Microsomal triglyceride transfer protein (MTP) is an intraluminal protein in the endoplasmic reticulum (ER) that is essential for the assembly of apolipoprotein B (apoB)-containing lipoproteins. In this study, we examine how the livers of mice respond to two distinct methods of blocking MTP function: Cre-mediated disruption of the gene for MTP and chemical inhibition of MTP activity. Blocking MTP significantly reduced plasma levels of triglycerides, cholesterol, and apoB-containing lipoproteins in both wild-type C57BL/6 and LDL receptor-deficient mice. While treating LDL receptor-deficient mice with an MTP inhibitor for 7 days lowered plasma lipids to control levels, liver triglyceride levels were increased by only 4-fold. Plasma levels of apoB-100 and apoB-48 fell by >90% and 65%, respectively, but neither apoB isoform accumulated in hepatic microsomes. Surprisingly, loss of MTP expression was associated with a nearly complete absence of apoB-100 in hepatic microsomes. Levels of microsomal luminal chaperone proteins [e.g., protein disulfide isomerase, glucose-regulated protein 78 (GRP78), and GRP94] and cytosolic heat shock proteins (HSPs) (e.g., HSP60, HSC, HSP70, and HSP90) were unaffected by MTP inhibition. These findings show that the liver responds rapidly to inhibition of MTP by degrading apoB and preventing its accumulation in the ER.The rapid degradation of secretion-incompetent apoB in the ER may block the induction of proteins associated with unfolded protein and heat shock responses. Microsomal triglyceride transfer protein (MTP) is an intraluminal protein in the endoplasmic reticulum (ER) that is essential for the assembly of apolipoprotein B (apoB)-containing lipoproteins. In this study, we examine how the livers of mice respond to two distinct methods of blocking MTP function: Cre-mediated disruption of the gene for MTP and chemical inhibition of MTP activity. Blocking MTP significantly reduced plasma levels of triglycerides, cholesterol, and apoB-containing lipoproteins in both wild-type C57BL/6 and LDL receptor-deficient mice. While treating LDL receptor-deficient mice with an MTP inhibitor for 7 days lowered plasma lipids to control levels, liver triglyceride levels were increased by only 4-fold. Plasma levels of apoB-100 and apoB-48 fell by >90% and 65%, respectively, but neither apoB isoform accumulated in hepatic microsomes. Surprisingly, loss of MTP expression was associated with a nearly complete absence of apoB-100 in hepatic microsomes. Levels of microsomal luminal chaperone proteins [e.g., protein disulfide isomerase, glucose-regulated protein 78 (GRP78), and GRP94] and cytosolic heat shock proteins (HSPs) (e.g., HSP60, HSC, HSP70, and HSP90) were unaffected by MTP inhibition. These findings show that the liver responds rapidly to inhibition of MTP by degrading apoB and preventing its accumulation in the ER. The rapid degradation of secretion-incompetent apoB in the ER may block the induction of proteins associated with unfolded protein and heat shock responses. VLDLs produced by the liver are the major source of LDLs in the plasma, which are causally related to the development of atherosclerotic cardiovascular disease (1MRC/BHF Heart Protection Study GroupMRC/BHF Heart Protection Study of cholesterol lowering with simvastatin in 20,536 high-risk individuals: a randomised placebo-controlled trial.Lancet. 2002; 360: 7-22Google Scholar). The importance of the hepatic secretion of apolipoprotein B (apoB) in cardiovascular disease was recognized in early studies of abetalipoproteinemic patients, who lack the ability to secrete apoB-containing lipoproteins (2Kayden H.J. Abetalipoproteinemia.Annu. Rev. Med. 1972; 23: 285-296Google Scholar) and are markedly resistant to cardiovascular disease (3Kayden H.J. Traber M.G. Clinical, nutritional and biochemical consequences of apolipoprotein B deficiency.Adv. Exp. Med. Biol. 1986; 201: 67-81Google Scholar). Subsequent studies showed that specific mutations in the microsomal triglyceride transfer protein (MTP) gene are responsible for abetalipoproteinemia (4Wetterau J.R. Aggerbeck L.P. Bouma M.-E. Eisenberg C. Munck A. Hermier M. Schmitz J. Gay G. Rader D. Gregg R.E. Absence of microsomal triglyceride transfer protein in individuals with abetalipoproteinemia.Science. 1992; 258: 999-1001Google Scholar, 5Gregg R.E. Wetterau J.R. The molecular basis of abetalipoproteineimia.Curr. Opin. Lipidol. 1994; 5: 81-86Google Scholar). MTP exists in a functional complex with protein disulfide isomerase (PDI) (6Wetterau J.R. Zilversmit D.B. Purification and characterization of microsomal triglyceride and cholesteryl ester transfer protein from bovine liver microsomes.Chem. Phys. Lipids. 1985; 38: 205-222Google Scholar, 7Wetterau J.R. Combs K.A. Spinner S.N. Joiner B.J. Protein disulfide isomerase is a component of the microsomal triglyceride transfer protein complex.J. Biol. Chem. 1990; 265: 9801-9807Google Scholar). The loss of MTP function blocks the secretion of apoB-containing lipoproteins from both the liver and the intestine (5Gregg R.E. Wetterau J.R. The molecular basis of abetalipoproteineimia.Curr. Opin. Lipidol. 1994; 5: 81-86Google Scholar). Apart from neuropathy, which can be prevented by vitamin E supplements (8Iannaccone S.T. Sokol R.J. Vitamin E deficiency in neuropathy of abetalipoproteinemia.Neurology. 1986; 361009Google Scholar) and moderate steatosis in enterocytes and hepatocytes, abetalipoproteinemia is not usually associated with liver failure or cirrhosis (3Kayden H.J. Traber M.G. Clinical, nutritional and biochemical consequences of apolipoprotein B deficiency.Adv. Exp. Med. Biol. 1986; 201: 67-81Google Scholar). The absence of severe symptoms has suggested that inactivation of MTP might be a useful strategy for combating hyperlipidemia and cardiovascular disease. Several chemical inhibitors of the lipid transfer activity of MTP have been developed (9Jamil H. Gordon D.A. Eustice D.C. Brooks C.M. Dickson J.J. Chen Y. Ricci B. Chu C.H. Harrity T.W. Ciosek C.J. Biller S.A. Gregg R.E. Wetterau J.R. An inhibitor of the microsomal triglyceride transfer protein inhibits apoB secretion from HepG2 cells.Proc. Natl. Acad. Sci. USA. 1996; 93: 11991-11995Google Scholar, 10Bakillah A. Nayak N. Saxena U. Medford R.M. Hussain M.M. Decreased secretion of ApoB follows inhibition of ApoB-MTP binding by a novel antagonist.Biochemistry. 2000; 39: 4892-4899Google Scholar, 11Ksander G.M. deJesus R. Yuan A. Fink C. Moskal M. Carlson E. Kukkola P. Bilci N. Wallace E. Neubert A. Feldman D. Mogelesky T. Poirier K. Jeune M. Steele R. Wasvery J. Stephan Z. Cahill E. Webb R. Navarrete A. Lee W. Gibson J. Alexander N. Sharif H. Hospattankar A. Diaminoindanes as microsomal triglyceride transfer protein inhibitors.J. Med. Chem. 2001; 44: 4677-4687Google Scholar, 12Chang G. Ruggeri R.B. Harwood Jr., H.J. Microsomal triglyceride transfer protein (MTP) inhibitors: discovery of clinically active inhibitors using high-throughput screening and parallel synthesis paradigms.Curr. Opin. Drug Discov. Devel. 2002; 5: 562-570Google Scholar). Many of these inhibitors lower plasma lipid levels in animal models (11Ksander G.M. deJesus R. Yuan A. Fink C. Moskal M. Carlson E. Kukkola P. Bilci N. Wallace E. Neubert A. Feldman D. Mogelesky T. Poirier K. Jeune M. Steele R. Wasvery J. Stephan Z. Cahill E. Webb R. Navarrete A. Lee W. Gibson J. Alexander N. Sharif H. Hospattankar A. Diaminoindanes as microsomal triglyceride transfer protein inhibitors.J. Med. Chem. 2001; 44: 4677-4687Google Scholar, 12Chang G. Ruggeri R.B. Harwood Jr., H.J. Microsomal triglyceride transfer protein (MTP) inhibitors: discovery of clinically active inhibitors using high-throughput screening and parallel synthesis paradigms.Curr. Opin. Drug Discov. Devel. 2002; 5: 562-570Google Scholar, 13Wetterau J.R. Gregg R.E. Harrity T.W. Arbeeny C. Cap M. Connolly F. Chu C.H. George R.J. Gordon D.A. Jamil H. Jolibois K.G. Kunselman L.K. Lan S.J. Maccagnan T.J. Ricci B. Yan M. Young D. Chen Y. Fryszman O.M. Logan J.V. Musial C.L. Poss M.A. Robl J.A. Simpkins L.M. Slusarchyk W.A. Sulsky R. Taunk P. Magnin D.R. Tino J.A. Lawrence R.M. Dickson J. Biller S.A. An MTP inhibitor that normalizes atherogenic lipoprotein levels in WHHL rabbits.Science. 1998; 282: 751-754Google Scholar). Especially encouraging results were obtained in Watanabe-heritable hyperlipidemic rabbits, a model of homozygous familial hypercholesterolemia (13Wetterau J.R. Gregg R.E. Harrity T.W. Arbeeny C. Cap M. Connolly F. Chu C.H. George R.J. Gordon D.A. Jamil H. Jolibois K.G. Kunselman L.K. Lan S.J. Maccagnan T.J. Ricci B. Yan M. Young D. Chen Y. Fryszman O.M. Logan J.V. Musial C.L. Poss M.A. Robl J.A. Simpkins L.M. Slusarchyk W.A. Sulsky R. Taunk P. Magnin D.R. Tino J.A. Lawrence R.M. Dickson J. Biller S.A. An MTP inhibitor that normalizes atherogenic lipoprotein levels in WHHL rabbits.Science. 1998; 282: 751-754Google Scholar). Administration of an MTP inhibitor to Watanabe-heritable hyperlipidemic rabbits reduced plasma lipid and lipoprotein levels to normal (13Wetterau J.R. Gregg R.E. Harrity T.W. Arbeeny C. Cap M. Connolly F. Chu C.H. George R.J. Gordon D.A. Jamil H. Jolibois K.G. Kunselman L.K. Lan S.J. Maccagnan T.J. Ricci B. Yan M. Young D. Chen Y. Fryszman O.M. Logan J.V. Musial C.L. Poss M.A. Robl J.A. Simpkins L.M. Slusarchyk W.A. Sulsky R. Taunk P. Magnin D.R. Tino J.A. Lawrence R.M. Dickson J. Biller S.A. An MTP inhibitor that normalizes atherogenic lipoprotein levels in WHHL rabbits.Science. 1998; 282: 751-754Google Scholar). Since many homozygous familial hypercholesterolemias are resistant to statin therapies (14Uauy R. Vega G.L. Grundy S.M. Bilheimer D.M. Lovastatin therapy in receptor-negative homozygous familial hypercholesterolemia: lack of effect on low-density lipoprotein concentrations or turnover.J. Pediatr. 1988; 113: 387-392Google Scholar), MTP inhibitors might provide a more attractive treatment to liver transplantation, which effectively reduces atherosclerosis in these patients (15Bilheimer D.W. Goldstein J.L. Grundy S.M. Starzl T.E. Brown M.S. Liver transplantation to provide low-density-lipoprotein receptors and lower plasma cholesterol in a child with homozygous familial hypercholesterolemia.N. Engl. J. Med. 1984; 311: 1658-1664Google Scholar). MTP inhibitor drugs have provided the opportunity to examine the processes regulating the assembly, secretion, and degradation of apoB-containing lipoproteins. Studies of cultured cells suggest that the cotranslational translocation of apoB into the lumen of the endoplasmic reticulum (ER) governs the fate of newly synthesized apoB [reviewed in refs. (16Yao Z. Tran K. McLeod R.S. Intracellular degradation of newly synthesized apolipoprotein B.J. Lipid Res. 1997; 38: 1937-1953Google Scholar, 17Davis R.A. Cell and molecular biology of the assembly and secretion of apolipoprotein B-containing lipoproteins by the liver.Biochim. Biophys. Acta. 1999; 1440: 1-31Google Scholar, 18Olofsson S.O. Asp L. Boren J. The assembly and secretion of apolipoprotein B-containing lipoproteins.Curr. Opin. Lipidol. 1999; 10: 341-346Google Scholar, 19Davidson N.O. Shelness G.S. Apolipoprotein B: mRNA editing, lipoprotein assembly, and presecretory degradation.Annu. Rev. Nutr. 2000; 20: Scholar, in the the assembly and secretion of apolipoprotein B-containing Biol. Chem. 2002; proteins by the apoB-100 be into the ER lumen MTP E. J. P. R.A. secretion of the of apolipoprotein B: characterization of a translocation Biol. Chem. 1994; Scholar, M. M.M. M.A. C.H. J. Young of the of microsomal triglyceride transfer protein in the liver of 1999; Scholar, W. L. M. D. L. inactivation of the abetalipoproteinemia gene lipoprotein in a Biol. Chem. 1999; Scholar). MTP to both the and of apoB translocation H.J. Sokol R. L.K. R.A. of apolipoprotein B the endoplasmic reticulum is in Lipid Res. 1996; Scholar, F. degradation of apolipoprotein by the is prevented by microsomal triglyceride transfer studies on HepG2 cells with an inhibitor of microsomal triglyceride transfer Biol. Chem. 1997; Scholar, L. The and of isomerase in apolipoprotein B Biol. Chem. 1997; Scholar, M.M. A. Jamil H. Apolipoprotein B binding to microsomal triglyceride transfer protein with in and in lipoprotein 1997; Scholar, H. M. H. P. H. to and lipid of apolipoprotein B are by the of Biol. Chem. 1998; Scholar, P. K. Gordon D. S.O. The microsomal triglyceride transfer protein the assembly of apolipoprotein lipoprotein in Biol. Chem. 1998; Scholar, D.M. M. R. H. has a with the which its and translocation from on the microsomal triglyceride transfer protein to Natl. Acad. Sci. USA. 1998; Scholar, E. F. McLeod R. Z. J. of in apolipoprotein that a for the microsomal triglyceride transfer Biol. Chem. 1999; Scholar, A. Microsomal transfer protein is for of not associated with as as for ApoB Biol. Chem. 2002; Scholar). In the absence of apoB translocation is in the rapid cotranslational degradation of the of apoB R.A. Apolipoprotein B is both into and the endoplasmic reticulum for two distinct Biol. Chem. 1990; 265: Scholar) the S.J. Chen L. degradation of apolipoprotein 1996; Scholar, M. D.M. H. The degradation of apolipoprotein is by the and heat shock protein Biol. Chem. 1997; Scholar, J. The of apolipoprotein B not translocation from the endoplasmic reticulum to the degradation of apolipoprotein the of the apolipoprotein is in its Biol. Chem. 2000; Scholar). of the of apoB is from the ER the and can be or E. J. P. R.A. secretion of the of apolipoprotein B: characterization of a translocation Biol. Chem. 1994; Scholar, H.J. Sokol R. L.K. R.A. of apolipoprotein B the endoplasmic reticulum is in Lipid Res. 1996; Scholar, J.A. R.A. In HepG2 not the fate of synthesized apolipoprotein B.J. Biol. Chem. Scholar). The that plasma from abetalipoproteinemic patients was with an with plasma from unaffected suggested that translocation in the liver H.J. Sokol R. L.K. R.A. of apolipoprotein B the endoplasmic reticulum is in Lipid Res. 1996; Scholar). Several processes to that secretion-incompetent apoB not [reviewed in refs. (16Yao Z. Tran K. McLeod R.S. Intracellular degradation of newly synthesized apolipoprotein B.J. Lipid Res. 1997; 38: 1937-1953Google Scholar, 17Davis R.A. Cell and molecular biology of the assembly and secretion of apolipoprotein B-containing lipoproteins by the liver.Biochim. Biophys. Acta. 1999; 1440: 1-31Google Scholar, 18Olofsson S.O. Asp L. Boren J. The assembly and secretion of apolipoprotein B-containing lipoproteins.Curr. Opin. Lipidol. 1999; 10: 341-346Google Scholar, 19Davidson N.O. Shelness G.S. Apolipoprotein B: mRNA editing, lipoprotein assembly, and presecretory degradation.Annu. Rev. Nutr. 2000; 20: Scholar, in the the assembly and secretion of apolipoprotein B-containing Biol. Chem. 2002; the accumulation of apoB the may be essential in preventing an induction of ER the on Biol. 2000; 10: Scholar, F. A. D. and from the endoplasmic Cell Sci. 2000; 113: Scholar, C. P. Intracellular from the endoplasmic reticulum to the the unfolded protein in and Opin. Cell Biol. 2001; Scholar). have been studies that have how the liver in responds to loss of MTP in to the accumulation of apoB and induction of unfolded protein heat shock responses. studies that the inactivation of MTP gene disruption or chemical to a block in the secretion of apoB and prevented its accumulation in the as as the induction of unfolded protein heat shock responses. The MTP inhibitor (11Ksander G.M. deJesus R. Yuan A. Fink C. Moskal M. Carlson E. Kukkola P. Bilci N. Wallace E. Neubert A. Feldman D. Mogelesky T. Poirier K. Jeune M. Steele R. Wasvery J. Stephan Z. Cahill E. Webb R. Navarrete A. Lee W. Gibson J. Alexander N. Sharif H. Hospattankar A. Diaminoindanes as microsomal triglyceride transfer protein inhibitors.J. Med. Chem. 2001; 44: 4677-4687Google Scholar) was provided by were from homozygous for both a and the have been M. M.M. M.A. C.H. J. Young of the of microsomal triglyceride transfer protein in the liver of 1999; Scholar). C57BL/6 mice and C57BL/6 LDL mice were obtained from The were on a on from to MTP expression in the mice were with two days for mice or was from the into and plasma was by The mice were by and the livers were and to R.A. Apolipoprotein B is both into and the endoplasmic reticulum for two distinct Biol. Chem. 1990; 265: Scholar). were by the and of The inhibitor was as a in and was a of for 7 or using as a of The liver was in and and were obtained by and of as R.A. Apolipoprotein B is both into and the endoplasmic reticulum for two distinct Biol. Chem. 1990; 265: Scholar). The protein in the was using a protein of proteins from liver or plasma were by to and with as E. J. P. R.A. secretion of the of apolipoprotein B: characterization of a translocation Biol. Chem. 1994; Scholar). were by The of the was with a of plasma from in were and a protein with two in R.A. expression of atherosclerosis in Biol. 2002; Scholar). were a of with an and in plasma and were with from as R.A. expression of atherosclerosis in Biol. 2002; Scholar). are as the was by with were to be we mice. expression in these mice can be with which of and the of a functional M. M.M. M.A. C.H. J. Young of the of microsomal triglyceride transfer protein in the liver of 1999; Scholar). The absence of MTP expression by the liver not but increased liver reduced the plasma levels of and cholesterol a and LDLs were and levels were reduced by were increased and hepatic cholesterol was increased by was reduced to levels in plasma, and plasma levels of apoB-48 were reduced by Surprisingly, loss of MTP expression was associated with a nearly complete absence of apoB-100 in hepatic microsomes. The of apoB-48 was unaffected The lack of MTP expression not the levels of microsomal luminal proteins (e.g., glucose-regulated protein 78 and or cytosolic heat shock proteins (HSPs) (e.g., HSP60, HSC, HSP70, and HSP90) from mice for with MTP protein showed that apoB mRNA levels were by treatment in apoB were the of the absence of hepatic MTP These suggest that of hepatic MTP expression blocks the assembly and secretion of apoB-containing lipoproteins apoB-100 or apoB-48 to in the ER. was with results how mice to chemical inhibition of 7 days of treatment with the of C57BL/6 mice was the as that of mice hepatic The liver increased the plasma levels of triglyceride and cholesterol and the liver of triglyceride and cholesterol increased The MTP inhibitor markedly plasma levels of apoB-48 and apoB-100 from mice and was accumulation of apoB-48 The MTP inhibitor not the levels of microsomal luminal chaperone proteins or of cytosolic These findings suggest that the liver to inhibition of apoB secretion and the accumulation of apoB in the ER. the hepatic to MTP inhibition in mice. inhibition of MTP not liver mice have were in the plasma levels of cholesterol triglyceride apoB-100 and apoB-48 a plasma and LDL and levels by In the livers of the of increased and cholesterol increased the in apoB secretion, hepatic and was accumulation of apoB-48 from mice not with the MTP inhibitor markedly more apoB-100 from wild-type mice the absence of the LDL apoB-100 to in the ER of mice not with The MTP inhibitor not the of microsomal luminal chaperone proteins or the of cytosolic These show that inhibition of MTP severe hypercholesterolemia accumulation of apoB in the hepatic or how rapidly apoB degradation is in to MTP we the of a of the MTP of not liver plasma levels of and cholesterol apoB-100 and apoB-48 apoB isoform accumulated in the microsomal levels of of the and unfolded protein were unaffected These findings show that the hepatic to MTP inhibition and apoB secretion is rapid to the apoB accumulation in the ER. rapid may to the absence of an accumulation of proteins in the ER and an associated for the that blocking hepatic apoB secretion in in mice results in a rapid degradation that the accumulation of apoB in the ER heat shock or unfolded protein responses. Blocking MTP function by Cre-mediated gene disruption or chemical inhibition reduced plasma lipid levels markedly These findings suggest that MTP be an for The processes which apoB is into lipoproteins and by the liver are complex and many levels the [reviewed in refs. (16Yao Z. Tran K. McLeod R.S. Intracellular degradation of newly synthesized apolipoprotein B.J. Lipid Res. 1997; 38: 1937-1953Google Scholar, 17Davis R.A. Cell and molecular biology of the assembly and secretion of apolipoprotein B-containing lipoproteins by the liver.Biochim. Biophys. Acta. 1999; 1440: 1-31Google Scholar, 18Olofsson S.O. Asp L. Boren J. The assembly and secretion of apolipoprotein B-containing lipoproteins.Curr. Opin. Lipidol. 1999; 10: 341-346Google Scholar, 19Davidson N.O. Shelness G.S. Apolipoprotein B: mRNA editing, lipoprotein assembly, and presecretory degradation.Annu. Rev. Nutr. 2000; 20: Scholar, in the the assembly and secretion of apolipoprotein B-containing Biol. Chem. 2002; Since MTP is to the of the the J.R. Jamil H. Microsomal triglyceride transfer Biophys. Acta. 1997; Scholar), we have these studies on how blocking MTP the ER of apoB and of proteins that in the unfolded protein findings are the to show that in of MTP function by Cre-mediated gene disruption or chemical hepatic secretion of apoB-100 apoB to in the ER. These findings are with the that loss of MTP function blocks apoB apoB not in the ER E. J. P. R.A. secretion of the of apolipoprotein B: characterization of a translocation Biol. Chem. 1994; Scholar, F. degradation of apolipoprotein by the is prevented by microsomal triglyceride transfer studies on HepG2 cells with an inhibitor of microsomal triglyceride transfer Biol. Chem. 1997; Scholar, J. R.A. of apolipoprotein B the endoplasmic reticulum is in a Natl. Acad. Sci. USA. 1992; Scholar, G.M. R.A. apolipoprotein B degradation a block in Biol. Chem. 1999; Scholar, McLeod R.S. Gordon D.A. Z. The microsomal triglyceride transfer protein assembly and secretion of apolipoprotein B-containing lipoproteins and cotranslational degradation of apolipoprotein B in Biol. Chem. 1996; Scholar) is D.M. M. R. H. has a with the which its and translocation from on the microsomal triglyceride transfer protein to Natl. Acad. Sci. USA. 1998; Scholar, J.A. R.A. In HepG2 not the fate of synthesized apolipoprotein B.J. Biol. Chem. Scholar, W. L. degradation of apolipoprotein B both translocation and apolipoprotein B translocation into the endoplasmic Biol. Chem. 1998; Scholar, R. H. of B with the and lipoprotein assembly or to the Biol. Chem. 2001; Scholar). that of MTP function results in the rapid and degradation of secretion-incompetent apoB in apoB not in hepatic ER. findings may blocking the secretion of apoB-containing lipoproteins by the liver in mice is not associated with the associated with the accumulation of secretion-incompetent protein in the and heat shock ER the on Biol. 2000; 10: Scholar, F. A. D. and from the endoplasmic Cell Sci. 2000; 113: Scholar, C. P. Intracellular from the endoplasmic reticulum to the the unfolded protein in and Opin. Cell Biol. 2001; Scholar). is by the that by of MTP expression in the livers of mice is not associated with hepatic or J. A. J.J. Young Blocking the secretion of hepatic lipoproteins the liver more to Biol. Chem. 2002; Scholar). The livers of mice more apoB-100 in the ER livers of C57BL/6 mice Since apoB mRNA expression was in the two of this in the degradation of apoB in the ER. findings are with studies that from mice secrete more apoB-100 and of in the ER from wild-type mice J. A. L. The of the LDL in apolipoprotein B 2000; Scholar). the of the LDL with apoB-100 its from the ER or its degradation A. reticulum of the lipoprotein presecretory degradation of apolipoprotein Natl. Acad. Sci. USA. 2002; Scholar). The of the LDL in the ER is in the lumen M.S. Goldstein J.L. the of Scholar). Since the LDL binding of apoB is in the T.J. R.J. L.M. B. Y. R. D. M. B.J. B. J. protein and of of apolipoprotein 1986; Scholar, Chen W.A. M. D.A. H. M. Lee F. L. and of apolipoprotein 1986; Scholar), is that the LDL with apoB its translocation into the ER lumen is that blocking MTP a in the apoB-100 in the ER that the of the LDL not the degradation of apoB-100 in to These findings suggest the that the absence of MTP function increased degradation of and the absence of the LDL reduces the degradation of luminal The that D.R. in Scholar) not (2Kayden H.J. Abetalipoproteinemia.Annu. Rev. Med. 1972; 23: 285-296Google Scholar, S.T. Sokol R.J. Vitamin E deficiency in neuropathy of abetalipoproteinemia.Neurology. 1986; 361009Google Scholar, K. J. R. K. N. F. Y. Y. R. D.R. T. N. mutations in the microsomal triglyceride transfer protein gene Lipid Res. 2000; abetalipoproteinemic patients liver disease that the of the liver to MTP inhibition may be by and In the mice we in this study, of MTP by liver but to liver J. A. J.J. Young Blocking the secretion of hepatic lipoproteins the liver more to Biol. Chem. 2002; Scholar). increased may be by of essential lipid as vitamin E (8Iannaccone S.T. Sokol R.J. Vitamin E deficiency in neuropathy of abetalipoproteinemia.Neurology. 1986; 361009Google Scholar, K. J. R. K. N. F. Y. Y. R. D.R. T. N. mutations in the microsomal triglyceride transfer protein gene Lipid Res. 2000; Scholar, K. T. M. of vitamin E deficiency in familial Scholar). The studies that MTP inhibitors the hypercholesterolemia in Watanabe-heritable hyperlipidemic rabbits (13Wetterau J.R. Gregg R.E. Harrity T.W. Arbeeny C. Cap M. Connolly F. Chu C.H. George R.J. Gordon D.A. Jamil H. Jolibois K.G. Kunselman L.K. Lan S.J. Maccagnan T.J. Ricci B. Yan M. Young D. Chen Y. Fryszman O.M. Logan J.V. Musial C.L. Poss M.A. Robl J.A. Simpkins L.M. Slusarchyk W.A. Sulsky R. Taunk P. Magnin D.R. Tino J.A. Lawrence R.M. Dickson J. Biller S.A. An MTP inhibitor that normalizes atherogenic lipoprotein levels in WHHL rabbits.Science. 1998; 282: 751-754Google Scholar) provided a treatment for homozygous familial a by liver transplantation (15Bilheimer D.W. Goldstein J.L. Grundy S.M. Starzl T.E. Brown M.S. Liver transplantation to provide low-density-lipoprotein receptors and lower plasma cholesterol in a child with homozygous familial hypercholesterolemia.N. Engl. J. Med. 1984; 311: 1658-1664Google Scholar). The studies in Watanabe-heritable hyperlipidemic rabbits not provide liver function or (13Wetterau J.R. Gregg R.E. Harrity T.W. Arbeeny C. Cap M. Connolly F. Chu C.H. George R.J. Gordon D.A. Jamil H. Jolibois K.G. Kunselman L.K. Lan S.J. Maccagnan T.J. Ricci B. Yan M. Young D. Chen Y. Fryszman O.M. Logan J.V. Musial C.L. Poss M.A. Robl J.A. Simpkins L.M. Slusarchyk W.A. Sulsky R. Taunk P. Magnin D.R. Tino J.A. Lawrence R.M. Dickson J. Biller S.A. An MTP inhibitor that normalizes atherogenic lipoprotein levels in WHHL rabbits.Science. 1998; 282: 751-754Google Scholar). studies show that inhibition of MTP the hyperlipidemia in a model of homozygous familial hypercholesterolemia liver or induction of heat shock or unfolded protein responses. findings provide that MTP may be a useful for plasma levels of atherogenic lipoproteins in homozygous familial The and G. for on the The are to and for of MTP was by of and an Heart and a from the of was an Liver A. Liver endoplasmic reticulum glucose-regulated protein heat shock protein microsomal triglyceride transfer protein protein disulfide isomerase
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