Lupus nephritis is a severe organ manifestation of systemic lupus
erythematosus (SLE), and is characterized by the production of anti-dsDNA
antibodies. It is an important cause of renal failure. The mechanism through which
anti-dsDNA antibodies bind to tissues and mediate kidney injury remains to be fully
elucidated. Emerging evidence suggests that anti-dsDNA antibodies can bind to cells
and extracellular antigens directly through cross-reactivity, independent of bridging
chromatin material.
Mesangial cells play an important role in normal kidney structure and
functions, and its pathophysiology. Mesangial abnormalities in lupus nephritis
precede more severe injuries such as lesions in the glomerular capillary loop. We
previously demonstrated that the binding of human anti-dsDNA antibodies to
mesangial cells (HMC) correlated with disease activity and induced inflammatory as
well as fibrotic pathways. The aim of this project is to identify the cross-reactive
antigen(s) on the mesangial cell surface that mediates anti-dsDNA antibody binding
and the alterations in cell functions that result from this interaction.
HMC plasma membrane proteins were purified. Using proteomic and
biochemical approaches, we identified annexin II as the predominant cross-reactive
antigen on the HMC surface that mediated human polyclonal anti-dsDNA antibody
binding. Following this interaction, anti-dsDNA antibodies were internalized in a
time- and temperature-dependent manner, and translocated to both the cytoplasm and
nucleus within 30 min. This resulted in induction of annexin II synthesis, IL-6
secretion and cell proliferation, which was mediated through the activation of p38
MAPK, JNK and AKT. The binding activity to annexin II in the serum
immunoglobulin fraction correlated with the titre of anti-dsDNA antibody. Binding
activity of anti-dsDNA antibodies to annexin II correlated with clinical disease
activity and circulating anti-dsDNA antibody levels. These correlations were more
prominent in male patients with lupus nephritis. Glomerular annexin II expression
was increased in patients with active lupus nephritis and co-localized with IgG and
C3 deposition. Gene silencing of annexin II in HMC reduced anti-dsDNA antibody
binding, which was accompanied by reduced IL-6 secretion and cell proliferation.
Using female NZB/W F1 mice, an established murine model of lupus
nephritis, we demonstrated that intra-glomerular annexin II expression increased
with disease progression and was accompanied by an increase in the expression of
p11, its cellular protein ligand. Our data suggest that annexin II may exist in the
kidney as a heterotetramer and is involved in disease pathogenesis. At the
ultrastructural level, annexin II was detected in the mesangial matrix, amongst
electron dense deposits in the glomerular basement membrane, on the foot processes
in podocytes and within the Bowman’s capsule.
In conclusion, our data demonstrated that annexin II is the major cell
surface antigen on HMC that mediates the cross-reactive binding of human anti-DNA
antibodies. Through this interaction, cellular processes are triggered that contribute to
the pathogenesis of lupus nephritis. / published_or_final_version / Medicine / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/182310 |
| Date | January 2012 |
| Creators | Cheung, Kwok-fan, Stephen, 張國勛 |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47869343 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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