Endothelial cells drive organ fibrosis in mice by inducing expression of the transcription factor SOX9

Fibrosis is a hallmark of chronic disease. Although fibroblasts are involved, it is unclear to what extent endothelial cells also might contribute. We detected increased expression of the transcription factor Sox9 in endothelial cells in several different mouse fibrosis models. These models included systolic heart failure induced by pressure overload, diastolic heart failure induced by high-fat diet and nitric oxide synthase inhibition, pulmonary fibrosis induced by bleomycin treatment, and liver fibrosis due to a choline-deficient diet. We also observed up-regulation of endothelial SOX9 in cardiac tissue from patients with heart failure. To test whether SOX9 induction was sufficient to cause disease, we generated mice with endothelial cell-specific overexpression of Sox9, which promoted fibrosis in multiple organs and resulted in signs of heart failure. Endothelial Sox9 deletion prevented fibrosis and organ dysfunction in the two mouse models of heart failure as well as in the lung and liver fibrosis mouse models. Bulk and single-cell RNA sequencing of mouse endothelial cells across multiple vascular beds revealed that SOX9 induced extracellular matrix, growth factor, and inflammatory gene expression, leading to matrix deposition by endothelial cells. Moreover, mouse endothelial cells activated neighboring fibroblasts that then migrated and deposited matrix in response to SOX9, a process partly mediated by the secreted growth factor CCN2, a direct SOX9 target; endothelial cell-specific Sox9 deletion reversed these changes. These findings suggest a role for endothelial SOX9 as a fibrosis-promoting factor in different mouse organs during disease and imply that endothelial cells are an important regulator of fibrosis.

Single-nuclear transcriptome profiling identifies persistent fibroblast activation in hypertrophic and failing human hearts of patients with longstanding disease

AIMS

Cardiac fibrosis drives the progression of heart failure in ischaemic and hypertrophic cardiomyopathy. Therefore, the development of specific anti-fibrotic treatment regimens to counteract cardiac fibrosis is of high clinical relevance. Hence, this study examined the presence of persistent fibroblast activation during longstanding human heart disease at a single-cell resolution to identify putative therapeutic targets to counteract pathological cardiac fibrosis in patients.

METHODS AND RESULTS

We used single-nuclei RNA sequencing with human tissues from two samples of one healthy donor, and five hypertrophic and two failing hearts. Unsupervised sub-clustering of 7110 nuclei led to the identification of 7 distinct fibroblast clusters. De-convolution of cardiac fibroblast heterogeneity revealed a distinct population of human cardiac fibroblasts with a molecular signature of persistent fibroblast activation and a transcriptional switch towards a pro-fibrotic extra-cellular matrix composition in patients with established cardiac hypertrophy and heart failure. This sub-cluster was characterized by high expression of POSTN, RUNX1, CILP, and a target gene adipocyte enhancer-binding protein 1 (AEBP1) (all P < 0.001). Strikingly, elevated circulating AEBP1 blood level were also detected in a validation cohort of patients with confirmed cardiac fibrosis and hypertrophic cardiomyopathy by cardiac magnetic resonance imaging (P < 0.01). Since endogenous AEBP1 expression was increased in patients with established cardiac hypertrophy and heart failure, we assessed the functional consequence of siRNA-mediated AEBP1 silencing in human cardiac fibroblasts. Indeed, AEBP1 silencing reduced proliferation, migration, and fibroblast contractile capacity and α-SMA gene expression, which is a hallmark of fibroblast activation (all P < 0.05). Mechanistically, the anti-fibrotic effects of AEBP1 silencing were linked to transforming growth factor-beta pathway modulation.

CONCLUSION

Together, this study identifies persistent fibroblast activation in patients with longstanding heart disease, which might be detected by circulating AEBP1 and therapeutically modulated by its targeted silencing in human cardiac fibroblasts.

Cardiomyocyte hyperplasia and immaturity but not hypertrophy are characteristic features of patients with RASopathies

AIMS

RASopathies are caused by mutations in genes that alter the MAP kinase pathway and are marked by several malformations with cardiovascular disorders as the predominant cause of mortality. Mechanistic insights in the underlying pathogenesis in affected cardiac tissue are rare. The aim of the study was to assess the impact of RASopathy causing mutations on the human heart.

METHODS AND RESULTS

Using single cell approaches and histopathology we analyzed cardiac tissue from children with different RASopathy-associated mutations compared to age-matched dilated cardiomyopathy (DCM) and control hearts. The volume of cardiomyocytes was reduced in RASopathy conditions compared to controls and DCM patients, and the estimated number of cardiomyocytes per heart was ~4-10 times higher. Single nuclei RNA sequencing of a 13-year-old RASopathy patient (carrying a PTPN11 c.1528C > G mutation) revealed that myocardial cell composition and transcriptional patterns were similar to <1 year old DCM hearts. Additionally, immaturity of cardiomyocytes is shown by an increased MYH6/MYH7 expression ratio and reduced expression of genes associated with fatty acid metabolism. In the patient with the PTPN11 mutation activation of the MAP kinase pathway was not evident in cardiomyocytes, whereas increased phosphorylation of PDK1 and its downstream kinase Akt was detected.

CONCLUSION

In conclusion, an immature cardiomyocyte differentiation status appears to be preserved in juvenile RASopathy patients. The increased mass of the heart in such patients is due to an increase in cardiomyocyte number (hyperplasia) but not an enlargement of individual cardiomyocytes (hypertrophy).

The role of pericytes in cardiac ageing and disease

Introduction

Cardiac disease induces remodelling which can include fibrosis, cardiomyocyte hypertrophy, cardiac dilation, and finally can lead to heart failure. Age is one of the main risk factors of cardiovascular disease and induces heart remodelling, in particular, it has profound effects on the microcirculation. Pericytes are microvascular mural cells involved in the maintenance of stability and homeostasis of the vascular network. Although the phenotypes that arise from cardiac remodelling have been well studied in cardiomyocytes, endothelial cells and fibroblasts, the effect of aging on pericytes remain largely unknown.

Purpose

The purpose of this study is to characterise pericyte responses to cardiac ageing and disease in order to determine the therapeutic potential of these mural cells to reverse, or at least reduce, structural remodelling.

Methods

We have studied 12-week-old and 18-month-old mice. We have performed histological analysis and single-nucleus-RNA-sequencing (snRNAseq). For our in vitro experiments we have used primary human pericytes.

Results

Age affects the structure of the microcirculation in the heart. Pericyte coverage is reduced and capillary diameter is increased. Gene ontology analysis of differentially expressed genes in pericytes revealed an upregulation of genes related to filopodia and actin cytoskeleton, while a reduction of genes related to focal adhesion in the pericytes of the aged heart. Interestingly, we detected a downregulation of Regulator of G-protein signalling 5 (RGS5), a repressor of GPCRs signalling. RGS5 knockdown induces a contractile, pro-inflammatory and pro-fibrotic gene expression profile reducing pericytes proliferation and migration. Mechanistically, we show that RGS5 post-transcriptionally regulates PDGFRβ, a crucial tyrosine kinase receptor for pericyte-endothelial cell interaction. RGS5 knockdown reduces the expression of the receptor at the protein level, but not at the gene expression level and furthermore reduces the phosphorylation of AKT, a downstream signal of PDGFRβ activity. Furthermore, we have identified that T-Box Transcription Factor 20 (Tbx20), a cardiogenic transcription factor, is enriched in aged pericytes. Silencing and upregulation studies have revealed that Tbx20 is a repressor of PDGFRB, the gene that encodes for PDGFRβ, and that it controls pericyte adhesion.

Conclusions

Together, these observations have identified RGS5 and Tbx20 as crucial key players maintaining pericyte function in the aged heart. We propose that RGS5 and Tbx20 regulate pericyte function by controlling PDGFRβ signalling and cellular proliferation, adhesion and migration. Given the importance of pericytes in keeping vessel homeostasis, maintaining or recovering pericyte function in context of cardiac stress would be a potential approach to reduce the malignant effects of cardiac remodelling in the aged heart.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): SFB1366 (DFG)

Fibroblast-mediated intercellular crosstalk in the healthy and diseased heart

Cardiac fibroblasts constitute a major cell population in the heart. They secrete extracellular matrix components and various other factors shaping the microenvironment of the heart. In silico analysis of intercellular communication based on single-cell RNA sequencing revealed that fibroblasts are the source of the majority of outgoing signals to other cell types. This observation suggests that fibroblasts play key roles in orchestrating cellular interactions that maintain organ homeostasis but that can also contribute to disease states. Here, we will review the current knowledge of fibroblast interactions in the healthy, diseased, and aging heart. We focus on the interactions that fibroblasts establish with other cells of the heart, specifically cardiomyocytes, endothelial cells and immune cells, and particularly those relying on paracrine, electrical, and exosomal communication modes.

The human cell atlas of the hypertrophic heart reveals impaired inter-cellular cross-talks

Introduction

The pathophysiology of cardiac hypertrophy is multifactorial and is accompanied by the dysregulation of various signaling pathways contributing to cardiac dysfunction and heart failure. While the hypertrophic response of cardiomyocytes (CM) has been extensively studied, the interplay of CMs with the non-parenchymal cells in the heart is less explored. Here, we apply high-resolution transcriptomic analysis on single cell level allowing the identification of cellular responses and communication in the hypertrophic human heart.

Results

We analyzed single nuclei RNA sequencing data of cardiac tissues from five patients with aortic stenosis and cardiac hypertrophy and 13 matched healthy subjects. Bioinformatic data analysis of 88,536 nuclei followed by clustering led to the identification of specific heterogenic cell type signatures. Analyzing cell type specific gene expression signatures, we found the expected up-regulation of the cardiac stress MYH7 (4.15-fold), CMYA5 (4.89-fold) and XIRP2 (6.13-fold) in cardiomyocytes (CM) (all p&lt;0.0001). Fibroblasts showed increased expression of genes associated with fibrosis and activation markers such as periostin (POSTN; 6.84-fold, p&lt;0.0001). In-silico analysis of intercellular communication pathways revealed a striking downregulation of ligand-receptor interactions between CMs and other cells in hypertrophic compared to healthy controls indicating that CMs are less responsive to signals from fibroblasts and endothelial cells (ECs) in the hypertrophied heart. Particularly, CM showed reduced expression of receptor tyrosine kinases of the Ephrin family and FGF-family members. Specifically, Ephrin-B1 was significantly downregulated in CMs of the hypertrophic hearts (0.01-fold, p&lt;0.0001). The down-regulation of Ephrin-B1 was additionally validated on protein level using histological sections of hypertrophic cardiomyopathy patients (n=6) versus healthy controls (n=5) (0.66-fold, p=0.02). In-vitro studies in neonatal cardiomyocytes further demonstrated that activation of the Ephrin-B1 receptor by the agonist Ephrin-B2 induced cardioprotective effects. Thus, Ephrin-B2 inhibited phenylephrine (PE) induced Nppb expression by 0.775-fold (vs. PE) and hypertrophic growth (0.774-fold reduction of cell size vs. PE). Similar findings were observed in PE-stimulated human cardiac organoids, which showed a 0.58-fold reduction of size in response to Ephrin-B2 treatments compared to PE alone.

Conclusion

Investigating the cross-talk in cardiac hypertrophy reveals novel disturbed communication signatures, with a striking reduction in the intercellular communication pathways of CMs. Reduced expression of receptors of the Ephrin family, particularly Ephrin-B1, in CM may prevent cardioprotective signaling by the agonist Ephrin-B2, which is highly expressed in ECs, leading to inhibition of cardioprotective cross-talk between ECs and CMs in the hypertrophic heart.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Dr. Rolf M. Schwiete StiftungDie Deutsche ForschungsgemeinschaftGerman Center for Cardiovascular Research

Increased susceptibility of human endothelial cells to infections by SARS-CoV-2 variants

Coronavirus disease 2019 (COVID-19) spawned a global health crisis in late 2019 and is caused by the novel coronavirus SARS-CoV-2. SARS-CoV-2 infection can lead to elevated markers of endothelial dysfunction associated with higher risk of mortality. It is unclear whether endothelial dysfunction is caused by direct infection of endothelial cells or is mainly secondary to inflammation. Here, we investigate whether different types of endothelial cells are susceptible to SARS-CoV-2. Human endothelial cells from different vascular beds including umbilical vein endothelial cells, coronary artery endothelial cells (HCAEC), cardiac and lung microvascular endothelial cells, or pulmonary arterial cells were inoculated in vitro with SARS-CoV-2. Viral spike protein was only detected in HCAECs after SARS-CoV-2 infection but not in the other endothelial cells tested. Consistently, only HCAEC expressed the SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2), required for virus infection. Infection with the SARS-CoV-2 variants B.1.1.7, B.1.351, and P.2 resulted in significantly higher levels of viral spike protein. Despite this, no intracellular double-stranded viral RNA was detected and the supernatant did not contain infectious virus. Analysis of the cellular distribution of the spike protein revealed that it co-localized with endosomal calnexin. SARS-CoV-2 infection did induce the ER stress gene EDEM1, which is responsible for clearance of misfolded proteins from the ER. Whereas the wild type of SARS-CoV-2 did not induce cytotoxic or pro-inflammatory effects, the variant B.1.1.7 reduced the HCAEC cell number. Of the different tested endothelial cells, HCAECs showed highest viral uptake but did not promote virus replication. Effects on cell number were only observed after infection with the variant B.1.1.7, suggesting that endothelial protection may be particularly important in patients infected with this variant.

Single Nuclei Sequencing Reveals Novel Insights Into the Regulation of Cellular Signatures in Children With Dilated Cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is a leading cause of death in children with heart failure. The outcome of pediatric heart failure treatment is inconsistent, and large cohort studies are lacking. Progress may be achieved through personalized therapy that takes age- and disease-related pathophysiology, pathology, and molecular fingerprints into account. We present single nuclei RNA sequencing from pediatric patients with DCM as the next step in identifying cellular signatures.

METHODS

We performed single nuclei RNA sequencing with heart tissues from 6 children with DCM with an age of 0.5, 0.75, 5, 6, 12, and 13 years. Unsupervised clustering of 18 211 nuclei led to the identification of 14 distinct clusters with 6 major cell types.

RESULTS

The number of nuclei in fibroblast clusters increased with age in patients with DCM, a finding that was confirmed by histological analysis and was consistent with an age-related increase in cardiac fibrosis quantified by cardiac magnetic resonance imaging. Fibroblasts of patients with DCM >6 years of age showed a profoundly altered gene expression pattern with enrichment of genes encoding fibrillary collagens, modulation of proteoglycans, switch in thrombospondin isoforms, and signatures of fibroblast activation. In addition, a population of cardiomyocytes with a high proregenerative profile was identified in infant patients with DCM but was absent in children >6 years of age. This cluster showed high expression of cell cycle activators such as cyclin D family members, increased glycolytic metabolism and antioxidative genes, and alterations in ß-adrenergic signaling genes.

CONCLUSIONS

Novel insights into the cellular transcriptomes of hearts from pediatric patients with DCM provide remarkable age-dependent changes in the expression patterns of fibroblast and cardiomyocyte genes with less fibrotic but enriched proregenerative signatures in infants.

Single nuclei sequencing reveals novel insights into cardiac cell signatures in human pediatric dilated cardiopathy

 

The mechanism underlying dilated cardiomyopathy (DCM) in children without a known genetic disorder are unclear. In contrast to adult DCM patients, there is an unmet need for therapeutic options that improve survival in pediatric DCM. Therefore, we performed single nuclei RNA sequencing (snRNA-seq) from heart tissue obtained from children undergoing heart transplantation due to severe heart failure.

We processed heart tissue from 6 children with DCM (EF: 18.67±2.11%) of an age of 0.5, 0.75, 5, 6, 12 and 13 years (y). After snRNA-seq, unsupervised clustering was performed identifying 8 major cell types, including cardiomyocytes (CM), fibroblasts (FB), endothelial cells, leukocytes, pericytes, smooth muscle cells, neuronal-like cells and an endothelial-fibroblast-like cluster. Relative numbers of FB clusters correlated with increasing age of the children which was clinically validated by measuring late enhancement (LE) with cardiac magnetic resonance imaging in 68 pediatric DCM patients. The mean age of patients with LE was 5.86±0.53y vs. 2.36±0.53y in patients without LE (p&lt;0.05). Further analysis of unique highly expressed genes (DEGs) between the 3 age groups identified a profound alteration of gene expression in FB clusters. FBs of explants of &lt;1y old patients showed high expression of anti-fibrotic, development and remodeling associated genes. In contrast, FBs of 12–13y old children highly expressed pro-fibrotic and FB activation associated genes as transforming growth factor beta binding protein (6.63 fold), cytochrome P450 1B1 (3.79 fold), and periostin (7.67 fold) (all p&lt;0.05). Moreover, we observed a switch in collagen expression patterns and in thrombospondin isoforms (from THBS1 to THBS4). Furthermore, our analysis revealed most profound transcriptional changes in CMs. We identified a cluster of CMs with a pro-regenerative profile in &lt;1y old patients, which could not be detected during adolescence. This CM cluster showed high expression of genes associated with proliferation (e.g. cyclin D2), glycolytic metabolism and anti-oxidant markers. Increased cyclin D2 was confirmed by immunostaining (1.43 fold higher in &lt;1y vs. 12–13y). Since all of these gene expression patterns might be affected by the underlying disease of the pediatric heart recipients, we explored their expression in FBs and CMs of postnatal vs. adult mice. Importantly, we could recapitulate the vast majority of the findings from humans in the mice experiments.

Together, these data demonstrate an age-dependent decrease in CM numbers concomitant with increased FBs in pediatric DCM. FBs of &lt;1y old pediatric patients revealed a distinct collagen expression profile and showed lower levels of pro-fibrotic genes. CMs of &lt;1y old donors where characterized with a regeneration enabling gene expression profile, which include pro-proliferative genes. The expression patterns of the CMs indicates, that regeneration might also occur in humans during the firs year of life.

Funding Acknowledgement

Type of funding source: Public grant(s) – EU funding. Main funding source(s): Dr. Rolf M. Schwiete Stiftung, DZHK

An In Vitro Model for Identifying Cardiac Side Effects of Anesthetics

The understanding of anesthetic side effects on the heart has been hindered by the lack of sophisticated clinical models. Using micropatterned human-induced pluripotent stem cell-derived cardiomyocytes, we obtained cardiac muscle depressant profiles for propofol, etomidate, and our newly identified anesthetic compound KSEB01-S2. Propofol was the strongest depressant among the 3 compounds tested, exhibiting the largest decrease in contraction velocity, depression rate, and beating frequency. Interestingly, KSEB01-S2 behaved similarly to etomidate, suggesting a better cardiac safety profile. Our results provide a proof-of-concept for using human-induced pluripotent stem cell-derived cardiomyocytes as an in vitro platform for future drug design.

Ethyl pyruvate ameliorates hepatic injury following blunt chest trauma and hemorrhagic shock by reducing local inflammation, NF-kappaB activation and HMGB1 release

BACKGROUND

The treatment of patients with multiple trauma including blunt chest/thoracic trauma (TxT) and hemorrhagic shock (H) is still challenging. Numerous studies show detrimental consequences of TxT and HS resulting in strong inflammatory changes, organ injury and mortality. Additionally, the reperfusion (R) phase plays a key role in triggering inflammation and worsening outcome. Ethyl pyruvate (EP), a stable lipophilic ester, has anti-inflammatory properties. Here, the influence of EP on the inflammatory reaction and liver injury in a double hit model of TxT and H/R in rats was explored.

METHODS

Female Lewis rats were subjected to TxT followed by hemorrhage/H (60 min, 35±3 mm Hg) and resuscitation/R (TxT+H/R). Reperfusion was performed by either Ringer`s lactated solution (RL) alone or RL supplemented with EP (50 mg/kg). Sham animals underwent all surgical procedures without TxT+H/R. After 2h, blood and liver tissue were collected for analyses, and survival was assessed after 24h.

RESULTS

Resuscitation with EP significantly improved haemoglobin levels and base excess recovery compared with controls after TxT+H/R, respectively (p<0.05). TxT+H/R-induced significant increase in alanine aminotransferase levels and liver injury were attenuated by EP compared with controls (p<0.05). Local inflammation as shown by increased gene expression of IL-6 and ICAM-1, enhanced ICAM-1 and HMGB1 protein expression and infiltration of the liver with neutrophils were also significantly attenuated by EP compared with controls after TxT+H/R (p<0.05). EP significantly reduced TxT+H/R-induced p65 activation in liver tissue. Survival rates improved by EP from 50% to 70% after TxT+H/R.

CONCLUSIONS

These data support the concept that the pronounced local pro-inflammatory response in the liver after blunt chest trauma and hemorrhagic shock is associated with NF-κB. In particular, the beneficial anti-inflammatory effects of ethyl pyruvate seem to be regulated by the HMGB1/NF-κB axis in the liver, thereby, restraining inflammatory responses and liver injury after double hit trauma in the rat.