Abstract 1586: Critical Role for Leukocyte Hypoxia Inducible Factor-1α Expression in Post-MI Left Ventricular Remodeling
HIF-1α is an inducible protein stabilized by hypoxia; it regulates cytokines involved in the inflammatory response after myocardial infarction (MI); it affects white blood cells (WBCs) function by stimulating glycolysis, the sole energy source of WBCs. The effect of modulation of the inflammatory response on the myocardium by inhibiting HIF-1α in HSC is unknown. We hypothesized that decreasing HIF-1α in hematopoietic stem cells (HSC) would result in reduced inflammation through inhibition of WBCs recruitment to ischemic myocardium and improve heart function.
Methods: Bone marrow (BM) was harvested from 4 – 6 week-old Rosa mice by flushing femurs; HSC (lin−, cKit+) were transfected with a lentivirus encoding siRNA to HIF-1a and GFP. Cells expressing GFP were sorted by FACS. Eight week old C57/BL6J mice received 50,000 HIF-1α or scramble siRNA transfected HSC. LAD ligation was done 6 weeks after BM transplantation; echocardiography was done at 3, 7, and 28 days after AMI. Peritonitis was induced by Thioglycollate injection intraperitoneally. Cytokines gene array was done to assess the modulation of cytokines genes in both groups after peritonitis.
Results: In the peritonitis model, HIF-1α siRNA group (n=6) had a significant decrease in WBC migration to the peritoneum compared to control mice (n=4) (4088.6 ± 2447.7 vs. 9445.0 ± 4009, p= 0.021). The fractional shortening (FS) was similar in both groups at baseline and 3 days post MI. Consistent with decreased inflammation after AMI in the HIF-1a: siRNA mice we observed an improvement in FS at 7 days in the HIF siRNA group; at 28 days, FS became significantly higher in the HIF-1α siRNA group (n=5) vs. control group (n=5) (27.4 ± 13.4 vs. 10.2 ± 5.7, p= 0.03). Gene array results comparing circulating leukocytes following intraperitoneal thioglycolate injection suggested suppression of genes responsible for WBCs migration in response to cytokines namely ccr1, 2, 3, and 4 in the WBCs lacking HIF-1α.
Conclusion: Down regulation of leukocyte HIF-1α expression decreased the recruitment of WBCs to the sites of inflammation and improved heart function after MI. These results suggest that down regulation of HIF-1α suppresses WBC cytokine receptors ccr1, 2, 3, and 4 necessary for WBC recruitment to inflammatory cytokines after MI.