Boosting mTOR-dependent autophagy via upstream TLR4-MyD88-MAPK signalling and downstream NF-κB pathway quenches intestinal inflammation and oxidative stress injury

Abstract

Background and aims Defective autophagy has been proposed as an important event in a growing number of autoimmune and inflammatory diseases such as rheumatoid arthritis and lupus. However, the precise role of mechanistic target of rapamycin (mTOR)-dependent autophagy and its underlying regulatory mechanisms in the intestinal epithelium in response to inflammation and oxidative stress remain poorly understood. Methods The levels of p-mTOR, LC3B, p62 and autophagy in mice and LPS-treated cells were examined by immunoblotting, immunohistochemistry, confocal microscopy and transmission electron microscopy (TEM). We evaluated the expression of IL-1β, IL-8, TNF-α, MDA, SOD and T-AOC by quantitative real time-polymerase chain reaction (qRT-PCR) and commercially available kits after silencing of mTOR and ATG5. In vivo modulation of mTOR and autophagy was achieved by using AZD8055, rapamycin and 3-methyladenine. Finally, to verify the involvement of TLR4 signalling and the NF-κB pathway in cells and active ulcerative colitis (UC) patients, immunofluorescence, qRT-PCR, immunoblotting and TEM were performed to determine TLR4 signalling relevance to autophagy and inflammation. Results The mTOR-dependent autophagic flux impairment in a murine model of colitis, human intestinal epithelial cells and active UC patients is probably regulated by TLR4-MyD88-MAPK signalling and the NF-κB pathway. Silencing mTOR remarkably attenuated, whereas inhibiting ATG5 aggravated, LPS-induced inflammation and oxidative injury. Pharmacological administration of mTOR inhibitors and autophagy stimulators markedly ameliorated experimental colitis and oxidative stress in vivo. Conclusions Our findings not only shed light on the regulatory mechanism of mTOR-dependent autophagy, but also provided potential therapeutic targets for intestinal inflammatory diseases such as refractory inflammatory bowel disease.

Restoring mitochondrial function and normalizing ROS‐JNK/MAPK pathway exert key roles in glutamine ameliorating bisphenol A‐induced intestinal injury

“…As the result of cell proliferation, apoptosis and recovery mechanism, intestinal epithelial cell turnover is governed by the coordination of signaling pathways 58 . MAPK pathways have been well documented to be activated in oxidative stress‐induced intestinal cell injury and intestinal inflammation 59 . For instance, the JNK/MAPK pathway was activated by ROS, and subsequently regulated diverse biological functions including apoptosis and epithelial homeostasis in response to environmental stresses 60,61 .…”

Xiao Qing Long Tang essential oil exhibits inhibitory effects on the release of pro-inflammatory mediators by suppressing NF-κB, AP-1, and IRF3 signalling in the lipopolysaccharide-stimulated RAW264.7 cells

“…2 Aer an LPS binds to the TLR4 in the outer membrane of macrophages, various intracellular signalling pathways will be activated; this will lead to the activation of transcription factors such as nuclear factor-kB (NF-kB), activator protein-1 (AP-1), and interferon regulatory factor 3 (IRF3). [3][4][5] Subsequently, these transcription factors will enter the nucleus and promote the secretion of pro-inammatory cytokines and chemokines. 6 Then, these inammatory mediators will trigger inammatory responses, initiating cellular damage and tissue injury.…”

mTOR-dependent autophagy contributes to end-organ resistance and serves as target for treatment in autoimmune disease

“…mTOR plays a central role in sensing metabolic stress and promoting growth and proliferation by inhibiting autophagy in most types of mammalian cells [ 2 ]. In EBioMedicine , Zhou et al recently unveiled an mTOR-dependent impairment of autophagy in patients with ulcerative colitis (UC), which is a form of autoimmune inflammatory bowel disease (IBD) and in mice with experimental colitis [ 3 ]. Using human intestinal epithelial cells as models, mTOR was found to modulate TLR4-MyD88-MAPK signaling and the activation of the NF-κB pathway.…”

“…Using human intestinal epithelial cells as models, mTOR was found to modulate TLR4-MyD88-MAPK signaling and the activation of the NF-κB pathway. Silencing mTOR remarkably attenuated, while genetically inactivating autophagy-controller ATG5 aggravated, inflammation and oxidative injury induced by lipopolysaccharide (LPS) [ 3 ]. Importantly, pharmacological blockade of mTOR with rapamycin mitigated the LPS-induced intestinal inflammation as measured by weight loss, colon length shortening, and inflammatory cell infiltration of the bowel wall epithelium.…”

“…In addition, rapamycin reduced LPS-induced splenomegaly and oxidative stress, suggesting that its anti-inflammatory effects were likely mediated through redox-dependent modulation of the immune system. By contrast, inhibition of autophagy with 3-methyladenine (3-MA) remarkably aggravated oxidative injury and colonic inflammation in LPS-treated mice [ 3 ]. These findings are consistent with earlier observations that mTOR activation causes oxidative stress in the immune system as well as hepatocytes of mice genetically predisposed to autoimmune disease, systemic lupus erythematosus (SLE) [ 4 ].…”