Osteoprotegerin/RANK/RANKL axis in cardiac remodeling due to immuno-inflammatory myocardial disease.

OBJECTIVE: Osteoprotegerin (OPG) and the receptor activator of nuclear factor-kappaB ligand (RANKL) are inflammatory cytokines traditionally linked to the regulation of bone remodeling. We hypothesize that the OPG/RANK/RANKL axis may be involved in extracellular matrix remodeling in immuno-inflammatory heart diseases, and explore the probable underlying mechanisms by using anti-IL-17 in the model of experimental autoimmune myocarditis.

METHODS: EAM was induced in Lewis rats by injection of porcine cardiac myosin. All the rats were randomly distributed into day 0, day 7, day 14 and day 28 groups, which means rats in certain group were cervical dislocated on day 0, day 7, day 14 and day 28 respectively. HE staining and Masson's staining were used for measurement of cardiac hypertrophy and interstitial fibrosis. Hydroxyproline content and collagen cross-linking were determined in heart section. Anti-IL-17 or control antibody was injected i.p. 2 h before and 3 days and 7 days after the first myosin immunization in EAM model, that is, group anti-IL-17 or group control antibody. IL-17 and OPG/RANK/RANKL axis expressions were detected by realtime RT-PCR in all the six groups. In the in vitro studies, cardiac fibroblasts were cultured and treated with IL-17 or vehicle for 48 h. Total RNA was isolated from harvested cells and realtime RT-PCR was performed to detect the RANK, RANKL, OPG and MMP-2, MMP-9, TIMP-1 and TIMP-2 expressions, then matrix metalloproteinase activity was assayed.

RESULTS: Our in vivo results revealed that expression of IL-17 and the OPG/RANK/RANKL axis increased significantly from day 0 to day 28, with IL-17 and OPG increased relatively steeply. In the in vitro study, we detected OPG, RANK and RANKL mRNA expressions in the cultured fibroblasts with or without IL-17 stimulation. We found that IL-17 increased the OPG/RANK/RANKL axis activity (P<0.05). Although IL-17 induced a significant increase in MMP-2 and MMP-9 gene expressions in cardiac fibroblasts, there was no change in TIMP-2 and TIMP-1 expressions.

CONCLUSIONS: Our results suggest that the OPG/RANK/RANKL axis may be involved in cardiac remodeling in immuno-inflammatory myocardial diseases and progression of chronic HF and thus may represent targets for intervention in this disorder.