A Recycling Pathway for Resecretion of Internalized Apolipoprotein E in Liver Cells

We have investigated the recycling of apoE in livers of apoE−/− mice transplanted with wild type bone marrow (apoE+/+ → apoE−/−), a model in which circulating apoE is derived exclusively from macrophages. Nascent Golgi lipoproteins were recovered from livers of apoE+/+ → apoE−/− mice 8 weeks after transplantation. ApoE was identified with nascent d < 1.006 and withd 1.006–1.210 g/ml lipoproteins at a level ∼6% that of nascent lipoproteins from C57BL/6 mice. Hepatocytes from apoE+/+ → apoE−/− mice were isolated and cultured in media free of exogenous apoE. ApoE was found in the media primarily on the d < 1.006 g/ml fraction, indicating a resecretion of internalized apoprotein. Secretion of apoE from C57BL/6 hepatocytes was consistent with constitutive production, whereas the majority of apoE secreted from apoE+/+ → apoE−/− hepatocytes was recovered in the last 24 h of culture. This suggests that release may be triggered by accumulation of an acceptor, such as very low density lipoproteins, in the media. In agreement with the in vivo data, total recovery of apoE from apoE+/+ → apoE−/− hepatocytes was ∼6% that of the apoE recovered from C57BL/6 hepatocytes. Since plasma apoE levels in the transplanted mice are ∼10% of control levels, the findings indicate that up to 60% of the internalized apoE may be reutilized under physiologic conditions. These studies provide definitive evidence for the sparing of apoE and its routing through the secretory pathway and demonstrate that internalized apoE can be resecreted in a quantitatively significant fashion. We have investigated the recycling of apoE in livers of apoE−/− mice transplanted with wild type bone marrow (apoE+/+ → apoE−/−), a model in which circulating apoE is derived exclusively from macrophages. Nascent Golgi lipoproteins were recovered from livers of apoE+/+ → apoE−/− mice 8 weeks after transplantation. ApoE was identified with nascent d < 1.006 and withd 1.006–1.210 g/ml lipoproteins at a level ∼6% that of nascent lipoproteins from C57BL/6 mice. Hepatocytes from apoE+/+ → apoE−/− mice were isolated and cultured in media free of exogenous apoE. ApoE was found in the media primarily on the d < 1.006 g/ml fraction, indicating a resecretion of internalized apoprotein. Secretion of apoE from C57BL/6 hepatocytes was consistent with constitutive production, whereas the majority of apoE secreted from apoE+/+ → apoE−/− hepatocytes was recovered in the last 24 h of culture. This suggests that release may be triggered by accumulation of an acceptor, such as very low density lipoproteins, in the media. In agreement with the in vivo data, total recovery of apoE from apoE+/+ → apoE−/− hepatocytes was ∼6% that of the apoE recovered from C57BL/6 hepatocytes. Since plasma apoE levels in the transplanted mice are ∼10% of control levels, the findings indicate that up to 60% of the internalized apoE may be reutilized under physiologic conditions. These studies provide definitive evidence for the sparing of apoE and its routing through the secretory pathway and demonstrate that internalized apoE can be resecreted in a quantitatively significant fashion. apolipoprotein low density lipoprotein very LDL bone marrow transplantation 4-morpholinepropanesulfonic acid polyacrylamide gel electrophoresis 2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)propane-1,3-diol Apolipoprotein E (apoE)1is unique among the plasma lipoprotein apoproteins because of its many different functions in the metabolism of lipids and lipoproteins. Its role as a ligand for the receptor-mediated endocytosis of lipoproteins is well established (1Beisiegel U. Weber W. Ihrke G. Herz J. Stanley K.K. Nature. 1989; 341: 162-164Crossref PubMed Scopus (594) Google Scholar, 2Innerarity T.L. Friedlander E.J. Rall Jr., S.C. Weisgraber K.H. Mahley R.W. J. Biol. Chem. 1983; 258: 12341-12347Abstract Full Text PDF PubMed Google Scholar, 3Pitas R.E. Innerarity T.L. Arnold K.S. Mahley R.W. Proc. Natl. Acad. Sci. U. S. A. 1979; 76: 2311-2315Crossref PubMed Scopus (134) Google Scholar). Additionally, apoE interacts with lipoprotein lipase and hepatic lipase to modulate triglyceride hydrolysis (4Rensen P.C.N. van Berkel T.J.C. J. Biol. Chem. 1996; 271: 14791-14799Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar, 5Jong M.C. Dahlmans V.E.H. van Gorp P.J.J. Breuer M.L. Mol M.J.T.M. van der Zee A. Frants R.R. Hofker M.H. Havekes L.M. Arterioscler. Thromb. Vasc. Biol. 1996; 16: 934-940Crossref PubMed Scopus (53) Google Scholar). Even within the cell, apoE is known to serve biologically relevant roles. Studies suggest that apoE directs the intracellular routing of internalized remnant lipoproteins, with smaller β-migrating very low density lipoproteins (VLDL) particles routed to the perinuclear region of the mouse macrophage in a fashion similar to low density lipoproteins (LDL), whereas larger β-VLDL remain closer to the plasma membrane (6Tabas I. Myers J.N. Innerarity T.L. Xu X.-X. Arnold K. Boyles J. Maxfield F.R. J. Cell Biol. 1991; 115: 1547-1560Crossref PubMed Scopus (64) Google Scholar, 7Tabas I. Lim S. Xu X.-X. Maxfield F.R. J. Cell Biol. 1990; 111: 929-940Crossref PubMed Scopus (104) Google Scholar). Schwiegelshohn et al. (8Schwiegelshohn B. Presley J.F. Gorecki M. Vogel T. Carpentier Y.A. Maxfield F.R. Deckelbaum R.J. J. Biol. Chem. 1995; 270: 1761-1769Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar) report that apoE modulates intracellular lipid metabolism, in particular the hydrolysis and utilization of triglyceride. ApoE is also linked to and may be a regulator of cholesterol efflux from macrophages (9Kinoshita M. Kawamura M. Maeda T. Fujimaki Y. Fujita M. Kojima K. Teramoto T. J. Atheroscler. Thromb. 2000; 6: 22-27Crossref PubMed Scopus (12) Google Scholar, 10Langer C. Huang Y. Cullen P. Wiesenhutter B. Mahley R.W. Assmann G. von Eckardstein A. J. Mol. Med. 2000; 78: 217-227Crossref PubMed Scopus (62) Google Scholar, 11Lin C.-Y. Duan H. Mazzone T. J. Lipid Res. 1999; 40: 1618-1626Abstract Full Text Full Text PDF PubMed Google Scholar), an effect with significant repercussions on vascular health and the process of atherogenesis. Finally, increasing evidence points to a role for apoE in hepatic lipoprotein assembly and the incorporation of triglycerides into newly forming VLDL (12Huang Y. Ji Z.-S. Brecht W.J. Rall Jr., S.C. Taylor J.M. Mahley R.W. Arterioscler. Thromb. Vasc. Biol. 1999; 19: 2952-2959Crossref PubMed Scopus (78) Google Scholar, 13Kuipers F. Jong M.C. Lin Y. van Eck M. Havinga R. Blocks V. Verkade H.J. Hofker M.H. Moshage H. van Berkel T.J.C. Vonk R.J. Havekes L.M. J. Clin. Invest. 1997; 100: 2915-2922Crossref PubMed Scopus (150) Google Scholar, 14Mensenkamp A.R. Jong M.C. van Goor H. van Luyn M.J.A. Blocks V. Havinga R. Voshol P.J. Hofker M.H. van Dijk K.W. Havekes L.M. Kuipers F. J. Biol. Chem. 1999; 274: 35711-35718Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar). Due to its critical role in a number of biological processes within the cell, apoE may follow unique pathways of secretion and internalization that maximize its impact on cellular functions. Wong (15Wong L. J. Cell. Physiol. 1989; 141: 441-452Crossref PubMed Scopus (11) Google Scholar) was among the first to suggest that apoE may be recirculated. He reported that 62–66% of the intrahepatic apoE, compared with 7–10% of the intrahepatic apoB, was derived from plasma. This suggested that internalized apoE may not undergo complete degradation and may therefore follow a unique intracellular routing pathway. We previously reported that a portion of the apoE component of internalized lipoproteins is spared degradation and routed through the Golgi apparatus (16Fazio S. Linton M.F. Hasty A.H. Swift L.L. J. Biol. Chem. 1999; 274: 8247-8253Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar). After injection of radioiodinated moused < 1.019 g/ml lipoproteins into C57BL/6 mice, radioactivity found in the Golgi apparatus-rich fractions from livers of the recipient mice was almost exclusively due to apoE, although the injected lipoproteins had less than 10% of their label associated with apoE. The ratio of apoE/apoB48 in the Golgi fraction increased 10-fold relative to serum, and only traces of apoB100 were detected. Furthermore, the apoE recovered in the Golgi fraction was part of ad 1.019–1.210 g/ml complex, indicating an association of recycled apoE with newly formed lipoproteins. Quantitatively, similar results were obtained when labeled VLDL was injected into mice deficient in either apoE or the LDL receptor, indicating that the phenomenon of apoE recycling is not influenced by the production of endogenous apoE and is not dependent on the presence of LDL receptors. Although our studies clearly demonstrated the presence of a mechanismin vivo by which apoE escapes degradation, the appearance of internalized apoE within the liver Golgi may have been influenced in part by the bolus delivery of apoE in this model. To address this issue and to explore hepatic apoE recycling in the steady state, we have completed experiments utilizing an in vivo model based on bone marrow transplantation. Reconstitution of lethally irradiated apoE−/− mice with wild type bone marrow results in a mouse model in which all apoE present in the mouse is derived from macrophages. Our laboratory (17Linton M.F. Atkinson J.B. Fazio S. Science. 1995; 267: 1034-1037Crossref PubMed Scopus (417) Google Scholar) has shown that within 3 weeks of the introduction of normal macrophages into the apoE−/− mouse, serum apoE levels reach 10% of normal, resulting in complete normalization of plasma cholesterol levels by virtue of an active hepatic clearance of remnant lipoproteins. Since hepatocytes in this model do not produce endogenous apoE but internalize apoE on remnant lipoproteins, this approach provides an excellent model for investigating the routing of internalized apoE through the secretory pathway via the Golgi apparatus in the of apoE. The studies reported in this demonstrate clearly that internalized apoE a unique routing through the secretory pathway and is mice on the C57BL/6 were obtained from The of mice is established in our mice were on a and were a normal and were ad were in with with from the of was as previously (17Linton M.F. Atkinson J.B. Fazio S. Science. 1995; 267: 1034-1037Crossref PubMed Scopus (417) Google Scholar). and weeks after and were to the marrow was from mice by with media serum and mice were lethally irradiated and h bone marrow in were transplanted by were for studies from to weeks after transplantation. Golgi apparatus-rich fractions were as previously L.L. K. C. C. J. Lipid Res. Full Text Full Text PDF PubMed Google Scholar). Golgi fractions were isolated from mice liver we are to of Golgi from of Nascent lipoproteins were from the Golgi apparatus Y. S. J. Cell Biol. PubMed Scopus Google Scholar) and lipoprotein isolated by as Hepatocytes were isolated from mouse livers as by et al. H. J. Clin. Invest. 1999; PubMed Scopus Google Scholar). The mice were a and a was The was with a and the liver was with and at a of 3 for The was to liver and was for The liver was from the in media in a with and at for The were by by through The liver and were with of low serum and of and of The were by for at The media was total and media was to The were and was by The of hepatocytes from 3 to of and was than The were mouse at a density of in of the The media the and not serum to introduction of exogenous apoE into the was at and h after and or were by were recovered at the of the in and were from the media the was in of normal and was to of media. The were for and the lipoproteins were In our laboratory this has been shown to of the apoE in media and of apoE in isolated lipoprotein fractions not Furthermore, apoE is from and lipoproteins with The were with the and on as lipoproteins were recovered by the with for h at Y. S. J. Cell Biol. PubMed Scopus Google Scholar). The and were by a and The was normal and lipoproteins were as were isolated from Golgi and media by the Golgi lipoprotein < 1.006 g/ml and d 1.006–1.210 were isolated as previously a L.L. K. C. C. J. Lipid Res. Full Text Full Text PDF PubMed Google Scholar). from the media were recovered the The d < 1.006 g/ml lipoproteins were isolated in h at and recovered The density of the was to g/ml and 1.006–1.210 g/ml fraction was isolated in h at and recovered by The fractions were and of the apoproteins by gel hepatocytes were isolated and cultured for h in low serum as media was and the were for with in The media was and the were with and for and h in the media. ApoE was from the media an and as previously L.L. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Google Scholar). The were and by as The were with acid and to a for up to ApoE was with were a with The were in and were the The were to the with 10% The were in with and with were VLDL triglyceride production was were with and injected via the with of was in normal at a of studies in our laboratory demonstrated a in VLDL triglyceride a this of evidence that plasma VLDL clearance is under conditions. were from the injection and and h after triglycerides were to of the were by triglyceride production were from the and as of triglyceride the plasma to be of the Scholar). mice were transplanted with bone marrow from C57BL/6 mice (apoE+/+ → apoE−/−), and 8 weeks hepatic Golgi apparatus-rich fractions were studies in our laboratory that the Golgi fractions are in with from of the L.L. K. C. C. J. Lipid Res. Full Text Full Text PDF PubMed Google Scholar). Reconstitution of apoE−/− mice with marrow from C57BL/6 mice to the appearance of apoE on plasma lipoproteins, clearance of lipoprotein and normalization of plasma cholesterol (17Linton M.F. Atkinson J.B. Fazio S. Science. 1995; 267: 1034-1037Crossref PubMed Scopus (417) Google Scholar). In C57BL/6 mice, apoE was in < d g/ml fractions and the relative of apoE among the fractions as by was and ApoE was also found in the nascent Golgi lipoproteins from the apoE+/+ → apoE−/− mice with a that was very similar to that of control C57BL/6 in the d < 1.006 and in the g/ml apoE was in g/ml fraction, the of total apoE recovered with the Golgi The apoE on nascent hepatic Golgi lipoproteins from apoE+/+ → apoE−/− to the of was ∼6% that found with Golgi lipoproteins from control To the apoE that was internalized was hepatocytes were isolated from C57BL/6 mice and apoE+/+ → apoE−/− mice. a of the cultured hepatocytes from C57BL/6 mice with and The were also for the presence of the Cell from from different less than of the with 3 the results of experiments in which the media from the first points and were and lipoproteins were can be apoE is clearly present in the media from the apoE+/+ → apoE−/− mice. This suggests that apoE, internalized in is routed to the secretory pathway and is resecreted from the hepatocytes in of apoE from hepatocytes from apoE+/+ → apoE mice. mice were transplanted with bone marrow from C57BL/6 mice, and weeks hepatocytes were isolated as under Hepatocytes from C57BL/6 mice as from the and h points was and lipoproteins were were by to and for The of appearance of apoE in the media of the hepatocytes from C57BL/6 mice and apoE+/+ → apoE−/− mice is shown in A. ApoE was present in the media from the C57BL/6 hepatocytes at The of apoE to the in culture. In apoE was found in the at the of the ApoE was also in the media of the hepatocytes from apoE+/+ → apoE−/− mice. the apoE was but at the points to be a release of the apoprotein. was to apoE in the from the apoE+/+ → apoE−/− mice at the of the Furthermore, the after the with evidence of In C57BL/6 ∼10% of the total apoE was secreted in the first h with secreted in the h and secreted in the last 24 h This suggests a production of apoE the In in hepatocytes from the apoE−/− mice transplanted with C57BL/6 only of the total secreted apoE was recovered in the media after whereas in the and was recovered in the 24 h of In experiments the total apoE secreted from the hepatocytes the was of the apoE secreted from C57BL/6 hepatocytes the The secretion of apoE from hepatocytes from C57BL/6 mice and apoE+/+ → apoE−/− mice is shown in apoE was in the media from C57BL/6 hepatocytes but was not in the from apoE+/+ → apoE−/− mice at of the the recycling of apoE was at all points not These results demonstrate clearly that apoE in the media of hepatocytes from apoE+/+ → apoE−/− mice not from but apoE internalized in vivo and resecreted in culture. In the media from C57BL/6 apoE was the d < 1.006 and d 1.006–1.210 g/ml whereas in the hepatocytes from apoE+/+ → apoE−/− mice, of the apoE was found with the d < 1.006 g/ml fraction This may the of apoE for lipoproteins in the media that are but may also suggest that lipoproteins in the media apoE release from the or that recycling apoE assembly of lipoproteins, a that was investigated in the of triglyceride production the were in apoE−/− mice, apoE+/+ → apoE−/− mice, and apoE−/− mice transplanted with apoE−/− The production for all were the with of for the has been shown previously F. Jong M.C. Lin Y. van Eck M. Havinga R. Blocks V. Verkade H.J. Hofker M.H. Moshage H. van Berkel T.J.C. Vonk R.J. Havekes L.M. J. Clin. Invest. 1997; 100: 2915-2922Crossref PubMed Scopus (150) Google A.R. Jong M.C. van Goor H. van Luyn M.J.A. Blocks V. Havinga R. Voshol P.J. Hofker M.H. van Dijk K.W. Havekes L.M. Kuipers F. J. Biol. Chem. 1999; 274: 35711-35718Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar), hepatic triglyceride production in apoE−/− mice were that found in C57BL/6 mice triglyceride production in mice transplanted with marrow from either apoE+/+ or apoE−/− mice were similar and not different from the found in apoE−/− mice, that effect of recycling apoE on triglyceride production is not of the to a in lipoprotein The present the recycling of apoE in the livers of apoE−/− mice transplanted with wild type bone In this model all of the apoE from and plasma apoE levels are at steady state, with the production of apoE by macrophages and its internalization and resecretion by the liver at apoE in the secretory pathway in the liver or recovered in the media of hepatocytes isolated from mice is derived from internalized apoE. the model we have demonstrated the presence of apoE within nascent hepatic Golgi lipoproteins, evidence that at a portion of internalized apoE is routed to the secretory pathway. studies hepatocytes from the apoE+/+ → apoE−/− mice not only the routing of internalized apoE to the secretory pathway but also demonstrated the resecretion of internalized apoE. These results with our in vivo studies (16Fazio S. Linton M.F. Hasty A.H. Swift L.L. J. Biol. Chem. 1999; 274: 8247-8253Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar) provide for the that a portion of apoE that is internalized with lipoproteins is not but is in The physiologic of the and recycling of apoE is Our studies that introduction of apoE via not hepatic triglyceride production but the of an effect may of intracellular recycling apoE. the role of recycling apoE may be linked to that are from or than the secretion of lipoproteins. Our of apoE with nascent lipoproteins in Golgi apparatus-rich fractions from apoE+/+ → apoE−/− mice in the present provides definitive evidence for the routing of internalized apoE through the secretory pathway under physiologic conditions. The of apoE within the Golgi fractions was not due to of the with of the as studies in our laboratory have established the of the hepatic Golgi fractions by this L.L. K. C. C. J. Lipid Res. Full Text Full Text PDF PubMed Google Scholar). of our fractions with Golgi from a of apoE, is not to a role of in liver is less than at 8 weeks and only of total macrophages after transplantation 1997; PubMed Google Scholar). In is that Golgi apparatus with Golgi as do not produce lipoproteins that to the of the P. J. Cell Biol. PubMed Scopus Google Scholar). the appearance of apoE in the hepatic Golgi fractions of the apoE+/+ → apoE−/− mice routing of internalized apoE through the secretory pathway. The resecretion of apoE from of hepatocytes from apoE+/+ → apoE−/− mice evidence for apoE In to the constitutive of secretion of apoE from hepatocytes from C57BL/6 mice, the majority of apoE recovered in the media of hepatocytes from apoE+/+ → apoE−/− mice was in the last 24 h This release was not by as the from control and transplanted after the et al. P.C.N. Jong M.C. van van der H. van Berkel T.J.C. Havekes L.M. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar), the of apoE from report that the presence of density lipoproteins or lipid in the media in a increased of secretion of compared with media with et al. J. Weber W. U. J. Cell Sci. 1999; PubMed Google Scholar) also report that density lipoprotein to serve as an for the resecretion of apoE from Although in our experiments the media not an exogenous to the release of apoE, the hepatocytes do VLDL which may serve as for and of apoE release from hepatocytes. of only the may be to the release of apoE. In this is to that apoE recovered in the media is found with the d < 1.006 g/ml lipoproteins Although in our may to the apoE recovered in the our suggest that their is to an established for that less than of the in is of macrophage et al. L.M. J. Lipid Res. 1989; Full Text PDF PubMed Google Scholar) report that in liver for less than of the total liver apoE and that the level of apoE in was that of hepatocytes. The total recovery of apoE in the media of the hepatocytes from apoE+/+ → apoE−/− mice is of apoE recovered in the media from C57BL/6 hepatocytes. the secretion of apoE is to the apoE of the and the number of in our for the of apoE found in the media. In the of appearance of apoE in the media is not consistent with be for a secreted as in the secretion of apoE from C57BL/6 and as the of liver in mice after is less than of total macrophages 8 weeks after transplantation 1997; PubMed Google Scholar). and newly apoE not be in from apoE+/+ → apoE−/− mice based on the of apoE found in the the number of identified as the secretion the of of liver and the of newly apoE in from apoE+/+ → apoE−/− mice, we that the apoE recovered in the media not from but recycled apoE. The of apoE with nascent hepatic Golgi VLDL from apoE+/+ → apoE−/− mice was ∼6% that found with control Golgi and the of apoE from hepatocytes from apoE+/+ → apoE−/− mice was ∼6% that of apoE secreted by hepatocytes from C57BL/6 mice. Since serum apoE levels in the apoE+/+ → apoE−/− mice are ∼10% of control levels (17Linton M.F. Atkinson J.B. Fazio S. Science. 1995; 267: 1034-1037Crossref PubMed Scopus (417) Google Scholar), the results suggest that as as 60% of the internalized apoE is normal when the is with apoE, the of apoE that is recycled may et al. J. Weber W. U. J. Cell Sci. 1999; PubMed Google Scholar) lipoproteins with and and demonstrated that of the labeled internalized by the was into the after a The apoproteins were primarily apoE and et al. P.C.N. Jong M.C. van van der H. van Berkel T.J.C. Havekes L.M. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar) also report that as as of the apoE up on by was Finally, and Y. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar) that as as of apoE internalized by the macrophage was that the process of apoE sparing and may be among different but is not to the liver and is quantitatively The physiologic of apoE and resecretion is may provide a the impact of apoE on intracellular and functions can be evidence points to a critical role for apoE in VLDL VLDL triglyceride production is by in the apoE−/− mice compared with C57BL/6 mice F. Jong M.C. Lin Y. van Eck M. Havinga R. Blocks V. Verkade H.J. Hofker M.H. Moshage H. van Berkel T.J.C. Vonk R.J. Havekes L.M. J. Clin. Invest. 1997; 100: 2915-2922Crossref PubMed Scopus (150) Google Scholar, 14Mensenkamp A.R. Jong M.C. van Goor H. van Luyn M.J.A. Blocks V. Havinga R. Voshol P.J. Hofker M.H. van Dijk K.W. Havekes L.M. Kuipers F. J. Biol. Chem. 1999; 274: 35711-35718Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar), and the of apoE via with the apoE hepatic VLDL triglyceride production K. C. J.M. J. Lipid Res. 2000; Full Text Full Text PDF PubMed Google Scholar). Our studies that hepatic triglyceride production are in apoE−/− mice compared with C57BL/6 mice introduction of apoE via not this that apoE is routed to a in the secretory pathway to VLDL assembly or triglyceride introduction of apoE via an that only 10% of the total serum apoE, may not provide intracellular of apoE to hepatic triglyceride production and VLDL Finally, is that recycling apoE may have such as increasing remnant through the Z.-S. Fazio S. Mahley R.W. J. Biol. Chem. Full Text PDF PubMed Google Scholar, M.F. Hasty A.H. Fazio S. J. Clin. Invest. PubMed Scopus Google Scholar, H. Y. J. Kawamura M. K. M. T. K. Y. J. Clin. Invest. PubMed Scopus Google Scholar). In apoE internalized by the liver as a component of lipoprotein particles escapes the is routed to the Golgi and is secreted in quantitatively significant studies are to the of this newly cellular