DNA methylation age in paired tumor and adjacent normal breast tissue in Chinese women with breast cancer

BACKGROUND

Few studies have examined epigenetic age acceleration (AA), the difference between DNA methylation (DNAm) predicted age and chronological age, in relation to somatic genomic features in paired cancer and normal tissue, with less work done in non-European populations. In this study, we aimed to examine DNAm age and its associations with breast cancer risk factors, subtypes, somatic genomic profiles including mutation and copy number alterations and other aging markers in breast tissue of Chinese breast cancer (BC) patients from Hong Kong.

METHODS

We performed genome-wide DNA methylation profiling of 196 tumor and 188 paired adjacent normal tissue collected from Chinese BC patients in Hong Kong (HKBC) using Illumina MethylationEPIC array. The DNAm age was calculated using Horvath's pan-tissue clock model. Somatic genomic features were based on data from RNA sequencing (RNASeq), whole-exome sequencing (WES), and whole-genome sequencing (WGS). Pearson's correlation (r), Kruskal-Wallis test, and regression models were used to estimate associations of DNAm AA with somatic features and breast cancer risk factors.

RESULTS

DNAm age showed a stronger correlation with chronological age in normal (Pearson r = 0.78, P < 2.2e-16) than in tumor tissue (Pearson r = 0.31, P = 7.8e-06). Although overall DNAm age or AA did not vary significantly by tissue within the same individual, luminal A tumors exhibited increased DNAm AA (P = 0.004) while HER2-enriched/basal-like tumors exhibited markedly lower DNAm AA (P = < .0001) compared with paired normal tissue. Consistent with the subtype association, tumor DNAm AA was positively correlated with ESR1 (Pearson r = 0.39, P = 6.3e-06) and PGR (Pearson r = 0.36, P = 2.4e-05) gene expression. In line with this, we found that increasing DNAm AA was associated with higher body mass index (P = 0.039) and earlier age at menarche (P = 0.035), factors that are related to cumulative exposure to estrogen. In contrast, variables indicating extensive genomic instability, such as TP53 somatic mutations, high tumor mutation/copy number alteration burden, and homologous repair deficiency were associated with lower DNAm AA.

CONCLUSIONS

Our findings provide additional insights into the complexity of breast tissue aging that is associated with the interaction of hormonal, genomic, and epigenetic mechanisms in an East Asian population.

Associations between Preserved foods and Breast Cancer Risk in Hong Kong Chinese Women

Preserved food such as cured foods may contain nitrate and nitrite that may contribute to the breast cancer development. Evidence on the associations between these preserved food intakes and risk of breast cancer is sparse. This study aimed to examine the associations between preserved foods (i.e. cured meat, pickled vegetables, canned meat, canned fruit/vegetables) and breast cancer risk in Hong Kong Chinese women. A total of 1307 breast cancer cases and 1050 age-matched controls were recruited from three hospitals during 11/2011-01/2018. We used a standardized questionnaire to collect information on dietary factors including preserved foods. Unconditional multiple logistic regression was performed to calculate the adjusted odds ratio(AOR) of breast cancer in relation to preserved food with adjustment of potential confounders. We further performed stratified analysis according to the breast cancer biology subtypes. We found that cured meat consumption was significantly associated with the risk of breast cancer [AOR=1.32, 95% confidence interval 95%CI)=1.06-1.64]. Compared to no cured meat consumption, cured meat intake {greater than or equal to} once per week was associated with an AOR of 2.66 (95%CI=1.38-5.35). Women with canned fruit/vegetable {greater than or equal to} consumption once per week had a higher risk of breast cancer (OR=1.19, 95%CI=1.00-1.41), particularly for the HER2-positive subtypes, but it became borderline after adjustment of confounders. Our study reveals a positive association between consumption of cured meat and breast cancer risk in Chinese population. Cured meat intake might be a potential novel risk factor for breast cancer but this would have to be confirmed by large prospective cohort studies.

Ceruloplasmin promotes iron uptake rather than release in BT325 cells

This study was initiated to investigate the mechanism of ceruloplasmin (CP)-mediated iron release from brain cells using BT325 cells (a glioblastoma cell line); however, negative results were obtained. The BT325 cells were preloaded with 1 microM 59Fe2+ in sucrose (pH 5.8) for 60 min, and then with CP (0-300 microg/ml) for 30 min at 37 degrees C. The addition of CP, either at low (25 microg/ml) or high (300 microg/ml) concentrations, did not lead to a significant change in iron release from iron-loaded BT325 cells. No significant difference in total iron of cells was found between all CP treated groups and the control (P>0.05). Although apotransferrin (apoTf) was shown to have a role in iron release from the cells, the effect of apoTf was not significantly affected by the addition of different concentrations of CP. When the cells were incubated with 1 microM 59Fe2+ in the presence of varying amounts of CP for 30 min at 37 degrees C, it was found that CP increased iron uptake. The total iron uptake by BT325 cells in CP treatment groups (25, 75, 150, 300 microg/ml) was significantly higher than that in the control (no CP addition) (all P<0.01). Furthermore, in contrast to our expectation, CP was shown to promote significantly iron uptake in not only iron-sufficient but also iron-deficient cells. These results showed that CP had a role in iron uptake rather than release in BT325 cells.

Transferrin-bound and transferrin free iron uptake by cultured rat astrocytes

Previously we had demonstrated the presence of transferrin receptor (TfR) on the plasma membrane of cultured rat cortical astrocytes. In this study, we investigated the roles of TfR in transferrin-bound iron (Tf-Fe) as well as transferrin-free iron (Fe II) uptake by the cells. The cultured rat astrocytes were incubated with 1 microM of double-labelled transferrin (125I-Tf-59Fe) in serum- free DMEM F12 medium or 59Fe II in isotonic sucrose solution at 37 degrees C or 4 degrees C for varying times. The cellular Tf-Fe, Tf and Fe II uptake was analyzed by measuring the intracellular radioactivity with gamma counter. The result showed that Tf-Fe uptake kept increasing in a linear manner at least in the first 30-min. In contrast to Tf-Fe uptake, the internalization of Tf into the cells was rapid initially but then slowed to a plateau level after 10 min. of incubation. The addition of either NH4Cl or CH3NH2, the blockers of Tf-Fe uptake via inhibiting iron release from Tf within endosomes, decreased the cellular Tf-Fe uptake but had no significant effect on Tf uptake. Pre-treated cells with trypsin inhibited significantly the cellular uptake of Tf-Fe as well as Tf. These findings suggested that Tf-Fe transport across the membrane of astrocytes is mediated by Tf-TfR endocytosis. The results of transferrin-free iron uptake indicated that the cultured rat cortical astrocytes had the capacity to acquire Fe II. The highest uptake of Fe II occurred at pH 6.5. The Fe II uptake was time and temperature dependent, iron concentration saturable, inhibited by several divalent metal ions, such as Co2+, Zn2+, Mn2+ and Ni2+ and not significantly affected by phenylarsine oxide treatment. These characteristics of Fe II uptake by the cultured astrocytes suggested that Fe II uptake is not mediated by TfR and implied that a carrier-mediated iron transport system might be present on the membrane of the cultured cells.