Post-transcriptional Fibroblast Fate Switching By MBNL1 Regulates Fibrotic and Myocardial Remodeling During Cardiac Wound Healing
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ABSTRACT: Dynamic fibroblast state transitions underlie the heart’s fibrotic response, raising the possibility that tactical control of these transitions could alter maladaptive fibrotic outcomes. Transcriptome maturation by Muscleblind-like 1 (MBNL1) has emerged as a driver of differentiated cell states. Indeed, MBNL1 expression is elevated in conjunction with profibrotic transcripts in lineage traced myofibroblasts and modeling this gain in function by fibroblast-specific overexpression of an MBNL1 transgene induced a myofibroblast transcriptional identity in healthy hearts and promoted maladaptive myocyte remodeling and scar maturation following injury. Both fibroblast-specific and myofibroblast-specific loss of MBNL1 limited scar production and maturation, which was ascribed to negligible myofibroblast activity. MBNL1 deletion drove expansion of all quiescent cardiac fibroblast states and promoted mesenchymal stem cell characteristics while forced MBNL1 expression restricted state diversity by transitioning most fibroblasts to the most mature myofibroblast identity. These data suggest MBNL1 is a post-transcriptional switch controlling quiescent to myofibroblast transitions during cardiac wound healing.
Project description:The differentiation of fibroblasts into myofibroblasts mediates tissue wound healing and fibrotic remodeling. To better understand this process we performed a genome-wide screen in fibroblasts, which identified the RNA-binding protein muscleblind-like 1 (MBNL1) as a potent regulator of myofibroblast differentiation. MBNL1 promoted transformation of fibroblasts into myofibroblasts, while loss of Mbnl1 abrogated myofibroblast differentiation and impaired the fibrotic phase of wound healing in mouse models of myocardial infarction and dermal injury. Conditional fibroblast-specific MBNL1 transgenic mice showed a fibrotic phenotype in the absence of injury. Mechanistically, MBNL1 directly bound to and regulated the alternative splicing and stability of a network of myofibroblast differentiation specific genes, such as the nodal transcriptional regulator serum response factor (SRF). CRISPR-Cas9 mediated gene editing of the MBNL1 binding site in Srf impaired myofibroblast differentiation. These data establish a new RNA-dependent paradigm through MBNL1 that underlies global myofibroblast differentiation, the fibrotic response, and tissue wound healing.
Project description:Activated hepatic stellate cells orchestrate scar formation during fibrotic liver injury. Recent evidence has shown limited quiescent precursor derivation from the mesoderm during development. Here, we use lineage-tracing from development, through adult homeostasis, to adult fibrotic injury, to show that discreet subpopulations of activated hepatic stellate cells are defined by expression of WT1, a transcription factor controlling morphological transitions in organogenesis and adult homeostasis. Morphologically and transcriptionally distinct subpopulations are evident in fibrotic human disease and animal models. Populations defined by WT1 expression after injury derive from a discreet population of quiescent adult precursors originating from the embryonic mesothelium. WT1-deletion permits morphological transition to an enhanced fibrotic myofibroblast phenotype. Our findings demonstrate functional heterogeneity of adult scar-forming cells that can be whole-life traced back through specific quiescent precursors in adult homeostasis to differential origin in development, and defines WT1 as a paradoxical anti-fibrotic regulator during adult injury.
Project description:Mammalian skin wounds heal by forming fibrotic scars. We report that reindeer antler velvet exhibits regenerative wound healing, whereas identical injury to back skin forms scar. This regenerative capacity was retained following ectopic transplantation of velvet to scar-forming sites. Single-cell mRNA/ATAC-Sequencing revealed that while uninjured velvet fibroblasts resembled human fetal fibroblasts, back skin fibroblasts were enriched in pro-inflammatory features resembling adult human fibroblasts. Injury elicited site-specific immune polarization; back skin fibroblasts amplified the immune response, whereas velvet fibroblasts adopted an immunosuppressive state leading to restrained myeloid maturation and hastened immune resolution ultimately enabling myofibroblast reversion to a regeneration-competent state. Finally, regeneration was blunted following application of back skin associated immunostimulatory signals or inhibition of pro-regenerative factors secreted exclusive to velvet fibroblasts. This study highlights a unique model to interrogate mechanisms underlying divergent healing outcomes and nominates both decoupling of stromal-immune crosstalk and reinforcement of pro-regenerative fibroblast programs to mitigate scar.
Project description:Skin fibrotic disease representsa major global healthcare burden, characterized by fibroblast hyperproliferation and excessive accumulation of extracellular matrix.Fibroblasts are found to be heterogeneous in multiple fibrotic diseases,but the fibroblast heterogeneity of skin fibrotic diseases remains unknown.In this study, we performed single-cell RNA-seq in keloid, a paradigm of skin fibrotic diseases, andnormal scardermis tissues.Our results indicate that keloid and normal scar fibroblasts could be divided into 4 subpopulations: secretory-papillary, secretory-reticular, mesenchymal and pro-inflammatory.The percentage of mesenchymal fibroblast subpopulationincreased significantly in keloid compared to normal scar. Interestingly, we also found increasing mesenchymal fibroblast subpopulation in scleroderma, another skin fibrotic disease.Function studies showed that the mesenchymal fibroblasts promoted collagen synthesis of the other fibroblasts in keloid partiallythrough secreting POSTN. These findings will help us understandskin fibroticpathogenesis in depth,and provided potential target cells for fibrotic diseases therapies.
Project description:Skin fibrotic disease representsa major global healthcare burden, characterized by fibroblast hyperproliferation and excessive accumulation of extracellular matrix.Fibroblasts are found to be heterogeneous in multiple fibrotic diseases,but the fibroblast heterogeneity of skin fibrotic diseases remains unknown.In this study, we performed single-cell RNA-seq in keloid, a paradigm of skin fibrotic diseases, andnormal scardermis tissues.Our results indicate thatkeloid and normal scar fibroblasts could be divided into 4 subpopulations: secretory-papillary, secretory-reticular, mesenchymal and pro-inflammatory.The percentage of mesenchymal fibroblast subpopulationincreased significantly in keloid compared to normal scar. Interestingly, we also found increasing mesenchymal fibroblast subpopulation in scleroderma, another skin fibrotic disease.Function studies showed that the mesenchymal fibroblasts promoted collagen synthesis of the other fibroblasts in keloid partiallythrough secreting POSTN. These findings will help us understandskin fibroticpathogenesis in depth,and provided potential target cells for fibrotic diseases therapies.
Project description:Myocardial infarctions cause hypoxic injury to downstream tissue and a consequent fibrotic remodeling process to replace injured tissue with a scar. Scar formation occurs through phases of wound healing in which stimuli such as transforming growth factor-beta (TGF-β) drive cardiac fibroblasts to activate into a myofibroblast phenotype and deposit matrix molecules that form a scar. While this is necessary to repair injured tissue, excessive fibrosis commonly occurs which is correlated with heart failure. Therefore, defining cardiac fibroblast phenotypes under hypoxic stimuli and TGF-β is essential for understanding and treating pathological fibrosis. We robustly characterized fibroblast phenotype through immunofluorescence, quantitative RT-PCR, and proteomic analysis, after either TGF-β treatment or hypoxia durations that mimic acute hypoxic injury post-infarction. We find that hypoxic fibroblasts respond to low oxygen with increased hypoxia inducible factor 1 (HIF-1) but not HIF-2 activity by 4h. This is accompanied by increased gene and protein levels of VEGFA and LOX, respectively, which are both targets of HIF-1. Both TGF-β1 and hypoxia inhibit proliferation by 24h. While TGF-β1 treatment upregulated various fibrotic pathways, hypoxia causes a global reduction in protein synthesis, including collagen biosynthesis. This study discerns overlapping from distinctive outcomes of TGF-β1 and hypoxia treatment, which is important for elucidating their roles in fibrotic remodeling post-MI.
Project description:In diseased organs, stress-activated signaling cascades alter chromatin, triggering broad shifts in transcription and cell state that exacerbate pathology. Fibroblast activation is a common stress response that worsens lung, liver, kidney and heart disease, yet its mechanistic basis remains poorly understood. Pharmacologic inhibition of the BET family of transcriptional coactivators alleviates cardiac dysfunction and associated fibrosis, providing a tool to mechanistically interrogate maladaptive fibroblast states and modulate their plasticity as a potential therapeutic approach. Here, we leverage dynamic single cell transcriptomic and epigenomic interrogation of heart tissue with and without BET inhibition to reveal a reversible transcriptional switch underlying stress-induced fibroblast activation. Transcriptomes of resident cardiac fibroblasts demonstrated robust and rapid toggling between the quiescent fibroblast and activated myofibroblast state in a manner that directly correlated with BET inhibitor exposure and cardiac function. Correlation of single cell chromatin accessibility with cardiac function revealed a novel set of reversibly accessible DNA elements that correlated with disease severity. Among the most dynamic elements was an enhancer regulating the transcription factor MEOX1, which was specifically expressed in activated myofibroblasts, occupied putative regulatory elements of a broad fibrotic gene program, and was required for TGFβ-induced myofibroblast activation. CRISPR interference of the most dynamic cis-element within the enhancer, marked by nascent transcription, prevented TGFβ-induced activation of Meox1. These findings identify MEOX1 as a central regulator of stress-induced myofibroblast activation associated with cardiac dysfunction. The plasticity and specificity of the BET-dependent regulation of MEOX1 in endogenous tissue fibroblasts provides new trans- and cis- targets for treating fibrotic disease.
Project description:Fibrotic scarring drives the progression of heart failure after myocardial infarction (MI). Therefore, the development of specific treatment regimens to counteract fibrosis is of high clinical relevance. The transcription factor SOX9 functions as an important regulator during embryogenesis, but recent data point towards an additional causal role in organ fibrosis. We show here that SOX9 is upregulated in the scar after MI in mice. Fibroblast specific deletion of Sox9 ameliorated MI-induced left ventricular dysfunction, dilatation and myocardial scarring in vivo. Unexpectedly, deletion of Sox9 also potently eliminated persisting leukocyte infiltration of the scar in the chronic phase after MI. RNA-sequencing from the infarct scar revealed that Sox9 deletion in fibroblasts resulted in strongly downregulated expression of genes related to extracellular matrix, proteolysis and inflammation. Importantly, Sox9 deletion in isolated cardiac fibroblasts in vitro similarly affected gene expression as in the cardiac scar and prevented their activation and myofibroblast differentiation. Together, our data demonstrate that fibroblast SOX9 functions as a master regulator of cardiac fibrosis and inflammation and might constitute a novel therapeutic target during MI.
Project description:In diseased organs, stress-activated signaling cascades alter chromatin, triggering maladaptive cell state transitions. Fibroblast activation is a common tissue stress response that worsens lung, liver, kidney and heart disease, yet its mechanistic basis remains obscure. Pharmacologic BET inhibition alleviates cardiac dysfunction, providing a tool to interrogate and modulate cardiac cell states as a potential therapeutic approach. Here, we leverage single-cell epigenomic interrogation of hearts dynamically exposed to BET inhibitors to reveal a reversible transcriptional switch underlying fibroblast activation. Resident cardiac fibroblasts demonstrated robust toggling between the quiescent and activated state in a manner directly correlating with BET inhibitor exposure and cardiac function. Single-cell chromatin accessibility revealed novel DNA elements whose accessibility dynamically correlated with cardiac performance. Among the most dynamic elements was an enhancer regulating the transcription factor MEOX1, which was specifically expressed in activated fibroblasts, occupied putative regulatory elements of a broad fibrotic gene program, and was required for TGFβ-induced fibroblast activation. Selective CRISPR inhibition of the single most dynamic cis-element within the enhancer blocked TGFβ-induced Meox1 activation. We identify MEOX1 as a central regulator of fibroblast activation associated with cardiac dysfunction, and also demonstrate its upregulation upon activation of human lung, liver and kidney fibroblasts. The plasticity and specificity of BET-dependent regulation of MEOX1 in tissue fibroblasts provide new trans- and cis- targets for treating fibrotic disease.
Project description:Transforming growth factor-β (TGFβ) is a key mediator of fibroblast activation in fibrotic diseases including systemic sclerosis. Here we show that Engrailed 1 (EN1) is re-expressed in multiple fibroblast subpopulations in the skin of SSc patients. We characterize EN1 as a molecular amplifier of TGFβ signaling in myofibroblast differentiation: TGFβ induces EN1 expression in a SMAD3-dependent manner, and, in turn, EN1 mediates the pro-fibrotic effects of TGFβ. RNA sequencing demonstrates that EN1 induces a pro-fibrotic gene expression profile functionally related to the cytoskeleton organization and ROCK activation. EN1 regulates gene expression by modulating the activity of SP1 and other SP-transcription factors, as confirmed by ChIP-seq experiments for EN1 and SP1. Functional experiments confirm the coordinating role of EN1 on ROCK activity and the re-organization of cytoskeleton during myofibroblast differentiation both in standard fibroblast culture systems and in in vitro skin models. Consistently, mice with fibroblast-specific knockout of En1 demonstrate impaired fibroblast-to-myofibroblast transition and are partially protected from experimental skin fibrosis.