Abstract 11585: Lipid Nanoparticle Encapsulated SiRNA Against CCR2 Ameliorates Autoimmune Myocarditis and Impacts Myeloid Progenitor Trafficking
Background: Myocarditis is characterized by the infiltration of inflammatory cells which damage cardiac myocytes. Monocytes are the most prominent population of accumulating leukocytes. Here we investigated whether in vivo administration of lipid nanoparticle encapsulated siRNA against CCR2 - a receptor crucial for accumulation of pro-inflammatory Ly6Chigh monocytes - reduces inflammation in mice with autoimmune myocarditis.
Methods and Results: Flow cytometric analysis showed that siRNA against CCR2 (siCCR2) reduced the number of Ly6Chigh monocytes in acute myocarditis by 69% (p < 0.05), corroborated by histological assessment. T2* weighted MRI after injection of iron-oxide nanoparticle detected myocarditis noninvasively (Contrast-to-noise-ratio: 14 ± 4 in controls vs. -0.1 ± 2 in mice with myocarditis; p = 0.008). A longitudinal imaging trial combined molecular imaging to quantify myeloid cells on day 21 with MRI volumetry on day 60 for cardiac function. Mice with acute myocarditis showed a drastic reduction of signal, which was prevented by siCCR2 treatment. At follow-up, mice that received siCCR2 showed a significantly better ejection fraction than control-treated mice. The therapeutic nanoparticle was found to be incorporated by monocytes in the bone marrow. In addition, an uptake and subsequent reduction of CCR2-expression was observed in myeloid progenitor cells (GMP). Treatment with siCCR2 prevented the release of monocytes and GMPs from the bone marrow (control treatment: 2.9 x 10_5 ± 9 x 10_4 vs. siCCR2: 5.9 x 10_5 ± 7 x 10_4; p < 0.05). Finally, while autoimmune myocarditis induced extramedullary hematopoiesis in the spleen, accumulation of GMPs and monocytes was reduced in mice treated with siCCR2 (15.4 x 10_4 ± 2 x 10_4 vs. 7.1 x 10_4 ± 1 x 10_4; p = 0.01).
Conclusion: Therapeutic silencing of CCR2 reduced cardiac inflammation by inhibition of monocyte recruitment. We report in vivo RNAi in blood stem cells for the first time, which prevented splenic seeding of GMPs and attenuated monocytopoiesis.
- © 2012 by American Heart Association, Inc.