Danny Guo

Angiotensin-Converting Enzyme 2 Suppresses Pathological Hypertrophy, Myocardial Fibrosis, and Cardiac Dysfunction

Background— Angiotensin-converting enzyme 2 (ACE2) is a pleiotropic monocarboxypeptidase capable of metabolizing several peptide substrates. We hypothesized that ACE2 is a negative regulator of angiotensin II (Ang II)–mediated signaling and its adverse effects on the cardiovascular system. Methods and Results— Ang II infusion (1.5 mg · kg−1 · d−1) for 14 days resulted in worsening cardiac fibrosis and pathological hypertrophy in ACE2 knockout (Ace2−/y) mice compared with wild-type (WT) mice. Daily treatment of Ang II–infused wild-type mice with recombinant human ACE2 (rhACE2; 2 mg · kg−1 · d−1 IP) blunted the hypertrophic response and expression of hypertrophy markers and reduced Ang II–induced superoxide production. Ang II–mediated myocardial fibrosis and expression of procollagen type I&agr;1, procollagen type III&agr;1, transforming growth factor-&bgr;1, and fibronectin were also suppressed by rhACE2. Ang II–induced diastolic dysfunction was inhibited by rhACE2 in association with reduced plasma and myocardial Ang II and increased plasma Ang 1-7 levels. rhACE2 treatment inhibited Ang II–mediated activation of protein kinase C-&agr; and protein kinase C-&bgr;1 protein levels and phosphorylation of the extracellular signal-regulated 1/2, Janus kinase 2, and signal transducer and activator of transcription 3 signaling pathways in wild-type mice. A subpressor dose of Ang II (0.15 mg · kg−1 · d−1) resulted in a milder phenotype that was strikingly attenuated by rhACE2 (2 mg · kg−1 · d−1 IP). In adult ventricular cardiomyocytes and cardiofibroblasts, Ang II–mediated superoxide generation, collagen production, and extracellular signal-regulated 1/2 signaling were inhibited by rhACE2 in an Ang 1-7–dependent manner. Importantly, rhACE2 partially prevented the development of dilated cardiomyopathy in pressure-overloaded wild-type mice. Conclusions— Elevated Ang II induced hypertension, myocardial hypertrophy, fibrosis, and diastolic dysfunction, which were exacerbated by ACE2 deficiency, whereas rhACE2 attenuated Ang II– and pressure-overload–induced adverse myocardial remodeling. Hence, ACE2 is an important negative regulator of Ang II–induced heart disease and suppresses adverse myocardial remodeling.

Prevention of angiotensin II-mediated renal oxidative stress, inflammation, and fibrosis by angiotensin-converting enzyme 2.

Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase capable of metabolizing angiotensin (Ang) II into Ang 1 to 7. We hypothesized that ACE2 is a negative regulator of Ang II signaling and its adverse effects on the kidneys. Ang II infusion (1.5 mg/kg−1/d−1) for 4 days resulted in higher renal Ang II levels and increased nicotinamide adenine dinucleotide phosphate oxidase activity in ACE2 knockout (Ace2−/y) mice compared to wild-type mice. Expression of proinflammatory cytokines, interleukin-1&bgr; and chemokine (C-C motif) ligand 5, were increased in association with greater activation of extracellular-regulated kinase 1/2 and increase of protein kinase C-&agr; levels. These changes were associated with increased expression of fibrosis-associated genes (&agr;-smooth muscle actin, transforming growth factor-&bgr;, procollagen type I&agr;1) and increased protein levels of collagen I with histological evidence of increased tubulointerstitial fibrosis. Ang II-infused wild-type mice were then treated with recombinant human ACE2 (2 mg/kg−1/d−1, intraperitoneal). Daily treatment with recombinant human ACE2 reduced Ang II-induced pressor response and normalized renal Ang II levels and oxidative stress. These changes were associated with a suppression of Ang II–mediated activation of extracellular-regulated kinase 1/2 and protein kinase C pathway and Ang II–mediated renal fibrosis and T-lymphocyte-mediated inflammation. We conclude that loss of ACE2 enhances renal Ang II levels and Ang II-induced renal oxidative stress, resulting in greater renal injury, whereas recombinant human ACE2 prevents Ang II-induced hypertension, renal oxidative stress, and tubulointerstitial fibrosis. ACE2 is an important negative regulator of Ang II-induced renal disease and enhancing ACE2 action may have therapeutic potential for patients with kidney disease.

Loss of Angiotensin-Converting Enzyme 2 Accelerates Maladaptive Left Ventricular Remodeling in Response to Myocardial Infarction

Background—Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that metabolizes Ang II into Ang 1-7, thereby functioning as a negative regulator of the renin-angiotensin system. We hypothesized that ACE2 deficiency may compromise the cardiac response to myocardial infarction (MI). Methods and Results—In response to MI (induced by left anterior descending artery ligation), there was a persistent increase in ACE2 protein in the infarct zone in wild-type mice, whereas loss of ACE2 enhanced the susceptibility to MI, with increased mortality, infarct expansion, and adverse ventricular remodeling characterized by ventricular dilation and systolic dysfunction. In ACE2-deficient hearts, elevated myocardial levels of Ang II and decreased levels of Ang 1-7 in the infarct-related zone was associated with increased production of reactive oxygen species. ACE2 deficiency leads to increased matrix metalloproteinase (MMP) 2 and MMP9 levels with MMP2 activation in the infarct and peri-infarct regions, as well as increased gelatinase activity leading to a disrupted extracellular matrix structure after MI. Loss of ACE2 also leads to increased neutrophilic infiltration in the infarct and peri-infarct regions, resulting in upregulation of inflammatory cytokines, interferon-γ, interleukin-6, and the chemokine, monocyte chemoattractant protein-1, as well as increased phosphorylation of ERK1/2 and JNK1/2 signaling pathways. Treatment of Ace2−/y-MI mice with irbesartan, an AT1 receptor blocker, reduced nicotinamide-adenine dinucleotide phosphate oxidase activity, infarct size, MMP activation, and myocardial inflammation, ultimately resulting in improved post-MI ventricular function. Conclusions—We conclude that loss of ACE2 facilitates adverse post-MI ventricular remodeling by potentiation of Ang II effects by means of the AT1 receptors, and supplementing ACE2 can be a potential therapy for ischemic heart disease.

Loss of ACE2 accelerates maladaptive left ventricular remodeling in response to myocardial infarction

Background—Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that metabolizes Ang II into Ang 1-7, thereby functioning as a negative regulator of the renin-angiotensin system. We hypothesized that ACE2 deficiency may compromise the cardiac response to myocardial infarction (MI). Methods and Results—In response to MI (induced by left anterior descending artery ligation), there was a persistent increase in ACE2 protein in the infarct zone in wild-type mice, whereas loss of ACE2 enhanced the susceptibility to MI, with increased mortality, infarct expansion, and adverse ventricular remodeling characterized by ventricular dilation and systolic dysfunction. In ACE2-deficient hearts, elevated myocardial levels of Ang II and decreased levels of Ang 1-7 in the infarct-related zone was associated with increased production of reactive oxygen species. ACE2 deficiency leads to increased matrix metalloproteinase (MMP) 2 and MMP9 levels with MMP2 activation in the infarct and peri-infarct regions, as well as increased gelatinase activity leading to a disrupted extracellular matrix structure after MI. Loss of ACE2 also leads to increased neutrophilic infiltration in the infarct and peri-infarct regions, resulting in upregulation of inflammatory cytokines, interferon-γ, interleukin-6, and the chemokine, monocyte chemoattractant protein-1, as well as increased phosphorylation of ERK1/2 and JNK1/2 signaling pathways. Treatment of Ace2−/y-MI mice with irbesartan, an AT1 receptor blocker, reduced nicotinamide-adenine dinucleotide phosphate oxidase activity, infarct size, MMP activation, and myocardial inflammation, ultimately resulting in improved post-MI ventricular function. Conclusions—We conclude that loss of ACE2 facilitates adverse post-MI ventricular remodeling by potentiation of Ang II effects by means of the AT1 receptors, and supplementing ACE2 can be a potential therapy for ischemic heart disease.

Enhanced susceptibility to biomechanical stress in ACE2 null mice is prevented by loss of the p47phox NADPH oxidase subunit

AIMS Angiotensin-converting enzyme 2 (ACE2) is an important negative regulator of the renin-angiotensin system. Loss of ACE2 enhances the susceptibility to heart disease but the mechanism remains elusive. We hypothesized that ACE2 deficiency activates the NADPH oxidase system in pressure overload-induced heart failure. METHODS AND RESULTS Using the aortic constriction model, we subjected wild-type (Ace2(+/y)), ACE2 knockout (ACE2KO, Ace2(-/y)), p47(phox) knockout (p47(phox)KO, p47(phox-)(/-)), and ACE2/p47(phox) double KO mice to pressure overload. We examined changes in peptide levels, NADPH oxidase activity, gene expression, matrix metalloproteinases (MMP) activity, pathological signalling, and heart function. Loss of ACE2 resulted in enhanced susceptibility to biomechanical stress leading to eccentric remodelling, increased pathological hypertrophy, and worsening of systolic performance. Myocardial angiotensin II (Ang II) levels were increased, whereas Ang 1-7 levels were lowered. Activation of Ang II-stimulated signalling pathways in the ACE2-deficient myocardium was associated with increased expression and phosphorylation of p47(phox), NADPH oxidase activity, and superoxide generation, leading to enhanced MMP-mediated degradation of the extracellular matrix. Additional loss of p47(phox) in the ACE2KO mice normalized the increased NADPH oxidase activity, superoxide production, and systolic dysfunction following pressure overload. Ang 1-7 supplementation suppressed the increased NADPH oxidase and rescued the early dilated cardiomyopathy in pressure-overloaded ACE2KO mice. CONCLUSION In the absence of ACE2, biomechanical stress triggers activation of the myocardial NAPDH oxidase system with a critical role of the p47(phox) subunit. Increased production of superoxide, activation of MMP, and pathological signalling leads to severe adverse myocardial remodelling and dysfunction in ACE2KO mice.

Loss of PI3Kγ Enhances cAMP-Dependent MMP Remodeling of the Myocardial N-Cadherin Adhesion Complexes and Extracellular Matrix in Response to Early Biomechanical Stress

Rationale: Mechanotransduction and the response to biomechanical stress is a fundamental response in heart disease. Loss of phosphoinositide 3-kinase (PI3K)&ggr;, the isoform linked to G protein–coupled receptor signaling, results in increased myocardial contractility, but the response to pressure overload is controversial. Objective: To characterize molecular and cellular responses of the PI3K&ggr; knockout (KO) mice to biomechanical stress. Methods and Results: In response to pressure overload, PI3K&ggr;KO mice deteriorated at an accelerated rate compared with wild-type mice despite increased basal myocardial contractility. These functional responses were associated with compromised phosphorylation of Akt and GSK-3&agr;. In contrast, isolated single cardiomyocytes from banded PI3K&ggr;KO mice maintained their hypercontractility, suggesting compromised interaction with the extracellular matrix as the primary defect in the banded PI3K&ggr;KO mice. &bgr;-Adrenergic stimulation increased cAMP levels with increased phosphorylation of CREB, leading to increased expression of cAMP-responsive matrix metalloproteinases (MMPs), MMP2, MT1-MMP, and MMP13 in cardiomyocytes and cardiofibroblasts. Loss of PI3K&ggr; resulted in increased cAMP levels with increased expression of MMP2, MT1-MMP, and MMP13 and increased MMP2 activation and collagenase activity in response to biomechanical stress. Selective loss of N-cadherin from the adhesion complexes in the PI3K&ggr;KO mice resulted in reduced cell adhesion. The &bgr;-blocker propranolol prevented the upregulation of MMPs, whereas MMP inhibition prevented the adverse remodeling with both therapies, preventing the functional deterioration in banded PI3K&ggr;KO mice. In banded wild-type mice, long-term propranolol prevented the adverse remodeling and systolic dysfunction with preservation of the N-cadherin levels. Conclusions: The enhanced propensity to develop heart failure in the PI3K&ggr;KO mice is attributable to a cAMP-dependent upregulation of MMP expression and activity and disorganization of the N-cadherin/&bgr;-catenin cell adhesion complex. &bgr;-Blocker therapy prevents these changes thereby providing a novel mechanism of action for these drugs.

Mobile teledermatology: a promising future in clinical practice.

Background: As a product of electronic health, teledermatology is a cost-effective means of improving access to care, facilitating specialist consultations, and supporting patient self-management. Even so, use of traditional teledermatology services is limited by infrastructure and costs in the form of digital cameras, computers, and Internet access. Methods: Considering the significant improvement in smartphone camera resolution and the rapidly increasing number of physicians using smartphones, we explored the use of smartphones as reliable, effective clinical tools in store-and-forward teledermatology. We describe the technical specifications of modern smartphone cameras, the widespread use of smartphones by physicians, and the advantages of smartphones over traditional camera and Internet teledermatology, and we propose recommendations as to how mobile teledermatology may be more effectively used in modern dermatologic practice.

Uncoupling between enhanced excitation-contraction coupling and the response to heart disease: lessons from the PI3Kγ knockout murine model.

The heart is a mechanosensitive organ that adapts its morphology to changing hemodynamic conditions via a process named mechanotransduction, which is the primary means of detecting mechanical stress in the extracellular environment. In the heart, mechanical signals are propagated into the intracellular space primarily via cell adhesion complexes and are subsequently transmitted from cell to cell via paracrine signaling. Enhanced excitation-contraction coupling increases myocardial contractility in various experimental models. However, these animal models routinely show increased susceptibility to biomechanical stress with the development of early ventricular dilation and reduced systolic function in the setting of adverse myocardial remodeling. The enhanced susceptibility of the PI3Kγ knockout mice to biomechanical stress is linked to a cAMP-dependent up-regulation of matrix metalloproteinase with a loss of N-cadherin mediated cell adhesion. Enhancing cell-cell adhesion and cell-ECM interaction will promote the salutary effects of enhanced intracellular Ca(2+) cycling on whole heart function and booster the therapeutic potential of normalizing intracellular Ca(2+) cycling in patients with heart failure.

Role of Signaling Pathways in the Myocardial Response to Biomechanical Stress and in Mechanotransduction in the Heart

The heart is a mechanosensitive organ that adapts its morphology to changing hemodynamic conditions via a process named mechanotransduction, which is the primary means of detecting mechanical stress in the extracellular environment. In the heart, mechanical signals are propagated into the intracellular space primarily via integrin-linked complexes, and are subsequently transmitted from cell to cell via paracrine signaling. The biochemical signals derived from mechanical stimuli activate both acute phosphorylation of signaling cascades, such as in the PI3K, FAK, and ILK pathways, and long-term morphological modifications via intracellular cytoskeletal reorganization and extracellular matrix remodelling. Mechanotransduction plays a fundamental role in cardiac (and vascular) function and involves interaction between extracellular matrix and intracellular cytoskeletal proteins via cell adhesion complexes, which are modulated by PI3Ks. Loss of PI3K signaling enhances the susceptibility to biomechanical stress while the loss of its negative regulator, PTEN, is associated with a wide variety of adaptive mechanisms necessary to resist the progression of maladaptive ventricular remodelling and heart failure. In this chapter, we discuss several of the key players involved in mechanotransduction in the heart.