Genetic control of HDL levels and composition in an interspecific mouse cross (CAST/Ei × C57BL/6J)

Strain CAST/Ei (CAST) mice exhibit unusually low levels of high density lipoproteins (HDL) as compared with most other strains of mice, including C57BL/6J (B6). This appears to be due in part to a functional deficiency of lecithin:cholesterol acyltransferase (LCAT). LCAT mRNA expression in CAST mice is normal, but the mice exhibit several characteristics consistent with functional deficiency. First, the activity and mass of LCAT in plasma and in HDL of CAST mice were reduced significantly. Second, the HDL of CAST mice were relatively poor in phospholipids and cholesteryl esters, but rich in free cholesterol and apolipoprotein A-I (apoA-I). Third, the adrenals of CAST mice were depleted of cholesteryl esters, a phenotype similar to that observed in LCAT- and acyl-CoA:cholesterol acyltransferase-deficient mice. Fourth, in common with LCAT-deficient mice, CAST mice contained triglyceride-rich lipoproteins with “panhandle”-like protrusions. To examine the genetic bases of these differences, we studied HDL lipid levels in an intercross between strain CAST and the common laboratory strain B6 on a low fat, chow diet as well as a high fat, atherogenic diet. HDL levels exhibited complex inheritance, as 12 quantitative trait loci with significant or suggestive likelihood of observed data scores were identified. Several of the loci occurred over plausible candidate genes and these were investigated. The results indicate that the functional LCAT deficiency is unlikely to be due to variations of the LCAT gene. Our results suggest that novel genes are likely to be important in the control of HDL metabolism, and they provide evidence of genetic factors influencing the interaction of LCAT with HDL.—Mehrabian, M., L. W. Castellani, P-Z. Wen, J. Wong, T. Rithaporn, S. Y. Hama, G. P. Hough, D. Johnson, J. J. Albers, G. A. Mottino, J. S. Frank, M. Navab, A. M. Fogelman, and A. J. Lusis. Genetic control of HDL levels and composition in an interspecific mouse cross (CAST/Ei × C57BL/6J). J. Lipid Res. 2000. 41: 1936–1946. Strain CAST/Ei (CAST) mice exhibit unusually low levels of high density lipoproteins (HDL) as compared with most other strains of mice, including C57BL/6J (B6). This appears to be due in part to a functional deficiency of lecithin:cholesterol acyltransferase (LCAT). LCAT mRNA expression in CAST mice is normal, but the mice exhibit several characteristics consistent with functional deficiency. First, the activity and mass of LCAT in plasma and in HDL of CAST mice were reduced significantly. Second, the HDL of CAST mice were relatively poor in phospholipids and cholesteryl esters, but rich in free cholesterol and apolipoprotein A-I (apoA-I). Third, the adrenals of CAST mice were depleted of cholesteryl esters, a phenotype similar to that observed in LCAT- and acyl-CoA:cholesterol acyltransferase-deficient mice. Fourth, in common with LCAT-deficient mice, CAST mice contained triglyceride-rich lipoproteins with “panhandle”-like protrusions. To examine the genetic bases of these differences, we studied HDL lipid levels in an intercross between strain CAST and the common laboratory strain B6 on a low fat, chow diet as well as a high fat, atherogenic diet. HDL levels exhibited complex inheritance, as 12 quantitative trait loci with significant or suggestive likelihood of observed data scores were identified. Several of the loci occurred over plausible candidate genes and these were investigated. The results indicate that the functional LCAT deficiency is unlikely to be due to variations of the LCAT gene. Our results suggest that novel genes are likely to be important in the control of HDL metabolism, and they provide evidence of genetic factors influencing the interaction of LCAT with HDL.—Mehrabian, M., L. W. Castellani, P-Z. Wen, J. Wong, T. Rithaporn, S. Y. Hama, G. P. Hough, D. Johnson, J. J. Albers, G. A. Mottino, J. S. Frank, M. Navab, A. M. Fogelman, and A. J. Lusis. Genetic control of HDL levels and composition in an interspecific mouse cross (CAST/Ei × C57BL/6J). J. Lipid Res. 2000. 41: 1936–1946. The inverse relationship between high density lipoprotein (HDL) levels and coronary artery disease (CAD) (1Rhoads G.G. Gulbrandsen C.L. Kugan A. Serum lipoproteins and coronary artery disease in a population study of Hawaii Japanese men.N. Engl. J. Med. 1976; 294: 293-298Google Scholar) has generated interest in the metabolism of HDL and the environmental and genetic factors contributing to variations in HDL levels. The major structural proteins of HDL are apolipoprotein A-I (apoA-I) and apoA-II, but HDL also contains numerous other proteins, including lecithin: cholesterol acyl-transferase (LCAT), serum paraoxonase (PON1), platelet-activating factor acetylhydrolase (PAF-AH), apoE, apoA-IV, cholesteryl ester transfer protein (CETP), and phospholipid transfer protein (PLTP). HDL are extremely heterogeneous, and various species of HDL differ in functions relevant to CAD, such as the ability to promote cholesterol efflux and to inhibit LDL oxidation (2Castellani L.W. Navab M. Van Lenten B.J. Hedrick C.C Hama S.Y. Goto A.M. Fogelman A.M. Lusis A.J. Overexpression of apolipoprotein AII in transgenic mice converts high density lipoproteins to proinflammatory particles.J. Clin. Invest. 1997; 100: 464-474Google Scholar). Biochemical and physiologic studies have revealed that HDL are derived from the transfer of surface components of triglyceride-rich lipoproteins into HDL (3Havel R.J. Kane J.P. Kashyae M.L. Interchange of apolipoproteins between chylomicrons and high density lipoproteins during alimentary lipenia in man.J. Clin. Invest. 1973; 52: 32-38Google Scholar, 4Tall A.R. Green P.H.R. Glickman R.M. Riley J.W. Metabolic fate of chylomicron phospholipids and apoproteins in the rat.J. Clin. Invest. 1979; 64: 977-989Google Scholar) and from the association of cellular plasma membranes with apoA-I (3Havel R.J. Kane J.P. Kashyae M.L. Interchange of apolipoproteins between chylomicrons and high density lipoproteins during alimentary lipenia in man.J. Clin. Invest. 1973; 52: 32-38Google Scholar, 5Hamilton R.H. Williams M.C. Fielding C.J. Havel R.J. Discoidal bilayer structure of nascent high density lipoproteins from perfused rat liver.J. Clin. Invest. 1976; 58: 667-680Google Scholar). Studies of human mutations and transgenic/knockout mice have clarified the functions of various HDL proteins in vivo. Human metabolic studies have also indicated that common variations in HDL cholesterol levels are strongly related to the fractional catabolic rate of apoA-I (6Brinton E.A. Eisenberg S. Breslow J.L. Human HDL cholesterol levels are determined by apoA-1 fractional catabolic rate, which correlates inversely with estimates of HDL particle size. Effects of gender, hepatic and lipoprotein lipases, triglyceride and insulin levels, and body fat distribution.Arterioscler. Thromb. 1994; 14: 707-720Google Scholar). However, the genetic factors contributing to common variation in HDL levels and functional differences among human populations are poorly understood. One significant genetic determinant of HDL levels is a polymorphism of the promoter region of hepatic lipase, which contributes to HDL levels in males (7Cohen J.C. Vega G.L. Grundy S.M. Hepatic lipase: new insights from genetic and metabolic studies.Curr. Opin. Lipidol. 1999; 10: 259-267Google Scholar). The identification of the ATPase-binding cassette transporter responsible for Tangier disease has revealed a novel pathway for HDL metabolism, and some evidence suggests that variations of the transporter could contribute to common HDL deficiencies (8Bodzioch M. Orso E. Klucken J. Langmann T. Böttcher A. Diederich W. Drobnik W. Barlage S. Büchler C. Porsch-Özcürümez M. Kaminski W.E. Hahmann H.W. Oette K. Rothe G. Aslanidis C. Lackner K.J. Schmitz G. The gene encoding ATP-binding cassette transporter 1 is mutated in Tangier 1999; Scholar, A. M. S.M. K. M. L. C. K. S. S. M. D. J. K. S. J. in in Tangier disease and lipoprotein 1999; Scholar, S. M. J. J.C. P. G. Tangier disease is by mutations in the gene encoding ATP-binding cassette transporter 1999; Scholar). studies of the genetic control of HDL levels in a mouse The mouse has for the study of complex compared with human the of the of environmental and Genetic of complex 1994; Scholar). laboratory strains of mice exhibit variations in HDL levels, and A.J. Genetic control of lipid in mice. structure of high density and we have and genetic studies of some of these variations D. K. A. Lusis A.J. a gene and high density lipoprotein levels in Scholar, Lusis A.J. polymorphism apolipoprotein high density lipoprotein and Scholar, M. R.H. D. C. Lusis A.J. of the gene on HDL levels and in Thromb. Scholar, A. L.W. M. Lusis A.J. Genetic factors in lipoprotein of a genetic cross between mouse strains and a Clin. Invest. Scholar, S.M. P-Z. Lusis A.J. of loci in a mouse Clin. Invest. Scholar, L. Hama S. Y. Navab M. Fogelman A.M. Lusis A.J. of serum paraoxonase expression and in in a mouse Clin. Invest. Scholar, C.L. M. S. Lusis A.J. Genetic of cholesterol of candidate Lipid Res. Scholar, D. C.L. L. K. Lusis A.J. genetic control of HDL levels in mice in to an atherogenic of HDL levels and Clin. Invest. 1997; Scholar, M. P-Z. J. Lusis A.J. Genetic loci body fat, lipoprotein metabolism, and insulin levels in a mouse Clin. Invest. Scholar). the we have the genetic control of HDL levels in an intercross between the laboratory strain C57BL/6J and the related strain CAST/Ei which is derived from a of studies were with a low fat, chow diet and the other a high fat, atherogenic to examine The results have revealed a complex of inheritance, with a loci contributing to HDL levels and on the genes some of the loci were for The results suggest that a significant of the genetic in HDL metabolism is unlikely to be by the for plasma lipid also that CAST mice have low HDL levels in to reduced LCAT and that in results in a of lipid the low LCAT activity is due to reduced LCAT to a genetic factor influencing the interaction of LCAT with mice were from the and were for and of CAST males were with B6 and the were to the The mice were of chow of from fat and of they were to a high fat, high cholesterol diet for This diet chow with in of from and also of and and The mice were to and were on a mice were of and were into the of the The and adrenals were for and other lipoproteins were and were as M. R.H. D. C. Lusis A.J. of the gene on HDL levels and in Thromb. Scholar). LCAT activity and activity in plasma were determined as A. T. Y. S. density lipoprotein in cholesteryl from Scholar, M.C. G. phospholipid mass transfer relationship to plasma phospholipid and cholesteryl ester transfer and lipid Scholar). lipoproteins were by density or by L.W. Lusis A.J. of mouse apolipoprotein on plasma lipoproteins in transgenic Scholar). of plasma in and lipoproteins with and in of were The lipoprotein determined by and were determined by an as M. R.H. D. C. Lusis A.J. of the gene on HDL levels and in Thromb. Scholar). The lipoproteins were to the in the membranes were by 1 of in of 1 1 low by the for and for The in an for 1 and the The in 1 of by a with a The to a new of and the for The and the in of 1 and were determined by the protein or as by were membranes and by of the protein with of membranes to and to and with a of mouse by M. C. of LCAT a of human LCAT to LCAT protein in mouse plasma HDL by density or mouse apoA-I or were from and of and a of human to in of mouse from to the to the mRNA levels of of and to × were and a high were with a mouse LCAT The and the The were also with to the of the for the with and as M. P-Z. J. Lusis A.J. Genetic loci body fat, lipoprotein metabolism, and insulin levels in a mouse Clin. Invest. Scholar). for were from were with the for and of genetic Scholar) of quantitative between as in the by of and of the observed data scores for quantitative were with the Green P. J. A. M. S. L. an for genetic of and Scholar). The data were for the of and by lipid were by a of lipid a to the and for the which to and in a from CAST and B6 on a chow and high fat diet were for were from of CAST and B6 mice, were a by were in a with from to The were and with an The results were by several and a and The into were with the of various strains of mice A.J. Genetic control of lipid in mice. structure of high density CAST are in low levels of HDL cholesterol on a chow diet as well as a high fat, atherogenic diet strains of mice, such as and relatively high levels of HDL cholesterol on an atherogenic diet CAST mice and B6 mice exhibit a have that the in HDL cholesterol in strain C57BL/6J mice in to the atherogenic diet is related to expression of cholesterol D. C.L. L. K. Lusis A.J. genetic control of HDL levels in mice in to an atherogenic of HDL levels and Clin. Invest. 1997; Scholar). The results with CAST mice are consistent with CAST mice also exhibited a in mRNA levels The lipoprotein of CAST mice is in to these differences in HDL levels, CAST mice were unusually to an atherogenic diet in of the levels of low density high density lipoprotein cholesterol genetic HDL levels with levels, that the low HDL and high in CAST mice in from genetic The composition of CAST HDL also as compared with common laboratory strains of mice, including by density the HDL from CAST mice were determined to have relatively low levels of phospholipids and cholesteryl but high levels of free cholesterol of HDL levels and related in CAST and B6 mice on cholesterol mRNA activity activity activity cholesterol triglyceride mRNA mRNA protein high density mice of were studied on a chow diet or an atherogenic diet for the of to between CAST and B6 mice are indicated with an in a new density lipoprotein (HDL) from CAST mice exhibit reduced levels of HDL were from CAST and B6 mice, on chow or atherogenic and by mass for the of of of HDL protein in The phospholipid species in the HDL were and fat atherogenic diet or were high density mice of were studied on a chow diet or an atherogenic diet for the of to between CAST and B6 mice are indicated with an The composition and low levels of HDL cholesterol in CAST mice that they exhibit a deficiency of we LCAT in of CAST and B6 mice on chow and atherogenic CAST mice exhibited levels, on the atherogenic diet To the activity due to a reduced mass or a structural of LCAT LCAT mass with a The of LCAT in plasma by similar in CAST and B6 mice on strains exhibited similar levels of hepatic LCAT mRNA on that a promoter variation of the LCAT gene is One for the reduced LCAT activity is that the LCAT poorly to in and HDL depleted in cholesteryl To examine we LCAT protein in HDL by B6 mice, most of the plasma LCAT with the in CAST mice, levels were observed the of HDL by the to high and we also the association of LCAT with HDL in low the levels of LCAT activity and mass with HDL were similar in CAST and B6 mice CAST LCAT appears to be with HDL physiologic but is in part the of To examine the that structural differences in LCAT between the strains to a in high hepatic LCAT to for mutations that could the of the protein hepatic mRNA and to of of the were but of these in relatively and data suggest that the deficiency in LCAT activity is most likely due to interaction of LCAT with HDL or other lipoproteins in CAST mice. is that results from the unlikely the of the and the genetic data CAST HDL or plasma a factor or factors influencing the interaction of LCAT with of LCAT from CAST and B6 mRNA for LCAT and from CAST and B6 mice and in in the are indicated in and the are and mRNA for LCAT and from CAST and B6 mice and in in the are indicated in and the are in a new of the unusually low levels of HDL and cholesteryl in CAST mice, we the mice exhibited lipid from the of the adrenals to cholesterol from HDL M. of lecithin:cholesterol acyltransferase gene of lipid and of 1997; Scholar). CAST adrenals were and for cholesteryl with a deficiency observed as compared with B6 an atherogenic the of cholesteryl in CAST adrenals that of B6 mice. The in cholesterol levels occurred the that LCAT activity and HDL cholesterol on the atherogenic diet. This have from the in which also cholesterol to by from plasma of CAST and B6 mice on chow or The of the in the CAST and B6 mice between and the from the CAST mice on the of the lipoprotein contained a that on from the surface of the particle from the B6 mice on the diet or chow diet were free of lipid from the CAST mice a chow diet were free of 1 particle with a observed of have observed in LCAT-deficient mice M. of lecithin:cholesterol acyltransferase gene of lipid and of 1997; the that CAST mice have a functional LCAT deficiency. and HDL were for apoA-I levels by to mouse were significant differences in apoA-I levels between CAST and B6 mice on a chow or high fat diet CAST mice have HDL cholesterol levels B6 mice, they have similar levels of apoA-I in plasma and the reduced levels of cholesteryl and phospholipids in CAST these are apoA-I rich as compared with B6 HDL were significant differences in or between the To apoA-I in CAST mice is in a that in poor LCAT and we apoA-I in B6 and CAST mice mRNA and by were in and of from CAST and B6 mRNA for apoA-I from B6 and CAST mice and in the and are and mRNA for apoA-I from B6 and CAST mice and in the and are in a new mice from a cross of B6 and CAST mice exhibited plasma lipid between the on a chow diet the levels of HDL cholesterol in and B6 mice were and the levels in mice were and the of lipoprotein levels in × mice. were on a low fat chow diet and also for with a high fat, atherogenic diet. The of the variation observed in the and mice, genetic the of triglyceride levels, the exhibited consistent with of plasma lipoprotein levels in × mice. an The for the CAST for B6 for × of the with an of M. P-Z. J. Lusis A.J. Genetic loci body fat, lipoprotein metabolism, and insulin levels in a mouse Clin. Invest. Scholar). trait with for the of results were by and L. Genetic of complex for and Scholar). an suggestive is indicated by scores and significant is indicated by scores of 12 loci for HDL cholesterol with scores were for the of the loci scores with diet the of on observed in the × genetic cross are The levels of HDL cholesterol or cholesterol for mice of and are indicated with the likelihood of observed data in a new observed in the × genetic cross are The levels of HDL cholesterol or cholesterol for mice of and are indicated with the likelihood of observed data The on HDL cholesterol on chow as well as the high fat diet loci with loci for body fat and insulin levels, as M. P-Z. J. Lusis A.J. Genetic loci body fat, lipoprotein metabolism, and insulin levels in a mouse Clin. Invest. Scholar). One candidate gene the is the gene. To gene could the activity determined in of The activity with the that the gene is unlikely to the lipoprotein levels have with body fat in likely that the loci from metabolic for HDL cholesterol observed on in a region in which for HDL have observed in between strains B6 and and between and candidate encoding the HDL the To the of the expression in the strains the of mRNA and the of protein B6 mice levels of mRNA in CAST mice on chow and high fat significant differences were observed the of protein in To CAST and B6 mice differ in protein such that be we the of hepatic mRNA to The results revealed of which the The results indicate that the is due to gene variation in HDL for HDL cholesterol levels. are the for HDL cholesterol on an atherogenic diet. The of genetic and the gene are indicated the of from B6 and CAST mRNA for and in differences, and are and mRNA for and in differences, and are in a new The on is over the gene for in LCAT activity reduced in CAST mice as compared with B6 mice, the also to with the levels of plasma the gene is on mouse the be due to variations of the structural gene. the deficiency of LCAT results from a CAST mice have levels of LCAT the reduced levels of LCAT from factors with LCAT that are for or interaction with on for HDL cholesterol is over the gene for plasma human significant differences between the strains of mice on a chow or high fat diet for HDL levels observed on the gene for to region of by J. However, levels were similar among strains that is unlikely to be observed the of but an candidate gene. have genetic factors contributing to variations in HDL levels and in studies of strains of mice, CAST and a chow CAST mice exhibited reduced levels of HDL as compared with other common strains The composition of the HDL also as a surface unusually rich in free cholesterol and poor in Our results indicated that these differences were due in part to a functional deficiency of plasma an atherogenic CAST mice low levels of HDL and high levels of of an intercross between CAST and B6 mice significant to the genetic control of First, numerous genes to variations in HDL levels. Second, most of the observed variation by the candidate such as lipoprotein or in HDL Our studies have revealed an contributing to the low levels of HDL cholesterol in CAST mice. the mice the levels of LCAT mRNA as B6 and other strains C. J.W. Lusis A.J. and of the evidence for expression in and as well as liver.J. is reduced activity in the This deficiency appears to in part from an interaction of LCAT with HDL The of reduced interaction is likely to from the composition of the HDL an of the LCAT of the LCAT mRNA revealed in CAST B6 mice and a of the of HDL cholesterol levels could be to the LCAT on is that a significant of cholesteryl in mouse plasma are generated on lipoproteins and that is in CAST mice. CAST mice exhibit unusually high levels of cholesterol in CAST mice, the plasma of cholesterol to cholesterol is the HDL This could from interaction of LCAT with lipoproteins in CAST mice. The functional deficiency of LCAT in CAST mice by related observed in LCAT-deficient lipid and protrusions. lipid is by depleted of cholesteryl in the the of CAST mice, is likely that the results from the low levels of HDL cholesterol in the the of the cholesterol are derived by from HDL M. of lecithin:cholesterol acyltransferase gene of lipid and of 1997; Scholar). of lipid in strain mice, results from the to cholesterol due to a deficiency of acyl-CoA:cholesterol acyltransferase C.L. S. E. Lusis A.J. lipid gene in mice is with acyl-CoA:cholesterol acyltransferase Scholar). similar to observed in CAST mice are also observed in LCAT-deficient mice, that LCAT deficiency is the of the M. of lecithin:cholesterol acyltransferase gene of lipid and of 1997; Scholar). Human LCAT deficiency results in but of of CAST mice evidence of we also in an to genetic factors influencing HDL levels. Our studies revealed a influencing HDL levels, most to candidate of these loci observed in genetic including the and loci A. L.W. M. Lusis A.J. Genetic factors in lipoprotein of a genetic cross between mouse strains and a Clin. Invest. Scholar, D. C.L. L. K. Lusis A.J. genetic control of HDL levels in mice in to an atherogenic of HDL levels and Clin. Invest. 1997; but most were loci for HDL levels with significant scores have observed in various mouse A. L.W. M. Lusis A.J. Genetic factors in lipoprotein of a genetic cross between mouse strains and a Clin. Invest. Scholar, D. C.L. L. K. Lusis A.J. genetic control of HDL levels in mice in to an atherogenic of HDL levels and Clin. Invest. 1997; Scholar, M. P-Z. J. Lusis A.J. Genetic loci body fat, lipoprotein metabolism, and insulin levels in a mouse Clin. Invest. Scholar, L. Lusis A.J. trait of plasma lipoprotein levels in an mouse between and Thromb. 1999; Scholar) and The identification of the Tangier disease gene revealed a novel pathway for of HDL metabolism (8Bodzioch M. Orso E. Klucken J. Langmann T. Böttcher A. Diederich W. Drobnik W. Barlage S. Büchler C. Porsch-Özcürümez M. Kaminski W.E. Hahmann H.W. Oette K. Rothe G. Aslanidis C. Lackner K.J. Schmitz G. The gene encoding ATP-binding cassette transporter 1 is mutated in Tangier 1999; Scholar, A. M. S.M. K. M. L. C. K. S. S. M. D. J. K. S. J. in in Tangier disease and lipoprotein 1999; Scholar, S. M. J. J.C. P. G. Tangier disease is by mutations in the gene encoding ATP-binding cassette transporter 1999; Scholar). mutations of the gene have to the of HDL to the in A.R. HDL particle in and lipid Clin. Invest. Scholar). Our results suggest that are as genes that contribute to HDL to a of the of HDL metabolism, results provide an for the identification of new genetic factors HDL metabolism in mice and the candidate these be for we several including and exhibited similar levels of expression between CAST and B6 mice, and the of and LCAT exhibited or these are unlikely to the the of candidate is in the to from strain the of a in a strain differ from the strain a contributing to the trait of strains be to examine between the loci in to structure and of the gene the are in the of strains for the various in the be to genetic of loci contributing to human HDL the observed in a genetic cross between strains and the to that human a contributing to body fat and insulin levels. genetic on human were for in for of significant observed with insulin levels and body fat L. J. A. Lusis A.J. C. of an quantitative trait on mouse and evidence of to body fat and insulin on the human region Clin. Invest. 1997; 100: Scholar). the of CAST mice, a variation for studies the interaction of LCAT with and genetic results suggest that the the LCAT gene is of the other observed in study is responsible is the the genetic cross the interaction trait To studies with CAST and B6 mice have to be with or for the is that loci control the interaction of LCAT with appears that of common variations influencing HDL levels and composition is significant for HDL levels were observed in several candidate Our results suggest novel genetic variation the interaction of LCAT with This variation and genetic but is to that similar variations in human studies were in part by and and by the J. C. and for and for in the of apolipoprotein A-I atherogenic C57BL/6J CAST/Ei coronary artery disease cholesteryl ester transfer protein high density lipoprotein lecithin:cholesterol acyltransferase likelihood of the observed data platelet-activating factor acetylhydrolase phospholipid transfer protein serum paraoxonase quantitative trait loci