Abstract 801: Pivotal Role of Lnk Adaptor Protein for Endothelial Progenitor Cells Commitment and Neovascularization
The origin of EPCs and differentiation cascade of EPCs in microenvironment are still unclear. We here demonstrate that Lnk, a negative regulator for the HSCs proliferation, controls EPC expansion and commitment in bone marrow and vasculogenesis in response to ischemic disease. In lnk −/− mice, CD34 (−) /KSL, supposed hemangioblastic cells, increased in number and presented higher incidence of small EPC-CFU (early EPC colony) in EPC colony assay. The CD34(dim) fraction in CD34 (+) KSL, committing KSL population, increased in number and demonstrated higher incidence of large EPC-CFU (late EPC colony) in lnk −/− mice. In ex vivo expansion, 34(−) and 34(dim) fractions were main populations to be expanded in lnk null KSL, resulting in further early and late EPC colony formations, indicating that Lnk functions as the definitive regulator of expansion and commitment signals in hemangioblast. FACS analysis of BM and peripheral blood in lnk −/− mice clearly supported EPC enrichment in vivo, showing the significant increase in EPCs, expressing flk-1, sca-1, CD31, CXCR4 and VE-cadherin. In ischemia model of hindlimb, we found augmentation of ischemia recovery via enhanced EPC pools in lnk −/− mice. Especially EPC kinetics was initiated by the administration of stem cell factor (SCF) or vascular endothelial growth factors (VEGF) in lnk −/− mice. This is also supported by the finding of signal stimulation for phosphorylation cascade of Akt (Ser473) and eNOS (Ser1117) ), relating signals for SCF and VEGF, in lnk deficient EPCs. Retina ischemia (neonatal retinopathy) model demonstrated the augmented recovery of blood vessel and astrocyte structure in retina of lnk −/− mice, compared to the incidence of avascular area with astrocyte disarray in control retina. Furthermore, BM transplantation (BMT) from lnk −/− (co-encoding GFP) BM showed enhanced capillary structure. BMT from GFP-marked wild-type BM into lnk −/− mice did not restore neovascularization of the ischemic limb, suggesting that Lnk regulates signals only in EPC, but not in situ endothelial cells. Our present data suggest that Lnk is a definitive regulator of signals for EPC biology. The selective targeting of Lnk may be a potential therapeutic approach for the treatment of vascular diseases by modulating EPC function.