Endothelial nitric oxide synthase: from structure to function in one aspartic substitution

Cherney and co-workers examine the functional phenotype of the G894T eNOS polymorphism in a selected group of apparently healthy subjects. The investigators used L-arginine infusion and induced changes in renal hemodynamics. While L-arginine increased effective plasma flow and glomerular filtration rate in GG subjects, these responses were blunted in GT/TT subjects, suggesting that either the G894T polymorphism impairs eNOS function, or GG subjects exhibit augmented eNOS responsiveness to L-arginine. The complexity of this seemingly straightforward conclusion deserves elaboration

Mechanical stimulation induces Ca2+i transients and membrane depolarization in cultured endothelial cells Effects on Ca2+i in co-perfused smooth muscle cells

AbstractCytosolic Ca2+ concentration and membrane potential were monitored in individual cultured enothelial cells mechanically stimulated with a micropipette attached to the stage of a microscope. Both dimpling and poking of endothelial cells resulted in Ca2+i transients (from 63 ± 12 to 397 ± 52 nM, characterized by a refractory period of approx. 2 min) and cell depolarization. Ca2+i transients of the reduced amplitude (201 ± 41 nM) were evoked by mechanical stimulation of endothelial cells incubated in a Ca2+-free medium. Dimpling-induced Ca2+i transients were refractory to the pretreatments with pertussis toxin, colchicine, or cytochalasin B, and were not mimicked by an increase in the hydrodynamic pressure. In a co-perfusion system (endothelium: smooth muscle), both the KCl-induced depolarization and ionomycin-induced increase in Ca2+i in the endothelial cells resulted in the reduction of Ca2+i in the smooth muscle cells. The data reported are consistent with the phenomenon of vascular relaxation in response to the increased blood flow. We hypothesize that the mechanical interaction of the formed elements with the microvascular endothelium can serve as a pacemaker for the sustained relaxation of vascular smooth muscle

TLR4 and HMGB1: partners in crime?

Chen et al. confirmed the role of Toll-like receptor 4 (TLR4) in ischemic kidney injury using mice harboring spontaneous disabling mutations of the receptor and generated chimeras between TLR4−/− and TLR4+/+ mice. The major findings demonstrate the necessity of TLR4 in leukocytes, as well as in epithelial and endothelial cells, for the full-blown ischemic response and strongly suggest that the release of high-mobility group box 1 protein (HMGB1) from injured epithelia and/or endothelia activates leukocytes to generate proinflammatory cytokines, further exacerbating the injury to ischemic kidneys. These important findings provide an excellent platform for discussing the complexity of danger/alarm signaling in the kidney

Pathogenesis of endothelial cell dysfunction in chronic kidney disease: a retrospective and what the future may hold

AbstractCardiovascular complications dominate the landscape of chronic kidney diseases (CKD). Endothelial cell dysfunction (ECD) is a well-known culprit of cardiovascular morbidity and it develops in CKD with remarkable frequency. This brief overview of ECD in CKD scans two decades of studies performed in my laboratory, from genetic analyses to proteomic and metabolomics screens. I provide a detailed description of findings related to the premature senescence of endothelial cells, cell transition from the endothelial to mesenchymal phenotype, and stages of development of ECD. Clinical utility of some of these findings is illustrated with data on laser-Doppler flowmetry and imaging in patients with CKD. Some currently available and emerging therapeutic options for the management of ECD are briefly presented

Perioperative Implication of the Endothelial Glycocalyx

The endothelial glycocalyx (EG) is a gel-like layer lining the luminal surface of healthy vascular endothelium. Recently, the EG has gained extensive interest as a crucial regulator of endothelial funtction, including vascular permeability, mechanotransduction, and the interaction between endothelial and circulating blood cells. The EG is degraded by various enzymes and reactive oxygen species upon pro-inflammatory stimulus. Ischemia-reperfusion injury, oxidative stress, hypervolemia, and systemic inflammatory response are responsible for perioperative EG degradation. Perioperative damage of the EG has also been demonstrated, especially in cardiac surgery. However, the protection of the EG and its association with perioperative morbidity needs to be elucidated in future studies. In this review, the present knowledge about EG and its perioperative implication is discussed from an anesthesiologist\u27s perspective

Fibrogenic Secretome of Sirtuin 1-Deficient Endothelial Cells: Wnt, Notch and Glycocalyx Rheostat

Sirtuins (SIRT) are ubiquitous histone and protein deacetylases and a member of this family, SIRT1, is the best-studied one. Its functions in endothelial cells encompass branching angiogenesis, activation of endothelial nitric oxide synthase, regulation of proapoptotic and proinflammatory pathways, among others. Defective SIRT1 activity has been described in various cardiovascular, renal diseases and in aging-associated conditions. Therefore, understanding of SIRT1-deficient, endothelial dysfunctional phenotype has much to offer clinically. Here, we summarize recent studies by several investigative teams of the characteristics of models of global endothelial SIRT1 deficiency, the causes of facilitative development of fibrosis in these conditions, dissect the protein composition of the aberrant secretome of SIRT1-deficient endothelial cells and present several components of this aberrant secretome that are involved in fibrogenesis via activation of fibroblasts to myofibroblasts. These include ligands of Wnt and Notch pathways, as well as proteolytic fragments of glycocalyx core protein, syndecan-4. The latter finding is crucial for understanding the degradation of glycocalyx that accompanies SIRT1 deficiency. This spectrum of abnormalities associated with SIRT1 deficiency in endothelial cells is essential for understanding the origins and features of endothelial dysfunction in a host of cardiovascular and renal diseases

Interleukin-6 Increases Matrix Metalloproteinase-14 (MMP-14) Levels via Down-Regulation of p53 to Drive Cancer Progression

Matrix metalloproteinases (MMPs) play critical roles in cancer invasion and metastasis by digesting basement membrane and extracellular matrix (ECM). Much attention has focused on the enzymatic activities of MMPs; however, the regulatory mechanism of MMP expression remains elusive. By employing bioinformatics analysis, we identified a potential p53 response element within the MMP-14 promoter. Experimentally, we found that p53 can repress MMP-14 promoter activity, whereas deletion of this p53 response element abrogated this effect. Furthermore, we found that p53 expression decreases MMP-14 mRNA and protein levels and attenuates MMP-14-mediated cellular functions. Additional promoter analysis and chromatin immunoprecipitation studies identified a mechanism of regulation of MMP-14 expression by which p53 and transcription factor Sp1 competitively bind to the promoter. As the correlation between inflammation and cancer aggressiveness is well described, we next sought to evaluate if inflammatory cytokines could differentially affect p53 and MMP-14 levels. We demonstrate that interleukin-6 (IL-6) down-regulates p53 protein levels and thus results in a concomitant increase in MMP-14 expression, leading to enhanced cancer cell invasion and metastasis. Our data collectively indicate a novel mechanism of regulation of MMP-14 by a cascade of IL-6 and p53, demonstrating that the tumor microenvironment directly stimulates molecular changes in cancer cells to drive an invasive phenotype

Instructive Role of the Microenvironment in Preventing Renal Fibrosis

Accumulation of myofibroblasts is a hallmark of renal fibrosis. A significant proportion of myofibroblasts has been reported to originate via endothelial-mesenchymal transition. We initially hypothesized that exposing myofibroblasts to the extract of endothelial progenitor cells (EPCs) could reverse this transition. Indeed, in vitro treatment of transforming growth factor-beta1 (TGF-beta1)-activated fibroblasts with EPC extract prevented expression of alpha-smooth muscle actin (alpha-SMA); however, it did not enhance expression of endothelial markers. In two distinct models of renal fibrosis-unilateral ureteral obstruction and chronic phase of folic acid-induced nephropathy-subcapsular injection of EPC extract to the kidney prevented and reversed accumulation of alpha-SMA-positive myofibroblasts and reduced fibrosis. Screening the composition of EPC extract for cytokines revealed that it is enriched in leukemia inhibitory factor (LIF) and vascular endothelial growth factor. Only LIF was capable of reducing fibroblast-to-myofibroblast transition of TGF-beta1-activated fibroblasts. In vivo subcapsular administration of LIF reduced the number of myofibroblasts and improved the density of peritubular capillaries; however, it did not reduce the degree of fibrosis. A receptor-independent ligand for the gp130/STAT3 pathway, hyper-interleukin-6 (hyper-IL-6), not only induced a robust downstream increase in pluripotency factors Nanog and c-Myc but also exhibited a powerful antifibrotic effect. In conclusion, EPC extract prevented and reversed fibroblast-to-myofibroblast transition and renal fibrosis. The component of EPC extract, LIF, was capable of preventing development of the contractile phenotype of activated fibroblasts but did not eliminate TGF-beta1-induced collagen synthesis in cultured fibroblasts and models of renal fibrosis, whereas a receptor-independent gp130/STAT3 agonist, hyper-IL-6, prevented fibrosis. In summary, these studies, through the evolution from EPC extract to LIF and then to hyper-IL-6, demonstrate the instructive role of microenvironmental cues and may provide in the future a facile strategy to prevent and reverse renal fibrosis. Stem Cells Translational Medicine 2017;6:992-1005

Untargeted Plasma Metabolite Profiling Reveals the Broad Systemic Consequences of Xanthine Oxidoreductase Inactivation in Mice

A major challenge in systems biology is integration of molecular findings for individual enzyme activities into a cohesive high-level understanding of cellular metabolism and physiology/pathophysiology. However, meaningful prediction for how a perturbed enzyme activity will globally impact metabolism in a cell, tissue or intact organisms is precluded by multiple unknowns, including in vivo enzymatic rates, subcellular distribution and pathway interactions. To address this challenge, metabolomics offers the potential to simultaneously survey changes in thousands of structurally diverse metabolites within complex biological matrices. The present study assessed the capability of untargeted plasma metabolite profiling to discover systemic changes arising from inactivation of xanthine oxidoreductase (XOR), an enzyme that catalyzes the final steps in purine degradation. Using LC-MS coupled with a multivariate statistical data analysis platform, we confidently surveyed >3,700 plasma metabolites (50–1,000 Da) for differential expression in XOR wildtype vs. mice with inactivated XOR, arising from gene deletion or pharmacological inhibition. Results confirmed the predicted derangements in purine metabolism, but also revealed unanticipated perturbations in metabolism of pyrimidines, nicotinamides, tryptophan, phospholipids, Krebs and urea cycles, and revealed kidney dysfunction biomarkers. Histochemical studies confirmed and characterized kidney failure in xor-nullizygous mice. These findings provide new insight into XOR functions and demonstrate the power of untargeted metabolite profiling for systemic discovery of direct and indirect consequences of gene mutations and drug treatments