Smooth muscle cells (SMCs) play a key role in atherogenesis. However, mechanisms regulating expansion and fate of pre-existing SMCs in atherosclerotic plaques remain poorly defined. Here we show that multiple SMC progenitors mix to form the aorta during development. In contrast, during atherogenesis, a single SMC gives rise to the smooth muscle-derived cells that initially coat the cap of atherosclerotic plaques. Subsequently, highly proliferative cap cells invade the plaque core, comprising the majority of plaque cells. Reduction of integrin β3 (Itgb3) levels in SMCs induces toll-like receptor 4 expression and thereby enhances Cd36 levels and cholesterol-induced transdifferentiation to a macrophage-like phenotype. Global Itgb3 deletion or transplantation of Itgb3(−/−) bone marrow results in recruitment of multiple pre-existing SMCs into plaques. Conditioned medium from Itgb3-silenced macrophages enhances SMC proliferation and migration. Together, our results suggest SMC contribution to atherogenesis is regulated by integrin β3-mediated pathways in both SMCs and bone marrow-derived cells.

Excess and ectopic smooth muscle cells (SMCs) are central to cardiovascular disease pathogenesis, but underlying mechanisms are poorly defined. For instance, pulmonary hypertension (PH) or elevated pulmonary artery blood pressure is a devastating disease with distal extension of smooth muscle to normally unmuscularized pulmonary arterioles. We identify novel SMC progenitors that are located at the pulmonary arteriole muscular-unmuscular border and express both SMC markers and the undifferentiated mesenchyme marker platelet-derived growth factor receptor-β (PDGFR-β). We term these cells “primed” because in hypoxia-induced PH, they express the pluripotency factor Kruppel-like factor 4 (KLF4), and in each arteriole, one of them migrates distally, dedifferentiates, and clonally expands, giving rise to the distal SMCs. Furthermore, hypoxia-induced expression of the ligand PDGF-B regulates primed cell KLF4 expression, and enhanced PDGF-B and KLF4 levels are required for distal arteriole muscularization and PH. Finally, in PH patients, KLF4 is markedly up-regulated in pulmonary arteriole smooth muscle, especially in proliferating SMCs. In sum, we have identified a pool of SMC progenitors that are critical for the pathogenesis of PH, and perhaps other vascular disorders, and therapeutic strategies targeting this cell type promise to have profound implications.

No abstract

The reconstitution of anti-viral cellular immunity following hematopoietic stem cell transplantation (HSCT) is crucial in preventing cytomegalovirus (CMV)-associated complications. Thus immunological monitoring has emerged as an important tool to better target pre-emptive anti-viral therapies. However, traditional laboratory-based assays are too cumbersome and complicated to implement in a clinical setting. Here we conducted a prospective study of a new whole blood assay (referred to as QuantiFERON-CMV®) to determine the clinical utility of measuring CMV-specific CD8+ T-cell responses as a prognostic tool. Forty-one evaluable allogeneic HSCT recipients underwent weekly immunological monitoring from day 21 post-transplant and of these 21 (51.2%) showed CMV reactivation and 29 (70.7%) developed acute graft-versus-host disease (GvHD). Patients with acute GvHD (grade≥2) within 6 weeks of transplant showed delayed reconstitution of CMV-specific T-cell immunity (p = 0.013) and a higher risk of CMV viremia (p = 0.026). The median time to stable CMV-specific immune reconstitution was 59 days and the incidence of CMV reactivation was lower in patients who developed this than those who did not (27% versus 65%; p = 0.031). Furthermore, a failure to reconstitute CMV-specific immunity soon after the onset of CMV viraemia was associated with higher peak viral loads (5685 copies/ml versus 875 copies/ml; p = 0.002). Hence, QuantiFERON-CMV® testing in the week following CMV viremia can be useful in identifying HSCT recipients at risk of complicated reactivation.

Metastasis is a multi-step process which requires the conversion of polarized epithelial cells to mesenchymal cells, Epithelial–Mesenchymal Transition (EMT). EMT is essential during embryonic morphogenesis and has been implicated in the progression of primary tumors towards metastasis. Hypoxia is known to induce EMT; however the molecular mechanism is still poorly understood. Using the A431 epithelial cancer cell line, we show that cells grown under hypoxic conditions migrated faster than cells grown under normal oxygen environment. Cells grown under hypoxia showed reduced adhesion to the extracellular matrix (ECM) probably due to reduced number of Vinculin patches. Growth under hypoxic conditions also led to down regulation of E-cadherin and up regulation of vimentin expression. The increased motility of cells grown under hypoxia could be due to redistribution of Rac1 to the plasma membrane as opposed to increased expression of Rac1. EGF (Epidermal Growth Factor) is a known inducer of EMT and growth of A431 cells in the absence of oxygen led to increased expression of EGFR (EGF Receptor). Treatment of A431 cells with EGF led to reduced cell adhesion to ECM, increased cell motility and other EMT characteristics. Furthermore, this transition was blocked by the monoclonal antibody Cetuximab. Cetuximab also blocked the hypoxia-induced EMT suggesting that cell growth under hypoxic conditions led to activation of EGFR signaling and induction of EMT phenotype.