Adenylyl cyclase activity and function are decreased in rat cardiac fibroblasts after myocardial infarction

Optimized New Shengmai Powder modulation of cAMP/Rap1A signaling pathway attenuates myocardial fibrosis in heart failure

BACKGROUND

Optimized New Shengmai Powder (ONSMP) is a traditional Chinese medicine formula with significant anti-heart failure and myocardial fibrosis effects, but the specific molecular biological mechanisms are not fully understood.

METHODS

In this study, we first used network pharmacology to analyze the ONSMP's active ingredients, core signaling pathways, and core targets. Second, calculate the affinity and binding modes of the ONSMP components to the core targets using molecular docking. Finally, the heart failure rat model was established by ligating the left anterior descending branch of the coronary artery and assessing the effect of ONSMP on myocardial fibrosis in heart failure using echocardiography, cardiac organ coefficients, heart failure markers, and pathological sections after 4 weeks of drug intervention. The cAMP level in rat myocardium was determined using Elisa, the α-SMA and FSP-1 positive expression determined by immunohistochemistry, and the protein and mRNA levels of the cAMP/Rap1A signaling pathway were detected by Western Blotting and quantitative real-time PCR, respectively.

RESULTS

The result shows that the possible mechanism of ONSMP in reducing myocardial fibrosis also includes the use of 12 active ingredients such as baicalin, vitamin D, resveratrol, tanshinone IIA, emodin, 15,16-dihydrotanshinone-i to regulate β1-AR, AC6, EPAC1, Rap1 A, STAT3, and CCND1 on the cAMP/Rap1A signaling pathway, thereby inhibiting the proliferation of cardiac fibroblasts and reduce the excessive secretion of collagen, effectively improve cardiac function and ventricular remodeling in heart failure rats.

CONCLUSION

This research shows that ONSMP can inhibit myocardial fibrosis and delay heart failure through the cAMP/Rap1A signaling pathway.

Cardiac cAMP-PKA Signaling Compartmentalization in Myocardial Infarction

Under physiological conditions, cAMP signaling plays a key role in the regulation of cardiac function. Activation of this intracellular signaling pathway mirrors cardiomyocyte adaptation to various extracellular stimuli. Extracellular ligand binding to seven-transmembrane receptors (also known as GPCRs) with G proteins and adenylyl cyclases (ACs) modulate the intracellular cAMP content. Subsequently, this second messenger triggers activation of specific intracellular downstream effectors that ensure a proper cellular response. Therefore, it is essential for the cell to keep the cAMP signaling highly regulated in space and time. The temporal regulation depends on the activity of ACs and phosphodiesterases. By scaffolding key components of the cAMP signaling machinery, A-kinase anchoring proteins (AKAPs) coordinate both the spatial and temporal regulation. Myocardial infarction is one of the major causes of death in industrialized countries and is characterized by a prolonged cardiac ischemia. This leads to irreversible cardiomyocyte death and impairs cardiac function. Regardless of its causes, a chronic activation of cardiac cAMP signaling is established to compensate this loss. While this adaptation is primarily beneficial for contractile function, it turns out, in the long run, to be deleterious. This review compiles current knowledge about cardiac cAMP compartmentalization under physiological conditions and post-myocardial infarction when it appears to be profoundly impaired.

Contrasting Effects of Inhibition of Phosphodiesterase 3 and 5 on Cardiac Function and Interstitial Fibrosis in Rats With Isoproterenol-Induced Cardiac Dysfunction

Myocardial relaxation and stiffness are influenced by fibrillar collagen content. Cyclic nucleotide signaling regulators have been investigated targeting more effective modulation of collagen deposition during myocardial healing process. To assess the effects of phosphodiesterase type 3 and phosphodiesterase type 5 inhibitors on cardiac function and left ventricular myocardial fibrosis in catecholamine-induced myocardial injury, sildenafil and pimobendan were administered to male Wistar rats 24 hours after isoproterenol injection. Echocardiography and electrocardiogram were performed to assess kinetic and rhythm changes during 45 days of drug administration. At the end of study, type I and type III collagen were measured through immunohistochemistry analysis, and left ventricular pressure was assessed through invasive method. Echocardiography assessment showed increased relative wall thickness at 45 days in pimobendan group with significant diastolic dysfunction and increased collagen I deposition compared with nontreated positive group (3.03 ± 0.31 vs. 2.73 ± 0.28%, P < 0.05). Diastolic pressure correlated positively with type I collagen (r = 0.54, P < 0.05). Type III collagen analysis did not demonstrate difference among the groups. Sildenafil administration attenuated type I collagen deposition (2.15 ± 0.51 vs. positive group, P < 0.05) and suggested to be related to arrhythmic events. Arrhythmic events were not related to the quantity of fibrillar collagen deposition. Although negative modulation of collagen synthesis through cyclic nucleotides signaling have shown promising results, in this study, pimobendan postconditioning resulted in increased collagen type I formation and severe diastolic dysfunction while sildenafil postconditioning reduced collagen type I deposition and attenuated diastolic dysfunction.

The Role of Cyclic AMP Signaling in Cardiac Fibrosis

Myocardial stress and injury invariably promote remodeling of the cardiac tissue, which is associated with cardiomyocyte death and development of fibrosis. The fibrotic process is initially triggered by the differentiation of resident cardiac fibroblasts into myofibroblasts. These activated fibroblasts display increased proliferative capacity and secrete large amounts of extracellular matrix. Uncontrolled myofibroblast activation can thus promote heart stiffness, cardiac dysfunction, arrhythmias, and progression to heart failure. Despite the well-established role of myofibroblasts in mediating cardiac disease, our current knowledge on how signaling pathways promoting fibrosis are regulated and coordinated in this cell type is largely incomplete. In this respect, cyclic adenosine monophosphate (cAMP) signaling acts as a major modulator of fibrotic responses activated in fibroblasts of injured or stressed hearts. In particular, accumulating evidence now suggests that upstream cAMP modulators including G protein-coupled receptors, adenylyl cyclases (ACs), and phosphodiesterases (PDEs); downstream cAMP effectors such as protein kinase A (PKA) and the guanine nucleotide exchange factor Epac; and cAMP signaling organizers such as A-kinase anchoring proteins (AKAPs) modulate a variety of fundamental cellular processes involved in myocardial fibrosis including myofibroblast differentiation, proliferation, collagen secretion, and invasiveness. The current review will discuss recent advances highlighting the role of cAMP and AKAP-mediated signaling in regulating pathophysiological responses controlling cardiac fibrosis.

Regulation of cardiac fibroblast-mediated maladaptive ventricular remodeling by β-arrestins

Cardiac fibroblasts (CF) play a critical role in post-infarction remodeling which can ultimately lead to pathological fibrosis and heart failure. Recent evidence demonstrates that remote (non-infarct) territory fibrosis is a major mechanism for ventricular dysfunction and arrhythmogenesis. β-arrestins are important signaling molecules involved in β-adrenergic receptor (β-AR) desensitization and can also mediate signaling in a G protein independent fashion. Recent work has provided evidence that β-arrestin signaling in the heart may be beneficial, however, these studies have primarily focused on cardiac myocytes and their role in adult CF biology has not been well studied. In this study, we show that β-arrestins can regulate CF biology and contribute to pathological fibrosis. Adult male rats underwent LAD ligation to induce infarction and were studied by echocardiography. There was a significant decline in LV function at 2–12 weeks post-MI with increased infarct and remote territory fibrosis by histology consistent with maladaptive remodeling. Collagen synthesis was upregulated 2.9-fold in CF isolated at 8 and 12 weeks post-MI and β-arrestin expression was significantly increased. β-adrenergic signaling was uncoupled in the post-MI CF and β-agonist-mediated inhibition of collagen synthesis was lost. Knockdown of β-arrestin1 or 2 in the post-MI CF inhibited transformation to myofibroblasts as well as basal and TGF-β-stimulated collagen synthesis. These data suggest that β-arrestins can regulate CF biology and that targeted inhibition of these signaling molecules may represent a novel approach to prevent post-infarction pathological fibrosis and the transition to HF.

Systems approaches in integrative cardiac biology: illustrations from cardiac heterocellular signalling studies

Understanding the complexity of cardiac physiology requires system-level studies of multiple cardiac cell types. Frequently, however, the end result of published research lacks the detail of the collaborative and integrative experimental design process, and the underlying conceptual framework. We review the recent progress in systems modelling and omics analysis of the heterocellular heart environment through complementary forward and inverse approaches, illustrating these conceptual and experimental frameworks with case studies from our own research program. The forward approach begins by collecting curated information from the niche cardiac biology literature, and connecting the dots to form mechanistic network models that generate testable system-level predictions. The inverse approach starts from the vast pool of public omics data in recent cardiac biological research, and applies bioinformatics analysis to produce novel candidates for further investigation. We also discuss the possibility of combining these two approaches into a hybrid framework, together with the benefits and challenges. These interdisciplinary research frameworks illustrate the interplay between computational models, omics analysis, and wet lab experiments, which holds the key to making real progress in improving human cardiac wellbeing.

Adenylyl cyclase regulation in heart failure due to myocardial infarction in rats

Cardiac adenylyl cyclase (AC) activity was described to be differentially regulated in left and right ventricles (LVs and RVs) of rats with heart failure (HF) due to LV myocardial infarction (MI) (Sethi et al. Am J Physiol 272:H884-H893, 1997). AC activities in LVs and RVs were increased and decreased respectively in rats 8 and 16 weeks post MI under basal and stimulatory conditions including AC activation via β-adrenergic receptors (β-ARs), stimulatory G protein (Gs), and direct AC activation with forskolin (FS). The current study aimed to detect alterations in rat heart AC activities in a comparable model of HF 9 weeks post LV MI. Therefore, cardiac AC activities were measured under basal and β-AR-, Gs-, or FS-stimulated conditions as well as under inhibition with various MANT [2'(3')-O-(N-methylanthraniloyl)]-nucleotide AC inhibitors and the P-site AC inhibitors NKY80 [2-amino-7-(2-furanyl)-7,8-dihydro-5(6H)-quinazolinone] and vidarabine (9-β-D-arabinosyladenine, AraAde). Basal and stimulated AC activities along with AC inhibition experiments did not reveal evidence for changes in AC activity in LVs and RVs from MI group animals despite the presence of congestive HF. However, our study is indeterminate. Further studies are required to identify the factors responsible for previously described changes in cardiac AC activity in MI induced HF and to elucidate the role of altered AC regulation in the pathophysiology of HF. In order to detect small changes in AC regulation, larger group sizes than the ones used in our present study are required.

Increase in cellular cyclic AMP concentrations reverses the profibrogenic phenotype of cardiac myofibroblasts: a novel therapeutic approach for cardiac fibrosis

Tissue fibrosis is characterized by excessive production, deposition, and contraction of the extracellular matrix (ECM). The second messenger cAMP has antifibrotic effects in fibroblasts from several tissues, including cardiac fibroblasts (CFs). Increased cellular cAMP levels can prevent the transformation of CFs into profibrogenic myofibroblasts, a critical step that precedes increased ECM deposition and tissue fibrosis. Here we tested two hypotheses: 1) myofibroblasts have a decreased ability to accumulate cAMP in response to G protein-coupled receptor (GPCR) agonists, and 2) increasing cAMP will not only prevent, but also reverse, the myofibroblast phenotype. We found that myofibroblasts produce less cAMP in response to GPCR agonists or forskolin and have decreased expression of several adenylyl cyclase (AC) isoforms and increased expression of multiple cyclic nucleotide phosphodiesterases (PDEs). Furthermore, we found that forskolin-promoted increases in cAMP or N(6)-phenyladenosine-cAMP, a protein kinase A-selective analog, reverse the myofibroblast phenotype, as assessed by the expression of collagen Iα1, α-smooth muscle actin, plasminogen activator inhibitor-1, and cellular contractile abilities, all hallmarks of a fibrogenic state. These results indicate that: 1) altered expression of AC and PDE isoforms yield a decrease in cAMP concentrations of cardiac myofibroblasts (relative to CFs) that likely contributes to their profibrotic state, and 2) approaches to increase cAMP concentrations not only prevent fibroblast-to-myofibroblast transformation but also can reverse the profibrotic myofibroblastic phenotype. We conclude that therapeutic strategies designed to enhance cellular cAMP concentrations in CFs may provide a means to reverse excessive scar formation following injury and to treat cardiac fibrosis.

Improved function of the failing rat heart by regulated expression of insulin-like growth factor I via intramuscular gene transfer

Current methods of gene transfer for heart disease include injection into heart muscle or intracoronary coronary delivery, approaches that typically provide limited expression and are cumbersome to apply. To circumvent these problems, we selected a transgene, insulin-like growth factor-I (IGF-I), which may, in theory, have favorable effects on heart function when secreted from a remote site. We examined the feasibility and efficacy of skeletal muscle injection of adeno-associated virus 5 encoding IGF-I under Tet regulation (AAV5.IGFI-tet) to treat heart failure. Myocardial infarction (MI) was induced in rats by coronary occlusion; 1 week later, rats with impaired left ventricular (LV) function received 2×10(12) genome copies (GC) of AAV5.IGFI-tet in the anterior tibialis muscle, and 4 weeks later, were randomly assigned to receive doxycycline in drinking water to activate IGF-I expression (IGF-On; n=10), or not to receive doxycycline (IGF-Off; n=10). Ten weeks after MI (5 weeks after activation of IGF-I expression), LV size and function were assessed by echocardiography and physiological studies. IGF-On rats showed reduced LV end-systolic dimension (p=0.03) and increased LV ejection fraction (p=0.02). In addition, IGF-On rats showed, before and during dobutamine infusion, increases in cardiac output (p=0.02), stroke work (p=0.0001), LV + dP/dt (p<0.0001), LV relaxation (LV - dP/dt; p=0.03), and systolic arterial blood pressure (p=0.0003). Mean arterial pressure and systemic vascular resistance were unchanged. Activation of IGF-I expression reduced cardiac fibrosis (p=0.048), apoptosis (p<0.0001), and caspase-3/7 activity (p=0.04). Serum IGF-I was increased 5 weeks after transgene activation (p=0.008). These data indicate that skeletal muscle injection of AAV5.IGFI-tet enables tetracycline-activated expression, increases serum IGF-I levels, and improves function of the failing heart.

Reduced collagen deposition in infarcted myocardium facilitates induced pluripotent stem cell engraftment and angiomyogenesis for improvement of left ventricular function

OBJECTIVES

The purpose of this study was to assess the effect of scar tissue composition on engraftment of progenitor cells into infarcted myocardium.

BACKGROUND

Scar tissue formation after myocardial infarction creates a barrier that severely compromises tissue regeneration, limiting potential functional recovery.

METHODS

In vitro: A tricell patch (Tri-P) was created from peritoneum seeded and cultured with induced pluripotent stem cell-derived cardiomyocytes, endothelial cells, and mouse embryonic fibroblasts. The expression of fibrosis-related molecules from mouse embryonic fibroblasts and infarcted heart was measured by Western blot and quantitative reverse transcriptase polymerase chain reaction. In vivo: A Tri-P was affixed over the entire infarcted area 7 days after myocardial infarction in mice overexpressing adenylyl cyclase 6 (AC6). Engraftment efficiency of progenitor cells in hearts of AC6 mice was compared with that of control wild-type (WT) mice using a combination of in vivo bioluminescence imaging, post-mortem ex vivo tissue analysis, and the number of green fluorescent protein-positive cells. Echocardiography of left ventricular (LV) function was performed weekly. Hearts were harvested for analysis 4 weeks after Tri-P application. Mouse embryonic fibroblasts were stimulated with forskolin before an anoxia/reoxygenation protocol. Fibrosis-related molecules were analyzed.

RESULTS

In AC6 mice, infarcted hearts treated with Tri-P showed significantly higher bioluminescence imaging intensity and numbers of green fluorescent protein-positive cells than in WT mice. LV function improved progressively in AC6 mice from weeks 2 to 4 and was associated with reduced LV fibrosis.

CONCLUSIONS

Application of a Tri-P in AC6 mice resulted in significantly higher induced pluripotent stem cell engraftment accompanied by angiomyogenesis in the infarcted area and improvement in LV function.

Unanticipated signaling events associated with cardiac adenylyl cyclase gene transfer

The published papers on the effects of increased cardiac expression of adenylyl cyclase type 6 (AC6) are reviewed. These include the effects of AC on normal and failing left ventricle in several pathophysiological models in mice and pigs. In addition, the effects of increased expression of AC6 in cultured neonatal and adult rat cardiac myocytes are discussed in the context of attempting to establish mechanisms for the unanticipated beneficial effects of AC6 on the failing heart. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Uridine triphosphate (UTP) induces profibrotic responses in cardiac fibroblasts by activation of P2Y2 receptors

Cardiac fibroblasts (CFs) play a key role in response to injury and remodeling of the heart. Nucleotide (P2) receptors regulate the heart but limited information is available regarding such receptors in CFs. We thus sought to determine if extracellular nucleotides regulate fibrotic responses (e.g., proliferation, migration and expression of profibrotic markers) of CFs in primary culture. UTP increased rat CF migration 3-fold (p<0.001), proliferation by 30% (p<0.05) and mRNA expression of profibrotic markers: alpha smooth muscle actin (alpha-SMA), plasminogen activator inhibitor-1 (PAI-1), transforming growth factor beta, soluble ST2, interleukin-6 and monocyte chemoattractant protein-1 (MCP-1) by 3.0-, 15-, 2.0-, 7.6-, 11-, and 6.1-fold, respectively (p<0.05). PAI-1 protein expression induced by UTP was dependent on protein kinase C (PKC) and extracellular signal-regulated kinase (ERK), based on blockade by the PKC inhibitor Ro-31-8220 and the ERK inhibitor U0126, respectively. The rank order for enhanced expression of PAI-1 and alpha-SMA by nucleotides (UTPgammaS>>UDPbetaS>>ATPgammaS), the expression of P2Y2 receptors as the most abundantly expressed P2Y receptor in rat CFs and a blunted response to UTP in P2Y2(-/-) mice all implicate P2Y2 as the predominant P2Y receptor that mediates nucleotide-promoted profibrotic responses. Additional results indicate that P2Y2 receptor-promoted profibrotic responses in CFs are transient, perhaps as a consequence of receptor desensitization. We conclude that P2Y2 receptor activation is profibrotic in CFs; thus inhibition of P2Y2 receptors may provide a novel means to diminish fibrotic remodeling and turnover of extracellular matrix in the heart.