Injury-induced inflammation progresses along one of two trajectories: wound healing or chronic inflammation. Lymphatic vessel (LV) remodeling contributes to both processes by regulating fluid homeostasis and immune cell traffic to draining lymph nodes. Lymphatic endothelial cells (LECs) respond to acute inflammation by forming new LVs through lymphangiogenesis (LA). These newly-synthesized LVs then regress as inflammation resolves, supporting wound healing. Dysregulation of wound healing impairs LV regression and leads to recurrent LA and chronic inflammation. The mechanisms that govern sustained LV regression vs. activation of recurrent LA are unknown. Our long-term goal is to develop strategies targeting LV remodeling to promote wound healing and prevent or reverse chronic inflammation. The overall objective of this proposal is to define the cellular events of LV regression during wound healing and to identify the cellular events and signals that reactivate regressed LV fragments for recurrent LA. Our preliminary data indicate that macrophages critically coordinate lymphatic remodeling. We hypothesize that differentially polarized macrophages perform distinct functions in regression and recurrent LA, first supporting fragmentation by engulfment of apoptotic LECs and later elaborating LA factors to reactivate LECs and degrading collagen to support fragment migration and anastomosis. We will test this hypothesis with two specific aims: (1) Define the mechanisms by which macrophage presence and polarization regulate LEC fate in regression and reactivation in recurrent LA; and (2) Identify signals governing the transition from LV regression to recurrent LA.
The first aim will employ a novel dual-color transgenic mouse model to track the interactions and fates of eGFP+ macrophages and tdTomato+ LECs by intravital microscopy.
The second aim will use an innovative in vivo approach to identify and validate candidate protein regulators of recurrent LA, pairing protein cytokine arrays with the corneal micropocket model. This will expand basic knowledge of LEC and macrophage functional phenotypes and inform therapeutic development for lymphatic dysfunction, macrophage modulation, and chronic inflammation.
Completion of this project will provide new mechanistic insight into how the dysregulation of lymphatic vessel regression contributes to chronic inflammation. It will identify novel targetable regulators of recurrent lymphangiogenesis derived from and validated in an in vivo preclinical model. This has the potential to significantly improve patient disease outcomes in the setting of chronic inflammation.