Downregulation of G protein-coupled receptor kinase 4 protects against kidney ischemia-reperfusion injury.

Ischemia/reperfusion injury of the kidney is associated with high morbidity and mortality, and treatment of this injury remains a challenge. G protein-coupled receptor kinase 4 (GRK4) plays a vital role in essential hypertension and myocardial infarction, but its function in kidney ischemia/reperfusion injury remains undetermined. Among the GRK subtypes (GRK2-6) expressed in kidneys, the increase in GRK4 expression was much more apparent than that of the other four GRKs 24 hours after injury and was found to accumulate in the nuclei of injured mouse and human renal tubule cells. Gain- and loss-of-function experiments revealed that GRK4 overexpression exacerbated acute kidney ischemia/reperfusion injury, whereas kidney tubule-specific knockout of GRK4 decreased injury-induced kidney dysfunction. Necroptosis was the major type of tubule cell death mediated by GRK4, because GRK4 significantly increased receptor interacting kinase (RIPK)1 expression and phosphorylation, subsequently leading to RIPK3 and mixed lineage kinase domain-like protein (MLKL) phosphorylation after kidney ischemia/reperfusion injury, but was reversed by necrostatin-1 pretreatment (an RIPK1 inhibitor). Using co-immunoprecipitation, mass spectrometry, and siRNA screening studies, we identified signal transducer and activator of transcription (STAT)1 as a GRK4 binding protein, which co-localized with GRK4 in the nuclei of renal tubule cells. Additionally, GRK4 phosphorylated STAT1 at serine 727, whose inactive mutation effectively reversed GRK4-mediated RIPK1 activation and tubule cell death. Kidney-targeted GRK4 silencing with nanoparticle delivery considerably ameliorated kidney ischemia/reperfusion injury. Thus, our findings reveal that GRK4 triggers necroptosis and aggravates kidney ischemia/reperfusion injury, and its downregulation may provide a promising therapeutic strategy for kidney protection.

Hypoxia-reoxygenation enhances murine afferent arteriolar vasoconstriction by angiotensin II.

We tested the hypothesis that hypoxia-reoxygenation (H/R) augments vasoreactivity to angiotensin II (ANG II). In particular, we compared an in situ live kidney slice model with isolated afferent arterioles (C57Bl6 mice) to assess the impact of tubules on microvessel response. Hematoxylin and eosin staining was used to estimate slice viability. Arterioles in the slices were located by differential interference contrast microscopy, and responses to vasoactive substances were assessed. Cytosolic calcium transients and NADPH oxidase (NOX) mRNA expression were studied in isolated afferent arterioles. SOD activity was measured in live slices. Both experimental models were subjected to control and H/R treatment (60 min). Slices were further analyzed after 30-, 60-, and 90-min hypoxia followed by 10- or 20-min reoxygenation (H/R). H/R resulted in enhanced necrotic tissue damage compared with control conditions. To characterize the slice model, we applied ANG II (10-7 M), norepinephrine (NE; 10-5 M), endothelin-1 (ET-1; 10-7 M), and ATP (10-4 M), reducing the initial diameter to 44.5 ± 2.8, 50.0 ± 2.2, 45.3 ± 2.6, and 74.1 ± 1.8%, respectively. H/R significantly increased the ANG II response compared with control in live slices and in isolated afferent arterioles, although calcium transients remained similar. TEMPOL incubation prevented the H/R effect on ANG II responses. H/R significantly increased NOX2 mRNA expression in isolated arterioles. SOD activity was significantly decreased after H/R. Enhanced arteriolar responses after H/R occurred independently from the surrounding tissue, indicating no influence of tubules on vascular function in this model. The mechanism of increased ANG II response after H/R might be increased oxidative stress and increased calcium sensitivity of the contractile apparatus.

Renal hemodynamic effects of glucagon-like peptide-1 agonist are mediated by nitric oxide but not prostaglandin.

The incretin hormone, glucagon-like peptide-1 (GLP-1), is known for responding to dietary fat and carbohydrate. It elicits effects on pancreas, gut, and brain to stabilize blood glucose levels. We have previously reported that the GLP-1 agonist, exenatide, vasodilates the kidney and suppresses proximal reabsorption. The present study was undertaken to determine whether the renal effects of exenatide are mediated by nitric oxide (NO) and/or prostaglandins. Inulin clearance (glomerular filtration rate, GFR) and urine flow rate (UV) were measured in anesthetized rats before and during exenatide infusion (1 nmol/h iv). Animals were pretreated with cyclooxygenase (COX) inhibitor (meclofenamate), NO synthase (NOS) inhibitor (NG-monomethyl-l-arginine, l-NMMA), NO clamp (l-NMMA + sodium nitroprusside), or placebo. Effectiveness of COX inhibition was tested by measuring urinary prostaglandin E2 (UPGE2). Effectiveness of NOS blockade and NO clamp was determined by urinary NO degradation products (UNOx). Exenatide increased GFR, UV, UPGE2, and UNOx. Pretreatment with meclofenamate reduced UPGE2 by 75% and reduced the effect of exenatide on UPGE2 by 30% but did not modify the effects of exenatide on GFR or UV. Pretreatment with l-NMMA reduced UNOx and the impact of exenatide on GFR and UV by 50%. Pretreatment by NO clamp did not prevent UNOx from increasing during exenatide but blunted the effects of exenatide on GFR and UV. In conclusion, exenatide is a potent renal vasodilator and diuretic in the rat. These effects of exenatide are insensitive to COX inhibition but are mediated, in part, by NO.

Neuregulin-1 attenuates development of nephropathy in a type 1 diabetes mouse model with high cardiovascular risk.

Neuregulin-1 (NRG-1) is an endothelium-derived growth factor with cardioprotective and antiatherosclerotic properties and is currently being tested in clinical trials as a treatment for systolic heart failure. In clinical practice, heart failure often coexists with renal failure, sharing an overlapping pathophysiological background. In this study, we hypothesized that NRG-1 might protect against cardiomyopathy, atherosclerosis, and nephropathy within one disease process. We tested this hypothesis in a hypercholesterolemic apolipoprotein E-deficient (apoE(-/-)) type 1 diabetes mouse model prone to the development of cardiomyopathy, atherosclerosis, and nephropathy and compared the effects of NRG-1 with insulin. Upon onset of hyperglycemia induced by streptozotocin, apoE(-/-)mice were treated with vehicle, insulin, or recombinant human (rh)NRG-1 for 14 wk and were compared with nondiabetic apoE(-/-)littermates. Vehicle-treated diabetic apoE(-/-)mice developed left ventricular (LV) dilatation and dysfunction, dense atherosclerotic plaques, and signs of nephropathy. Nephropathy was characterized by abnormalities including hyperfiltration, albuminuria, increased urinary neutrophil gelatinase-associated lipocalin (NGAL), upregulation of renal fibrotic markers, and glomerulosclerosis. rhNRG-1 treatment induced systemic activation of ErbB2 and ErbB4 receptors in both heart and kidneys and prevented LV dilatation, improved LV contractile function, and reduced atherosclerotic plaque size. rhNRG-1 also significantly reduced albuminuria, NGALuria, glomerular fibrosis, and expression of fibrotic markers. Regarding the renal effects of rhNRG-1, further analysis showed that rhNRG-1 inhibited collagen synthesis of glomerular mesangial cells in vitro but did not affect AngII-induced vasoconstriction of glomerular arterioles. In conclusion, systemic administration of rhNRG-1 in hypercholesterolemic type 1 diabetic mice simultaneously protects against complications in the heart, arteries and kidneys.

Iodinated contrast media cause direct tubular cell damage, leading to oxidative stress, low nitric oxide, and impairment of tubuloglomerular feedback.

Iodinated contrast media (CM) have adverse effects that may result in contrast-induced acute kidney injury. Oxidative stress is believed to play a role in CM-induced kidney injury. We test the hypothesis that oxidative stress and reduced nitric oxide in tubules are consequences of CM-induced direct cell damage and that increased local oxidative stress may increase tubuloglomerular feedback. Rat thick ascending limbs (TAL) were isolated and perfused. Superoxide and nitric oxide were quantified using fluorescence techniques. Cell death rate was estimated using propidium iodide and trypan blue. The function of macula densa and tubuloglomerular feedback responsiveness were measured in isolated, perfused juxtaglomerular apparatuses (JGA) of rabbits. The expression of genes related to oxidative stress and the activity of superoxide dismutase (SOD) were investigated in the renal medulla of rats that received CM. CM increased superoxide concentration and reduced nitric oxide bioavailability in TAL. Propidium iodide fluorescence and trypan blue uptake increased more in CM-perfused TAL than in controls, indicating increased rate of cell death. There were no marked acute changes in the expression of genes related to oxidative stress in medullary segments of Henle's loop. SOD activity did not differ between CM and control groups. The tubuloglomerular feedback in isolated JGA was increased by CM. Tubular cell damage and accompanying oxidative stress in our model are consequences of CM-induced direct cell damage, which also modifies the tubulovascular interaction at the macula densa, and may therefore contribute to disturbances of renal perfusion and filtration.

Novel hemoglobin particles--promising new-generation hemoglobin-based oxygen carriers.

During the last 30 years, artificial oxygen carriers have been investigated intensively with the aim to develop universal blood substitutes. Favorably, hemoglobin-based oxygen carriers (HBOCs) are expected to meet the sophisticated requirements. However, the HBOCs tested until now show serious side effects, which resulted in failure of clinical trials and Food and Drug Administration disapproval. The main problem consists in vasoconstriction triggered by nitric oxide (NO) scavenging or/and oxygen oversupply in the pre-capillary arterioles. HBOCs with a size between 100 nm and 1 µm and high oxygen affinity are needed. Here we present a highly effective and simple fabrication procedure, which can provide hemoglobin particles (HbPs) with a narrow size distribution of around 700 nm, nearly uniform morphology, high oxygen affinity, and low immunogenicity. Isolated mouse glomeruli are successfully perfused with concentrated HbP suspensions without any observable vasoconstriction of the afferent arterioles. The results suggest no oxygen oversupply and limited NO scavenging by these particles, featuring them as a highly promising blood substitute.

Iodinated contrast media cause endothelial damage leading to vasoconstriction of human and rat vasa recta.

Contrast-induced acute kidney injury is an important clinical event with a worldwide increasing number of cases. Medullary hypoperfusion and hypoxia due to constriction of vasa recta are main factors in the pathophysiology of acute kidney injury. However, the mechanism of contrast media (CM)-induced vessel constriction is not known. We tested the hypothesis that vasa recta constriction is a consequence of endothelial dysfunction due to the cytotoxicity of CM. Human and rat descending vasa recta (DVR) were isolated and perfused with CM, and the luminal diameter was analyzed. For morphological analysis of the endothelium, renal arteries were CM perfused and then processed for electron microscopy. Transcellular electrical resistance was used to estimate CM-induced changes in the permeability of human umbilical vein endothelial cell (HUVEC) layers. Perfusion with CM constricted human and rat DRV (to 54.3 and 50.9% of initial diameter, respectively). This was blunted by adrenomedullin (77.7 and 77.1%, respectively). The ANG II response was enhanced by CM in rat DVR (reduction to 15.6 and 35.0% of initial diameter, respectively). Adrenomedullin blunted this effect (67.5%). CM led to endothelial damage of renal arteries characterized by a ragged surface, with sharply protruding intimal folds, spindle-like shape, and bulging in the lumen. These phenomena were reduced by adrenomedullin. The permeability of HUVEC cell layers was increased by CM, and this went along with increased myosin light chain phosporylation. Again, adremonedullin reduced the CM effect. Our study suggests that the constrictor effect of CM on the renal medullary microvasculature is a consequence of endothelial cell damage and the resulting endothelial dysfunction.

Gastrin mediates cardioprotection through angiogenesis after myocardial infarction by activating the HIF-1α/VEGF signalling pathway.

Acute myocardial infarction (MI) is one of the leading causes of death in humans. Our previous studies showed that gastrin alleviated acute myocardial ischaemia-reperfusion injury. We hypothesize that gastrin might protect against heart injury after MI by promoting angiogenesis. An MI model was simulated by ligating the anterior descending coronary artery in adult male C57BL/6J mice. Gastrin was administered twice daily by intraperitoneal injection for 2 weeks after MI. We found that gastrin reduced mortality, improved myocardial function with reduced infarct size and promoted angiogenesis. Gastrin increased HIF-1α and VEGF expression. Downregulation of HIF-1α expression by siRNA reduced the proliferation, migration and tube formation of human umbilical vein endothelial cells. These results indicate that gastrin restores cardiac function after MI by promoting angiogenesis via the HIF-1α/VEGF pathway.

Magnesium Presence Prevents Removal of Antigenic Nuclear-Associated Proteins from Bovine Pericardium for Heart Valve Engineering.

Current heart valve prostheses are associated with significant complications, including aggressive immune response, limited valve life expectancy, and inability to grow in juvenile patients. Animal derived "tissue" valves undergo glutaraldehyde fixation to mask tissue antigenicity; however, chronic immunological responses and associated calcification still commonly occur. A heart valve formed from an unfixed bovine pericardium (BP) extracellular matrix (ECM) scaffold, in which antigenic burden has been eliminated or significantly reduced, has potential to overcome deficiencies of current bioprostheses. Decellularization and antigen removal methods frequently use sequential solutions extrapolated from analytical chemistry approaches to promote solubility and removal of tissue components from resultant ECM scaffolds. However, the extent to which such prefractionation strategies may inhibit removal of antigenic tissue components has not been explored. We hypothesize that presence of magnesium in prefractionation steps causes DNA precipitation and reduces removal of nuclear-associated antigenic proteins. Keeping all variables consistent bar the addition or absence of magnesium (2 mM magnesium chloride hexahydrate), residual BP ECM scaffold antigenicity and removed antigenicity were assessed, along with residual and removed DNA content, ECM morphology, scaffold composition, and recellularization potential. Furthermore, we used proteomic methods to determine the mechanism by which magnesium presence or absence affects scaffold residual antigenicity. This study demonstrates that absence of magnesium from antigen removal solutions enhances solubility and subsequent removal of antigenic nuclear-associated proteins from BP. We therefore conclude that the primary mechanism of action for magnesium removal during antigen removal processes is avoidance of DNA precipitation, facilitating solubilization and removal of nuclear-associated antigenic proteins. Future studies are necessary to further facilitate solubility and removal of nuclear-associated antigenic proteins from xenogeneic ECM scaffolds, in addition to an in vivo assessing of the material.

Renal Oxygenation in the Pathophysiology of Chronic Kidney Disease.

Chronic kidney disease (CKD) is a significant health problem associated with high morbidity and mortality. Despite significant research into various pathways involved in the pathophysiology of CKD, the therapeutic options are limited in diabetes and hypertension induced CKD to blood pressure control, hyperglycemia management (in diabetic nephropathy) and reduction of proteinuria, mainly with renin-angiotensin blockade therapy. Recently, renal oxygenation in pathophysiology of CKD progression has received a lot of interest. Several advances have been made in our understanding of the determinants and regulators of renal oxygenation in normal and diseased kidneys. The goal of this review is to discuss the alterations in renal oxygenation (delivery, consumption and tissue oxygen tension) in pre-clinical and clinical studies in diabetic and hypertensive CKD along with the underlying mechanisms and potential therapeutic options.

Renal Oxygenation and Hemodynamics in Kidney Injury.

Acute kidney injury (AKI) continues to be a major therapeutic challenge. Despite significant advances made in cellular and molecular pathophysiology of AKI, major gaps in knowledge exist regarding the changes in renal hemodynamics and oxygenation in the early stages and through the continuum of AKI. Particular features of renal hemodynamics and oxygenation increase the susceptibility of the kidney to sustain injury due to oxygen demand-supply mismatch and also play an important role in the recovery and repair from AKI as well as the transition of AKI to chronic kidney disease. However, lack of well-established physiological biomarkers and noninvasive imaging techniques limit our understanding of the interactions between renal macro and microcirculation and tissue oxygenation in AKI. Advances in our ability to assess these parameters in preclinical and clinical AKI will enable the development of targeted therapeutics to improve clinical outcomes.

Effect of bovine pericardial extracellular matrix scaffold niche on seeded human mesenchymal stem cell function.

Numerous studies have focused on generation of unfixed bovine pericardium (BP) extracellular matrix (ECM) for clinical application. However, the extent to which maintenance of native ECM niche is capable of directing behavior of repopulating cells remains relatively unexplored. By exploiting the sidedness of BP scaffolds (i.e., serous or fibrous surface), this study aims to determine the effect of ECM niche preservation on cellular repopulation using different scaffold generation methods. BP underwent either sodium dodecyl sulfate (SDS) decellularization or stepwise, solubilization-based antigen removal using amidosulfobetaine-14 (ASB-14). SDS scaffolds were toxic to repopulating human mesenchymal stem cells (hMSC). Scanning electron microscopy revealed distinct surface ultrastructure of ASB-14 scaffolds based on native BP sidedness. Basement membrane structures on the serous side stimulated hMSC cell monolayer formation, whereas fibrous side facilitated cell penetration into scaffold. Additionally, serous side seeding significantly increased hMSC adhesion and proliferation rate compared to the fibrous side. Furthermore, scaffold ECM niche stimulated sidedness dependent differential hMSC human leukocyte antigen expression, angiogenic and inflammatory cytokine secretion. This work demonstrates that ECM scaffold preparation method and preservation of BP side-based niches critically affects in vitro cell growth patterns and behavior, which has implications for use of such ECM biomaterials in clinical practice.

Nonvasoconstrictive hemoglobin particles as oxygen carriers.

Artificial oxygen carriers, favorably hemoglobin-based oxygen carriers (HBOCs), are being investigated intensively during the last 30 years with the aim to develop a universal blood substitute. However, serious side effects mainly caused by vasoconstriction triggered by nitric oxide (NO) scavenging due to penetration of nanosized HBOCs through the endothelial gaps of the capillary walls and/or oxygen oversupply in the precapillary arterioles due to their low oxygen affinity led to failure of clinical trials and FDA disapproval. To avoid these effects, HBOCs with a size between 100 and 1000 nm and high oxygen affinity are needed. Here we present for the first time unique hemoglobin particles (HbPs) of around 700 nm with high oxygen affinity and low immunogenicity using a novel, highly effective, and simple technique. The fabrication procedure provides particles with a narrow size distribution and nearly uniform morphology. The content of hemoglobin (Hb) in the particles corresponded to 80% of the Hb content in native erythrocytes. Furthermore, we demonstrate a successful perfusion of isolated mouse glomeruli with concentrated HbP suspensions in vitro. A normal, nonvasoconstrictive behavior of the afferent arterioles is observed, suggesting no oxygen oversupply and limited NO scavenging by these particles, making them a highly promising blood substitute.