Podocyte Injury Associated with Mutant α-Actinin-4

Focal segmental glomerulosclerosis (FSGS) is an important cause of proteinuria and nephrotic syndrome in humans. The pathogenesis of FSGS may be associated with glomerular visceral epithelial cell (GEC; podocyte) injury, leading to apoptosis, detachment, and “podocytopenia”, followed by glomerulosclerosis. Mutations in α-actinin-4 are associated with FSGS in humans. In cultured GECs, α-actinin-4 mediates adhesion and cytoskeletal dynamics. FSGS-associated α-actinin-4 mutants show increased binding to actin filaments, compared with the wild-type protein. Expression of an α-actinin-4 mutant in mouse podocytes in vivo resulted in proteinuric FSGS. GECs that express mutant α-actinin-4 show defective spreading and motility, and such abnormalities could alter the mechanical properties of the podocyte, contribute to cytoskeletal disruption, and lead to injury. The potential for mutant α-actinin-4 to injure podocytes is also suggested by the characteristics of this mutant protein to form microaggregates, undergo ubiquitination, impair the ubiquitin-proteasome system, enhance endoplasmic reticulum stress, and exacerbate apoptosis

Decarbonization of aviation via hydrogen propulsion: technology performance targets and energy system impacts

The aviation sector is challenging to decarbonize since aircraft require high power and energy per unit of weight. Liquid hydrogen is an interesting solution due to its high gravimetric energy density, minimal warming impact, and low-carbon production potential. We quantify the performance targets for fuel cell systems and on-board storage to enable hydrogen-powered regional aviation. We then explore the energy infrastructure impacts of meeting this additional H2 demand in the European context under deep decarbonization scenarios. We find that minimal payload reduction would be needed for powering regional aviation up to 1000 nmi if fuel cell system specific power of 2 kW/kg and tank gravimetric index of 50% can be achieved. The energy systems analysis highlights the importance of utilizing multiple technology options: such as nuclear expansion and natural gas reforming with CCS for hydrogen production. Levelized cost of liquid hydrogen as low as 3.5 Euros/kg demonstrates pathways for Europe to achieve cost-competitive production.Comment: 25 pages, 6 figures. (38 pages with SI, 7 SI figures

Mesenteroaxial volvulus in an adult: time is of the essence in acute presentation

Acute gastric volvulus is an uncommon condition with severe repercussions if untreated in the acute presentation. We describe such a case. We assert that computed tomography (CT) should be the first line of investigatio

Cytosolic calcium and protein kinase C reduce complement-mediated glomerular epithelial injury

Cytosolic calcium and protein kinase C reduce complement-mediated glomerular epithelial injury. In rat membranous nephropathy, proteinuria is due to formation of the C5b-9 membrane attack complex of complement (C), and is associated with morphological evidence of glomerular epithelial cell (GEC) injury. Analogous morphological changes are induced by C5b-9 in cultured GEC. In addition, in cultured GEC C5b-9 induces Ca2+ influx, as well as Ca2+ mobilization and increased 1,2-diacylglycerol due to the activation of phospholipase C. In this study we investigated how this GEC activation pattern might influence C-mecliated GEC injury. We demonstrate that the C5b-9-induced increase in cytosolic Ca2+ concentration ([Ca2+]i) did not impair ATP generation by mitochondria, suggesting that it does not contribute to cytotoxicity. Moreover, this increase in [Ca2+]i protected GEC from C-mediated cytolysis. However, a large increase in [Ca2+]i (produced by the Ca2+ ionophore A23187) impaired ATP generation and aggravated C-mediated cytotoxicity, suggesting that intact mitochondrial activity is necessary for GEC to withstand C attack. Activation of protein kinase C (PKC) by phorbol myristate acetate (PMA) also decreased C-mediated cytolysis. Conversely, C lysis was enhanced in GEC that had been pretreated for 18 hours with a high dose of PMA to deplete PKC, and following PKC inhibition with H-7. Therefore, PKC activation, possibly resulting from C5b-9-induced increase in 1,2-diacylglycerol, triggered mechanisms that protected GEC from C-mediated injury. Thus, as a consequence of C5b-9-induced phospholipase activation, the amount of C-induced GEC injury is diminished

Glomerular epithelial cell products stimulate mesangial cell proliferation in culture

Glomerular epithelial cell products stimulate mesangial cell proliferation in culture. Glomerular epithelial cells (GEC) and mesangial cells (MC) are both involved in glomerular diseases. To elucidate potential interactions between these glomerular cell types, we examined whether products of GEC affect the proliferative activity of MC. We found that cultured rat GEC secrete soluble factors into the supernate (GEC-CM) that induce proliferation of quiescent rat MC. The mitogenic activity was trypsin sensitive and partially heat-labile. Biochemical analysis of GEC-CM by gel filtration HPLC, reverse phase HPLC, and isoelectric focusing revealed at least three mitogenic fractions as well as inhibitory activity present in GEC-CM. Competitive binding assays with 125I-labeled PDGF did not show significant amounts of PDGF in GEC-CM. The biochemical features of the GEC-derived MC growth factors are distinct from IL-6, PDGF, bFGF, and endothelin, previously described GEC-derived MC growth factors. Additionally, significant contributions of known growth factors such as IL-1, IL-2, IL-3, IL-4, IL-5, TNFα, TGFβ, and GM-CSF are unlikely. The results indicate that GEC produce several biochemically-distinct MC growth regulators. While these epithelial cell-derived mitogens for MC require further characterization, they may play an important role in the regulation of MC replication, such as during embryogenesis and glomerular disease

Genetic ablation of calcium-independent phospholipase A2γ induces glomerular injury in mice

Glomerular visceral epithelial cells (podocytes) play a critical role in the maintenance of glomerular permselectivity. Podocyte injury, manifesting as proteinuria, is the cause of many glomerular diseases. We reported previously that calcium-independent phospholipase A(2)γ (iPLA(2)γ) is cytoprotective against complement-mediated glomerular epithelial cell injury. Studies in iPLA(2)γ KO mice have demonstrated an important role for iPLA(2)γ in mitochondrial lipid turnover, membrane structure, and metabolism. The aim of the present study was to employ iPLA(2)γ KO mice to better understand the role of iPLA(2)γ in normal glomerular and podocyte function as well as in glomerular injury. We show that deletion of iPLA(2)γ did not cause detectable albuminuria; however, it resulted in mitochondrial structural abnormalities and enhanced autophagy in podocytes as well as loss of podocytes in aging KO mice. Moreover, after induction of anti-glomerular basement membrane nephritis in young mice, iPLA(2)γ KO mice exhibited significantly increased levels of albuminuria, podocyte injury, and loss of podocytes compared with wild type. Thus, iPLA(2)γ has a protective functional role in the normal glomerulus and in glomerulonephritis. Understanding the role of iPLA(2)γ in glomerular pathophysiology provides opportunities for the development of novel therapeutic approaches to glomerular injury and proteinuria

Low-grade chronic inflammation in regions of the normal mouse arterial intima predisposed to atherosclerosis

Atherosclerotic lesions develop in regions of arterial curvature and branch points, which are exposed to disturbed blood flow and have unique gene expression patterns. The cellular and molecular basis for atherosclerosis susceptibility in these regions is not completely understood. In the intima of atherosclerosis-predisposed regions of the wild-type C57BL/6 mouse aorta, we quantified increased expression of several proinflammatory genes that have been implicated in atherogenesis, including vascular cell adhesion molecule–1 (VCAM-1) and a relative abundance of dendritic cells, but only occasional T cells. In contrast, very few intimal leukocytes were detected in regions resistant to atherosclerosis; however, abundant macrophages, including T cells, were found throughout the adventitia (Adv). Considerably lower numbers of intimal CD68+ leukocytes were found in inbred atherosclerosis-resistant C3H and BALB/c mouse strains relative to C57BL/6 and 129; however, leukocyte distribution throughout the Adv of all strains was similar. The predominant mechanism for the accumulation of intimal CD68+ cells was continued recruitment of bone marrow–derived blood monocytes, suggestive of low-grade chronic inflammation. Local proliferation of intimal leukocytes was low. Intimal CD68+ leukocytes were reduced in VCAM-1–deficient mice, suggesting that mechanisms of leukocyte accumulation in the intima of normal aorta are analogous to those in atherosclerosis

Vitamin E-modified filters modulate Jun N-terminal kinase activation in peripheral blood mononuclear cells

n/

Conditional Vascular Cell Adhesion Molecule 1 Deletion in Mice: Impaired Lymphocyte Migration to Bone Marrow

We generated vascular cell adhesion molecule (VCAM)-1 “knock-in” mice and Cre recombinase transgenic mice to delete the VCAM-1 gene (vcam-1) in whole mice, thereby overcoming the embryonic lethality seen with conventional vcam-1–deficient mice. vcam-1 knock-in mice expressed normal levels of VCAM-1 but showed loss of VCAM-1 on endothelial and hematopoietic cells when interbred with a “TIE2Cre” transgene. Analysis of peripheral blood from conditional vcam-1–deficient mice revealed mild leukocytosis, including elevated immature B cell numbers. Conversely, the bone marrow (BM) had reduced immature B cell numbers, but normal numbers of pro-B cells. vcam-1–deficient mice also had reduced mature IgD+ B and T cells in BM and a greatly reduced capacity to support short-term migration of transferred B cells, CD4+ T cells, CD8+ T cells, and preactivated CD4+ T cells to the BM. Thus, we report an until now unappreciated dominant role for VCAM-1 in lymphocyte homing to BM