BackgroundQualitative and quantitative changes in human mitochondrial DNA (mtDNA) have been implicated in various cancer types. A 4,977 bp deletion in the major arch of the mitochondrial genome is one of the most common mutations associated with a variety of human diseases and aging.MethodsWe conducted a comprehensive study on clinical features and mtDNA of 104 colorectal cancer patients in the Wenzhou area of China. In particular, using a quantitative real time PCR method, we analyzed the 4,977 bp deletion and mtDNA content in tumor tissues and paired non-tumor areas from these patients.ResultsWe found that the 4,977 bp deletion was more likely to be present in patients of younger age (≤65 years, p = 0.027). In patients with the 4,977 bp deletion, the deletion level decreased as the cancer stage advanced (p = 0.031). Moreover, mtDNA copy number in tumor tissues of patients with this deletion increased, both compared with that in adjacent non-tumor tissues and with in tumors of patients without the deletion. Such mtDNA content increase correlated with the levels of the 4,977 bp deletion and with cancer stage (p < 0.001).ConclusionsOur study indicates that the mtDNA 4,977 bp deletion may play a role in the early stage of colorectal cancer, and it is also implicated in alteration of mtDNA content in cancer cells.

Haplogroup G predisposes one to an increased risk of osteoarthritis (OA) occurrence, while haplogroup B4 is a protective factor against OA onset. However, the underlying mechanism is not known. Here, by using trans-mitochondrial technology, we demonstrate that the activity levels of mitochondrial respiratory chain complex I and III are higher in G cybrids than in haplogroup B4. Increased mitochondrial oxidative phosphorylation (OXPHOS) promotes mitochondrial-related ATP generation in G cybrids, thereby shifting the ATP generation from glycolysis to OXPHOS. Furthermore, we found that lower glycolysis in G cybrids decreased cell viability under hypoxia (1% O2) compared with B4 cybrids. In contrast, G cybrids have a lower NAD(+)/NADH ratio and less generation of reactive oxygen species (ROS) under both hypoxic (1% O2) and normoxic (20% O2) conditions than B4 cybrids, indicating that mitochondrial-mediated signaling pathways (retrograde signaling) differ between these cybrids. Gene expression profiling of G and B4 cybrids using next-generation sequencing technology showed that 404 of 575 differentially expressed genes (DEGs) between G and B4 cybrids are enriched in 17 pathways, of which 11 pathways participate in OA. Quantitative reverse transcription PCR (qRT-PCR) analyses confirmed that G cybrids had lower glycolysis activity than B4 cybrids. In addition, we confirmed that the rheumatoid arthritis pathway was over-activated in G cybrids, although the remaining 9 pathways were not further tested by qRT-PCR. In conclusion, our findings indicate that mtDNA haplogroup G may increase the risk of OA by shifting the metabolic profile from glycolysis to OXPHOS and by over-activating OA-related signaling pathways.

Non-alcoholic fatty liver disease (NAFLD) affects obesity-associated metabolic syndrome, which exhibits hepatic steatosis, insulin insensitivity and glucose intolerance. Previous studies indicated that hepatic microRNAs (miRs) play critical roles in the development of NAFLD. In this study, we aim to explore the pathophysiological role of miR-194 in obesity-mediated metabolic dysfunction. Our findings show that the high fat diet or palmitic acid treatment significantly increase hepatic miR-194 levels in vivo and in vitro. Silence of miR-194 protects palmitic acid-induced inflammatory response in cultured hepatocytes, and attenuates structural disorders, lipid deposits and inflammatory response in fatty liver. MiR-194 inhibitor also improves glucose and insulin intolerance in obese mice. Through dual luciferase assay, we demonstrate that miR-194 directly binds to FXR/Nr1h4 3'-UTR, and inhibits gene expression of FXR/Nr1h4. Furthermore, overexpression of miR-194 downregulates FXR/Nr1h4 in cultured hepatocytes, but miR-194 inhibitor reversely increases FXR/Nr1h4 expression in obese mouse liver tissues. On the contrast, silence of FXR/Nr1h4 abolishes the hepatic benefits in obese mice treated with miR-194 inhibitor. Present study provides a novel finding that suppression of miR-194 attenuates dietary-induced NAFLD via upregulation of FXR/Nr1h4. The findings suggest miR-194/FXR are potential diagnostic markers and therapeutic targets for NAFLD.

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Mitochondrial dysfunction has been long proposed to play a major role in tumorigenesis. Mitochondrial DNA (mtDNA) mutations, especially the mtDNA 4,977 bp deletion has been found in patients of various types of cancer. In order to comprehend the mtDNA 4,977 bp deletion status in various cancer types, we performed a meta-analysis composed of 33 publications, in which a total of 1613 cancer cases, 1516 adjacent normals and 638 healthy controls were included. When all studies were pooled, we found that cancerous tissue carried a lower mtDNA 4,977 bp deletion frequency than adjacent non-cancerous tissue (OR = 0.43, 95% CI = 0.20–0.92, P = 0.03 for heterogeneity test, I2 = 91.5%) among various types of cancer. In the stratified analysis by cancer type the deletion frequency was even lower in tumor tissue than in adjacent normal tissue of breast cancer (OR = 0.19, 95% CI = 0.06–0.61, P = 0.005 for heterogeneity test, I2 = 82.7%). Interestingly, this observation became more significant in the stratified studies with larger sample sizes (OR = 0.70, 95% CI = 0.58–0.86, P = 0.0005 for heterogeneity test, I2 = 95.1%). Furthermore, when compared with the normal tissue from the matched healthy controls, increased deletion frequencies were observed in both adjacent non-cancerous tissue (OR = 3.02, 95% CI = 2.13–4.28, P<0.00001 for heterogeneity test, I2 = 53.7%), and cancerous tissue (OR = 1.36, 95% CI = 1.04–1.77, P = 0.02 for heterogeneity test, I2 = 83.5%). This meta-analysis suggests that the mtDNA 4,977 bp deletion is often found in cancerous tissue and thus has the potential to be a biomarker for cancer occurrence in the tissue, but at the same time being selected against in various types of carcinoma tissues. Larger and better-designed studies are still warranted to confirm these findings.