Fig. 5: Brain endothelial loss of NEMO induces string vessel formation and influences the neurovascular unit.

a, Cerebral microvasculature of Nemo^beKO mice deficient of NEMO in brain endothelial cells and Nemo^fl controls. Arrowheads indicate string vessels. Confocal images are representative of five Nemo^fl and five Nemo^beKO mice (six sections per animal) 28 d after tamoxifen treatment. Scale bar, 50 µm. b, STED microscopy showed that string vessels are thin tubes with a typical diameter of 0.5–1 µm. The image is representative of three Nemo^beKO mice. Scale bars, 1 µm. c,d, String vessels (arrowhead) were often adjacent to dying, TUNEL⁺ or active caspase-3⁺ endothelial cells in Nemo^beKO mice. ERG co-staining indicated TUNEL⁺ nuclei in the endothelium. Representative images in c were obtained from the dataset in e. Images in d are representative of two Nemo^beKO mice. Scale bar, 20 µm. e, Increased numbers of TUNEL⁺ cells localized in collagen IV-stained microvessels of Nemo^beKO mice (N = 5 mice per genotype). f, More string vessels were present in higher branch orders of the vascular tree in the cortices of Nemo^beKO mice (N = 3 mice per genotype). Branch orders were defined by α-SMA staining of arterioles (Extended Data Fig. 8a). g, Nemo^beKO mice (N = 3 mice per genotype) preferentially lost vessels with small diameters. The diameters of collagen IV⁺ vessels are shown as a histogram. h, Nemo^beKO mice (N = 7) demonstrated patchy cerebral hypoxia detected by the hypoxia probe (HP) in contrast to Nemo^fl controls (N = 10). i, Pericyte coverage of vessels was reduced in Nemo^beKO mice (N = 8) compared to Nemo^fl controls (N = 6). Scale bar, 50 µm. j, Nemo^beKO mice (N = 3–4) showed an increased number of activated microglia cells as shown by increased Iba1⁺ soma area in comparison to that of Nemo^fl controls (N = 4–5). Scale bar, 100 µm. k, Nemo^beKO mice (N = 4) demonstrated astrogliosis as shown by an increased GFAP⁺ area in the cortex compared to that of Nemo^fl controls (N = 5). Scale bar, 100 µm. *P < 0.05, **P < 0.01. Means ± s.e.m. are shown. Detailed information on the exact test statistics, sidedness and values is provided in Supplementary Table 5.