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Abstract: FR-PO1065

Neuraminidase Activity Mediates IL-6 Secretion from Activated Lupus Mesangial Cells Through TLR4 and MAPK p38

Session Information

Category: Glomerular Diseases

  • 1202 Glomerular Diseases: Immunology and Inflammation

Authors

  • Nowling, Tamara, Medical University of South Carolina, Charleston, South Carolina, United States
  • Sundararaj, Kamala, Medical University of South Carolina, Charleston, South Carolina, United States
  • Rodgers, Jessalyn Ierardi, Medical University of South Carolina, Charleston, South Carolina, United States
Background

Glycosphingolipid (GSL) levels and the activity/levels of the enzyme neuraminidase (NEU), which mediates GSL catabolism, are elevated in the kidneys and/or urine of lupus mice and human patients with nephritis compared to their non-nephritic counterparts and healthy controls. We recently demonstrated that NEU activity mediates IL-6 secretion from mesangial cells (MCs) in response to activation by heat aggregated IgG (HA-IgG) and lupus serum. Our previous results demonstrated that NEU1 and NEU3 staining partially overlapped with IgG deposits in cell cultures of primary MCs stimulated with HA-IgG and in renal sections of kidneys from nephritic lupus mice. Both Fcγ receptors (FcγRs) and TLRs can mediate immune complex activation of cells, are expressed by MCs, and were shown to be involved in progression of lupus nephritis. In this study, we examined the role of FcγRs and toll like receptors (TLRs), and downstream signaling pathways in NEU-mediated secretion of IL-6 by activated lupus prone MCs.

Methods

Cell surface receptors and MAPK pathways were identified by treating MC cultures with antibodies and inhibitors, respectively, prior to activation with HA-IgG or lupus serum. Phosphorylation of p38 was analyzed by western immunoblot. Cellular localization of NEUs and TLR4 was performed by immunofluorescence. Screening of cytokines secreted by MCs was performed using a 20-plex Luminex cytokine array. Levels of individual cytokines were quantified by ELISA.

Results

Blocking TLR4 significantly inhibited, while blocking FcγRs had no effect on, NEU-mediated IL-6 secretion by activated MCs. Preliminary results show overlap between TLR4 and NEU1 at the plasma membrane of MCs. An inhibitor of the p38 MAPK pathway significantly blocked NEU mediated IL-6 secretion. Phosphorylation of p38 was increased following activation of MCs with HA-IgG or lupus serum and was blocked when NEU activity was inhibited or NEU1 expression was reduced. Although several cytokines were secreted in response to activation by both HA-IgG and lupus serum, only IL-6 and IP-10 (CXCL10) were blocked when NEU activity was inhibited.

Conclusion

Together our results suggest that NEU specifically mediates secretion of IL-6 and IP-10, two cytokines important during early development of lupus nephritis, from activated lupus prone MCs through a TLR4-p38 MAPK pathway.

Funding

  • Other U.S. Government Support