Macrophage-derived extracellular vesicle-packaged WNTs rescue intestinal stem cells and enhance survival after radiation injury

Abstract

WNT/β-catenin signalling is crucial for intestinal homoeostasis. The intestinal epithelium and stroma are the major source of WNT ligands but their origin and role in intestinal stem cell (ISC) and epithelial repair remains unknown. Macrophages are a major constituent of the intestinal stroma. Here, we analyse the role of macrophage-derived WNT in intestinal repair in mice by inhibiting their release using a macrophage-restricted ablation of Porcupine, a gene essential for WNT synthesis. Such Porcn-depleted mice have normal intestinal morphology but are hypersensitive to radiation injury in the intestine compared with wild-type (WT) littermates. Porcn-null mice are rescued from radiation lethality by treatment with WT but not Porcn-null bone marrow macrophage-conditioned medium (CM). Depletion of extracellular vesicles (EV) from the macrophage CM removes WNT function and its ability to rescue ISCs from radiation lethality. Therefore macrophage-derived EV-packaged WNTs are essential for regenerative response of intestine against radiation.

Defining key concepts of intestinal and epithelial cancer biology through the use of mouse models

“…This is supported by the observation that Fzd7, the Wnt receptor transmitting Wnt signalling in Lgr5 + intestinal stem cells can bind Wnt3 and Wnt2b with equal affinity (145). Recently it has been proposed that Wnt ligands can be secreted in extracellular vesicles by macrophages during intestinal regeneration (152), which may also suggest that under different stimuli Wnt secretion from different cells can regulate either homeostasis (low Wnt levels expressed from epithelium allowing normal differentiation) or regeneration in the intestine (higher Wnt levels expressed from macrophages to drive hyperproliferation and repair).…”

Lysosomes ‘in control’

“…56 While plasma CatD responded to the intervention, changes in plasma CK-18 levels following intervention of NASH patients have not been defined so far. 57 Contradictive results have been found concerning plasma transaminases after surgical intervention, while others demonstrated a correlation between histological improvement of NASH and lower ALT and AST after follow-up, 58 some did not find a difference postoperatively. 56 Thus, besides NASH diagnosis, plasma CatD can potentially be used in the clinical follow-up of NASH.…”

“…57 Exposing regular C57BL/6 mice on a methionine and cholinedeficient (MCD) diet results in advanced stages of NASH with severe inflammation and fibrosis; however, this diet leads to significant weight loss and reduced plasma triglyceride levels, features not found in man. 58 Additionally, another factor complicating the translation of mechanistic insight from animal models to humans is the heterogeneity of human NAFLD (and NASH), presenting with many different phenotypes that have overlapping and non-overlapping elements. 59 Therefore, 1 additional models are necessary to represent a complete overview of the mechanisms governing NASH.…”

“…58,59 Therefore, regardless of their unknown functions, oxyphytosterols might contribute to inflammatory processes in the liver, which justifies further research of these compounds in the context of NASH. In summary, it is important to identify which lipids have undergone which type of oxidation reaction in order to assess the possible associated detrimental effects.…”

“…56,57 Relevantly, immune cells such as macrophages show the highest degree of EV secretion. 38,58,59 Therefore, changes in plasma CTSD levels in NASH patients (Chapters 5 & 6) might be triggered by oxLDL-induced lysosomal dysfunction in macrophages (Chapter 2 & 4), which activates the ASMase-ceramide pathway. The regulated exocytosis of endo-/lysosomal content should be considered an essential function of lysosomes and might therefore explain the presence of CTSD in the circulation.…”