Increased respiration and ATP production in cytotrophoblast compared to syncytiotrophoblast mitochondria

Abstract

Objectives: The placenta contains underlying cytotrophoblasts (CT) whichfuse to form the syncytiotrophoblast (ST). During this transformation, theassociated mitochondria undergo morphologic alterations. Mitochondriaare dynamic organelles undergoing cycles of fusion andfission (joiningand separation) to maintain homeostatic balance of ATP. ATP and bio-energetics are mediated by the complexes of the electron transport chain(ETC) in conjunction with mitochondrial membrane potential. The aim ofthis research is to better characterise CT and ST mitochondria, providing afoundation for future research into alterations induced by gestationaldisorders. Methods: Mitochondria were isolated from term placenta and differen-tially separated by centrifugation. Respiration was determined in realtime using an O2K oxygraph (Oroboros). ATP production was quantifiedbyflourometric assay. Western blotting was performed to assessmitochondrial complex expression and analyse proteins involved inmitochondrial dynamics. Membrane potential was obtained byflowcytometry, and liquid chromatography-mass spectrometry assessed pro-teomic profiles. Results: Respiration was greater in CT than ST mitochondria in ETC com-plex I (p¼0.03; 5 fold), complex II (p¼0.0004; 3 fold), and maximumrespiratory capacity (p¼0.0003; 3 fold). ATP production was higher in CTmitochondria (p¼0.0016; 5 fold). No changes in protein levels of com-plexes I, II, or proteins involved with mitochondrial dynamics, were foundbetween CT and ST mitochondria. Mitochondrial membrane potential washigher in CT mitochondria when compared to ST. Conclusion: CT mitochondria have a greater bioenergetic capacity thantheir ST counterparts, capable of higher respiration and producing moreATP. This study illustrates that bioenergetic differences are likely not due toalterations in total complex expression or changes infission and fusionmachinery, but may be a result of membrane potential alterations. Thisresearch provides a foundation to assess mitochondrial function in CT andST with potential for defining the role of mitochondria in the pathogenesisof gestational diseases.