Abstract 1671 A compositionally unique population of mitochondria target to filopodia to support cellular migration

Mitochondria perform a variety of critical cellular functions, including producing energy via oxidative phosphorylation, hosting a number of anabolic reactions, and maintaining cellular calcium homeostasis. Cells have distinct subcellular local metabolic needs, which begs the question of whether different populations of mitochondria are specialized to play unique roles. Mitochondrial form and function are intricately linked, and in order to perform these diverse functions, mitochondria are organized into distinct functional and morphological domains by the Mitochondrial Contact Site and Cristae Organizing System (MICOS) complex. To explore whether "all mitochondria are created equal," we examined the sub-organellar distribution of MICOS complexes within mitochondria in cultured human cells. Remarkably, we discovered that MICOS complexes are heterogeneously distributed within mitochondria and are drastically enriched at the tips of a subset of mitochondria found in the extreme cellular periphery. Utilizing live cell confocal microscopy, we observed that the MICOS complex dynamically reorganizes within mitochondria as they move into a subset of filopodia, thin actin-mediated membrane projections that extend from the cell surface and are implicated in promoting cellular motility. To gain functional insight into the role of these filopodial mitochondria, we examined their protein composition by performing immunofluorescence staining for key metabolic enzymes. Remarkably, MICOS-enriched filopodial mitochondria are de-enriched in several enzymes, including TCA cycle components and the pyruvate dehydrogenase complex which supports acetyl-CoA production. Instead, filopodial mitochondria are highly enriched for the Mitochondrial Calcium Uniporter (MCU), suggesting these mitochondria may play a role in locally supporting calcium homeostasis, a known contributor to filopodial directional movements. Using a candidate-approach, we found that this unique MICOS distribution and the localization of mitochondria to filopodia relies on MYO19, a mitochondrially-associated myosin. Strikingly, depletion of MYO19 prevents targeting of mitochondrial to filopodia as well as the redistribution of MICOS and the MCU. Importantly, MYO19 is not required for the formation or proper density of filopodia, but its loss specifically leads to a significant shortening of filopodia. Lastly, we found that in MYO19 depleted cells, cellular migration is severely inhibited, presumably as a consequence of loss of mitochondrial targeting. Together, our data suggest that a compositionally unique and specialized population of mitochondria localize to filopodia in order to facilitate filopodial elongation and normal cellular motility. JF is funded by awards from NIGMS and the UTSW endowed scholars program.