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Akt1 regulates pathological angiogenesis, vascular maturation and permeability in vivo

Abstract

Akt kinases control essential cellular functions, including proliferation, apoptosis, metabolism and transcription, and have been proposed as promising targets for treatment of angiogenesis-dependent pathologies, such as cancer and ischemic injury. But their precise roles in neovascularization remain elusive. Here we show that Akt1 is the predominant isoform in vascular cells and describe the unexpected consequences of Akt1 knockout on vascular integrity and pathological angiogenesis. Angiogenic responses in three distinct in vivo models were enhanced in Akt1−/− mice; these enhanced responses were associated with impairment of blood vessel maturation and increased vascular permeability. Although impaired vascular maturation in Akt1−/− mice may be attributed to reduced activation of endothelial nitric oxide synthase (eNOS), the major phenotypic changes in vascular permeability and angiogenesis were linked to reduced expression of two endogenous vascular regulators, thrombospondins 1 (TSP-1) and 2 (TSP-2). Re-expression of TSP-1 and TSP-2 in mice transplanted with wild-type bone marrow corrected the angiogenic abnormalities in Akt1−/− mice. These findings establish a crucial role of an Akt-thrombospondin axis in angiogenesis.

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Figure 1: Deficiency of Akt1, the predominant Akt isoform in endothelial cells, impairs their function ex vivo.
Figure 2: Enhanced in vivo angiogenesis in Akt1−/− mice.
Figure 3: Neovasculature in Akt1−/− mice is immature and leaky.
Figure 4: Characterization of vascular responses in Akt1−/− mice.
Figure 5: Akt1 deficiency results in reduction of TSP levels.
Figure 6: An Akt1-TSP axis regulates vascular permeability and angiogenesis.

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Acknowledgements

We acknowledge support from the US National Institutes of Health (HL071625 and DK060933 to T.V.B. and CA90764 to N.H). We thank J. Li for his help in statistical analysis, J. Drazba, A. Vasantji and Imaging Core, Cleveland Clinic Foundation for the help in tissue processing and image analysis and L. Mavrakis and S. Bundy for supply of HUVEC, harvested through Birthing Services Department at the Cleveland Clinic Foundation and Perinatal Clinical Research Center at the MetroHealth Hospital.

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Correspondence to Tatiana V Byzova.

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Supplementary information

Supplementary Fig. 1

Akt1 is the major Akt isoform in vascular cells. (PDF 279 kb)

Supplementary Fig. 2

Characteristics of vasculature in Akt1 null mice. (PDF 339 kb)

Supplementary Fig. 3

Absence of Akt1 results in impaired collagen matrix organization. (PDF 165 kb)

Supplementary Fig. 4

Tumor vasculature and TSP-1 expression are inversely related. (PDF 267 kb)

Supplementary Fig. 5

Basal levels of eNOS phosphorylation is reduced in Akt1−/− endothelial cells (EC). (PDF 69 kb)

Supplementary Fig. 6

Reduced vascular maturation in eNOS null mice. (PDF 274 kb)

Supplementary Methods (PDF 51 kb)

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Chen, J., Somanath, P., Razorenova, O. et al. Akt1 regulates pathological angiogenesis, vascular maturation and permeability in vivo. Nat Med 11, 1188–1196 (2005). https://doi.org/10.1038/nm1307

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