Discipline: Biological Sciences
Subcategory: Biomedical Engineering
Xingyue Delan Hao - Northwestern University
Co-Author(s): Benjamin Brenner, Northwestern University, Evanston, ILWenan Qiang, Northwestern University, Evanston, ILHao F. Zhang, Northwestern University, Evanston, IL
Breast cancer is the most common cancer in women; hence, understanding the disease at the cellular and molecular levels to develop effective treatment and therapy is critical to improving patient outcomes. The shape and structure of mitochondria within breast cancer cells have been linked to the severity of the disease. Mitochondrial fission and fusion are two significant morphological changes that affect cell functions. During fusion, two mitochondria combine, promoting greater metabolic activity. Fission occurs when a mitochondrion splits into two mitochondria, allowing for apoptosis and degradation of damaged mitochondria in mitophagy. Within breast cancer cells, these changes are impaired; fusion is inhibited while fission is promoted, increasing breast cancer cell proliferation.Though this phenomenon is known, no methods exist to quantitatively correlate mitochondria fusion and fission with cancer progression and treatment. Super-resolution images allow for sub-cellular imaging of mitochondria, which could determine mitochondrial length and volume within cells. This information would be especially powerful as studies analyzing the mitochondrial morphological changes rely on qualitative analysis of mitochondrial shape. As such, we show a quantitative method for assessing mitochondria volume and length through the analysis of images derived from our super- resolution imaging technique, 3D single-molecule localization microscopy, to prove that fragmented mitochondria are linked to metastatic potential.We used MCF-7 and MDA-MB-468 breast cancer cells to analyze and compare their respective mitochondrial volumes using 3D SMLM. MCF-7 cells are nonmalignant and are used extensively in breast cancer research. However, SIRT3 is a gene that regulates mitochondria expression of NAD+ dependent deacetylase and acts as a tumor suppressor. To examine the role of SIRT3 in tumorigenesis, we knockdown SIRT3 in MCF-7 cells to compare mitochondria between MCF-7 control and MCF-7 shSIRT3 cells. We then compare the mitochondria within these cells to those found within 468 triple negative breast cancer cells which have higher metastatic potential. To normalize the widths and lengths of the mitochondria, we calculate the ratio between the length and width of each mitochondrion as the aspect ratio. We report that the mean aspect ratio of the MCF-7 control was significantly smaller than that of the 468 cells (p = 0.0023). Though the mean aspect ratio was not significantly different between the two MCF-7 groups, the MCF-7 shSIRT3 was significantly smaller than the 468 cells (p = 0.0035). These results support the idea that mitochondria fission is promoted within breast cancer cells and that breast cancer cells with higher metastatic potential have more fragmented mitochondria. This also validates our method of quantitative analysis. Future research involves expanding our analysis to other diseases, including additional types of cancer cells with metastatic potential.
Funder Acknowledgement(s): Northwestern University Summer Research Opportunity ProgramNorthwestern University Research Experience and Mentoring Program
Faculty Advisor: Hao F. Zhang, firstname.lastname@example.org
Role: I performed cell fixation, immunofluorescence staining, imaging, post-imaging processing, quantitative analysis, and statistical tests.