Lipids synthesized in astrocytes are distributed to other brain cells in high-density lipoprotein-like ApoE particles. ApoE, which is a powerful genetic risk factor for developing Alzheimer's disease, is secreted differently depending on genotype. Secretion of ApoE from mouse astrocytes is regulated by the mevalonate pathway.
Objective
We aimed to understand if the regulation of ApoE secretion from astrocytes by the mevalonate pathway was the same between mouse ApoE and ApoE from humanized mice, and if this is impacted by ApoE isoform.
Methods
Astrocyte-enriched glial cultures from wild-type and humanized ApoE targeted-replacement mice were treated with pharmacological inhibitors of various steps along the mevalonate pathway and ApoE in the conditioned media was measured.
Results
We show that statins and prenylation inhibitors, but not specific cholesterol inhibitors, reduce extracellular ApoE lipoparticle levels in astrocyte-enriched glial cultures, and that this occurs in cells harboring either the mouse ApoE or any of the three human ApoE genotypes to a similar extent. We find that geranylgeranylation modulates ApoE release from astrocytes, and it does so independent of ApoE genotype.
Conclusions
Our results suggest that prenylation broadly regulates ApoE secretion from astrocytes regardless of ApoE genotype, and that this is mediated specifically by geranylgeranylation. Therefore, our data implicates geranylgeranylation as a general mechanism modulating ApoE release from astrocytes, but likely is not responsible for the reported baseline differences in ApoE secretion seen in vivo and in vitro across genotypes.
CorderEHSaundersAMStrittmatterWJ, et al.Gene dose of apolipoprotein E type 4 allele and the risk of Alzheimer’s disease in late onset families. Science1993; 261: 921–923.
2.
CorderEHSaundersAMRischNJ, et al.Protective effect of apolipoprotein E type 2 allele for late onset Alzheimer disease. Nat Genet1994; 7: 180–184.
3.
CoonKDMyersAJCraigDW, et al.A high-density whole-genome association study reveals that APOE is the major susceptibility gene for sporadic late-onset Alzheimer’s disease. J Clin Psychiatry2007; 68: 613–618.
4.
ReimanEMArboleda-VelasquezJFQuirozYT, et al.Exceptionally low likelihood of Alzheimer’s dementia in APOE2 homozygotes from a 5,000-person neuropathological study. Nat Commun2020; 11: 667.
5.
FeringaFMHertogSJKWangL, et al.The Neurolipid Atlas: a lipidomics resource for neurodegenerative diseases uncovers cholesterol as a regulator of astrocyte reactivity impaired by ApoE4. bioRxiv2024. [Preprint]. Posted July 3, 2024.
6.
GetzGSReardonCA. Apoprotein E and reverse cholesterol transport. Int J Mol Sci2018; 19: 3479.
7.
WangHKulasJAWangC, et al.Regulation of beta-amyloid production in neurons by astrocyte-derived cholesterol. Proc Natl Acad Sci U S A2021; 118: e2102191118.
8.
JungDBachmannHS. Regulation of protein prenylation. Biomed Pharmacother2023; 164: 114915.
9.
HooffGPWoodWGMüllerWE, et al.Isoprenoids, small GTPases and Alzheimer’s disease. Biochim Biophys Acta2010; 1801: 896.
10.
EckertGPHooffGPStrandjordDM, et al.Regulation of the brain isoprenoids farnesyl- and geranylgeranylpyrophosphate is altered in male Alzheimer patients. Neurobiol Dis2009; 35: 251.
11.
JeongAChengSZhongR, et al.Protein farnesylation is upregulated in Alzheimer’s human brains and neuron-specific suppression of farnesyltransferase mitigates pathogenic processes in Alzheimer’s model mice. Acta Neuropathol Commun2021; 9: 129.
12.
ChengSCaoDHottmanDA, et al.Farnesyltransferase haplodeficiency reduces neuropathology and rescues cognitive function in a mouse model of Alzheimer disease. J Biol Chem2013; 288: 35952.
13.
JeongAAugerSAMaityS, et al.In vivo prenylomic profiling in the brain of a transgenic mouse model of Alzheimer’s disease reveals increased prenylation of a key set of proteins. ACS Chem Biol2022; 17: 2863–2876.
14.
HernandezILunaGRauchJN, et al.A farnesyltransferase inhibitor activates lysosomes and reduces tau pathology in mice with tauopathy. Sci Transl Med2019; 11: eaat3005.
15.
NaiduAXuQCatalanoR, et al.Secretion of apolipoprotein E by brain glia requires protein prenylation and is suppressed by statins. Brain Res2002; 958: 100–111.
16.
RiddellDRZhouHAtchisonK, et al.Impact of apolipoprotein E (ApoE) polymorphism on brain ApoE levels. J Neurosci2008; 28: 11445–11453.
17.
RamaswamyGXuQHuangY, et al.Effect of domain interaction on apolipoprotein E levels in mouse brain. J Neurosci2005; 25: 10658–10663.
18.
FlowersSARebeckGW. APOE In the normal brain. Neurobiol Dis2020; 136: 104724.
19.
LanfrancoMFSepulvedaJKopetskyG, et al.Expression and secretion of apoE isoforms in astrocytes and microglia during inflammation. Glia2021; 69: 1478.
20.
BalesKRVerinaTDodelRC, et al.Lack of apolipoprotein E dramatically reduces amyloid β-peptide deposition. Nat Genet1997; 17: 263–264.
21.
LiaoFLiAXiongM, et al.Targeting of nonlipidated, aggregated apoE with antibodies inhibits amyloid accumulation. J Clin Invest2018; 128: 2144.
22.
GratuzeMJiangHWangC, et al.APOE Antibody inhibits Aβ-associated tau seeding and spreading in a mouse model. Ann Neurol2022; 91: 847–852.
23.
WangCXiongMGratuzeM, et al.Selective removal of astrocytic APOE4 strongly protects against tau-mediated neurodegeneration and decreases synaptic phagocytosis by microglia. Neuron2021; 109: 1657–1674. e7.
24.
IlyasILittlePJLiuZ, et al.Mouse models of atherosclerosis in translational research. Trends Pharmacol Sci2022; 43: 920–939.
25.
SchildgeSBohrerCBeckK, et al.Isolation and culture of mouse cortical astrocytes. J Vis Exp2013; (71): 50079.
26.
GaultierAWuXLe MoanN, et al.Low-density lipoprotein receptor-related protein 1 is an essential receptor for myelin phagocytosis. J Cell Sci2009; 122: 1155.
27.
Fernández-CastañedaAChappellMSRosenDA, et al.The active contribution of OPCs to neuroinflammation is mediated by LRP1. Acta Neuropathol2019; 139: 365.
28.
RajavashisthTBKapteinJSReueKL, et al.Evolution of apolipoprotein E: mouse sequence and evidence for an 11-nucleotide ancestral unit. Proc Natl Acad Sci U S A1985; 82: 8085.
29.
MaloneyBGeYWAlleyGM, et al.Important differences between human and mouse APOE gene promoters: limitation of mouse APOE model in studying Alzheimer’s disease. J Neurochem2007; 103: 1237–1257.
30.
LiaoFZhangTJJiangH, et al.Murine versus human apolipoprotein E4: differential facilitation of and co-localization in cerebral amyloid angiopathy and amyloid plaques in APP transgenic mouse models. Acta Neuropathol Commun2015; 3: 70.
31.
KaziAXiangSYangH, et al.Dual farnesyl and geranylgeranyl transferase inhibitor thwarts mutant KRAS-driven patient-derived pancreatic tumors. Clin Cancer Res2019; 25: 5984.
32.
FazioSLintonMFSwiftLL. The cell biology and physiologic relevance of ApoE recycling. Trends Cardiovasc Med2000; 10: 23–30.
33.
KockxMTrainiMKritharidesL. Cell-specific production, secretion, and function of apolipoprotein E. J Mol Med2018; 96: 361–371.
34.
ZhaoYMazzoneT. Transport and processing of endogenously synthesized ApoE on the macrophage cell surface. J Biol Chem2000; 275: 4759–4765.
35.
KockxMJessupWKritharidesL. Regulation of endogenous apolipoprotein e secretion by macrophages. Arterioscler Thromb Vasc Biol2008; 28: 1060–1067.
36.
WindhamIACohenS. The cell biology of APOE in the brain. Trends Cell Biol2024; 34: 338–348.
37.
WindhamIAPowersAERagusaJV, et al.APOE Traffics to astrocyte lipid droplets and modulates triglyceride saturation and droplet size. J Cell Biol2024; 223: e202305003.
38.
ChangSMaTRMirandaRD, et al.Lipid- and receptor-binding regions of apolipoprotein E4 fragments act in concert to cause mitochondrial dysfunction and neurotoxicity. Proc Natl Acad Sci U S A2005; 102: 18694–18699.
39.
LucicDZhiHHDeSG, et al.Regulation of macrophage apoE secretion and sterol efflux by the LDL receptor. J Lipid Res2007; 48: 366–372.
40.
KockxMGuoDLHubyT, et al.Secretion of apolipoprotein E from macrophages occurs via a protein kinase A- and calcium-dependent pathway along the microtubule network. Circ Res2007; 101: 607–616.
41.
CastilhoLNChamberlandABouletL, et al.Effect of atorvastatin on ApoE and ApoC-I synthesis and secretion by THP-1 macrophages. J Cardiovasc Pharmacol2003; 42: 251–257.
42.
HuangZHGuDSMazzoneT. Oleic acid modulates the post-translational glycosylation of macrophage ApoE to increase its secretion. J Biol Chem2004; 279: 29195–29201.
43.
KockxMKarunakaranDTrainiM, et al.Pharmacological inhibition of dynamin II reduces constitutive protein secretion from primary human macrophages. PLoS One2014; 9: e111186.
44.
FanJStukasSWongC, et al.An ABCA1-independent pathway for recycling a poorly lipidated 8.1nm apolipoprotein E particle from glia. J Lipid Res2011; 52: 1605–1616.
45.
WahrleSEJiangHParsadanianM, et al.ABCA1 Is required for normal central nervous system ApoE levels and for lipidation of astrocyte-secreted apoE. J Biol Chem2004; 279: 40987–40993.
46.
HerzineASekkatGKaminskiS, et al.Lipolysis-stimulated lipoprotein receptor acts as sensor to regulate ApoE release in astrocytes. Int J Mol Sci2022; 23: 8630.
47.
CashikarAGToral-RiosDTimmD, et al.Regulation of astrocyte lipid metabolism and ApoE secretionby the microglial oxysterol, 25-hydroxycholesterol. J Lipid Res2023; 64: 100350.
OhkawaraHIshibashiTSakamotoT, et al.Thrombin-induced rapid geranylgeranylation of RhoA as an essential process for RhoA activation in endothelial cells. J Biol Chem2005; 280: 10182–10188.
50.
LamazeCChuangTHTerleckyLJ, et al.Regulation of receptor-mediated endocytosis by Rho and Rac. Nature1996; 382: 177–179.
51.
KroschewskiRHallAMellmanI. Cdc42 controls secretory and endocytic transport to the basolateral plasma membrane of MDCK cells. Nat Cell Biol1999; 1: 8–13.
52.
AkulaMKIbrahimMXIvarssonEG, et al.Protein prenylation restrains innate immunity by inhibiting Rac1 effector interactions. Nat Commun2019; 10: 3975.
53.
ZhouYJohnsonJLCerioneRA, et al.Prenylation and membrane localization of Cdc42 are essential for activation by DOCK7. Biochemistry2013; 52: 4354.
54.
ChiXWangSHuangY, et al.Roles of Rho GTPases in intracellular transport and cellular transformation. Int J Mol Sci2013; 14: 7089.
55.
SuazoKFJeongAAhmadiM, et al.Metabolic labeling with an alkyne probe reveals similarities and differences in the prenylomes of several brain-derived cell lines and primary cells. Sci Rep2021; 11: 4367.
56.
TaylorJSReidTSTerryKL, et al.Structure of mammalian protein geranylgeranyltransferase type-I. EMBO J2003; 22: 5963.
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
