GUCY2C maintains intestinal LGR5+ stem cells by opposing ER stress.

Crystal L Kraft,Jeffrey A Rappaport,Scott A Waldman,Adam E Snook,John P Lynch,Amanda M Pattison

doi:10.18632/oncotarget.22084

Crystal L Kraft, Jeffrey A Rappaport + Show 4 more

Open Access

https://doi.org/10.18632/oncotarget.22084

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Abstract

Long-lived multipotent stem cells (ISCs) at the base of intestinal crypts adjust their phenotypes to accommodate normal maintenance and post-injury regeneration of the epithelium. Their long life, lineage plasticity, and proliferative potential underlie the necessity for tight homeostatic regulation of the ISC compartment. In that context, the guanylate cyclase C (GUCY2C) receptor and its paracrine ligands regulate intestinal epithelial homeostasis, including proliferation, lineage commitment, and DNA damage repair. However, a role for this axis in maintaining ISCs remains unknown. Transgenic mice enabling analysis of ISCs (Lgr5-GFP) in the context of GUCY2C elimination (Gucy2c–/–) were combined with immunodetection techniques and pharmacological treatments to define the role of the GUCY2C signaling axis in supporting ISCs. ISCs were reduced in Gucy2c–/– mice, associated with loss of active Lgr5+ cells but a reciprocal increase in reserve Bmi1+ cells. GUCY2C was expressed in crypt base Lgr5+ cells in which it mediates canonical cyclic (c) GMP-dependent signaling. Endoplasmic reticulum (ER) stress, typically absent from ISCs, was elevated throughout the crypt base in Gucy2c–/– mice. The chemical chaperone tauroursodeoxycholic acid resolved this ER stress and restored the balance of ISCs, an effect mimicked by the GUCY2C effector 8Br-cGMP. Reduced ISCs in Gucy2c–/–mice was associated with greater epithelial injury and impaired regeneration following sub-lethal doses of irradiation. These observations suggest that GUCY2C provides homeostatic signals that modulate ER stress and cell vulnerability as part of the machinery contributing to the integrity of ISCs.

Highlights

The intestinal epithelium is highly dynamic, undergoing continuous cycles of renewal and repair
The total number of intestinal stem cells (ISC) in the crypt base was reduced in the absence of guanylyl cyclase C (GUCY2C) (Figure 1B)
These results suggest that eliminating GUCY2C signaling rebalances stem cell populations, favoring a “reserve” ISC phenotype

Summary

Introduction

The intestinal epithelium is highly dynamic, undergoing continuous cycles of renewal and repair. Absorptive cells are sloughed off into the intestinal lumen in a conveyor belt fashion on a weekly basis, while secretory cells such as tuft cells and Paneth cells survive for weeks [2, 3] Beyond this programmed turnover, intestinal insults, such as inflammation, oxidative damage, and radiation [4, 5] induce cell death, requiring replacement to maintain the epithelial barrier. Lgr5+, or crypt base columnar (CBC), cells are long-lived multipotent stem cells located at crypt cell positions 0–4 that www.impactjournals.com/oncotarget divide daily to drive weekly turnover of the epithelium, making them the “active” stem cells [6] These cells are exquisitely sensitive to insult and are intimately associated with differentiated cells that supply essential regulatory signals, including Paneth cells [6,7,8]. While the identity and function of intestinal stem cell populations are emerging, mechanisms contributing to their maintenance and relative balance continue to be refined [6,7,8, 11]

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