Sonic Hedgehog acts as a macrophage chemoattractant during regeneration of the gastric epithelium

Jayati Chakrabarti,Jennifer Hawkins,Yana Zavros,Michael Schumacher,Martha Dua-Awereh,Michael A Helmrath,Amy Engevik

doi:10.1038/s41536-021-00196-2

Abstract

Sonic Hedgehog (Shh), secreted from gastric parietal cells, contributes to the regeneration of the epithelium. The recruitment of macrophages plays a central role in the regenerative process. The mechanism that regulates macrophage recruitment in response to gastric injury is largely unknown. Here we tested the hypothesis that Shh stimulates macrophage chemotaxis to the injured epithelium and contributes to gastric regeneration. A mouse model expressing a myeloid cell-specific deletion of Smoothened (LysMcre/+;Smof/f) was generated using transgenic mice bearing loxP sites flanking the Smo gene (Smo loxP) and mice expressing a Cre recombinase transgene from the Lysozyme M locus (LysMCre). Acetic acid injury was induced in the stomachs of both control and LysMcre/+;Smof/f (SmoKO) mice and gastric epithelial regeneration and macrophage recruitment analyzed over a period of 7 days post-injury. Bone marrow-derived macrophages (BM-Mø) were collected from control and SmoKO mice. Human-derived gastric organoid/macrophage co-cultures were established, and macrophage chemotaxis measured. Compared to control mice, SmoKO animals exhibited inhibition of ulcer repair and normal epithelial regeneration, which correlated with decreased macrophage infiltration at the site of injury. Bone marrow chimera experiments using SmoKO donor cells showed that control chimera mice transplanted with SmoKO bone marrow donor cells exhibited a loss of ulcer repair, and transplantation of control bone marrow donor cells to SmoKO mice rescued epithelial cell regeneration. Histamine-stimulated Shh secretion in human organoid/macrophage co-cultures resulted in macrophage migration toward the gastric epithelium, a response that was blocked with Smo inhibitor Vismodegib. Shh-induced macrophage migration was mediated by AKT signaling. In conclusion, Shh signaling acts as a macrophage chemoattractant via a Smo-dependent mechanism during gastric epithelial regeneration in response to injury.

Highlights

IntroductionSonic Hedgehog (Shh) signaling plays a fundamental role in the regulation of (1) normal epithelial cell differentiation and proliferation, (2) tissue homeostasis, (3) the gastric immune response to Helicobacter pylori (H. pylori) infection, and (4) regeneration within the adult stomach[1,2,3,4,5,6,7]
Sonic Hedgehog (Shh) is expressed in a number of adult organs including the stomach
The current study demonstrates that Shh plays a fundamental role in the chemotaxis of macrophages to the gastric epithelium in response to injury

Summary

Introduction

Shh signaling plays a fundamental role in the regulation of (1) normal epithelial cell differentiation and proliferation, (2) tissue homeostasis, (3) the gastric immune response to Helicobacter pylori (H. pylori) infection, and (4) regeneration within the adult stomach[1,2,3,4,5,6,7]. We have documented that Shh may act as a macrophage chemoattractant in response to infection and injury[7,8]. Previous work supports the concept that Shh acts as a macrophage chemoattractant as mice expressing a tamoxifen-inducible parietal cell-specific deletion of Shh exhibit decreased macrophage infiltration and neovascularization that coincides with failure to repair and regenerate the gastric epithelium in response to injury[8]

Methods

Results

Conclusion