Project description:In this study, we investigate how matrix stiffness regulates chromatin reorganization and cell reprogramming, and find that matrix stiffness acts as a biphasic regulator of epigenetic state and fibroblast-to-neuron conversion efficiency, maximized at an intermediate stiffness of 20 kPa. ATAC-sequencing analysis shows the same trend of chromatin accessibility to neuronal genes at these stiffness levels. Concurrently, we observe peak levels of histone acetylation and histone acetyltransferase (HAT) activity in the nucleus on matrices at 20 kPa, and inhibiting HAT activity abolishes matrix stiffness effects. G-actin and cofilin, the co-transporters shuttling HAT into the nucleus, rises with decreasing matrix stiffness; however, reduced importin-9 on soft matrices limits nuclear transport. These two factors result in a biphasic regulation of HAT transport into the nucleus, which is directly demonstrated on matrices with dynamically tunable stiffness. These findings unravel a mechanism of the mechano-epigenetic regulation that is valuable for cell engineering in disease modeling and regenerative medicine applications.
Project description:The transcriptional regulator YAP orchestrates important cell functions, determining tissue homeostasis, organ growth control, and tumorigenesis. Mechanical stimuli are a key input to YAP activity, but the mechanisms controlling this regulation remain largely uncharacterized. We show that CAV1 positively modulates the YAP mechanoresponse to substrate stiffness through actin cytoskeleton-dependent and Hippo kinase-independent mechanisms. RHO activity is necessary but not sufficient for CAV1-dependent mechanoregulation of YAP activity. Systematic quantitative interactomic studies and image-based siRNA screenings provide evidence that this actin-dependent regulation is determined by YAP interaction with the 14-3-3 protein YWHAH. Constitutive YAP activation rescued phenotypes associated with CAV1 loss, including defective ECM remodeling. CAV1-mediated control of YAP activity was validated in vivo in a model of pancreatitis-driven acinar-to-ductal metaplasia. We propose that this CAV1-YAP mechanotransduction system controls a significant share of cell programs linked to these two pivotal regulators, with potentially broad physiological and pathological implications.
Project description:Precise control of the innate immune response is required for resistance to microbial infections and maintenance of normal tissue homeostasis. Because this response involves coordinate regulation of hundreds of genes, it provides a powerful biological system to elucidate the molecular strategies that underlie signal- and time-dependent transitions of gene expression. Using a combination of genome-wide and gene-specific approaches, we provide evidence that rather than representing off/on transitions, Toll-like receptor 4 (TLR4)-dependent activation of nearly all immediate/early (I/E) and late response genes results from a sequential process in which signal-independent factors, exemplified by Gabpa, initially establish basal levels of gene expression that are then amplified by signal-dependent transcription factors. Promoters of I/E genes are distinguished from those of late genes by the use of distinct sets of signal-dependent transcription factors, preferential binding of TBP and basal enrichment for RNA Pol II immediately downstream of transcriptional start sites. Global nuclear run-on (GRO) sequencing and total RNA sequencing further indicates that TLR4 signaling markedly increases efficiency of transcriptional elongation of nearly all I/E genes, while RNA splicing is largely unaffected. NCoR/SMRT co-repressor complexes are unexpectedly found to be associated with H3K4me3-positive promoters of TLR4-responsive genes that exhibit a broad range of basal expression levels, implying a dynamic, rather than static role in regulation of gene expression. Collectively, these findings reveal mechanisms underlying temporally distinct patterns of TLR4-dependent gene activation required for homeostasis and effective immune responses. ChIP-Seq, Total RNA-Seq, Gro-Seq, and gene expression profiling was performed in macrophages treated with Kdo2 Lipid A. Control samples for H3K4me3 and Input in Macrophages and B cells, in addition to control microarray data are included in GEO accession# GSE21512
Project description:Precise control of the innate immune response is required for resistance to microbial infections and maintenance of normal tissue homeostasis. Because this response involves coordinate regulation of hundreds of genes, it provides a powerful biological system to elucidate the molecular strategies that underlie signal- and time-dependent transitions of gene expression. Using a combination of genome-wide and gene-specific approaches, we provide evidence that rather than representing off/on transitions, Toll-like receptor 4 (TLR4)-dependent activation of nearly all immediate/early (I/E) and late response genes results from a sequential process in which signal-independent factors, exemplified by Gabpa, initially establish basal levels of gene expression that are then amplified by signal-dependent transcription factors. Promoters of I/E genes are distinguished from those of late genes by the use of distinct sets of signal-dependent transcription factors, preferential binding of TBP and basal enrichment for RNA Pol II immediately downstream of transcriptional start sites. Global nuclear run-on (GRO) sequencing and total RNA sequencing further indicates that TLR4 signaling markedly increases efficiency of transcriptional elongation of nearly all I/E genes, while RNA splicing is largely unaffected. NCoR/SMRT co-repressor complexes are unexpectedly found to be associated with H3K4me3-positive promoters of TLR4-responsive genes that exhibit a broad range of basal expression levels, implying a dynamic, rather than static role in regulation of gene expression. Collectively, these findings reveal mechanisms underlying temporally distinct patterns of TLR4-dependent gene activation required for homeostasis and effective immune responses. ChIP-Seq, Total RNA-Seq, Gro-Seq, and gene expression profiling was performed in macrophages treated with Kdo2 Lipid A. Control samples for H3K4me3 and Input in Macrophages and B cells, in addition to control microarray data are included in GEO accession# GSE21512
Project description:Precise control of the innate immune response is required for resistance to microbial infections and maintenance of normal tissue homeostasis. Because this response involves coordinate regulation of hundreds of genes, it provides a powerful biological system to elucidate the molecular strategies that underlie signal- and time-dependent transitions of gene expression. Using a combination of genome-wide and gene-specific approaches, we provide evidence that rather than representing off/on transitions, Toll-like receptor 4 (TLR4)-dependent activation of nearly all immediate/early (I/E) and late response genes results from a sequential process in which signal-independent factors, exemplified by Gabpa, initially establish basal levels of gene expression that are then amplified by signal-dependent transcription factors. Promoters of I/E genes are distinguished from those of late genes by the use of distinct sets of signal-dependent transcription factors, preferential binding of TBP and basal enrichment for RNA Pol II immediately downstream of transcriptional start sites. Global nuclear run-on (GRO) sequencing and total RNA sequencing further indicates that TLR4 signaling markedly increases efficiency of transcriptional elongation of nearly all I/E genes, while RNA splicing is largely unaffected. NCoR/SMRT co-repressor complexes are unexpectedly found to be associated with H3K4me3-positive promoters of TLR4-responsive genes that exhibit a broad range of basal expression levels, implying a dynamic, rather than static role in regulation of gene expression. Collectively, these findings reveal mechanisms underlying temporally distinct patterns of TLR4-dependent gene activation required for homeostasis and effective immune responses. ChIP-Seq, Total RNA-Seq, Gro-Seq, and gene expression profiling was performed in macrophages treated with Kdo2 Lipid A. Control samples for H3K4me3 in Macrophages and B cells, in addition to control microarray data are included in GEO accession# GSE21512. FASTA files are available for older experiments that lack quality read information (i.e. no FASTQ file)
Project description:Energy metabolism and extracellular matrix function are closely connected to orchestrate and maintain tissue organization, but the crosstalk is poorly understood. Here, we used scRNA-seq analysis to uncover the importance of respiration for extracellular matrix homeostasis in mature cartilage. Genetic inhibition of respiration in cartilage results in the expansion of a central area of 1-month-old mouse femur head cartilage showing disorganized chondrocytes and increased deposition of extracellular matrix material. scRNA-seq analysis identified a cluster-specific decrease in mitochondrial DNA-encoded respiratory chain genes and a unique regulation of extracellular matrix-related genes in nonarticular chondrocyte clusters. These changes were associated with alterations in extracellular matrix composition, a shift in the collagen/non-collagen protein content and an increase of collagen crosslinking and ECM stiffness. The results demonstrate, based on findings of the scRNA-seq analysis, that respiration is a key factor contributing to ECM integrity and mechanostability in cartilage and presumably also in many other tissues.
Project description:Purpose: Endothelial cells respond to changes in subendothelial stiffness altering their proliferation, migration and barrier integrity but whether that is due to transcriptional reprogramming was largely unknown. Using RNA-Sequencing, we performed gene expression profiling for two endothelial cell types grown on soft or stiff matrices: primary human umbilical vein endothelial cells (HUVEC) and immortalized human microvascular endothelial cells (HMEC-1), to understand whether subendothelial stiffness-dependent changes in endothelial cell mechanics are due to transcriptional regulation. Methods and Results: By analyzing the differentially expressed genes between all samples we found that endothelial cell type rather that subendothelial stiffness is the primary determinant of the endothelial cell transcriptome. Both cell types respond to changes in their subendothelial stiffness by increasing the traction stresses they exert on stiffer as opposed to softer matrices, however it is apparently not the endothelial cell transcriptome that regulates this universal biomechanical response to subendothelial stiffness. Only a handful of genes were differentially expressed in each cell type in a stiffness-dependent manner, and none were shared between the two cell types examined. In contrast, thousands of genes were differentially regulated in HUVEC as compared to HMEC-1. HUVEC (but not HMEC-1) upregulate expression of TGF-2 on stiffer matrices, and also enhance their endogenous TGF-2 expression and their cell-matrix traction stresses in response to application of exogenous TGF-2. Conclusions: Altogether, these findings provide insights into the relationship between subendothelial stiffness, endothelial mechanics and variation of the transcriptome between distinct endothelial cell types, and reveal that subendothelial stiffness while critically impacting endothelial cell mechanics is minimally altering their transcriptome.