Lymphedema (LD) is characterized by the accumulation of protein-rich interstitial fluid, lipids and a significant inflammatory cell infiltrate in the limb. It causes a significant morbidity and is a common disabling disease affecting more than 150 million people worldwide, however there is no yet curative treatment. Here, we found that LD tissues from patients exhibit inflamed gene expression profile compared to their normal arm. Lipidomic analysis revealed severe decrease in arachidonic acid-derived lipid mediators generated by the 15-lipoxygenase (15-LO) in lymphedematous arms. Using a mouse model of lymphedema, we reproduced the etiology of the human pathology including the loss of specialized pro-resolving lipid mediators that play essential role in resolution of inflammation. This was associated with a lack of nonlymphoid PPARg-positive regulatory T cells (Treg) recruitment in the injured limb adipose tissue. Importantly, we identified the lymphatic endothelial 15-LO as responsible for the chemoattraction and survival of this Treg subpopulation. These results were confirmed by an aggravation of LD and degradation of the lymphatic network in an original transgenic mouse model in which ALOX15 gene has been selectively deleted in the lymphatic system (ALOX15lecKO). Importantly, this phenotype was rescued by the injection of ALOX15-expressing lentivectors. These results provide evidence that lymphatic 15-LO may represent a novel therapeutic target for LD by serving as a mediator of nonlymphoid Treg cell population invasion into lymphedematous adipose tissue to resolve inflammation.

Secondary lymphedema (LD) corresponds to a severe lymphatic dysfunction leading to the accumulation of fluid and fibrotic adipose tissue in a limb. Here, we identified apelin (APLN) as a powerful molecule for regenerating lymphatic function in LD. We identified the loss of APLN expression in lymphedematous arm compared to normal arm in patients. The role of APLN in LD was confirmed in APLN-knockout mice, in which LD is increased and associated with fibrosis and dermal backflow. This was reversed by intradermal injection of APLN-lentivectors. Mechanistically, APLN stimulates lymphatic endothelial cell gene expression and induces the binding of E2F8 transcription factor to the promoter of CCBE1 that controls VEGF-C processing. In addition, APLN induces Akt and eNOS pathways to stimulate lymphatic collector pumping. Our results show that APLN represents a novel partner for VEGF-C to restore lymphatic function in both initial and collecting vessels. As LD appears after cancer treatment, we validated the APLN-VEGF-C combination using a novel class of safe and non-integrative RNA-delivery LentiFlash® vector that will be evaluated for phase I/IIa clinical trial.