Abstract
Dysfunctions in the intestinal barrier, associated with an altered paracellular pathway, are commonly observed in inflammatory bowel disease (IBD). The AMP-activated protein kinase (AMPK), principally known as a cellular energy sensor, has also been shown to play a key role in the stabilization and assembly of tight junctions. Here, we aimed to investigate the contribution of intestinal epithelial AMPK to the initiation, progression and resolution of acute colitis. We also tested the hypothesis that protection mediated by metformin administration on intestinal epithelium damage required AMPK activation. A dextran sodium sulfate (DSS)-induced colitis model was used to assess disease progression in WT and intestinal epithelial cell (IEC)-specific AMPK KO mice. Barrier integrity was analyzed by measuring paracellular permeability following dextran-4kDa gavage and pro-inflammatory cytokines and tight junction protein expression. The deletion of intestinal epithelial AMPK delayed intestinal injury repair after DSS exposure and was associated with a slower re-epithelization of the intestinal mucosa coupled with severe ulceration and inflammation, and altered barrier function. Following intestinal injury, IEC AMPK KO mice displayed a lower goblet cell counts with concomitant decreased Muc2 gene expression, unveiling an impaired restitution of goblet cells and contribution to wound healing process. Metformin administration during the recovery phase attenuated the severity of DSS-induced colitis through improvement in intestinal repair capacity in both WT and IEC AMPK KO mice. Taken together, these findings demonstrate a critical role for IEC-expressed AMPK in regulating mucosal repair and epithelial regenerative capacity following acute colonic injury. Our studies further underscore the therapeutic potential of metformin to support repair of the injured intestinal epithelium, but this effect is conferred independently of intestinal epithelial AMPK.
Highlights
The intestinal barrier is the greatest surface of the body in contact with the external environment, allowing the transfer of nutrients to the organism, but it is essential to maintain an efficient protection against toxins and bacteria
To explore the clinical importance of AMPK in intestinal epithelial cell (IEC) and its contribution in the control of mucosal barrier integrity, we utilized an inflammatory injury model in which colitis is induced by administration of 4% (w/v) dextran sodium sulfate (DSS) in drinking water for 4 days to promote intestinal inflammation (Figure 1A)
Enhanced expression of thepro-inflammatory gene Interleukin 6 (IL-6) was similar on day 4 of 4% DSS-induced colitis measured by real-time quantitative PCR in full-thickness samples taken from the colons of WT and IEC AMPK KO mice, there was a significant increase in proinflammatory cytokines Tumor necrosis factor α (TNFα) and Interleukin 1β (IL-1β) gene expression levels in DSS-treated IEC AMPK KO mice, indicating higher colonic inflammation in the absence of IEC AMPK in response to acute experimental ulcerative colitis (Figure 1E)
Summary
The intestinal barrier is the greatest surface of the body in contact with the external environment, allowing the transfer of nutrients to the organism, but it is essential to maintain an efficient protection against toxins and bacteria This intestinal barrier arises from the diversity of its architecture and constituents; it includes the mucus layer (with secreted immunoglobulins and antimicrobial peptides), lamina propria (containing lymphoid tissues with macrophages and peyers patches), mesenteric lymph nodes (hosting immune cells) and the intestinal epithelium, called the intestinal epithelial barrier (IEB). Under low energy conditions (characterized by rising AMP:ATP ratio), AMPK is activated by the upstream liver kinase B1 (LKB1) that phosphorylates the catalytic AMPKα subunit on Thr-172 residue. The role of AMPK in IEB function and maintenance under pathological conditions is still relatively less explored in vivo
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