Renal C3 Production Drives Acute Kidney Injury and Acute Kidney Disease in Diabetics with Sepsis

Introduction: Type 2 diabetics (T2D) suffer the greatest sepsis mortality due to the development of acute kidney injury (AKI), which progresses to acute kidney disease (AKD), renal failure, and death. Systemic inflammation and complement production are known to provoke AKI during sepsis. We hypothesize that sepsis induced renal inflammation and complement production drives progression of AKI to AKD in T2D.

Methods: C3-/-, TLR2-/-, TNF-/-, C57BL/6, and Diet Induced Obese (T2D) 30 week old mice underwent sepsis from cecal ligation and puncture (CLP_LD20) or sham procedure. At serial time points, plasma and kidneys were harvested (n=5 mice/group). Multiplex RT-PCR arrays were used to evaluate toll like receptors (TLR), complement, and immune signaling cascades. TNF, BUN, creatinine, and NGAL were evaluated by ELISA.

Results: In lean mice, renal NGAL, representing AKI, peaked at 1 day and returned to baseline 7 days after CLP. In T2D mice, NGAL persisted past 7 days and peaked after 14 days, indicating transition to AKD (p<0.001). Renal C3 mRNA levels were eight-fold higher 1 day after CLP in lean and T2D mice compared to sham (p<0.001). In lean mice, C3 levels returned to baseline at 7 days. C3 levels in T2D mice peaked at 2 weeks and persisted. Renal in-situ hybridization showed significantly more C3 in septic T2D mice compared to lean mice. RT-PCR analysis showed significantly more renal TLR2, TNF, and C3 mRNA in T2D mice compared to lean mice. C3, TLR2, and TNF null mice each produced less renal C3 and NGAL, demonstrating less AKI and AKD (p<0.001). In T2D mice, TNF inhibition blocked C3 and NGAL production, representing prevention of AKI and AKD after sepsis.

Conclusion: Lean mice resolve sepsis induced AKI by 7 days. In T2D mice, AKI persists past 7 days and progresses to AKD. The T2D AKI to AKD progression is dependent on local renal C3 production through TLR2 and TNF signaling. TNF inhibition is a novel strategy to prevent AKI progression to AKD, preserve renal function, and improve T2D sepsis mortality.