RAMP1 signaling improves lymphedema and promotes lymphangiogenesis in mice

Abstract

BackgroundSecondary lymphedema commonly arises as a complication of cancer surgery and radiation treatment; however, the underlying mechanisms are poorly understood. Receptor activity-modifying protein 1 (RAMP1) forms a complex with calcitonin receptor–like receptor to generate the receptor for calcitonin gene–related peptide. The present study examined whether RAMP1 plays a role in increased lymphangiogenesis during secondary lymphedema. MethodsA model of lymphedema was generated by surgical removal of pre-existing lymphatic vessels from the subcutaneous tissue on the tails of RAMP1-deficient (RAMP1−/−) mice and their wild-type (WT) counterparts. The maximum diameter of the tail, lymphangiogenesis, and macrophage recruitment were then examined. ResultsCompared with that in WT mice, lymphedema in the tails in RAMP1−/− mice was sustained, with suppressed lymphangiogenesis and reduced expression of vascular endothelial growth factor-C and vascular endothelial growth factor receptor 3 at the distal edge of the lesions. The newly formed lymphatic vessels in RAMP1−/− mice were dilated, with impaired lymphatic flow. RAMP1 was expressed by macrophages recruited into edematous tail tissues distal to the wound. The number of macrophages in RAMP1−/− mice was higher than that in WT mice. Expression of messenger RNA encoding M1 macrophage-related genes, including tumor necrosis factor-α and interleukin-1, was higher in RAMP1−/− mice than in WT mice, whereas expression of messenger RNA encoding M2 macrophage genes, including interleukin-10, was lower. ConclusionsRAMP1 signaling improves lymphedema and accelerates lymphangiogenesis associated with reduced recruitment of pro-inflammatory macrophages.