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Thesis Format



Master of Science


Anatomy and Cell Biology


Singh, Krishna K.


Doxorubicin (Dox) is a chemotherapeutic drug used to treat various malignancies including breast and ovarian cancers. Accumulating evidence implicates cardiac impairments associated with Dox treatment. The Breast Cancer Susceptibility Gene 2 (BRCA2) functions to maintain genome-wide stability by promoting DNA-damage repair. Accordingly, cardiomyocyte damage is specifically regulated by contributors of DNA damage repair such as BRCA2. The endothelium, the innermost cells of every blood vessel, act to protect our tissues from noxious elements, however, recent evidence suggests that BRCA2 knockdown compromises endothelial cell function. A putative role of endothelial BRCA2 during Dox-induced cardiotoxicity (DIC) remains unknown. We hypothesized that endothelial-specific loss of BRCA2 will induce endothelial dysfunction and exacerbate DIC. Our findings indicate that Dox treatment promoted weight loss and induced cardiomyocyte dysfunction in endothelial-specific BRCA2 knockdown mice in vivo, alongside profound endothelial dysfunction in vitro, and suggests a novel mechanism for DIC in the absence of BRCA2.

Summary for Lay Audience

Changes in the genetic makeup of cells can increase one's susceptibility to the development of cancer. Mutations in the BRCA2 gene, an important gene that maintains the integrity of the genome, have been implicated in the development of breast and ovarian cancers. BRCA2 plays an important role in repairing DNA damage, and thus, when BRCA2 does not function as intended due to a deleterious change in the gene, there is an accumulation of DNA damage that increases the likelihood of breast or ovarian cancer development. The most used chemotherapeutic drug for breast cancer is Dox, an agent that kills tumour cells by causing DNA damage. Unfortunately, Dox has many undesirable side effects, the most severe of which is heart failure which raises concern about Dox use as a clinical therapeutic. The endothelium, or the innermost cell layer of our blood vessels, acts as a barrier to harmful agents from entering important tissues, like the heart. In people with BRCA2 mutations, the endothelial barrier is compromised due to the accumulation of DNA damage in endothelial cells, and thus agents like Dox can access the heart at much higher concentrations. This results in cardiac cell death that can lead to heart failure, a fatal clinical outcome. This thesis aims to elucidate the role of BRCA2 in the endothelium and its importance in preventing endothelial dysfunction and cardiac dysfunction during Dox treatment. We employ a mouse model with BRCA2 expression knocked down in endothelial cells and administer Dox to observe changes in mortality, cardiac functionality, and cardiac structure. Next, we employ endothelial cell culture systems to examine the functional mechanisms by which BRCA2 protects the endothelium in the presence of Dox. We found increased mortality and cardiac dysfunction in our BCRA2 knockdown mice exposed to Dox and Dox decreased the survival, proliferation, and tube formation in cultured endothelial cells. This thesis's findings provide important context for recognizing a critical role for BRCA2 in the endothelium in the protection of heart tissue.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.