Mediation of FoxO1 in Activated Neuroglia Deficient for Nucleoside Diphosphate Kinase B during Vascular Degeneration

Abstract

Abstract:The pathogenesis of diabetic retinopathy is closely associated with the breakdown of the neurovascular unit including the glial cells. Deficiency of nucleoside diphosphate kinase B (NDPK-B) results in retinal vasoregression mimicking diabetic retinopathy. Increased retinal expression of Angiopoietin-2 (Ang-2) initiates vasoregression. In this study, Müller cell activation, glial Ang-2 expression, and the underlying mechanisms were investigated in streptozotocin-induced diabetic NDPK-B deficient (KO) retinas and Müller cells isolated from the NDPK-B KO retinas. Müller cells were activated and Ang-2 expression was predominantly increased in Müller cells in normoglycemic NDPK-B KO retinas, similar to diabetic wild type (WT) retinas. Diabetes induction in the NDPK-B KO mice did not further increase its activation. Additionally, cultured NDPK-B KO Müller cells were more activated and showed higher Ang-2 expression than WT cells. Müller cell activation and Ang-2 elevation were observed upon high glucose treatment in WT, but not in NDPK-B KO cells. Moreover, increased levels of the transcription factor forkhead box protein O1 (FoxO1) were detected in non-diabetic NDPK-B KO Müller cells. The siRNA-mediated knockdown of FoxO1 in NDPK-B deficient cells interfered with Ang-2 upregulation. These data suggest that FoxO1 mediates Ang-2 upregulation induced by NDPK-B deficiency in the Müller cells and thus contributes to the onset of retinal vascular degeneration.

Involvement of NDPK-B in Glucose Metabolism-Mediated Endothelial Damage via Activation of the Hexosamine Biosynthesis Pathway and Suppression of O-GlcNAcase Activity

“…Therefore, changes in a small subset of cells may escape detection, especially when the detection method used analyses components which are present in most cell types, such as nucleotides or their derivatives. Hypothesizing that the elevation of UDP-GlcNAc upon NDPK-B deficiency is specific to ECs and maybe the Müller glia, another source of protein O-GlcNAcylation-induced Ang-2 in the retina [ 35 ] could explain how it escaped detection in the pool of total UDP-GlcNAc in the retinal lysate. This interpretation is corroborated by the results obtained from the nucleotide content analysis.…”

Chemical Tools for Studying Phosphohistidine: Generation of Selective τ‐Phosphohistidine and π‐Phosphohistidine Antibodies**

“…Müller WT and NDPK B KO cells were provided by Dr Yuxi Feng and Professor Thomas Wieland. The cells were isolated and cultured as previously described [57–59] …”

“…The cells were isolated and cultured as previously described. [57][58][59] Human induced pluripotent stem cell (iPSCs) cell culture and neuronal differentiation. Human iPS cells used in this study named control MIFF1 [60] was kindly provided by Professor Peter Andrews and Dr Ivana Barbaric (Centre for Stem Cell Biology, the University of Sheffield).…”

Contribution of the hexosamine biosynthetic pathway in the hyperglycemia-dependent and -independent breakdown of the retinal neurovascular unit

“…Both Ang-1- and Tie2-deficient mice die due to severe defects in vascular remodeling. ECs are one of the main sources of Ang-2 in the retina and can release Ang-2 under stress conditions [ 83 , [98] , [99] , [100] ]. Levels of Ang-1 and Ang-2 in vitreous humor from patients with NPDR and diabetic macular edema are significantly elevated compared with controls [ 101 ].…”

“…Both hyperglycemia and hypoxia can harm Müller cells and promote a breakdown of the NVU in diabetes [ 139 ]. Müller cells are activated and produce excessive GFAP in STZ-induced diabetic animals at the early stage of DR [ 98 , 140 ]. Besides ECs, macroglia is the largest source of Ang-2 in hyperglycemic conditions in the retina [ 98 ].…”