SAT-662 - Obesity Is Associated with Mitochondrial Swelling and Increased Mitochondrial Superoxide Production: Possible Role in Driving DNA Damage in BRCA1+/- Breast Epithelium

Obesity (BMI ≥30) is associated with an increased risk of breast cancer, including in women with a genetic predisposition, e.g. carrying a germline mutation in BRCA1. Our prior work demonstrates that elevated BMI induces DNA damage in the breast epithelium of BRCA1 mutation carriers, potentially promoting tumorigenesis (Bhardwaj et al., 2023, Sci Transl Med). We have also shown that adipose-derived factors reprogram mitochondrial function in breast cancer cells, with obesity increasing mitochondrial density and respiration, leading to dysregulated mitochondrial metabolism (Liu et al., 2023). Based on this, we hypothesize that human breast adipose tissue-derived factors from women with obesity will promote mitochondrial dysfunction in normal breast epithelial MCF10A cells heterozygous for BRCA1 by increasing mitochondrial reactive oxygen species (ROS) production and DNA damage which eventually leads to breast cancer.
To test this hypothesis, 3D spheroids of BRCA1+/− MCF10A cells were treated with breast adipose tissue-derived conditioned media (CM) from a woman with obesity (BMI 37.18) or a healthy BMI donor (BMI 21.9) for 24 hours (acute) or 2 weeks (chronic). Transmission electron microscopy (TEM) was used to evaluate effects on mitochondrial structure in chronically-treated samples. MitoSOX staining, confocal imaging and IMARIS image analysis were used to assess effects on mitochondrial superoxide formation in the acute setting. RNA-Seq of primary human breast epithelial cells from BRCA1 mutation carriers was also evaluated.
TEM revealed mitochondrial swelling and cristae disruption in BRCA1+/− MCF10A spheroids exposed to high-BMI adipose CM, an effect not seen in healthy BMI control conditions. These effects can be driven by ROS and/or cause ROS. Acute treatment with CM from women with obesity led to a significantly higher level of mitochondrial ROS in BRCA1+/- MCF10A spheroids compared to healthy BMI CM (25.12 ± 2.21 vs 17.61 ± 1.08; p < 0.01). Our RNA-seq analysis of primary patient-derived organoids also revealed significantly reduced CDK5 expression (p-value 0.04) in samples from individuals with higher BMI. Reduced CDK5 expression and has been linked to inhibition of mitochondrial permeability transition pore (mPTP) opening and impaired calcium homeostasis, processes that contribute to mitochondrial swelling.
These mechanisms remain incompletely understood and ongoing experiments aim to investigate the role of adipose-derived factors in driving mitochondrial dysfunction mechanistically and its relationship to DNA damage and tumor development. Clarifying this relationship may help elucidate tumor development in women with BRCA1 mutations and inform novel risk-reduction strategies.

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