Vascularization is an essential process involved in embryonic development and vascular remodeling. Numerous stimuli (i.e. shear stress, cytokines, growth factors) promote vessel growth through PI3K-dependent Akt activation. Activated Akt (Akt1/Akt2/Akt3) targets a wide range of substrates involved in key endothelial functions, including regulation of vascular tone, angiogenesis, and cellular recruitment to vessel walls. Endothelial cells (EC) and vascular smooth muscle cells (SMC) express predominantly the Akt1 isoform. Several groups have demonstrated impaired migratory and proliferative responses in cultured Akt1-null EC and SMC, thereby supporting the pro-angiogenic role of PI3K/Akt signaling across vascular cell types. PI3K/Akt signaling is also critical during adult angiogenesis, as global loss of Akt1 results in impaired ischemia- and VEGF-induced angiogenesis. Global knockout models of the Akt isoforms have helped unravel the physiological roles of Akt. However, the emergence of nonredundant phenotypes along with ubiquitous expression of Akt1 limits our understanding of Akt1 function in a cell-specific manner. We have therefore generated conditional Akt1flox/flox mice to examine the importance of EC- and SMC-specific Akt1 loss during embryonic and postnatal angiogenesis. We have additionally bred the conditional Akt1 mice to an Akt2-null background, effectively creating an inducible double knockout mouse to address possible compensation effects. We intend to examine how EC-specific Akt1 deletion affects the retinal vasculature and adult ischemia-induced angiogenesis. Given that the endothelium regulates vascular tone through Akt-dependent nitric oxide production, we will include vascular reactivity studies to measure consequent effects on vessel tone. The hind-limb ischemia model will also be applied to investigate how the SMC-specific loss of Akt1 influences resulting arteriogenesis/angiogenesis and vascular remodeling. These studies will be further complemented with use of our inducible double knockout mice to examine the consequent effect of dual Akt1/2 loss. Thus, the overall focus of this proposal is to elucidate the roles of Akt1 and Akt2 in two major vascular cell types (EC and SMC) using several established molecular, cellular, and genetic approaches.
Vascular development and growth are essential biological processes involving multiple cell types and signaling pathways, where dysregulation is associated with various human pathologies. Research in the last several years has led to approval of anti-angiogenic drugs for treatment of cancer, ocular, and cardiovascular disease. Deciphering the functional role of key signaling intermediates, such as those described in this proposal, will allow for a more thorough understanding of angiogenesis and facilitate future therapeutic design.