Changes in Mitochondrial Stability During the Progression of the Barrett’S Esophagus Disease Sequence N
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O’Farrell et al. BMC Cancer (2016) 16:497 DOI 10.1186/s12885-016-2544-2 RESEARCH ARTICLE Open Access Changes in mitochondrial stability during the progression of the Barrett’s esophagus disease sequence N. J. O’Farrell1, R. Feighery1, S. L. Picardo1, N. Lynam-Lennon1, M. Biniecka2, S. A. McGarrigle1, J. J. Phelan1, F. MacCarthy3,D.O’Toole3, E. J. Fox4, N. Ravi1, J. V. Reynolds1 and J. O’Sullivan1* Abstract Background: Barrett’s esophagus follows the classic step-wise progression of metaplasia-dysplasia-adenocarcinoma. While Barrett’s esophagus is a leading known risk factor for esophageal adenocarcinoma, the pathogenesis of this disease sequence is poorly understood. Mitochondria are highly susceptible to mutations due to high levels of reactive oxygen species (ROS) coupled with low levels of DNA repair. The timing and levels of mitochondria instability and dysfunction across the Barrett’s disease progression is under studied. Methods: Using an in-vitro model representing the Barrett’s esophagus disease sequence of normal squamous epithelium (HET1A), metaplasia (QH), dysplasia (Go), and esophageal adenocarcinoma (OE33), random mitochondrial mutations, deletions and surrogate markers of mitochondrial function were assessed. In-vivo and ex-vivo tissues were also assessed for instability profiles. Results: Barrett’s metaplastic cells demonstrated increased levels of ROS (p < 0.005) and increased levels of random mitochondrial mutations (p < 0.05) compared with all other stages of the Barrett’s disease sequence in-vitro. Using patient in-vivo samples, Barrett’s metaplasia tissue demonstrated significantly increased levels of random mitochondrial deletions (p = 0.043) compared with esophageal adenocarcinoma tissue, along with increased expression of cytoglobin (CYGB) (p < 0.05), a gene linked to oxidative stress, compared with all other points across the disease sequence. Using ex-vivo Barrett’s metaplastic and matched normal patient tissue explants, higher levels of cytochrome c (p = 0.003), SMAC/Diablo (p = 0.008) and four inflammatory cytokines (all p values <0.05) were secreted from Barrett’s metaplastic tissue compared with matched normal squamous epithelium. Conclusions: We have demonstrated that increased mitochondrial instability and markers of cellular and mitochondrial stress are early events in the Barrett’s disease sequence. Keywords: Barrett’s esophagus, Mitochondrial instability, Oxidative stress Background Following the classic metaplasia-dysplasia-adenocarcinoma Esophageal cancer is one of the most rapidly increasing sequence, it is speculated cancer development does not malignancies in the Western world [1]. Overall 5-year occur directly from non-dysplastic disease [4]. While survival rates are low at approximately 14 % [2]. The last Barrett’s esophagus follows this natural stepwise progres- several decades have seen a change in the histological trend sion, the exact cellular instability mechanisms triggering of this malignancy with adenocarcinoma now representing cancer conversion are not fully elucidated. the leading sub-type in the West [3]. Barrett’sesophagusis The rate of mutagenesis in mitochondrial DNA is a pathologic precursor of esophageal adenocarcinoma. approximately 10-times higher than mutation rates in nuclear DNA. This is due to a combination of factors such as less proficient DNA repair mechanisms and high * Correspondence: [email protected] 1Trinity Translational Medicine Institute, Department of Surgery, Trinity levels of exposure to ROS generated by the mitochon- College Dublin, St. James’s Hospital, Dublin 8, Ireland dria themselves [5, 6]. The Warburg effect describes a Full list of author information is available at the end of the article © 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. O’Farrell et al. BMC Cancer (2016) 16:497 Page 2 of 9 phenomenon of altered energy metabolism in cancer cells, cultured in BEBM enhanced with BEGM® SingleQuots® and with increased lactate production despite sufficient oxygen supplemented with 10 % foetal calf serum (FCS) (Lonza, to power oxidative phosphorylation [7]. This state of MD, USA) and 1 % penicillin/streptomycin (Lonza). OE33 aerobic glycolysis does not arise in normal functioning esophageal adenocarcinoma cells were sourced from the cells and it is speculated that cancer cells divert from European Collection of Cell Cultures (Sailsbury, UK) and normal energy pathways as a protective mechanism to maintained in Roswell Park Memorial Institute (RPMI) promote cell survival [8, 9]. These factors of increased 1640 medium (Lonza) supplemented with 10 % FCS and susceptibility to DNA injury, along with evidence of 1 % penicillin/streptomycin. All cell lines were maintained altered energy metabolism in the cancer setting, have at 37 °C. highlighted the potential role of the mitochondria in human cancer development [10–12]. Mitochondrial random mutation capture (RMC) assay in To date, research has primarily focussed on clonal cell lines and patient tissue mitochondrial mutations in relation to esophageal cancer All research was carried out in accordance with the [13]. Little work has explored the role of random mito- Declaration of Helsinki, with all patients providing in- chondrial point mutations as a trigger for Barrett’scancer formed written consent, and approval for this study development. With each cell containing hundreds of mito- was granted by the St James’s Hospital and Adelaide, chondria and correspondingly thousands of strands of the Meath and National Children’s Hospital Institutional mitochondrial genome, it is possible for wild type and mu- Review Board. In vivo patient samples were snap frozen tated mitochondrial DNA to co-exist [12]. It is hypothe- in liquid nitrogen and stored at −80 °C for RMC assay ex- sized that during tumor development cancer cells exhibit periments. Patients with histologically confirmed SIM and a mutator phenotype, with higher frequencies of random Barrett’s-associated EAC were recruited while in at- mutations, which are not supported by the normal rates tendance of Barrett’s esophagus surveillance endoscopy of mutagenesis seen in non-cancerous cells [14]. The or esophagectomy at the National Esophageal and Gastric mutator phenotype hypothesis proposes that cancer cells Centre at St. James’s Hospital, Dublin. In-vitro, HET1A, must incur increased rates of mutagenesis during disease QH, Go and OE33 cells, of similar cell passage number progression [14, 15], and as such, this theory suggests that were grown to 70–80 % confluence in 25 cm2 flasks to benign tumors with low levels of random mutations will isolate DNA for the RMC assay. In order to examine not progress to malignancy. Lee et al. [16] have demon- mitochondrial instability, random mitochondrial point strated significantly increased random mitochondrial mu- mutations and deletions were quantified using detailed tations in Barrett’s specialized intestinal metaplasia (SIM) methods previously published by our group [18]. This compared with adjacent normal tissue. It was hypothe- RMC assay allows the quantification of point mutations sized that instability within the mitochondria play a crucial and deletions in the mitochondrial genome at single role in Barrett’s cancer development, however, profiling molecule resolution. All tissues were analyzed in a these changes along the Barrett’s disease sequence remain blinded fashion. All PCR products were sequenced by the largely unexplored. High-Throughput Sequencing Facility at the University of With respect to Barrett’sesophagus,withlessthan Washington. 0.12 % of cases per year progressing to esophageal adeno- carcinoma [17], it is prudent that we understand the early Evaluation of mitochondrial function using mitochondrial instability mechanisms involved in the cancer switch. The assays for reactive oxygen species (ROS) purpose of this study was to identify changes in mito- To further examine mitochondrial biology, ROS levels chondrial mutation rates and function along the Barrett’s were examined in vitro. Cells were seeded in 96 well diseasesequenceusingin-vitro, in-vivo and ex-vivo models. plates at density 2500 to 8000 cells/well, depending on the cell line. Seeding at different concentrations was ne- Methods cessary to compensate for different growth rates between In-vitro cell line sequence different cell lines, in order to ensure the same degree of Four esophageal cell lines were used; HET1A, QH, Go confluence at the initiation of functional experiments. and OE33 cells representing the normal squamous Following 24 h, ROS levels were assessed. Cells were epithelium-SIM-high grade dysplasia (HGD)-esophageal incubated with 5 μM 2, 7-dichlorofluorescein diacetate adenocarcinoma (EAC) sequence, respectively. HET1A (Sigma-Aldrich) using our previously published proto- cells were obtained from American Type Culture Collec- cols [18]. Following 40 min incubation, the ROS probe tion (ATCC) (LGC Standards, Middlesex, UK), and main- was removed, cells were analyzed using