Abstract 549: Extracellular Heat Shock Protein 27 Signals Through NF-κB to Favorably Modulate Macrophage Inflammation
Background: Previously we demonstrated that recombinant Heat Shock Protein 27 (rHSP27) reduces atherosclerotic lesion formation when administered to ApoE-/- mice. In addition, administration of rHSP27 to ApoE-/- mice with established atherosclerotic lesions halts lesion progression and is associated with lesion modifications that are consistent with resilience to plaque rupture. However, the mechanism(s) for these therapeutic effects remain elusive.
Objective: To determine whether rHSP27 favorably modulates macrophage inflammation by focusing on NF-kB signaling.
Methods/Results: Activation of the NF-kB signaling pathway by rHSP27 was observed in peritoneal macrophages from ApoE-/- mice. Treatment with rHSP27 for 30 minutes activated the translocation of the NF-kB p65 subunit from the cytosol to the nucleus as observed by immunolabeling. A dose-dependant increase in rHSP27 mediated NF-kB activation was observed in RAW 264.7 macrophages stably transfected with an NF-kB inducible reporter gene (15 fold; p<0.05). The use of an N-terminal deletion mutant of rHSP27, rC1, at equimolar concentrations did not induce NF-kB activation, demonstrating specificity of the full-length protein. In addition, NF-kB inhibitors (BAY 11-7082 and MG-132) attenuated the induction of the NF-kB reporter gene by rHSP27, thereby implicating the involvement of IkBa phosphorylation and degradation by the proteasome. A consequence of rHSP27 signaling in macrophages was the up-regulation of the transcript for the haematopoietic growth factor/regulator, GM-CSF (300 fold; p<0.05) and subsequently its secretion (400 fold, p<0.05). In the presence of BAY, GM-CSF expression was inhibited suggesting the involvement of NF-kB.
Conclusions: rHSP27 promotes the nuclear translocation and activation of NF-kB in macrophages which results in the up-regulation of GM-CSF, a haematopoietic growth factor/regulator that may be responsible for the observed therapeutic effects of rHSP27 in vivo. Current studies are testing rHSP27 therapy in ApoE-/- mice deficient in GM-CSF in order to evaluate the importance of macrophage modulation for the beneficial affects of rHSP27 in atherogenesis.
- © 2012 by American Heart Association, Inc.