Modulation of mitochondrial fission activity maintains ovarian tumor initiating cells dependent on mitochondrial energetics

Self-renewing, therapy resistant ovarian tumor initiating cells (ovTICs) clearly contribute to development and recurrence of epithelial ovarian cancer (EOC), and recurrent EOC is incurable. Depending on the genetic and physiological context of a patient ovTICs can be dependent on mitochondrial energetics, specifically ATP production and redox homeostasis. Mitochondrial energetics can be repressed through fragmentation of mitochondria through elevated activity of mitochondrial fission protein Dynamin-related protein 1 (Drp1). Conversely, repression of Drp1 activity can augment mitochondrial energetics. Drp1 has also been implicated in maintenance of some stem cell lineages. However, Drp1 regulation of the stem-like ovTICs and the impact of fission activity on the mitochondrial energetics of these cells have not been well characterized. Hypothesis Modulation of mitochondrial energetics by fission, likely mediated by cyclic changes in Drp1 activity, maintains undifferentiated ovTICs. We studied mitochondrial properties in a derived chemoresistant EOC cell line previously shown to be enriched for ovTICs compared to its parental line. We found that the chemoresistant line has boosted mitochondrial energetics and repressed Drp1 activity compared to its parental line. We then FACS-sorted the chemoresistant line based on a TIC marker (Aldh) and mitochondrial membrane potential (ΔΨ) into 4 populations (Aldh - ΔΨ lo , Aldh - ΔΨ hi , Aldh + ΔΨ lo , and Aldh + ΔΨ hi ). The sorted Aldh + populations are dependent on mitochondrial energetics and cycle between ΔΨ hi and ΔΨ lo energetic states as they form in vitro tumorspheres, unlike the Aldh - populations. These energetic states have characteristic mitochondrial fission activity. Importantly, regulation of ATP production or redox state by fission is mutually exclusive for each energetic state. Understanding how fission can modulate the mitochondrial energetics of ovTICs that depend on mitochondria for ATP production and/or redox homeostasis will allow us to better identify and directly target TICs.