The mTOR Signal Pathway Is Overactivated in Human Lymphatic Malformations

Lymphatic malformations (LMs) are congenital low-flow vascular anomalies resulting from abnormal embryogenesis. Clinical researches have shown that rapamycin, a specific inhibitor of mTOR, is effective in treating LMs. It suggests the abnormality of mTOR signal pathway in LMs. From January 2009 to December 2018, 10 patients who accepted the resection of LMs were enrolled into the study. Samples of each subtype of LMs (macrocystic, microcystic, and mixed subtypes) were further investigated. Expression of molecules in mTOR signal pathway-mTORC1, p70 S6, p-p70 S6, elF4EBP1, and p-elF4EBP1-in LMs were investigated by immunohistochemical staining. Location of mTORC1, p70 S6, and elF4EBP1 in LMs were shown by immunofluorescence co-staining. Phosphorylation level of mTOR signal pathway in LMs was examined by Western blotting. Immunohistochemical staining showed the expression of mTORC1, p70 S6, p-p70 S6, eIF4EBP1, and p-eIF4EBP1 in LMs. Immunofluorescence staining further verified the co-expression of mTORC1, p70 S6, and eIF4EBP1 in the lymphatic endothelium of LMs. Western blotting analysis revealed obviously higher phosphorylation level of mTOR signal pathway in LMs than that in normal skins (P < 0.05). The results showed that the mTOR signal pathway was overactivated in LMs. The study provides compelling evidence for treating LMs or syndromes with lymphatic anomalies by inhibiting mTOR signaling.