A DNA element in the alpha1 type III collagen promoter mediates a stimulatory response by angiotensin II

CB1 cannabinoid receptor antagonist attenuates left ventricular hypertrophy and Akt-mediated cardiac fibrosis in experimental uremia

Cannabinoid receptor type 1 (CB1R) plays an important role in the development of myocardial hypertrophy and fibrosis-2 pathological features of uremic cardiomyopathy. However, it remains unknown whether CB1R is involved in the pathogenesis of uremic cardiomyopathy. Here, we aimed to elucidate the role of CB1R in the development of uremic cardiomyopathy via modulation of Akt signalling. The heart size and myocardial fibrosis were evaluated by echocardiography and immunohistochemical staining, respectively, in 5/6 nephrectomy chronic kidney disease (CKD) mice treated with a CB1R antagonist. CB1R and fibrosis marker expression levels were determined by immunoblotting in H9c2 cells exposed to the uremic toxin indoxyl sulfate (IS), with an organic anion transporter 1 inhibitor or a CB1R antagonist or agonist. Akt phosphorylation was also assessed to examine the signaling pathways downstream of CB1R activation induced by IS in H9c2 cells. CKD mice exhibited marked left ventricular hypertrophy and myocardial fibrosis, which were reversed by treatment with the CB1R antagonist. CB1R, collagen I, transforming growth factor (TGF)-β, and α-smooth muscle actin (SMA) expression showed time- and dose-dependent upregulation in H9c2 cells treated with IS. The inhibition of CB1R by either CB1R antagonist or small interfering RNA-mediated knockdown attenuated the expression of collagen I, TGF-β, and α-SMA in IS-treated H9c2 cells, while Akt phosphorylation was enhanced by CB1R agonist and abrogated by CB1R antagonist in these cells. In summary, we conclude that CB1R blockade attenuates LVH and Akt-mediated cardiac fibrosis in a CKD mouse model. Uremic toxin IS stimulates the expression of CB1R and fibrotic markers and CB1R inhibition exerts anti-fibrotic effects via modulation of Akt signaling in H9c2 myofibroblasts. Therefore, the development of drugs targeting CB1R may have therapeutic potential in the treatment of uremic cardiomyopathy.

Effects of the Angiotensin Receptor Blocker Candesartan on Arterial Stiffness and Markers of Extracellular Matrix Metabolism in Patients with Essential Hypertension

Laboratory studies have shown that angiotensin receptor blockers (ARBs) can affect extracellular matrix (ECM) metabolism and thereby have a beneficial effect on vascular remodeling. The aim of this study was to examine the clinical effects of the ARB candesartan cilexetil on serum markers of synthesis and degradation of ECM, as well as their relation to changes in arterial stiffness in hypertensive patients. Twenty-three patients with essential hypertension were recruited for this study. Markers related to ECM synthesis and degradation (procollagen type 1 propeptide [PIP], procollagen type III propeptide [PIIIP], matrix metalloproteinase-3 [MMP-3, stromelysin-1], tissue inhibitor of matrix metalloproteinases [TIMP-1], and hyaluronic acid [HA]) were examined both before and after one year of treatment with candesartan. Pulse-wave velocity [PWV] and ankle-brachial pressure index [ABI] were measured two months (i.e., after achieving blood pressure reduction) and one year after the initiation of therapy. PWV values after one year of treatment with ARB were significantly decreased compared to previous values, whereas ABI values were unchanged. Treatment with ARB was also associated with a significant decrease in serum PIIIP values and an increase in serum stromelysin-1, whereas changes in PIP, TIMP-1, and HA did not achieve statistical significance. A significant relationship was found between the changes in PWV and the changes in stromelysin-1 levels after correction for blood pressure and heart rate (p = 0.02). These results suggest that the treatment for just one year with ARB results in significant changes in markers of ECM metabolism as well as PWV. These effects on ECM metabolism could have a beneficial effect in decreasing vascular pathology in patients with essential hypertension.

Influence of cytokines and growth factors in ANG II-mediated collagen upregulation by fibroblasts in rats: role of myocytes

Abnormal stiffness and altered cardiac function arising from abnormal collagen deposition occur in hypertrophy and heart failure. ANG II has been shown to play a role in this process. To evaluate the mechanism, we developed an in vitro model by subjecting fibroblasts to ANG II treatment in the presence or absence of myocytes in coculture (25). Employing this model, we demonstrated that ANG II-induced collagen gene transcription in cardiac fibroblasts was potentiated by myocyte-derived factors. In attempting to identify mechanisms of collagen upregulation and to define the role of myocytes, we found that interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, and the transforming growth factor (TGF)-beta superfamily were also involved in collagen upregulation. Collagen transcripts were increased after fibroblasts were treated with IL-6 (20-50 ng/ml) and TNF-alpha (0.1-0.5 ng/ml). In this study, we show that cardiomyocytes induce secretion of active TGF-beta in the presence of ANG II and that a paracrine action of TGF-beta subsequently induces different cytokines (IL-6) in fibroblasts, thereby promoting collagen synthesis. The cross-talk between myocytes and fibroblasts and involvement of these cytokines in the upregulation of collagen transcript levels are novel findings that may explain their possible roles in the upregulation of collagen.

Fibrosis in hypertensive heart disease: role of the renin-angiotensin-aldosterone system

Structural homogeneity of cardiac tissue is governed by mechanical and humoral factors that regulate cell growth, apoptosis, phenotype, and extracellular matrix turnover. ANGII has endocrine, autocrine, and paracrine properties that influence the behavior of cardiac cells and matrix by AT1 receptor binding. Various paradigms have been suggested, including ANGII-mediated up-regulation of collagen types I and III formation and deposition in cardiac conditions, such as HHD. A growing body of evidence, however, deals with the potential role of aldosterone, either local or systemic, in inducing cardiac fibrosis. Aldosterone might also mediate the profibrotic actions of ANGII. To reduce the risk of heart failure that accompanies HHD, its adverse structural remodeling (eg, myocardial hypertrophy and fibrosis) must be targeted for pharmacologic intervention. Cardioprotective agents must reverse not only the exaggerated growth of cardiac cells, but also regress existing abnormalities in fibrillar collagen. Available experimental and clinical data suggest that agents interfering with ACE, the AT1 receptor, or the mineralocorticoid receptor may provide such a cardioprotective effect.

Angiotensin II in the lesional skin of systemic sclerosis patients contributes to tissue fibrosis via angiotensin II type 1 receptors

OBJECTIVE

Tissue fibrosis in systemic sclerosis (SSc) is attributed to excessive deposition of extracellular matrix components produced by fibroblasts in skin lesions. Angiotensin II (Ang II), a vasoconstrictive peptide, is reported to have profibrotic activity as a result of induction of the extracellular matrix. The aim of the present study was to examine the expression of Ang II and its type 1 (AT(1)) and type 2 (AT(2)) receptors in affected skin and dermal fibroblasts from patients with SSc and to study the role of Ang II in collagen production by SSc dermal fibroblasts.

METHODS

Levels of Ang II in sera from SSc patients and normal subjects were measured by a solid-phase immobilized-epitope immunoassay. Expression of angiotensinogen (Angt) in the skin was evaluated by immunohistochemistry. Expression of Angt, AT(1), and AT(2) in cultured dermal fibroblasts was analyzed by reverse transcription-polymerase chain reaction and immunohistochemistry. Levels of type I procollagen produced by cultured dermal fibroblasts were measured by enzyme-linked immunosorbent assay.

RESULTS

Serum Ang II levels in patients with diffuse cutaneous SSc were significantly higher than those in patients with limited cutaneous SSc and in healthy donors. Immunohistochemical and immunoblotting analyses showed that Angt was present in skin from SSc patients, but not in normal skin. Angt messenger RNA (mRNA) was expressed in fibroblasts from patients with diffuse cutaneous SSc who had high levels of serum Ang II, but not in normal fibroblasts. AT(1) mRNA expression was found in both SSc and normal fibroblasts, whereas AT(2) mRNA was found only in SSc fibroblasts. Exogenous Ang II augmented the production of type I procollagen and transforming growth factor beta1 by cultured fibroblasts via activation of AT(1).

CONCLUSION

Aberrant Ang II production may be involved in tissue fibrosis through excessive production of the extracellular matrix components in SSc dermal fibroblasts. This suggests that the use of AT(1) receptor antagonists may be a novel strategy for the treatment of tissue fibrosis in SSc patients.

Treatment with an adenosine uptake inhibitor attenuates glomerulonephritis in mice

This study evaluated the effects of KF24345 (3-[1-(6,7-diethoxy-2-morpholinoquinazolin-4-yl)piperidin-4-yl]-1,6-dimethyl-2,4(1H,3H)-quinazolinedione hydrochloride), a novel adenosine uptake inhibitor, on experimental glomerulonephritis induced in mice by two intravenous injections of rabbit anti-mouse glomerular basement membrane antiserum. Mice with glomerulonephritis showed continuous proteinuria and the histological evaluation revealed glomerular and tubular damage at 7 weeks after the first antiserum injection. KF24345 as well as prednisolone and cyclophosphamide significantly inhibited proteinuria and glomerular damage when it was orally administered once a day from 2 to 7 weeks. Prednisolone elevated plasma bilirubin and glutamic-pyruvic transaminase levels, and cyclophosphamide decreased erythrocytes. Moreover, both prednisolone and cyclophosphamide decreased spleen and thymus weights. KF24345 did not show this kind of side effects. These results demonstrate that KF24345 ameliorates glomerulonephritis with minimal side effects in mice, suggesting that the adenosine uptake inhibitor may be useful for the treatment of glomerulonephritis.