Genetic Background–Dependent Thrombotic Microangiopathy Is Related to Vascular Endothelial Growth Factor Receptor 2 Signaling during Anti-Glomerular Basement Membrane Glomerulonephritis in Mice

Seronegative Atypical Anti-Glomerular Basement Membrane Glomerulonephritis Associated With Thrombotic Microangiopathy: Case Report and Literature Analysis

Anti-glomerular basement membrane (GBM) antibody nephritis is defined by linear immunofluorescence staining of GBM by immunoglobulin G (IgG), typically associated with GBM rupture, fibrinoid necrosis, and crescent formation. Clinically, the patients present with rapidly worsening renal function, often with hematuria. Typical renal pathologic findings include necrotizing and crescentic glomerulonephritis. In contrast, thrombotic microangiopathy (TMA) is characterized by microvascular thrombosis, which can also lead to acute kidney injury. Thrombotic microangiopathy is associated with some systemic diseases and has characteristic clinical features of microangiopathic hemolytic anemia, platelet consumption, and multiple organ failure. Anti-GBM nephritis associated with TMA has rarely been reported. We describe an unusual case of atypical anti-GBM disease without crescent formation or necrosis but with light microscopic and ultrastructural features consistent with endothelial cell injury and glomerular-limited TMA.

Heterozygous expression of Cre recombinase in podocytes has no impact on the anti-glomerular basement membrane glomerulonephritis model in C57BL/6J mice

A recent article described a thickening of the glomerular basement membrane (GBM) along with changes in the expression of key components of the extracellular matrix in 6-month-old NPHS2-Cre transgenic mice, which express the Cre recombinase specifically in podocytes. This transgenic line has been widely used to characterize the implication of candidate genes in glomerular diseases in younger mice. Using a different mouse strain (C57BL/6J) than the previous report (129S6/SvEvTac), we sought to characterize 3- and 6-month-old NPHS2-Cre^+/- mice in control and pathological conditions. At baseline, there was no difference in renal function and histology between control and NPHS2-Cre^+/- mice. Notably, GBM thickness evaluated by transmission electron microscopy was similar between the two groups. We then induced an immune-mediated severe glomerular insult, the anti-glomerular basement membrane glomerulonephritis model (anti-GBM-GN) in 3-month-old control and NPHS2-Cre^+/- mice. NPHS2-Cre^+/- mice exhibited the same alterations in renal function and structure as control mice. In summary, our study strongly suggests that NPHS2-Cre^+/- transgenic mice on a C57BL/6J background can be safely used for podocyte-specific gene inactivation in control conditions and in the anti-GBM-GN model.

Endothelial-Specific Deletion of CD146 Protects Against Experimental Glomerulonephritis in Mice

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Preservation of epoxyeicosatrienoic acid bioavailability prevents renal allograft dysfunction and cardiovascular alterations in kidney transplant recipients

This study addressed the hypothesis that epoxyeicosatrienoic acids (EETs) synthesized by CYP450 and catabolized by soluble epoxide hydrolase (sEH) are involved in the maintenance of renal allograft function, either directly or through modulation of cardiovascular function. The impact of single nucleotide polymorphisms (SNPs) in the sEH gene EPHX2 and CYP450 on renal and vascular function, plasma levels of EETs and peripheral blood monuclear cell sEH activity was assessed in 79 kidney transplant recipients explored at least one year after transplantation. Additional experiments in a mouse model mimicking the ischemia–reperfusion (I/R) injury suffered by the transplanted kidney evaluated the cardiovascular and renal effects of the sEH inhibitor t-AUCB administered in drinking water (10 mg/l) during 28 days after surgery. There was a long-term protective effect of the sEH SNP rs6558004, which increased EET plasma levels, on renal allograft function and a deleterious effect of K55R, which increased sEH activity. Surprisingly, the loss-of-function CYP2C9*3 was associated with a better renal function without affecting EET levels. R287Q SNP, which decreased sEH activity, was protective against vascular dysfunction while CYP2C8*3 and 2C9*2 loss-of-function SNP, altered endothelial function by reducing flow-induced EET release. In I/R mice, sEH inhibition reduced kidney lesions, prevented cardiac fibrosis and dysfunction as well as preserved endothelial function. The preservation of EET bioavailability may prevent allograft dysfunction and improve cardiovascular disease in kidney transplant recipients. Inhibition of sEH appears thus as a novel therapeutic option but its impact on other epoxyfatty acids should be carefully evaluated.

SMAD3-dependent and -independent pathways in glomerular injury associated with experimental glomerulonephritis

Glomerulonephritis (GN) is a common cause of end-stage kidney disease and is characterized by glomerular inflammation, hematuria, proteinuria, and progressive renal dysfunction. Transforming growth factor (TGF)-β is involved in glomerulosclerosis and interstitial fibrosis. TGF-β activates multiple signaling pathways, including the canonical SMAD pathway. We evaluated the role of SMAD signaling in renal injury and proteinuria in a murine model of GN. SMAD3^+/+ or SMAD3^-/- mice received anti-glomerular basement membrane antibodies to induce GN. We confirmed previous reports that demonstrated that SMAD3 is an important mediator of glomerulosclerosis and renal interstitial fibrosis. Proteinuria was highly SMAD3 dependent. We found differential effects of SMAD3 deletion on podocytes and glomerular endothelial cells. GN led to podocyte injury, including foot process effacement and loss of podocyte-specific markers. Interestingly, these changes were not SMAD3 dependent. Furthermore, there were significant changes to glomerular endothelial cells, including loss of fenestrations, swelling, and basement membrane reduplication, which were SMAD3 dependent. Despite ongoing markers of podocyte injury in SMAD3^-/- mice, proteinuria was transient. Renal injury in the setting of GN involves TGF-β and SMAD3 signaling. Cell populations within the glomerulus respond differently to SMAD3 deletion. Proteinuria correlated more with endothelial cell changes as opposed to podocyte injury in this model.

Impairment of the carnitine/organic cation transporter 1-ergothioneine axis is mediated by intestinal transporter dysfunction in chronic kidney disease

Carnitine/organic cation transporter 1 (OCTN1) is a specific transporter of the food-derived antioxidant ergothioneine. Ergothioneine is absorbed by intestinal OCTN1, distributed through the bloodstream, and incorporated into each organ by OCTN1. OCTN1 expression is upregulated in injured tissues, and promotes ergothioneine uptake to reduce further damage caused by oxidative stress. However, the role of the OCTN1-ergothioneine axis in kidney-intestine cross-talk and chronic kidney disease (CKD) progression remains unclear. Here we assessed ergothioneine uptake via intestinal OCTN1 and confirmed the expression of OCTN1. The ability of OCTN1 to absorb ergothioneine was diminished in mice with CKD. In combination with OCTN1 dysfunction, OCTN1 localization on the intestinal apical cellular membrane was disturbed in mice with CKD. Proteomic analysis, RT-PCR, Western blotting, and immunohistochemistry revealed that PDZ (PSD95, Dlg, and ZO1), a PDZK1 domain-containing protein that regulates the localization of transporters, was decreased in mice with CKD. Decreased intestinal ergothioneine uptake from food decreased ergothioneine levels in the blood of mice with CKD. Despite increased OCTN1 expression and ergothioneine uptake into the kidneys of mice with CKD, ergothioneine levels did not increase. To identify the role of the OCTN1-ergothioneine axis in CKD, we evaluated kidney damage and oxidative stress in OCTN1-knockout mice with CKD and found that kidney fibrosis worsened. Oxidative stress indicators were increased in OCTN1-knockout mice. Moreover, ergothioneine levels in the blood of patients with CKD decreased, which were restored after kidney transplantation. Thus, a novel inter-organ interaction mediated by transporters is associated with CKD progression.

Efficient second-harmonic imaging of collagen in histological slides using Bessel beam excitation

Second-harmonic generation (SHG) is the most specific label-free indicator of collagen accumulation in widespread pathologies such as fibrosis, and SHG-based measurements hold important potential for biomedical analyses. However, efficient collagen SHG scoring in histological slides is hampered by the limited depth-of-field of usual nonlinear microscopes relying on focused Gaussian beam excitation. In this work we analyze theoretically and experimentally the use of Bessel beam excitation to address this issue. Focused Bessel beams can provide an axially extended excitation volume for nonlinear microscopy while preserving lateral resolution. We show that shaping the focal volume has consequences on signal level and scattering directionality in the case of coherent signals (such as SHG) which significantly differ from the case of incoherent signals (two-photon excited fluorescence, 2PEF). We demonstrate extended-depth SHG-2PEF imaging of fibrotic mouse kidney histological slides. Finally, we show that Bessel beam excitation combined with spatial filtering of the harmonic light in wave vector space can be used to probe collagen accumulation more efficiently than the usual Gaussian excitation scheme. These results open the way to SHG-based histological diagnoses.

Modeling complement-driven diseases in transgenic mice: Values and limitations

Remarkable advances have been made over past decades in understanding the pathogenesis of complement-mediated diseases. This has led to development of new therapies for, and in some cases re-classification of, complement-driven diseases. This success is due to not only insight from human patients but also studies using transgenic animal models. Animal models that mimic human diseases are useful tools to understand the mechanism of disease and develop new therapies but there are also limitations due to species differences in their complement systems. This review provides a summary of transgenic animal models for three human diseases that are at the forefront of anti-complement therapy, paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G). They are discussed here as examples to highlight the values and limitations of animal modeling in complement-driven diseases.

Vascular growth factors play critical roles in kidney glomeruli

Kidney glomeruli ultrafilter blood to generate urine and they are dysfunctional in a variety of kidney diseases. There are two key vascular growth factor families implicated in glomerular biology and function, namely the vascular endothelial growth factors (VEGFs) and the angiopoietins (Angpt). We present examples showing not only how these molecules help generate and maintain healthy glomeruli but also how they drive disease when their expression is dysregulated. Finally, we review how manipulating VEGF and Angpt signalling may be used to treat glomerular disease.