Project description:The shear stress-induced transcription factor Krüppel-like factor 2 (KLF2) confers anti-inflammatory properties to endothelial cells through inhibition of activator protein 1, presumably by interfering with MAPK cascades. To gain insight into the regulation of these cascades by KLF2, we used antibody arrays in combination with time-course mRNA micro-array analysis. No gross changes in MAPKs were detected, rather phosphorylation of actin cytoskeleton-associated proteins, including Focal Adhesion Kinase, was markedly repressed by KLF2. Furthermore, we demonstrate that KLF2-mediated inhibition of Jun NH2-terminal kinase (JNK) and its downstream targets ATF2/c-Jun is dependent on the cytoskeleton. Specifically, KLF2 directs the formation of typical short basal actin filaments, we term shear fibers, which are distinct from thrombin- or TNF-α-induced stress fibers. KLF2 is shown to be essential for shear stress-induced cell alignment, concomitant shear fiber assembly and inhibition of JNK signaling. These findings link the specific effects of shear-induced KLF2 on endothelial morphology to the suppression of JNK MAPK signaling in vascular homeostasis via novel actin shear fibers.
Project description:The shear stress-induced transcription factor Krüppel-like factor 2 (KLF2) confers anti-inflammatory properties to endothelial cells through inhibition of activator protein 1, presumably by interfering with MAPK cascades. To gain insight into the regulation of these cascades by KLF2, we used antibody arrays in combination with time-course mRNA micro-array analysis. No gross changes in MAPKs were detected, rather phosphorylation of actin cytoskeleton-associated proteins, including Focal Adhesion Kinase, was markedly repressed by KLF2. Furthermore, we demonstrate that KLF2-mediated inhibition of Jun NH2-terminal kinase (JNK) and its downstream targets ATF2/c-Jun is dependent on the cytoskeleton. Specifically, KLF2 directs the formation of typical short basal actin filaments, we term shear fibers, which are distinct from thrombin- or TNF-α-induced stress fibers. KLF2 is shown to be essential for shear stress-induced cell alignment, concomitant shear fiber assembly and inhibition of JNK signaling. These findings link the specific effects of shear-induced KLF2 on endothelial morphology to the suppression of JNK MAPK signaling in vascular homeostasis via novel actin shear fibers. Tramscriptome profiling: Three independent isolates of Human Umbilical Vein Endothelial cells were transduced with lentiviral vectors expressing Kruppel Like Factor 2 (KLF2) or no protein (mock), and at time after transduction 24 h, 48 h, 72 h , RNA was isolated and hybridized to GPL4868 microarrays using dye swap procedure Kinome profiling: Two independent isolates of Human Umbilical Vein Endothelial cells were transduced with lentiviral vectors expressing Kruppel Like Factor 2 (KLF2) or no protein (mock), and at time after transduction 72 h , total cellular protein was isolated and hybridized to Kinexus KAM-1.1 phosphoprotein (kinexus) microarrays using dual color procedure in duplicate
Project description:The arterial endothelium’s response to its flow environment is critical to vascular homeostasis. The endothelial glycocalyx has been shown to play a major role in mechanotransduction, but the extent to which the components of the glycocalyx affect the overall function of the endothelium remains unclear. The objective of this study was to further elucidate the role of heparan sulfate as a mechanosensor on the surface of the arterial endothelium, by (1) expanding the variety of shear waveforms investigated, (2) continuously suppressing heparan sulfate expression rather than using a pre-flow batch treatment, and (3) performing microarray analysis on post-flow samples. Porcine aortic endothelial cells were exposed to non-reversing, reversing, and oscillatory shear waveforms for 24 hours with or without continuous heparan sulfate suppression with heparinase. All shear waveforms significantly increased the amount of heparan sulfate on the surface of the endothelium. Suppression of heparan sulfate to less than 25% of control levels did not inhibit shear-induced cell alignment or nitric oxide production, or alter gene expression, for any of the shear waveforms investigated. We infer that heparan sulfate on the surface of porcine aortic endothelial cells is not the primary mechanosensor for many shear-responsive endothelial cell functions in this species. Porcine aortic endothelial cells were exposed to 3 different shear waveforms for 24 hours with or without the addition of 300 mU/ml heparinase III to the flow media. The shear waveforms inculded Non-reversing (15 ± 15 dyne/cm2, 1 Hz), Steady (15 dyne/cm2), or Oscillatory (0 ± 15 dyne/cm2, 1 Hz) shear. Four replicates of each condition were performed for a total of 24 experiments. Each experimental sample was hybridized to an oligonucleotide array along with a standard reference sample (static cells).
Project description:The arterial endothelium’s response to its flow environment is critical to vascular homeostasis. The endothelial glycocalyx has been shown to play a major role in mechanotransduction, but the extent to which the components of the glycocalyx affect the overall function of the endothelium remains unclear. The objective of this study was to further elucidate the role of heparan sulfate as a mechanosensor on the surface of the arterial endothelium, by (1) expanding the variety of shear waveforms investigated, (2) continuously suppressing heparan sulfate expression rather than using a pre-flow batch treatment, and (3) performing microarray analysis on post-flow samples. Porcine aortic endothelial cells were exposed to non-reversing, reversing, and oscillatory shear waveforms for 24 hours with or without continuous heparan sulfate suppression with heparinase. All shear waveforms significantly increased the amount of heparan sulfate on the surface of the endothelium. Suppression of heparan sulfate to less than 25% of control levels did not inhibit shear-induced cell alignment or nitric oxide production, or alter gene expression, for any of the shear waveforms investigated. We infer that heparan sulfate on the surface of porcine aortic endothelial cells is not the primary mechanosensor for many shear-responsive endothelial cell functions in this species.
Project description:Biomechanical forces influence vascular function, but the molecular mechanisms regulating many of these mechano-activated cellular events remain largely uncharacterized. In particular, the vascular endothelium can sense alterations in hemodynamic shear stress which, in the context of adaptive remodeling or arteriogenesis, has been shown to lead to the generation of endothelial-derived signals critical for controlling blood vessel structure and function. Here, we sought to define the arteriogenic responses evoked in endothelial cells exposed to flow using transciptional profiling. Analysis of these transcriptional programs identified several genes previously shown to be important for endothelial-smooth muscle interactions and vascular remodeling, including the transcription factor kruppel-like factor 2 (KLF2).
Project description:Endothelial cell (EC)-enriched protein coding genes, such as endothelial nitric oxide synthase (eNOS), define quintessential EC-specific physiologic functions. It is not clear whether long noncoding RNAs (lncRNAs) also define cardiovascular cell-type specific phenotypes, especially in the vascular endothelium. Here, we report the existence of a set of EC-enriched lncRNAs and define a role for STEEL (spliced transcript – endothelial enriched lncRNA) in angiogenic potential, macrovascular/microvascular identity and shear stress responsiveness. STEEL is expressed from the terminus of the HOXD locus and is transcribed antisense to HOXD transcription factors. STEEL RNA increases the number and integrity of de novo perfused microvessels in an in vivo model and augments angiogenesis in vitro. The STEEL RNA is polyadenylated, nuclear-enriched and has microvascular predominance. Functionally, STEEL regulates a number of genes in diverse endothelial cells. Of interest, STEEL upregulates both eNOS and the transcription factor Kruppel-like factor 2 (KLF2), and is subject to feedback inhibition by both eNOS and shear-augmented KLF2. Mechanistically, STEEL upregulation of eNOS and KLF2 is transcriptionally mediated, in part, via interaction of chromatin-associated STEEL with the poly-ADP ribosylase, PARP1. For instance, STEEL recruits PARP1 to the KLF2 promoter. This work identifies a role for EC-enriched lncRNAs in the phenotypic adaptation of ECs to both body position and hemodynamic forces, and establishes a newer role for lncRNAs in the transcriptional regulation of EC identity.
Project description:d9 and d12 Mks were either cultured statically or subjected to shear flow for 30 min; at d9, half the Mks were placed back in culture for 30 min (60 min time point) Megakaryocytes (Mks) are exposed to shear flow as they migrate from the bone marrow hematopoietic compartment into circulation thus releasing platelets and pro/preplatelets directly into the blood stream. Shear forces have been now established as promoting Mk maturation and platelet biogenesis. In order to understand the underlying mechanisms that modulate the response of Mks to shear forces, we carried out transcriptional analysis on immature and mature stem cell-derived Mks that were exposed to physiologically-relevant shear (2.5 dyn/cm2). In immature (d9) Mks, shear exposure upregulated genes related to growth and Mk maturation, while in mature (d12) Mks, it upregulated genes involved in apoptosis and intracellular transport. Following shear-flow exposure, 6 AP-1 transcripts (ATF4, JUNB, JUN, FOSB, FOS, and JUND) were upregulated at d9 and two AP-1 proteins (JunD and c-Fos) were upregulated both at d9 and d12. Our data show that MAPK signaling is linked to both the shear-stress response and AP-1 upregulation. JNK phosphorylation increased significantly following shear stimulation, while JNK inhibition reduced shear-induced JunD protein expression. Although p38 phosphorylation did not increase following shear flow, its inhibition reduced shear-induced JunD and c-Fos protein expression. JNK inhibition reduced fibrinogen binding of d9 and d12 platelet-like particle s (PLPs) and P-selectin expression at d12 PLPs, while p38 inhibition reduced fibrinogen binding of d12 PLPs. Here we show that mechanotransduction of shear forces in Mks results in JNK activation, AP-1 upregulation, and downstream transcriptional changes that promote maturation of immature Mks and platelet biogenesis in mature Mks. Two- and Three-condition experiment (flow vs. static culture condition, d9 vs. d12, and 30 min vs. 60 min at d9); Biological replicates: 3; Technical replicates: 1 (dye-swap)
Project description:To investigate the regulation of the long non-coding RNA (lncRNA) transcriptome of endothelial cells in response to shear stress, gene expression profiling was performed using a microarray for both protein-coding genes and lncRNAs. The expression of known flow-induced protein coding genes, eNOS, KLF2, and KLF4, were quantified using real-time PCR. Identifying lncRNAs that are up-regulated or down-regulated in the presence or absence of laminar flow will provide insight into gene regulatory mechanisms that contribute to vascular homeostasis or disease.
Project description:d9 and d12 Mks were either cultured statically or subjected to shear flow for 30 min; at d9, half the Mks were placed back in culture for 30 min (60 min time point) Megakaryocytes (Mks) are exposed to shear flow as they migrate from the bone marrow hematopoietic compartment into circulation thus releasing platelets and pro/preplatelets directly into the blood stream. Shear forces have been now established as promoting Mk maturation and platelet biogenesis. In order to understand the underlying mechanisms that modulate the response of Mks to shear forces, we carried out transcriptional analysis on immature and mature stem cell-derived Mks that were exposed to physiologically-relevant shear (2.5 dyn/cm2). In immature (d9) Mks, shear exposure upregulated genes related to growth and Mk maturation, while in mature (d12) Mks, it upregulated genes involved in apoptosis and intracellular transport. Following shear-flow exposure, 6 AP-1 transcripts (ATF4, JUNB, JUN, FOSB, FOS, and JUND) were upregulated at d9 and two AP-1 proteins (JunD and c-Fos) were upregulated both at d9 and d12. Our data show that MAPK signaling is linked to both the shear-stress response and AP-1 upregulation. JNK phosphorylation increased significantly following shear stimulation, while JNK inhibition reduced shear-induced JunD protein expression. Although p38 phosphorylation did not increase following shear flow, its inhibition reduced shear-induced JunD and c-Fos protein expression. JNK inhibition reduced fibrinogen binding of d9 and d12 platelet-like particle s (PLPs) and P-selectin expression at d12 PLPs, while p38 inhibition reduced fibrinogen binding of d12 PLPs. Here we show that mechanotransduction of shear forces in Mks results in JNK activation, AP-1 upregulation, and downstream transcriptional changes that promote maturation of immature Mks and platelet biogenesis in mature Mks.
Project description:Human induced pluripotent stem cells (hiPSCs) are used to study organogenesis and model disease as well as being developed for regenerative medicine. Endothelial cells are among the many cell types differentiated from hiPSC, but their maturation and stabilization fall short of that in adult endothelium. We examined whether shear stress alone or in combination with pericyte co-culture would induce flow alignment and maturation of hiPSC-derived endothelial cells (hiPSC-ECs) but found no effects comparable to those in primary microvascular EC. In addition, hiPSC-ECs lacked a luminal glycocalyx, critical for vasculature homeostasis, shear stress sensing and signalling. We noted however, that hiPSC-EC have dysfunctional mitochondrial permeability transition pores, resulting in reduced mitochondrial function and increased reactive oxygen species (ROS). Closure of these pores by cyclosporine-A improved EC mitochondrial function but also restored the glycocalyx such that alignment to flow took place. These indicated that mitochondrial maturation is required for proper hiPSC-EC functionality.