Negative regulation of lymphangiogenesis by tenascin‐C controls the resolution of inflammation

Abstract

<Introduction> It has become apparent that the lymphangiogenic factors such as VEGF-C promote lymphangiogenesis during inflammation to resolve inflammatory responses. On the other hand, the anti-lymphangiogenic factors themselves or their roles during inflammation remain unclear. We herein investigated the functional role of anti-lymphangiogenic factors during inflammation and the molecular mechanisms of anti-lymphangiogenesis. <Methods> To clarify the relationships between anti-lymphangiogenic factors and lymphatic vessels during inflammation, we used several mouse models of inflammatory diseases in vivo. To clarify the molecular signaling associated with anti-lymphangiogenesis, we used human dermal lymphatic endothelial cells (HDLEC) in vitro. <Results> Tenascin-C (TNC) is an extracellular matrix protein that is transiently expressed during the early phase of inflammation. In a mouse model of lymphedema or auto-immune myocarditis, the number of lymphatic vessels increased in TNC-negative area or after the expression of TNC decreased. The genetic deletion of TNC promoted lymphangiogenesis and accelerated the resolution of inflammation in a model of lymphedema or auto-immune myocarditis, while its exogenous addition inhibited lymphangiogenesis and prolonged inflammation in a model of lymphedema. Furthermore, genetic deletion of TNC promoted lymphangiogenesis in a model of peritonitis and exogenous addition of TNC inhibited lymphangiogenesis in mouse ear sponge assay. These results confirmed that TNC directly inhibited the growth of lymphatic vessels and prolonged inflammatory responses in various tissues and in adapted as well as innate immunity. We also demonstrated that genetic deletion of TNC unaffected the density of lymphatic vessels in various tissues under normal condition. Thus, the negative regulation of lymphangiogenesis by TNC was limited to pathological conditions. We further explored the molecular mechanisms of anti-lymphangiogenesis by TNC. In lymphatic endothelial cells, TNC inhibited proliferation, promoted apoptosis, and disturbed tube formation via p38 MAPK and ATF2 signaling in vitro. TNC bound to integrin αv and increased the expression of integrin αvβ1 heterodimer, which phosphorylates FAK and SRC. Furthermore, TNC induced clustering of TGF-β receptor type II and integrin β1 to activate p38 MAPK via TAK1, known as non-canonical TGF-β signaling. <Conclusion> In conclusion, the present study confirmed that TNC, as a negative regulator, inhibits lymphangiogenesis in the early phase of inflammation. The p38 MAPK/ ATF-2 pathway is involved in mediating the negative effects of TNC on lymphatic endothelial cells, and clustering of TGF-β receptors and integrin β1 by TNC was required for the activation of p38 MAPK via TAK1. TNC may restrict the growth of lymphatic vessels in active inflammatory lesions to induce the accumulation of immune cells or fluid containing growth factors.