Targeting BACE1 to restore functional angiogenesis in type 2 diabetes

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): British Heart Foundation British Microcirculation and Vascular Biology Society Background β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is a transmembrane aspartyl protease notorious for its contribution to amyloid plaque formation in the pathophysiology of Alzheimer’s disease (AD) [1]. Further research has suggested a role for BACE1 in vascular homeostasis [2,3] and has shown that it proteolytically cleaves various angiogenic signalling factors including VEGF receptor 1 (VEGFR1) [2], NOTCH ligands [4] and the insulin receptor [5]. Similar to AD, BACE1 activity is elevated in models of type 2 diabetes [5], suggesting a potential role for its contribution to aberrant vessel growth characteristic of diabetes-related complications. Purpose Type 2 diabetes dramatically increases an individual's risk of developing microvascular complications and consequent lower limb amputations [6]. Therefore, identifying novel roles for BACE1 in angiogenic dysregulation will aid progression of future biomedical interventions in this field. Methods Retinal staining and the fibrin gel angiogenesis assay were used to identify a role for BACE1 in vessel growth in vivo and in vitro, respectively. Endothelium of the developing retinal vasculature in BACE1-/- and wild type (WT) mice was stained with IsolectinB4-Alexa488 and imaged using confocal microscopy. Sprout formation was further analysed using the fibrin gel angiogenesis assay with human umbilical vein endothelial cells (HUVECs) treated with or without a highly specific BACE1 inhibitor or transfected to over-express BACE1. Primary isolated pulmonary endothelial cells (PECs) were isolated from BACE1-/- and wild type control mice prior to Western blots, and real-time PCR. Results BACE1-/- retinas had increased branch points, vasculature area and quantity of filopodia compared to WT mice. Moreover, BACE1-/- PECs had reduced NOTCH1 signalling (26.73% ± 14.15, P=0.05) and soluble Jagged-1 protein (28.48% ± 14.61, P=<0.05). HUVECs treated with a BACE1 inhibitor had increased sprouting (18.70%± 5.92, P=<0.05) as well as increased phosphorylation of eNOS (83% ± 22, P=<0.05) and Akt (85.5% ± 9.24, P=NS) compared to untreated cells. Moreover, HUVECs transfected to over-express BACE1 had decreased sprouting (35.22% ± 7.34, P=<0.01) and increased NOTCH1 signalling (23.4% ± 2.42, P=0.01). Conclusion Our findings indicate a role of BACE1 in negatively regulating angiogenesis, possibly via NOTCH1 or Akt/eNOS/NO signalling. This provides a potential therapeutic purpose for BACE1 inhibitors, previously trialled to treat AD, in normalising BACE1 levels in individuals with type 2 diabetes and preventing associated microvascular complications.