Abstract 3753: Critical Role of Scavenger Receptor-BI Expressing Bone Marrow-Derived Endothelial Progenitor Cells in the Attenuation of Allograft Vasculopathy by Human Apo A-I Transfer
Background: Accelerated endothelial regeneration mediated by enhanced endothelial progenitor cell (EPC) incorporation may attenuate the development of allograft vasculopathy.
Hypothesis: We investigated the hypothesis that modulation of EPC biology and attenuation of allograft vasculopathy by increased HDL cholesterol following human apo A-I (AdA-I) transfer requires scavenger receptor (SR)-BI expression in bone marrow-derived EPCs.
Methods: Bone marrow transplantations with SR-BI+/+ or SR-BI−/− bone marrow were performed 4 weeks before gene transfer or saline injection. E1E3E4-deleted vectors containing a hepatocyte-specific human apo A-I expression cassette or containing no expression cassette were injected via the tail vein. Two weeks later, a common carotid artery of a female Balb/c donor mouse was transplanted paratopically into male recipient C57BL/6 mice. To analyse EPC incorporation, sex mismatch bone marrow transplantations were performed in female C57BL/6 mice and incorporated EPCs were quantified by in situ hybridization for the murine Y-chromosome.
Results: Following AdA-I transfer, the number of circulating EPCs increased 2.0-fold (p<0.0001) at different time-points in C57BL/6 mice transplanted with SR-BI+/+ bone marrow but was unaltered in mice with SR-BI−/− bone marrow. The effect of HDL on EPC migration in vitro requires signaling via SR-BI and extracellular signal-regulated kinases (ERK) and is dependent on increased NO production in EPCs. Human apo A-I transfer 2 weeks before paratopic artery transplantation reduced intimal area at day 21 3.7-fold (p<0.001) in mice with SR-BI+/+ bone marrow but had no effect in mice with SR-BI−/− bone marrow. The number of CD31 positive endothelial cells lining the lumen and the number of incorporated EPCs was increased 3.0-fold (p<0.001) and 9.7-fold (p<0.001), respectively, in AdA-I treated chimeric SR-BI+/+ mice compared to control mice with SR-BI+/+ bone marrow. Endothelial regeneration and EPC incorporation was not increased after AdA-I transfer in chimeric SR-BI−/−mice.
Conclusion: Human apo A-I transfer-mediated endothelial regeneration to prevent allograft vasculopathy is strictly dependent on SR-BI expressing bone marrow-derived EPCs.