Reduced mitochondrial activity in colonocytes facilitates AMPKα2‐dependent inflammation

Abstract

Intestinal inflammation is associated with low levels of mucosal ATP, highlighting the importance of mitochondrial function associated with ATP production in the pathophysiology of the disease. In the inflamed colon of humans and mice, we found decreased levels of mitochondrial complex cytochrome oxidase I/IV and lower ATP levels. Thus, we generated colonic ρ cells with reduced mitochondrial function linked to ATP production by selective depletion of mitochondrial DNA. In these cells, RNA sequencing revealed a substantial number of differentially expressed transcripts, among which 240 belonged to inflammatory pathways activated in human inflamed colon and TNF-α-treated cells (false discovery rate < 0.05). TNF-α treatment of colonic ρ cells augmented IL-8 expression by 9-fold ( < 0.01) NF-κB compared to TNF-α-treated control. Moreover, reduced mitochondrial function facilitated TNF-α-mediated NF-κB luciferase promoter activity as a result of lowered inhibitory IκBα (nuclear factor of κ light polypeptide gene enhancer in B-cell inhibitor, α), leading to elevated NF-κB. In cells with reduced mitochondrial function, TNF-α facilitated AMPKα2 activation by 8-fold ( < 0.01), which was involved in NF-κB-dependent IL-8 expression. Last, in human and mouse colon, anti-TNF-α treatment restored reduced mitochondria-dependent inflammation. We propose that selective targeting of this novel mechanism provides new treatment opportunities for intestinal inflammation.-Heller, S., Penrose, H. M., Cable, C., Biswas, D., Nakhoul, H., Baddoo, M., Flemington, E., Crawford, S. E., Savkovic, S. D. Reduced mitochondrial activity in colonocytes facilitates AMPKα2-dependent inflammation.

Gut bacteria signaling to mitochondria in intestinal inflammation and cancer

“…Mice treated with dextran sodium sulfate (DSS) to induce colitis exhibited swollen mitochondria, increased mtROS generation, decreased ETC activity and ATP level in the colonic mucosa that was ameliorated by anti-TNFα treatment. 54,64 Mice with deletion of IRGM, a CD susceptibility gene that affects mitochondrial fission and induces autophagy, exhibited increased susceptibility to experimental colitis. 65,66 Polymorphisms in SLC22A5, which encodes OCTN2 the carnitine transporter involved in mitochondrial FAO, are associated with CD risk.…”

“…54,77 Infliximab, an anti-TNFα biologic therapy for IBD, was shown to be beneficial to reduce mitochondrial dysfunction in cultured IECs and IBD patients. 54,78 The role of microbiome in mitochondrial alterations driving epithelial barrier dysfunction will be discussed in the following section.…”

In colonic ρ0 (rho0) cells reduced mitochondrial function mediates transcriptomic alterations associated with cancer

“…For example, alteration in expression of established MSI “driver” genes, such as MutL Homolog 1 (MLH1), did not meet the statistical threshold and thus was not a part of ρ 0 DE transcripts used for analysis. Also, as emerging findings show that mitochondria function could impact inflammation and nuclear DNA replication [ 21 , 26 , 28 ], we speculate, that in colonic ρ0 cells DE associated with MSI phenotype could be the consequence of both inflammation and aberrant DNA replication. Moreover, it is important to consider the colonic ρ 0 transcriptome might also be driven by parental HCT116 cell mutations in K-ras and β-catenin genes (KRAS, CNNTB1) [ 29 ], Thus we performed unsupervised hierarchical clustering of activated canonical pathways from ρ 0 transcriptomes with parental HCT116 cells and colon cancer RKO cells with wild-type K-ras and β-catenin.…”

“…We found that decreased ATP synthase subunit ATP5A1, the enzyme responsible for catalyzing ATP production, is linked with considerably reduced colon cancer patient survival (Fig 1A ) (p < 0.05). Since this supports a critical role for reduced mitochondrial energy function in colon cancer pathobiology, we analyzed in colonic ρ0 cells with decreased mitochondrial ATP production [ 21 ] if differentially expressed (DE) transcripts were associated with human colon cancer. Utilizing Ingenuity Pathway Analysis (IPA), we found that these DE transcripts were linked with cancer and cellular functions associated with cell cycle, proliferation, DNA replication and repair, cellular movement, cell survival, and tumor morphology (Fig 1B ) (FDR < 0.05).…”

“…It is plausible that dynamic mitochondrial function influences nuclear gene expression and methylation [ 18 , 19 ], thus affecting oncogenes, tumor suppressors, and signaling pathways associated with tumor growth. Cells devoid of mitochondrial DNA, known as ρ 0 (rho 0 ), are a reliable model to study cellular function dependent on mitochondria [ 20 ], so we generated and characterized human colon cancer ρ 0 (rho 0 ) cells [ 21 ]. As ρ 0 cells are resistant to ROS production and apoptosis [ 20 , 22 - 24 ], it is logical to anticipate that the transcriptome of human colonic ρ 0 cells is mainly dependent on loss of mitochondrial energy function.…”