Abstract 374: Overexpression of Kit Ligand-2 by Direct Cardiac Injection of Recombinant Lentiviruses Improves Cardiac Repair and Rescues Mice Post-Myocardial Infarction
Background: Treatment of myocardial infarctions (MI) with cytokines is an active area of research. We have recently demonstrated the importance of the c-kit receptor in cardiac remodeling post-MI through mobilization of BM-derived cells. In this present study, we develop lentiviral vectors (LvVs) that engineer expression of the c-kit ligand (KL; or stem cell factor, SCF), as a potential approach for therapy. KL has two isoforms (KL-1, KL-2) and activates anti-apoptotic, mitotic, mobilization, and neovascularization signaling. The KL-2 isoform is missing a predominant extra-membrane cleavage site.
Methods: We first synthesized novel recombinant LvVs for KL-1 and KL-2 and infected KL deficient cells. Transduced test cells expressed KL-1 and KL-2 at high levels. Next, membrane-bound KL deficient mice (Sl/Sld) and matched wild-type (WT) mice were subjected to permanent ligation of the LAD to induce MI. Either PBS or concentrated LvV/KL-1 or LvV/KL-2 supernatants were then directly injected into left ventricles. We monitored treated mice for 5 weeks and then evaluated them for in vivo left ventricular function at sacrifice. Mobilization of inflammatory cells and hematopoietic stem/ progenitor cells in the peripheral blood (PB) were also assessed by flow cytometry. Serum cytokine expression was analyzed by ELISA.
Results: Seven days after LvV/KL-2 injection, plasma KL levels were significantly increased. At 5 weeks post-MI, left ventricular ESV was also significantly reduced in the KL-2 injected group compared to controls. Sl/Sld mice injected with PBS vehicle alone demonstrated 87.5% mortality post-MI. In contrast, Sl/Sld mice injected with LvV/KL-2 only demonstrated 28.6% mortality. This result further emphasizes the role of the c-kit receptor/KL axis in recovery post-MI. Importantly, towards general therapeutic utility, WT mice survival following MI was also profoundly improved from 35% to 73.1% following LvV/KL-2 treatment (p<0.05). NO significant impact on survival was observed with LvV/KL-1.
Conclusion: Implementation of sustained KL-2 expression mediated by cardiac LvV delivery provides important information concerning the role of this receptor axis and may prove to be a clinically useful strategy following MI.