Fig. 1

The interaction between mitochondria and ER. Calcium is released via inositol 1,4,5 trisphosphate receptor (IP3R) of the endoplasmic reticulum (ER) and provides a relatively high calcium environment for mitochondria. Calcium enters the mitochondrial matrix through the voltage-dependent anion channels (VDACs) on the outer mitochondrial membrane (OMM) and through the low-affinity receptor, mitochondrial calcium uniporter (MCU) on the inner mitochondrial membrane (IMM). The glucose-regulated protein 75 (GRP-75) can be used as a partner to connect IP3R to VDACs. In addition, IP3R is regulated by numerous regulatory mechanisms. Mitofusin 2 (Mfn-2) on the ER interacts with Mfn-1 or Mfn-2 on the OMMs and regulates the connection between the two organelles. After lipid synthesis in the mitochondria or ER, a large amount of lipids is exchanged between the mitochondria and the ER in order to achieve the final lipid composition of the two organelles. This includes the processes of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) synthesis and cardiolipin (CL) synthesis