Abstract 16767: Exosomes Mediate Heat Shock Protein 27 Athero-Protective Signalling

Introduction: Exosomes represent a discrete population of nano-vesicles secreted by a variety of cells and may contain unique protein cargo that play a role in inter-cellular signalling. We previously showed (ATVB 2009, JACC 2013) that membrane-like vesicles mediate the release of the novel biomarker and athero-protective agent, Heat Shock Protein 27 (HSP27), however did not explore downstream signalling effects of HSP27-laden exosomes. Hypothesis: Monocyte derived exosomes facilitate the transfer of HSP27 to human aortic endothelial cells (HAEC) and THP-1 MΦ to elicit athero-protective signalling effects. Methods: Exosome particles were purified from conditioned medium of THP-1 monocytes. As we previously showed that HSP27 athero-protection involves activation of NF-kB (e.g., with resultant changes in the expression of key athero-protective genes) we sought to determine if exosomes alter NF-kB signalling, as well as augment the internalization of HSP27 into cells as a cell membrane receptor for HSP27 is yet to be established. Results: Purified THP-1 derived exosomes express the classical exosome biomarkers CD81 and MHC-II. Flow cytometry revealed that 18% and 23% of these exosomes are positive for HSP27 immunolabeling with 10 and 40 μg/ml anti-Hsp27-FITC, respectively. The fraction of positive exosomes dropped to 3% when 40 μg/ml of recombinant HSP27 (rHSP27) was co-mixed with these samples and 10 μg/ml anti-HSP27-FITC, thereby confirming immunolabeling specificity. In contrast, a FITC labeled truncated form of the C-terminus of HSP27 (referred to as rC1-FITC) did not bind to exosomes. Indeed, exogenous rHSP27 bound to exosomes potentiated a ~50% increase of triggered NF-κB signalling (p<0.001) in THP-1 MΦ containing an alkaline phosphatase NF-kB reporter construct, while the truncated form of HSP27 (or rC1) did not (p=0.56). In both THP-1 MΦ and HAEC internalization of rHSP27-FITC into cells improved dramatically after exosome binding (e.g., THP-1: 157% increase, p<0.0001), while rC1-FITC had no effect. Conclusion: Exosomes contain HSP27 cargo that provide a novel inter-cellular signalling mechanism for the athero-protective effects of HSP27 by activating NF-kB and facilitating HSP27 internalization into cells.