Epigenetic biomarkers of radiation-induced cardiovascular disease and secondary cancers
Ionizing radiation (IR) is routinely used in diagnosis and therapy. However, incidental radiation exposure of out-of-target tissues and organs may lead to long-term radiation-induced side effects including radiation induced cardiovascular disease (RICVD) and secondary cancers. Investigating the underlying biological mechanisms involved in RICVD and secondary cancers can contribute to the discovery of disease-specific biomarkers. These biomarkers can help identify at-risk patients before they develop pathological symptoms thereby tackling a primary clinical concern. Consequently, the aim of this PhD is to investigate epigenetic biomarkers for two IR delayed effects; RICVD and glioblastoma as a possible secondary cancer to IR.
RICVD is a delayed side effect of thoracic radiotherapy (RT) which occurs due to the incidental irradiation of the heart and large arteries. The underlying biological and molecular mechanisms of RICVD are not yet fully understood while presenting a pro-inflammatory environment and increased oxidative stress. DNA methylation is an epigenetic mechanism of gene expression regulation via the methylation of a cytosine in a CpG dinucleotide forming 5-methyl cytosine (5-mC). DNA methylation is altered in cardiovascular disease with evidence suggesting a pathophysiologic contribution. The underlying biological and molecular mechanisms of RICVD are not yet fully understood while presenting a pro-inflammatory environment and increased oxidative stress. DNA methylation is an epigenetic mechanism of gene expression regulation via the methylation of cytosine bases in CpG dinucleotides. DNA methylation is altered in cardiovascular disease with evidence suggesting a pathophysiologic contribution. DNA methylation is also altered in response to IR exposure. However, the involvement of DNA methylation in RICVD pathogenesis is underexplored. Therefore, IR-induced DNA methylation alterations were investigated in whole-heart irradiated rats and breast cancer patients receiving RT.
DIn rats, ifferentially methylated regions (DMRs) which are regions containing multiple differentially methylated positions (DMPs), ; differentially methylated CpG dinucleotides, DNA methylation alterations were detected up to 7 months in rats receiving 27.6 Gy dose. Pathway analysis of differentially methylated regions (DMRs) Pathway analysis of DMRs revealed enrichment of cardiac-specific pathways such as Dilated cardiomyopathy at 1.5 and 7 months. Furthermore, E2F6 inversely correlated with decreased global longitudinal strain after 27.6 Gy. In breast cancer patients, E2F6 and SLMAP exhibited differential expressions, mainly at higher mean heart doses (MHD) directly and 6 months after radiotherapy, respectively. Therefore, these results suggest a possible association of DNA methylation to RICVD pathophysiology which requires validations in future mechanistic studies.
Further, blood DNA methylation of breast cancer patients receiving adjuvant RT was assessed at different time points. DNA methylation alterations were detected in left sided patients 6 months after RT showing predominantly gene-specific hypermethylation. The expression of six DMRs and 2 differentially methylated positionsrobes (DMPs) was shown to be affected by either the breast cancer side (left/right) or MHD or both as in the case of ATP5G2. However, as most of these DMRs/DMPs are also dysregulated in breast cancer, future integration of cardiac function data (currently under analysis) is needed to identify clear functional associations.
On the other hand, Glioblastoma is a grade IV glioma of poor prognosis that can occur secondary to diagnostic or therapeutic radiation exposure. We performed a meta-analysis of publicly available glioblastoma tissue RNA-seq datasets to identify whole transcriptome changes, with special focus on non-coding RNA. Additionally, small RNA-seq was performed to identify differentially expressed microRNAs in glioblastoma tissues. 98 long noncoding RNAs (lncRNAs) as well as 360 mRNAs were found to be differentially expressed by meta-analysis. 5 differentially expressed microRNAs were also identified by small RNA-seq. Pathway analysis of differentially lncRNAs and mRNAs revealed an association with ferroptosis, a novel cell death pathway implicated in cancer development and therapeutic responses. Therefore, our results confirm the involvement of ferroptosis in glioblastoma pathophysiology while presenting a number of candidates for future research as biomarkers and/or therapeutic targets.
In conclusion, the current thesis identifies several candidate epigenetic biomarkers for both RICVD and glioblastoma. However, these candidates require validation by integration of DMR methylation/expression profiles with patient cardiac functional data for RICVD and investigation of meta-analysis miRNAs/lncRNAs in radiation-induced glioblastoma.
Pieter-Jan Guns (UANTWERPEN)
SCK CEN mentors:
Rafi Benotmane (SCK CEN)
Raghda Ramadan (SCK CEN)
Click here for a list of obtained PhD degrees.