Diabetes 54:2251-2255, 2005 © 2005 by the American Diabetes Association, Inc.
Hepatic Lipase Gene Variant –514C>T Is Associated With Lipoprotein and Insulin Sensitivity Response to Regular ExerciseThe HERITAGE Family Study
1 Human Genomics Laboratory, Pennington Biomedical Research Center, Baton Rouge, Louisiana
We investigated the associations between the hepatic lipase gene (LIPC) –514C>T polymorphism and lipases, lipoproteins, and insulin sensitivity (Si) responses to exercise training. Hepatic lipase and lipoprotein lipase activities, plasma lipoprotein levels, and Si were measured in the sedentary state and post–exercise training in the Health, Risk Factors, Exercise Training, and Genetics (HERITAGE) Family Study (n = 662). The LIPC –514C allele frequency was 0.516 (blacks) and 0.796 (whites). Baseline and post–exercise training hepatic lipase activities were 40% higher in CC homozygotes (P < 0.0001) in both races. Black CC homozygotes had lower baseline lipoprotein lipase activity, HDL cholesterol, HDL3, and apolipoprotein (apo)A-1 concentrations. White CC homozygotes had lower baseline HDL cholesterol, apoA-1, LDL cholesterol, and apoB levels that remained low post–exercise training. Baseline Si was not associated with the LIPC genotypes. However, training-induced improvements in Si both in blacks and whites were greater in CC homozygotes (+1.25 ± 0.2 and +0.22 ± 0.2 µU · min–1 · ml–1) than in the TT genotype (+0.27 ± 0.3 and –0.97 ± 0.3 µU · min–1 · ml–1) (P = 0.008 and P = 0.002, respectively). The LIPC –514C allele was associated with higher hepatic lipase activity in sedentary and physically active states and better Si responses to regular exercise both in black and white individuals. The benefits from an exercise program on Si are likely to be substantial in the general population given the high frequency of the LIPC –514C allele, particularly in whites.
Address correspondence and reprint requests to Claude Bouchard, Human Genomics Laboratory, Pennington Biomedical Research Center, 6400 Perkins Rd., Baton Rouge, LA 70808. E-mail: bouchac{at}pbrc.edu
Abbreviations: apo, apolipoprotein; CHD, coronary heart disease; HERITAGE, Health, Risk Factors, Exercise Training, and Genetics; LPL, lipoprotein lipase Hepatic lipase hydrolyzes triglyceride and phospholipids from high-, intermediate-, and low-density lipoproteins, transforming them into smaller and denser particles, and promotes the cellular uptake of HDL cholesterol (1). The hepatic lipase gene (LIPC), located on chromosome 15q21-q23, is expressed in the liver. Hepatic lipase has been the subject of recent reviews for its molecular (1) and pathophysiologic significance in obesity, dyslipidemia, and atherogenesis (2). There is familial resemblance for plasma postheparin lipoprotein lipase (LPL) and postheparin hepatic lipase activities (3), and exercise training–induced improvement in insulin sensitivity (Si) correlates with decreased postheparin hepatic lipase activity. Genetic polymorphisms in the LIPC gene are associated with postheparin hepatic lipase activity (4–6). Four frequently reported genetic variants in the LIPC promoter are in almost complete linkage disequilibrium, forming two haplotypes (2). The less common T allele in the –514C>T variant has been associated with a 30–40% decrease in postheparin hepatic lipase activity and higher HDL cholesterol levels (4). However, the relevance of this polymorphism for the transcriptional regulation of the LIPC gene remains controversial (7–10). The benefits of regular physical activity in decreasing the risk of developing insulin resistance and coronary heart disease (CHD) are well documented, although individual responses vary considerably (11,12). Regular exercise affects lipid-lipoprotein profiles and peripheral glucose utilization (12,13). We investigated associations between the LIPC –514C>T variant and plasma lipoprotein levels, Si and postheparin hepatic lipase, and postheparin LPL activities in a biracial cohort under sedentary-state conditions and their responses to endurance exercise training.
The Health, Risk Factors, Exercise Training, and Genetics (HERITAGE) Family Study design and methods have been described previously (14). Briefly, the HERITAGE Family Study was designed to investigate the role of genetic factors in cardiovascular, metabolic, and hormonal responses to endurance training in white and black families. All subjects were required to be sedentary and in good health to participate in the HERITAGE Family Study, as well as to fulfill a series of inclusion criteria (14). For the present study we only excluded individuals without genotype or phenotype data. Data from 219 black adults (79 males and 140 females) and 443 white adults (218 males and 225 females) were available. Each institutional review board of the HERITAGE Family Study research consortium approved the study protocol. Written informed consent was obtained from each participant.
Exercise training program.
Phenotype measurements.
Measurement of Si.
Postheparin lipase activities, lipids, and lipoproteins.
Genetic analyses.
Statistical analyses.
The LIPC –514C allele frequency was 0.516 (blacks) and 0.796 (whites). Genotype distributions were in Hardy-Weinberg equilibrium. The LIPC –514C>T polymorphism showed a strong association with postheparin hepatic lipase activity, which was 40% higher in the CC homozygotes at baseline (P 0.0001) and posttraining (P 0.0001) in both ethnic groups (Fig. 1).
The LIPC –514C>T polymorphism was also associated with postheparin LPL activity. The black CC homozygotes had 32 and 21% lower postheparin LPL activity before and after exercise training than the LIPC TT homozygotes (P = 0.0005 and 0.009, respectively). White CC homozygotes had 12 and 19% lower postheparin LPL activity before and after exercise training than TT homozygotes (P = 0.0004 and <0.0001, respectively) (Fig. 2).
Associations of LIPC –514C>T genotypes with lipids and lipoprotein concentrations in the sedentary state and their training responses in blacks and whites are shown in Table 1. In blacks, the TT homozygotes exhibited higher baseline HDL cholesterol, HDL3, and apoA-1 concentrations than the CC homozygotes. The LIPC –514 polymorphism was also associated with apoB (P = 0.04) training response, with the greatest reduction observed in the TT homozygotes. White TT homozygotes also had higher HDL cholesterol and apoA-1 concentrations in the sedentary state, as well as significantly higher plasma trigylceride, VLDL cholesterol, LDL cholesterol, and apoB concentrations.
There were no differences in Si between the LIPC –514 genotypes in blacks and whites in the sedentary state (Table 2). However, training–induced improvements in Si in blacks and whites were greater in the CC homozygotes (+1.25 ± 0.2 and +0.22 ± 0.2 µU · min–1 · ml–1) than in the TT genotype (+0.27 ± 0.3 and –0.97 ± 0.32 µU · min–1 · ml–1), with heterozygotes showing intermediary values.
Our data demonstrate significant associations between the LIPC –514C>T polymorphism and plasma postheparin hepatic lipase and postheparin LPL activities and lipoprotein levels in the sedentary state as well as with endurance training–induced changes in Si. Several studies have shown that DNA sequence variations at the LIPC locus contribute to postheparin hepatic lipase plasma levels and the lipoprotein profile (2,6). A recent meta-analysis concluded that the LICP –514C>T polymorphism is important in determining hepatic lipase activity and HDL concentration (18). However, associations between this polymorphism and changes in lipoprotein levels or Si in response to exercise training have not been addressed before. The LIPC –514TT homozygotes had 30% lower postheparin hepatic lipase activity compared with the CC homozygotes, and the genotype accounted for 7–8% of the variation in postheparin hepatic lipase activity. This association remained after exercise training. Blacks had lower postheparin hepatic lipase activity, an ethnic difference found in both sexes and concordant with previous observations (19,20). Several in vitro studies have reported a 30–40% reduction in transcriptional activity in cells transfected with the T allele compared with the C allele (rev. in 2). Other studies found no functional effects of this allelic variant, perhaps because of differences in cell lines, transfection efficiencies, and reporter vectors used (7,8,10). Overall, our data strengthen reports that associate postheparin hepatic lipase activity with the LIPC –514C>T polymorphism (4,7,9). Recently, a prospective cohort study found that the TT genotype had increased susceptibility to CHD in sedentary or moderately physically active subjects but not among the vigorously active (21). Individuals carrying the LIPC –514T allele had higher postheparin LPL activity at baseline and after exercise training. We have reported earlier higher postheparin LPL activity in blacks in the sedentary state (22) and that increased LPL activity was associated with an improved lipoprotein-lipid profile in response to an exercise training program (13). Here we report that the TT homozygotes had 25% higher LPL activity after exercise training than the CC homozygotes. The increase in LPL activity after endurance exercise training in combination with the higher HDL cholesterol observed in the TT homozygotes could impact CHD risk. Hepatic lipase deficiency modifies the lipoprotein profile. It has been related to increased plasma cholesterol and trigylceride levels and mass redistribution within HDL particles (2). The most consistent finding in hepatic lipase deficiency is increased HDL2. The LIPC –250G>A variant, which is in complete linkage disequilibrium with the LIPC –514C>T, also leads to decreased hepatic lipase activity in the A allele carriers and to buoyant LDL particles and high HDL cholesterol (4). We found associations between the LIPC –514C>T polymorphism and the lipoprotein profile in the sedentary state, with higher HDL cholesterol and apoA-1 levels in the TT homozygotes. Although there were no significant associations with other lipoproteins, the association for HDL cholesterol levels remained significant in the trained state. Increased risk of atherosclerosis has been associated with the LIPC –514T allele, and CC homozygotes benefit the most from intensive lipid-lowering therapy (4,23). This study is the first to examine the associations between the LIPC –514C>T genotypes and Si and the responses of postheparin lipase to an exercise training intervention. The LIPC –514C>T genotypes showed associations with Si and postheparin hepatic lipase activity after exercise training. The enhanced Si after exercise training, primarily in the CC homozygotes, was associated with higher postheparin hepatic lipases activity. Remarkably, these Si differences appeared only in response to exercise training. The second European Atherosclerosis Research Study reported that T allele carriers have the lowest glucose tolerance (24). Recently, the LIPC-205G>A polymorphism, which is in complete linkage disequilibrium with the LIPC –514C>T, has been reported to predict the conversion from impaired glucose tolerance to type 2 diabetes in a 3-year follow-up lifestyle intervention (25). The mechanisms behind the association of the LIPC –514C>T polymorphism and Si are unclear. Changes in blood lipids in response to decreased postheparin hepatic lipase activity and increased postheparin LPL activity may accompany changes in intramyocellular lipid storage, affecting Si (26). Several regulatory elements have been identified in the rat LIPC promoter, and consensus analysis with the human sequence suggests that the LIPC –514C>T variant may be in a DNA motif containing the sequences necessary for insulin/glucose responses. Insulin regulation of the LIPC gene could be mediated by either upstream stimulatory factor or sterol regulatory element–binding protein-1c transcription factors, which bind to the E-box motif located in the LIPC promoter region at –514 bp, although this has not been demonstrated (9). One could speculate that human variation in Si response to exercise training associated with the LIPC genotype is the consequence of transcriptional effects on the LIPC gene by insulin and the binding (or lack of) of transcription factors to the E-box motif. Finally, the present study suggests that regular exercise may not influence the lipoprotein profile or improve Si at the same rate for all individuals and that the efficacy of regular exercise could be related in part to the LIPC –514C>T genotype. C allele carriers may not only have more clinical benefit from intensive lipid-lowering therapy, as reported (4), but are more likely to benefit from an exercise training program. The improvement in Si with regular exercise in individuals with the LIPC –514C allele has significant clinical applications due to its high frequency in various populations (4,5,7). Arguably, screening for T allele carriers may allow the identification of subjects at elevated risk requiring individualized therapeutic strategies to decrease cardiovascular and metabolic disease risks. In summary, results from the HERITAGE Family Study indicate that the C allele at –514 in the promoter region of the LIPC gene is associated with higher postheparin hepatic lipase activity and better Si response to regular exercise. The benefits on Si from an exercise program could be of considerable importance in the general population given the high frequency of the LIPC –514C allele.
The HERITAGE Family Study is supported by National Heart, Lung, and Blood Institute Grants HL-45670 (to C.B.), HL-47323 (to A.S.L.), HL-47317 (to D.C.R.), HL-47327 (to J.S.S.), and HL-47321 (to J.H.W.). A.S.L. is partially supported by the Henry L. Taylor endowed Professorship in Exercise Science and Health Enhancement, and C.B. is partially supported by the George A. Bray Chair in Nutrition. Gratitude is expressed to Dr. Jack H. Wilmore for the critical reading of the manuscript and his comments. We thank Anik Boudreau for her expert contribution to the single nucleotide polymorphism genotyping. Thanks are expressed to Nina Laidlaw for her editorial support. Received for publication July 26, 2004 and accepted in revised form April 1, 2005
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