Researchers have reduced scar formation and improved heart function in mice with heart failure using a monoclonal antibody.
In a recent study published in Nature, researchers investigated the immune-fibroblast communication in human cardiac disease and mouse models.
They found that interleukin 1 beta (IL-1β) signaling between C-C chemokine receptor type 2 (CCR2+) macrophages and fibroblasts contributes to cardiac fibrosis and disrupting IL-1β signaling potentially reduces fibrosis and improves heart function.
Background
Inflammation and fibrosis, key factors in heart dysfunction, are prevalent in various heart diseases, particularly myocardial infarction (MI) and cardiomyopathies. Despite its clinical significance, there remains a dearth of therapeutic strategies targeting fibrosis. While mouse models have been used to identify the subtypes of fibroblasts involved in cardiac injury, the exact fibroblast populations driving fibrosis in human hearts, along with their regulatory mechanisms, remain unclear.
Preclinical models do not fully capture human fibroblast subtypes. High-throughput sequencing technologies, such as single-nucleus ribonucleic acid sequencing (snRNA-seq), have advanced our understanding of heart disease, but these studies lack detailed cellular transcriptomic, epigenetic, and proteomic data.
Additionally, challenges in obtaining fresh human cardiac tissue have prevented large-scale studies using single-cell or epitope-based sequencing to uncover immune-fibroblast interactions in cardiac fibrosis fully.
In the present study, researchers used cellular indexing of transcriptomes and epitopes (CITE-seq), multiomic sequencing, and spatial transcriptomics to analyze fibroblast populations and immune interactions in human and mouse hearts.
About the study
Cardiac fibrosis was investigated using advanced single-cell sequencing on left-ventricle specimens from healthy donors and heart failure patients with acute MI (n = 4), ischemic cardiomyopathy (ICM, n = 6), and non-ischemic cardiomyopathy (NICM, n = 6).
A total of 143,804 cells were obtained and distinct fibroblast states were identified through weighted nearest neighbor clustering, differential gene expression (DGE), and peak calling (MACS2). The researchers performed Gene Ontology and KEGG analyses alongside spatial transcriptomics to assess fibroblast distribution, comparing diseased and healthy fibroblasts with Pseudobulk differential expression.
Dynamic modeling helped to characterize fibroblast differentiation trajectories, confirmed through genetic lineage tracing in mice. Additionally, chromatin accessibility was analyzed to understand the epigenetic landscape of disease-associated fibroblasts.
Various experimental models were evaluated, and label-transfer techniques were employed to map mouse fibroblasts onto human datasets, including cultured human fibroblasts treated with tranforming growth factor beta (TGFβ) or IL-1β. IL-1β expression was assessed in myeloid cells in injury models, and genetically modified mice were generated to explore the potential role of IL-1β in the development of fibrosis.
Results and discussion
A total of 11 distinct cell types were identified, particularly expanded myeloid and T cells, in human heart tissue following acute MI, with notable changes occurring within the first week. Pseudobulk DGE analysis showed significant differences between healthy donors and heart failure conditions across multiple cell types. Multiome sequencing provided unique chromatin accessibility profiles in cardiomyocytes, myeloid cells, and fibroblasts, identifying transcription factors linked to regulatory elements that may contribute to gene regulatory networks specific to heart disease.
Thirteen distinct fibroblast cell states were identified, notably F2 (myofibroblasts) and F9 (fibroblast activator protein and periostin [FAP/POSTN] secreting fibroblasts), which were enriched in heart failure after MI. F9 fibroblasts, associated with extracellular matrix remodeling and immune interactions, were implicated as a potential pathogenic state. Spatial transcriptomics indicated that different fibroblast states were localized in infarct, border, and remote myocardial zones, with F9 fibroblasts colocalizing with myeloid cells.
Fibroblasts were found to predominantly transition toward F2, F4, and F9 states, with increased expression of FAP in the F9 lineage. Transcription factor analysis identified MEOX1 as a key regulator of the F9 lineage. Chromatin accessibility analysis revealed significant changes in heart failure fibroblasts, linking genes like POSTN and RUNX1 to F9 fibroblasts’ regulatory network in cardiac fibrosis.
Mapping mouse myocardial infarction data to human CITE-seq revealed strong similarities across fibroblast populations. Treatment with the BRD4 inhibitor JQ1 showed that loss of F9 fibroblasts improved cardiac function and fibrosis, suggesting a reversible effect. TGFβ and IL-1β were found to be key signals received by fibroblasts in fibrotic niches. Mice lacking IL-1 receptors in fibroblasts exhibited reduced activation and fibrosis, highlighting IL-1β’s critical role in cardiac fibrosis and its potential as a therapeutic target.
The study advances our understanding of the potential role of inflammation in cardiac fibrosis and highlights potential therapeutic strategies for heart failure. However, the study is limited by a small sample size and incomplete fibrosis reversal with IL-1β blockade. Further investigation into IL-1β/TGFβ interactions and fibroblast-immune cell communication is needed to confirm these findings and their potential clinical applications.
“We are hopeful that the combination of all of this evidence, including our work on the IL-1β pathway, will lead to the design of a clinical trial to specifically test the role of targeted immunotherapy in heart failure patients.”
Conclusion
In conclusion, the researchers revealed a distinct fibroblast lineage marked by FAP that gives rise to POSTN-expressing fibroblasts, separate from myofibroblasts. The study demonstrated that IL-1β regulates the specification of FAP/POSTN fibroblasts, suggesting that immunomodulators could be a promising therapeutic approach for targeting cardiac fibrosis.
