Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Chirackal Manavalan, A.
Functional Characterization of Phospholipid Transfer Protein at the Blood-Brain Barrier
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Medical University of Graz; 2014. pp. 128
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- Autor*innen der Med Uni Graz:
- Chirackal Manavalan Anil Paul
- Betreuer*innen:
- Kresse Adelheid
- Panzenboeck Ute
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- Abstract:
- Phospholipid transfer protein (PLTP) is a key protein involved in biogenesis and remodeling of plasma HDL. Several neuro-protective properties have been ascribed to HDL. We reported earlier that liver-X receptor (LXR) activation promotes cellular cholesterol efflux and formation of HDL-like particles in an established in vitro model of the blood-brain barrier (BBB) consisting of primary, porcine brain capillary endothelial cells (pBCEC). Here we report PLTP synthesis, regulation, and its key role in HDL metabolism at the BBB. We demonstrate that PLTP is highly expressed and secreted by pBCEC. In a polarized in vitro model mimicking the BBB, pBCEC secreted phospholipid-transfer active PLTP preferentially to the basolateral (‘brain parenchymal’) compartment. PLTP expression levels and phospholipid transfer activity were enhanced (up to 2.5-fold) by LXR activation using 24(S)-hydroxycholesterol (a cerebral cholesterol metabolite) or TO901317 (a synthetic LXR agonist). TO901317 administration elevated PLTP activity in BCEC from C57/BL6 mice. Under simulated diabetic conditions in vitro via treatment with supraphysiological concentration of glucose/insulin in pBCEC, we detected a significant increase (up to 2.2-fold) in PLTP protein levels but a reduced (up to 40% and 35%, respectively) PLTP mRNA levels and activity. Pre-incubation of HDL3 with human plasma-derived active PLTP resulted in the formation of smaller and larger HDL particles and enhanced the capacity of the generated HDL particles to remove cholesterol from pBCEC by up to 3-fold. Pre-ß-HDL, detected by two-dimensional crossed immunoelectrophoresis, was generated from HDL3 in pBCEC-derived supernatants, and their generation was markedly enhanced (1.9-fold) upon LXR activation. Furthermore, RNA interference-mediated PLTP silencing (up to 75%) reduced both apoA-I dependent (67%) and HDL3 dependent (30%) cholesterol efflux from pBCEC. Decreased (up to 63%) amyloid beta (Aß) oligomerisation is observed in pBCEC treated with HDL3 and active PLTP, and also detected an increased (1.8-fold) levels of beta-secretase (BACE1) mRNA in PLTP-silenced cells. Based on these findings, we propose that PLTP is actively involved in lipid transfer, cholesterol efflux, HDL biogenesis and remodeling, and Aß metabolism at the BBB.