Onset of Telomere Dysfunction and Fusions in Human Ovarian Carcinoma

Telomeres and SIRT1 as Biomarkers of Gamete Oxidative Stress, Fertility, and Potential IVF Outcome

The number of infertile couples undergoing in vitro fertilisation (IVF) has increased significantly. The efficacy of this procedure is contingent upon a multitude of factors, including gamete quality. One factor influencing gamete quality is oxidative stress, which leads to telomere damage and accelerates cellular ageing. Identifying new biomarkers that can predict the success of assisted reproduction techniques is a current relevant area of research. In this review, we discuss the potential role of SIRT1, a protein known to protect against oxidative stress and telomeres, which are responsible for genome stability, as biomarkers of gamete quality and assisted reproduction technique outcomes.

Telomere length as a predictor of therapy response and survival in patients diagnosed with ovarian carcinoma

Impaired telomere length (TL) maintenance in ovarian tissue may play a pivotal role in the onset of epithelial ovarian cancer (OvC). TL in either target or surrogate tissue (blood) is currently being investigated for use as a predictor in anti-OvC therapy or as a biomarker of the disease progression, respectively. There is currently an urgent need for an appropriate approach to chemotherapy response prediction. We performed a monochrome multiplex qPCR measurement of TL in peripheral blood leukocytes (PBL) and tumor tissues of 209 OvC patients. The methylation status and gene expression of the shelterin complex and telomerase catalytic subunit (hTERT) were determined within tumor tissues by High-Throughput DNA methylation profiling and RNA sequencing (RNA-Seq) analysis, respectively. The patients sensitive to cancer treatment (n = 46) had shorter telomeres in PBL compared to treatment-resistant patients (n = 93; P = 0.037). In the patients with a different therapy response, transcriptomic analysis showed alterations in the peroxisome proliferator-activated receptor (PPAR) signaling pathway (q = 0.001). Moreover, tumor TL shorter than the median corresponded to better overall survival (OS) (P = 0.006). TPP1 gene expression was positively associated with TL in tumor tissue (P = 0.026). TL measured in PBL could serve as a marker of platinum therapy response in OvC patients. Additionally, TL determined in tumor tissue provides information on OvC patients' OS.

High-throughput screen to identify compounds that prevent or target telomere loss in human cancer cells

Chromosome instability (CIN) is an early step in carcinogenesis that promotes tumor cell progression and resistance to therapy. Using plasmids integrated adjacent to telomeres, we have previously demonstrated that the sensitivity of subtelomeric regions to DNA double-strand breaks (DSBs) contributes to telomere loss and CIN in cancer. A high-throughput screen was created to identify compounds that affect telomere loss due to subtelomeric DSBs introduced by I-SceI endonuclease, as detected by cells expressing green fluorescent protein (GFP). A screen of a library of 1832 biologically-active compounds identified a variety of compounds that increase or decrease the number of GFP-positive cells following activation of I-SceI. A curated screen done in triplicate at various concentrations found that inhibition of classical nonhomologous end joining (C-NHEJ) increased DSB-induced telomere loss, demonstrating that C-NHEJ is functional in subtelomeric regions. Compounds that decreased DSB-induced telomere loss included inhibitors of mTOR, p38 and tankyrase, consistent with our earlier hypothesis that the sensitivity of subtelomeric regions to DSBs is a result of inappropriate resection during repair. Although this assay was also designed to identify compounds that selectively target cells experiencing telomere loss and/or chromosome instability, no compounds of this type were identified in the current screen.

Telomere Shortening and Fusions: A Link to Aneuploidy in Early Human Embryo Development

Importance

It is known that oocytes undergo aging that is caused by exposure to an aged ovarian microenvironment. Telomere length in mouse and bovine oocytes declines with age, and age-associated telomere shortening in oocytes is considered a sign of poor development competency. Women with advanced age undergoing assisted reproductive technologies have poor outcomes because of increasing aneuploidy rates with age. Research has shown that aneuploidy is associated with DNA damage, reactive oxygen species, and telomere dysfunction.

Objective

In this review, we focus on the possible relationship between telomere dysfunction and aneuploidy in human early embryo development and several reproductive and perinatal outcomes, discussing the mechanism of aneuploidy caused by telomere shortening and fusion in human embryos.

Evidence Acquisition

We reviewed the current literature evidence concerning telomere dysfunction and aneuploidy in early human embryo development.

Results

Shorter telomeres in oocytes, leukocytes, and granulosa cells, related to aging in women, were associated with recurrent miscarriage, trisomy 21, ovarian insufficiency, and decreasing chance of in vitro fertilization success. Telomere length and telomerase activity in embryos have been related to the common genomic instability at the cleavage stage of human development. Complications of assisted reproductive technology pregnancies, such as miscarriage, birth defects, preterm births, and intrauterine growth restriction, also might result from telomere shortening as observed in oocytes, polar body, granulosa cells, and embryos.

Conclusions and Relevance

Telomere length clearly plays an important role in the development of the embryo and fetus, and the abnormal shortening of telomeres is likely involved in embryo loss during early human development. However, telomere fusion studies have yet to be performed in early human development.

An Overview of Candidate Therapeutic Target Genes in Ovarian Cancer

Ovarian cancer (OC) shows the highest mortality rate among gynecological malignancies and, because of the absence of specific symptoms, it is frequently diagnosed at an advanced stage, mainly due to the lack of specific and early biomarkers, such as those based on cancer molecular signature identification. Indeed, although significant progress has been made toward improving the clinical outcome of other cancers, rates of mortality for OC are essentially unchanged since 1980, suggesting the need of new approaches to identify and characterize the molecular mechanisms underlying pathogenesis and progression of these malignancies. In addition, due to the low response rate and the high frequency of resistance to current treatments, emerging therapeutic strategies against OC focus on targeting single factors and pathways specifically involved in tumor growth and metastasis. To date, loss-of-function screenings are extensively applied to identify key drug targets in cancer, seeking for more effective, disease-tailored treatments to overcome lack of response or resistance to current therapies. We review here the information relative to essential genes and functional pathways recently discovered in OC, often strictly interconnected with each other and representing promising biomarkers and molecular targets to treat these malignancies.