Cardiac Fibrosis in Human Transplanted Hearts Is Mainly Driven by Cells of Intracardiac Origin

Cardiac magnetic resonance imaging in detection of progressive graft dysfunction in pediatric heart transplantation

BACKGROUND

Chronic graft failure (CGF) in pediatric heart transplant (PHT) is multifactorial and may present with findings of fibrosis and microvessel disease (MVD) on endomyocardial biopsy (EMB). There is no optimal CGF surveillance method. We evaluated associations between cardiac magnetic resonance imaging (CMR) and historical/EMB correlates of CGF to assess CMR's utility as a surveillance method.

METHODS

Retrospective analysis of PHT undergoing comprehensive CMR between September 2015 and January 2022 was performed. EMB within 6 months was graded for fibrosis (scale 0-5) and MVD (number of capillaries with stenotic wall thickening per field of view). Correlation analysis and logistic regression were performed.

RESULTS

Forty-seven PHT with median age at CMR of 15.7 years (11.6, 19.3) and time from transplant of 6.4 years (4.1, 11.0) were studied. Cardiac allograft vasculopathy (CAV) was present in 11/44 (22.0%) and historical rejection in 14/41 (34.2%). CAV was associated with higher global T2 (49.0 vs. 47.0 ms; p = 0.038) and peak T2 (57.0 vs. 53.0 ms; p = 0.013) on CMR. Historical rejection was associated with higher global T2 (49.0 vs. 47.0 ms; p = 0.007) and peak T2 (57.0 vs. 53.0 ms; p = 0.03) as well as global extracellular volume (31.0 vs. 26.3%; p = 0.03). Higher fibrosis score on EMB correlated with smaller indexed left ventricular mass (rho = -0.34; p = 0.019) and greater degree of MVD with lower indexed left ventricular end-diastolic volume (rho = -0.35; p = 0.017).

CONCLUSION

Adverse ventricular remodeling and abnormal myocardial characteristics on CMR are present in PHT with CAV, historical rejection, as well as greater fibrosis and MVD on EMB. CMR has the potential use for screening of CGF.

Cardiac Fibroblast Activation Induced by Oxygen-Glucose Deprivation Depends on the HIF-1α/miR-212-5p/KLF4 Pathway

It is widely accepted that miRNAs play an important role in the pathogenesis of myocardial fibrosis. This study aimed to identify a new pathway of miR-212-5p in the activation of human cardiac fibroblasts (HCFs) induced by oxygen-glucose deprivation (OGD). First, we found that KLF4 protein was markedly decreased in OGD-induced HCFs. Then, bioinformatics analysis and verification experiments were used to identify the existence of an interaction of KLF4 with miR-212-5p. Functional experiments indicated that OGD significantly upregulated the expression of hypoxia inducible factor-1 alpha (HIF-1α) in HCFs, which positively regulated miR-212-5p transcription by binding to its promoter. MiR-212-5p inhibited the expression of Krüppel-like factor 4 (KLF4) protein by binding to the 3' untranslated coding regions (UTRs) of KLF4 mRNA. Inhibition of miR-212-5p effectively inhibited the activation of OGD-induced HCFs by upregulating KLF4 expression and inhibited cardiac fibrosis in vivo and in vitro.

Donor-But Not Recipient-Derived Cells Produce Collagen-1 in Chronically Rejected Cardiac Allografts

Fibrosis is a prominent feature of chronic allograft rejection, caused by an excessive production of matrix proteins, including collagen-1. Several cell types produce collagen-1, including mesenchymal fibroblasts and cells of hematopoietic origin. Here, we sought to determine whether tissue-resident donor-derived cells or allograft-infiltrating recipient-derived cells are responsible for allograft fibrosis, and whether hematopoietic cells contribute to collagen production. A fully MHC-mismatched mouse heterotopic heart transplantation model was used, with transient depletion of CD4⁺ T cells to prevent acute rejection. Collagen-1 was selectively knocked out in recipients or donors. In addition, collagen-1 was specifically deleted in hematopoietic cells. Tissue-resident macrophages were depleted using anti-CSF1R antibody. Allograft fibrosis and inflammation were quantified 20 days post-transplantation. Selective collagen-1 knock-out in recipients or donors showed that tissue-resident cells from donor hearts, but not infiltrating recipient-derived cells, are responsible for production of collagen-1 in allografts. Cell-type-specific knock-out experiments showed that hematopoietic tissue-resident cells in donor hearts substantially contributed to graft fibrosis. Tissue resident macrophages, however, were not responsible for collagen-production, as their deletion worsened allograft fibrosis. Donor-derived cells including those of hematopoietic origin determine allograft fibrosis, making them attractive targets for organ preconditioning to improve long-term transplantation outcomes.

The Latest Developments in Immunomodulation of Mesenchymal Stem Cells in the Treatment of Intrauterine Adhesions, Both Allogeneic and Autologous

Intrauterine adhesion (IUA) is an endometrial fibrosis disease caused by repeated operations of the uterus and is a common cause of female infertility. In recent years, treatment using mesenchymal stem cells (MSCs) has been proposed by many researchers and is now widely used in clinics because of the low immunogenicity of MSCs. It is believed that allogeneic MSCs can be used to treat IUA because MSCs express only low levels of MHC class I molecules and no MHC class II or co-stimulatory molecules. However, many scholars still believe that the use of allogeneic MSCs to treat IUA may lead to immune rejection. Compared with allogeneic MSCs, autologous MSCs are safer, more ethical, and can better adapt to the body. Here, we review recently published articles on the immunomodulation of allogeneic and autologous MSCs in IUA therapy, with the aim of proving that the use of autologous MSCs can reduce the possibility of immune rejection in the treatment of IUAs.

Melatonin Synergizes With Mesenchymal Stromal Cells Attenuates Chronic Allograft Vasculopathy

Background

Chronic rejection characterized by chronic allograft vasculopathy (CAV) remains a major obstacle to long-term graft survival. Due to multiple complicated mechanisms involved, a novel therapy for CAV remains exploration. Although mesenchymal stromal cells (MSCs) have been ubiquitously applied to various refractory immune-related diseases, rare research makes a thorough inquiry in CAV. Meanwhile, melatonin (MT), a wide spectrum of immunomodulator, plays a non-negligible role in transplantation immunity. Here, we have investigated the synergistic effects of MT in combination with MSCs in attenuation of CAV.

Methods

C57BL/6 (B6) mouse recipients receiving BALB/c mouse donor aorta transplantation have been treated with MT and/or adipose-derived MSCs. Graft pathological changes, intragraft immunocyte infiltration, splenic immune cell populations, circulating donor-specific antibodies levels, cytokine profiles were detected on post-operative day 40. The proliferation capacity of CD4+ and CD8+ T cells, populations of Th1, Th17, and Tregs were also assessed in vitro.

Results

Grafts in untreated recipients developed a typical pathological feature of CAV characterized by intimal thickening 40 days after transplantation. Compared to untreated and monotherapy groups, MT in combination with MSCs effectively ameliorated pathological changes of aorta grafts indicated by markedly decreased levels of intimal hyperplasia and the infiltration of CD4+ cells, CD8+ cells, and macrophages, but elevated infiltration of Foxp3+ cells. MT either alone or in combination with MSCs effectively inhibited the proliferation of T cells, decreased populations of Th1 and Th17 cells, but increased the proportion of Tregs in vitro. MT synergized with MSCs displayed much fewer splenic populations of CD4+ and CD8+ T cells, Th1 cells, Th17 cells, CD4+ central memory T cells (Tcm), as well as effector memory T cells (Tem) in aorta transplant recipients. In addition, the percentage of splenic Tregs was substantially increased in the combination therapy group. Furthermore, MT combined with MSCs markedly reduced serum levels of circulating allospecific IgG and IgM, as well as decreased the levels of pro-inflammatory IFN-γ, TNF-α, IL-1β, IL-6, IL-17A, and MCP-1, but increased the level of IL-10 in the recipients.

Conclusions

These data suggest that MT has synergy with MSCs to markedly attenuate CAV and provide a novel therapeutic strategy to improve the long-term allograft acceptance in transplant recipients.

Cadherin-11 and cardiac fibrosis: A common target for a common pathology

Cardiac fibrosis represents an enormous health concern as it is prevalent in nearly every form of cardiovascular disease, the leading cause of death worldwide. Fibrosis is characterized by the activation of fibroblasts into myofibroblasts, a contractile cell type that secretes significant amounts of extracellular matrix components; however, the onset of this condition is also due to persistent inflammation and the cellular responses to a changing mechanical environment. In this review, we provide an overview of the pro-fibrotic, pro-inflammatory, and biomechanical mechanisms that lead to cardiac fibrosis in cardiovascular diseases. We then discuss cadherin-11, an intercellular adhesion protein present on both myofibroblasts and inflammatory cells, as a potential link for all three of the fibrotic mechanisms. Since experimentally blocking cadherin-11 dimerization prevents fibrotic diseases including cardiac fibrosis, understanding how this protein can be targeted for therapeutic use could lead to better treatments for patients with heart disease.

CTRP15 derived from cardiac myocytes attenuates TGFβ1-induced fibrotic response in cardiac fibroblasts

PURPOSE

Cardiac fibrosis is characterized by net accumulation of extracellular matrix (ECM) components in the  myocardium and facilitates the development of heart failure. C1q/tumor necrosis factor-related protein 15 (CTRP15) is a novel member of the CTRP family, and its gene expression is detected in adult mouse hearts. The present study was performed to determine the effect of CTRP15 on pressure overload-induced fibrotic remodeling.

METHODS

Mice were subjected to transverse aortic constriction (TAC) surgery, and adeno-associated virus serotype 9 (AAV9)-carrying mouse CTRP15 gene was injected into mice to achieve CTRP15 overexpression in the myocardium. Adenovirus carrying the gene encoding CTRP15 or small interfering RNA (siRNA) of interest was infected into cultured neonatal mouse ventricular cardiomyocytes (NMVCs) or cardiac fibroblasts (CFs). Gene expression was measured by quantitative real-time PCR, and protein expression and distribution were determined by Western blotting, immunocytochemistry, and immunofluorescence staining.

RESULTS

CTRP15 was predominantly produced by cardiac myocytes. CTRP15 expression in the left ventricles was downregulated in mice that underwent TAC. AAV9-mediated CTRP15 overexpression alleviated ventricular remodeling and dysfunction in the pressure-overloaded mice. Treatment of CFs with recombinant CTRP15 or the conditioned medium containing CTRP15 inhibited transforming growth factor (TGF)-β1-induced Smad3 activation and myofibroblast differentiation. CTRP15 increased phosphorylation of insulin receptor (IR), insulin receptor substrate-1 (IRS-1), and Akt. Blockade of IR/IRS-1/Akt pathway reversed the inhibitory effect of CTRP15 on TGF-β1-induced Smad3 activation.

CONCLUSION

CTRP15 exerts an anti-fibrotic effect on pressure overload-induced cardiac remodeling. The activation of IR/IRS-1/Akt pathway contributes to the anti-fibrotic effect of CTRP15 through targeting Smad3.

Autophagy modulates mesenchymal-to-endothelial transition via p53

Mesenchymal-to-endothelial transition (MEndT) is one of the mechanisms that influences cardiac fibrosis, which is a key process in cardiac remodeling. It has been reported that autophagy inhibits endothelial cell transition. However, whether autophagy could modulate MEndT in cardiac fibrosis has not yet been investigated. Here, we discussed the association between autophagy and MEndT and its possible mechanism. In this study, we induced endothelial-to-mesenchymal transition using transforming growth factor-β to generate mesenchymal cells and fibroblasts in wild-type human umbilical vein endothelial cells and cells with p53 knockout or overexpression. Then, autophagy was induced by Earle's balanced salt solution (EBSS) and was inhibited by bafilomycin A1 or lentivirus-ATG5-shRNA. The expression levels of MEndT and the autophagy markers CD31, VE-Cadherin, Vimentin, α-SMA, LC3, p62 and p53 were examined. We found that activation of autophagy could promote MEndT and increase cytoplasmic and total expression of p53, that but nuclear p53 expression was decreased, and that inhibition of autophagy activation could reverse the effect of EBSS. Moreover, after knockout of nuclear p53, autophagy promoted MEndT, while autophagy inhibited MEndT in p53 overexpressing cells. Our results demonstrate that autophagy modulate MEndT by nuclear p53 provide a new strategy for the treatment of fibrosis diseases.

Cross-presentation of dead-cell-associated antigens by DNGR-1+ dendritic cells contributes to chronic allograft rejection in mice

The purpose of this study was to elucidate whether DC NK lectin group receptor-1 (DNGR-1)-dependent cross-presentation of dead-cell-associated antigens occurs after transplantation and contributes to CD8⁺ T cell responses, chronic allograft rejection (CAR), and fibrosis. BALB/c or C57BL/6 hearts were heterotopically transplanted into WT, Clec9a^-/- , or Batf3^-/- recipient C57BL/6 mice. Allografts were analyzed for cell infiltration, CD8⁺ T cell activation, fibrogenesis, and CAR using immunohistochemistry, Western blot, qRT² -PCR, and flow cytometry. Allografts displayed infiltration by recipient DNGR-1⁺ DCs, signs of CAR, and fibrosis. Allografts in Clec9a^-/- recipients showed reduced CAR (p < 0.0001), fibrosis (P = 0.0137), CD8⁺ cell infiltration (P < 0.0001), and effector cytokine levels compared to WT recipients. Batf3-deficiency greatly reduced DNGR-1⁺ DC-infiltration, CAR (P < 0.0001), and fibrosis (P = 0.0382). CD8 cells infiltrating allografts of cytochrome C treated recipients, showed reduced production of CD8 effector cytokines (P < 0.05). Further, alloreactive CD8⁺ T cell response in indirect pathway IFN-γ ELISPOT was reduced in Clec9a^-/- recipient mice (P = 0.0283). Blockade of DNGR-1 by antibody, similar to genetic elimination of the receptor, reduced CAR (P = 0.0003), fibrosis (P = 0.0273), infiltration of CD8⁺ cells (p = 0.0006), and effector cytokine levels. DNGR-1-dependent alloantigen cross-presentation by DNGR-1⁺ DCs induces alloreactive CD8⁺ cells that induce CAR and fibrosis. Antibody against DNGR-1 can block this process and prevent CAR and fibrosis.

Sex-specific regulation of collagen I and III expression by 17β-Estradiol in cardiac fibroblasts: role of estrogen receptors

Aims

Sex differences in cardiac fibrosis point to the regulatory role of 17β-Estradiol (E2) in cardiac fibroblasts (CF). We, therefore, asked whether male and female CF in rodent and human models are differentially susceptible to E2, and whether this is related to sex-specific activation of estrogen receptor alpha (ERα) and beta (ERβ).

Methods and results

In female rat CF (rCF), 24 h E2-treatment (10-8  M) led to a significant down-regulation of collagen I and III expression, whereas both collagens were up-regulated in male rCF. E2-induced sex-specific collagen regulation was also detected in human CF, indicating that this regulation is conserved across species. Using specific ERα- and ERβ-agonists (10-7 M) for 24 h, we identified ERα as repressive and ERβ as inducing factor in female and male rCF, respectively. In addition, E2-induced ERα phosphorylation at Ser118 only in female rCF, whereas Ser105 phosphorylation of ERβ was exclusively found in male rCF. Further, in female rCF we found both ER bound to the collagen I and III promoters using chromatin immunoprecipitation assays. In contrast, in male rCF only ERβ bound to both promoters. In engineered connective tissues (ECT) from rCF, collagen I and III mRNA were down-regulated in female ECT and up-regulated in male ECT by E2. This was accompanied by an impaired condensation of female ECT, whereas male ECT showed an increased condensation and stiffness upon E2-treatment, analysed by rheological measurements. Finally, we confirmed the E2-effect on both collagens in an in vivo mouse model with ovariectomy for E2 depletion, E2 substitution, and pressure overload by transverse aortic constriction.

Conclusion

The mechanism underlying the sex-specific regulation of collagen I and III in the heart appears to involve E2-mediated differential ERα and ERβ signaling in CFs.

Fibroblasts and Their Pathological Functions in the Fibrosis of Aortic Valve Sclerosis and Atherosclerosis

Cardiovascular diseases, such as atherosclerosis and aortic valve sclerosis (AVS) are driven by inflammation induced by a variety of stimuli, including low-density lipoproteins (LDL), reactive oxygen species (ROS), infections, mechanical stress, and chemical insults. Fibrosis is the process of compensating for tissue injury caused by chronic inflammation. Fibrosis is initially beneficial and maintains extracellular homeostasis. However, in the case of AVS and atherosclerosis, persistently active resident fibroblasts, myofibroblasts, and smooth muscle cells (SMCs) perpetually remodel the extracellular matrix under the control of autocrine and paracrine signaling from the immune cells. Myofibroblasts also produce pro-fibrotic factors, such as transforming growth factor-β1 (TGF-β1), angiotensin II (Ang II), and interleukin-1 (IL-1), which allow them to assist in the activation and migration of resident immune cells. Post wound repair, these cells undergo apoptosis or become senescent; however, in the presence of unresolved inflammation and persistence signaling for myofibroblast activation, the tissue homeostasis is disturbed, leading to excessive extracellular matrix (ECM) secretion, disorganized ECM, and thickening of the affected tissue. Accumulating evidence suggests that diverse mechanisms drive fibrosis in cardiovascular pathologies, and it is crucial to understand the impact and contribution of the various mechanisms for the control of fibrosis before the onset of a severe pathological consequence.

Multiparametric Cardiac Magnetic Resonance Imaging Can Detect Acute Cardiac Allograft Rejection After Heart Transplantation

OBJECTIVES

The purpose of this study was to evaluate the sensitivity of multiparametric cardiac magnetic resonance imaging (CMR) for the detection of acute cardiac allograft rejection (ACAR).

BACKGROUND

ACAR is currently diagnosed by endomyocardial biopsy, but CMR may be a noninvasive alternative because of its capacity for regional myocardial structure and function characterization.

METHODS

Fifty-eight transplant recipients (mean age 47.0 ± 14.7 years) and 14 control subjects (mean age 47.7 ± 16.7 years) were prospectively recruited from August 2014 to May 2017 and underwent 97 CMR studies (83 transplant recipients, 14 control subjects) for assessment of global left ventricular function and myocardial T2, T1, and extracellular volume fraction (ECV). CMR studies were divided into 4 groups on the basis of biopsy grade: control subjects (n = 14), patients with no ACAR (no history of ACAR; n = 36), patients with past ACAR (history of ACAR; n = 24), and ACAR+ patients (active grade ≥1R ACAR; n = 23).

RESULTS

Myocardial T2 was significantly higher in patients with past ACAR compared with those with no ACAR (51.0 ± 3.8 ms vs. 49.2 ± 4.0 ms; p = 0.02) and in patients with no ACAR compared with control subjects (49.2 ± 4.0 ms vs. 45.2 ± 2.3 ms; p < 0.01). ACAR+ patients demonstrated increased T2 compared with the no ACAR group (52.4 ± 4.7 ms vs. 49.2 ± 4.0 ms, p < 0.01) but not compared with the past ACAR group. In contrast, ECV was significantly elevated in ACAR+ patients compared with transplant recipients without ACAR regardless of history of ACAR (no ACAR: 31.5 ± 3.9% vs. 26.8 ± 3.3% [p < 0.01]; past ACAR: 31.5 ± 3.9% vs. 26.8 ± 4.0% [p < 0.01]). Receiver operating characteristic curve analysis revealed that a combined model of age at CMR, global T2, and global ECV was predictive of ACAR (area under the curve = 0.84).

CONCLUSIONS

The combination of CMR-derived myocardial T2 and ECV has potential as a noninvasive tissue biomarker for ACAR. Larger studies during acute ACAR are needed for continued development of multiparametric CMR for transplant recipient surveillance.

Assessment of sympathetic reinnervation after cardiac transplantation using hybrid cardiac PET/MRI: A pilot study

Background

Sympathetic reinnervation after heart transplantation (HTX) is a known phenomenon, which has an impact on patient heart rate variability and exercise capacity. The impact of reinnervation on myocardial structure has not been evaluated yet.

Propose

To evaluate the feasibility of simultaneous imaging of cardiac reinnervation and cardiac structure using a hybrid PET/MRI system.

Study type

Prospective / pilot study.

Subjects

Ten patients, 4–21 years after cardiac transplantation.

Field Strength/Sequence

3 T hybrid PET/MRI system. Cine SSFP, T₁ mapping (modified Look–Locker inversion recovery sequence) pre/postcontrast as well as dynamic [¹¹C]meta‐hydroxyephedrine ([¹¹C]mHED) PET.

Assessment

All MRI and PET parameters were evaluated by experienced readers using dedicated postprocessing software packages for cardiac MRI and PET. For all parameters a 16‐segment model for the left ventricle was applied.

Statistical Tests

Mann–Whitney U‐test; Spearman correlations.

Results

Thirty‐six of 160 myocardial segments showed evidence of reinnervation by PET. On a segment‐based analysis, mean native T₁ relaxation times were nonsignificantly altered in segments with evidence of reinnervation (1305 ± 151 msec vs. 1270 ± 112 msec; P = 0.1), whereas mean extracellular volume (ECV) was significantly higher in segments with evidence of reinnervation (35.8 ± 11% vs. 30.9 ± 7%; P = 0.019). There were no significant differences in wall motion (WM) and wall thickening (WT) between segments with or without reinnervation (mean WM: 7.6 ± 4 mm vs. group B: 9.3 ± 7 mm [P = 0.13]; WT: 79 ± 63% vs. 94 ± 74% [P = 0.27]) under resting conditions.

Data Conclusion

The assessment of cardiac reinnervation using a hybrid PET/MRI system is feasible. Segments with evidence of reinnervation by PET showed nonsignificantly higher T₁ relaxation times and a significantly higher ECV, suggesting a higher percentage of diffuse fibrosis in these segments, without impairment of rest WM and WT.

Level of Evidence: 3

Technical Efficacy: Stage 3

J. Magn. Reson. Imaging 2019;50:1326–1335.

ACE2 and ACE in acute and chronic rejection after human heart transplantation

OBJECTIVES

The authors sought to evaluate cardiac activity of angiotensin-converting enzyme (ACE) and ACE2 after heart transplantation (HT) and its relation with acute rejection (AR) and chronic allograft vasculopathy (CAV).

BACKGROUND

The renin-angiotensin system is altered in heart failure and HT. However, ACE and ACE2 activities in post-HT acute and chronic rejection have not been previously studied.

METHODS

HT patients (n = 45) were included when appropriate serial endomyocardial biopsies (EMB) and coronary angiography were available for analysis. In 21 patients, three post-HT time points were selected for CAV study in EMB tissue: basal (0-3 wks), second (2-3 months) and third (4-5 months). At 10 years post-HT, CAV was evaluated by coronary angiography (CA) and patients were grouped by degree of CAV: 0-1, non-CAV (n = 15) and 2-3, CAV (n = 6). For the AR study, 28 HT patients with evidence of one EMB rejection at grade 3 and two EMB grade 1A and/or 1B rejections were selected.

RESULTS

Post-HT, ACE2 activity was increased in the CAV group, compared to non-CAV. Patients with AR showed increased ACE, but not ACE2, activity.

CONCLUSIONS

Our results suggest that early post-HT cardiac ACE2 activity may have an important role in CAV development. In contrast, ACE activity was increased in AR. The renin-angiotensin system seems to be altered after HT and strategies to balance the system may be useful.

Interleukin-10 Inhibits Bone Marrow Fibroblast Progenitor Cell-Mediated Cardiac Fibrosis in Pressure-Overloaded Myocardium

BACKGROUND

Activated fibroblasts (myofibroblasts) play a critical role in cardiac fibrosis; however, their origin in the diseased heart remains unclear, warranting further investigation. Recent studies suggest the contribution of bone marrow fibroblast progenitor cells (BM-FPCs) in pressure overload-induced cardiac fibrosis. We have previously shown that interleukin-10 (IL10) suppresses pressure overload-induced cardiac fibrosis; however, the role of IL10 in inhibition of BM-FPC-mediated cardiac fibrosis is not known. We hypothesized that IL10 inhibits pressure overload-induced homing of BM-FPCs to the heart and their transdifferentiation to myofibroblasts and thus attenuates cardiac fibrosis.

METHODS

Pressure overload was induced in wild-type (WT) and IL10 knockout (IL10KO) mice by transverse aortic constriction. To determine the bone marrow origin, chimeric mice were created with enhanced green fluorescent protein WT mice marrow to the IL10KO mice. For mechanistic studies, FPCs were isolated from mouse bone marrow.

RESULTS

Pressure overload enhanced BM-FPC mobilization and homing in IL10KO mice compared with WT mice. Furthermore, WT bone marrow (from enhanced green fluorescent protein mice) transplantation in bone marrow-depleted IL10KO mice (IL10KO chimeric mice) reduced transverse aortic constriction-induced BM-FPC mobilization compared with IL10KO mice. Green fluorescent protein costaining with α-smooth muscle actin or collagen 1α in left ventricular tissue sections of IL10KO chimeric mice suggests that myofibroblasts were derived from bone marrow after transverse aortic constriction. Finally, WT bone marrow transplantation in IL10KO mice inhibited transverse aortic constriction-induced cardiac fibrosis and improved heart function. At the molecular level, IL10 treatment significantly inhibited transforming growth factor-β-induced transdifferentiation and fibrotic signaling in WT BM-FPCs in vitro. Furthermore, fibrosis-associated microRNA (miRNA) expression was highly upregulated in IL10KO-FPCs compared with WT-FPCs. Polymerase chain reaction-based selective miRNA analysis revealed that transforming growth factor-β-induced enhanced expression of fibrosis-associated miRNAs (miRNA-21, -145, and -208) was significantly inhibited by IL10. Restoration of miRNA-21 levels suppressed the IL10 effects on transforming growth factor-β-induced fibrotic signaling in BM-FPCs.

CONCLUSIONS

Our findings suggest that IL10 inhibits BM-FPC homing and transdifferentiation to myofibroblasts in pressure-overloaded myocardium. Mechanistically, we show for the first time that IL10 suppresses Smad-miRNA-21-mediated activation of BM-FPCs and thus modulates cardiac fibrosis.

A primer on current progress in cardiac fibrosis

Cardiac fibrosis is a significant global health problem that is closely associated with multiple forms of cardiovascular disease, including myocardial infarction, dilated cardiomyopathy, and diabetes. Fibrosis increases myocardial wall stiffness due to excessive extracellular matrix deposition, causing impaired systolic and diastolic function, and facilitating arrhythmogenesis. As a result, patient morbidity and mortality are often dramatically elevated compared with those with cardiovascular disease but without overt fibrosis, demonstrating that fibrosis itself is both a pathologic response to existing disease and a significant risk factor for exacerbation of the underlying condition. The lack of any specific treatment for cardiac fibrosis in patients suffering from cardiovascular disease is a critical gap in our ability to care for these individuals. Here we provide an overview of the development of cardiac fibrosis, and discuss new research directions that have recently emerged and that may lead to the creation of novel treatments for patients with cardiovascular diseases. Such treatments would, ideally, complement existing therapy by specifically focusing on amelioration of fibrosis.

Histological validation of cardiovascular magnetic resonance T1 mapping markers of myocardial fibrosis in paediatric heart transplant recipients

BACKGROUND

Adverse fibrotic remodeling is detrimental to myocardial health and a reliable method for monitoring the development of fibrotic remodeling may be desirable during the follow-up of patients after heart transplantation (HTx). Quantification of diffuse myocardial fibrosis with cardiovascular magnetic resonance (CMR) has been increasingly applied and validated histologically in adult patients with heart disease. However, comparisons of CMR findings with histological fibrosis burden in children are lacking. This study aimed to compare native T1 times and extracellular volume fraction (ECV) derived from CMR with the degree of collagen on endomyocardial biopsy (EmBx), and to investigate the association between myocardial fibrosis and clinical as well as functional markers in children after HTx.

METHODS

EmBx and CMR were performed on the same day. All specimens were stained with picrosirius red. The collagen volume fraction (CVF) was calculated as ratio of stained collagen area to total myocardial area on EmBx. Native T1 values and ECV were measured by CMR on a mid-ventricular short axis slice, using a modified look-locker inversion recovery approach.

RESULTS

Twenty patients (9.9 ± 6.2 years of age; 9 girls) after HTx were prospectively enrolled, at a median of 1.3 years (0.02-12.6 years) post HTx, and compared to 24 controls (13.9 ± 2.6 years of age; 12 girls). The mean histological CVF was 10.0 ± 3.4%. Septal native T1 times and ECV were higher in HTx patients compared to controls (1008 ± 32 ms vs 979 ± 24 ms, p < 0.005 and 0.30 ± 0.03 vs 0.22 ± 0.03, p < 0.0001, respectively). CVF showed a moderate correlation with native T1 (r = 0.53, p < 0.05) as well as ECV (r = 0.46, p < 0.05). Native T1 time, but not ECV and CVF, correlated with ischemia time (r = 0.46, p < 0.05).

CONCLUSIONS

CMR-derived fibrosis markers correlate with histological degree of fibrosis on EmBx in children after HTx. Further, native T1 times are associated with longer ischemia times.

Oxymatrine inhibits aldosterone-induced rat cardiac fibroblast proliferation and differentiation by attenuating smad-2,-3 and-4 expression: an in vitro study

BACKGROUND

We previously demonstrated oxymatrine, an alkaloid from the Chinese medicine radix Sophorae flavescentis, ameliorates hemodynamic disturbances and cardiac fibrosis; however, the underlying mechanisms are unclear. Here, we investigated the effect and mechanism of action of oxymatrine on aldosterone-induced cardiac fibroblast to myofibroblast differentiation in vitro.

METHODS

Cardiac fibroblasts were isolated purified from neonatal Sprague Dawley rats. The optimal concentration of aldosterone to stimulate cardiac fibroblast proliferation was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cardiac fibroblasts were pretreated with 7.57 × 10(-4) mol/L or 3.78 × 10(-4) mol/L oxymatrine or without oxymatrine for 2 h, and then coincubated with 1 × 10(-8) mol/L aldosterone for 48 h. The MTT assay and Masson staining were used to detect the cardiac fibroblast proliferation and myofibroblast differentiation. The secretion of type I and III collagen was measured by commercial ELISA kits, and the hydroxyproline content was determined by the colorimetric assay. Western blotting assayed the Smad-2, Smad-3, and Smad-4 protein expression in cardiac fibroblasts.

RESULTS

The present results confirmed that aldosterone induced cardiac fibroblast to myofibroblast proliferation and differentiation. The MTT assay and Masson staining indicated oxymatrine significantly inhibited aldosterone-induced cardiac fibroblast proliferation and myofibroblast differentiation. Oxymatrine significantly inhibited aldosterone-induced secretion of type I and III collagen, as indicated by commercial ELISA kits, and aldosterone-induced increase in hydroxyproline content, as indicated by a colorimetric assay. Western blotting revealed oxymatrine attenuated aldosterone-induced Smad-2, Smad-3, and Smad-4 expression in cardiac fibroblasts.

CONCLUSION

Oxymatrine can inhibit cardiac fibroblast proliferation and differentiation into myofibroblasts via a mechanism linked to attenuation of the Smad signaling pathway.

Diffuse Myocardial Fibrosis in Children After Heart Transplantations: A Magnetic Resonance T1 Mapping Study

BACKGROUND

It is unclear whether the myocardium undergoes accelerated fibrotic remodeling in children after heart transplantation (HTx).

METHODS

In this prospective study, cardiac magnetic resonance (CMR) studies in 17 patients 1.3 years (median, range 0.03-12.6 years) after HTx (mean age, 9.8 ± 6.2 years; 8 girls) were compared to CMR studies in 9 healthy controls (mean age, 12.4 ± 2.4 years; 4 girls). T1 measurements were performed at a midventricular short axis slice before (ie, native T1 times) and after the application of 0.2 mmol/kg gadopentetate dimeglumine in the interventricular septum, left ventricular (LV) free wall and encompassing the entire LV myocardium. The tissue-blood partition coefficient (TBPC), reflecting the degree of diffuse myocardial fibrosis, was calculated as a function of the ratio of T1 change of myocardium compared to blood. Native T1 times and TBPC were correlated with echocardiographic parameters of diastolic function.

RESULTS

Native T1 times were significantly higher in HTx patients compared to controls in all regions assessed (LV free wall 973 ± 42 vs 923 ± 12 ms; P < 0.005; interventricular septum 1003 ± 31 vs 974 ± 21 ms, P < 0.05; entire LV myocardium 987 ± 33 vs 951 ± 16 ms; P < 0.005) and correlated with LV E/e' as an echocardiographic marker of diastolic dysfunction (r = 0.54, P < 0.05). The TBPC was elevated in the LV free wall (0.45 ± 0.06 vs 0.40 ± 0.03, P < 0.005) and the entire LV myocardium (0.47 ± 0.06 vs 0.43 ± 0.03, P < 0.05).

CONCLUSIONS

Evidence of diffuse myocardial fibrosis and is already present in children after HTx. It appears to be associated with diastolic dysfunction.

miR-21 promotes fibrosis in an acute cardiac allograft transplantation model

AIMS

Cardiac transplantation is the only curative therapy for end-stage heart failure. Fibrosis is one of the major causes for impaired function of cardiac allografts. MicroRNAs, a class of small non-coding RNAs, play a critical role in the development of cardiovascular disease, but the role of microRNAs in cardiac allograft failure is not well understood.

METHODS AND RESULTS

To uncover a role of microRNAs during cardiac graft fibrosis, we generated global microRNA profiles in allogeneic (BALB/c in C57BL/6N) and isogeneic (C57BL/6N in C57BL/6N) murine hearts after transplantation. miR-21 together with cardiac fibrosis was increased in cardiac allografts compared with isografts. Likewise, patients with cardiac rejection after heart transplantation showed increased cardiac miR-21 levels. miR-21 was induced upon treatment with IL-6 in a monocyte cell line. Overexpression of miR-21 in this monocyte cell line activated a fibrotic gene programme and promoted monocyte-to-fibrocyte transition together with activation of chemokine (C-C) motif ligand 2 (monocyte chemoattractant protein 1) via the phosphatase and tensin homologue/activator protein 1 regulatory axis. In vivo, both genetic and pharmacological inhibition of miR-21 successfully reduced fibrosis and fibrocyte accumulation in cardiac allografts.

CONCLUSION

Thus, inhibition of miR-21 is a novel strategy to target fibrosis development in cardiac allografts.

Activation of common signaling pathways during remodeling of the heart and the bladder

The heart and the urinary bladder are hollow muscular organs, which can be afflicted by pressure overload injury due to pathological conditions such as hypertension and bladder outlet obstruction. This increased outflow resistance induces hypertrophy, marked by dramatic changes in the organs' phenotype and function. The end result in both the heart and the bladder can be acute organ failure due to advanced fibrosis and the subsequent loss of contractility. There is emerging evidence that microRNAs (miRNAs) play an important role in the pathogenesis of heart failure and bladder dysfunction. MiRNAs are endogenous non-coding single-stranded RNAs, which regulate gene expression and control adaptive and maladaptive organ remodeling processes. This Review summarizes the current knowledge of molecular alterations in the heart and the bladder and highlights common signaling pathways and regulatory events. The miRNA expression analysis and experimental target validation done in the heart provide a valuable source of information for investigators working on the bladder and other organs undergoing the process of fibrotic remodeling. Aberrantly expressed miRNA are amendable to pharmacological manipulation, offering an opportunity for development of new therapies for cardiac and bladder hypertrophy and failure.

Heart Regeneration with Embryonic Cardiac Progenitor Cells and Cardiac Tissue Engineering

Myocardial infarction (MI) is the leading cause of death worldwide. Recent advances in stem cell research hold great potential for heart tissue regeneration through stem cell-based therapy. While multiple cell types have been transplanted into MI heart in preclinical studies or clinical trials, reduction of scar tissue and restoration of cardiac function have been modest. Several challenges hamper the development and application of stem cell-based therapy for heart regeneration. Application of cardiac progenitor cells (CPCs) and cardiac tissue engineering for cell therapy has shown great promise to repair damaged heart tissue. This review presents an overview of the current applications of embryonic CPCs and the development of cardiac tissue engineering in regeneration of functional cardiac tissue and reduction of side effects for heart regeneration. We aim to highlight the benefits of the cell therapy by application of CPCs and cardiac tissue engineering during heart regeneration.

Cardiac allograft vasculopathy: a donor or recipient induced pathology?

Cardiac allograft vasculopathy (CAV) is one of the main causes of late-stage heart failure after heart transplantation. CAV is characterized by concentric luminal narrowing of the coronary arteries, but the exact pathogenesis of CAV is still not unraveled. Many researchers show evidence of an allogeneic immune response of the recipient, whereas others show contrasting results in which donor-derived cells induce an immune response against the graft. In addition, fibrosis of the neo-intima can be induced by recipient-derived circulating cells or donor-derived cells. In this review, both donor and recipient sides of the story are described to obtain better insight in the pathogenesis of CAV. Dual outcomes were found regarding the contribution of donor and recipient cells in the initiation of the immune response and the development of fibrosis during CAV. Future research could focus more on the potential synergistic interaction of donor and recipient cells leading to CAV.

Targeting cardiac fibroblasts to treat fibrosis of the heart: focus on HDACs

Cardiac fibrosis is implicated in numerous physiologic and pathologic conditions, including scar formation, heart failure and cardiac arrhythmias. However the specific cells and signaling pathways mediating this process are poorly understood. Lysine acetylation of nucleosomal histone tails is an important mechanism for the regulation of gene expression. Additionally, proteomic studies have revealed that thousands of proteins in all cellular compartments are subject to reversible lysine acetylation, and thus it is becoming clear that this post-translational modification will rival phosphorylation in terms of biological import. Acetyl groups are conjugated to lysine by histone acetyltransferases (HATs) and removed from lysine by histone deacetylases (HDACs). Recent studies have shown that pharmacologic agents that alter lysine acetylation by targeting HDACs have the remarkable ability to block pathological fibrosis. Here, we review the current understanding of cardiac fibroblasts and the fibrogenic process with respect to the roles of lysine acetylation in the control of disease-related cardiac fibrosis. Potential for small molecule HDAC inhibitors as anti-fibrotic therapeutics that target cardiac fibroblasts is highlighted. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium."

Therapeutic targets in heart failure: refocusing on the myocardial interstitium

New therapeutic targets, agents, and strategies are needed to prevent and treat heart failure (HF) after a decade of failed research efforts to improve long-term patient outcomes, especially in patients after hospitalization for HF. Conceptually, an accurate assessment of left ventricular structure is an essential step in the development of novel therapies because heterogeneous pathophysiologies underlie chronic HF and hospitalization for HF. Improved left ventricular characterization permits the identification and targeting of the intrinsic fundamental disease-modifying pathways that culminate in HF. Interstitial heart disease is one such pathway, characterized by extracellular matrix (ECM) expansion that is associated with mechanical, electrical, and vasomotor dysfunction and adverse outcomes. Previous landmark trials that appear to treat interstitial heart disease were effective in improving outcomes. Advances in cardiovascular magnetic resonance now enable clinicians and researchers to assess the interstitium and quantify ECM expansion using extracellular volume fraction measures and other derangements in cardiovascular structure. These capabilities may provide a mechanistic platform to advance understanding of the role of the ECM, foster the development of novel therapeutics, and target specific disease-modifying pathways intrinsic to the ventricle. Refocusing on the interstitium may potentially improve care through the identification and targeted treatment of key patient subgroups.

The pathogenesis of cardiac fibrosis

Cardiac fibrosis is characterized by net accumulation of extracellular matrix proteins in the cardiac interstitium, and contributes to both systolic and diastolic dysfunction in many cardiac pathophysiologic conditions. This review discusses the cellular effectors and molecular pathways implicated in the pathogenesis of cardiac fibrosis. Although activated myofibroblasts are the main effector cells in the fibrotic heart, monocytes/macrophages, lymphocytes, mast cells, vascular cells and cardiomyocytes may also contribute to the fibrotic response by secreting key fibrogenic mediators. Inflammatory cytokines and chemokines, reactive oxygen species, mast cell-derived proteases, endothelin-1, the renin/angiotensin/aldosterone system, matricellular proteins, and growth factors (such as TGF-β and PDGF) are some of the best-studied mediators implicated in cardiac fibrosis. Both experimental and clinical evidence suggests that cardiac fibrotic alterations may be reversible. Understanding the mechanisms responsible for initiation, progression, and resolution of cardiac fibrosis is crucial to design anti-fibrotic treatment strategies for patients with heart disease.

IL-13 signaling via IL-13Rα2 triggers TGF-β1-dependent allograft fibrosis

Background

Allograft fibrosis still remains a critical problem in transplantation, including heart transplantation. The IL-13/TGF-β₁ interaction has previously been identified as a key pathway orchestrating fibrosis in different inflammatory immune disorders. Here we investigate if this pathway is also responsible for allograft fibrosis and if interference with the IL-13/TGF-β₁ interaction prevents allograft fibrosis.

Methods

FVB or control DBA/1 donor hearts were transplanted heterotopically into DBA/1 recipient mice and hearts were explanted at day 60 and 100 post-transplantation. Cardiac tissue was examined by Masson’s trichrome staining and immunohistochemistry for CD4, CD8, CD11b, IL-13, Fas ligand, matrix metalloproteinase (MMP)-1, MMP-13, β2-microglobulin, and Gremlin-1. Graft-infiltrating cells were isolated and analyzed by flow cytometry. IL-13 and TGF-β₁ levels were determined by enzyme-linked immunosorbent assay (ELISA) and the amount of collagen was quantified using a Sircol assay; IL-13Rα₂ expression was detected by Western blotting. In some experiments IL-13/ TGF-β₁ signaling was blocked with specific IL-13Rα₂ siRNA. Additionally, a PCR array of RNA isolated from the allografts was performed to analyze expression of multiple genes involved in fibrosis.

Results

Both groups survived long-term (>100 days). The allogeneic grafts were infiltrated by significantly increased numbers of CD4⁺ (P <0.0001), CD8⁺ (P <0.0001), and CD11b⁺ cells (P = 0.0065) by day 100. Furthermore, elevated IL-13 levels (P = 0.0003) and numbers of infiltrating IL-13⁺ cells (P = 0.0037), together with an expression of IL-13Rα₂, were detected only within allografts. The expression of IL-13 and IL-13Rα₂ resulted in significantly increased TGF-β₁ levels (P <0.0001), higher numbers of CD11b^highGr1^intermediateTGF-β₁⁺ cells, and elevated cardiac collagen deposition (P = 0.0094). The allograft fibrosis found in these experiments was accompanied by upregulation of multiple profibrotic genes, which was confirmed by immunohistochemical stainings of allograft tissue. Blockage of the IL-13/TGF-β₁ interaction by IL-13Rα₂ siRNA led to lower numbers of CD11b^highGr1^intermediateTGF-β₁⁺, CD4⁺, CD8⁺, and CD11b⁺ cells, and prevented collagen deposition (P = 0.0018) within these allografts.

Conclusions

IL-13 signaling via IL-13Rα₂ induces TGF-β₁ and causes allograft fibrosis in a murine model of chronic transplant rejection. Blockage of this IL-13/TGF-β₁ interaction by IL-13Rα₂ siRNA prevents cardiac allograft fibrosis. Thus, IL-13Rα₂ may be exploitable as a future target to reduce allograft fibrosis in organ transplantation.

Role of stem/progenitor cells in reparative disorders

Adult stem cells are activated to proliferate and differentiate during normal tissue homeostasis as well as in disease states and injury. This activation is a vital component in the restoration of function to damaged tissue via either complete or partial regeneration. When regeneration does not fully occur, reparative processes involving an overproduction of stromal components ensure the continuity of tissue at the expense of its normal structure and function, resulting in a “reparative disorder”. Adult stem cells from multiple organs have been identified as being involved in this process and their role in tissue repair is being investigated. Evidence for the participation of mesenchymal stromal cells (MSCs) in the tissue repair process across multiple tissues is overwhelming and their role in reparative disorders is clearly demonstrated, as is the involvement of a number of specific signaling pathways. Transforming growth factor beta, bone morphogenic protein and Wnt pathways interact to form a complex signaling network that is critical in regulating the fate choices of both stromal and tissue-specific resident stem cells (TSCs), determining whether functional regeneration or the formation of scar tissue follows an injury. A growing understanding of both TSCs, MSCs and the complex cascade of signals regulating both cell populations have, therefore, emerged as potential therapeutic targets to treat reparative disorders. This review focuses on recent advances on the role of these cells in skeletal muscle, heart and lung tissues.

The origin and arrhythmogenic potential of fibroblasts in cardiac disease

Fibroblasts play a major role in normal cardiac physiology and in the response of the heart to injury and disease. Cardiac electrophysiological research has primarily focused on the mechanisms of remodeling that accompany cardiac disease with an emphasis on myocyte electrophysiology. Recently, there has been increasing interest in the potential role of fibroblasts in cardiac electrophysiology. This review focuses on the arrhythmia mechanisms involving interactions between myocytes and fibroblasts. We also discuss the available evidence supporting the contribution of intracardiac and extracardiac sources to the fibroblast and myofibroblast populations in diseased hearts.