Cardiac c-kit+AT2+ cell population is increased in response to ischemic injury and supports cardiomyocyte performance

Angiotensin AT2 receptors reduce inflammation and fibrosis in cardiovascular remodeling

The angiotensin AT2 receptor (AT2R), an important member of the "protective arm" of the renin-angiotensin system (RAS), has been recently defined as a therapeutic target in different pathological conditions. The AT2R activates complex signalling pathways linked to cellular proliferation, differentiation, anti-inflammation, antifibrosis, and induction or inhibition of apoptosis. The anti-inflammatory effect of AT2R activation is commonly associated with reduced fibrosis in different models. Current discoveries demonstrated a direct impact of AT2Rs on the regulation of cytokines, transforming growth factor beta1 (TGF-beta1), matrix metalloproteases (MMPs), and synthesis of the extracellular matrix components. This review article summarizes current knowledge on the AT2R in regard to immunity, inflammation and fibrosis in the heart and blood vessels. In particular, the differential influence of the AT2R on cardiovascular remodeling in preclinical models of myocardial infarction, heart failure and aneurysm formation are discussed. Overall, these studies demonstrate that AT2R stimulation represents a promising therapeutic approach to counteract myocardial and aortic damage in cardiovascular diseases.

N-(Heteroaryl)thiophene sulfonamides as angiotensin AT2 receptor ligands

Two series of N-(heteroaryl)thiophene sulfonamides, encompassing either a methylene imidazole group or a tert-butylimidazolylacetyl group in the meta position of the benzene ring, have been synthesized. An AT2R selective ligand with a Ki of 42 nM was identified in the first series and in the second series, six AT2R selective ligands with significantly improved binding affinities and Ki values of <5 nM were discovered. The binding modes to AT2R were explored by docking calculations combined with molecular dynamics simulations. Although some of the high affinity ligands exhibited fair stability in human liver microsomes, comparable to that observed with C21 undergoing clinical trials, most ligands displayed a very low metabolic stability with t½ of less than 10 min in human liver microsomes. The most promising ligand, with an AT2R Ki value of 4.9 nM and with intermediate stability in human hepatocytes (t½ = 77 min) caused a concentration-dependent vasorelaxation of pre-contracted mouse aorta.

Cardiotoxicity of Selected Vascular Endothelial Growth Factor Receptor Tyrosine Kinase Inhibitors in Patients with Renal Cell Carcinoma

Renal cell carcinoma (RCC) is one of the most frequent malignant neoplasms of the kidney. The therapeutic options available for the treatment of advanced or metastatic RCC include vascular endothelial growth factor receptor (VEGFR)-targeted molecules, for example, tyrosine kinase inhibitors (TKI). Various VEGFR-TKIs proved to be effective in the treatment of patients with solid tumours. The combination of two drugs may prove most beneficial in the treatment of metastatic RCC; however, it also enhances the risk of toxicity compared to monotherapy. Specific VEGFR-TKIs (e.g., sunitinib, sorafenib or pazopanib) may increase the rate of cardiotoxicity in metastatic settings. VEGF inhibitors modulate multiple signalling pathways; thus, the identification of the mechanism underlying cardiotoxicity appears challenging. VEGF signalling is vital for the maintenance of cardiomyocyte homeostasis and cardiac function; therefore, its inhibition can be responsible for the reported adverse effects. Disturbed growth factor signalling pathways may be associated with endothelial dysfunction, impaired revascularization, the development of dilated cardiomyopathy, cardiac hypertrophies and altered peripheral vascular load. Patients at high cardiovascular risk at baseline could benefit from clinical follow-up in the first 2-4 weeks after the introduction of targeted molecular therapy; however, there is no consensus concerning the surveillance strategy.

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

Suppression of Inflammatory Cardiac Cytokine Network in Rats with Untreated Obesity and Pre-Diabetes by AT2 Receptor Agonist NP-6A4

Obesity affects over 42% of the United States population and exacerbates heart disease, the leading cause of death in men and women. Obesity also increases pro-inflammatory cytokines that cause chronic tissue damage to vital organs. The standard-of-care does not sufficiently attenuate these inflammatory sequelae. Angiotensin II receptor AT2R is an anti-inflammatory and cardiovascular protective molecule; however, AT2R agonists are not used in the clinic to treat heart disease. NP-6A4 is a new AT2R peptide agonist with an FDA orphan drug designation for pediatric cardiomyopathy. NP-6A4 increases AT2R expression (mRNA and protein) and nitric oxide generation in human cardiovascular cells. AT2R-antagonist PD123319 and AT2RSiRNA suppress NP-6A4-effects indicating that NP-6A4 acts through AT2R. To determine whether NP-6A4 would mitigate cardiac damage from chronic inflammation induced by untreated obesity, we investigated the effects of 2-weeks NP-6A4 treatment (1.8 mg/kg delivered subcutaneously) on cardiac pathology of male Zucker obese (ZO) rats that display obesity, pre-diabetes and cardiac dysfunction. NP-6A4 attenuated cardiac diastolic and systolic dysfunction, cardiac fibrosis and cardiomyocyte hypertrophy, but increased myocardial capillary density. NP-6A4 treatment suppressed tubulointerstitial injury marker urinary β-NAG, and liver injury marker alkaline phosphatase in serum. These protective effects of NP-6A4 occurred in the presence of obesity, hyperinsulinemia, hyperglycemia, and hyperlipidemia, and without modulating blood pressure. NP-6A4 increased expression of AT2R (consistent with human cells) and cardioprotective erythropoietin (EPO) and Notch1 in ZO rat heart, but suppressed nineteen inflammatory cytokines. Cardiac miRNA profiling and in silico analysis showed that NP-6A4 activated a unique miRNA network that may regulate expression of AT2R, EPO, Notch1 and inflammatory cytokines, and mitigate cardiac pathology. Seventeen pro-inflammatory and pro-fibrotic cytokines that increase during lethal cytokine storms caused by infections such as COVID-19 were among the cytokines suppressed by NP-6A4 treatment in ZO rat heart. Thus, NP-6A4 activates a novel anti-inflammatory network comprised of 21 proteins in the heart that was not reported previously. Since NP-6A4's unique mode of action suppresses pro-inflammatory cytokine network and attenuates myocardial damage, it can be an ideal adjuvant drug with other anti-glycemic, anti-hypertensive, standard-of-care drugs to protect the heart tissues from pro-inflammatory and pro-fibrotic cytokine attack induced by obesity.

Angiotensin type 2 receptor activation limits kidney injury during the early phase and induces Treg cells during the late phase of renal ischemia

Kidney infiltrating immune cells such as monocytes, neutrophils, and T cells play critical roles in renal ischemia-reperfusion (IR) injury and repair. Recently, the angiotensin II type 2 receptor (AT2R) has been implicated in protecting kidneys against injury and monocyte infiltration, particularly in chronic kidney disease. However, the role of AT2R in IR injury and repair phases and T cell modulation is unknown. To address this question, Sprague-Dawley rats were subjected to IR with or without AT2R agonist C21 treatment. IR caused early (2 h postreperfusion) renal functional injury (proteinuria, plasma urea, and creatinine) and enhanced immune cells (T cells and CD4 T cells) infiltration and levels of the proinflammatory cytokines monocyte chemoattractant protein-1, TNF-α, and IL-6. C21 treatment reversed these changes but increased the anti-inflammatory IL-10 level. On day 3, C21 treatment increased CD4+FoxP3+ (regulatory T cells) and CD4+IL-10+ cells and reduced kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin in the kidney compared with the IR control, suggesting the involvement of AT2R in kidney repair. These data indicate that AT2R activation protects the kidney against IR injury and immune cell infiltration in the early phase and modulates CD4 T cells toward the regulatory T cell phenotype, which may have long-term beneficial effects on kidney function.NEW & NOTEWORTHY The angiotensin II type 2 receptor agonist C21 has been known to have a renoprotective role in various kidney pathologies. C21 treatment (before renal ischemia) attenuated postischemic kidney injury, kidney dysfunction, and immune cell infiltration during the injury phase. Also, C21 treatment modulated the kidney microenvironment by enhancing anti-inflammatory responses mainly mediated by IL-10. During the repair phase, C21 treatment enhanced IL-10-secreting CD4 T cells and FoxP3-secreting regulatory T cells in Sprague-Dawley rats.

Correcting the imbalanced protective RAS in COVID-19 with angiotensin AT2-receptor agonists

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that is responsible for the global corona virus disease 2019 (COVID-19) pandemic enters host cells via a mechanism that includes binding to angiotensin converting enzyme (ACE) 2 (ACE2). Membrane-bound ACE2 is depleted as a result of this entry mechanism. The consequence is that the protective renin-angiotensin system (RAS), of which ACE2 is an essential component, is compromised through lack of production of the protective peptides angiotensin-(1-7) and angiotensin-(1-9), and therefore decreased stimulation of Mas (receptor Mas) and angiotensin AT2-receptors (AT2Rs), while angiotensin AT1-receptors (AT1Rs) are overstimulated due to less degradation of angiotensin II (Ang II) by ACE2. The protective RAS has numerous beneficial actions, including anti-inflammatory, anti-coagulative, anti-fibrotic effects along with endothelial and neural protection; opposite to the deleterious effects caused by heightened stimulation of angiotensin AT1R. Given that patients with severe COVID-19 exhibit an excessive immune response, endothelial dysfunction, increased clotting, thromboses and stroke, enhancing the activity of the protective RAS is likely beneficial. In this article, we discuss the evidence for a dysfunctional protective RAS in COVID and develop a rationale that the protective RAS imbalance in COVID-19 may be corrected by using AT2R agonists. We further review preclinical studies with AT2R agonists which suggest that AT2R stimulation may be therapeutically effective to treat COVID-19-induced disorders of various organ systems such as lung, vasculature, or the brain. Finally, we provide information on the design of a clinical trial in which patients with COVID-19 were treated with the AT2R agonist Compound 21 (C21). This trial has been completed, but results have not yet been reported.

N-(Methyloxycarbonyl)thiophene sulfonamides as high affinity AT2 receptor ligands

A series of meta-substituted acetophenone derivatives, encompassing N-(alkyloxycarbonyl)thiophene sulfonamide fragments have been synthesized. Several selective AT2 receptor ligands were identified, among those a tert-butylimidazole derivative (20) with a K_i of 9.3 nM, that demonstrates a high stability in human liver microsomes (t_½ = 62 min) and in human hepatocytes (t_½ = 194 min). This methyloxycarbonylthiophene sulfonamide is a 20-fold more potent binder to the AT2 receptor and is considerably more stable in human liver microsomes, than a previously reported and broadly studied structurally related AT₂R prototype antagonist 3 (C38). Ligand 20 acts as an AT₂R agonist and caused an AT₂R mediated concentration-dependent vasorelaxation of pre-contracted mouse aorta. Furthermore, in contrast to imidazole derivative C38, the tert-butylimidazole derivative 20 is a poor inhibitor of CYP3A4, CYP2D6 and CYP2C9. It is demonstrated herein that smaller alkyloxycarbonyl groups make the ligands in this series of AT₂R selective compounds less prone to degradation and that a high AT2 receptor affinity can be retained after truncation of the alkyloxycarbonyl group. Binding modes of the most potent AT₂R ligands were explored by docking calculations combined with molecular dynamics simulations.

Emerging Role of Angiotensin AT2 Receptor in Anti-Inflammation: An Update

The hyperactive RAS and inflammation are closely associated. The angiotensin-II/AT1R axis of the RAS has been explored extensively for its role in inflammation and a plethora of pathological conditions. Understanding the role of AT2R in inflammation is an emerging area of research. The AT2R is expressed on a variety of immune and non-immune cells, which upon activation triggers the release of a host of cytokines and has multiple effects that coalesce to anti-inflammation and prevents maladaptive repair. The anti-inflammatory outcomes of AT2R activation are linked to its well-established signaling pathways involving formation of nitric oxide and activation of phosphatases. Collectively, these effects promote cell survival and tissue function. The consideration of AT2R as a therapeutic target requires further investigations.

Cardiovascular toxicity induced by anti-VEGF/VEGFR agents: a special focus on definitions, diagnoses, mechanisms and management

INTRODUCTION

Vascular endothelial growth factor (VEGF) is a key target in cancer therapy. However, cardiovascular safety has been one of the most challenging aspects of anti-VEGF/VEGF receptor (VEGFR) agent development and therapy. While accurate diagnostic modalities for assessment of cardiac function have been developed over the past few decades, a lack of an optimal definition and precise mechanism still places a significant limit on the effective management of cardiovascular toxicity.

AREAS COVERED

Here, we report the cardiovascular toxicity profile associated with anti-VEGF/VEGFR agents and summarize the clinical diagnoses as well as management that are already performed in clinical practice or are currently being investigated. Furthermore, the review discusses the potential molecular toxicological mechanisms, which may provide strategies to prevent toxicity and drive drug discovery.

EXPERT OPINION

Cardiovascular toxicity associated with anti-VEGF/VEGFR agents has been a substantial risk for cancer treatment. To improve its management, the development of guidelines for prevention, monitoring and treatment of cardiovascular toxicity has become a hot topic. The summary of cardiovascular toxicity profile, mechanisms and management given in this review is not only significant for the optimal use of existing anti-VEGF/VEGFR agents to protect patients predisposed to cardiovascular toxicity but is also beneficial for drug development.

Evolution of Angiotensin Peptides and Peptidomimetics as Angiotensin II Receptor Type 2 (AT2) Receptor Agonists

Angiotensin II receptor type 1 and 2 (AT1R and AT2R) are two G-protein coupled receptors that mediate most biological functions of the octapeptide Angiotensin II (Ang II). AT2R is upregulated upon tissue damage and its activation by selective AT2R agonists has become a promising approach in the search for new classes of pharmaceutical agents. We herein analyzed the chemical evolution of AT2R agonists starting from octapeptides, through shorter peptides and peptidomimetics to the first drug-like AT2R-selective agonist, C21, which is in Phase II clinical trials and aimed for idiopathic pulmonary fibrosis. Based on the recent crystal structures of AT1R and AT2R in complex with sarile, we identified a common binding model for a series of 11 selected AT2R agonists, consisting of peptides and peptidomimetics of different length, affinity towards AT2R and selectivity versus AT1R. Subsequent molecular dynamics simulations and free energy perturbation (FEP) calculations of binding affinities allowed the identification of the bioactive conformation and common pharmacophoric points, responsible for the key interactions with the receptor, which are maintained by the drug-like agonists. The results of this study should be helpful and facilitate the search for improved and even more potent AT2R-selective drug-like agonists.

Targeting Angiotensin-Converting Enzyme-2/Angiotensin-(1-7)/Mas Receptor Axis in the Vascular Progenitor Cells for Cardiovascular Diseases

Bone marrow-derived hematopoietic stem/progenitor cells are vasculogenic and play an important role in endothelial health and vascular homeostasis by participating in postnatal vasculogenesis. Progenitor cells are mobilized from bone marrow niches in response to remote ischemic injury and migrate to the areas of damage and stimulate revascularization largely by paracrine activation of angiogenic functions in the peri-ischemic vasculature. This innate vasoprotective mechanism is impaired in certain chronic clinical conditions, which leads to the development of cardiovascular complications. Members of the renin-angiotensin system-angiotensin-converting enzymes (ACEs) ACE and ACE2, angiotensin II (Ang II), Ang-(1-7), and receptors AT1 and Mas-are expressed in vasculogenic progenitor cells derived from humans and rodents. Ang-(1-7), generated by ACE2, is known to produce cardiovascular protective effects by acting on Mas receptor and is considered as a counter-regulatory mechanism to the detrimental effects of Ang II. Evidence has now been accumulating in support of the activation of the ACE2/Ang-(1-7)/Mas receptor pathway by pharmacologic or molecular maneuvers, which stimulates mobilization of progenitor cells from bone marrow, migration to areas of vascular damage, and revascularization of ischemic areas in pathologic conditions. This minireview summarizes recent studies that have enhanced our understanding of the physiology and pharmacology of vasoprotective axis in bone marrow-derived progenitor cells in health and disease. SIGNIFICANCE STATEMENT: Hematopoietic stem progenitor cells (HSPCs) stimulate revascularization of ischemic areas. However, the reparative potential is diminished in certain chronic clinical conditions, leading to the development of cardiovascular diseases. ACE2 and Mas receptor are key members of the alternative axis of the renin-angiotensin system and are expressed in HSPCs. Accumulating evidence points to activation of ACE2 or Mas receptor as a promising approach for restoring the reparative potential, thereby preventing the development of ischemic vascular diseases.

The Other Angiotensin II Receptor: AT2R as a Therapeutic Target

The active hormone of the renin-angiotensin system (RAS), angiotensin II (Ang II), is involved in several human diseases, driving the development and clinical use of several therapeutic drugs, mostly angiotensin I converting enzyme (ACE) inhibitors and angiotensin receptor type I (AT₁R) antagonists. However, angiotensin peptides can also bind to receptors different from AT₁R, in particular, angiotensin receptor type II (AT₂R), resulting in biological and physiological effects different, and sometimes antagonistic, of their binding to AT₁R. In the present Perspective, the components of the RAS and the therapeutic tools developed to control it will be reviewed. In particular, the characteristics of AT₂R and tools to modulate its functions will be discussed. Agonists or antagonists to AT₂R are potential therapeutics in cardiovascular diseases, for agonists, and in the control of pain, for antagonists, respectively. However, controlling their binding properties and their targeting to the target tissues must be optimized.

Mice lacking angiotensin type 2 receptor exhibit a sex-specific attenuation of insulin sensitivity

The renin-angiotensin system modulates insulin action. Pharmacological stimulation of angiotensin type 2 receptor (AT2R) was shown to have beneficial metabolic effects in various animal models of insulin resistance and type 2 diabetes and also to increase insulin sensitivity in wild type mice. In this study we further explored the role of the AT2R on insulin action and glucose homeostasis by investigating the glycemic profile and in vivo insulin signaling status in insulin-target tissues from both male and female AT2R knockout (KO) mice. When compared to the respective wild-type (WT) group, glycemia and insulinemia was unaltered in AT2RKO mice regardless of sex. However, female AT2RKO mice displayed decreased insulin sensitivity compared to their WT littermates. This was accompanied by a compensatory increase in adiponectinemia and with a specific attenuation of the activity of main insulin signaling components (insulin receptor, Akt and ERK1/2) in adipose tissue with no apparent alterations in insulin signaling in either liver or skeletal muscle. These parameters remained unaltered in male AT2RKO mice as compared to male WT mice. Present data show that the AT2R has a physiological role in the conservation of insulin action in female but not in male mice. Our results suggest a sexual dimorphism in the control of insulin action and glucose homeostasis by the AT2R and reinforce the notion that pharmacological modulation of the balance between the AT1R and AT2R receptor could be important for treatment of metabolic syndrome and type 2 diabetes.

A Series of Analogues to the AT2R Prototype Antagonist C38 Allow Fine Tuning of the Previously Reported Antagonist Binding Mode

We here report on our continued studies of ligands binding to the promising drug target angiotensin II type 2 receptor (AT2R). Two series of compounds were synthesized and investigated. The first series explored the effects of adding small substituents to the phenyl ring of the known selective nonpeptide AT2R antagonist C38, generating small but significant shifts in AT2R affinity. One compound in the first series was equipotent to C38 and showed similar kinetic solubility, and stability in both human and mouse liver microsomes. The second series was comprised of new bicyclic derivatives, amongst which one ligand exhibited a five-fold improved affinity to AT2R as compared to C38. The majority of the compounds in the second series, including the most potent ligand, were inferior to C38 with regard to stability in both human and mouse microsomes. In contrast to our previously reported findings, ligands with shorter carbamate alkyl chains only demonstrated slightly improved stability in microsomes. Based on data presented herein, a more adequate, tentative model of the binding modes of ligand analogues to the prototype AT2R antagonist C38 is proposed, as deduced from docking redefined by molecular dynamic simulations.

Cell-Specific Protective Signaling Induced by the Novel AT2R-Agonist NP-6A4 on Human Endothelial and Smooth Muscle Cells

Cardiovascular disease incidence continues to rise and new treatment paradigms are warranted. We reported previously that activation of Angiotensin II receptor (encoded by the X-linked Agtr2 gene) by a new peptide agonist, NP-6A4, was more effective in protecting mouse cardiomyocyte HL-1 cells and human coronary artery vascular smooth muscle cells (hCAVSMCs) from acute nutrient deficiency than other drugs tested. To elucidate further the protective effects of NP-6A4 in human cells, we studied the effects of NP-6A4 treatment on functions of human coronary artery endothelial cells (hCAECs), and hCAVSMCs. In hCAVSMCs, NP-6A4 (1 μM) increased Agtr2 mRNA (sixfold, p < 0.05) after 12-h exposure, whereas in hCAECs, significant increase in Agtr2 mRNA (hCAECs: eightfold) was observed after prolonged exposure. Interestingly, NP-6A4 treatment (1 μM, 12 h) increased AT2R protein levels in all human cells tested. Pre-treatment with AT2R-antagonist PD123319 (20 μM) and anti-AT2R siRNA (1 μM) suppressed this effect. Thus, NP-6A4 activates a positive feedback loop for AT2R expression and signaling in hCAVSMCs and hCAECs. NP-6A4 (1–20 μM) increased cell index (CI) of hCAVSMCs as determined by real time cell analyzer (RTCA), indicating that high concentrations of NP-6A4 were not cytotoxic for hCAVSMCs, rather promoting better cell attachment and growth. Seahorse Extracellular Flux Assay revealed that NP-6A4 (1 μM) treatment for 7 days increased whole cell-based mitochondrial parameters of hCAVSMCs, specifically maximal respiration (p < 0.05), spare respiratory capacity (p < 0.05) and ATP production (p < 0.05). NP-6A4 (1 μM; 7 days) also suppressed Reactive Oxygen Species (ROS) in hCAVSMCs. Exposure to Doxorubicin (DOXO) (1 μM) increased ROS in hCAVSMCs and this effect was suppressed by NP-6A4 (1 μM). In hCAECs grown in complete medium, NP-6A4 (1 μM) and Ang II (1 μM) exerted similar changes in CI. Additionally, NP-6A4 (5 μM: 12 h) increased expression of eNOS (sixfold, p < 0.05) and generation of nitric oxide (1.3-fold, p < 0.05) in hCAECs and pre-treatment with PD123319 (20 μM) suppressed this effect partially (65%). Finally, NP-6A4 decreased phosphorylation of Jun-N-terminal kinase, implicated in apoptosis of ECs in atherosclerotic sites. Taken together, NP-6A4, through its ability to increase AT2R expression and signaling, exerts different cell-specific protective effects in human VSMCs and ECs.

Diabetic Cardiomyopathy: Impact of Biological Sex on Disease Development and Molecular Signatures

Diabetic cardiomyopathy refers to a unique set of heart-specific pathological variables induced by hyperglycemia and insulin resistance. Given that cardiovascular disease (CVD) is the leading cause of death in the world, and type 2 diabetes incidence continues to rise, understanding the complex interplay between these two morbidities and developing novel therapeutic strategies is vital. Two hallmark characteristics specific to diabetic cardiomyopathy are diastolic dysfunction and cardiac structural mal-adaptations, arising from cardiac cellular responses to the complex toxicity induced by hyperglycemia with or without hyperinsulinemia. While type 2 diabetes is more prevalent in men compared to women, cardiovascular risk is higher in diabetic women than in diabetic men, suggesting that diabetic women take a steeper path to cardiomyopathy and heart failure. Accumulating evidence from randomized clinical trials indicate that although pre-menopausal women have lower risk of CVDs, compared to age-matched men, this advantage is lost in diabetic pre-menopausal women, which suggests estrogen availability does not protect from increased cardiovascular risk. Notably, few human studies have assessed molecular and cellular mechanisms regarding similarities and differences in the progression of diabetic cardiomyopathy in men versus women. Additionally, most pre-clinical rodent studies fail to include female animals, leaving a void in available data to truly understand the impact of biological sex differences in diabetes-induced dysfunction of cardiovascular cells. Elegant reviews in the past have discussed in detail the roles of estrogen-mediated signaling in cardiovascular protection, sex differences associated with telomerase activity in the heart, and cardiac responses to exercise. In this review, we focus on the emerging cellular and molecular markers that define sex differences in diabetic cardiomyopathy based on the recent clinical and pre-clinical evidence. We also discuss miR-208a, MED13, and AT2R, which may provide new therapeutic targets with hopes to develop novel treatment paradigms to treat diabetic cardiomyopathy uniquely between men and women.

Qualitative and Quantitative Analysis of Cardiac Progenitor Cells in Cases of Myocarditis and Cardiomyopathy

We aimed to identify and quantify CD117⁺ and CD90⁺ endogenous cardiac progenitor cells (CPC) in human healthy and diseased hearts. We hypothesize that these cells perform a locally acting, contributing function in overcoming medical conditions of the heart by endogenous means. Human myocardium biopsies were obtained from 23 patients with the following diagnoses: Dilatative cardiomyopathy (DCM), ischemic cardiomyopathy (ICM), myocarditis, and controls from healthy cardiac patients. High-resolution scanning microscopy of the whole slide enabled a computer-based immunohistochemical quantification of CD117 and CD90. Those signals were evaluated by Definiens Tissue Phenomics® Technology. Co-localization of CD117 and CD90 was determined by analyzing comparable serial sections. CD117⁺/CD90⁺ cardiac cells were detected in all biopsies. The highest expression of CD90 was revealed in the myocarditis group. CD117 was significantly higher in all patient groups, compared to healthy specimens (^*p < 0.05). The highest co-expression was found in the myocarditis group (6.75 ± 3.25 CD90⁺CD117⁺ cells/mm²) followed by ICM (4 ± 1.89 cells/mm²), DCM (1.67 ± 0.58 cells/mm²), and healthy specimens (1 ± 0.43 cells/mm²). We conclude that the human heart comprises a fraction of local CD117⁺ and CD90⁺ cells. We hypothesize that these cells are part of local endogenous progenitor cells due to the co-expression of CD90 and CD117. With novel digital image analysis technologies, a quantification of the CD117 and CD90 signals is available. Our experiments reveal an increase of CD117 and CD90 in patients with myocarditis.

Systems pharmacological analysis of mitochondrial cardiotoxicity induced by selected tyrosine kinase inhibitors

Tyrosine kinase inhibitors (TKIs) are targeted therapies rapidly becoming favored over conventional cytotoxic chemotherapeutics. Our study investigates two FDA approved TKIs, DASATINIB; indicated for IMATINIB-refractory chronic myeloid leukemia, and SORAFENIB; indicated for hepatocellular carcinoma and advanced renal cell carcinoma. Limited but crucial evidence suggests that these agents can have cardiotoxic side effects ranging from hypertension to heart failure. A greater understanding of the underlying mechanisms of this cardiotoxicity are needed as concerns grow and the capacity to anticipate them is lacking. The objective of this study was to explore the mitochondrial-mediated cardiotoxic mechanisms of the two selected TKIs. This was achieved experimentally using immortalized human cardiomyocytes, AC16 cells, to investigate dose- and time-dependent cell killing, along with measurements of temporal changes in key signaling proteins involved in the intrinsic apoptotic and autophagy pathways upon exposure to these agents. Quantitative systems pharmacology (QSP) models were developed to capture the toxicological response in AC16 cells using protein dynamic data. The developed QSP models captured well all the various trends in protein signaling and cellular responses with good precision on the parameter estimates, and were successfully qualified using external data sets. An interplay between the apoptotic and autophagic pathways was identified to play a major role in determining toxicity associated with the investigated TKIs. The established modeling platform showed utility in elucidating the mechanisms of cardiotoxicity of SORAFENIB and DASATINIB. It may be useful for other small molecule targeted therapies demonstrating cardiac toxicities, and may aid in informing alternate dosing strategies to alleviate cardiotoxicity associated with these therapies.

Cardiovascular disease progression in female Zucker Diabetic Fatty rats occurs via unique mechanisms compared to males

Population studies have shown that compared to diabetic men, diabetic women are at a higher risk of cardiovascular disease. However, the mechanisms underlying this gender disparity are unclear. Our studies in young murine models of type 2 diabetes mellitus (T2DM) and cardiovascular disease show that diabetic male rats develop increased cardiac fibrosis and suppression of intracardiac anti-fibrotic cytokines, while premenopausal diabetic female rats do not. This protection from cardiac fibrosis in female rats can be an estrogen-related effect. However, diabetic female rats develop early subclinical myocardial deformation, cardiac hypertrophy via elevated expression of pro-hypertrophic miR-208a, myocardial damage, and suppression of cardio-reparative Angiotensin II receptor 2 (Agtr2). Diabetic rats of both sexes exhibit a reduction in cardiac capillary density. However, diabetic female rats have reduced expression of neuropilin 1 that attenuates cardiomyopathy compared to diabetic male rats. A combination of cardiac hypertrophy and reduced capillary density likely contributed to increased myocardial structural damage in diabetic female rats. We propose expansion of existing cardiac assessments in diabetic female patients to detect myocardial deformation, cardiac hypertrophy and capillary density via non-invasive imaging, as well as suggest miR-208a, AT2R and neuropilin 1 as potential therapeutic targets and mechanistic biomarkers for cardiac disease in females.

AT2 receptors in cardiovascular and renal diseases

The renin-angiotensin system (RAS) plays an important role in the initiation and progression of cardiovascular and renal diseases. These actions mediated by AT1 receptor (AT1R) are well established and led to development of selective AT1R blockers (ARBs). In contrast, there is scientific evidence that AT2 receptor (AT2R) mediates effects different from and often opposing those of the AT1R. Meagrely expressed in healthy tissue the AT2R is upregulated in injuries providing an endogenous protection to inflammatory, oxidative and apoptotic processes. Interestingly the beneficial effects mediated by AT2R can be further enhanced by pharmacological intervention using the recently developed AT2R agonists. This review article summarizes our current knowledge about regulation, signalling and effects mediated by AT2R in health and disease, with emphasis on cardiac and renal systems. At the end a novel concept of natural protective systems will be introduced and discussed as an attractive target in drug development.

Human heart valve-derived scaffold improves cardiac repair in a murine model of myocardial infarction

Cardiac tissue engineering using biomaterials with or without combination of stem cell therapy offers a new option for repairing infarcted heart. However, the bioactivity of biomaterials remains to be optimized because currently available biomaterials do not mimic the biochemical components as well as the structural properties of native myocardial extracellular matrix. Here we hypothesized that human heart valve-derived scaffold (hHVS), as a clinically relevant novel biomaterial, may provide the proper microenvironment of native myocardial extracellular matrix for cardiac repair. In this study, human heart valve tissue was sliced into 100 μm tissue sheet by frozen-sectioning and then decellularized to form the hHVS. Upon anchoring onto the hHVS, post-infarct murine BM c-kit+ cells exhibited an increased capacity for proliferation and cardiomyogenic differentiation in vitro. When used to patch infarcted heart in a murine model of myocardial infarction, either implantation of the hHVS alone or c-kit+ cell-seeded hHVS significantly improved cardiac function and reduced infarct size; while c-kit+ cell-seeded hHVS was even superior to the hHVS alone. Thus, we have successfully developed a hHVS for cardiac repair. Our in vitro and in vivo observations provide the first clinically relevant evidence for translating the hHVS-based biomaterials into clinical strategies to treat myocardial infarction.

Sphingosine 1-phosphate elicits RhoA-dependent proliferation and MRTF-A mediated gene induction in CPCs

Although c-kit(+) cardiac progenitor cells (CPCs) are currently used in clinical trials there remain considerable gaps in our understanding of the molecular mechanisms underlying their proliferation and differentiation. G-protein coupled receptors (GPCRs) play an important role in regulating these processes in mammalian cell types thus we assessed GPCR mRNA expression in c-kit(+) cells isolated from adult mouse hearts. Our data provide the first comprehensive overview of the distribution of this fundamental class of cardiac receptors in CPCs and reveal notable distinctions from that of adult cardiomyocytes. We focused on GPCRs that couple to RhoA activation in particular those for sphingosine-1-phosphate (S1P). The S1P2 and S1P3 receptors are the most abundant S1P receptor subtypes in mouse and human CPCs while cardiomyocytes express predominantly S1P1 receptors. Treatment of CPCs with S1P, as with thrombin and serum, increased proliferation through a pathway requiring RhoA signaling, as evidenced by significant attenuation when Rho was inhibited by treatment with C3 toxin. Further analysis demonstrated that both S1P- and serum-induced proliferation are regulated through the S1P2 and S1P3 receptor subtypes which couple to Gα12/13 to elicit RhoA activation. The transcriptional co-activator MRTF-A was activated by S1P as assessed by its nuclear accumulation and induction of a RhoA/MRTF-A luciferase reporter. In addition S1P treatment increased expression of cardiac lineage markers Mef2C and GATA4 and the smooth muscle marker GATA6 through activation of MRTF-A. In conclusion, we delineate an S1P-regulated signaling pathway in CPCs that introduces the possibility of targeting S1P2/3 receptors, Gα12/13 or RhoA to influence the proliferation and commitment of c-kit(+) CPCs and improve the response of the myocardium following injury.

c-kit(+)AT2R(+) Bone Marrow Mononuclear Cell Subset Is a Superior Subset for Cardiac Protection after Myocardial Infarction

Although the bone marrow mononuclear cell (BMMNC) is known as an ideal cell type for cell-based therapy for MI treatment, the effective subpopulation still remains unknown. Our study aimed at identifying the optimal subset of BMMNCs suited for cardiac regeneration. In this study, we observed that MI led to (i) a significant increase of the c-kit⁺AT₂R⁺ BMMNC subpopulation in mice and (ii) a modest increase of AT₂R⁺ BMMNCs in humans. c-kit⁺AT₂R⁺ and c-kit⁺AT₂R⁻ BMMNC subpopulations were obtained from mice after MI. Then, we cocultured cardiac H9C2 cells with c-kit⁺AT₂R⁺, c-kit⁺AT₂R⁻, and unfractionated BMMNCs; finally, we found that the c-kit⁺AT₂R⁺ subset is superior to the c-kit⁺AT₂R⁻ subset in improving cardiomyocyte protection in vitro. Of note, c-kit⁺AT₂R⁺ BMMNCs showed a more robust migration capacity than c-kit⁺AT₂R⁻ and unfractionated BMMNCs in vitro and in vivo. Additionally, compared to c-kit⁺AT₂R⁻ and unfractionated BMMNCs, intravenous transplantation of c-kit⁺AT₂R⁺ BMMNC resulted in smaller infarct size and lower levels of inflammatory reactions in heart tissue, leading to a higher global heart function improvement. In conclusion, our results indicate that the c-kit⁺AT₂R⁺ BMMNC subpopulation exerts a protective effect against MI and shows promising therapeutic possibilities with regard to the treatment of ischemic heart disease.

Differential Effects of β-Blockers, Angiotensin II Receptor Blockers, and a Novel AT2R Agonist NP-6A4 on Stress Response of Nutrient-Starved Cardiovascular Cells

In order to determine differences in cardiovascular cell response during nutrient stress to different cardiovascular protective drugs, we investigated cell responses of serum starved mouse cardiomyocyte HL-1 cells and primary cultures of human coronary artery vascular smooth muscles (hCAVSMCs) to treatment with β-blockers (atenolol, metoprolol, carvedilol, nebivolol, 3μM each), AT1R blocker losartan (1μM) and AT2R agonists (CGP42112A and novel agonist NP-6A4, 300nM each). Treatment with nebivolol, carvedilol, metoprolol and atenolol suppressed Cell Index (CI) of serum-starved HL-1 cells (≤17%, ≤8%, ≤15% and ≤15% respectively) as measured by the Xcelligence Real-Time Cell Analyzer (RTCA). Conversely, CI was increased by Ang II (≥9.6%), CGP42112A (≥14%), and NP-6A4 (≥25%) respectively and this effect was blocked by AT2R antagonist PD123319, but not by AT1R antagonist losartan. Thus, the CI signature for each drug could be unique. MTS cell proliferation assay showed that NP-6A4, but not other drugs, increased viability (≥20%) of HL-1 and hCAVSMCs. Wheat Germ Agglutinin (WGA) staining showed that nebivolol was most effective in reducing cell sizes of HL-1 and hCAVSMCs. Myeloid Cell Leukemia 1 (MCL-1) is a protein critical for cardiovascular cell survival and implicated in cell adhesion. β-blockers significantly suppressed and NP-6A4 increased MCL-1 expression in HL-1 and hCAVSMCs as determined by immunofluorescence. Thus, reduction in cell size and/or MCL-1 expression might underlie β-blocker-induced reduction in CI of HL-1. Conversely, increase in cell viability and MCL-1 expression by NP-6A4 through AT2R could have resulted in NP-6A4 mediated increase in CI of HL-1. These data show for the first time that activation of the AT2R-MCL-1 axis by NP-6A4 in nutrient-stressed mouse and human cardiovascular cells (mouse HL-1 cells and primary cultures of hCAVSMCs) might underlie improved survival of cells treated by NP-6A4 compared to other drugs tested in this study.

Cardiac stem cells transplantation enhances the expression of connexin 43 via the ANG II/AT1R/TGF-beta1 signaling pathway in a rat model of myocardial infarction

BACKGROUND

In this study, we hypothesized that CSCs mediated the expression of Cx43 after transplantation post MI via the ANG II/AT1R/TGF-beta1 signaling pathway.

METHODS

Myocardial infarction (MI) was induced in twenty male Sprague-Dawley rats. The rats were randomized into two groups and were then received the injection of 5 × 10(6) CSCs labeled with PKH26 in phosphate buffer solution (PBS) or equal PBS alone into the infarct anterior ventricular free wall two weeks after MI. Six weeks later, relevant signaling molecules involved were all examined.

RESULTS

In the CSCs group, an increased expression of Cx43 could be observed in different zones of the left ventricle (P<0.01). There was a significant reduction of the angiotensin II (ANG II) level in plasma and different regions of the left ventricular cardiac tissues (P<0.05; P<0.01). The angiotensin II type I receptor (AT1R) was decreased accompanied with an enhanced expression of angiotensin II type II receptor (AT2R) (P<0.01). Transforming growth factor beta-1(TGF-beta1) was downregulated (P<0.01). The expression of mothers against decapentaplegic homolog (SMAD) proteins including SMAD2 and SMAD3 was attenuated whereas SMAD7 was elevated (P<0.01, P<0.01, P<0.05). In addition, the expression of mitogen-activated protein kinases (MAPKs) including extracellular kinases 1/2 (ERK1/2) and p38 was also found to be reduced (P<0.01).

CONCLUSION

CSCs transplantation could enhance the level of Cx43 after MI. They might function through intervening the ANGII/AT1R/TGF-beta1 signaling pathway to regulate the expression of Cx43.

The CD4(+) AT2R(+) T cell subpopulation improves post-infarction remodelling and restores cardiac function

Myocardial infarction (MI) is a major condition causing heart failure (HF). After MI, the renin angiotensin system (RAS) and its signalling octapeptide angiotensin II (Ang II) interferes with cardiac injury/repair via the AT1 and AT2 receptors (AT1R, AT2R). Our study aimed at deciphering the mechanisms underlying the link between RAS and cellular components of the immune response relying on a rodent model of HF as well as HF patients. Flow cytometric analyses showed an increase in the expression of CD4(+) AT2R(+) cells in the rat heart and spleen post-infarction, but a reduction in the peripheral blood. The latter was also observed in HF patients. The frequency of rat CD4(+) AT2R(+) T cells in circulating blood, post-infarcted heart and spleen represented 3.8 ± 0.4%, 23.2 ± 2.7% and 22.6 ± 2.6% of the CD4(+) cells. CD4(+) AT2R(+) T cells within blood CD4(+) T cells were reduced from 2.6 ± 0.2% in healthy controls to 1.7 ± 0.4% in patients. Moreover, we characterized CD4(+) AT2R(+) T cells which expressed regulatory FoxP3, secreted interleukin-10 and other inflammatory-related cytokines. Furthermore, intramyocardial injection of MI-induced splenic CD4(+) AT2R(+) T cells into recipient rats with MI led to reduced infarct size and improved cardiac performance. We defined CD4(+) AT2R(+) cells as a T cell subset improving heart function post-MI corresponding with reduced infarction size in a rat MI-model. Our results indicate CD4(+) AT2R(+) cells as a promising population for regenerative therapy, via myocardial transplantation, pharmacological AT2R activation or a combination thereof.

Sublethal caspase activation promotes generation of cardiomyocytes from embryonic stem cells

Generation of new cardiomyocytes is critical for cardiac repair following myocardial injury, but which kind of stimuli is most important for cardiomyocyte regeneration is still unclear. Here we explore if apoptotic stimuli, manifested through caspase activation, influences cardiac progenitor up-regulation and cardiomyocyte differentiation. Using mouse embryonic stem cells as a cellular model, we show that sublethal activation of caspases increases the yield of cardiomyocytes while concurrently promoting the proliferation and differentiation of c-Kit⁺/α-actinin^low cardiac progenitor cells. A broad-spectrum caspase inhibitor blocked these effects. In addition, the caspase inhibitor reversed the mRNA expression of genes expressed in cardiomyocytes and their precursors. Our study demonstrates that sublethal caspase-activation has an important role in cardiomyocyte differentiation and may have significant implications for promoting cardiac regeneration after myocardial injury involving exogenous or endogenous cell sources.

AT(2) receptor and tissue injury: therapeutic implications

The renin-angiotensin system (RAS) plays an important role in the initiation and progression of tissue injuries in the cardiovascular and nervous systems. The detrimental actions of the AT1 receptor (AT1R) in hypertension and vascular injury, myocardial infarction and brain ischemia are well established. In the past twenty years, protective actions of the RAS, not only in the cardiovascular, but also in the nervous system, have been demonstrated. The so-called protective arm of the RAS includes AT2-receptors and Mas receptors (AT2R and MasR) and is characterized by effects different from and often opposing those of the AT1R. These include anti-inflammation, anti-fibrosis, anti-apoptosis and neuroregeneration that can counterbalance pathological processes and enable recovery from disease. The recent development of novel, small-molecule AT2R agonists offers a therapeutic potential in humans with a variety of clinical indications.

TNF, acting through inducibly expressed TNFR2, drives activation and cell cycle entry of c-Kit+ cardiac stem cells in ischemic heart disease

TNF, signaling through TNFR2, has been implicated in tissue repair, a process that in the heart may be mediated by activated resident cardiac stem cells (CSCs). The objective of our study is to determine whether ligation of TNFR2 can induce activation of resident CSCs in the setting of ischemic cardiac injury. We show that in human cardiac tissue affected by ischemia heart disease (IHD), TNFR2 is expressed on intrinsic CSCs, identified as c-kit(+)/CD45(-)/VEGFR2(-) interstitial round cells, which are activated as determined by entry to cell cycle and expression of Lin-28. Wild-type mouse heart organ cultures subjected to hypoxic conditions both increase cardiac TNF expression and show induced TNFR2 and Lin-28 expression in c-kit(+) CSCs that have entered cell cycle. These CSC responses are enhanced by exogenous TNF. TNFR2(-/-) mouse heart organ cultures subjected to hypoxia increase cardiac TNF but fail to induce CSC activation. Similarly, c-kit(+) CSCs isolated from mouse hearts exposed to hypoxia or TNF show induction of Lin-28, TNFR2, cell cycle entry, and cardiogenic marker, α-sarcomeric actin (α-SA), responses more pronounced by hypoxia in combination with TNF. Knockdown of Lin-28 by siRNA results in reduced levels of TNFR2 expression, cell cycle entry, and diminished expression of α-SA. We conclude that hypoxia-induced c-kit(+) CSC activation is mediated by TNF/TNFR2/Lin-28 signaling. These observations suggest that TNFR2 signaling in resident c-kit(+) CSCs induces cardiac repair, findings which provide further understanding of the unanticipated harmful effects of TNF blockade in human IHD.

c-Kit identifies a subpopulation of mesenchymal stem cells in adipose tissue with higher telomerase expression and differentiation potential

The stromal vascular fraction (SVF) of adipose tissue is an easy to obtain source of adipose tissue-derived stem cells (ADSCs). We and others have achieved significant but suboptimal therapeutic effects with ADSCs in various settings, mainly due to low rates of differentiation into specific cell types and with the downside of undesired side effects as a consequence of the undifferentiated ADSCs. These data prompted us to find new stem cell-specific markers for ADSCs and/or subpopulations with higher differentiation potential to specific lineages. We found a subpopulation of human ADSCs, marked by c-Kit positiveness, resides in a perivascular location, and shows higher proliferative activity and self-renewal capacity, higher telomerase activity and expression, higher in vitro adipogenic efficiency, a higher capacity for the maintenance of cardiac progenitors, and higher pancreatogenic and hepatogenic efficiency independently of CD105 expression. Our data suggests that the isolation of ADSC subpopulations with anti-c-Kit antibodies allows for the selection of a more homogeneous subpopulation with increased cardioprotective properties and increased adipogenic and endodermal differentiation potential, providing a useful tool for specific therapies in regenerative medicine applications.

Local activation of cardiac stem cells for post-myocardial infarction cardiac repair

The prognosis of patients with myocardial infarction (MI) and resultant chronic heart failure remains extremely poor despite continuous advancements in optimal medical therapy and interventional procedures. Animal experiments and clinical trials using adult stem cell therapy following MI have shown a global improvement of myocardial function. The emergence of stem cell transplantation approaches has recently represented promising alternatives to stimulate myocardial regeneration. Regarding their tissue-specific properties, cardiac stem cells (CSCs) residing within the heart have advantages over other stem cell types to be the best cell source for cell transplantation. However, time-consuming and costly procedures to expanse cells prior to cell transplantation and the reliability of cell culture and expansion may both be major obstacles in the clinical application of CSC-based transplantation therapy after MI. The recognition that the adult heart possesses endogenous CSCs that can regenerate cardiomyocytes and vascular cells has raised the unique therapeutic strategy to reconstitute dead myocardium via activating these cells post-MI. Several strategies, such as growth factors, mircoRNAs and drugs, may be implemented to potentiate endogenous CSCs to repair infarcted heart without cell transplantation. Most molecular and cellular mechanism involved in the process of CSC-based endogenous regeneration after MI is far from understanding. This article reviews current knowledge opening up the possibilities of cardiac repair through CSCs activation in situ in the setting of MI.

Preconditioning via angiotensin type 2 receptor activation improves therapeutic efficacy of bone marrow mononuclear cells for cardiac repair

Background

The therapeutic efficiency of bone marrow mononuclear cells (BMMNCs) autologous transplantation for myocardial infarction (MI) remains low. Here we developed a novel strategy to improve cardiac repair by preconditioning BMMNCs via angiotensin II type 2 receptor (AT2R) stimulation.

Methods and Results

Acute MI in rats led to a significant increase of AT2R expression in BMMNCs. Preconditioning of BMMNCs via AT2R stimulation directly with an AT2R agonist CGP42112A or indirectly with angiotensin II plus AT1R antagonist valsartan led to ERK activation and increased eNOS expression as well as subsequent nitric oxide generation, ultimately improved cardiomyocyte protection invitro as measured by co-culture approach. Intramyocardial transplantation of BMMNCs preconditioned via AT2R stimulation improved survival of transplanted cells in ischemic region of heart tissue and reduced cardiomyocyte apoptosis and inflammation at 3 days after MI. At 4 weeks after transplantation, compared to DMEM and non-preconditioned BMMNCs group, AT2R stimulated BMMNCs group showed enhanced vessel density in peri-infarct region and attenuated infarct size, leading to global heart function improvement.

Conclusions

Preconditioning of BMMNCs via AT2R stimulation exerts protective effect against MI. Stimulation of AT2R in BMMNCs may provide a new strategy to improving therapeutic efficiency of stem cells for post MI cardiac repair.

Cardioprotective C-kit⁺ bone marrow cells attenuate apoptosis after acute myocardial infarction in mice - in-vivo assessment with fluorescence molecular imaging

Cardiomyocyte loss via apoptosis plays a crucial role in ventricular remodeling following myocardial infarction (MI). Cell-based therapy approaches using bone marrow derived c-kit⁺ pluripotent cells may attenuate apoptosis following ischemic injury. We therefore thought to examine the early course of apoptosis following myocardial infarction - in-vivo - and non-invasively determine the effect of c-kit⁺ bone marrow cells on post-MI remodeling. We studied apoptosis in wild-type Kit(+/+) , c-kit mutant Kit(W)/Kit(W-v) and Kit(W)/Kit(W-v) mice after cell therapy with bone-marrow derived c-kit⁺ cells after ischemia-reperfusion injury. Mice were followed by hybrid Fluorescence Molecular Tomography/X-ray Computed Tomography (FMT-XCT) at 6h, 24h and 7 days after ischemia-reperfusion injury using an Annexin V-based fluorescent nanosensor targeting phosphatidylserine. Kit(W)/Kit(W-v) mice showed increased and prolonged apoptosis compared to control Kit(+/+) mice while c-kit cell therapy was able to attenuate the altered apoptosis rates. Increased apoptosis was accompanied by severe decline in heart function, determined by cardiac Magnetic Resonance Imaging, and cell therapy was able to rescue the animals from deleterious heart failure. Post-mortem cryoslicing and immunohistochemistry localized the fluorescence signal of the Annexin V sensor within the infarcted myocardium. Flow cytometry of digested infarct specimens identified apoptotic cardiomyocytes as the major source for the in-vivo Annexin V signal. In-vivo molecular imaging using hybrid FMT-XCT reveals increased cardiomyocyte apoptosis in Kit(W)/Kit(W-v) mice and shows that c-kit⁺ cardioprotective cells are able to attenuate post-MI apoptosis and rescue mice from progressive heart failure.

Long-term effects of early overnutrition in the heart of male adult rats: role of the renin-angiotensin system

To analyze the long-term effects of early overfeeding on the heart and coronary circulation, the effect of ischemia-reperfusion (I/R) and the role of the renin-angiotensin system (RAS) was studied in isolated hearts from control and overfed rats during lactation. On the day of birth litters were adjusted to twelve pups per mother (controls) or to three pups per mother (overfed). At 5 months of age, the rats from reduced litters showed higher body weight and body fat than the controls. The hearts from these rats were perfused in a Langendorff system and subjected to 30 min of ischemia followed by 15 min of reperfusion (I/R). The myocardial contractility (dP/dt) and the coronary vasoconstriction to angiotensin II were lower, and the expression of the apoptotic marker was higher, in the hearts from overfed rats compared to controls. I/R reduced the myocardial contractily, the coronary vasoconstriction to angiotensin II and the vasodilatation to bradykinin, and increased the expression of (pro)renin receptor and of apoptotic and antiapoptotic markers, in both experimental groups. I/R also increased the expression of angiotensinogen in control but not in overfed rats. In summary, the results of this study suggest that early overnutrition induces reduced activity of the RAS and impairment of myocardial and coronary function in adult life, due to increased apoptosis. Ischemia-reperfusion produced myocardial and coronary impairment and apoptosis, which may be related to activation of RAS in control but not in overfed rats, and there may be protective mechanisms in both experimental groups.

Impact of the AT(2) receptor agonist C21 on blood pressure and beyond

It is now widely accepted that the angiotensin AT(2) receptor (AT(2)R) plays an important protective role during pathophysiologic conditions, acting as a repair system. The development of the first selective nonpeptide AT(2)R agonist C21 accelerated our understanding of AT(2)R-mediated protective signaling and actions. This article reviews the impact of C21 on blood pressure in normotensive and hypertensive animal models. Although C21 does not act as a classical antihypertensive drug, it could be useful in preventing hypertension-induced vascular and other end organ damages via anti-apoptotic, anti-fibrotic and anti-inflammatory actions. In particular, a strong body of evidence started to emerge around its anti-inflammatory feature. This property should be further investigated for potential clinical indications in cardiovascular diseases and beyond.

Cardiac primitive cells become committed to a cardiac fate in adult human heart with chronic ischemic disease but fail to acquire mature phenotype: genetic and phenotypic study

Adult human heart hosts a population of cardiac primitive CD117-positive cells (CPCs), which are responsible for physiological tissue homeostasis and regeneration. While the bona fide stem cells express telomerase, their progenies are no longer able to preserve telomeric DNA; hence the balance between their proliferation and differentiation has to be tightly controlled in order to prevent cellular senescence and apoptosis of CPCs before their maturation can be accomplished. We have examined at cellular and molecular level the proliferation, apoptosis and commitment of CPCs isolated from normal (CPC-N) and age-matched pathological adult human hearts (CPC-P) with ischemic heart disease. In the CPC-P, genes related to early stages of developmental processes, nervous system development and neurogenesis, skeletal development, bone and cartilage development were downregulated, while those involved in mesenchymal cell differentiation and heart development were upregulated, together with the transcriptional activation of TGFβ/BMP signaling pathway. In the pathological heart, asymmetric division was the prevalent type of cardiac stem cell division. The population of CPC-P consisted mainly of progenitors of cardiac cell lineages and less precursors; these cells proliferated more, but were also more susceptible to apoptosis with respect to CPC-N. These results indicate that CPCs fail to reach terminal differentiation and functional competence in pathological conditions. Adverse effects of underlying pathology, which disrupts cardiac tissue structure and composition, and cellular senescence, resulting from cardiac stem cell activation in telomere dysfunctional environment, can be responsible for such outcome.

Trophic actions of bone marrow-derived mesenchymal stromal cells for muscle repair/regeneration

Bone marrow-derived mesenchymal stromal cells (BM-MSCs) represent the leading candidate cell in tissue engineering and regenerative medicine. These cells can be easily isolated, expanded in vitro and are capable of providing significant functional benefits after implantation in the damaged muscle tissues. Despite their plasticity, the participation of BM-MSCs to new muscle fiber formation is controversial; in fact, emerging evidence indicates that their therapeutic effects occur without signs of long-term tissue engraftment and involve the paracrine secretion of cytokines and growth factors with multiple effects on the injured tissue, including modulation of inflammation and immune reaction, positive extracellular matrix (ECM) remodeling, angiogenesis and protection from apoptosis. Recently, a new role for BM-MSCs in the stimulation of muscle progenitor cells proliferation has been demonstrated, suggesting the potential ability of these cells to influence the fate of local stem cells and augment the endogenous mechanisms of repair/regeneration in the damaged tissues.

The regenerative potential of angiotensin AT2 receptor in cardiac repair

Angiotensin II, the main effector peptide of the renin–angiotensin system, interferes with cardiac remodeling and repair through its receptors, including AT1 and AT2 receptor (R). The functional relevance of the previously neglected AT2R is currently intensively studied. Pharmacological therapies with AT1R blockers have improved outcomes in patients with ischemic heart injury, probably involving an indirect stimulation of AT2R. Previous experimental studies have clearly shown a protective action of AT2R in tissue repair and regeneration. We have recently identified the c-kit+AT2R+ progenitor cell population in rat heart and bone marrow, which increases after induction of myocardial infarction. Further experimental evidence demonstrates that AT2R mediates cardiac homing and repair process of the c-kit+ progenitor cells. AT2R stimulation through AT1R blockers or directly by AT2R agonist or both in combination may potentially offer the translational options to improve the regenerative potentials of stem/progenitor cells derived from patients with cardiovascular disease.

Hematopoiesis leading to a diversity of dendritic antigen-presenting cell types

Hematopoietic stem cells (HSCs) undergo expansion and differentiation, giving rise to all terminally differentiated blood cells throughout life. HSCs are found in distinct anatomical sites during development, and in adults, hematopoiesis occurs predominantly on the luminal side of the bone cavity in bone marrow. Millions of newly formed blood cells are generated per second to accommodate the short half-life of hematopoietic cells. For this to happen, HSCs must sustain their self-renewal capacity as well as their capability to commit and differentiate toward multiple cell lineages. Development of the hematopoietic system is finely regulated as the animal ages, so that it does not become exhausted or misdirected. This review covers aspects of hematopoietic development from the embryonic period through adult life in relation to development of dendritic cells. It also considers a role for HSCs in extramedullary sites and their possible role in myelopoiesis, with formation of tissue-specific antigen-presenting cells.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.