Introduction: The autoimmune disease systemic lupus erythematosus predominantly affects women and can lead to lupus nephritis (LN) as a common and severe complication in approximately 50% of patients. The F1 hybrid of New Zealand Black (NZB) X New Zealand White (NZW) mice (NZBWF1) is a well-established mouse model to study LN. Our previous data indicated that the onset of albuminuria in female 34-week NZBWF1 mice was associated with renal iron accumulation, and iron may contribute to renal injury. This study tests the hypothesis that 34-week NZBWF1 lupus mice are sensitized to irons injurious and pro-inflammatory effects compared to 8-week normal NZBWF1 mice. As a means to differentiate effects of age as opposed to development of lupus, parallel experiments were performed in 8 and 34-week-old NZW mice as healthy controls.
Methods and
Results: Female 8-week (pre-autoimmune) and 34-week NZBWF1 (autoimmune, pre-albuminuric) mice together with age-matched healthy control NZW mice underwent 24 h urine collection to confirm non-albuminuric status. Mice were then were injected i.v. with a single dose of iron-sucrose (2 mg elemental iron) or vehicle (saline) and sacrificed 24 h later. Plasma blood urea nitrogen (BUN) was measured to determine renal health, SRY-Box Transcription Factor 9 (SOX-9)- positive cells were quantified in kidney sections as an early tubular injury marker, and plasma monocyte chemoattractant protein-1 (MCP-1) was measured by ELISA as an inflammatory marker. Lupus (NZBWF1) and control mice (NZW) were compared within strains by age (8-week vs. 34-week) and treatment (Vehicle vs. Treatment). All statistical analyses were done by 2-way ANOVA (n=7-12/group), and post-hoc testing was done using Bonferroni. Iron-sucrose treatment significantly increased plasma MCP-1 concentrations in the NZBWF1 and the control NZW mice (PTreatment lt; 0.01). There was no significant effect of age on this effect for NZW mice (PTreatment*Age = 0.2); however, in NZBWF1 mice, the iron-sucrose induced increase in MCP-1 was significantly greater in 34-week compared to 8-week mice (PTreatment*Age lt; 0.05; Plt;0.05 by posthoc test). BUN was significantly increased with age in both strains (PAgelt;0.05), but there was no significant effect of iron-sucrose (PTreatmentgt;0.05). The numbers of SOX-9+ tubular cells increased in the 34-week NZBWF1 mice compared to 8-week mice (Pagelt;0.05), consistent with early stages of renal injury, but iron sucrose treatment did not show any significant effect (PTreatment = 0.9).
Conclusion: Our data suggest that at the autoimmune but pre-albuminuric stage, 34-week NZBWF1 mice show increased pro-inflammatory responsiveness to iron-mediated stress. Further studies to determine whether the enhanced pro-inflammatory effects of iron contribute to pathology in lupus nephritis are ongoing.
Support or Funding Information
This work was supported by NIH Grant 1R01DK119337.
