Clinical-Pathological Features and Outcome of Atypical Anti-glomerular Basement Membrane Disease in a Large Single Cohort.

Background: Atypical cases of anti-glomerular basement membrane (GBM) disease had absent circulating antibodies but linear IgG deposits along GBM in the kidneys. Herein, we reported the clinical-pathological features and outcome of these rare cases. Methods: Linear IgG deposit along GBM were examined by immunofluorescence on renal specimens, with exclusion of diabetic kidney disease. Circulating anti-GBM antibodies were tested by commercial ELISA assay. Clinical, pathological and follow-up data were retrospectively analyzed. Results: From 2013 to 2018, a total of 60 patients were diagnosed as atypical anti-GBM disease. They had a male predominance, with an average age of 51.7 ± 15.6 years. Three (5.0%) patients had alveolar hemorrhage. Forty five percent of them presented with acute kidney disease. All patients had linear IgG deposit along GBM, some in addition on tubular basement membrane and/or Bowmans' capsules. C3 deposition was found in 65.0% of the patients. 41.7% (25/60) of the patients showed crescent formation and the percentage of crescent was (34.7 ± 23.5)% in those patients. They had higher prevalence of hematuria and C3 deposit, higher levels of serum creatinine, worse renal and patient survival than those without crescent (P < 0.05). During the follow-up of 35.7 ± 21.4 months, 14 (23.3%) patients progressed to ESRD. The serum creatinine on diagnosis [per 200 µmol/L increase, HR (95% CI): 2.663 (1.372, 5.172), P = 0.004], serum C3 [per 0.1 g/L increase, HR (95% CI): 0.689(0.483, 0.984), P = 0.040] and the intensity of kidney C3 staining [per 1+ increase, HR (95% CI): 2.770 (1.115, 6.877), P = 0.028] were independent predictive factors for kidney outcome. Nine (15.0%) patients died of all causes. Conclusions: Atypical anti-GBM disease manifested milder kidney injury and scarce pulmonary hemorrhage compared to the classical cases. Though heterogeneous, a substantial number of the patients had complement activation and crescent formation. Patients having crescents presented with more severe clinical course and worse outcomes. The poor kidney and patient prognosis emphasize prompt interventions from physicians. The immunosuppressive intervention was not associated with kidney or patient outcome. Further studies are needed to address the optimal therapeutic regimen.

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)-ß is involved in glomerulosclerosis and interstitial fibrosis. TGF-ß 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-ß 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.

Recombinant human soluble thrombomodulin attenuates anti-glomerular basement membrane glomerulonephritis in Wistar-Kyoto rats through anti-inflammatory effects.

BACKGROUND: Since recombinant human soluble thrombomodulin (RH-TM) has anti-inflammatory properties through neutralizing high-mobility group box 1 protein (HMGB1), the protective effects of RH-TM were examined in anti-glomerular basement membrane (GBM) glomerulonephritis (GN) in Wistar-Kyoto rats. METHODS: Rats were injected with nephrotoxic serum (NTS) to induce anti-GBM GN on Day 0, and were given either RH-TM or vehicle from Day 0 to Day 6. Rats were sacrificed 7 days after NTS injection. RESULTS: RH-TM-treated rats had decreased proteinuria and serum creatinine level. RH-TM significantly reduced the percentage of glomeruli with crescentic features and fibrinoid necrosis. In addition, RH-TM-treated rats had significantly reduced glomerular ED1+ macrophage accumulation as well as reduced renal cortical proinflammatory cytokine expression. Furthermore, RH-TM had a potent effect in reducing intercellular adhesion molecule-1 (ICAM-1) expression in kidneys and urine. RH-TM significantly reduced renal cortical mRNA levels for toll-like receptor -2 and -4, known as receptors for HMGB1, and their downstream adopter protein, myeloid differentiation primary respond protein 88 (MyD88). CONCLUSIONS: We showed for the first time that anti-inflammatory effects, which were characterized by reduced glomerular macrophage influx concomitant with a marked reduction in proinflammatory cytokines, were involved in the mechanism of attenuating experimental anti-GBM GN by RH-TM. The observed effects might be attributable to the downregulation of ICAM-1 by reducing the HMGB1/TLR/MyD88 signaling pathway.

Successful pregnancy in a patient with pulmonary renal syndrome double-positive for anti-GBM antibodies and p-ANCA
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BACKGROUND: Antiglomerular basement membrane (anti-GBM) antibody disease is a rare condition causing pulmonary hemorrhage and necrotizing glomerulonephritis (pulmonary renal syndrome). CASE: We report a 30-year-old woman who presented with life-threatening pulmonary hemorrhage and an active urinary sediment, with normal glomerular filtration rate in the 13th week of pregnancy. Anti-GBM antibodies in serum were negative, but perinuclear antineutrophil cytoplasmatic antibodies (p-ANCA) were detected. A renal biopsy revealed necrotizing glomerulonephritis with linear IgG deposits along the glomerular basement membrane. A diagnosis of pulmonary renal syndrome caused by anti-GBM antibodies and p-ANCA (double-positive) was made. Plasma exchange was started but had to be changed to immunoadsorption because of an allergic reaction to fresh frozen plasma. Oral steroids were introduced. The patient also received one dose of intravenous cyclophosphamide followed by two 1-g doses of rituximab. The patient responded quickly to treatment with resolution of pulmonary hemorrhage and urinary abnormalities. The infant was delivered in the 38th week of pregnancy by caesarian section. It was small for age but otherwise completely healthy with a normal B-cell count. CONCLUSION: To our knowledge, this is the first report of a double-positive pulmonary renal syndrome in pregnancy. Presentation in mid-pregnancy allowed for the application of cyclophosphamide without causing malformations and rituximab without B-cell depletion in the infant.
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Characterization of Glomerular Sox9+ Cells in Anti-Glomerular Basement Membrane Nephritis in the Rat.

Mechanisms of glomerular crescent formation and podocyte repair processes are still unclear. Therefore, we investigated the expression of the transcription factor Sox9 as a potential marker of a subpopulation of parietal epithelial cells (PECs) with potential regenerative properties. Glomerular Sox9 expression was characterized in detail in a rat anti-glomerular basement membrane (GBM) nephritis model using immunofluorescence and confocal laser scanning microscopy. In healthy kidneys Sox9 is expressed in a subpopulation of PECs restricted to approximately 20% to 50% of PEC nuclei and was highly conserved in all investigated species. During rat anti-GBM nephritis the number of glomerular Sox9+ cells increased and was associated with proliferation activity. In nephritic glomeruli Sox9 expression was not restricted to Bowman's capsule lining but was also found on cells of the glomerular tuft. Nearly all Sox9+ cells also expressed the PEC marker Pax8, whereas endothelial cells, mesangial cells, macrophages, and T lymphocytes lacked Sox9 expression. At the margins of crescents Sox9+/Pax8+ cells additionally expressed podocyte markers. In contrast, in sclerotic lesions a minority of Sox9+/Pax8+ cells expressed the myofibroblast marker α-smooth muscle actin. In glomerular Sox9+ cells Jagged 1 was up-regulated. During anti-GBM nephritis Sox9+ PECs proliferate and migrate onto the glomerular tuft. Future studies are needed to confirm the origin of Sox9+ cells from PECs and differentiation in both podocytes and/or myofibroblasts.

Neutrophil exocytosis induces podocyte cytoskeletal reorganization and proteinuria in experimental glomerulonephritis.

Acute glomerulonephritis is characterized by rapid glomerular neutrophil recruitment, proteinuria, and glomerular hypercellularity. The current study tested the hypothesis that the release of neutrophil granule contents plays a role in both the loss of filtration barrier leading to proteinuria and the increase in glomerular cells. Inhibition of neutrophil exocytosis with a peptide inhibitor prevented proteinuria and attenuated podocyte and endothelial cell injury but had no effect on glomerular hypercellularity in an experimental acute glomerulonephritis model in mice. Cultivation of podocytes with neutrophil granule contents disrupted cytoskeletal organization, an in vitro model for podocyte effacement and loss of filtration barrier. Activated, cultured podocytes released cytokines that stimulated neutrophil chemotaxis, primed respiratory burst activity, and stimulated neutrophil exocytosis. We conclude that crosstalk between podocytes and neutrophils contributes to disruption of the glomerular filtration barrier in acute glomerulonephritis. Neutrophil granule products induce podocyte injury but do not participate in the proliferative response of intrinsic glomerular cells.

Goodpasture's autoimmune disease - A collagen IV disorder.

Goodpasture's (GP) disease is an autoimmune disorder characterized by the deposition of pathogenic autoantibodies in basement membranes of kidney and lung eliciting rapidly progressive glomerulonephritis and pulmonary hemorrhage. The principal autoantigen is the α345 network of collagen IV, which expression is restricted to target tissues. Recent discoveries include a key role of chloride and bromide for network assembly, a novel posttranslational modification of the antigen, a sulfilimine bond that crosslinks the antigen, and the mechanistic role of HLA in genetic susceptibility and resistance to GP disease. These advances provide further insights into molecular mechanisms of initiation and progression of GP disease and serve as a basis for developing of novel diagnostic tools and therapies for treatment of Goodpasture's disease.

CD44 is required for the pathogenesis of experimental crescentic glomerulonephritis and collapsing focal segmental glomerulosclerosis.

A key feature of glomerular diseases such as crescentic glomerulonephritis and focal segmental glomerulosclerosis is the activation, migration and proliferation of parietal epithelial cells. CD44-positive activated parietal epithelial cells have been identified in proliferative cellular lesions in glomerular disease. However, it remains unknown whether CD44-positive parietal epithelial cells contribute to the pathogenesis of scarring glomerular diseases. Here, we evaluated this in experimental crescentic glomerulonephritis and the transgenic anti-Thy1.1 model for collapsing focal segmental glomerulosclerosis in CD44-deficient (cd44-/-) and wild type mice. For both models albuminuria was significantly lower in cd44-/- compared to wild type mice. The number of glomerular Ki67-positive proliferating cells was significantly reduced in cd44-/- compared to wild type mice, which was associated with a reduced number of glomerular lesions in crescentic glomerulonephritis. In collapsing focal segmental glomerulosclerosis, the extracapillary proliferative cellular lesions were smaller in cd44-/- mice, but the number of glomerular lesions was not different compared to wild type mice. For crescentic glomerulonephritis the influx of granulocytes and macrophages into the glomerulus was similar. In vitro, the growth of CD44-deficient murine parietal epithelial cells was reduced compared to wild type parietal epithelial cells, and human parietal epithelial cell migration could be inhibited using antibodies directed against CD44. Thus, CD44-positive proliferating glomerular cells, most likely parietal epithelial cells, are essential in the pathogenesis of scarring glomerular disease.

Therapeutic Mechanism of Glucocorticoids on Cellular Crescent Formation in Patients With Antiglomerular Basement Membrane Disease.

BACKGROUND: This study aimed to explore the therapeutic mechanism of glucocorticoids (GCs) in antiglomerular basement membrane disease. MATERIALS AND METHODS: Thirty-four patients with biopsy-proven antiglomerular basement membrane nephritis were divided into the following 2 groups: group 1 (patients treated with GCs, n = 22) and group 2 (patients who were not treated with GCs, n = 12). The expression of parietal epithelial cells (PECs), activated PECs and glucocorticoid receptors (GRs) was examined quantitatively and compared between the 2 groups. Correlations between GR expression in glomeruli and patients' clinicopathological indices were also analyzed. RESULTS: Compared with patients in group 2, patients in group 1 showed lower levels of serum creatinine (SCr) (P = 0.03), average cellular crescent percentage (P = 0.005) and macrophages infiltrating in renal interstitium (P = 0.03). PECs (P = 0.007) and activated PECs (P = 0.03) were strongly detected in the cellular components of classic crescents, and both were significantly reduced in group 1 compared to group 2. GR expression either in glomeruli (P = 0.01) or interstitium (P = 0.009) was lower in group 1 after GCs treatment than in group 2. Additionally, GR expression in glomeruli was strongly correlated with renal function (SCr: r = 0.45, P = 0.009; eGFR: r = -0.35, P = 0.046), the proportion of cellular crescents (r = 0.67, P < 0.001), PECs (r = 0.64, P < 0.001) and activated PECs (r = 0.72, P < 0.001), and the degree of interstitial (r = 0.50, P = 0.004) and glomerular (r = 0.49, P = 0.007) macrophage infiltration. CONCLUSIONS: GCs might exert their therapeutic effects via inhibiting the activation and proliferation of PECs, as well as macrophage infiltration, which could contribute to crescent formation and determine renal survival. GRs are involved in this process as well.

Aliskiren Regulates Neonatal Fc Receptor and IgG Metabolism with Attenuation of Anti-GBM Glomerulonephritis in Mice.

BACKGROUND: Renin, in addition to its activation of the renin-angiotensin system, binds to the (pro)renin receptor (PRR) and triggers inflammatory and fibrogenic signaling in tissue. In addition, aliskiren, a direct renin inhibitor, has been shown to affect IgG metabolism by altering PRR and neonatal Fc receptors (FcRns). METHODS: We investigated the effect of aliskiren on proteinuria, glomerular extracellular matrix, expressions of fibronectin, transforming growth factor ß1 (TGF-ß1), PRR, FcRn and renal metabolism of IgG in a mice model of anti-glomerular basement membrane glomerulonephritis (anti-GBM GN). RESULTS: IgG deposition and expressions of FcRn and PRR were enhanced at glomeruli and urinary IgG levels increased in anti-GBM GN. Aliskiren attenuated anti-GBM GN with reduction of proteinuria and cortical expressions of fibronectin and TGF-ß1. In addition, aliskiren suppressed the renal cortical expressions of FcRn and PRR. Aliskiren also reduced the glomerular IgG depositions and the urinary IgG levels albeit with increased circulating serum IgG levels. CONCLUSION: These results suggest that suppression of FcRn and PRR and regulation of IgG metabolism may be related to the attenuation of anti-GBM GN by aliskiren.

T cell infiltration is associated with kidney injury in patients with anti-glomerular basement membrane disease.

Cell-mediated autoimmunity, particularly that involving autoreactive T cells, participates in mediating anti-glomerular basement membrane (GBM) disease. However, direct kidney injury mediated by renal infiltrated T cells has not been clearly elucidated in humans. The T cell profile (CD3, CD4, CD8, IL-17, and foxp3) and macrophage (CD68) were examined by immunohistochemistry on renal biopsy tissues from 13 patients with anti-GBM disease. The correlation between cell infiltration and clinical data was also analyzed. We found that the distribution of T cell infiltration was predominant in the peri-glomerular and interstitial areas. CD3+ T cell infiltratrion around the glomeruli with cellular crescent formations was significantly higher than that around the glomeruli with mild mesangial proliferation. CD8+ T cells significantly accumulated around the glomeruli with cellular crescents without IgG deposits compared to those with IgG deposits. The prevalence of infiltrating CD8+ T cells was correlated with the percentage of ruptured Bowman's capsules. In conclusion, cellular immunity may play a crucial role in the inflammatory kidney injury in anti-GBM patients. The periglomerular infiltration of T cells, especially CD8+ T cells, may participate in the pathogenic mechanism of glomerular damage.

Antibodies to α5 chain of collagen IV are pathogenic in Goodpasture's disease.

Autoantibody against glomerular basement membrane (GBM) plays a direct role in the initiation and development of Goodpasture's (GP) disease. The principal autoantigen is the non-collagenous domain 1 (NC1) of α3 chain of collagen IV, with two immunodominant epitopes, EA-α3 and EB-α3. We recently demonstrated that antibodies targeting α5NC1 are bound to kidneys in GP patients, suggesting their pathogenic relevance. In the present study, we sought to assess the pathogenicity of the α5 autoantibody with clinical and animal studies. Herein, we present a special case of GP disease with circulating autoantibody reactive exclusively to the α5NC1 domain. This autoantibody reacted with conformational epitopes within GBM collagen IV hexamer and produced a linear IgG staining on frozen sections of human kidney. The antibody binds to the two regions within α5NC1 domain, EA and EB, and inhibition ELISA indicates that they are targeted by distinct sub-populations of autoantibodies. Sequence analysis highlights five residues that determine specificity of antibody targeting EA and EB epitopes of α5NC1 over homologous regions in α3NC1. Furthermore, immunization with recombinant α5NC1 domain induced crescentic glomerulonephritis and alveolar hemorrhage in Wistar-Kyoto rats. Thus, patient data and animal studies together reveal the pathogenicity of α5 antibodies. Given previously documented cases of GP disease with antibodies selectively targeting α3NC1 domain, our data presents a conundrum of why α3-specific antibodies developing in majority of GP patients, with α5-specific antibodies emerged in isolated cases, the answer for which is critical for understanding of etiology and progression of the GP disease.

Amino acid metabolism inhibits antibody-driven kidney injury by inducing autophagy.

Inflammatory kidney disease is a major clinical problem that can result in end-stage renal failure. In this article, we show that Ab-mediated inflammatory kidney injury and renal disease in a mouse nephrotoxic serum nephritis model was inhibited by amino acid metabolism and a protective autophagic response. The metabolic signal was driven by IFN-γ-mediated induction of indoleamine 2,3-dioxygenase 1 (IDO1) enzyme activity with subsequent activation of a stress response dependent on the eIF2α kinase general control nonderepressible 2 (GCN2). Activation of GCN2 suppressed proinflammatory cytokine production in glomeruli and reduced macrophage recruitment to the kidney during the incipient stage of Ab-induced glomerular inflammation. Further, inhibition of autophagy or genetic ablation of Ido1 or Gcn2 converted Ab-induced, self-limiting nephritis to fatal end-stage renal disease. Conversely, increasing kidney IDO1 activity or treating mice with a GCN2 agonist induced autophagy and protected mice from nephritic kidney damage. Finally, kidney tissue from patients with Ab-driven nephropathy showed increased IDO1 abundance and stress gene expression. Thus, these findings support the hypothesis that the IDO-GCN2 pathway in glomerular stromal cells is a critical negative feedback mechanism that limits inflammatory renal pathologic changes by inducing autophagy.

Genetic background-dependent thrombotic microangiopathy is related to vascular endothelial growth factor receptor 2 signaling during anti-glomerular basement membrane glomerulonephritis in mice.

Because genetic background plays a pivotal role in humans and in various experimental models, we carefully monitored its impact on glomerular pathological characteristics during experimental anti-glomerular basement membrane glomerulonephritis (anti-GBM-GN), using two leading mouse strains, 129S2/SvPas (129Sv) and C57bl/6J (B6J). These mice exhibited different severities of renal failure, hypertension, and glomerular lesions, according to their genetic background. In addition to the classic glomerular proliferative lesions, glomerular thrombotic microangiopathy (TMA) was found as a common genetic background-dependent histopathological hallmark of anti-GBM-GN, combined with hemolytic anemia and thrombocytopenia. Glomerular expression profiling, using microarrays and Western blot analysis in B6J TMA-resistant and 129Sv TMA-prone mice, demonstrated major differences in vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) 2 pathways, despite similar Vegfa expression levels. Further analysis revealed a lower basal glomerular endothelial Vegfr2 expression level in 129Sv TMA-prone mice compared with B6J TMA-resistant mice. This difference was even more pronounced during anti-GBM-GN, explaining why an exogenous VEGFA supply failed to rescue any 129Sv TMA lesions. Conversely, the systemic blocking of Vegfr2 amplified TMA lesions only in B6J mice. Herein, we specified the role that genetic background plays in determining, in particular, the level of Vegfr2 expression. We also demonstrated that glomerular Vegfr2-dependent TMA lesions are an underevaluated common hallmark of anti-GBM-GN in mice.

Myeloid mineralocorticoid receptor activation contributes to progressive kidney disease.

Clinical and experimental studies have shown that mineralocorticoid receptor (MR) antagonists substantially reduce kidney injury. However, the specific cellular targets and mechanisms by which MR antagonists protect against kidney injury must be identified. We used conditional gene deletion of MR signaling in myeloid cells (MR(flox/flox) LysM(Cre) mice; MyMRKO) or podocytes (MR(flox/flox) Pod(Cre) mice; PodMRKO) to establish the role of MR in these cell types in the development of mouse GN. Accelerated anti-glomerular basement membrane GN was examined in groups of mice: MyMRKO, PodMRKO, wild-type (WT) littermates, and WT mice receiving eplerenone (100 mg/kg twice a day; EPL-treated). At day 15 of disease, WT mice had glomerular crescents (37%±5%), severe proteinuria, and a 6-fold increase in serum cystatin-C. MyMRKO, PodMRKO, and EPL-treated mice with GN displayed proteinuria similar to that in these disease controls. However, MyMRKO and EPL-treated groups had a 35% reduction in serum cystatin-C levels and reduced crescent numbers compared with WT mice, whereas PodMRKO mice were not protected. The protection observed in MyMRKO mice appeared to result predominantly from reduced recruitment of macrophages and neutrophils into the inflamed kidney. Suppression of kidney leukocyte accumulation in MyMRKO mice correlated with reductions in gene expression of proinflammatory molecules (TNF-α, inducible nitric oxide synthase, chemokine (C-C motif) ligand 2, matrix metalloproteinase-12), tubular damage, and renal fibrosis and was similar in EPL-treated mice. In conclusion, MR signaling in myeloid cells, but not podocytes, contributes to the progression of renal injury in mouse GN, and myeloid deficiency of MR provides protection similar to eplerenone in this disease.

Modulation of heparan sulfate in the glomerular endothelial glycocalyx decreases leukocyte influx during experimental glomerulonephritis.

The glomerular endothelial glycocalyx is postulated to be an important modulator of permeability and inflammation. The glycocalyx consists of complex polysaccharides, the main functional constituent of which, heparan sulfate (HS), is synthesized and modified by multiple enzymes. The N-deacetylase-N-sulfotransferase (Ndst) enzymes initiate and dictate the modification process. Here we evaluated the effects of modulation of HS in the endothelial glycocalyx on albuminuria and glomerular leukocyte influx using mice deficient in endothelial and leukocyte Ndst1 (TEKCre+/Ndst1flox/flox). In these mice, glomerular expression of a specific HS domain was significantly decreased, whereas the expression of other HS domains was normal. In the endothelial glycocalyx, this specific HS structure was not associated with albuminuria or with changes in renal function. However, glomerular leukocyte influx was significantly reduced during antiglomerular basement membrane nephritis, which was associated with less glomerular injury and better renal function. In vitro decreased adhesion of wild-type and Ndst1-deficient granulocytes to Ndst1-silenced glomerular endothelial cells was found, accompanied by a decreased binding of chemokines and L-selectin. Thus, modulation of HS in the glomerular endothelial glycocalyx significantly reduced the inflammatory response in antiglomerular basement membrane nephritis.