REPETITIVE TARGETED DELIVERY OF GDF11 BY ULTRASOUND-MEDIATED CATIONIC MICROBUBBLE DESTRUCTION REJUVENATES AND PROTECTS THE AGED MOUSE HEART

Abstract

Preclinical studies demonstrated dramatic improvements in ventricular function with the implantation of stem cells into the damaged myocardium. However, stem cells in aged recipients have reduced regenerative potential, and aged tissues have diminished renewal capacity even with potent stem cells. Growth differentiation factor 11 (GDF11), a member of the TGF-β superfamily, has been shown to reverse age-related cardiac hypertrophy and skeletal muscular dysfunction, remodel the cerebral vasculature of aged mice and enhance olfactory neurogenesis. However, systemic delivery of recombinant GDF11 protein may not be the ideal method to rejuvenate specific organs. To evaluate a non-invasive method to protect aged hearts from ischemic injury, we tested whether a GDF11 expression plasmid construct could be delivered via ultrasound-targeted microbubble destruction (UTMD) using our effective cationic microbubbles (CMBs). Young (aged 3 months) and old (aged 20-22 months) C57BL/6 mice were used to evaluate the expression of GDF11 mRNA and protein at baseline and after ischemia/reperfusion (I/R) injury. GDF11 mRNA and protein expression at baseline in old mice was significantly lower than in young mice. GDF11 transcript and protein expression were significantly upregulated in the ischemic hearts of young and old mice 3 days after I/R compared to baseline, but the increase in the aged ischemic hearts was less than in young mice after I/R injury. To enhance the expression of GDF11 in aged mouse hearts, UTMD was used to deliver a mouse GDF11 expression plasmid to the ischemic hearts of aged mice 3 and 6 days after I/R. A control group received the empty vector. UTMD-mediated delivery of GDF11 effectively increased the expression of GDF11 specifically in cardiac tissue, but not in other organs of the old mice. UTMD-mediated delivery of GDF11 improved cardiac systolic and diastolic function and reduced infarct size in the aged mice 21 days after I/R. Additional investigations to determine the underlying mechanism of this functional benefit revealed that UTMD-mediated delivery of GDF11 stimulated cKit+ and Sca-1+ cardiac stem cell proliferation and decreased the expression of senescence markers (p16, p53) and the number of p16+ CSCs in the hearts of old mice post-I/R. Repetitive targeted delivery of GDF11 plasmid via UTMD using CMBs can rejuvenate aged mouse hearts and protect them from I/R injury.