Binding of anti-dsDNA antibodies to proximal tubular epithelial cells contributes to renal tubulointerstitial inflammation

Abstract

Immune deposits are often observed along the tubular basement membrane in patients with lupus nephritis, but the role of anti-dsDNA antibody (Ab) deposition on tubulointerstitial inflammation remains to be investigated. We examined the effect of human polyclonal anti-dsDNA Abs on inflammatory processes in cultured proximal renal tubular epithelial cells (PTEC, HK-2 cells) and their association with serum levels of interleukin (IL)-6, IL-8 and monocyte chemoattractant protein-1 (MCP-1) in patients. Binding of anti-dsDNA Abs to HK-2 cells was investigated by cellular ELISA, flow cytometry and immunohistochemistry. IL-6, IL-8 and MCP-1 secretion, mitogen-activated protein kinase (MAPK) activation and the effect of mycophenolic acid (MPA) were investigated by ELISAs and Western blot analysis. NZBWF1/J mice with active nephritis were randomized to receive either mycophenolate mofetil (MMF) (100 mg/kg per day) or vehicle for up to 12 weeks to study renal histopathology focusing on tubulointerstitial changes. Our results demonstrated that anti-dsDNA Abs bound to HK-2 cell surface and induced IL-6, IL-8 and MCP-1 secretion through distinct MAPK pathways. MPA inhibited anti-dsDNA Ab binding to HK-2 cells and suppressed apical and basolateral IL-6 and IL-8, but not MCP-1, secretion. Anti-dsDNA Ab level correlated with serum and tubulointerstitial expression of IL-6, IL-8 and MCP-1. MMF treatment in NZBWF1/J mice reduced anti-dsDNA Ab production and MAPK activation in the renal tubulointerstitium, together with decreased IL-6 and MCP-1 expression. Our data demonstrate that anti-dsDNA Abs contribute to inflammatory processes in the tubulointerstitium in lupus nephritis through their binding to proximal renal tubular epithelial cells and induction of pro-inflammatory mediators, and MPA ameliorates anti-dsDNA Ab induced IL-6 and IL-8 secretion in these cells.

Recent advances in the understanding of renal inflammation and fibrosis in lupus nephritis

“…The induction of these pro-inflammatory mediators is facilitated through the binding of high-mobility group box 1 protein, engagement of Toll-like receptor 2 (TLR-2) and receptor for advanced glycation end-products (RAGE), activation of the MAPK, protein kinase C (PKC), inhibitor of kappa-light chain-enhancer of activated B cells (IκB) and nuclear factor kappa B (NF-κB) signaling pathways, and endoplasmic reticulum stress 20, 32– 35 . Correlation between serum levels of IL-1β, IL-6, TNF-α, hyaluronan, and lipocalin and disease activity in patients with SLE further highlights the importance of these inflammatory markers in the pathogenesis of LN 17, 36– 39 .…”

“…The current standard-of-care induction treatments for severe LN are corticosteroids combined with either cyclophosphamide (CYC) or MPA 96– 99 . We have reported that MPA can exert a beneficial role on inflammatory and fibrotic processes induced by anti-dsDNA antibodies in human mesangial cells and PTECs and that this role is independent of its immunosuppressive actions 14– 16, 39 . We have also demonstrated that MPA together with methylprednisolone (MP) was more effective than CYC and MP in preserving renal histology with reduced severity of renal fibrosis in New Zealand black and white first-generation (NZB/W F1) mice, possibly through the ability of MPA to decrease PKC-α activation and TGF-β1 expression 15 .…”

“…We reported that anti-dsDNA antibodies isolated from patients with LN during nephritic flare can induce secretion of pro-inflammatory mediators such as IL-6, IL-8, TNF-α, and MCP-1 through distinct MAPK pathways in cultured PTECs 14, 39 and contribute to the establishment of chemotactic gradients that permit infiltration of immune cells into the tubulo-interstitium. Bi-directional communication occurs between mesangial cells and PTECs, and inflammatory responses occurring in either kidney compartment induced by anti-dsDNA antibodies can provoke a response in the other compartment 10 .…”

Impact of Non-Human Leukocyte Antigen-Specific Antibodies in Kidney and Heart Transplantation

“…Anti DNA/histone antibodies found in the kidney with lupus nephritis can promote pathogenesis by stimulating cytokine production and inflammation (61, 62). Since DNA/histone are only exposed after cell breakdown as happened in cell apoptosis or necrosis, these antibodies are unlikely to be the initiating autoantibodies in lupus nephritis.…”

Lupus nephritis: An update on treatments and pathogenesis

“…While anti‐double‐stranded DNA (dsDNA) is a commonly used disease activity marker in LN, there is also data showing their active participation in pathogenic mechanisms that involve interactions with resident renal cells. Data from our group showed that the binding of anti‐dsDNA to proximal renal tubular epithelial cells induced the cells to adopt a more mesenchymal morphology and transform into pro‐inflammatory and pro‐fibrotic phenotypes . Data from animal and in vitro studies also showed that mycophenolic acid treatment could attenuate these cellular changes and suppress relevant pro‐inflammatory cytokine pathways, thus suggesting direct effects of treatment on renal inflammation distinct from the immunosuppressive actions of the drug …”