Rab8a vesicles regulate Wnt ligand delivery and Paneth cell maturation at the intestinal stem cell niche

Abstract

Communication between stem and niche supporting cells maintains the homeostasis of adult tissues. Wnt signaling is a crucial regulator of the stem cell niche, but the mechanism that governs Wnt ligand delivery in this compartment has not been fully investigated. We identified that Wnt secretion is partly dependent on Rab8a-mediated anterograde transport of Gpr177 (wntless), a Wnt-specific transmembrane transporter. Gpr177 binds to Rab8a, depletion of which compromises Gpr177 traffic, thereby weakening the secretion of multiple Wnts. Analyses of generic Wnt/β-catenin targets in Rab8a knockout mouse intestinal crypts indicate reduced signaling activities; maturation of Paneth cells – a Wnt-dependent cell type – is severely affected. Rab8a knockout crypts show an expansion of Lgr5+ and Hopx+ cells in vivo. However, in vitro, the knockout enteroids exhibit significantly weakened growth that can be partly restored by exogenous Wnts or Gsk3β inhibitors. Immunogold labeling and surface protein isolation identified decreased plasma membrane localization of Gpr177 in Rab8a knockout Paneth cells and fibroblasts. Upon stimulation by exogenous Wnts, Rab8a-deficient cells show ligand-induced Lrp6 phosphorylation and transcriptional reporter activation. Rab8a thus controls Wnt delivery in producing cells and is crucial for Paneth cell maturation. Our data highlight the profound tissue plasticity that occurs in response to stress induced by depletion of a stem cell niche signal.

Intestinal GPCRs Control Paneth Cell Maturation and Susceptibility to Experimental Colitis

“…Blocked Paneth cell maturation seen in this study is echoed by at least another recently reported knockout mouse model in which the crypt Wnt signaling activity was weakened because of a reduced Wnt ligand secretion 7, 8. The enhanced colitis susceptibility shown in G αq/11 DKO mice suggests that the mucosal regenerative program induced by the chemical injury probably increased the cellular demands for G αq/11 -mediated signaling activities in the intestine.…”

Requirement of Gα q /Gα 11 Signaling in the Preservation of Mouse Intestinal Epithelial Homeostasis

“…However, in Int-G q /G 11 DKO mice, mRNA levels of EphB3 and EphB2 were not altered (Supplementary Figure 2). Rab8a knock-out mice have been reported recently 40 . Wnt secretion is regulated partly by Rab8a-mediated anterograde transport.…”

A Dynamic WNT/β-CATENIN Signaling Environment Leads to WNT-Independent and WNT-Dependent Proliferation of Embryonic Intestinal Progenitor Cells

“…Maintenance of the adult stem cell population requires β-CATENIN-dependent WNT signaling (“canonical” WNT signaling, herein referred to as WNT/β-CATENIN signaling). Inhibition or loss of WNT/β-CATENIN signaling in the epithelium results in loss of stem cells in the crypt (Chiacchiera et al., 2016, Das et al., 2015, Farin et al., 2012, Pinto et al., 2003, Valenta et al., 2016), while activating mutations leading to constitutive WNT activation are causative in colorectal cancer (Barker et al., 2009, Fearon and Spence, 2012, Fearon and Wicha, 2014, Korinek et al., 1997, Morin et al., 1997). Unlike the plethora of information about regulation of the adult ISC, it is much less clear whether and when WNT/β-CATENIN signaling plays a role in the embryonic intestine, and in particular we understand very little about intestine development prior to the formation of villi.…”