Nerve growth factor regulates endothelial cell survival and pathological retinal angiogenesis

The mechanism underlying vasoproliferative retinopathies like retinopathy of prematurity (ROP) is hypoxia‐triggered neovascularisation. Nerve growth factor (NGF), a neurotrophin supporting survival and differentiation of neuronal cells may also regulate endothelial cell functions. Here we studied the role of NGF in pathological retinal angiogenesis in the course of the ROP mouse model. Topical application of NGF enhanced while intraocular injections of anti‐NGF neutralizing antibody reduced pathological retinal vascularization in mice subjected to the ROP model. The pro‐angiogenic effect of NGF in the retina was mediated by inhibition of retinal endothelial cell apoptosis. In vitro, NGF decreased the intrinsic (mitochondria‐dependent) apoptosis in hypoxia‐treated human retinal microvascular endothelial cells and preserved the mitochondrial membrane potential. The anti‐apoptotic effect of NGF was associated with increased BCL2 and reduced BAX, as well as with enhanced ERK and AKT phosphorylation, and was abolished by inhibition of the AKT pathway. Our findings reveal an anti‐apoptotic role of NGF in the hypoxic retinal endothelium, which is involved in promoting pathological retinal vascularization, thereby pointing to NGF as a potential target for proliferative retinopathies.     

High molecular weight kininogen regulates platelet-leukocyte interactions by bridging Mac-1 and glycoprotein Ib

Leukocyte-platelet interaction is important in mediating leukocyte adhesion to a thrombus and leukocyte recruitment to a site of vascular injury. This interaction is mediated at least in part by the beta2-integrin Mac-1 (CD11b/CD18) and its counter-receptor on platelets, glycoprotein Ibalpha (GPIbalpha). High molecular weight kininogen (HK) was previously shown to interact with both GPIbalpha and Mac-1 through its domains 3 and 5, respectively. In this study we investigated the ability of HK to interfere with the leukocyte-platelet interaction. In a purified system, HK binding to GPIbalpha was inhibited by HK domain 3 and the monoclonal antibody (mAb) SZ2, directed against the epitope 269-282 of GPIbalpha, whereas mAb AP1, directed to the region 201-268 of GPIbalpha had no effect. In contrast, mAb AP1 inhibited the Mac-1-GPIbalpha interaction. Binding of GPIbalpha to Mac-1 was enhanced 2-fold by HK. This effect of HK was abrogated in the presence of HK domains 3 or 5 or peptides from the 475-497 region of the carboxyl terminus of domain 5 as well as in the presence of mAb SZ2 but not mAb AP1. Whereas no difference in the affinity of the Mac-1-GPIbalpha interaction was observed in the absence or presence of HK, maximal binding of GPIbalpha to Mac-1 doubled in the presence of HK. Moreover, HK/HKa increased the Mac-1-dependent adhesion of myelomonocytic U937 cells and K562 cells transfected with Mac-1 to immobilized GPIbalpha or to GPIbalpha-transfected Chinese hamster ovary cells. Finally, Mac-1-dependent adhesion of neutrophils to surface-adherent platelets was enhanced by HK. Thus, HK can bridge leukocytes with platelets by interacting via its domain 3 with GPIbalpha and via its domain 5 with Mac-1 thereby augmenting the Mac-1-GPIbalpha interaction. These distinct molecular interactions of HK with leukocytes and platelets contribute to the regulation of the adhesive behavior of vascular cells and provide novel molecular targets for reducing atherothrombotic pathologies.     

Multiscale, structure-based modeling for the elastic mechanical behavior of arterial walls

Passive elastic behavior of arterial wall remains difficult to model. Although phenomenological and structural models exist, the question of how the three-dimensional network structure of the collagen in the artery determines its mechanical properties is still open. A model is presented that incorporates a collagen network as well as the noncollagenous material that comprise the artery. The collagen architecture is represented as a network of interconnected fibers, and a neo-Hookean constitutive equation is used to describe the contribution of the noncollagenous matrix. The model is multiscale in that volume-averaging theory is applied to the collagen network, and it is structural in that parameters of the microstructure of the collagen network were considered instead of a macroscopic constitutive law. The computational results provided a good fit to published experimental data for decellularized porcine carotid arteries. The model predicted increased circumferential compliance for increased axial stretch, consistent with previously published reports, and a relatively small sensitivity to open angle. Even at large extensions, the model predicted that the noncollagenous matrix would be in compression, preventing collapse of the collagen network. The incorporation of fiber-fiber interactions led to an accurate model of artery wall behavior with relatively few parameters. The counterintuitive result that the noncollagenous component is in compression during extension and inflation of the tissue suggests that the collagen is important even at small strains, with the noncollagenous components supporting the network, but not resisting the load directly. More accurate representation of the microstructure of the artery wall is needed to explore this issue further.     

A novel pathway of HMGB1-mediated inflammatory cell recruitment that requires Mac-1-integrin

High-mobility group box 1 (HMGB1) is released extracellularly upon cell necrosis acting as a mediator in tissue injury and inflammation. However, the molecular mechanisms for the proinflammatory effect of HMGB1 are poorly understood. Here, we define a novel function of HMGB1 in promoting Mac-1-dependent neutrophil recruitment. HMGB1 administration induced rapid neutrophil recruitment in vivo. HMGB1-mediated recruitment was prevented in mice deficient in the beta2-integrin Mac-1 but not in those deficient in LFA-1. As observed by bone marrow chimera experiments, Mac-1-dependent neutrophil recruitment induced by HMGB1 required the presence of receptor for advanced glycation end products (RAGE) on neutrophils but not on endothelial cells. In vitro, HMGB1 enhanced the interaction between Mac-1 and RAGE. Consistently, HMGB1 activated Mac-1 as well as Mac-1-mediated adhesive and migratory functions of neutrophils in a RAGE-dependent manner. Moreover, HMGB1-induced activation of nuclear factor-kappaB in neutrophils required both Mac-1 and RAGE. Together, a novel HMGB1-dependent pathway for inflammatory cell recruitment and activation that requires the functional interplay between Mac-1 and RAGE is described here.     

Transforming growth factor-β modulates pancreatic cancer associated fibroblasts cell shape,stiffness and invasion

Background

Tumor microenvironment consists of the extracellular matrix (ECM), stromal cells, such as fibroblasts (FBs) and cancer associated fibroblasts (CAFs), and a myriad of soluble factors. In many tumor types, including pancreatic tumors, the interplay between stromal cells and the other tumor microenvironment components leads to desmoplasia, a cancer-specific type of fibrosis that hinders treatment. Transforming growth factor beta (TGF-β) and CAFs are thought to play a crucial role in this tumor desmoplastic reaction, although the involved mechanisms are unknown.

Regulation of integrin activity and signalling

The ability of cells to attach to each other and to the extracellular matrix is of pivotal significance for the formation of functional organs and for the distribution of cells in the body. Several molecular families of proteins are involved in adhesion, and recent work has substantially improved our understanding of their structures and functions. Also, these molecules are now being targeted in the fight against disease. However, less is known about how their activity is regulated. It is apparent that among the different classes of adhesion molecules, the integrin family of adhesion receptors is unique in the sense that they constitute a large group of widely distributed receptors, they are unusually complex and most importantly their activities are strictly regulated from the inside of the cell. The activity regulation is achieved by a complex interplay of cytoskeletal proteins, protein kinases, phosphatases, small G proteins and adaptor proteins. Obviously, we are only in the beginning of our understanding of how the integrins function, but already now fascinating details have become apparent. Here, we describe recent progress in the field, concentrating mainly on mechanistical and structural studies of integrin regulation. Due to the large number of articles dealing with integrins, we focus on what we think are the most exciting and rewarding directions of contemporary research on cell adhesion and integrins.