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

During the present study the contribution of lipoprotein lipase (LPL) to low density lipoprotein (LDL) holoparticle and LDL-lipid (alpha-tocopherol (alphaTocH)) 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 upregulation. The addition of LPL increased selective uptake of LDL-associated alphaTocH in BCECs up to 5-fold. LPL-dependent selective alphaTocH 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 alphaTocH 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-alphaTocH 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 alphaTocH, 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 alphaTocH depletion of LDL particles that were resecreted into the basolateral compartment. The relevance of LPL-dependent alphaTocH uptake across the BBB was confirmed in LPL-deficient mice. The absence of LPL resulted in significantly lower cerebral alphaTocH concentrations than observed in control animals.