Developmental Pathways of Cardiac Fibroblasts

ptx3a+ fibroblast/epicardial cells provide a transient macrophage niche to promote heart regeneration

Macrophages conduct critical roles in heart repair, but the niche required to nurture and anchor them is poorly studied. Here, we investigated the macrophage niche in the regenerating heart. We analyzed cell-cell interactions through published single-cell RNA sequencing datasets and identified a strong interaction between fibroblast/epicardial (Fb/Epi) cells and macrophages. We further visualized the association of macrophages with Fb/Epi cells and the blockage of macrophage response without Fb/Epi cells in the regenerating zebrafish heart. Moreover, we found that ptx3a+ epicardial cells associate with reparative macrophages, and their depletion resulted in fewer reparative macrophages. Further, we identified csf1a expression in ptx3a+ cells and determined that pharmacological inhibition of the csf1a pathway or csf1a knockout blocked the reparative macrophage response. Moreover, we found that genetic overexpression of csf1a enhanced the reparative macrophage response with or without heart injury. Altogether, our studies illuminate a cardiac Fb/Epi niche, which mediates a beneficial macrophage response after heart injury.

SPADE: spatial deconvolution for domain specific cell-type estimation

Understanding gene expression in different cell types within their spatial context is a key goal in genomics research. SPADE (SPAtial DEconvolution), our proposed method, addresses this by integrating spatial patterns into the analysis of cell type composition. This approach uses a combination of single-cell RNA sequencing, spatial transcriptomics, and histological data to accurately estimate the proportions of cell types in various locations. Our analyses of synthetic data have demonstrated SPADE's capability to discern cell type-specific spatial patterns effectively. When applied to real-life datasets, SPADE provides insights into cellular dynamics and the composition of tumor tissues. This enhances our comprehension of complex biological systems and aids in exploring cellular diversity. SPADE represents a significant advancement in deciphering spatial gene expression patterns, offering a powerful tool for the detailed investigation of cell types in spatial transcriptomics.

Neutrophils facilitate the epicardial regenerative response after zebrafish heart injury

Despite extensive studies on endogenous heart regeneration within the past 20 years, the players involved in initiating early regeneration events are far from clear. Here, we assessed the function of neutrophils, the first-responder cells to tissue damage, during zebrafish heart regeneration. We detected rapid neutrophil mobilization to the injury site after ventricular amputation, peaking at 1-day post-amputation (dpa) and resolving by 3 dpa. Further analyses indicated neutrophil mobilization coincides with peak epicardial cell proliferation, and recruited neutrophils associated with activated, expanding epicardial cells at 1 dpa. Neutrophil depletion inhibited myocardial regeneration and significantly reduced epicardial cell expansion, proliferation, and activation. To explore the molecular mechanism of neutrophils on the epicardial regenerative response, we performed scRNA-seq analysis of 1 dpa neutrophils and identified enrichment of the FGF and MAPK/ERK signaling pathways. Pharmacological inhibition of FGF signaling indicated its' requirement for epicardial expansion, while neutrophil depletion blocked MAPK/ERK signaling activation in epicardial cells. Ligand-receptor analysis indicated the EGF ligand, hbegfa, is released from neutrophils and synergizes with other FGF and MAPK/ERK factors for induction of epicardial regeneration. Altogether, our studies revealed that neutrophils quickly motivate epicardial cells, which later accumulate at the injury site and contribute to heart regeneration.

Heart-on-a-chip systems: disease modeling and drug screening applications

Cardiovascular disease (CVD) is the leading cause of death worldwide, casting a substantial economic footprint and burdening the global healthcare system. Historically, pre-clinical CVD modeling and therapeutic screening have been performed using animal models. Unfortunately, animal models oftentimes fail to adequately mimic human physiology, leading to a poor translation of therapeutics from pre-clinical trials to consumers. Even those that make it to market can be removed due to unforeseen side effects. As such, there exists a clinical, technological, and economical need for systems that faithfully capture human (patho)physiology for modeling CVD, assessing cardiotoxicity, and evaluating drug efficacy. Heart-on-a-chip (HoC) systems are a part of the broader organ-on-a-chip paradigm that leverages microfluidics, tissue engineering, microfabrication, electronics, and gene editing to create human-relevant models for studying disease, drug-induced side effects, and therapeutic efficacy. These compact systems can be capable of real-time measurements and on-demand characterization of tissue behavior and could revolutionize the drug development process. In this review, we highlight the key components that comprise a HoC system followed by a review of contemporary reports of their use in disease modeling, drug toxicity and efficacy assessment, and as part of multi-organ-on-a-chip platforms. We also discuss future perspectives and challenges facing the field, including a discussion on the role that standardization is expected to play in accelerating the widespread adoption of these platforms.

Src tyrosine kinase promotes cardiac remodeling induced by chronic sympathetic activation

Cardiac remodeling serves as the underlying pathological basis for numerous cardiovascular diseases and represents a pivotal stage for intervention. The excessive activation of β-adrenergic receptors (β-ARs) assumes a crucial role in cardiac remodeling. Nonetheless, the underlying molecular mechanisms governing β-AR-induced cardiac remodeling remain largely unresolved. In the present study, we identified Src tyrosine kinase as a key player in the cardiac remodeling triggered by excessive β-AR activation. Our findings demonstrated that Src mediates isoproterenol (ISO)-induced cardiac hypertrophy, fibrosis, and inflammation in vivo. Furthermore, Src facilitates β-AR-mediated proliferation and transdifferentiation of cardiac fibroblasts, and hypertrophy and cardiomyocytes in vitro. Subsequent investigations have substantiated that Src mediates β-AR induced the extracellular signal-regulated protein kinase (ERK1/2) signaling pathway activated by β-AR. Our research presents compelling evidence that Src promotes β-AR-induced cardiac remodeling in both in vivo and in vitro settings. It establishes the promoting effect of the β-AR/Src/ERK signaling pathway on overall cardiac remodeling in cardiac fibroblasts and underscores the potential of Src as a therapeutic target for cardiac remodeling.

Heterogeneity and Functional Analysis of Cardiac Fibroblasts in Heart Development

Background

As one of the major cell types in the heart, fibroblasts play critical roles in multiple biological processes. Cardiac fibroblasts are known to develop from multiple sources, but their transcriptional profiles have not been systematically compared. Furthermore, while the function of a few genes in cardiac fibroblasts has been studied, the overall function of fibroblasts as a cell type remains uninvestigated.

Methods

Single-cell mRNA sequencing (scRNA-seq) and bioinformatics approaches were used to analyze the genome-wide genes expression and extracellular matrix genes expression in fibroblasts, as well as the ligand-receptor interactions between fibroblasts and cardiomyocytes. Single molecular in situ hybridization was employed to analyze the expression pattern of fibroblast subpopulation-specific genes. The Diphtheria toxin fragment A (DTA) system was utilized to ablate fibroblasts at each developmental phase.

Results

Using RNA staining of Col1a1 at different stages, we grouped cardiac fibroblasts into four developmental phases. Through the analysis of scRNA-seq profiles of fibroblasts at 18 stages from two mouse strains, we identified significant heterogeneity, preserving lineage gene expression in their precursor cells. Within the main fibroblast population, we found differential expressions of Wt1, Tbx18, and Aldh1a2 genes in various cell clusters. Lineage tracing studies showed Wt1- and Tbx18-positive fibroblasts originated from respective epicardial cells. Furthermore, using a conditional DTA system-based elimination, we identified the crucial role of fibroblasts in early embryonic and heart growth, but not in neonatal heart growth. Additionally, we identified the zone- and stage-associated expression of extracellular matrix genes and fibroblast-cardiomyocyte ligand-receptor interactions. This comprehensive understanding sheds light on fibroblast function in heart development.

Conclusion

We observed cardiac fibroblast heterogeneity at embryonic and neonatal stages, with preserved lineage gene expression. Ablation studies revealed their distinct roles during development, likely influenced by varying extracellular matrix genes and ligand-receptor interactions at different stages.

Sevoflurane Improves Ventricular Conduction by Exosomes Derived from Rat Cardiac Fibroblasts After Hypothermic Global Ischemia-Reperfusion Injury

Purpose

This study investigated the effect of exosomes derived from sevoflurane-treated cardiac fibroblasts (Sev-CFs-Exo) on reperfusion arrhythmias (RA), ventricular conduction, and myocardial ischemia-reperfusion injury (MIRI).

Methods

Primary cardiac fibroblasts (CFs) were isolated from the hearts of neonatal rats and identified by morphology and immunofluorescence. Exosomes were isolated from CFs at passages 2-3 after they had been treated with 2.5% sevoflurane for an hour and cultivated for 24-48 hours. The control group was CFs that did not receive any treatment. The hypothermic global ischemia-reperfusion injury model was established using the Langendorff perfusion technique following injection with exosomes through the caudal vein. Multi-electrode array (MEA) mapping was used to investigate the changes in RA and ventricular conduction in isolated hearts. Western blots and immunofluorescence were used to examine the relative expression and location of connexin 43 (Cx43). In addition, the MIRI was evaluated with triphenyl tetrazolium chloride and Hematoxylin-Eosin staining.

Results

The primary CFs had a variety of morphologies, no spontaneous pulsation, and were vimentin-positive, which confirmed their successful isolation. Sev-CFs-Exo increased the heart rate (HR) at reperfusion for 15 minutes (T₂) and 30 minutes (T₃) and lowered the score and duration of RA and the time for restoration of heartbeat in reperfusion. Meanwhile, Sev-CFs-Exo increased conduction velocity (CV), decreased absolute inhomogeneity (P_5-95) and inhomogeneity index (P_5-95/P₅₀) at T₂ and T₃, as well as promoted the recovery of HR, CV, P_5-95 and P_5-95/P₅₀ after hypothermic global ischemia-reperfusion injury. Furthermore, Sev-CFs-Exo raised expression and reduced lateralization of Cx43, and improved myocardial infarct sizes and cellular necrosis. However, while cardiac fibroblast-derived exosomes (CFs-Exo) showed similar cardioprotective effects, the outcomes were not as significant.

Conclusion

Sevoflurane reduces the risk of RA and improves ventricular conduction and MIRI by CFs-Exo, and this may be driven by the expression and location of Cx43.

SPADE: Spatial Deconvolution for Domain Specific Cell-type Estimation

The advent of spatial transcriptomics technology has allowed for the acquisition of gene expression profiles with multi-cellular resolution in a spatially resolved manner, presenting a new milestone in the field of genomics. However, the aggregate gene expression from heterogeneous cell types obtained by these technologies poses a significant challenge for a comprehensive delineation of cell type-specific spatial patterns. Here, we propose SPADE (SPAtial DEconvolution), an in-silico method designed to address this challenge by incorporating spatial patterns during cell type decomposition. SPADE utilizes a combination of single-cell RNA sequencing data, spatial location information, and histological information to computationally estimate the proportion of cell types present at each spatial location. In our study, we showcased the effectiveness of SPADE by conducting analyses on synthetic data. Our results indicated that SPADE was able to successfully identify cell type-specific spatial patterns that were not previously identified by existing deconvolution methods. Furthermore, we applied SPADE to a real-world dataset analyzing the developmental chicken heart, where we observed that SPADE was able to accurately capture the intricate processes of cellular differentiation and morphogenesis within the heart. Specifically, we were able to reliably estimate changes in cell type compositions over time, which is a critical aspect of understanding the underlying mechanisms of complex biological systems. These findings underscore the potential of SPADE as a valuable tool for analyzing complex biological systems and shedding light on their underlying mechanisms. Taken together, our results suggest that SPADE represents a significant advancement in the field of spatial transcriptomics, providing a powerful tool for characterizing complex spatial gene expression patterns in heterogeneous tissues.

Origin and diversification of fibroblasts from the sclerotome in zebrafish

Fibroblasts play an important role in maintaining tissue integrity by secreting components of the extracellular matrix and initiating response to injury. Although the function of fibroblasts has been extensively studied in adults, the embryonic origin and diversification of different fibroblast subtypes during development remain largely unexplored. Using zebrafish as a model, we show that the sclerotome, a sub-compartment of the somite, is the embryonic source of multiple fibroblast subtypes including tenocytes (tendon fibroblasts), blood vessel associated fibroblasts, fin mesenchymal cells, and interstitial fibroblasts. High-resolution imaging shows that different fibroblast subtypes occupy unique anatomical locations with distinct morphologies. Long-term Cre-mediated lineage tracing reveals that the sclerotome also contributes to cells closely associated with the axial skeleton. Ablation of sclerotome progenitors results in extensive skeletal defects. Using photoconversion-based cell lineage analysis, we find that sclerotome progenitors at different dorsal-ventral and anterior-posterior positions display distinct differentiation potentials. Single-cell clonal analysis combined with in vivo imaging suggests that the sclerotome mostly contains unipotent and bipotent progenitors prior to cell migration, and the fate of their daughter cells is biased by their migration paths and relative positions. Together, our work demonstrates that the sclerotome is the embryonic source of trunk fibroblasts as well as the axial skeleton, and local signals likely contribute to the diversification of distinct fibroblast subtypes.

The dynamic cellular landscape of grafts with acute rejection after heart transplantation

BACKGROUND

Acute cellular rejection (ACR) is a major barrier to the long-term survival of cardiac allografts. Although immune cells are well known to play critical roles in ACR, the dynamic cellular landscape of allografts with ACR remains obscure.

METHODS

Single-cell RNA sequencing (scRNA-seq) was carried out for mouse cardiac allografts with ACR. Bioinformatic analysis was performed, and subsequent transplant experiments were conducted to validate the findings.

RESULTS

Despite an overall large depletion of cardiac fibroblasts (CFBs), highly expanded cytotoxic T lymphocytes and a CXCL10+Gbp2+ subcluster of CFBs were enriched within grafts at the late stage. CXCL10+Gbp2+ CFBs featured strong interferon responsiveness and high expression of chemokines and major histocompatibility complex molecules, implying their involvement in the recruitment and activation of immune cells. Cell‒cell communication analysis revealed that CXCL9/CXCL10-CXCR3 might contribute to regulating CXCL10+Gbp2+ CFB-induced chemotaxis and immune cell recruitment. In vivo transplant studies revealed the therapeutic potential of CXCR3 antagonism in transplant rejection.

CONCLUSIONS

The findings of our study unveiled a novel CFB subcluster that might mediate acute cardiac rejection. Targeting CXCR3 could prolong allograft survival.

Immune cells drive new immunomodulatory therapies for myocardial infarction: From basic to clinical translation

The high incidence of heart failure secondary to myocardial infarction (MI) has been difficult to effectively address. MI causes strong aseptic inflammation, and infiltration of different immune cells and changes in the local inflammatory microenvironment play a key regulatory role in ventricular remodeling. Therefore, the possibility of improving the prognosis of MI through targeted immunity has been of interest and importance in MI. However, previously developed immune-targeted therapies have not achieved significant success in clinical trials. Here, we propose that the search for therapeutic targets from different immune cells may be more precise and lead to better clinical translation. Specifically, this review summarizes the role and potential therapeutic targets of various immune cells in ventricular remodeling after MI, especially monocytes/macrophages and neutrophils, as a way to demonstrate the importance and potential of immunomodulatory therapies for MI. In addition, we analyze the reasons for the failure of previous immunomodulatory therapies and the issues that need to be addressed, as well as the prospects and targeting strategies of using immune cells to drive novel immunomodulatory therapies, hoping to advance the development of immunomodulatory therapies by providing evidence and new ideas.

Cardiac fibroblasts and mechanosensation in heart development, health and disease

The term 'mechanosensation' describes the capacity of cells to translate mechanical stimuli into the coordinated regulation of intracellular signals, cellular function, gene expression and epigenetic programming. This capacity is related not only to the sensitivity of the cells to tissue motion, but also to the decryption of tissue geometric arrangement and mechanical properties. The cardiac stroma, composed of fibroblasts, has been historically considered a mechanically passive component of the heart. However, the latest research suggests that the mechanical functions of these cells are an active and necessary component of the developmental biology programme of the heart that is involved in myocardial growth and homeostasis, and a crucial determinant of cardiac repair and disease. In this Review, we discuss the general concept of cell mechanosensation and force generation as potent regulators in heart development and pathology, and describe the integration of mechanical and biohumoral pathways predisposing the heart to fibrosis and failure. Next, we address the use of 3D culture systems to integrate tissue mechanics to mimic cardiac remodelling. Finally, we highlight the potential of mechanotherapeutic strategies, including pharmacological treatment and device-mediated left ventricular unloading, to reverse remodelling in the failing heart.

Hippo signaling in cardiac fibroblasts during development, tissue repair, and fibrosis

The evolutionarily conserved Hippo signaling pathway plays key roles in regulating the balance between cell proliferation and apoptosis, cell differentiation, organ size control, tissue repair, and regeneration. Recently, the Hippo pathway has been shown to regulate heart fibrosis, defined as excess extracellular matrix (ECM) deposition and increased tissue stiffness. Cardiac fibroblasts (CFs) are the primary cell type that produces, degrades, and remodels the ECM during homeostasis, aging, inflammation, and tissue repair and regeneration. Here, we review the available evidence from the current literature regarding how the Hippo pathway regulates the formation and function of CFs during heart development and tissue repair.

Role of Cardiac Fibroblasts in Cardiac Injury and Repair

PURPOSE OF REVIEW

The pathological remodeling of cardiac tissue after injury or disease leads to scar formation. Our knowledge of the role of nonmyocytes, especially fibroblasts, in cardiac injury and repair continues to increase with technological advances in both experimental and clinical studies. Here, we aim to elaborate on cardiac fibroblasts by describing their origins, dynamic cellular states after injury, and heterogeneity in order to understand their role in cardiac injury and repair.

RECENT FINDINGS

With the improvement in genetic lineage tracing technologies and the capability to profile gene expression at the single-cell level, we are beginning to learn that manipulating a specific population of fibroblasts could mitigate severe cardiac fibrosis and promote cardiac repair after injury. Cardiac fibroblasts play an indispensable role in tissue homeostasis and in repair after injury. Activated fibroblasts or myofibroblasts have time-dependent impacts on cardiac fibrosis. Multiple signaling pathways are involved in modulating fibroblast states, resulting in the alteration of fibrosis. Modulating a specific population of cardiac fibroblasts may provide new opportunities for identifying novel treatment options for cardiac fibrosis.

Heart regeneration: beyond new muscle and vessels

The most striking consequence of a heart attack is the loss of billions of heart muscle cells, alongside damage to the associated vasculature. The lost cardiovascular tissue is replaced by scar formation, which is non-functional and results in pathological remodelling of the heart and ultimately heart failure. It is, therefore, unsurprising that the heart regeneration field has centred efforts to generate new muscle and blood vessels through targeting cardiomyocyte proliferation and angiogenesis following injury. However, combined insights from embryological studies and regenerative models, alongside the adoption of -omics technology, highlight the extensive heterogeneity of cell types within the forming or re-forming heart and the significant crosstalk arising from non-muscle and non-vessel cells. In this review, we focus on the roles of fibroblasts, immune, conduction system, and nervous system cell populations during heart development and we consider the latest evidence supporting a function for these diverse lineages in contributing to regeneration following heart injury. We suggest that the emerging picture of neurologically, immunologically, and electrically coupled cell function calls for a wider-ranging combinatorial approach to heart regeneration.