ORP5 Transfers Phosphatidylserine to Mitochondria and Regulates Mitochondrial Calcium Uptake at Endoplasmic Reticulum - Mitochondria Contact Sites

Abstract

Mitochondria are dynamic organelles essential for cell survival whose structural and functional integrity rely on selective and regulated transport of lipids from/to the endoplasmic reticulum (ER) and across the two mitochondrial membranes. As they are not connected by vesicle transport, the exchange of lipids between ER and mitochondria occurs at sites of close organelle apposition called membrane contact sites. However, the mechanisms and proteins involved in these processes are only beginning to emerge. Here, we show that ORP5/8 mediate non-vesicular transport of Phosphatidylserine (PS) from the ER to mitochondria in mammalian cells. We also show that ER-mitochondria contacts where ORP5/8 reside are physically and functionally linked to the MIB/MICOS complexes that bridge the mitochondria membranes, cooperating with them to facilitate PS transfer from the ER to the mitochondria. Finally, we show that ORP5 but not ORP8, additionally regulates import of calcium to mitochondria and consequently cell senescence.