Jeffrey R. Bender MD
Robert I. Levy Professor of Medicine (Cardiology) and Professor of Immunobiology; Associate Chief, Cardiovascular Medicine
Inflammatory, Immune, Metabolic and Hormonal Effects on the Endothelium
Defining cellular, molecular and immunological mechanisms governing leukocyte-endothelial cell (EC) interactions and endothelial dysfunction, and testing these molecular discoveries in animal vascular pathology models, include studies of:
- molecular mechanisms of intercellular adhesion;
- leukocyte-mediated vascular injury;
- influence of ovarian steroid hormones on endothelial activation; and
- effects of lipid abnormalities associated with the metabolic syndrome on angiogenesis.
Studying the integrin LFA-1 as a transmembrane signaling molecule in T lymphocytes and macrophages, evaluating nuclear targets and stabilization of activation mRNAs encoding cytokines and chemokines involved in atherogenesis, plaque instability, allograft rejection and angiogenesis; also using recently generated mice with leukocyte-specific, integrin-induced, mRNA regulatory gene deletions. Studying the effects of 17b-estradiol on rapid, novel membrane estrogen receptor-mediated signaling in EC, leading to nitric oxide synthase activation. Newest interest is “molecular imaging”, merging in vivo imaging methods with basic biologic principles to evaluate disease mechanisms and progression.
Extensive Research Description
My laboratory has had a longstanding interest in inflammation and immunity, as they relate to vascular physiology and pathology. The interactions between mononuclear leukocytes and endothelial cells play major roles in atherogenesis, acute and chronic manifestations of atherosclerosis, angiogenesis and allograft rejection. We have extended these studies to evaluating effects of ovarian steroid hormones on endothelial function. The work is performed at the cellular, molecular, and pre-clinical animal model levels. Our major efforts are directed at:
(1) Integrin-dependent leukocyte adhesion and T cell/macrophage gene expression.
We have discovered that when β2 integrins are engaged in T lymphocytes, labile mRNAs that are normally rapidly degraded are markedly stabilized. This includes transcripts encoding many immune and pro-inflammatory cytokines, such as TNF, IFN-γ, IL-1, and IL-17. We have defined the signal transduction cascade, which involves Rho family GTPases, and modulation of select RNA-binding proteins, most notably HuR. Through proteomics approaches, we have recently defined integrin-induced nuclear protein-protein interactions, which we believe will be important targets for molecular therapeutics. In addition to our studies on cells of the adaptive immune system, we have recently extended our work to innate immune cells, namely monocyte/macrophages. Many of the aforementioned signaling events occur in these cells as well. Relevant integrin-stabilized mRNAs in macrophages include those encoding angiogenic molecules, such as VEGF, MMPs and angiopoietins, and many of the pro-inflammatory molecules mentioned above. To determine the role of this adhesion-induced mRNA stabilization mechanism in vivo, we have recently targeted the HuR gene, and are using tissue-specific knockout mice for pre-clinical studies.
Macrophage-specific HuR knockouts indeed have prominent angiogenic defects in response to inflammation or ischemia. Vascular remodeling, atherosclerosis and allograft rejection models are being developed with these genetically modified animals.
(2) Influence of ovarian steroid hormones on endothelial activation and endothelial progenitor cell function.
The effects of estrogen on the endothelium remains a major question, despite clinical controversies regarding hormone replacement therapy in postmenopausal women, We have defined a splice form of estrogen receptor (ER)α, ER46, that is plasma membrane-targeted in endothelial cells and which initiates rapid signaling responses, leading to eNOS activation, nitric oxide release and vasodilation in vivo. Most recently, we have used a variety of cell imaging techniques, including FRET and TIRF microscopy, to demonstrate that ER46 has transmembrane spanning and ectodomains, and multiple membrane pools. This has never been described for a steroid hormone receptor, and provides a tremendous opportunity for differential therapeutic targeting.
(3) Effects of metabolic syndrome-associated lipids on endothelial function.
We have recently defined a series of endothelial cell signaling defects imparted by free fatty acids, leading to a state of "VEGF resistance", and greatly impaired responses to angiogenic growth factors. We have documented a mechanistic role of ceramide generation, in vitro, and demonstrated that such lipids cause impaired angiogenic responses to hindlimb ischemia in murine models. Current studies include mapping the cellular and molecular defects, those which occur both at the plasma membrane and Golgi.