Cardiac Mast Cell Research Articles

Abstract We097: Dual Targeting CXCR4 and CXCR7 Prevents Doxorubicin-Induced Cardiotoxicity by Eliminating Cardiac Inflammation and Preserving Cardiomyocyte Function

Background: Doxorubicin (DOX)-induced cardiotoxicity (DICT) has become a serious health burden for cancer survivors. The detrimental effects of CXCR4-mediated excessive inflammation in myocardium and the protective effects of CXCR7 in cardiomyocytes have been demonstrated. Aims: We tested the protective effects against DICT of a dual-targeting compound TC14012, which has specific antagonistic activity against CXCR4 and potent agonistic activity on CXCR7. Methods: Eight-week-old male C57BL/6J mice were injected with DOX for consecutive 5 weeks, during which mice were treated with TC14012 twice a week. One week after the last dose injection, mice were euthanized after heart function examination. Markers of cardiac inflammation and fibrosis were evaluated. Cardiac RNA-seq was performed to explore the underlying molecular pathways. Key findings: TC14012 supplement significantly prevented DOX-induced cardiac systolic dysfunction, reflected by improved ejection fraction and fraction shortening, along with remarkable attenuation of DOX-induced cardiac perivascular and interstitial collagen deposition and neutrophils and macrophage infiltration. RNA-seq revealed that TC14012 prevention of DICT was accompanied with a remarkable stimulation of signals involving in cardiac contraction and energy reserve metabolic process, particularly glycogen and glucan metabolism that are crucial for meeting the cardiac energy demand in response to DOX induction. These signals could be further enriched into AMPK signaling pathway and validated by upregulation of AMPK phosphorylation. Besides, TC14012 prevention of DICT was accompanied with a significant reduction in cardiac mast cell activation and degranulation. These signals could be further enriched into Rap1 signaling pathway, and TC14012 was validated to inhibit Rap1 activity and mast cell activation. Most importantly, TC14012 treatment did not affect the suppressive effects of DOX on tumor growth in a syngeneic EL4 lymphoma-bearing, immunocompetent mouse model. Conclusions: We preliminary conclude that TC14012 prevents DICT by activating cardiac CXCR7 to reprogram cardiomyocyte metabolism and prevent cardiac damage and dysfunction via activating AMPK, and by antagonizing CXCR4 to inhibit cardiac mast cell infiltration and activation via blunting Rap1 activity but does not affect the anti-tumor activity of DOX.

Oxytocin Attenuates Sympathetic Innervation with Inhibition of Cardiac Mast Cell Degranulation in Rats after Myocardial Infarction.

Sympathetic hyperinnervation is the leading cause of fatal ventricular arrhythmia (VA) after myocardial infarction (MI). Cardiac mast cells cause arrhythmias directly through degranulation. However, the role and mechanism of mast cell degranulation in sympathetic remodeling remain unknown. We investigated the role of oxytocin (OT) in stabilizing cardiac mast cells and improving sympathetic innervation in rats. MI was induced by coronary artery ligation. Western blotting, immunofluorescence, and toluidine staining of mast cells were performed to determine the expression and location of target protein. Mast cells accumulated significantly in peri-infarcted tissues and were present in a degranulated state. They expressed OT receptor (OTR), and OT infusion reduced the number of degranulated cardiac mast cells post-MI. Sympathetic hyperinnervation was attenuated as assessed by immunofluorescence for tyrosine hydroxylase (TH). Seven days post-MI, the arrhythmia score of programmed electrical stimulation was higher in vehicle-treated rats with MI than in rats treated with OT. An in vitro study showed that OT stabilized mast cells via the phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) signaling pathway. Further in vivo studies on OTR-deficient mice showed worsening mast cell degranulation and worsening sympathetic innervation. OT pretreatment inhibited cardiac mast cell degranulation post-MI and prevented sympathetic hyperinnervation, along with mast cell stabilization via the PI3K/Akt pathway. SIGNIFICANCE STATEMENT: This is the first study to elucidate the role and mechanism of oxytocin (OT) in inflammatory-sympathetic communication mediated sympathetic hyperinnervation after myocardial infarction (MI), providing new approaches to prevent fatal arrhythmias.

Retraction: Myocardial Remodeling in Diabetic Cardiomyopathy Associated with Cardiac Mast Cell Activation.

Retraction: Myocardial Remodeling in Diabetic Cardiomyopathy Associated with Cardiac Mast Cell Activation.

Mast cells: a novel therapeutic avenue for cardiovascular diseases?

Mast cells are tissue-resident immune cells strategically located in different compartments of the normal human heart (the myocardium, pericardium, aortic valve, and close to nerves) as well as in atherosclerotic plaques. Cardiac mast cells produce a broad spectrum of vasoactive and proinflammatory mediators, which have potential roles in inflammation, angiogenesis, lymphangiogenesis, tissue remodelling, and fibrosis. Mast cells release preformed mediators (e.g. histamine, tryptase, and chymase) and de novo synthesized mediators (e.g. cysteinyl leukotriene C4 and prostaglandin D2), as well as cytokines and chemokines, which can activate different resident immune cells (e.g. macrophages) and structural cells (e.g. fibroblasts and endothelial cells) in the human heart and aorta. The transcriptional profiles of various mast cell populations highlight their potential heterogeneity and distinct gene and proteome expression. Mast cell plasticity and heterogeneity enable these cells the potential for performing different, even opposite, functions in response to changing tissue contexts. Human cardiac mast cells display significant differences compared with mast cells isolated from other organs. These characteristics make cardiac mast cells intriguing, given their dichotomous potential roles of inducing or protecting against cardiovascular diseases. Identification of cardiac mast cell subpopulations represents a prerequisite for understanding their potential multifaceted roles in health and disease. Several new drugs specifically targeting human mast cell activation are under development or in clinical trials. Mast cells and/or their subpopulations can potentially represent novel therapeutic targets for cardiovascular disorders.

The TTN p. Tyr4418Ter mutation causes cardiomyopathy in human and mice.

To generate a mouse model carrying TTNtv Y4370* simulating the newly discovered human heterozygous nonsense TTNtv c.13254T>G (p.Tyr4418Ter) to supplement and improve the functional evidence of pathogenic mutation TTNtv c.13254T>G on the pathogenic type of dilated cardiomyopathy. We generated 4 mice carrying TTNtv p. Y4370* through CRISPR/Cas-mediated genome engineering. Monthly serological detection, bimonthly echocardiography, and histology evaluation were carried out to observe and compare alterations of cardiac structure and function between 4 TTN+/- mice and 4 wild-type (WT) mice. For the two-month-old TTN+/- mice, serum glutamic-oxalacetic transaminase (AST), lactic dehydrogenase (LDH), and creatine kinase (CK) were significantly increased, the diastolic Left Ventricular Systolic Anterior Wall (LVAW), and the LV mass markedly rose, with the left ventricular volume displaying an increasing trend and Ejection Fraction (EF) and Fractional Shortening (FS) showing a decreasing trend. Besides, the histological evaluation showed that cardiac fibrosis level and positive rate of cardiac mast cell of TTN+/- mice were obviously increased compared with WT mice. TTNtv Y4370* could lead to cardiac structure and function alterations in mice, supplementing the evidence of TTNtv c.13254T>G pathogenicity in human.

Involvement of Polyamines From Cardiac Mast Cells in Myocardial Remodeling Induced by Pressure Overload Through Mitochondrial Permeability Transition Pore Opening.

ObjectivePolyamines mainly contain spermine (SPM), spermidine (SPD), and putrescine (PUT). Many research results suggest that polyamines participate in cell proliferation, differentiation, and the regulation of gene expression, and have a close relationship with the occurrence and development of many diseases. However, the role and possible mechanisms of action of polyamines from cardiac mast cells in myocardial remodeling induced by pressure overload remain to be elucidated.MethodsPressure overload was induced by abdominal aortic constriction (AAC). Toluidine blue staining was used to visualize mast cells in cardiac tissue. The polyamine content of cardiac tissue was analyzed using high-performance liquid chromatography. Opening of the mitochondrial permeability transition pore (MPTP) was determined by the Ca2+-induced swelling of isolated cardiac mitochondria, measured as a reduction in A520.ResultsCompared with sham rats, the cardiac mast cell density, the polyamine content (PUT, SPB, and SPM), and myocardial MPTP opening in rats with AAC were significantly increased (P < 0.05), and were accompanied by increased myocardial fibrosis and heart weight/body weight ratio. Intraperitoneal injection of polyamines mimicked these results, and these effects were reversed by cromolyn sodium, a mast cell stabilizer (P < 0.05). Myocardial MPTP opening increased in rats with AAC (P < 0.05), and the three polyamines also increased myocardial MPTP opening (P < 0.05).ConclusionMast cell-derived polyamines are involved in pressure overload-induced myocardial remodeling by increasing opening of the MPTP.

Dexmedetomidine preconditioning mitigates myocardial ischemia/reperfusion injury via inhibition of mast cell degranulation

The degranulation of cardiac mast cells is associated with occurrence and development of myocardial ischemia/reperfusion (I/R) injury. Dexmedetomidine has a cardioprotective effect from I/R injury. The purpose of this study was to investigate whether dexmedetomidine preconditioning induced cardioprotection is related to suppression of degranulation of cardiac mast cell. Both in vivo and in vitro experimental results revealed that hemodynamic disorder, arrhythmia, infarct size, histopathological score, and mast cell degranulation were dramatically increased in I/R injury groups compared with non-I/R groups, and mastocyte secretagogue compound 48/80 aggravated these damages, but it can be improved by dexmedetomidine preconditioning. Similarly, compound 48/80 increased levels of cardiac troponin I (cTnI) and tryptase, cardiomyocytes apoptosis, and expression of high-mobility group box 1 (HMGB1), toll-like receptor 4 (TLR4), and nuclear factor-kappa B p65 (NF-κB p65) in cardiac tissues induced by I/R injury, but it can be partially decreased by dexmedetomidine pretreatment. Compound 48/80 inhibited proliferation of H9C2(2−1) and RBL-2H3, exacerbated apoptosis of H9C2(2−1), and elevated levels of cTnI and tryptase, while both of which were abolished by dexmedetomidine pretreatment. Our data suggest that dexmedetomidine preconditioning alleviates the degranulation of mast cells and the apoptosis of cardiomyocytes caused by I/R injury, and inhibits the activation of inflammatory related factors HMGB1, TLR4, and NF-κB p65.

Recommendations for the Recognition, Diagnosis, and Management of Patients with Post COVID-19 Condition ('Long COVID'): A Delphi Study

Background: The present work aims to provide a rapid expert guide for Post Covid-19 Condition (“long covid”) clinical services. In the absence of research into mechanisms, therapies and care pathways, yet faced with an urgent need, guidance based on “emerging experience” is required.Methods: The authors generated 33 recommendations pertaining to the recognition, investigation, and management of long covid. These were distributed online to a Delphi panel of UK doctors (any specialty) with an interest in, lived experience of, and/or experience treating long covid. Over two rounds of Delphi testing, panellists indicated their agreement with each recommendation (a 5-point Likert scale) and gave comments. Recommendations eliciting a response of “strongly agree”, “agree”, or “neither agree nor disagree” from ≥90% of respondents were taken as showing consensus. Findings: Thirty-three UK-based clinicians representing 14 specialties completed both rounds of the Delphi. Twenty-nine (88%) had lived experience of long covid and five (15%) were clinicians developing services for long covid. Of the 33 recommendations presented in Round 1, 18 were incorporated into the final list, 13 were amended to reflect respondents’ feedback, and two were excluded. Of the 19 presented in Round 2, 17 were added to the final list and two were excluded. The final list thus comprised 35 recommendations: six pertaining to clinic organisation, 13 to diagnosis of the underlying disorder, and 16 to management.Interpretation: Long covid clinics need to operate not in isolation but in the context of rapidly evolving practice amongst both GPs and specialists. Care pathways in holistic care, investigation of specific complications, management of potential symptom clusters in cardiac disease, dysautonomia and mast cell disorder, and individualised rehabilitation are needed.Funding: The first author is funded by the NIHR Imperial PSTRC; however, this research received no specific grant from any funding agency.Declaration of Interest: There are no conflicts of interest.Ethical Approval: As this is considered service development, ethical approval was not required for this study. Delphi participants gave informed consent before taking part. All aspects of the study were conducted in the UK in January-March 2021.

Mast cell peptidases (carboxypeptidase A and chymase)-mediated hydrolysis of human angiotensin-(1–12) substrate

Angiotensin processing peptidases (carboxypeptidase A (CPA) and chymase) are stored in cardiac mast cell (MC) secretory granules in large quantity and are co-released into the extracellular environment after activation/degranulation. In the human heart, chymase is primarily responsible for angiotensin II (Ang II) generation from the alternate substrate angiotensin-(1–12) (Ang-(1–12)). We investigated the individual and combined hydrolytic specificity of CPA and chymase enzymes (1:1 and 1:⅓ ratio) in the processing of the human Ang-(1–12) (hAng-(1–12)) substrate. To determine the Km and Vmax, the CPA and recombinant human chymase (rhChymase) enzymes were incubated with increasing concentrations of hAng-(1–12) substrate (0–300 μM). We found that CPA alone sequentially metabolized hAng-(1–12) substrate into angiotensin-(1–9) (Ang-(1–9), 53%), Ang II (22%) and angiotensin-(1–7) (Ang-(1–7), 11%) during a 15 min incubation. In the presence of rhChymase alone, 125I-hAng-(1–12) was directly metabolized into Ang II (89%) and no further hydrolysis of Ang II was detected. In the presence of both CPA + rhChymase enzymes (1:1 or 1:⅓ ratio), the amount of Ang II formation from 125I-hAng-(1–12) within a 5 min incubation period were 68% or 65%, respectively. In the presence of both (CPA + rhChymase), small amounts of Ang-(1–9) and Ang-(1–7) were generated from 125I-hAng-(1–12). The Km and Vmax values were 150 ± 5 μM and 384 ± 23 nM/min/mg of CPA and 40 ± 9 μM and 116 ± 20 nM/min/mg of rhChymase. The catalytic efficiency (Vmax/Km ratio) was higher for rhChymase/hAng-(1–12) compared to CPA/hAng-(1–12). Compared to CPA, chymase has a much higher affinity to hydrolyze the hAng-(1–12) substrate directly into Ang II. In addition, Ang II and Ang-(1–7) are the end products of chymase and CPA, respectively. Overall, our findings suggest that the Ang II generation from hAng-(1–12) is primarily mediated by chymase rather than CPA.

Regulation of Cardiac Mast Cell Maturation and Function by the Neurokinin-1 Receptor in the Fibrotic Heart

Cardiac fibrosis is an underlying cause of diastolic dysfunction, contributing to heart failure. Substance P (SP) activation of the neurokinin-1 receptor (NK-1R) contributes to cardiac fibrosis in hypertension. However, based on in vitro experiments, this does not appear to be via direct activation of cardiac fibroblasts. While numerous cells could mediate the fibrotic effects of SP, herein, we investigate mast cells (MC) as a mechanism mediating the fibrotic actions of SP, since MCs are known to play a role in cardiac fibrosis and respond to SP. Spontaneously hypertensive rats (SHR) were treated with the NK-1R antagonist L732138 (5 mg/kg/d) from 8 to 12 weeks of age. L732138 prevented increased MC maturation of resident immature MCs. NK-1R blockade also prevented increased cardiac MC maturation in angiotensin II-infused mice. MC-deficient mice were used to test the importance of MC NK-1Rs to MC activation. MC-deficient mice administered angiotensin II did not develop fibrosis; MC-deficient mice reconstituted with MCs did develop fibrosis. MC-deficient mice reconstituted with MCs lacking the NK-1R also developed fibrosis, indicating that NK-1Rs are not required for MC activation in this setting. In conclusion, the NK-1R causes MC maturation, however, other stimuli are required to activate MCs to cause fibrosis.

Mast Cell Peptidases (Carboxypeptidase A and Chymase)‐Mediated Hydrolysis of Human Angiotensin‐(1‐12)

IntroductionAngiotensin processing peptidases [carboxypeptidase A (CPA) and chymase] are stored in cardiac mast cell secretory granules and are co‐released into the extracellular environment after activation/degranulation. In the human heart, we showed that chymase is primarily responsible for angiotensin II (Ang II) generation from the alternate substrate angiotensin‐(1‐12) [Ang‐(1‐12)], which is present in human heart. In this study, we investigated whether there are any synergistic effects of CPA and chymase in the processing of Ang‐(1‐12).MethodRadiolabeled human Ang‐(1‐12) [125I‐Ang‐(1‐12)] substrate was incubated with CPA alone (0.325 μg/mL), human recombinant chymase (hrChymase) (0.325 μg/mL) or a combination of CPA + hrChymase (1:1 or 1: ⅓ ratio) in 50 mM Tris‐HCl buffer solution containing 150 mM NaCl (pH 8.0) for 0–15 min at 37 °C. The reaction was stopped by adding an equal volume of 1% phosphoric acid and injected on a C18 column. Eluted 125I‐Ang‐(1‐12) metabolic products were quantified by HPLC connected to in‐line flow‐through gamma detector. To determine the Km and Vmax, CPA and hrChymase were incubated with increasing concentrations (0–300 μM) of human Ang‐(1‐12) substrate for 20 min at 37 °C. The Km and Vmax were calculated using the Michaelis‐Menten equation.ResultsWe found that after 15 min of incubation, CPA sequentially metabolized Ang‐(1‐12) substrate into angiotensin‐(1‐9) [Ang‐(1‐9), 53% (major product)], Ang II (22%) and angiotensin‐(1‐7) [Ang‐(1‐7), 11%]. No further hydrolysis of Ang‐(1‐7) was detected during CPA incubation. In the presence of hrChymase alone, 125I‐Ang‐(1‐12) was directly metabolized into Ang II (89%) and no further hydrolysis of Ang II was detected. In the presence of both CPA + hrChymase (1:1 ratio), the amount of Ang II formation was 68% from 125I‐Ang‐(1‐12) within a 5 min incubation period. The formation of Ang‐(1‐9) and Ang‐(1‐7) were only 11% and 10%, respectively. When CPA + hrChymase were added in 1: ⅓ ratio for 5 min, the Ang II, Ang‐(1‐9) and Ang‐(1‐7) formations were 65%, 27%, 6%, respectively. The Km and Vmax values were 150 ± 5 μM and 384 ± 23 nM/min/mg of CPA and 40 ± 9 μM and 116 ± 20 nM/min/mg of hrChymase.ConclusionsThese findings suggest that compared to CPA, chymase shows a much higher affinity to metabolize Ang‐(1‐12) into Ang II. In addition, Ang II and Ang‐(1‐7) are the end products of chymase and CPA, respectively. Overall, our findings suggest that chymase, rather than CPA, is primarily responsible for Ang II generation from Ang‐(1‐12).Support or Funding InformationThis work was supported by grant from the National Heart, Lung and Blood Institute of the National Institutes of Health (P01 HL‐051952).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Role of cardiac mast cells in exercise training-mediated cardiac remodeling in angiotensin II-infused ovariectomized rats

AimsRegular exercise is recommended in postmenopausal women to prevent the development of heart disease, but mechanism underlying the protection is not completely understood. Many studies have suggested that exercise training notably mediated whole body immune and inflammatory functions. Whether exercise training prevents cardiac dysfunction after deprivation of female sex hormones by inhibiting cardiac immune activation is therefore interesting. Main methodsNine-week treadmill running program was introduced in sham-operated and ovariectomized rats. In addition, chronic angiotensin II infusion was further challenged to activate pathological cardiac remodeling. Cardiac remodeling in associated with the density and degranulation of cardiac mast cells was then evaluated. Key findingsWith exogenous angiotensin II-induced hypertension, cardiac hypertrophy with myocardial fibrosis was shown similarly in both sham-operated controls and ovariectomized rats. Although exercise training did not prevent cardiac hypertrophy, myocardial fibrosis was abolished by exercise. While ovariectomy increased both cardiac mast cell density and degranulation percentage, angiotensin II infusion only enhanced mast cell density. Exercise training could not decrease the density of mast cells, but it did normalize the percentage of degranulation in all groups. Correlation analysis suggested that cardiac mast cell activation is inversely associated with cardiomyocyte hypertrophy due to exercise training but is directly correlated to cardiac hypertrophy by angiotensin II infusion. SignificanceExercise training could attenuate cardiac mast cell hyperactivation induced by either deprivation of female sex hormones or excessive angiotensin II. Additionally, cardiac mast cells could be a solution in the distinction between physiological and pathological hypertrophic development.

Substance P-mediated cardiac mast cell activation: An in vitro study

The neuropeptide substance P can induce degranulation of cardiac mast cells at high concentrations. Herein, we seek to further understand substance P activation of cardiac mast cells in the context of other neuropeptides as well as modulation by non-neuropeptides. This is important given the increasingly recognized role of both cardiac mast cells and substance P in adverse cardiac remodeling. To address this, we isolated cardiac mast cells and compared their response to substance P as well as other members from the tachykinin family of peptides, including neurokinin A and hemokinin-1. We also tested the ability of other factors to manipulate the cardiac mast cell response to substance P. We found that while neurokinin A did not induce cardiac mast cell degranulation, both substance P and hemokinin-1 induced a concentration-dependent release of histamine; the maximal response to hemokinin-1 was greater than to substance P. Neurokinin-1 receptor blockade prevented substance P-induced histamine release, while only partially attenuating hemokinin-1-induced histamine release. The antioxidant N-acetylcysteine attenuated histamine release in response to hemokinin-1 and had no effect on substance P-induced histamine release. Selective PPAR-γ agonists attenuated histamine release in response to substance P. These data indicate that substance P activates cardiac mast cells via the neurokinin-1 receptor, and that the activation response is different to other tachykinins. That the response to substance P is receptor mediated and can be modulated by activation of other receptors (PPAR-γ), argues that substance P activation of cardiac mast cells has potential biological significance.

GPER Agonist G1, but Not Other Specific ERs Improves Diastolic Function and Attenuates Cardiac RAS Activation in Estrogen‐deficient SHR

IntroductionLeft ventricular diastolic dysfunction (LVDD) increases the risk of developing heart failure with preserved ejection fraction (HFpEF), the predominant type of heart failure seen in women. Emerging epidemiologic evidence suggests that early menopause is positively associated with incident HF, which suggests potential protective roles of estrogens in LVDD development and progression. There are three estrogen receptors (ER) expressed in the heart, ER‐α, ER‐β, and G‐protein coupled ER (GPER). We previously found that GPER plays greater protective roles in cultured myocyte and mast cell lines than ER‐α or ER‐β, by inhibiting Ang II‐induced cell hypertrophy and serum‐induced cell proliferation, respectively. Moreover, estrogen loss‐induced LVDD in the hypertensive mRen2. Lewis rat was linked to increases in cardiac mast cell number, chymase, and Ang II. The aim of this study was to investigate how different specific agonists of estrogen receptors (ER‐α agonist PPT; ER‐β agonist DPN; and GPER agonist G‐1) influence diastolic function and cardiac renin angiotensin system (RAS) components.MethodsTwenty‐four SHR females underwent bilateral ovariectomy (OVX) at 12 weeks of age; 8 weeks post‐surgery, rats were randomized (n=6/group) to receive equipotent, daily treatments (0.24 μMol/kg/day, s.c.) of one of the above ER agonists (PPT‐ 94 μg/kg; DPN‐ 58 μg/kg; G‐1‐100 μg/kg), or vehicle (peanut oil). Following four weeks of treatment, rats were anesthetized (isoflurane) for direct blood pressure and Doppler echo measures of diastolic function, defined by e′ and E/e′. LV tissue for RAS activity and expression were evaluated. Data were analyzed by one‐way ANOVA. P&lt;0.05 was significant.ResultsAs expected, the doses chosen for the specific ER agonists did not overtly affect blood pressure. Of the ER agonists, G‐1 had the most profound and significant impact on diastolic function, increasing myocardial relaxation (e′) and decreasing Doppler‐derived LV filling pressures (E/e′) by 53% and 24% versus control, respectively. Neither DPN nor PPT modified the altered cardiac function induced by OVX. GPER activation by G‐1 had a significant inhibitory effect on cardiac ACE activity when compared to vehicle, while the other Ang II‐forming pathway in the heart, Ang‐1–12/chymase, was not overtly altered by ER activation. All three agonists suppressed cardiac ACE2 activity. AT1R gene expression was increased in OVX‐vehicle by 47 to 61% when compared to hearts from OVX‐ERs (P=0.051) (Figure).ConclusionThese data imply that of the three estrogen receptors, GPER has a unique role in the preservation of diastolic function and modulation of the cardiac RAS, which would contribute to the protection in LVDD disease progression after estrogen loss, if pharmacologically activated.Support or Funding InformationNIH AG033727 (LG) and NIH HL 051952 (CMF and LG) INCT‐INOFAR ‐ Proc. 465249/2014‐0 (GZS and RTS) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (JS) Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq) (GZS and RTS)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Mast Cells: Key Contributors to Cardiac Fibrosis.

Historically, increased numbers of mast cells have been associated with fibrosis in numerous cardiac pathologies, implicating mast cells in the development of cardiac fibrosis. Subsequently, several approaches have been utilised to demonstrate a causal role for mast cells in animal models of cardiac fibrosis including mast cell stabilising compounds, rodents deficient in mast cells, and inhibition of the actions of mast cell-specific proteases such as chymase and tryptase. Whilst most evidence supports a pro-fibrotic role for mast cells, there is evidence that in some settings these cells can oppose fibrosis. A major gap in our current understanding of cardiac mast cell function is identification of the stimuli that activate these cells causing them to promote a pro-fibrotic environment. This review will present the evidence linking mast cells to cardiac fibrosis, as well as discuss the major questions that remain in understanding how mast cells contribute to cardiac fibrosis.

Chymase released from hypoxia-activated cardiac mast cells cleaves human apoA-I at Tyr192 and compromises its cardioprotective activity

ApoA-I, the main structural and functional protein of HDL particles, is cardioprotective, but also highly sensitive to proteolytic cleavage. Here, we investigated the effect of cardiac mast cell activation and ensuing chymase secretion on apoA-I degradation using isolated rat hearts in the Langendorff perfusion system. Cardiac mast cells were activated by injection of compound 48/80 into the coronary circulation or by low-flow myocardial ischemia, after which lipid-free apoA-I was injected and collected in the coronary effluent for cleavage analysis. Mast cell activation by 48/80 resulted in apoA-I cleavage at sites Tyr192 and Phe229, but hypoxic activation at Tyr192 only. In vitro, the proteolytic end-product of apoA-I with either rat or human chymase was the Tyr192-truncated fragment. This fragment, when compared with intact apoA-I, showed reduced ability to promote migration of cultured human coronary artery endothelial cells in a wound-healing assay. We propose that C-terminal truncation of apoA-I by chymase released from cardiac mast cells during ischemia impairs the ability of apoA-I to heal damaged endothelium in the ischemic myocardium.

Propofol attenuates myocardial ischemia reperfusion injury partly through inhibition of resident cardiac mast cell activation

Cardiac mast cell activation is involved in the process of myocardial ischemia reperfusion (I/R) injury and exacerbates myocardial infarction. Propofol, an anesthetic with antioxidant property, can reduce myocardial infarct size in I/R injury. The present study was designed to investigate whether propofol can attenuate myocardial I/R injury by inhibiting resident cardiac mast cell activation by a Langendorff model. Thirty rats were randomly assigned to 5 groups (n=6 per group): control group and four test groups (I/R, I/R+compound 48/80, I/R+propofol, I/R+compound 48/80+propofol). Cultured RBL-2H3 cells were pretreated with propofol and subjected to mast cell degranulator compound48/80 (C48/80).Microscopically, degradation of myofibrillar and degranulation of mast cells were studied using hematoxylin-eosin toluidine blue staining techniques. After the effluent was assayed for tryptase, LDH, CK-MB and cTnI, myocardial tissue was evaluated for cytokine levels and infarct area. Heart subjected to I/R showed significantly increased expression of cytokines (TNF-α and IL-6), LDH, CK-MB and cTnI. In addition, the I/R-induced heart also showed greater histopathological injury and a larger infarction zone, following increased mast cell degranulation with concomitant rise in tryptase. Mast cell degranulation by C48/80 further aggravated I/R injury. However, all of these effects were suppressed by propofol pretreatment, which also abrogated C48/80-mediated exacerbation of I/R injury. Also, propofol attenuated the C48/80-evoked tryptase and histamine release in RBL-2H3 cells. It is concluded that pretreatment of propofol confers protection against I/R injury partly by inhibiting resident cardiac mast cell activation.

Mast Cell Inhibition Attenuates Cardiac Remodeling and Diastolic Dysfunction in Middle-aged, Ovariectomized Fischer 344 × Brown Norway Rats.

The incidence of left ventricular diastolic dysfunction (LVDD) increases in women after menopause, yet the mechanisms are unclear. Because mast cells participate in the pathological processes of various cardiac diseases, we hypothesized that mast cell inhibition would protect against estrogen loss-induced LVDD. The mast cell stabilizer, cromolyn sodium (30 mg·kg·d), or vehicle was administered subcutaneously by osmotic minipump to ovariectomized (OVX) female Fischer 344 × Brown Norway (F344BN) rats starting at 4 weeks after surgery. Eight weeks after OVX, systolic blood pressure increased by 20% in OVX versus sham rats, and this effect was attenuated after 4 weeks of cromolyn treatment. Also, cromolyn mitigated the adverse reductions in myocardial relaxation (e') and increases in left ventricle (LV) filling pressures (E/e'), LV mass, wall thicknesses, and interstitial fibrosis from OVX. Although cardiac mast cell number was increased after OVX, cardiac chymase activity was not overtly altered by estrogen status and tended to decrease by cromolyn. Contrariwise, Ang II content was greater in hearts of OVX versus sham rats, and cromolyn attenuated this effect. Taken together, mast cell inhibition with cromolyn attenuates LV remodeling and LVDD in OVX-Fischer 344 × Brown Norway rats possibly through actions on the heart level and/or through vasodilatory effects at the vascular level.

Regulation of Cardiac Mast Cell Density and Tryptase Production as a Mechanism of Substance P‐Induced Cardiac Fibrosis

Regulation of Cardiac Mast Cell Density and Tryptase Production as a Mechanism of Substance P‐Induced Cardiac Fibrosis

The ATAK complex (Adrenaline, Takotsubo, Anaphylaxis, and Kounis hypersensitivity -associated coronary syndrome) in neurological conditions.

Sir, Takotsubo syndrome, transient left ventricular apical ballooning, takotsubo cardiomyopathy, apical ballooning syndrome, atypical apical ballooning, ampulla cardiomyopathy, broken heart syndrome, transient left ventricular dysfunction syndrome, and stress cardiomyopathy were named after a round-bottomed and narrow-necked fishing pot - takotsubo in Japanese - for trapping octopus because of its resemblance to left ventriculogram. In the interesting report published in Indian Journal of Critical Care Medicine,[1] a 48-year-old man with progressive loss of vision, hypotension, tachycardia, and acidosis was found to have takotsubo syndrome while the coronary arteries were normal. Computerized tomography revealed dense sellar-suprasellar mass lesion extending into the hypothalamus resembling pituitary adenoma with hypocortisolism suggesting hypopituitarism. With dobutamine, atenolol, and noradrenaline, his condition improved. This case raises some issues concerning neurological conditions, mental stress adrenaline, anaphylaxis, and Kounis syndrome. Mental stress commences with impulses from high brain cortical centers that are relayed through the limbic system to hypothalamus resulting in the release of corticotropin-releasing hormone (main coordinator of the mental stress response) and norepinephrine, serotonin, acetylcholine, proopiomelanocortin, adrenocorticotropic hormone, glucagon, growth hormone, and homocysteine that stimulate sympathetic nervous system. These substances can induce heightened cardiovascular activity, endothelial injury, induction of adhesion molecules on the endothelial cells, to which recruited inflammatory cells adhere and translocate to the arterial wall and finally myocardial damage. An acute phase response is engendered, resulting in production of cytokines interleukin-1 (IL-1), IL-6, tumor necrosis factor-alpha, acute phase proteins, macrophage, mast cell, and platelet activation that eventually culminate in the development of Kounis syndrome.[2] Stress-induced cytokine production has been incriminated for multivessel coronary artery spasm at epicardial or microvascular levels that induce takotsubo cardiomyopathy. Inflammatory mediators released during anaphylaxis can induce coronary spasm and takotsubo syndrome and adrenaline given for anaphylaxis might contribute to coronary spasm and transient takotsubo syndrome. Adrenaline and noradrenaline released by the renin-angiotensin-aldosterone system together with histamine stimulate the release of more catecholamines by direct action on the adrenal medullary cells. Administration of catecholamines for hemodynamic support of anaphylactic shock would also increase the plasma catecholamines. Catecholamine increase in patients with angina, renders blood platelets more sensitive and more prone to aggregation and thrombosis. Therefore, measurement of anaphylactic inflammatory mediators including histamine, chymase, leukotrienes, thromboxane, and platelet activating factor or the use of corticosteroids or mast cell stabilizers for prevention and treatment may shed light on etiology and pathophysiology of takotsubo cardiomyopathy. The concurrence of acute coronary syndromes with conditions associated with mast cell activation, involving interrelated and interacting inflammatory cells constitute the Kounis syndrome.[3] Inflammatory cells, such as mast cells, T-cells, and macrophages, activate each other via multidirectional stimuli and release mediators capable to induce coronary events. Experimental findings suggest that cardiac mast cell activation by acute stress may contribute to myocardial ischemia through the release of histamine or proinflammatory mediators.[4] Therefore, takotsubo cardiomyopathy should be always considered in neurological conditions with prolonged addisonian crisis. Furthermore, Adrenaline, takotsubo, Anaphylaxis, and Kounis syndrome (ATAK) seem to constitute a challenging contemporary complex that needs inexorable “attack” to elucidate its etiology, pathophysiology, and treatment.[5] Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest