Contributions of intrinsic renal cells to crescentic glomerulonephritis

MAD2B contributes to parietal epithelial cell activation and crescentic glomerulonephritis via Skp2

Mitotic spindle assembly checkpoint protein 2 (MAD2B), a well-known anaphase-promoting complex/cyclosome (APC/C) inhibitor and a small subunit of DNA polymerase-ζ, is critical for mitotic control and DNA repair. Previously, we detected a strong increase of MAD2B in the glomeruli from patients with crescentic glomerulonephritis and anti-glomerular basement membrane (anti-GBM) rats, which predominantly originated from activated parietal epithelial cells (PECs). Consistently, in vitro MAD2B was increased in TNF-α-treated PECs, along with cell activation and proliferation, as well as extracellular matrix accumulation, which could be reversed by MAD2B genetic depletion. Furthermore, we found that expression of S phase kinase-associated protein 2 (Skp2), an APC/C^CDH1 substrate, was increased in the glomeruli of anti-GBM rats, and TNF-α-stimulated PECs and could be suppressed by MAD2B depletion. Additionally, genetic deletion of Skp2 inhibited TNF-α-induced PEC activation and dysfunction. Finally, TNF-α blockade or glucocorticoid therapy administered to anti-GBM rats could ameliorate MAD2B and Skp2 accumulation as well as weaken PEC activation. Collectively, our data suggest that MAD2B has a pivotal role in the pathogenesis of glomerular PEC activation and crescent formation through induction of Skp2 expression.

Compound effects of aging and experimental FSGS on glomerular epithelial cells

Advanced age portends a poorer prognosis in FSGS. To understand the impact of age on glomerular podocytes and parietal epithelial cells (PECs), experimental FSGS was induced in 3m-old mice (20-year old human age) and 27m-old mice (78-year old human age) by abruptly depleting podocytes with a cytopathic anti-podocyte antibody. Despite similar binding of the disease-inducing antibody, podocyte density was lower in aged FSGS mice compared to young FSGS mice. Activated PEC density was higher in aged versus young FSGS mice, as was the percentage of total activated PECs. Additionally, the percentage of glomeruli containing PECs with evidence of phosphorylated ERK and EMT was higher in aged FSGS mice. Extracellular matrix, measured by collagen IV and silver staining, was higher in aged FSGS mice along Bowman's capsule. However, collagen IV accumulation in the glomerular tufts alone and in glomeruli with both tuft and Bowman's capsule accumulation were similar in young FSGS and aged FSGS mice. Thus, the major difference in collagen IV staining in FSGS was along Bowman's capsule in aged mice. The significant differences in podocytes, PECs and extracellular matrixaccumulation between young mice and old mice with FSGS might explain the differences in outcomes in FSGS based on age.

A case of membranous nephropathy and myeloperoxidase anti-neutrophil cytoplasmic antibody-associated glomerulonephritis

Membranous nephropathy (MN) may be a primary disease or secondary to autoimmune conditions such as systemic lupus erythematosus, infection (for example, with hepatitis B or C virus), cancer or drugs. In primary MN, crescents are rarely observed. Therefore, the presence of crescents suggests another underlying disease, for example lupus nephritis, anti-glomerular basement membrane disease or anti-neutrophil cytoplasmic antibody-associated glomerulonephritis (ANCA-GN). The coexistence of primary MN and ANCA-GN is rare. In the present case, a 51-year-old female with mild edema in the lower extremities for 1 year was admitted to hospital for renal biopsy. The serum test for myeloperoxidase (MPO)-ANCA was positive. The patient was diagnosed with stage 2 MN with crescentic glomerulonephritis type 3; however, no causal association was found between these two diseases in this case. Treatment was initiated with 500 mg methylprednisolone for 3 days followed by 40 mg of oral methylprednisolone together with 50 mg cyclophosphamide twice per day. One month following treatment, the biochemical data results of the patient had improved.

Expression of tight junction protein claudin-1 in human crescentic glomerulonephritis

The origin of crescent forming cells in human glomerulonephritis (GN) remains unknown. Some animal studies demonstrated that parietal epithelial cells of Bowman's capsule (PECs) were the main component of proliferating cells and PEC-specific tight junction protein claudin-1 was expressed in crescentic lesions. We investigated the expression of claudin-1 in human GN. Immunohistochemistry for claudin-1 was performed on 17 kidney biopsy samples with crescent formation. Colocalization of claudin-1 with intracellular tight junction protein ZO-1 was also evaluated by immunofluorescence double staining. Claudin-1 is expressed mainly at the cell to cell contact site of proliferating cells in cellular crescentic lesions in patients with these forms of human GN. Small numbers of crescent forming cells showed extrajunctional localization of claudin-1. Colocalization of claudin-1 with ZO-1 was found at cell to cell contact sites of adjacent proliferating cells. In control samples, staining of claudin-1 was positive in PECs, but not in podocytes. Our findings suggest that claudin-1 contributes to crescent formation as a component of the tight junction protein complex that includes ZO-1. Co-localization of claudin-1 with ZO-1 implies the formation of functional tight junction complexes in crescentic lesions to prevent the interstitial damage caused by penetration of filtered molecules from Bowman's space.

Lupus nephritis: current update

Lupus nephritis is a major cause of morbidity and mortality in patients with systemic lupus erythematosus. The general consensus is that 60% of lupus patients will develop clinically relevant nephritis at some time in the course of their illness. Prompt recognition and treatment of renal disease is important, as early response to therapy is correlated with better outcome. The present review summarizes our current understanding of the pathogenic mechanisms underlying lupus nephritis and how the disease is currently diagnosed and treated.

The enigmatic parietal epithelial cell is finally getting noticed: a review

Although the normal glomerulus comprises four resident cell types, least is known about the parietal epithelial cells (PECs). This comprehensive review addresses the cellular origin of PECs, discusses the normal structure and protein makeup of PECs, describes PEC function, and defines the responses to injury in disease and how these events lead to clinical events. The data show that PECs have unique properties and that new functions are being recognized such as their role in differentiating into podocytes during disease.

Activated renal macrophages are markers of disease onset and disease remission in lupus nephritis

Costimulatory blockade with CTLA4Ig and anti-CD40L along with a single dose of cyclophosphamide induces remission of systemic lupus erythematosus nephritis in NZB/W F(1) mice. To understand the mechanisms for remission and for impending relapse, we examined the expression profiles of 61 inflammatory molecules in the perfused kidneys of treated mice and untreated mice at different stages of disease. Further studies using flow cytometry and immunohistochemistry allowed us to determine the cellular origins of several key markers. We show that only a limited set of inflammatory mediators is expressed in the kidney following glomerular immune complex deposition but before the onset of proteinuria. Formation of a lymphoid aggregate in the renal pelvis precedes the invasion of the kidney by inflammatory cells. Regulatory molecules are expressed early in the disease process and during remission but do not prevent the inevitable progression of active inflammation. Onset of proliferative glomerulonephritis and proteinuria is associated with activation of the renal endothelium, expression of chemokines that mediate glomerular cell infiltration, and infiltration by activated dendritic cells and macrophages that migrate to different topographical areas of the kidney but express a similar profile of inflammatory cytokines. Increasing interstitial infiltration by macrophages and progressive tubular damage, manifested by production of lipocalin-2, occur later in the disease process. Studies of treated mice identify a type II (M2b)-activated macrophage as a marker of remission induction and impending relapse and suggest that therapy for systemic lupus erythematosus nephritis should include strategies that prevent both activation of monocytes and their migration to the kidney.

Genes expressed by both mesangial cells and bone marrow-derived cells underlie genetic susceptibility to crescentic glomerulonephritis in the rat

The Wistar-Kyoto (WKY) rat shows marked susceptibility to crescentic glomerulonephritis. In the model of nephrotoxic nephritis (NTN) that is induced by a small dose of nephrotoxic globulin, WKY rats developed crescents in 80 +/- 2% of glomeruli at day 10, whereas no crescents were seen in Lewis rats. This was associated with marked increase in monocyte chemoattractant protein-1 synthesis in WKY glomeruli. It was posited whether susceptibility depended on circulating cells or intrinsic renal cells. Bone marrow (BM) isografts from WKY to WKY or Lewis to Lewis did not affect susceptibility to NTN. When BM was transferred from WKY to Lewis rats, crescents developed in 35 +/- 9% of glomeruli 10 d after induction of NTN, indicating that susceptibility could be transferred by BM cells. However, crescents were also seen in WKY rats that were given Lewis marrow. For assessment of the contribution of intrinsic renal cells, kidneys from WKY or Lewis rats were transplanted into F1 animals. In NTN, the ratio of crescents in the transplanted kidney to the native kidney was significantly higher for WKY-to-F1 than for Lewis-to-F1 transplants, demonstrating that the kidney itself also influences susceptibility. Mesangial cell responses were then examined in the two strains. Mesangial cells that were derived from WKY rats synthesized significantly more monocyte chemoattractant protein-1 basally and after stimulation with heat-aggregated rabbit IgG or TNF-alpha. These results show that susceptibility to NTN in the WKY rat depends on both circulating and intrinsic renal cells and that there are genetic differences between the strains in mesangial responses to inflammatory stimuli.

Cell adhesion molecules in chemically-induced renal injury

Cell adhesion molecules are integral cell-membrane proteins that maintain cell-cell and cell-substrate adhesion and in some cases act as regulators of intracellular signaling cascades. In the kidney, cell adhesion molecules, such as the cadherins, the catenins, the zonula occludens protein-1 (ZO-1), occludin and the claudins are essential for maintaining the epithelial polarity and barrier integrity that are necessary for the normal absorption/excretion of fluid and solutes. A growing volume of evidence indicates that these cell adhesion molecules are important early targets for a variety of nephrotoxic substances including metals, drugs, and venom components. In addition, it is now widely appreciated that molecules, such as intracellular adhesion molecule-1 (ICAM-1), integrins, and selectins play important roles in the recruitment of leukocytes and inflammatory responses that are associated with nephrotoxic injury. This review summarizes the results of recent in vitro and in vivo studies indicating that these cell adhesion molecules may be primary molecular targets in many types of chemically-induced renal injury. Some of the specific agents that are discussed include cadmium (Cd), mercury (Hg), bismuth (Bi), cisplatin, aminoglycoside antibiotics, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), and various venom toxins. This review also includes a discussion of the various mechanisms, by which these substances can affect cell adhesion molecules in the kidney.