Cyclic GMP catabolism up-regulation in MRL/lpr lupus-prone mice is associated with organ remodeling

Production of high titer of antibodies against nuclear components is a hallmark of systemic lupus erythematosus, an autoimmune disease characterized by the progressive chronic inflammation of multiple joints and organs. Organ damage and dysfunction such as renal failure are typical clinical features in lupus. Cell hypermetabolism and hypertrophy can accelerate organ dysfunction. In this study we focus on a specific murine model of lupus, the MRL/lpr strain, and investigated the role of cyclic guanosine monophosphate (cGMP) catabolism in organ remodeling of main target tissues (kidney, spleen and liver) in comparison with age-matched control mice. In MRL/lpr-prone mice, the cGMP-phosphodiesterase (PDE) activities were significantly increased in the kidney (3-fold, P<0.001), spleen (2-fold, P<0.001) and liver (1.6-fold, P<0.05). These raised activity levels were paralleled by both an increased activity of PDE1 in the kidney (associated with nephromegaly) and in the liver, and PDE2 in the spleen of lupus-prone mice. The up-regulation of PDE1 and PDE2 activities were associated with a decrease in intracellular cGMP levels. This underlines an alteration of cGMP-PDE signaling in the kidney, spleen and liver targeting different PDEs according to organs. In good agreement with these findings, a single intravenous administration to MRL/lpr mice of nimodipine (PDE1 inhibitor) but not of EHNA (PDE2 inhibitor) was able to significantly lower peripheral hypercellularity (P=0.0401), a characteristic feature of this strain of lupus-prone mice. Collectively, our findings are important for generating personalized strategies to prevent certain forms of the lupus disease as well as for understanding the role of PDEs and cGMP in the pathophysiology of lupus.