Abstract 1384: Gene Deficiency of Lnk Upregulates Cardiac Myoangiogenesis via Enhancing Proliferation of Bone Marrow-Derived Endothelial Progenitor Cells and Cardiac Stem Cells Post Myocardial Infarction
Background: Lnk is a negative regulator of self-renewal capacity of hematopoietic stem cells (HSCs). We have recently reported that lack of Lnk adaptor protein upregulates endothelial progenitor cell (EPC)-mediated signaling cascade, resulting in improvement of neovasculariza-tion in mouse model of hind limb ischemia. However, morphometrical and functional contribution of Lnk gene deletion to cardiac repair in myocardial ischemia is unknown.
Methods and Results: The c-kit+/ Sca-1+/ lineage− cells (KSL) were isolated from bone marrow (BM) of Lnk−/− mice and wild type (WT) mice as an EPC and HSC-enriched population. BrdU incorporation and number of KSL in BM was significantly greater in Lnk−/− mice compared with WT (WT, 0.4±0.0 × 105; Lnk−/−, 3.2±0.4 ×105 cells/ mouse, P<0.05). The number of cardiac stem cells (CSCs; c-kit+/ lineage− cells) isolated from whole heart tissue was greater in Lnk−/− mice than WT (WT, 2.4±0.3 × 104; Lnk−/−, 7.8±0.8 x104 cells/ heart, P<0.05). Next, MI was induced by ligating LAD of WT and Lnk−/− mice. Echocardiography and a micro-tip catheter at day 28 revealed significant preservation of LV function in Lnk−/− mice compared with WT [(1) Fractional shortening: WT, 21.0±0.2; Lnk−/−, 28.5±0.5%, P<0.01, (2) Regional wall motion score: WT, 28.2±0.2; Lnk−/−, 23.5±0.5, P<0.01, (3) +dP/dt: WT, 6896±309; Lnk−/−, 9384±292 mmHg/sec, P<0.01]. Necropsy examination disclosed significant augmentation of capillary density (WT, 91.7±2.4; Lnk−/−, 168.3±5.6 /mm2, P<0.05) and inhibition of LV fibrosis area (WT, 13.5±2.0; Lnk−/−, 6.9 ±2.2%. P<0.05) in Lnk−/− mice. The percentage of KSL in BM 7 days after MI was greater in Lnk−/− mice compared with WT (WT, 7.1±0.1; Lnk, 16.3±0.3%, P<0.05). Number of Sca-1+/ lineage− cells in peripheral blood at day 10 was also higher in Lnk−/ mice than WT (WT, 1.7±0.3 x105; Lnk, 3.6 ±0.6 x105 cells/ ml. P<0.05). Double immunohistochemistry for c-kit and GATA4 or Nkx2.5 demonstrated that CSCs in ischemic myocardium at day 7 were more frequently observed in Lnk−/− mice than WT.
Conclusions: Deficiency of Lnk represents favorable impact on EPC and CSC kinetics, resulting in functional and histological recovery from MI. Inhibition of Lnk gene expression may be a novel therapeutic target for cardiac myoangiogenesis post MI.