Mitochondrial trafficking in primary microglia cells is influenced by the TRPV4 ion channel

Abstract

Microglia are highly dynamic cells that use a lot of energy to move around. Mitochondria are functional organelles that ensure energy for the fast cytoskeletal rearrangement that the microglia require. Microglia react to a disturbance in brain homeostasis by directed process extension and/ or migration towards a specific cue. Both types of microglial movement involve the reorganization of the cytoskeleton, which is dependent on the levels of Ca 2+ inside the cells. Recently, the temperature-sensitive ion channels, transient receptor potential vanilloid 4 (TRPV4) have been proven to aid in phagocytic motility either as a primary mechanism or as a mediator for other molecular cues. The activation of this channel increases the intracellular concentration of Ca 2+ and has been identified alongside proteins that are part of the cytoskeleton, such as actin. Adaptor proteins such as Miro and TRAK bind kinesin-1 and dynein to mitochondria and ensure the microtubule and actin-based movement of these organelles. Previously, mitochondrial trafficking was studied mostly in neurons and cancer cells, but not in the highly motile microglial cells. However, in regards to microglia and mitochondria, only metabolic studies have been performed so far. By performing tracking of the mitochondria in branched primary microglia we determined the baseline of the parameters, such as speed, distance, number of static mitochondria, anterograde and retrograde distances. These parameters are usually used in assessing the trafficking of this organelle in neurons. Due to these recordings, now mitochondrial movement can be compared between the two cell types. Recently, it has been demonstrated that by administering GSK2193874, a TRPV4 channel antagonist, the movement of microglial branches stops. We assessed what happens with the mitochondrial movements when the branches are immobile. This information can be compared to the homeostatic state in order to better understand the molecular mechanisms behind the mitochondrial movement. Understanding mitochondrial trafficking in microglia will help to elucidate the molecular mechanisms behind cell homeostasis and cell movement with the hopes of translating it into disease models.