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Cholesterol-regulated signaling and transport in endo-lysosomes
Chemistry and Physics of Lipids 164S (2011) S9–S11
Contents lists available at ScienceDirect
Chemistry and Physics of Lipids journal homepage: www.elsevier.com/locate/chemphyslip
Session 3: Lipids in signaling and intracellular trafficking
PL 10
PL 9 Cholesterol-regulated lysosomes Ikonen 1,∗ ,
signaling
and
Uronen 1 ,
Elina Riikka-Liisa Blom 1 , Zaiguo Li 2 , Robert Bittman 2
transport
Kristiina
in
Kanerva 1 ,
endo-
Sphingolipid signaling and neuronal function
Tomas
Shun-ichi Nakamura ∗ , Eri Fukai, Satoshi Miya, Henryk Jesko, Taro Okada Kobe University, Graduate School of Medicine, Japan
1
Institute of Biomedicine, Anatomy, University of Helsinki, Finland 2 Department of Chemistry and Biochemistry, Queens College of the City University of New York, USA Cholesterol is taken up by cells through receptor mediated endocytosis of low density lipoprotein (LDL)-particles. While LDLreceptors recycle to the plasma membrane (PM), LDL-cholesteryl esters are hydrolyzed by acid lipase. The Niemann-Pick type C2 and C1 proteins co-operate in capturing the hydrolyzed cholesterol for delivery to the lysosomal limiting membrane. How cholesterol then leaves lysosomes and what signals are needed to activate the following transfer processes is less clear. We searched for proteins involved in the transfer of cholesterol from lysosomes to a cholesterol-rich membrane, the PM, under conditions where cells have been starved of lipoproteins and upon LDL feeding, will replenish their PM cholesterol stores. For this purpose, we characterized a novel fluorescent imaging tool, LDL-particles labeled with esterified BODIPY-cholesterol. We provide evidence that the hydrolysis of BODIPY-cholesteryl ester endocytosed in LDL depends on acid lipase and its exit from lysosomes on NPC1 and NPC2. The transfer of BODIPY-cholesterol from lysosomes to the PM can be quantitatively monitored in living cells. By using this strategy we identified, based on pharmacological and siRNA screens, a novel Rab GTPase interactome that controls the PM delivery of lysosome-derived cholesterol. The functionality of this machinery is important for physiological processes that rely on cholesterolrich PM domains, such as cell motility. doi:10.1016/j.chemphyslip.2011.05.022
Neuronal activity greatly influences the formation and stabilization of synapses. Although receptors for sphingosine-1-phosphate (S1P), a lipid mediator regulating diverse cellular processes, are abundant in central nervous system, neuron-specific functions of S1P remain largely undefined. Here I present novel actions of S1P using primary hippocampal neurons as a model system, i.e., S1P triggers neurotransmitter release in a dosen-dependent manner. Sphingosine kinase 1 (SK1), a key enzyme for S1P production, was enriched in hippocampal neurons. Silencing SK1 expression by siRNA resulted in a strong inhibition of depolarization-evoked glutamate release. FRET analysis demonstrated that S1P1 receptor at the presynaptic membranes was activated during depolarization and that depolarization-induced S1P1 receptor activation was inhibited in SK1-knockeddown cells. Importantly, exogenously added S1P at nanomolar concentrations by itself elicited glutamate release from hippocampal neurons even when Na+ -channel was blocked by tetrodotoxin, suggesting that S1P acts on presynaptic membranes. These findings indicate that S1P, through its autocrine action, facilitates spontaneous glutamate release from hippocampal neurons. I will also present data using electrophysiological approaches and behavioral analysis using SK1-knockout mice showing a vital role of SK/S1P signaling in memory formation and learning in the hippocampus. doi:10.1016/j.chemphyslip.2011.05.023 PL 11 Statins – Do we really know all mechanisms of action of this group of drugs? Maciej Banach Medical University of Lodz, Lodz The role of statins in the treatment and prevention of cardiovascular diseases, such as coronary artery disease, acute coronary syndromes, diabetes or stroke is well established. However, there are still many questions regarding the role of statins in patients with
0009-3084/$ – see front matter
Contents lists available at ScienceDirect
Chemistry and Physics of Lipids journal homepage: www.elsevier.com/locate/chemphyslip
Session 3: Lipids in signaling and intracellular trafficking
PL 10
PL 9 Cholesterol-regulated lysosomes Ikonen 1,∗ ,
signaling
and
Uronen 1 ,
Elina Riikka-Liisa Blom 1 , Zaiguo Li 2 , Robert Bittman 2
transport
Kristiina
in
Kanerva 1 ,
endo-
Sphingolipid signaling and neuronal function
Tomas
Shun-ichi Nakamura ∗ , Eri Fukai, Satoshi Miya, Henryk Jesko, Taro Okada Kobe University, Graduate School of Medicine, Japan
1
Institute of Biomedicine, Anatomy, University of Helsinki, Finland 2 Department of Chemistry and Biochemistry, Queens College of the City University of New York, USA Cholesterol is taken up by cells through receptor mediated endocytosis of low density lipoprotein (LDL)-particles. While LDLreceptors recycle to the plasma membrane (PM), LDL-cholesteryl esters are hydrolyzed by acid lipase. The Niemann-Pick type C2 and C1 proteins co-operate in capturing the hydrolyzed cholesterol for delivery to the lysosomal limiting membrane. How cholesterol then leaves lysosomes and what signals are needed to activate the following transfer processes is less clear. We searched for proteins involved in the transfer of cholesterol from lysosomes to a cholesterol-rich membrane, the PM, under conditions where cells have been starved of lipoproteins and upon LDL feeding, will replenish their PM cholesterol stores. For this purpose, we characterized a novel fluorescent imaging tool, LDL-particles labeled with esterified BODIPY-cholesterol. We provide evidence that the hydrolysis of BODIPY-cholesteryl ester endocytosed in LDL depends on acid lipase and its exit from lysosomes on NPC1 and NPC2. The transfer of BODIPY-cholesterol from lysosomes to the PM can be quantitatively monitored in living cells. By using this strategy we identified, based on pharmacological and siRNA screens, a novel Rab GTPase interactome that controls the PM delivery of lysosome-derived cholesterol. The functionality of this machinery is important for physiological processes that rely on cholesterolrich PM domains, such as cell motility. doi:10.1016/j.chemphyslip.2011.05.022
Neuronal activity greatly influences the formation and stabilization of synapses. Although receptors for sphingosine-1-phosphate (S1P), a lipid mediator regulating diverse cellular processes, are abundant in central nervous system, neuron-specific functions of S1P remain largely undefined. Here I present novel actions of S1P using primary hippocampal neurons as a model system, i.e., S1P triggers neurotransmitter release in a dosen-dependent manner. Sphingosine kinase 1 (SK1), a key enzyme for S1P production, was enriched in hippocampal neurons. Silencing SK1 expression by siRNA resulted in a strong inhibition of depolarization-evoked glutamate release. FRET analysis demonstrated that S1P1 receptor at the presynaptic membranes was activated during depolarization and that depolarization-induced S1P1 receptor activation was inhibited in SK1-knockeddown cells. Importantly, exogenously added S1P at nanomolar concentrations by itself elicited glutamate release from hippocampal neurons even when Na+ -channel was blocked by tetrodotoxin, suggesting that S1P acts on presynaptic membranes. These findings indicate that S1P, through its autocrine action, facilitates spontaneous glutamate release from hippocampal neurons. I will also present data using electrophysiological approaches and behavioral analysis using SK1-knockout mice showing a vital role of SK/S1P signaling in memory formation and learning in the hippocampus. doi:10.1016/j.chemphyslip.2011.05.023 PL 11 Statins – Do we really know all mechanisms of action of this group of drugs? Maciej Banach Medical University of Lodz, Lodz The role of statins in the treatment and prevention of cardiovascular diseases, such as coronary artery disease, acute coronary syndromes, diabetes or stroke is well established. However, there are still many questions regarding the role of statins in patients with
0009-3084/$ – see front matter