Abstract 16934: Targeted Cardiac Delivery of miR-29b Mimic via Ultrasound-Mediated Microbubble Cavitation Attenuates Myocardial Fibrosis

Abstract

Introduction: Cardiac fibrosis contributes to adverse ventricular remodeling in ischemic or hypertensive heart disease, increases heart failure risk, and is associated with loss of microRNA-29b (miR-29b). Plasmid or i.v. injection of miR-29b mimic has proven the concept that restoring miR-29b blunts cardiac fibrosis, but these are inefficient, non-targeted delivery strategies with low clinical translational potential. We hypothesized that ultrasound (US) mediated cavitation of microbubbles (MBs) loaded with miR-29b mimic would inhibit cardiac fibrosis. We first tested effects of US-targeted cavitation of miR29b-MBs (UTMC) on cardiac fibroblasts in vitro , then performed in vivo studies in a mouse model of angiotensin II (ANGII)-induced hypertension/fibrosis. Methods: Cationic lipid MBs were loaded with miR-29b mimic or negative control (NC) miRNA, placed with cultured neonatal cardiac fibroblasts, then treated with 10 sec pulsed US ( f =1.3 MHz, MI 1.6, 4 frames/burst, 4 bursts/second). Cells were harvested at 24 hrs to measure downstream fibrotic mediators. Mice received continuous ANGII infusion via osmotic pump and UTMC with miRNA-loaded MBs at days 0, 3, 7. Serial echo was performed; the heart was harvested on day 10. Results: In cardiac fibroblasts, UTMC treatment with MBs loaded with miR-29b mimic vs NC miRNA caused a 543±51% increase in miR-29b ( p <0.01) and knockdown in transcripts for collagen 1A1 (26±6%, p <0.01), collagen 1A2 (53±8%, p <0.01), collagen III (31±5%, p <0.01), and fibrillin (43±10%, p <0.05) ( n =4/group). ANGII mice treated with UTMC + miR-29b mimic vs. NC miRNA ( n =8-9/group) had downregulated cardiac fibrillin (37±8%, p <0.05); trends of lower collagen IA1, 1A2, and III by RT-PCR; decreased cardiac α-SMA protein by immunoblot ( p <0.05); and preservation of ejection fraction and fractional shortening ( p <0.01). Conclusion: UTMC-mediated delivery of miR-29b mimic blunts pathologic expression of fibrosis markers and is associated with preservation of left ventricular function in ANGII-induced murine cardiac fibrosis. This is the first demonstration of UTMC-delivery of a miRNA mimic for attenuating cardiac fibrosis, and has promising implications for targeted RNA-based approaches for treating cardiac disease.