Li-Jing Chen

Shear Stress Inhibits Smooth Muscle Cell–Induced Inflammatory Gene Expression in Endothelial Cells Role of NF-κB

Objectives—Vascular endothelial cells (ECs) are influenced by shear stress and neighboring smooth muscle cells (SMCs). We investigated the inflammation-relevant gene expression in EC/SMC cocultures under static condition and in response to shear stress. Materials and Methods—Under static condition, DNA microarrays and reverse-transcription polymerase chain reaction identified 23 inflammation-relevant genes in ECs whose expression was significantly affected by coculture with SMCs, with 18 upregulated and 5 downregulated. Application of shear stress (12 dynes/cm2) to the EC side of the coculture for 6 hours inhibited most of the proinflammatory gene expressions in ECs induced by coculture with SMCs. Inhibition of nuclear factor-&kgr;B (NF-&kgr;B) activation by the p65-antisense, lactacystin, and N-acetyl-cysteine blocked the coculture-induced EC expression of proinflammatory genes, indicating that the NF-&kgr;B binding sites in the promoters of these genes play a significant role in their expression as a result of coculture with SMCs. Chromatin immunoprecipitation assays demonstrated the in vivo regulation of NF-&kgr;B recruitment to selected target promoters. Shear stress inhibited the SMC coculture-induced NF-&kgr;B activation in ECs and monocytic THP-1 cell adhesion to ECs. Conclusions—Our findings suggest that shear stress plays an inhibitory role in the proinflammatory gene expression in ECs located in close proximity to SMCs.

MicroRNA Mediation of Endothelial Inflammatory Response to Smooth Muscle Cells and Its Inhibition by Atheroprotective Shear Stress

RATIONALE In atherosclerotic lesions, synthetic smooth muscle cells (sSMCs) induce aberrant microRNA (miR) profiles in endothelial cells (ECs) under flow stagnation. Increase in shear stress induces favorable miR modulation to mitigate sSMC-induced inflammation. OBJECTIVE To address the role of miRs in sSMC-induced EC inflammation and its inhibition by shear stress. METHODS AND RESULTS Coculturing ECs with sSMCs under static condition causes initial increases of 4 anti-inflammatory miRs (146a/708/451/98) in ECs followed by decreases below basal levels at 7 days; the increases for miR-146a/708 peaked at 24 hours and those for miR-451/98 lasted for only 6 to 12 hours. Shear stress (12 dynes/cm(2)) to cocultured ECs for 24 hours augments these 4 miR expressions. In vivo, these 4 miRs are highly expressed in neointimal ECs in injured arteries under physiological levels of flow, but not expressed under flow stagnation. MiR-146a, miR-708, miR-451, and miR-98 target interleukin-1 receptor-associated kinase, inhibitor of nuclear factor-κB kinase subunit-γ, interleukin-6 receptor, and conserved helix-loop-helix ubiquitous kinase, respectively, to inhibit nuclear factor-κB signaling, which exerts negative feedback control on the biogenesis of these miRs. Nuclear factor-E2-related factor (Nrf)-2 is critical for shear-induction of miR-146a in cocultured ECs. Silencing either Nrf-2 or miR-146a led to increased neointima formation of injured rat carotid artery under physiological levels of flow. Overexpressing miR-146a inhibits neointima formation of rat or mouse carotid artery induced by injury or flow cessation. CONCLUSIONS Nrf-2-mediated miR-146a expression is augmented by atheroprotective shear stress in ECs adjacent to sSMCs to inhibit neointima formation of injured arteries.

Regulation of fibrillar collagen-mediated smooth muscle cell proliferation in response to chemical stimuli by telomere reverse transcriptase through c-Myc

Human telomerase reverse transcriptase (hTERT) and oncogene c-Myc have been shown to regulate cell proliferation. Our previous studies demonstrated that fibrillar collagen mediates vascular smooth muscle cell (SMC) cycle progression and proliferation in response to platelet-derived growth factor (PDGF)-BB and interleukin (IL)-1β. However, whether hTERT and c-Myc are involved in these fibrillar collagen-mediated SMC responses remain unclear. The present study elucidated the regulatory role of hTERT and c-Myc in PDGF-BB/IL-1β-induced cell cycle progression in SMCs on fibrillar collagen and its underlying mechanisms. Our results showed that PDGF-BB and IL-1β exert synergistic effects to induce hTERT expression, but not its activity, in human arterial SMCs on fibrillar collagen. This PDGF-BB/IL-1β-induced up-regulation of hTERT contributes to cell cycle progression in SMCs through the up-regulation of cyclin-dependent kinase-6 and down-regulations of p27(KIP1) and p21(CIP1). In addition, PDGF-BB/IL-1β induces up-regulation of c-Myc in SMCs on fibrillar collagen; this response is mediated by the increased binding of hTERT, which can form complexes with TPP1 and hnRNPK, to the guanine-rich region of the c-Myc promoter and consequently contributes to cell cycle progression in SMCs on fibrillar collagen. Moreover, the PDGF-BB/IL-1β-induced hTERT and c-Myc expressions are regulated by phosphatidylinositol 3-kinase/Akt in SMCs on fibrillar collagen. Our findings provide insights into the mechanisms by which hTERT and c-Myc regulates SMC cell cycle progression and proliferation on fibrillar collagen in response to chemical stimuli.

Vascular Endothelial Mechanosensors in Response to Fluid Shear Stress

The endothelium consists of a single layer of vascular endothelial cells (ECs) and serves as a selective barrier between the blood and arteries. ECs are constantly exposed to blood flow- and pulsatile blood pressure-induced hemodynamic forces. The cells are able to convert these mechanical stimuli into biochemical signals and then transmit the signals into the cell interior to affect cellular functions. These mechanical stimuli are detected by multiple mechanosensors in ECs that activate signaling pathways through their associated adaptor proteins, eventually leading to the maintenance of vascular homeostasis or the development of the pathogenesis of vascular disorders. These mechanosensors are distributed in different parts of the ECs, including the cell membrane, cell-to-cell junctions, the cytoplasm, and the nucleus. This review attempts to bring together recent findings on these mechanosensors and presents a conceptual framework for understanding the regulation of endothelial mechanosensors in response to hemodynamic forces. With verification by in vitro and in vivo evidence, endothelial mechanosensors have been demonstrated to contribute to health and disease by regulating physiological and pathophysiological processes in response to mechanical stimuli.