Background/Purpose: Liver dysfunction, characterized by serum elevation of liver enzymes, is detectable in 20% of patients with systemic lupus erythematosus (SLE.)  Males had a higher prevalence of liver dysfunction (12/33: 36%) than females (65/387; 18%; p=0.014; Yu and Perl submitted). Patients with SLE have mitochondrial dysfunction with increased mitochondrial mass and transmembrane potential, yet the biochemical consequences of mitochondrial accumulation in SLE have yet to be determined.  ATP generation is reduced in SLE, a process which is regulated by O₂ consumption through the electron transport chain (ETC) of mitochondria.  Here, we characterize utilization of O₂through the ETC and the generation of oxidative stress in pre-disease lupus-prone MRL/lpr mice to determine whether mitochondrial dysfunction precedes onset of SLE.

Methods: Mitochondrial ETC activity of isolated liver mitochondria was assessed in 4-week-old MRL/lpr lupus-prone mice as well as C57BL/6, MRL/MpJ, and Black 6/lpr age and gender-matched controls mice.  ETC was measured O₂ with a Clark electrode.  State IV respiration, a measurement of O₂ consumption through complex II, was measured by addition of succinate, ADP, and inorganic phosphate to isolated mitochondria.  Hydrogen peroxide (DCF-DA), superoxide (HE), peroxynitrite (DAR-4M), nitric oxide (DAF-FM),  mitochondrial potential (JC-1, TMRM), and mitochondrial mass (NAO) were measured by flow cytometry of isolated liver mitochondria.  Statistical analysis of data was done by paired t-tests and Pearson’s correlation analysis using GraphPad 5.0 software, with a cutoff of p<0.05 considered significant. 

Results: 4 week old male MRL/lpr mice exhibited increased mitochondrial respiratory capacity, measured by complex II respiration, in comparison to C57BL/6 (25.8%, p=.03) and Black 6/lpr (11.4%, p=.004) control strains.  Mitochondrial mass was increased in male MRL/lpr mice in comparison to C57BL/6 (+26.5%, p=.04) and Black 6/lpr (+55.5%, p=.001).  Male MRL/lpr mitochondria also had increased mitochondrial potential (+64.2%, p=.006), production of hydrogen peroxide (+60.0%, p=.02), superoxide (+72.4%, p=.03), nitric oxide (56.1%, p=.0004), and peroxynitrite (107.9%, p=.0005) relative to Black 6/lpr controls.  Mitochondrial potential positively correlated with production of hydrogen peroxide (r= 0.883, p=0.047), superoxide (r= 0.881, p=0.049), and peroxynitrite (r= 0.912, p=0.031).  MRL/lpr females had increased complex II state 4 respiration (+51.2%, p=0.02) relative to Black 6 controls.

Conclusion: Mitochondrial dysfunction, characterized by increased respiratory capacity and increased mitochondrial mass, precedes disease onset in lupus-prone MRL/lpr mice.   We show these changes correlate with increased production of reactive oxygen and nitrogen intermediates, which cause oxidative stress in SLE. Mitochondrial dysfunction in MRL/lpr was more robust in males than females that may account for a higher prevalence of liver disease in men than women with SLE.

---

« Back to 2012 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/mitochondrial-dysfunction-in-the-liver-of-lupus-prone-mrllpr-mice-prior-to-disease-onset/