Wnt signaling suppresses MAPK-driven proliferation of intestinal stem cells
Zahra Kabiri, Gediminas Greicius, Hamed Zaribafzadeh, Amanda Hemmerich, Christopher M. Counter, David M. Virshup
Zahra Kabiri, Gediminas Greicius, Hamed Zaribafzadeh, Amanda Hemmerich, Christopher M. Counter, David M. Virshup
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Concise Communication Gastroenterology

Wnt signaling suppresses MAPK-driven proliferation of intestinal stem cells

Abstract

Intestinal homeostasis depends on a slowly proliferating stem cell compartment in crypt cells, followed by rapid proliferation of committed progenitor cells in the transit amplifying (TA) compartment. The balance between proliferation and differentiation in intestinal stem cells (ISCs) is regulated by Wnt/β-catenin signaling, although the mechanism remains unclear. We previously targeted PORCN, an enzyme essential for all Wnt secretion, and demonstrated that stromal production of Wnts was required for intestinal homeostasis. Here, a PORCN inhibitor was used to acutely suppress Wnt signaling. Unexpectedly, the treatment induced an initial burst of proliferation in the stem cell compartment of the small intestine, due to conversion of ISCs into TA cells with a loss of intrinsic ISC self-renewal. This process involved MAPK pathway activation, as the proliferating cells in the base of the intestinal crypt contained phosphorylated ERK1/2, and a MEK inhibitor attenuated the proliferation of ISCs and their differentiation into TA cells. These findings suggest a role for Wnt signaling in suppressing the MAPK pathway at the crypt base to maintain a pool of ISCs. The interaction between Wnt and MAPK pathways in vivo has potential therapeutic applications in cancer and regenerative medicine.

Authors

Zahra Kabiri, Gediminas Greicius, Hamed Zaribafzadeh, Amanda Hemmerich, Christopher M. Counter, David M. Virshup

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Figure 1

Wnt inhibition enhances proliferation of intestinal stem cells.

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Wnt inhibition enhances proliferation of intestinal stem cells. (A) C59 ...
(A) C59 induced proliferation in the crypt base. Representative images of jejunal samples from mice treated with 1 dose of vehicle or C59 (100 mg/kg) 1 day prior to euthanasia. Proliferative cells were marked with EdU given 2 hours prior to euthanasia and DAPI stained the nuclei of cells. Arrows indicate EdU+ cells in crypt base. Scale bar, 25 μm. Image on right is higher magnification of outlined area of crypt (scale bar, 10 μm). (B) Quantification of EdU+ cells within 10 counted cells in the crypt base. Fifteen to twenty crypts were counted for each region of each mouse intestine (vehicle, n = 9 mice; C59, n = 8 mice; 3 experimental replicates). (C) Representative images of Ki67 staining in the vehicle- or C59-treated mice. Scale bar, 20 μm. Arrows indicate Ki67+ cells in the crypt base. (D) Enrichment of Ki67+ cells in the crypt base of vehicle- versus C59-treated mice. Twenty crypts were counted for each region of intestine per mouse (vehicle, n = 4; C59, n = 7; 2 experimental replicates). (E) C59 does not induce apoptosis in intestinal crypts. Representative images of cleaved-caspase 3 (CAS3) staining in jejunal sections of mice treated as described above. Arrows mark the apoptotic cells in villi as an internal positive control. Scale bar, 50 μm. ***P < 0.001, Mann-Whitney U test.