Exploring the Role of BRCA2 in Endothelial Dysfunction and Cardiovascular Complications in Diabetes: Mechanisms and Implications

Sepideh Nikfarjam

Abstract

Loss of function mutations in the breast cancer susceptibility gene 2 (BRCA2) impair DNA damage repair which can eventually culminate in cancer or apoptosis. Hyperglycemia induces oxidative stress and triggers DNA damage and apoptosis, which are common contributors to endothelial dysfunction in diabetes. Here, we tested the hypothesis that BRCA2 plays a protective role in hyperglycemia-induced DNA damage in endothelial cells. BRCA2 was significantly upregulated in the aorta of streptozotocin (STZ)-induced hyperglycemic mice and upon high glucose challenge in cultured human endothelial cells. High glucose augmented oxidative stress, DNA double-strand breaks, and p53-associated apoptosis in BRCA2-silenced human umbilical vein endothelial cells (HUVECs). BRCA2 knockdown in HUVECs was further associated with impaired cell proliferation, tube-forming potential, and decreased expression of endothelial nitric oxide synthase (eNOS). Next, we aimed to explore the alterations in gene expression patterns following BRCA2 silencing in HUVECs. In total, 3152 differentially expressed genes were identified, of which 1852 genes were upregulated, and 1344 genes were downregulated in BRCA2-silenced HUVECs. This indicates an important role for BRCA2 in regulation of the endothelial cell transcriptome. Finally, we generated an endothelium-specific BRCA2 knockout (BRCA2^endo) mouse model using the Cre-loxP system and induced diabetes via five low-dose (50 mg/kg) injections of STZ. Left femoral artery ligation and laser doppler imaging were performed to assess blood flow recovery. Seven days post-surgery, we observed decreased blood flow in the ischemic limb of vehicle-injected BRCA2^endo mice compared to WTmice. This effect was further exacerbated in diabetic BRCA2^endo mice. Pressure-volume assessments revealed reduction of first derivative of pressure during isovolumic contraction (dP/dt max) and relaxation (dP/dt min) along with increased end-diastolic volume-to-pressure ratio in diabetic BRCA2^endo mice, indicating diastolic cardiac dysfunction. Collectively, our findings reveal an important role for BRCA2 in the endothelium and cardiovascular system especially during diabetes and suggest that BRCA2 mutation carriers, in addition to risk of cancer, may be at an increased risk of cardiovascular dysfunction that can be augmented by concurrent DNA stressors such as hyperglycemia in diabetes.