osteoprotegerin and Reperfusion-Injury

The RANK (receptor activator of nuclear factor κB)/RANKL (RANK ligand)/OPG (osteoprotegerin) axis is activated after myocardial infarction (MI), but its pathophysiological role is not well understood. Here, we investigated how global and cell compartment-selective inhibition of RANKL affects cardiac function and remodeling after MI in mice. Global RANKL inhibition was achieved by treatment of human RANKL knock-in (huRANKL-KI) mice with the monoclonal antibody AMG161. huRANKL-KI mice express a chimeric RANKL protein wherein part of the RANKL molecule is humanized. AMG161 inhibits human and chimeric but not murine RANKL. To dissect the pathophysiological role of RANKL derived from hematopoietic and mesenchymal cells, we selectively exchanged the hematopoietic cell compartment by lethal irradiation and across-genotype bone marrow transplantation between wild-type and huRANKL-KI mice, exploiting the specificity of AMG161. After permanent coronary artery ligation, mice were injected with AMG161 or an isotype control antibody over 4 weeks post-MI. MI increased RANKL expression mainly in cardiomyocytes and scar-infiltrating cells 4 weeks after MI. Only inhibition of RANKL derived from hematopoietic cellular sources, but not global or mesenchymal RANKL inhibition, improved post-infarct survival and cardiac function. Mechanistically, hematopoietic RANKL inhibition reduced expression of the pro-inflammatory cytokine IL-1ß in the cardiac cellular infiltrate. In conclusion, inhibition of RANKL derived from hematopoietic cellular sources is beneficial to maintain post-ischemic cardiac function by reduction of pro-inflammatory cytokine production. KEY MESSAGES: Experimental myocardial infarction (MI) augments cardiac RANKL expression in mice. RANKL expression is increased in cardiomyocytes and scar-infiltrating cells after MI. Global or mesenchymal cell RANKL inhibition has no influence on cardiac function after MI. Inhibition of RANKL derived from hematopoietic cells improves heart function post-MI. Hematopoietic RANKL inhibition reduces pro-inflammatory cytokines in scar-infiltrating cells.

Topics: Animals; Cytokines; Hematopoietic Stem Cells; Male; Mesenchymal Stem Cells; Mice, Inbred C57BL; Mice, Transgenic; Myocardial Infarction; Myocytes, Cardiac; Osteoprotegerin; RANK Ligand; Receptor Activator of Nuclear Factor-kappa B; Reperfusion Injury

The transcription factor nuclear factor kappaB (NF-κB) plays diverse roles in the acute injury response to hepatic ischemia/reperfusion (I/R). Activation of NF-κB in Kupffer cells promotes inflammation through cytokine expression, whereas activation in hepatocytes may be cell protective. The interaction of receptor activator of NF-κB (RANK) and its ligand (RANKL) promotes NF-κB activation; however, this ligand-receptor system has not been studied in acute liver injury. In the current study, we sought to determine if RANK and RANKL were important in the hepatic response to I/R. Mice were subjected to partial hepatic ischemia followed by reperfusion. In some experiments, mice received recombinant RANKL or neutralizing antibodies to RANKL 1 hour prior to surgery or at reperfusion to assess the role of RANK/RANKL signaling during I/R injury. RANK was constitutively expressed in the liver and was not altered by I/R. RANK was strongly expressed in hepatocytes and very weakly expressed in Kupffer cells. Serum RANKL concentrations increased after I/R and peaked 4 hours after reperfusion. Serum levels of osteoprotegerin (OPG), a decoy receptor for RANKL, steadily increased over the 8-hour period of reperfusion. Treatment with RANKL, before ischemia or at reperfusion, increased hepatocyte NF-κB activation and significantly reduced liver injury. These beneficial effects occurred without any effect on cytokine expression or liver inflammation. Treatment with anti-RANKL antibodies had no effect on liver I/R injury.. During the course of injury, endogenous OPG appears to suppress the effects of RANKL. However, exogenous administration of RANKL, given either prophylactically or postinjury, reduces liver injury in a manner associated with increased hepatocyte NF-κB activation. The data suggest that RANK/RANKL may be a viable therapeutic target in acute liver injury.

Topics: Animals; Cells, Cultured; Hepatocytes; In Vitro Techniques; Kupffer Cells; Liver; Male; Mice; Mice, Inbred C57BL; Models, Animal; NF-kappa B; Osteoprotegerin; RANK Ligand; Receptor Activator of Nuclear Factor-kappa B; Recombinant Proteins; Reperfusion Injury; Signal Transduction