Effects of Lipoprotein Lipase on Uptake and Transcytosis of Low Density Lipoprotein (LDL) and LDL-associated α-Tocopherol in a Porcine in Vitro Blood-Brain Barrier Model

Abstract During the present study the contribution of lipoprotein lipase (LPL) to low density lipoprotein (LDL) holoparticle and LDL-lipid (α-tocopherol (αTocH)) turnover in primary porcine brain capillary endothelial cells (BCECs) was investigated. The addition of increasing LPL concentrations to BCECs resulted in up to 11-fold higher LDL holoparticle cell association. LPL contributed to LDL holoparticle turnover, an effect that was substantially increased in response to LDL-receptor up-regulation. The addition of LPL increased selective uptake of LDL-associated αTocH in BCECs up to 5-fold. LPL-dependent selective αTocH uptake was unaffected by the lipase inhibitor tetrahydrolipstatin but was substantially inhibited in cells where proteoglycan sulfation was inhibited by treatment with NaClO3. Thus, selective uptake of LDL-associated αTocH requires interaction of LPL with heparan-sulfate proteoglycans. Although high level adenoviral overexpression of scavenger receptor BI (SR-BI) in BCECs resulted in a 2-fold increase of selective LDL-αTocH uptake, SR-BI did not act in a cooperative manner with LPL. Although the addition of LPL to BCEC Transwell cultures significantly increased LDL holoparticle cell association and selective uptake of LDL-associated αTocH, holoparticle transcytosis across this porcine blood-brain barrier (BBB) model was unaffected by the presence of LPL. An important observation during transcytosis experiments was a substantial αTocH depletion of LDL particles that were resecreted into the basolateral compartment. The relevance of LPL-dependent αTocH uptake across the BBB was confirmed in LPL-deficient mice. The absence of LPL resulted in significantly lower cerebral αTocH concentrations than observed in control animals.