Recruitable ACE and tissue repair in the infarcted heart

IL-2 availability regulates the tissue specific phenotype of murine intra-hepatic Tregs

CD4+CD25+Foxp3+ Tregs are known to acquire tissue-specific features and exert cytoprotective and regenerative functions. The extent to which this applies to liver-resident Tregs is unknown. In this study, we aimed to explore the phenotypic and functional characteristics of adult murine liver resident Tregs during homeostasis. Additionally, we investigated their role in ameliorating liver inflammation and tissue damage. Quantification of Foxp3+CD4+CD25+ cells comparing different tissues showed that the liver contained significantly fewer resident Tregs. A combination of flow cytometry phenotyping and microarray analysis of intra-hepatic and splenic Tregs under homeostatic conditions revealed that, although intra-hepatic Tregs exhibited the core transcriptional Treg signature, they expressed a distinct transcriptional profile. This was characterized by reduced CD25 expression and increased levels of pro-inflammatory Th1 transcripts Il1b and Ifng. In vivo ablation of Tregs in the Foxp3-DTR mouse model showed that Tregs had a role in reducing the magnitude of systemic and intra-hepatic inflammatory responses following acute carbon tetrachloride (CCl₄) injury, but their absence did not impact the development of hepatocyte necrosis. Conversely, the specific expansion of Tregs by administration of IL-2 complexes increased the number of intra-hepatic Tregs and significantly ameliorated tissue damage following CCl₄ administration in C57BL/6 mice. The cytoprotective effect observed in response to IL-2c was associated with the increased expression of markers known to regulate Treg suppressive function. Our results offer insight into the transcriptome and complex immune network of intra-hepatic Tregs and suggest that strategies capable of selectively increasing the pool of intra-hepatic Tregs could constitute effective therapies in inflammatory liver diseases.

Prior hypoxia prevents downregulation of ACE-2 by hyperoxia in fetal human lung fibroblasts

Purpose/Aim of Study: The renin angiotensin system is involved in experimentally induced lung fibrosis. Angiotensin (ANG)-II is profibrotic. Angiotensin converting enzyme-2 (ACE-2) cleaves ANG-II and is thus protective. ACE-2 has recently been reported to be significantly decreased under hyperoxic conditions. Hyperoxia is linked to Bronchopulmonary Dysplasia and lung fibrosis. Fetal lung cells normally do not undergo fibrotic changes with physiologic hypoxemia. We hypothesized that hypoxia prior to hyperoxic exposure in fetal lung fibroblasts (IMR-90 cell line) might be protective by preventing ACE-2 downregulation.

MATERIALS AND METHODS

IMR-90 cells were exposed to hypoxia (1%O2/99%N2) followed by hyperoxia (95%O2/5%CO2) or normoxia (21%O2) in vitro. Cells and culture media were recovered separately for assays of ACE-2, TNF-α-converting enzyme (TACE), αSmooth muscle actin (αSMA)-myofibroblast marker-, N-cadherin, and β-catenin immunoreactive protein.

RESULTS

ACE-2 significantly increased when IMR-90 were hypoxic prior to hyperoxic exposure with no recovery. In contrast to hyperoxia alone, ACE-2 did not decrease when IMR-90 were hypoxic prior to hyperoxic exposure with recovery. TACE/ADAM17 protein and mRNA were significantly decreased under these conditions. αSMA N-cadherin, and β-catenin proteins were significantly decreased with or without normoxic recovery.

CONCLUSIONS

Hypoxia prior to hyperoxic exposure of fetal lung fibroblasts prevented ACE-2 downregulation and decreased ADAM17/TACE protein and mRNA. αSMA, N-cadherin, and β-catenin were also significantly decreased under these conditions.

PKC δ and βII regulate angiotensin II-mediated fibrosis through p38: a mechanism of RV fibrosis in pulmonary hypertension

Pulmonary hypertension (PH) eventually leads to right ventricular (RV) fibrosis and dysfunction that is associated with increased morbidity and mortality. Although angiotensin II plays an important role in RV remodeling associated with hypoxic PH, the molecular mechanisms underlying RV fibrosis in PH largely remain unresolved. We hypothesized that PKC-p38 signaling is involved in RV collagen accumulation in PH and in response to angiotensin II stimulation. Adult male Sprague-Dawley rats were exposed to 3 wk of normoxia or hypoxia (10% FiO2 ) as a model of PH. Hypoxic rats developed RV hypertrophy and fibrosis associated with an increase in PKC βII and δ protein expression and p38 dephosphorylation in freshly isolated RV cardiac fibroblasts. Further mechanistic studies were performed in cultured primary cardiac fibroblasts stimulated with angiotensin II, a key activator of ventricular fibrosis in PH. Angiotensin II induced a reduction in p38 phosphorylation that was attenuated following chemical inhibition of PKC βII and δ. Molecular and chemical inhibition of PKC βII and δ abrogated angiotensin II-induced cardiac fibroblast proliferation and collagen deposition in vitro. The effects of PKC inhibition on proliferation and fibrosis were reversed by chemical inhibition of p38. Conversely, constitutive activation of p38 attenuated angiotensin II-induced increase of cardiac fibroblast proliferation and collagen accumulation. PKC βII- and δ-dependent inactivation of p38 regulates cardiac fibroblast proliferation and collagen deposition in response to angiotensin II, which suggests that the PKC-p38 signaling in cardiac fibroblasts may be involved and important in the pathophysiology of RV fibrosis in PH.

Hyperoxia downregulates angiotensin-converting enzyme-2 in human fetal lung fibroblasts

BACKGROUND

Angiotensin (ANG) II is involved in experimental hyperoxia-induced lung fibrosis. Angiotensin-converting enzyme-2 (ACE-2) degrades ANG II and is thus protective, but is downregulated in adult human and experimental lung fibrosis. Hyperoxia is a known cause of chronic fibrotic lung disease in neonates, but the role of ACE-2 in neonatal lung fibrosis is unknown. We hypothesized that ACE-2 in human fetal lung cells might be downregulated by hyperoxic gas.

METHODS

Fetal human lung fibroblast IMR90 cells were exposed to hyperoxic (95% O2/5% CO2) or normoxic (21% O2/5% CO2) gas in vitro. Cells and culture media were recovered separately for assays of ACE-2 enzymatic activity, mRNA, and immunoreactive protein.

RESULTS

Hyperoxia decreased ACE-2 immunoreactive protein and enzyme activity in IMR90 cells (both P < 0.01), but did not change ACE-2 mRNA. ACE-2 protein was increased in the cell supernatant, suggesting protease-mediated ectodomain shedding. TAPI-2, an inhibitor of TNF-α-converting enzyme (TACE/ADAM17), prevented both the decrease in cellular ACE-2 and the increase in soluble ACE-2 (both P < 0.05).

CONCLUSION

These data show that ACE-2 is expressed in fetal human lung fibroblasts but is significantly decreased by hyperoxic gas. They also suggest that hyperoxia decreases ACE-2 through a shedding mechanism mediated by ADAM17/TACE.

EPAC expression and function in cardiac fibroblasts and myofibroblasts

In the heart, cardiac fibroblasts (CF) and cardiac myofibroblasts (CMF) are the main cells responsible for wound healing after cardiac insult. Exchange protein activated by cAMP (EPAC) is a downstream effector of cAMP, and it has been not completely studied on CF. Moreover, in CMF, which are the main cells responsible for cardiac healing, EPAC expression and function are unknown. We evaluated in both CF and CMF the effect of transforming growth factor β1 (TGF-β1) on EPAC-1 expression. We also studied the EPAC involvement on collagen synthesis, adhesion, migration and collagen gel contraction.

METHOD

Rat neonatal CF and CMF were treated with TGF-β1 at different times and concentrations. EPAC-1 protein levels and Rap1 activation were measured by western blot and pull down assay respectively. EPAC cellular functions were determined by adhesion, migration and collagen gel contraction assay; and collagen expression was determined by western blot.

RESULTS

TGF-β1 through Smad and JNK significantly reduced EPAC-1 expression in CF, while in CMF this cytokine increased EPAC-1 expression through ERK1/2, JNK, p38, AKT and Smad3. EPAC activation was able to induce higher Rap1-GTP levels in CMF than in CF. EPAC and PKA, both cAMP effectors, promoted CF and CMF adhesion on fibronectin, as well as CF migration; however, this effect was not observed in CMF. EPAC but not PKA activation mediated collagen gel contraction in CF, while in CMF both PKA and EPAC mediated collagen gel contraction. Finally, the EPAC and PKA activation reduced collagen synthesis in CF and CMF.

CONCLUSION

TGF-β1 differentially regulates the expression of EPAC in CF and CMF; and EPAC regulates differentially CF and CMF functions associated with cardiac remodeling.

Angiotensinogen promoter polymorphisms predict low diffusing capacity in U.S. and Spanish IPF cohorts

BACKGROUND

Single nucleotide polymorphisms (SNPs) in angiotensinogen (AGT) at positions -20 and -6 are associated with increased severity and progression of various fibrotic diseases. Our earlier work demonstrated that the progression of idiopathic pulmonary fibrosis (IPF) was associated with the A-6 allele. This study examined the hypothesis that the homozygous CC genotype at -20 and the AA genotype at -6 would confer worse measures of pulmonary function (measured by pulmonary function tests) in IPF.

METHODS

Multiple logistic regression analysis was applied to a NIH Lung Tissue Research Consortium cohort and a Spanish cohort, while also adjusting for covariates to determine the effects of these SNPs on measures of pulmonary function.

RESULTS

Analysis demonstrated that the CC genotype at -20 was strongly associated with reduced diffusing capacity in males in both cohorts (p = 0.0028 for LTRC and p = 0.017 for the Spanish cohort). In females, the AA genotype was significantly associated with lower FVC (p = 0.0082) and V alv (p = 0.022). In males, the haplotype CA at -20 and -6 in AGT was also strongly associated with reduced diffusing capacity in both cohorts.

CONCLUSIONS

This study is the first to demonstrate an association of AGT polymorphisms (-20A > C and -6G > A) with lower measures of pulmonary function in IPF. It is also the first to relate the effect of gender in lung fibrosis with polymorphisms in AGT.

Absence of circulating aldosterone attenuates foreign body reaction around surgical sutures

BACKGROUND AND AIMS

Adrenal hormones influence inflammatory and fibrotic activity and thereby are involved in wound-healing process. Any excess as well as any shortage of glucocorticoids leads to a delayed wound healing. Mineralocorticoids like aldosterone have a pro-fibrotic and pro-inflammatory impact; thus, reduction of circulating aldosterone should result in an attenuated inflammatory response to implanted foreign bodies.

MATERIAL AND METHODS

Eighteen rats were bilaterally adrenalectomized and substituted with dexamethasone (12 microg/kg per day) and 1% salt in their drinking water; 22 rats were sham-operated. The surgical suture material was removed after 3 weeks and analyzed for size of granuloma, ratio of collagen type I/III, apoptotic cells (terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling), expression of matrix metalloproteinase (MMP)-2, cyclooxygenase 2, tumor necrosis factor receptor 2 (TNF-R2), cluster of differentiation 68 (CD68), Ki67, and cold shock protein Y box binding protein 1 (YB-1). Cell expression was scored according to Remmele.

RESULTS

All animals developed foreign body granulomas around the sutures. Absence of circulating aldosterone after adrenalectomy (ADX) was associated with smaller granuloma size and a reduced ratio of collagen type I/III. Ki67 and MMP-2 showed the strongest expression in cells of the infiltrate around suture. In adrenalectomized rats, we observed significantly less CD68-positive macrophages and less Ki67-positive cells but no significant differences in the expression of YB-1, TNF-R2, or MMP-2. Looking for correlations and co-expressions of proteins, the number of significant Spearman correlations was reduced in the ADX group compared to controls (one and four, respectively).

CONCLUSION

The absence of circulating aldosterone attenuates inflammatory intensity around suture material. Foreign body granuloma seems to be an appropriate model to study chronic inflammatory process.

JunD and HIF-1alpha mediate transcriptional activation of angiotensinogen by TGF-beta1 in human lung fibroblasts

Earlier work showed that TGF-beta1 potently increases angiotensinogen (AGT) gene mRNA in primary human lung fibroblasts. Here the mechanism of TGF-beta1-induced AGT expression was studied in the IMR90 human lung fibroblast cell line. The increase in AGT mRNA induced by TGF-beta1 was completely blocked by actinomycin-D. TGF-beta1 increased the activity of a full-length human AGT promoter-luciferase reporter (AGT-LUC) but did not alter AGT mRNA half-life. Serial deletion analyses revealed that 67% of TGF-beta-inducible AGT-LUC activity resides in a small domain of the AGT core promoter; this domain contains binding sites for hypoxia-inducible factor (HIF)-1 and activation protein-1 (AP-1) transcription factors. TGF-beta1 increased HIF-1alpha protein abundance and the activity of a hypoxia-responsive element reporter; overexpression of HIF-1 increased basal AGT-LUC activity. Both oligonucleotide pulldown and chromatin immunoprecipitation assays revealed increased binding of JunD and HIF-1alpha to the AGT core promoter in response to TGF-beta1. TGF-beta1-inducible AGT-LUC was reduced by an AP-1 dominant negative or by mutation of the AP-1 site. Knockdown of either JunD or HIF-1alpha individually by siRNA partially reduced AGT-LUC. In contrast, simultaneous knockdown of both JunD and HIF-1alpha completely eliminated TGF-beta1-inducible AGT-LUC activity. These data suggest that TGF-beta1 up-regulates AGT transcription in human lung fibroblasts through a mechanism that requires both JunD and HIF-1alpha binding to the AGT core promoter. They also suggest a molecular mechanism linking hypoxia signaling and fibrogenic stimuli in the lungs.

Synthesis and evaluation of a series of 99mTc(CO)3+ lisinopril complexes for in vivo imaging of angiotensin-converting enzyme expression

In animal models of cardiac disease and in human congestive heart failure, expression of angiotensin-converting enzyme (ACE) is upregulated in the failing heart and has been associated with disease progression leading to cardiac failure and fibrosis. To develop probes for imaging ACE expression, a series of di(2-pyridylmethyl)amine (D) chelates capable of binding M(CO)3+ (M = technetium, rhenium) was conjugated to lisinopril by acylation of the epsilon-amine of the lysine residue with a series of di(2-pyridylmethylamino)alkanoic acids where the distance of the chelator from the lisinopril core was investigated by varying the number of methylene spacer groups to produce di(2-pyridylmethyl)amine(Cx)lisinopril analogs: D(C4)lisinopril, D(C5)lisinopril, and D(C8)lisinopril. The inhibitory activity of each rhenium complex was evaluated in vitro against purified rabbit lung ACE and was shown to vary directly with the length of the methylene spacer: Re[D(C8)lisinopril], inhibitory concentration of 50% (IC50) = 3 nM; Re[D(C5)lisinopril], IC50 = 144 nM; and Re[D(C4)lisinopril], IC50 = 1,146 nM, as compared with lisinopril, IC50 = 4 nM. The in vivo specificity for ACE was determined by examining the biodistribution of the 99mTc-[D(C8)lisinopril] analog in rats with and without pretreatment with unlabeled lisinopril. Uptake in the lungs, a tissue that constitutively expresses ACE, was 15.2 percentage injected dose per gram at 10 min after injection and was dramatically reduced by pretreatment with lisinopril, supporting ACE-mediated binding in vivo. Planar anterior imaging analysis of 99mTc-[D(C8)lisinopril] corroborated these data. Thus, high-affinity 99mTc-labeled ACE inhibitor has been designed with potency similar to that of lisinopril and has been demonstrated to specifically localize to tissues that express ACE in vivo. This agent may be useful in monitoring ACE as a function of disease progression in relevant diseases such as heart failure.

Angiotensin converting enzyme-2 is protective but downregulated in human and experimental lung fibrosis

Earlier work from this laboratory showed that local generation of angiotensin (ANG) II is required for the pathogenesis of experimental pulmonary fibrosis and that ANG peptides are expressed robustly in the lungs of patients with idiopathic pulmonary fibrosis (IPF). Angiotensin converting enzyme-2 (ACE-2) degrades the octapeptide ANG II to form the heptapeptide ANG1-7 and thereby limits ANG II accumulation. On this basis, we hypothesized that ACE-2 would be protective against experimental lung fibrogenesis and might be downregulated in human and experimental lung fibrosis. In lung biopsy specimens from patients with IPF, ACE-2 mRNA and enzyme activity were decreased by 92% (P<0.01) and 74% (P<0.05), respectively. ACE-2 mRNA and activity were also decreased similarly in the lungs of bleomycin-treated rats and C57-BL6 mice. In mice exposed to low doses of bleomycin, lung collagen accumulation was enhanced by intratracheal administration of either ACE-2-specific small interfering RNAs (siRNAs) or the peptide DX(600), a competitive inhibitor of ACE-2 (P<0.05). Administration of either ACE-2 siRNA or DX(600) significantly increased the ANG II content of mouse lung tissue above the level induced by bleomycin alone. Coadministration of the ANG II receptor antagonist saralasin blocked the DX(600)-induced increase in lung collagen. Moreover, purified recombinant human ACE-2, delivered to mice systemically by osmotic minipump, attenuated bleomycin-induced lung collagen accumulation. Together, these data show that ACE-2 mRNA and activity are severely downregulated in both human and experimental lung fibrosis and suggest that ACE-2 protects against lung fibrogenesis by limiting the local accumulation of the profibrotic peptide ANG II.

The role and regulation of cardiac angiotensin-converting enzyme for noninvasive molecular imaging in heart failure

Congestive heart failure is a pathologic condition characterized by progressive decrease in left ventricular contractility and consequent decline of cardiac output. There is convincing clinical and experimental evidence that the renin-angiotensin system (RAS) and its primary effector peptide, angiotensin II, are linked to the pathophysiology of interstitial fibrosis, cardiac remodeling, and heart failure. In addition to the traditional endocrine or circulating RAS, an active tissue RAS has been characterized. Tissue angiotensin-converting enzyme and locally synthesized angiotensin II, for example, by chymase, exert local trophic effects that modulate gene expression, which regulates growth and proliferation in both myocytes and nonmyocytes. The existence of the tissue RAS offers an opportunity for targeted imaging, which may be of considerable value for guiding medical therapy.

Extravascular sources of lung angiotensin peptide synthesis in idiopathic pulmonary fibrosis

Previous work from this laboratory demonstrated de novo synthesis of angiotensin (ANG) peptides by apoptotic pulmonary alveolar epithelial cells (AEC) and by lung myofibroblasts in vitro and in bleomycin-treated rats. To determine whether these same cell types also synthesize ANG peptides de novo within the fibrotic human lung in situ, we subjected paraffin sections of normal and fibrotic (idiopathic pulmonary fibrosis, IPF) human lung to immunohistochemistry (IHC) and in situ hybridization to detect ANG peptides and angiotensinogen (AGT) mRNA. These were analyzed both alone and in combination with cell-specific markers of AEC [monoclonal antibody (MAb) MNF-116] and myofibroblasts [α-smooth muscle actin (α-SMA) MAb] and an in situ DNA end labeling (ISEL) method to detect apoptosis. In normal human lung, IHC detected AGT protein in smooth muscle underlying normal bronchi and vessels, but not elsewhere. Real-time RT-PCR and Western blotting revealed that AGT mRNA and protein were 21-fold and 3.6-fold more abundant, respectively, in IPF lung biopsies relative to biopsies of normal human lung (both P < 0.05). In IPF lung, both AGT protein and mRNA were detected in AEC that double-labeled with MAb MNF-116 and with ISEL, suggesting AGT expression by apoptotic epithelia in situ. AGT protein and mRNA also colocalized to myofibroblast foci detected by α-SMA MAb, but AGT mRNA was not detected in smooth muscle. These data are consistent with earlier data from isolated human lung cells in vitro and bleomycin-induced rat lung fibrosis models, and they suggest that apoptotic AEC and myofibroblasts constitute key sources of locally derived ANG peptides in the IPF lung.

Mineralocorticoid receptor blocker increases angiotensin-converting enzyme 2 activity in congestive heart failure patients

Aldosterone plays an important role in the pathophysiology of congestive heart failure (CHF), and spironolactone improves cardiovascular function and survival rates in patients with CHF. We hypothesized that the mineralocorticoid receptor blockade (MRB) exerted its beneficial effects by reducing oxidative stress and changing the balance between the counter-acting enzymes angiotensin-converting enzyme (ACE) and ACE2. Monocyte-derived macrophages were obtained from 10 patients with CHF before and after 1 month of treatment with spironolactone (25 mg/d). Spironolactone therapy significantly (P<0.005) reduced oxidative stress, as expressed by reduced lipid peroxide content, superoxide ion release, and low-density lipoprotein oxidation by 28%, 53%, and 70%, respectively. Although spironolactone significantly (P<0.01) reduced macrophage ACE activity by 47% and mRNA expression by 53%, ACE2 activity and mRNA expression increased by 300% and 654%, respectively. In mice treated for 2 weeks with eplerenone (200 mg.kg(-1).d(-1)), cardiac ACE2 activity significantly (P<0.05) increased by 2-fold and was paralleled by increased ACE2 activity in macrophages. The mechanism of aldosterone antagonist action was studied in mouse peritoneal macrophages (MPMs) in vitro. Although ACE activity and mRNA were significantly increased by 250 nmol/L aldosterone, ACE2 was significantly reduced. Cotreatment with eplerenone (2 micromol/L) attenuated these effects. In MPM obtained from p47 knockout mice, where NADPH oxidase is inactive, as well as in control MPMs treated with NADPH oxidase inhibitor, aldosterone did not increase ACE or decrease ACE2. MRB reduced oxidative stress, decreased ACE activity, and increased ACE2 activity, suggesting a protective role for MRB by possibly increasing generation of angiotensin (1-7) and decreasing formation of angiotensin II. These effects are mediated, at least in part, by NADPH oxidase.

Inflammatory cells in the formation of tumor-related sarcoid reactions

Tumor-related sarcoid reactions were analyzed in 14 lymph nodes in comparison with sarcoidosis using immunohistochemical markers to lymphocytes (CD3, CD4, CD8, and CD20), myeloid-related protein (MRP) 8 and MRP14 (S100A8 and S100A9), angiotensin I-converting enzyme (CD143), and mature or immature dendritic cells (S100, HLA-DR, fascin, CD83, and CD1a). We found that solitary epithelioid cell granuloma (ECG) first occur between lymph sinus and T-zone and that multiple ECGs mainly occur within T-zone, whereas confluent types often occupy the whole lymph node except some residual lymphoid follicles. This pattern suggests a continuous spread and growth of ECGs in sarcoid reactions along T-zone, where antigen presentation mainly takes place. Irrespective of granuloma type, a constant invasion of freshly recruited MRP8 + and MRP14 + macrophages was observed. Similar to sarcoidosis, angiotensin I-converting enzyme expression was a constant finding in epithelioid and giant cells, suggesting a common inflammatory pathway. An increasing ratio of CD4 + to CD8 + T lymphocytes (r = 0.789, P = .001) and a decreasing number of S100 + and CD83 + dendritic cells (r = 0.787, P = .001) within ECGs correlated with granuloma growth, whereas CD1a + immature dendritic cells were never observed inside ECGs. Our findings show that sarcoid reactions represent a T-cell-mediated immune response, leading to histological appearance and cell distribution similar to sarcoidosis and other granulomatous conditions, but the mechanism is different from dendritic cell-based tumor vaccination. Furthermore, mature dendritic cells occur inside ECGs especially of early sarcoid reactions but may not be required for the enlargement and further maintenance of ECGs, in contrast to CD4 + lymphocytes.

Autoantibody-associated congenital heart block: TGFβ and the road to scar

Few diseases exemplify the integration of research from bench to bedside as well as neonatal lupus (NL), often referred to as a model of passively acquired autoimmunity. The signature histologic lesion of autoimmune congenital heart block (CHB) is fibrosis of the conducting tissue and, in some cases, the surrounding myocardium. It is astounding how rapid, and in most cases, irreversible, the fibrotic response to injury is. The mechanism by which maternal anti-SSA/Ro-SSB/La antibodies initiate and finally eventuate in atrioventricular (AV) nodal scarring is not yet defined. In vitro and in vivo studies suggest that one pathologic cascade leading to scarring may be initiated via apoptosis, resulting in the translocation of SSA/Ro-SSB/La antigens and surface binding by maternal autoantibodies. Subsequently, the Fc portion of the bound immunoglobulin engages Fcgamma receptors on tissue macrophages, resulting in the release of TGFbeta at a threshold that favors a pro-fibrotic milieu and irreversible scarring. This cascade also involves a tissue-specific activation of TGFbeta, which promotes the transdifferentiation of fibroblasts into myofibroblasts, a scarring phenotype. Phagocytosis of opsonized apoptotic cardiocytes is distinct from macrophage pathways engaged in physiologic clearance of dying tissue, which also results in the release of TGFbeta but in the latter case appropriately serves to dampen inflammation. Downregulation of TGFbeta (activation/secretion pathway) may provide the basis of a novel approach to treatment of CHB in the future.

Inhibition of cardiac myofibroblast formation and collagen synthesis by activation and overexpression of adenylyl cyclase

Transformation of fibroblasts to myofibroblasts, characterized by expression of alpha-smooth muscle actin (alpha-SMA) and production of extracellular matrix (ECM) components, is a key event in connective tissue remodeling. Approaches to inhibit this transformation are needed in tissues, such as the heart, where excessive ECM production by cardiac fibroblasts (CFs) causes fibrosis, myocardial stiffening, and cardiac dysfunction. We tested whether adenylyl cyclase (AC) activation (increased cAMP levels) modulates the transformation of adult rat CF to myofibroblasts, as assessed by immunofluorescent microscopy, immunoblotting, and collagen synthesis. A 24-h incubation of CF with TGF-beta or angiotensin II increased alpha-SMA expression, which was inhibited by the AC agonist forskolin and a cAMP analog that activates protein kinase A. Treatment with forskolin blunted serum-, TGF-beta-, and angiotensin II-stimulated collagen synthesis. CFs engineered to overexpress type 6 AC had enhanced forskolin-promoted cAMP formation, greater inhibition by forskolin of TGF-beta-stimulated alpha-SMA expression, and a decrease in the EC(50) of forskolin to reduce serum-stimulated collagen synthesis. The AC stimulatory agonist adrenomedullin inhibited collagen synthesis in CF that overexpressed AC6 but not in controls. Thus, AC stimulation blunts collagen synthesis and, in parallel, the transformation of adult rat CF to myofibroblasts. AC overexpression enhances these effects, "uncovering" an inhibition by adrenomedullin. These findings implicate cAMP as an inhibitor of ECM formation by means of blockade of the transformation of CF to myofibroblasts and suggest that increasing AC expression, thereby enhancing cAMP generation through stimulation of receptors expressed on CF, could provide a means to attenuate and prevent cardiac fibrosis and its sequelae.

TRANSITORY REDUCTION IN ANGIOTENSIN AT2 RECEPTOR EXPRESSION LEVELS IN POSTINFARCT REMODELLING IN RAT MYOCARDIUM

1. Myocardial infarction (MI) poses a significant risk for sudden cardiac death. The effectiveness of angiotensin-converting enzyme (ACE) inhibitors and AT1 receptor blockade in attenuating unfavourable post-MI outcomes indicates an important role for angiotensin (Ang) II signalling in the post-MI remodelling process. 2. AT1 and AT2 receptor expression is known to be altered during the early postinjury period and at the later failure stage in the infarcted heart. The aim of the present investigation was to characterize AngII receptor expression shifts in the intermediate, adaptive phases of post-MI hypertrophic remodelling. 3. The present study investigated relative cardiac AT1 and AT2 receptor expression levels using semiquantitative reverse transcription-polymerase chain reaction (GAPDH normalized) in rats at 4 and 20 weeks after ligation of the left anterior descending coronary artery. 4. Heart weight and normalized heart weight were significantly higher in the MI group than in the sham group 4 weeks post-MI, with significant hypertrophy of the left ventricle, left atrium and right ventricle in MI rats. At 20 weeks post-MI, left ventricular hypertrophy remained significant, whereas the mass of the other cardiac tissues was not different to that of sham controls. 5. AT2 receptor expression was markedly reduced in both the non-infarct and infarcted areas of the left ventricular wall in the MI group compared with the sham-operated group 4 weeks after surgery. Expression levels were reduced to 8 and 13% of sham values in the viable and scar tissue regions, respectively. By 20 weeks post-MI, there was no evidence of AT2 receptor expression suppression in the left ventricle. No significant relative changes in AT1 receptor mRNA levels were observed at either 4 or 20 weeks post-MI. 6. The present study demonstrates, for the first time, a selective downregulation of left ventricular AT2 receptor expression in the intermediate phase of post-MI ventricular remodelling in the rat. This downregulation may provide an enhanced AT1 receptor-mediated compensatory progrowth signal in the early adaptive post-MI growth phase. A more detailed understanding of the time-course of differential AT1 and AT2 receptor expression regulation post-MI may potentially identify an optimal window for targeted pharmacological intervention in the treatment of MI.