Knockdown of Cardiolipin Synthase in Human Brain Microvessel Endothelial Cells Modulates Blood Brain Barrier Transport Properties

Abstract

The blood brain barrier (BBB) is formed by microvessel endothelial cells and is a restrictively permeable interface that allows transport of only specific compounds into the brain. Cardiolipin (CL) a mitochondrial (MITO) lipid is required for activity/integrity of the respiratory chain. We examined the role of CL in maintaining barrier properties of brain microvessel endothelial cells. We show that human brain capillary endothelial cells (hCMEC/D3) produce a significant proportion of their basal ATP requirement through MITO oxidative phosphorylation. siRNA knockdown (KD) of the CL biosynthetic enzyme CL synthase (CLS) significantly reduced these cells ability to increase MITO function under conditions of increased metabolic demand compared to controls. In addition, KD of CLS acted as a metabolic switch causing hCMEC/D3 cells to become more dependent on glycolysis. KD of CLS increased [3H]‐2‐deoxyglucose ([3H]‐2DG) uptake compared to controls, and this may thus serve as a mechanism to compensate for the cells reduced MITO energy production efficiency. Finally, KD of CLS did not affect movement of the permeability marker fluorescent dextran across confluent hCMEC/D3 monolayers grown on Transwell®plates, an in vitro model for the human BBB, but caused in an increase in [3H]‐2DG transport across the monolayer compared to controls. The results suggest that brain endothelial MITO energy status play a role in regulating glucose transport across the human BBB. These observations may, in part, explain why brain capillary endothelial cells possess higher MITO content than endothelial cells derived from non‐BBB regions of the body. (Supported by NSERC and the CRC Program)