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Oxidative stress induces angiogenesis by activating TLR2 with novel endogenous ligands

Abstract

Reciprocity of inflammation, oxidative stress and neovascularization is emerging as an important mechanism underlying numerous processes from tissue healing and remodelling to cancer progression1,2. Whereas the mechanism of hypoxia-driven angiogenesis is well understood3,4, the link between inflammation-induced oxidation and de novo blood vessel growth remains obscure. Here we show that the end products of lipid oxidation, ω-(2-carboxyethyl)pyrrole (CEP) and other related pyrroles5, are generated during inflammation and wound healing and accumulate at high levels in ageing tissues in mice and in highly vascularized tumours in both murine and human melanoma. The molecular patterns of carboxyalkylpyrroles are recognized by Toll-like receptor 2 (TLR2), but not TLR4 or scavenger receptors on endothelial cells, leading to an angiogenic response that is independent of vascular endothelial growth factor. CEP promoted angiogenesis in hindlimb ischaemia and wound healing models through MyD88-dependent TLR2 signalling. Neutralization of endogenous carboxyalkylpyrroles impaired wound healing and tissue revascularization and diminished tumour angiogenesis. Both TLR2 and MyD88 are required for CEP-induced stimulation of Rac1 and endothelial migration. Taken together, these findings establish a new function of TLR2 as a sensor of oxidation-associated molecular patterns, providing a key link connecting inflammation, oxidative stress, innate immunity and angiogenesis.

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Figure 1: CEP, an end product of lipid oxidation, is present in wounds, is elevated in melanoma and accumulates in ageing tissues.
Figure 2: Proangiogenic effects of oxidized adducts are dependent on pyrrole moiety and are mediated by TLR2 but not VEGFR signalling.
Figure 3: CEP-induced angiogenesis in vivo is mediated by TLR2.
Figure 4: Endogenous CEP contributes to wound recovery and melanoma vascularization; TLR2-dependent responses to CEP involve MyD88 and Rac1.

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Acknowledgements

We thank L. Hong for the help with synthesis of CEP and CPP adducts, Y. Cui for expressing and purifying anti-CEP monoclonal antibodies, and J. Crabb for providing anti-CEP monoclonal antibody hybridoma cells. This work was supported by NIH grants HL073311, HL071625, CA126847 to T.V.B., HL077213 to E.A.P. and GM021249 to R.G.S. and an American Heart Association grant (10SDG4300062) to N.L.M.

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Contributions

N.L.M., E.A.P. and T.V.B. designed experiments. In vivo and ex vivo experiments were performed by X.Z.W. with a help from A.A.M. and M.T. In vitro experiments were performed by N.L.M. with help from B.A.K. Melanoma samples and their analysis was done by E.C.B. Synthesis of CAPs was performed by R.G.S. The data were analysed and plotted by X.Z.W. The manuscript was written by N.L.M. and T.V.B.

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Correspondence to Tatiana V. Byzova.

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The authors declare no competing financial interests.

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West, X., Malinin, N., Merkulova, A. et al. Oxidative stress induces angiogenesis by activating TLR2 with novel endogenous ligands. Nature 467, 972–976 (2010). https://doi.org/10.1038/nature09421

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