Mitochondria are responsible for the maintenance of energy homeostasis by breaking
down nutrients while also supporting cell growth through the generation of building
blocks required for the biosynthesis of proteins, lipids and nucleic acids. Recent
experimental work has shown that changes in mitochondrial function are mirrored by
alterations in mitochondrial dynamics. This term refers to changes in mitochondrial
quantity, number, morphology, and position relative to other cellular structures.
Interactions of mitochondria with lipid droplets are required for fatty acid oxidation
and energy production, but these interactions also support the synthesis of lipids and
their accumulation in lipid droplets. However, the mechanisms that control the
coupling of the functions of lipid droplets and mitochondria in various cellular
environments remain poorly known. The challenge in this work was to find out
whether changes in lipid droplet metabolism are associated with distinct alterations in
mitochondrial dynamics. To establish methods for the analysis of mitochondrial
dynamics in our lab, we induced specific changes in mitochondrial function by
modulating cellular nutrient conditions and used flow cytometry, confocal microscopy
and image analysis to quantify mitochondrial content, their shape, size and interactions
with lipid droplets. We then used genetic and pharmacological approaches in the
MDA-MB-231 cell line to modulate key nodes in lipid droplet metabolism and
measured the resulting changes in mitochondrial dynamics. Our results demonstrate
that the two primary mechanisms of lipid droplet breakdown – lipolysis and lipophagy
– have distinct influences on mitochondrial dynamics, revealing a possible functional
separation of lipid droplet breakdown mechanisms.
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