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.
ABBREVIATIONS
- APOO
- Apolipoprotein O
- APOOL
- Apolipoprotein O-like
- CHCHD3/6
- Coiled-Coil-Helix-Coiled-Coil-Helix Domain Containing 3/6
- Ca2+
- Calcium
- CCCP
- Carbonyl cyanide 3-chlorophenylhydrazone
- CJ
- cristae junctions
- CV-ATP5A
- complex V alpha subunit
- EM
- electron microscopy
- ER
- endoplasmic reticulum
- FFAT
- two phenylalanines (FF) in an Acidic Tract
- GRP75
- glucose-regulated protein 75
- HRP
- horseradish peroxidase
- IF
- immunofluorescence
- IMM
- inner mitochondrial membrane
- IMS
- intermembrane space
- IP3R
- Inositol trisphosphate receptor
- LAR-GECO
- low-affinity red fluorescent genetically encoded Ca2+ indicators for optical imaging
- LTPs
- lipid transfer proteins
- MAM
- mitochondria-associated ER membrane
- MCU
- mitochondrial calcium uniporter
- MIB
- Mitochondrial intermembrane space bridging complex
- MICOS
- Mitochondrial Contact Sites and Cristae Junction Organizing System
- MINOS1
- mitochondrial inner membrane organizing system 1
- MS
- mass spectrometry
- mt-Pericam
- mitochondrial permuted YFP and a CaM (calmodulin)
- OMM
- outer mitochondrial membrane
- ORD
- OSBP-related lipid-binding/transfer domain
- ORP
- Oxysterol binding protein (OSBP)-related proteins
- Osh
- oxysterol-binding homology
- PC
- Phosphatidylcholine
- PDI
- Protein disulfide isomerase
- PE
- phosphatidylethanolamine
- PH
- pleckstrin homology
- PI4P
- Phosphatidylinositol-4-phosphate
- PIP2
- Phosphatidylinositol 4,5-bisphosphate
- POPC
- Palmitoyloleoylphosphatidylcholine
- PS
- phosphatidylserine
- PTPIP51
- Protein tyrosine phosphatase interacting protein 51
- QIL1
- MICOS complex subunit MIC13
- R-GECO
- Red fluorescent, genetically-encoded Ca2+ indicator for optical imaging
- SA β-gal
- Senescence-associated β –galactosidase
- SAM
- Sorting and Assembly Machinery
- SAM50
- Sorting Assembly Machinery 50
- TLC
- thin layer chromatography
- TMRE
- Tetramethylrhodamine ethyl ester
- VAPB
- Vesicle-associated membrane protein-associated protein B
- VDAC
- Voltage Dependent Anion Channel
- WB
- western blotting