant reduction in survival rate after myocardial infarction as compared with Cast(+/+) mice. Notably, immunofluorescence revealed that at 28 days after myocardial infarction, calpains were activated in cardiomyocytes exclusively at the border zone and that Cast(-/-) mice showed higher intensity and a broader extent of calpain activation at the border zone than Cast(+/+) mice. In the border zone of Cast(-/-) mice, pronounced activation of calpains was associated with a decrease in N-cadherin expression and up-regulation of molecular markers for cardiac hypertrophy and fibrosis. In cultured rat neonatal cardiomyocytes, calpain activation by treatment with ionomycin induced cleavage of N-cadherin and decreased expression levels of ?-catenin and connexin 43, which was attenuated by calpain inhibitor. These results thus demonstrate that activation of calpains disassembles cell-cell adhesion at intercalated discs by degrading N-cadherin and thereby promotes left ventricular remodeling after myocardial infarction.
Engineering of three-dimensional (3D) cardiac tissues using decellularized extracellular matrix could be a new technique to create an "organ-like" structure of the heart. To engineer artificial hearts functionally comparable to native hearts, however, much remain to be solved including stable excitation-propagation. To elucidate the points, we examined conduction properties of engineered tissues. We repopulated the decellularized hearts with neonatal rat cardiac cells and then, we observed excitation-propagation of spontaneous beatings using high resolution cameras. We also conducted immunofluorescence staining to examine morphological aspects. Live tissue imaging revealed that GFP-labeled-isolated cardiac cells were migrated into interstitial spaces through extravasation from coronary arteries. Engineered hearts repopulated with Ca(2+)-indicating protein (GCaMP2)-expressing cardiac cells were subjected to optical imaging experiments. Although the engineered hearts generally showed well-organized stable excitation-propagation, the hearts also demonstrated arrhythmogenic propensity such as disorganized propagation. Immunofluorescence study revealed randomly-mixed alignment of cardiomyocytes, endothelial cells and smooth muscle cells. The recellularized hearts also showed disarray of cardiomyocytes and markedly decreased expression of connexin43. In conclusion, we successfully demonstrated that the recellularized hearts showed dynamic excitation-propagation as a "whole organ". Our strategy could provide prerequisite information to construct a 3D-engineered heart, functionally comparable to the native heart.
Periodontitis is known to be a risk factor for abdominal aortic aneurysm (AAA). However, the influence of periodontitis on AAA in Japanese patients has not yet been elucidated. The aim of this clinical investigation was to assess the relationship between periodontal bacterial burden in AAA patients.We studied 12 AAA patients and 24 age- and sex-matched non-AAA cardiovascular patients. We examined periodontitis and the presence of the periodontal pathogens Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Prevotella intermedia in oral samples using polymerase chain reaction assays.We found that the AAA patients had deeper pocket depth compared to the non-AAA patients (3.53 ± 0.38 mm versus 2.67 ± 0.17 mm, P < 0.05). However, the populations of periodontal bacteria were comparable between the two groups. Periodontitis may have a greater effect on aneurysm progression compared to other cardiovascular diseases.
Although there is a link between periodontitis and cardiovascular disease (CVD), the influence of periodontitis on CVD is unclear. The aim of this study was to assess the relationship between periodontal bacterial burden and CVD. We studied 142 patients with tachyarrhythmia (TA) and 25 patients with abdominal aortic aneurysm (AAA). We examined periodontitis and the presence of Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans and Prevotella intermedia in the patients' saliva and subgingival plaque using PCR. We also measured serum antibody titers against the pathogens using ELISA. We found that the patients with AAA had fewer remaining teeth (14.6 ± 2.0 vs. 20.9 ± 0.7, P < 0.05) and deeper pocket depth (3.01 ± 0.26 vs. 2.52 ± 0.05 mm, P < 0.05) compared to the TA patients. The existence of each periodontal bacterium in their saliva or subgingival plaque and serum antibody titers was comparable between the two groups. Periodontitis may have a larger affect on aneurysm progression compared to arrhythmia.
Cardiac hypertrophy is an adaptive response to physiological and pathological overload. In response to the overload, individual cardiac myocytes become mechanically stretched and activate intracellular hypertrophic signaling pathways to re-use embryonic transcription factors and to increase the synthesis of various proteins, such as structural and contractile proteins. These hypertrophic responses increase oxygen demand and promote myocardial angiogenesis to dissolve the hypoxic situation and to maintain cardiac contractile function; thus, these responses suggest crosstalk between cardiac myocytes and microvasculature. However, sustained pathological overload induces maladaptation and cardiac remodeling, resulting in heart failure. In recent years, specific understanding has increased with regard to the molecular processes and cell-cell interactions that coordinate myocardial growth and angiogenesis. In this review, we summarize recent advances in understanding the regulatory mechanisms of coordinated myocardial growth and angiogenesis in the pathophysiology of cardiac hypertrophy and heart failure.
Although periodontitis is a risk factor for cardiovascular disease (CVD), the influence of periodontitis on Marfan syndrome (MFS) with CVD is unclear. The aim of this study was to assess the relationship between periodontal bacterial burden and MSF with CVD.
The octapeptide angiotensin II (Ang II) plays a homeostatic role in the regulation of blood pressure and water and electrolyte balance, and also contributes to the progression of cardiovascular remodeling. Ang II activates Ang II type 1 (AT1) receptor and type 2 (AT2) receptor, both of which belong to the seven-transmembrane, G protein-coupled receptor family. Most of the actions of Ang II such as promotion of cellular prolifaration, hypertrophy, and fibrosis are mediated by AT1 receptor. However, in some pathological situations, AT2 receptor shows an increase in tissue expression and functions to antagonize the actions induced by AT1 receptor. Recent studies have advanced our understanding of the molecular mechanisms underlying receptor activation and signal transduction of AT1 and AT2 receptor in the cardiovascular system.
Recent epidemiological studies suggest that periodontitis is a major risk factor for renal failure and cerebral infarction. The aim of this study was to evaluate the association among periodontitis, renal failure, and cerebral infarction, focusing on microbiological and immunological features.
A growing body of evidence has suggested that the use of angiotensin II (Ang II) type 1 (AT1) receptor blockers (ARBs) leads to a significant decrease in mortality and morbidity in patients with congestive heart failure. The AT1 receptor is a seven-transmembrane G protein-coupled receptor, and is involved in regulating the physiological and pathological process of the cardiovascular system. Systemically and locally generated Ang II has agonistic action on AT1 receptor. However, recent in vitro studies have demonstrated that AT1 receptor is structurally flexible and instable, and has significant and varying levels of spontaneous activity in an Ang II-independent manner. Furthermore, mechanical stress activates AT1 receptor by inducing conformational switch without the involvement of Ang II. Experimental studies have demonstrated that Ang II-independent activation of AT1 receptor is profoundly relevant to the pathogenesis of cardiac remodeling in vivo, and that these agonist-independent activities of AT1 receptor can be inhibited by inverse agonists, but not by neutral antagonists. Therefore, inverse agonist activity emerges as an important pharmacological parameter that contributes to cardioprotective effects of ARBs through inhibiting both Ang II-dependent and -independent activation of AT1 receptor.
Marfan syndrome (MFS) is a systemic connective tissue disorder caused by mutations in the extracellular matrix protein fibrillin-1. While it is known that patients with MFS are at high risk of dental disorders and cardiovascular diseases, little information has been provided to date. To clarify the prevalence of periodontitis in patients with MFS, their oral condition and cardiovascular complications were evaluated. The subjects were patients with MFS (n = 40) who attended the University of Tokyo hospital; age- and gender-matched healthy individuals (n = 14) constituted a control group. Cardiovascular complications and full-mouth clinical measurements, including number of teeth, probing of pocket depth (PD), bleeding on probing (BOP), and community periodontal index (CPI) were recorded. MFS patients had more frequent cardiovascular complications (95 %) compared with the controls (0 %). MFS patients had periodontitis (CPI 3 and 4) more frequently (87.5 %) than the age- and gender-matched control subjects (35.7 %). Furthermore, MFS patients had significantly more severe periodontitis (CPI 2.90 ± 0.12 vs 1.64 ± 0.32) and fewer remaining teeth (26.7 ± 0.4 vs 28.4 ± 0.4) compared with the controls. However, PD and BOP were comparable between MFS patients and the control group. A high incidence of periodontitis and cardiovascular complications was observed in Japanese MFS patients.
Calpains are Ca(2 +) -dependent cysteine proteases. Fifteen gene products of calpains are expressed in mammals. Among them, Calpain 1 and Calpain 2 are ubiquitously expressed and have been investigated extensively. Under the physiological conditions, calpain activity is strictly regulated by endogenous inhibitory protein, Calpastatin. Calpains are activated in the various cardiovascular diseases and implicated in their pathogenesis by degrading numerous target proteins. Here we briefly summarize the physiological and pathological role of calpains in the cardiovascular diseases.
Notch signaling is involved in an intercellular communication mechanism that is essential for coordinated cell fate determination and tissue morphogenesis. The biological effects of Notch signaling are context-dependent. We investigated the functional and hierarchical relationship between angiotensin (Ang) II receptor signaling and Notch signaling in vascular smooth muscle cells (VSMCs). A fluorogenic substrate assay revealed directly that the enzymatic activity of ?-secretase was enhanced after 10 min of Ang II stimulation in HEK293 cells expressing Ang II type 1 receptor. Notch cleavage by ?-secretase was consistently induced and peaked at 10 min after Ang II stimulation, and the Ang II-stimulated increase in Notch intracellular domain production was significantly suppressed by treatment with the ?-secretase inhibitor DAPT. Treatment with DAPT also significantly reduced the Ang II-stimulated proliferation and migration of human aortic VSMCs, as revealed by BrdU incorporation and the Boyden chamber assay, respectively. Systemic administration of the ?-secretase inhibitor dibenzazepine reduced Ang II-induced medial thickening and perivascular fibrosis in the aortas of wild-type mice. These findings suggest that the hierarchical Ang II receptor-Notch signaling pathway promotes the proliferation and migration of VSMCs, and thereby contributes to the progression of vascular remodeling.
Adrenomedullin (AM) was identified as a vasodilating and hypotensive peptide mainly produced by the cardiovascular system. The AM receptor calcitonin receptor-like receptor associates with receptor activity-modifying protein (RAMP), one of the subtypes of regulatory proteins. Among knockout mice ((-/-)) of RAMPs, only RAMP2(-/-) is embryonically lethal with cardiovascular abnormalities that are the same as AM(-/-). This suggests that the AM-RAMP2 system is particularly important for the cardiovascular system. Although AM and RAMP2 are highly expressed in the heart from embryo to adulthood, their analysis has been limited by the embryonic lethality of AM(-/-) and RAMP2(-/-). For this study, we generated inducible cardiac myocyte-specific RAMP2(-/-) (C-RAMP2(-/-)). C-RAMP2(-/-) exhibited dilated cardiomyopathy-like heart failure with cardiac dilatation and myofibril disruption. C-RAMP2(-/-) hearts also showed changes in mitochondrial structure and downregulation of mitochondria-related genes involved in oxidative phosphorylation, ?-oxidation, and reactive oxygen species regulation. Furthermore, the heart failure was preceded by changes in peroxisome proliferator-activated receptor-? coactivator 1? (PGC-1?), a master regulator of mitochondrial biogenesis. Metabolome and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) imaging analyses revealed early downregulation of cardiolipin, a mitochondrial membrane-specific lipid. Furthermore, primary-cultured cardiac myocytes from C-RAMP2(-/-) showed reduced mitochondrial membrane potential and enhanced reactive oxygen species production in a RAMP2 deletion-dependent manner. C-RAMP2(-/-) showed downregulated activation of cAMP response element binding protein (CREB), one of the main regulators of mitochondria-related genes. These data demonstrate that the AM-RAMP2 system is essential for cardiac metabolism and homeostasis. The AM-RAMP2 system is a promising therapeutic target of heart failure.
Macrophages are integrated into adipose tissues and interact with adipocytes in obese subjects, thereby exacerbating adipose insulin resistance. This study aimed to elucidate the molecular mechanism underlying the insulin-sensitizing effect of the angiotensin II receptor blocker (ARB) valsartan, as demonstrated in clinical studies. Insulin signaling, i.e., insulin receptor substrate-1 and Akt phosphorylations, in 3T3-L1 adipocytes was impaired markedly by treatment with tumor necrosis factor-? (TNF?) or in the culture medium of lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophages, and valsartan had no effects on these impairments. However, in contrast, when cocultured with RAW 264.7 cells using a transwell system, the LPS-induced insulin signaling impairment in 3T3-L1 adipocytes showed almost complete normalization with coaddition of valsartan. Furthermore, valsartan strongly suppressed LPS-induced productions of cytokines such as interleukin (IL)-1?, IL-6, and TNF? with nuclear factor-?B activation and c-Jun NH(2)-terminal kinase phosphorylation in RAW 264.7 and primary murine macrophages. Very interestingly, this effect of valsartan was also observed in THP-1 cells treated with angiotensin II type 1 (AT1) siRNA or a peroxisome proliferator-activated receptor-? (PPAR?) antagonist as well as macrophages from AT1a receptor-knockout mice. We conclude that valsartan suppresses the inflammatory response of macrophages, albeit not via PPAR? or the AT1a receptor. This suppression appears to secondarily improve adipose insulin resistance.
Ryanodine receptor type 2 (RyR-2) mediates Ca(2+) release from sarcoplasmic reticulum and contributes to myocardial contractile function. However, the role of RyR-2 in the development of cardiac hypertrophy is not completely understood. Here, mice with or without reduction of RyR-2 gene (RyR-2(+/-) and wild-type, respectively) were analyzed. At baseline, there was no difference in morphology of cardiomyocyte and heart and cardiac contractility between RyR-2(+/-) and wild-type mice, although Ca(2+) release from sarcoplasmic reticulum was impaired in isolated RyR-2(+/-) cardiomyocytes. During a 3-week period of pressure overload, which was induced by constriction of transverse aorta, isolated RyR-2(+/-) cardiomyocytes displayed more reduction of Ca(2+) transient amplitude, rate of an increase in intracellular Ca(2+) concentration during systole, and percentile of fractional shortening, and hearts of RyR-2(+/-) mice displayed less compensated hypertrophy, fibrosis, and contractility; more apoptosis with less autophagy of cardiomyocytes; and similar decrease of angiogenesis as compared with wild-type ones. Moreover, constriction of transverse aorta-induced increases in the activation of calcineurin, extracellular signal-regulated protein kinases, and protein kinase B/Akt but not that of Ca(2+)/calmodulin-dependent protein kinase II, and its downstream targets in the heart of wild-type mice were abolished in the RyR-2(+/-) one, suggesting that RyR-2 is a regulator of calcineurin, extracellular signal-regulated protein kinases, and Akt but not of calmodulin-dependent protein kinase II activation during pressure overload. Taken together, our data indicate that RyR-2 contributes to the development of cardiac hypertrophy and adaptation of cardiac function during pressure overload through regulation of the sarcoplasmic reticulum Ca(2+) release; activation of calcineurin, extracellular signal-regulated protein kinases, and Akt; and cardiomyocyte survival.
Infusion of bone marrow-derived mononuclear cells (BMMNC) has been reported to ameliorate cardiac dysfunction after acute myocardial infarction. In this study, we investigated whether infusion of BMMNC is also effective for non-ischemic heart failure model mice and the underlying mechanisms. Intravenous infusion of BMMNC showed transient cardioprotective effects on animal models with dilated cardiomyopathy (DCM) without their engraftment in heart, suggesting that BMMNC infusion improves cardiac function via humoral factors rather than their differentiation into cardiomyocytes. Using conditioned media from sorted BMMNC, we found that the cardioprotective effects were mediated by growth hormone (GH) secreted from myeloid (Gr-1(+)) cells and the effects was partially mediated by signal transducer and activator of transcription 3 in cardiomyocytes. On the other hand, the GH expression in Gr-1(+) cells was significantly downregulated in DCM mice compared with that in healthy control, suggesting that the environmental cue in heart failure might suppress the Gr-1(+) cells function. Activin A was upregulated in the serum of DCM models and induced downregulation of GH levels in Gr-1(+) cells and serum. Furthermore, humoral factors upregulated in heart failure including angiotensin II upregulated activin A in peripheral blood mononuclear cells (PBMNC) via activation of NF?B. Similarly, serum activin A levels were also significantly higher in DCM patients with heart failure than in healthy subjects and the GH levels in conditioned medium from PBMNC of DCM patients were lower than that in healthy subjects. Inhibition of activin A increased serum GH levels and improved cardiac function of DCM model mice. These results suggest that activin A causes heart failure by suppressing GH activity and that inhibition of activin A might become a novel strategy for the treatment of heart failure.
The activation of renin-angiotensin system contributes to the development of metabolic syndrome and diabetes as well as hypertension. However, it remains undetermined how renin-angiotensin system is implicated in feeding behavior. Here, we show that angiotensin II type 1 (AT(1)) receptor signaling regulates the hypothalamic neurocircuit that is involved in the control of food intake. Compared with wild-type Agtr1a(+/+) mice, AT(1) receptor knock-out (Agtr1a(-/-)) mice were hyperphagic and obese with increased adiposity on an ad libitum diet, whereas Agtr1a(-/-) mice were lean with decreased adiposity on a pair-fed diet. In the hypothalamus, mRNA levels of anorexigenic neuropeptide corticotropin-releasing hormone (Crh) were lower in Agtr1a(-/-) mice than in Agtr1a(+/+) mice both on an ad libitum and pair-fed diet. Furthermore, intracerebroventricular administration of CRH suppressed food intake both in Agtr1a(+/+) and Agtr1a(-/-) mice. In addition, the Crh gene promoter was significantly transactivated via the cAMP-responsive element by angiotensin II stimulation. These results thus demonstrate that central AT(1) receptor signaling plays a homeostatic role in the regulation of food intake by maintaining gene expression of Crh in hypothalamus and suggest a therapeutic potential of central AT(1) receptor blockade in feeding disorders.
In the normal heart, an insulating barrier separates the atria and ventricles. The only way in which electrical impulses can cross this barrier is via the atrioventricular (AV) node, which delays impulse conduction to ensure the forward flow of the blood. However, in some individuals, additional muscular bundles (accessory pathways) allow rapid conduction of electrical impulses from the atria to the ventricles, resulting in premature ventricular excitation and contraction. In this issue of the JCI, two independent research groups demonstrate that erroneous development of the embryonic AV canal, which performs a similar function to that of the adult AV node, is a novel mechanism by which accessory pathways can form.
The angiotensin II (AngII) type 1 (AT?) receptor is a seven-transmembrane G-protein-coupled receptor that plays a regulatory role in the physiological and pathological processes of the cardiovascular system. AT? receptor inherently shows constitutive activity even in the absence of AngII, and it is activated not only by AngII but also by AngII-independent mechanisms. Especially, mechanical stress induces cardiac hypertrophy through activation of AT? receptor without the involvement of AngII. These AngII-independent activities of AT? receptor can be inhibited by inverse agonists, but not by neutral antagonists. In this chapter, we describe the methods used for biochemical assessment of inverse agonism of a ligand for AT? receptor. Their applications will improve our understanding of receptor activation and inactivation at a molecular level, and contribute to the development of AT? receptor blockers possessing superior therapeutic efficacy in cardiovascular diseases.
The number of patients with coronary heart disease, including myocardial infarction, is increasing and novel therapeutic strategy is awaited. Tumor suppressor protein p53 accumulates in the myocardium after myocardial infarction, causes apoptosis of cardiomyocytes, and plays an important role in the progression into heart failure.
Although many animal studies indicate insulin has cardioprotective effects, clinical studies suggest a link between insulin resistance (hyperinsulinemia) and heart failure (HF). Here we have demonstrated that excessive cardiac insulin signaling exacerbates systolic dysfunction induced by pressure overload in rodents. Chronic pressure overload induced hepatic insulin resistance and plasma insulin level elevation. In contrast, cardiac insulin signaling was upregulated by chronic pressure overload because of mechanical stretch-induced activation of cardiomyocyte insulin receptors and upregulation of insulin receptor and Irs1 expression. Chronic pressure overload increased the mismatch between cardiomyocyte size and vascularity, thereby inducing myocardial hypoxia and cardiomyocyte death. Inhibition of hyperinsulinemia substantially improved pressure overload-induced cardiac dysfunction, improving myocardial hypoxia and decreasing cardiomyocyte death. Likewise, the cardiomyocyte-specific reduction of insulin receptor expression prevented cardiac ischemia and hypertrophy and attenuated systolic dysfunction due to pressure overload. Conversely, treatment of type 1 diabetic mice with insulin improved hyperglycemia during pressure overload, but increased myocardial ischemia and cardiomyocyte death, thereby inducing HF. Promoting angiogenesis restored the cardiac dysfunction induced by insulin treatment. We therefore suggest that the use of insulin to control hyperglycemia could be harmful in the setting of pressure overload and that modulation of insulin signaling is crucial for the treatment of HF.
Type 1 angiotensin II (AT(1)) receptor has a critical role in the development of load-induced cardiac hypertrophy. Recently, we showed that mechanical stretching of cells activates the AT(1) receptor without the involvement of angiotensin II (AngII) and that this AngII-independent activation is inhibited by the inverse agonistic activity of the AT(1) receptor blocker (ARB), candesartan. Although the inverse agonist activity of ARBs has been studied in terms of their action on constitutively active AT(1) receptors, the structure-function relationship of the inverse agonism they exert against stretch-induced AT(1) receptor activation has not been fully elucidated. Assays evaluating c-fos gene expression and phosphorylated extracellular signal-regulated protein kinases (ERKs) have shown that olmesartan has strong inverse agonist activities against the constitutively active AT(1) receptor and the stretch-induced activation of AT(1) receptor, respectively. Ternary drug-receptor interactions, which occur between the hydroxyl group of olmesartan and Tyr(113) and between the carboxyl group of olmesartan and Lys(199) and His(256), were essential for the potent inverse agonist action olmesartan exerts against stretch-induced ERK activation and the constitutive activity of the AT(1)-N111G mutant receptor. Furthermore, the inverse agonist activity olmesartan exerts against stretch-induced ERK activation requires an additional drug-receptor interaction involving the tetrazole group of olmesartan and Gln(257) of the AT(1) receptor. These results suggest that multivalent interactions between an inverse agonist and the AT(1) receptor are required to stabilize the receptor in an inactive conformation in response to the distinct processes that lead to an AngII-independent activation of the AT(1) receptor.
The angiotensin II (AngII) type 1 (AT(1)) receptor is a seven-transmembrane G protein-coupled receptor, and is involved in regulating the physiological and pathological process of the cardiovascular system. Systemically and locally generated AngII has agonistic action on AT(1) receptor, but recent studies have demonstrated that AT(1) receptor inherently shows spontaneous activity even in the absence of AngII. Furthermore, mechanical stress can activate AT(1) receptor by inducing conformational switch without the involvement of AngII, and induce cardiac hypertrophy in vivo. These agonist-independent activities of AT(1) receptor can be inhibited by inverse agonists, but not by neutral antagonists. Considerable attention has been directed to molecular mechanisms and clinical implications of agonist-independent AT(1) receptor activation, and inverse agonist activity emerges as an important pharmacological parameter for AT(1) receptor blockers that will improve efficacy and expand therapeutic potentials in cardiovascular medicine.
Atrial fibrillation (AF) is a common arrhythmia that increases the risk of stroke and heart failure. Here, we have shown that mast cells, key mediators of allergic and immune responses, are critically involved in AF pathogenesis in stressed mouse hearts. Pressure overload induced mast cell infiltration and fibrosis in the atrium and enhanced AF susceptibility following atrial burst stimulation. Both atrial fibrosis and AF inducibility were attenuated by stabilization of mast cells with cromolyn and by BM reconstitution from mast cell-deficient WBB6F1-KitW/W-v mice. When cocultured with cardiac myocytes or fibroblasts, BM-derived mouse mast cells increased platelet-derived growth factor A (PDGF-A) synthesis and promoted cell proliferation and collagen expression in cardiac fibroblasts. These changes were abolished by treatment with a neutralizing antibody specific for PDGF alpha-receptor (PDGFR-alpha). Consistent with these data, upregulation of atrial Pdgfa expression in pressure-overloaded hearts was suppressed by BM reconstitution from WBB6F1-KitW/W-v mice. Furthermore, injection of the neutralizing PDGFR-alpha-specific antibody attenuated atrial fibrosis and AF inducibility in pressure-overloaded hearts, whereas administration of homodimer of PDGF-A (PDGF-AA) promoted atrial fibrosis and enhanced AF susceptibility in normal hearts. Our results suggest a crucial role for mast cells in AF and highlight a potential application of controlling the mast cell/PDGF-A axis to achieve upstream prevention of AF in stressed hearts.
The 3-phosphoinositide-dependent kinase-1 (PDK1) plays an important role in the regulation of cellular responses in multiple organs by mediating the phosphoinositide 3-kinase (PI3-K) signaling pathway through activating AGC kinases. Here we defined the role of PDK1 in controlling cardiac homeostasis. Cardiac expression of PDK1 was significantly decreased in murine models of heart failure. Tamoxifen-inducible and heart-specific disruption of Pdk1 in adult mice caused severe and lethal heart failure, which was associated with apoptotic death of cardiomyocytes and beta(1)-adrenergic receptor (AR) down-regulation. Overexpression of Bcl-2 protein prevented cardiomyocyte apoptosis and improved cardiac function. In addition, PDK1-deficient hearts showed enhanced activity of PI3-Kgamma, leading to robust beta(1)-AR internalization by forming complex with beta-AR kinase 1 (betaARK1). Interference of betaARK1/PI3-Kgamma complex formation by transgenic overexpression of phosphoinositide kinase domain normalized beta(1)-AR trafficking and improved cardiac function. Taken together, these results suggest that PDK1 plays a critical role in cardiac homeostasis in vivo by serving as a dual effector for cell survival and beta-adrenergic response.
The octapeptide angiotensin II (AngII) plays a homeostatic role in the regulation of blood pressure and water and electrolyte balance, and contributes to the progression of cardiovascular remodeling. AngII activates AngII type 1 (AT1) receptor and type 2 (AT2) receptor, both of which belong to the seven-transmembrane, G protein-coupled receptor family. Most of the actions of AngII such as promotion of cellular proliferation, hypertrophy, and fibrosis are mediated by AT1 receptor. However, in some pathological situations, AT2 receptor showed an increase in expression level and functions to antagonize the actions by AT1 receptor stimulation. Recent studies have advanced our understanding of the molecular mechanisms underlying receptor activation and signal transduction, and elucidated the pathophysiological roles of AT1 and AT2 receptors in the cardiovascular system.
A growing body of evidence indicates that activation of angiotensin II (Ang II) type 1 (AT1) receptor, a seven -transmembrane G protein -coupled receptor, is critically involved in the development of various cardiovascular diseases. Inherently, AT1 receptor is structurally unstable, and shows spontaneous constitutive activity in an Ang II-independent manner. The constitutive activity of AT1 receptor under basal conditions contributes to the cardiac remodeling even in the absence of Ang II, when AT1 receptor is up-regulated in the heart. Furthermore, mechanical stress can activate AT1 receptor by inducing conformational switch without the involvement of Ang II, and induce cardiac hypertrophy in vivo. These agonist-independent activities of AT1 receptor can be inhibited by inverse agonists, but not by neutral antagonists. Therefore, inverse agonism of AT1 receptor blockers provides therapeutic benefits in the prevention of cardiac remodeling, and thus has potential impact on long-term outcomes in patients with cardiovascular diseases.
Pharmacological inhibitions of the renin-angiotensin-aldosterone system (RAAS) are crowned with one of the greatest success in the current field of cardiovascular medicine. In addition to the systemic effects including elevation of blood pressure and retention of sodium and water, sustained and excessive RAAS activation has direct and deleterious effects on a wide variety of tissues. Recent studies have deciphered the regulatory mechanisms underlying tissue RAAS activation at cellular and molecular levels, and suggested pathogenic roles of RAAS activation in hitherto unanticipated disorders such as muscular dystrophy, osteoporosis, cancer, and aging itself. Novel drugs targeting RAAS are under research and development in search for further efficacy, specificity, and even multifunctionality. This review will discuss the current progress and future perspective of RAAS research.
Wnt signaling plays critical roles in development of various organs and pathogenesis of many diseases, and augmented Wnt signaling has recently been implicated in mammalian aging and aging-related phenotypes. We here report that complement C1q activates canonical Wnt signaling and promotes aging-associated decline in tissue regeneration. Serum C1q concentration is increased with aging, and Wnt signaling activity is augmented during aging in the serum and in multiple tissues of wild-type mice, but not in those of C1qa-deficient mice. C1q activates canonical Wnt signaling by binding to Frizzled receptors and subsequently inducing C1s-dependent cleavage of the ectodomain of Wnt coreceptor low-density lipoprotein receptor-related protein 6. Skeletal muscle regeneration in young mice is inhibited by exogenous C1q treatment, whereas aging-associated impairment of muscle regeneration is restored by C1s inhibition or C1qa gene disruption. Our findings therefore suggest the unexpected role of complement C1q in Wnt signal transduction and modulation of mammalian aging.
The angiotensin II (Ang II) type 1 (AT(1)) receptor mainly mediates the physiological and pathological actions of Ang II, but recent studies have suggested that AT(1) receptor inherently shows spontaneous constitutive activity even in the absence of Ang II in culture cells. To elucidate the role of Ang II-independent AT(1) receptor activation in the pathogenesis of cardiac remodeling, we generated transgenic mice overexpressing AT(1) receptor under the control of ?-myosin heavy chain promoter in angiotensinogen-knockout background (AT(1)Tg-AgtKO mice). In AT(1)Tg-AgtKO hearts, redistributions of the G?(q11) subunit into cytosol and phosphorylation of extracellular signal-regulated kinases were significantly increased, compared with angiotensinogen-knockout mice hearts, suggesting that the AT(1) receptor is constitutively activated independent of Ang II. As a consequence, AT(1)Tg-AgtKO mice showed spontaneous systolic dysfunction and chamber dilatation, accompanied by severe interstitial fibrosis. Progression of cardiac remodeling in AT(1)Tg-AgtKO mice was prevented by treatment with candesartan, an inverse agonist for the AT(1) receptor, but not by its derivative candesartan-7H, deficient of inverse agonism attributed to a lack of the carboxyl group at the benzimidazole ring. Our results demonstrate that constitutive activity of the AT(1) receptor under basal conditions contributes to the cardiac remodeling even in the absence of Ang II, when the AT(1) receptor is upregulated in the heart.
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