Regulation of colonic epithelial cell homeostasis by mTORC1

Takenori Kotani,Tasuku Konno,Noriko Ihara,Yasuyuki Saito,Saki Okamoto,Takashi Matozaki,Yoji Murata,Tetsuo Noda,Jajar Setiawan

doi:10.1038/s41598-020-70655-1

Abstract

Cell signaling important for homeostatic regulation of colonic epithelial cells (CECs) remains poorly understood. Mammalian target of rapamycin complex 1 (mTORC1), a protein complex that contains the serine-threonine kinase mTOR, mediates signaling that underlies the control of cellular functions such as proliferation and autophagy by various external stimuli. We here show that ablation of tuberous sclerosis complex 2 (Tsc2), a negative regulator of mTORC1, specifically in intestinal epithelial cells of mice resulted in increased activity of mTORC1 of, as well as increased proliferative activity of, CECs. Such Tsc2 ablation also reduced the population of Lgr5-positive colonic stem cells and the expression of Wnt target genes in CECs. The stimulatory phosphorylation of the kinase Akt and inhibitory phosphorylation of glycogen synthase kinase 3β were both markedly decreased in the colon of the Tsc2 conditional knockout (CKO) mice. Development of colonic organoids with cryptlike structures was enhanced for Tsc2 CKO mice compared with control mice. Finally, Tsc2 CKO mice manifested increased susceptibility to dextran sulfate sodium–induced colitis. Our results thus suggest that mTORC1 activity promotes the proliferation of, as well as the expression of Wnt target genes in, CECs and thereby contributes to colonic organogenesis and homeostasis.

Highlights

Cell signaling important for homeostatic regulation of colonic epithelial cells (CECs) remains poorly understood
The activity of Mammalian target of rapamycin complex 1 (mTORC1) is negatively regulated by Tsc1/2 in the basal state[13]
We found that the number of green fluorescent protein (GFP)-positive colonic stem cells (CSCs) at the crypt base was markedly reduced in tuberous sclerosis complex (Tsc)[2] conditional knockout (CKO)/leucine‐rich repeat–containing G protein–coupled receptor 5 (Lgr5)-GFP mice compared with control/Lgr5-GFP mice (Fig. 2a and Supplementary Fig. S2)

Summary

Introduction

Cell signaling important for homeostatic regulation of colonic epithelial cells (CECs) remains poorly understood. ISCs generate proliferating progeny—known as transient amplifying (TA) cells—that migrate out of the stem cell niche, divide frequently, and terminally differentiate into distinct functional cell lineages of the epithelium including Paneth cells, goblet cells, and absorptive enterocytes[5] These terminally differentiated IECs, except Paneth cells, migrate upwards along each intestinal villus and are eventually shed from the villus tip into the gut lumen[5]. We and others have shown that the Ras–MAPK (mitogen–activated protein kinase) signaling pathway promotes the generation of both absorptive enterocytes and goblet c ells[7, 8], likely by counteracting the Wnt signaling p athway[9] In addition to their role in the maintenance of ISCs, Wnt ligands are important for the generation of Paneth cells in the c rypt[10]. Whereas intestinal tumorigenesis driven by mutations in the Apc gene requires the activity of m TORC114,15, the physiological role of mTORC1 in homeostatic regulation of CECs has remained unclear

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Results

Conclusion