Abstract
Ablation of nucleoside diphosphate kinase B (NDPK-B) in mice causes a breakdown of the neurovascular unit in the retina, mimicking diabetic retinopathy. The NDPK-B deficiency-induced vascular damage is mediated by excessive angiopoietin 2 (Ang2). Herein, the potential involvement of its receptor, Tie2, was investigated. NDPK-B-deficient mouse retinas showed an upregulation of Tie2, specifically in the deep capillary layer. A similar upregulation of Tie2 was observed in cultured endothelial cells (ECs) from different origins upon NDPK-B depletion, whereas high glucose (HG) treatment did not alter Tie2 expression. Immunofluorescence staining and subcellular fractionation showed that the majority of Tie2 upregulation occurred at the plasma membrane. Similar to HG, however, NDPK-B depletion reduced Tie2 tyrosine phosphorylation. Compared to HG, a stronger increase of Ang2 was observed in NDPK-B depleted ECs. Treatment of ECs with soluble Tie2 or siRNA-mediated Tie2 knockdown attenuated NDPK-B depletion- but not HG-induced Ang2 upregulation. Like NDPK-B depletion, overexpression of recombinant Ang2 in ECs enhanced Ang2 secretion and concomitantly promoted the upregulation of Tie2. Thus, we identified a new mechanism showing that after reaching a threshold level of secretion, Ang2 sustains its own expression and secretion by a Tie2-dependent positive feedback loop.
Highlights
Nucleoside diphosphate kinases (NDPKs) are housekeeping enzymes primarily involved in nucleoside triphosphate homeostasis in the cell [1]
To investigate the angiopoietin 2 (Ang2)–Tie2 axis in the retina under nucleoside diphosphate kinase B (NDPK-B)-deficient conditions, we first assessed the expression of Tie2 in 5-month-old NDPK-B−/− (KO) mouse retinas by immunoblotting
To identify the cellular localization of Tie2 upregulation in the NDPK-B KO retinas, we further examined the expression of Tie2 in the retina via whole-mount immunofluorescence staining
Summary
Nucleoside diphosphate kinases (NDPKs) are housekeeping enzymes primarily involved in nucleoside triphosphate homeostasis in the cell [1]. Besides this canonical function, an increasing number of publications show additional functions and highlight the moonlighting character of several isoforms [2,3,4]. NDPK-B apparently contributes to endothelial barrier function. NDPK-B-deficient mice exhibit increased vascular permeability in the brain compared to their wild type counterparts [8]. NDPK-B controls vascular permeability by regulating the distribution of caveolins and adherens junction proteins in endothelial cells (ECs), thereby contributing to pathological angiogenesis [8,9]. The hyperglycemia- as well as the NDPK-B deficiency-induced vascular damage was prevented in mice haplodeficient for the Ang encoding Angpt gene [11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
