Hepatic lipase gene -514C>T variant is associated with exercise training-induced changes in VLDL and HDL by lipoprotein lipase

Abstract

Our objective was to test the hypothesis that a common polymorphism in the hepatic lipase (HL) gene (LIPC -514C>T, rs1800588) influences aerobic exercise training-induced changes in TG, very-low-density lipoprotein (VLDL), and high-density lipoprotein (HDL) through genotype-specific increases in lipoprotein lipase (LPL) activity and that sex may affect these responses. Seventy-six sedentary overweight to obese men and women aged 50–75 yr at risk for coronary heart disease (CHD) underwent a 24-wk prospective study of the LIPC -514 genotype-specific effects of exercise training on lipoproteins measured enzymatically and by nuclear magnetic resonance, postheparin LPL and HL activities, body composition by dual energy x-ray absorptiometry and computer tomography scan, and aerobic capacity. CT genotype subjects had higher baseline total cholesterol, HDL-C, HDL₂-C, large HDL, HDL particle size, and large LDL than CC homozygotes. Exercise training elicited genotype-specific decreases in VLDL-TG (−22 vs. +7%; P < 0.05; CC vs. CT, respectively), total VLDL and medium VLDL, and increases in HDL-C (7 vs. 4%; P < 0.03) and HDL₃-C with significant genotype×sex interactions for the changes in HDL-C and HDL₃-C (P values = 0.01–0.02). There were also genotype-specific changes in LPL (+23 vs. −6%; P < 0.05) and HL (+7 vs. −24%; P < 0.01) activities, with LPL increasing only in CC subjects (P < 0.006) and HL decreasing only in CT subjects (P < 0.007). Reductions in TG, VLDL-TG, large VLDL, and medium VLDL and increases in HDL₃-C and small HDL particles correlated significantly with changes in LPL, but not HL, activity only in CC subjects. This suggests that the LIPC -514C>T variant significantly affects training-induced anti-atherogenic changes in VLDL-TG, VLDL particles, and HDL through an association with increased LPL activity in CC subjects, which could guide therapeutic strategies to reduce CHD risk.

abnormal plasma lipoproteins and their subclasses, specifically high levels of total cholesterol (TC), total low-density lipoprotein (LDL) cholesterol, small LDL, triglycerides (TG), very-low-density lipoprotein (VLDL) cholesterol, and intermediate-density lipoproteins (IDL), and low levels of high-density lipoprotein (HDL) cholesterol are risk factors for coronary heart disease (CHD) (10, 17). The metabolism of these lipoproteins by the enzymes hepatic lipase (HL) and lipoprotein lipase (LPL) affects their atherogenicity. HL catalyzes IDL to LDL, large LDL to small LDL, and large HDL to small HDL, resulting in smaller, denser, more atherogenic particles, while LPL hydrolyzes TG in chylomicrons and VLDL to lower TG levels and mediates the formation of large HDL to directly raise HDL-C levels and reduce CHD risk (11, 20). Moderate-intensity aerobic exercise training decreases TG and increases HDL-C with smaller effects on TC and LDL-C unless there is concomitant weight loss or reduced dietary fat intake (23). Several studies confirm that the anti-atherogenic effects of exercise training on HDL, VLDL, and LDL subclasses (16, 18) are mediated by increases in LPL and reductions in HL activity (4, 12, 25) and that some of these changes are influenced by genetic variants (4, 12, 23–25).

The commonly observed heterogeneity in the lipoprotein-lipid responses to exercise training is due to variations in the intensity and duration of the training, age, sex, changes in body composition and diet, as well as genetic effects on lipoprotein metabolism (5, 15, 23). One gene affecting lipoprotein metabolism is the HL (LIPC) gene that is located on chromosome 15q21 and has several polymorphisms in the proximal promoter region (6, 8). A single nucleotide polymorphism (SNP, rs1800588) located 557 base pairs upstream of the 5′-translation start site is a tag SNP marking the promoter of the LIPC gene (www.hapmap.org). This is traditionally identified as LIPC -514 C>T (or -480 C>T, rs1800588) and is in almost-complete linkage disequilibrium with other LIPC promoter SNPs, including -250G>A (rs2070895), -710T>C (rs1077634), and -763A>G (rs1077835) (8). These polymorphisms account for 20–30% of the variation in HL activity (29). The -514T allele is associated with lower HL activity, higher HDL-C and HDL₂-C, increased large HDL and large-LDL levels, and larger HDL and LDL particle sizes (8, 11, 28). Previous studies suggest that the LIPC polymorphisms might be useful for identifying women with higher HDL-C (9) and subjects more likely to improve lipoprotein profiles and insulin sensitivity in response to training (25), statin therapy (28), or dietary modification (21, 22). This study tested the hypothesis that the LIPC -514C>T polymorphism influences training-induced changes in TG, VLDL, and HDL lipoprotein lipids and particles through genotype-specific changes in HL and/or LPL activity and that sex affects these responses.

METHODS

Subjects were part of a University of Maryland College Park and Baltimore Institutional Review Board approved study investigating the effects of endurance exercise training and genetic polymorphisms on plasma lipoprotein-lipid levels. Potential volunteers responding to media advertisements were initially screened via telephone to assess their eligibility. Subjects were informed of the requirements of the study and provided written consent. One hundred seventy-two nonsmoking, sedentary Caucasian subjects underwent medical evaluation for entry, which included blood sampling in the morning after a 12-h overnight fast and then 2 h after ingesting 75 g of glucose to assess eligibility. Subjects with a body mass index >37 kg/m², blood pressure >160/90 mmHg on three occasions, hematocrit <35%, TG >400 mg/dl, fasting glucose >126 mg/dl or 2-h glucose >200 mg/dl, or on medication affecting lipid or glucose metabolism other than hormone replacement therapy were excluded. One hundred subjects qualified for the study (58 women, 42 men); they had no significant findings on physical examination that would preclude exercise training, at least one National Cholesterol Education Program (11a) lipid abnormality, and a maximal graded exercise test without evidence of cardiovascular, musculoskeletal or pulmonary symptoms, ECG changes, or diseases contraindicating participation in an exercise training program (1). All women were postmenopausal, and they remained on oral estrogen alone (n = 10), estrogen/progesterone (n = 10) or another estrogen preparation (n = 2), or off hormone therapy (n = 20) throughout the study. Twenty-four subjects (24%: 8/42 men, 16/58 women) dropped out due to an inability to exercise 3 days/wk, follow dietary guidelines, maintain body weight, or complete research testing. Data analysis was performed on the 76 subjects (34 men and 42 women) who completed all study requirements. Some of the body composition, V̇o_{2 max}, and lipid results, but not the effects of LIPC genotype or postheparin lipase data, were published previously (15, 16).

Dietary stabilization.

To control for the confounding effects of dietary and weight changes during training that may affect lipid responses, subjects completed 6 wk of dietary instruction and weight stabilization according to American Heart Association Dietary Guidelines prior to baseline testing (19). Subjects were monitored for dietary and weight compliance during the training intervention by measuring body weight weekly and collecting food records monthly to ensure compliance. Caloric intake was maintained constant during training.

Baseline testing.

After dietary stabilization, fasting plasma TG, TC, HDL-C, HDL₂-C, HDL₃-C, and LDL-C levels were determined after a 12-h overnight fast by conventional methods on three separate days and averaged to calculate baseline levels (16). Lipoprotein subclasses and particle sizes were measured by NMR spectroscopy, which provides an accurate and reproducible measure of the numbers of atherogenic particles within each lipoprotein subclass to assess the effects of exercise training on the cardiovascular disease risk associated with these particles (17). Total postheparin lipolytic activity (PHLA) was measured in plasma obtained 10 min after intravenous administration of 60 IU heparin/kg body wt using a glycerol tri[1-¹⁴C]oleate substrate emulsified with lecithin for 60 min at 37°C. ¹⁴C free fatty acids were extracted and counted, and HL activity (nmol·min⁻¹·ml⁻¹) was defined as the activity remaining in postheparin plasma after incubation with a monoclonal antibody that selectively inhibits LPL (5D2, gift from John Brunzell, MD) (7). Postheparin LPL activity was the difference between PHLA and HL activity. A human PHLA control pool stored in 0.2-ml aliquots at −80°C had a coefficient of variation (CV) of 9.2% for PHLA and 8.1% for HL activity in 20 previous assays. Baseline and final samples for a given individual were analyzed in the same assay, and the 18 assays for this study had a mean interassay CV of 8.3% for PHLA and 7.5% for HL. Assays with a pool CV for PHLA or HL >10% were repeated, and unknowns were adjusted by the interassay pools. Body weight was measured using a calibrated beam scale, total body fat was measured using dual energy x-ray absorptiometry (DPX-L, Lunar Corp, Madison, WI), and visceral fat was quantified midway between L4–5 by computerized tomography (15). A graded exercise treadmill test was performed to measure V̇o_{2 max}, (15) and V̇o_{2 max} was considered attained if there was no further increase in oxygen uptake with an increase in workload (<150 ml/min), heart rate exceeded age-predicted maximum, and respiratory exchange ratio was >1.15.

Exercise training intervention.

Subjects completed 24 wk of training, initially exercising 3 times/wk for 20 min at 50% V̇o_{2 max}, and gradually increasing training duration and intensity to 40 min at 70% V̇o_{2 max} (15). Subjects were required to complete >75% of their training sessions (average 92%) with weight loss <3 kg.

Final testing.

Subjects were weight and diet stabilized for 3 wk and continued exercise training until all testing was completed. Lipoproteins and lipase activities after training were assessed 24–36 h after a usual exercise training session.

Genotyping.

The LIPC -514C>T polymorphism was genotyped by PCR using unique sequence oligonucleotide primers: forward, 5′-TACTTTTCAGTCCTCTACACAGC-3′ and reverse, 5′-AGTCAGGCTCTTACCTGGTTTCA-3′. Genotypes were determined by digestion of amplification products with NlaIII, resolution of fragments on 2% agarose gels, and visualization of ethidium bromide-stained fragments by ultraviolet transillumination. Controls were sequence confirmed individuals of each genotype run on the same gel.

Statistical analysis.

There were no subjects with the TT genotype, thus all comparisons were between CC and CT genotype groups. Genotype frequencies were evaluated by an exact test of Hardy-Weinberg equilibrium. Student t-tests showed sex and hormone effects on lipoprotein levels (data not shown), therefore variables were adjusted for age and sex to the mean of the total group and for hormone therapy status where the variables were adjusted to not taking hormones. Differences by genotype at baseline were tested using the linear model <baseline variable> ∼ <age> + <hormone therapy status> + <sex> + <genotype> + <genotype×sex>. The associations between genotype and the relative changes in the dependent variables in response to training used the linear model <ln(post-training variable)> ∼ <ln(pretraining variable)> + <age> + <hormone status> + ln(change V̇o_{2 max}) + <genotype> + <sex> + <genotype×sex>, where ln(·) indicates natural logarithm. An alternate model was used for body fat, HDL₂-C, large HDL, large LDL, LPL activity, and HL activity since the data distribution indicated absolute rather than relative changes were the appropriate dependent variable: <change> ∼ <age> + <hormone status> + ln(change V̇o_{2 max}) + <genotype> + <sex> + <genotype×sex>. Dummy variables (hormone replacement therapy status, genotype, and sex) were assigned using effects coding and P values computed using partial-F tests on the main effect or the main effect and interaction term when important interactions were present. For all models, outlying and influential data were identified and eliminated. Primary outcome variables defined a priori do not require correction for multiple comparisons (3). Data are means ± SE. Statistical significance is defined as P ≤ 0.05.

RESULTS

Genotype distributions were in Hardy Weinberg equilibrium in all 76 subjects (CC = 51, CT = 25, and TT = 0; P = 0.20), men (CC = 24, CT = 10, TT = 0; P = 0.31), and women (CC = 27, CT = 15, TT = 0; P = 0.16). The -514T allele frequency (16%) is similar to reported values in Caucasians (14).

Baseline lipoprotein lipids and lipases by genotype and sex.

The subjects ranged from overweight to obese and were sedentary, with slightly elevated TC, LDL-C and TG levels, low-normal HDL-C and low HDL₂-C, and large HDL levels (Tables 1, 2). The CC and CT genotype groups were of similar age, body composition, and sex distribution, but the CT group had slightly lower V̇o_{2 max} (P = 0.02). Since ∼50% of females with each genotype were taking hormones, we adjusted all outcomes to no hormone use, thus controlling lipoprotein and lipase levels across sexes. This analysis showed the CT group had higher TC, HDL-C, and HDL₂-C, large LDL and HDL, and greater HDL particle size (P ≤ 0.05) than the CC group (Tables 1, 2). There were significant sex×genotype effects for TG (P = 0.02), HDL₂-C (P = 0.009), large HDL (P = 0.006), HDL particle size (P = 0.01), VLDL-TG (P < 0.03), large VLDL (P = 0.05), and total VLDL (P = 0.02), with CT women having higher HDL subclass levels and HDL particle size, as well as lower VLDL particle number, or less atherogenic lipid profiles, than CC women, while the converse existed for men. There also was a significant sex×genotype effect on LPL activity, with higher levels in CT than CC women and lower levels in CT than CC men (P = 0.01 for the interaction).

Table 1.

Subject characteristics, lipids, and postheparin lipase activity - baseline values and responses to aerobic exercise training

	Baseline Values				Response to Exercise Training
		LIPC genotype				LIPC genotype
Characteristic	Overall* (n = 76)	CC (n = 51)	CT (n = 25)	P	Overall* (n = 76)	CC (n = 51)	CT (n = 25)	P
Age, yr	58.0 ± 0.7	58.3 ± 0.9	57.5 ± 1.1
Women/Men	42/34	27/24	15/10
Females HRT, %	52	52	53
Weight, kg	83 ± 1.4	82 ± 1.6	86 ± 2.4		−1.2 ± 0.3%§	−1.0 ± 0.4%*	−1.8 ± 0.5%‡
BMI, kg/m2	28.3 ± 0.4	28.0 ± 0.5	28.8 ± 0.9		−1.3 ± 0.3%§	−1.0 ± 0.4%*	−1.9 ± 0.5%§
Body fat, %	36 ± 0.7	36 ± 0.9	38 ± 1.1		−1.5 ± 0.24§	−1.5 ± 0.29§	−1.5 ± 0.43‡
Visceral fat, cm2	132 ± 4	129 ± 5	138 ± 8		−7 ± 1.8%§	−7 ± 2.2%‡	−8 ± 3.3%*
V̇o2max, ml · kg−1 · min−1	25.5 ± 0.4	26.1 ± 0.5	24.2 ± 0.7	0.02
V̇o2max, l/min	2.10 ± 0.03	2.13 ± 0.04	2.03 ± 0.07		15.0 ± 0.4%§	14.9 ± 0.5%§	15.8 ± 0.6%§
Total cholesterol, mg/dl	211 ± 3	206 ± 4	220 ± 5	0.05	−1 ± 1.1%	0 ± 1.4%	−2 ± 1.5%
Triglycerides, mg/dl	152 ± 7	149 ± 9	156 ± 13		−6 ± 3%*	−7 ± 3%*	−2 ± 6%
HDL-C, mg/dl	44 ± 1.2	43 ± 1.4	48 ± 2.0	0.03	6 ± 1.1%§	7 ± 1.4%§	4 ± 1.8%*	0.03
HDL2-C, mg/dl	2.9 ± 0.5	2.2 ± 0.5	4.5 ± 1.0	0.05	0.9 ± 0.3†	0.6 ± 0.3	1.5 ± 0.8
HDL3-C, mg/dl	42 ± 0.9	41 ± 1.2	43 ± 1.4		5 ± 1.1%§	6 ± 1.3%§	2 ± 1.9%	0.03
LDL-C, mg/dl	134 ± 3	131 ± 4	140 ± 5		−1 ± 1.5%	1 ± 2.0%	−5 ± 2.1%*
HL activity, nmol · min−1 · ml−1	248 ± 10	260 ± 13	223 ± 14	(0.07)	−4 ± 6	7 ± 7	−24 ± 8†	0.01
LPL activity, nmol · min−1 · ml−1	189 ± 7	185 ± 7	197 ± 14		14 ± 7*	23 ± 8†	−6 ± 11	0.05

Values are means ± SE and are adjusted by age, sex, and hormone replacement therapy (HRT). SI unit conversion factors: To convert Triglycerides from mg/dL to mmol/l multiply by 0.0113. BMI, body mass index; HDL and LDL, high- and low-density lipoproteins, respectively. To convert cholesterol from mg/dL to mmol/l, multiply by 0.026.

^*P ≤ 0.05,

^†P ≤ 0.01,

^‡P ≤ 0.005,

^§≤ 0.001 for within-group responses to exercise training.

Table 2.

NMR measures of lipoprotein subclass particle numbers and baseline values and responses to aerobic exercise training

	Baseline Values				Response to Exercise Training
		LIPC genotype				LIPC genotype
Characteristic	Overall* (n = 76)	CC (n = 51)	CT (n = 25)	P	Overall* (n = 76)	CC (n = 51)	CT (n = 25)	P
VLDL-TG, mg/dl	112 ± 7	115 ± 8	105 ± 12		−14 ± 6%*	−22 ± 6%§	7 ± 12%	0.05
Large VLDL, nmol/l	5 ± 0.6	6 ± 0.7	5 ± 0.9		−30 ± 13%†	−40 ± 12%‡	−3 ± 33%
Med. VLDL, nmol/l	32 ± 2.0	32 ± 2.3	32 ± 3.8		−19 ± 6%‡	−29 ± 7%§	8 ± 10%	0.01
Small VLDL, nmol/l	44 ± 2.1	41 ± 2.5	48 ± 3.6		5 ± 5%	4 ± 5%	7 ± 11%
Total VLDL, nmol/l	79 ± 3	78 ± 3	80 ± 6		−3 ± 4%	−9 ± 4%*	10 ± 8%	0.03
VLDL size, nm	51 ± 1.3	53 ± 1.7	48 ± 1.5	(0.09)	−5 ± 1.8%†	−6 ± 2.2%†	−1 ± 3.0%
Large HDL, μmol/l	4.4 ± 0.3	3.9 ± 0.4	5.5 ± 0.5	0.02	1.1 ± 0.20§	1.2 ± 0.26§	0.7 ± 0.27†
Med. HDL, μmol/l	5 ± 0.6	6 ± 0.7	5 ± 0.9		−18 ± 14%	−19 ± 18%	−17 ± 20%
Small HDL, μmol/l	24 ± 0.7	23 ± 0.8	25 ± 1.2		4 ± 2.2%	4 ± 2.5%	3 ± 4.3%
Total HDL, μmol/l	34 ± 0.6	33 ± 0.7	35 ± 1.0	(0.08)	3 ± 0.8%§	3 ± 1.0%†	3 ± 1.5%*
HDL size, nm	8.66 ± 0.04	8.60 ± 0.04	8.78 ± 0.06	0.02	1.2 ± 0.20%§	1.2 ± 0.27%§	1.0 ± 0.27%‡
IDL, nmol/l	44 ± 3	44 ± 4	45 ± 5		12 ± 12%	4 ± 14%	30 ± 19%
Large LDL, nmol/l	386 ± 26	349 ± 31	461 ± 46	0.04	32 ± 17	49 ± 20*	−6 ± 29
MS-LDL, nmol/l	223 ± 12	236 ± 15	196 ± 20	(0.09)	−5 ± 3%	−7 ± 4%	−2 ± 5%
VS-LDL, nmol/l	775 ± 47	810 ± 60	703 ± 71		−10 ± 4%*	−11 ± 5%*	−6 ± 8%
Total LDL, nmol/l	1401 ± 46	1404 ± 58	1393 ± 76		−4 ± 1.8%*	−4 ± 2.2%	−5 ± 3.1%
LDL size, nm	20.7 ± 0.09	20.6 ± 0.11	20.8 ± 0.15		0.7 ± 0.3%*	0.9 ± 0.3%†	0.2 ± 0.5%

Values are means ± SE and are adjusted by age, sex, and HRT. VLDL, very-low-density lipoprotein; MS, medium small; VS, very small.

^*P ≤ 0.05,

^†P ≤ 0.01,

^‡P ≤ 0.005,

^§P ≤ 0.001 for within-group responses to exercise training.

V̇o_{2 max} and body composition responses to exercise training.

In the total group, training increased V̇o_{2 max} max (l/min) by 15%, and there were small, but significant reductions in body weight (1.2%) and body fat (1.5%) and a 7% decrease in visceral fat (all P values <0.001). V̇o_{2 max} (l/min) increased by 14.9% in the CC group and 15.8% in the CT group (P values <0.0001), and changes did not differ by genotype or sex. The reductions in body weight, body fat, and visceral fat were significant and of comparable magnitude in the CC and CT subjects (Table 1).

Lipoprotein-lipid, HL, and LPL responses to exercise training.

In the entire population, exercise training resulted in significant anti-atherogenic reductions in total LDL, very small LDL, and VLDL-TG and large VLDL particles, and increases in HDL-C, large HDL particles, and LDL subclass particle size generally due to improvements in lipoprotein subclass profiles in the CC homozygotes (Tables 1, 2). There were significant genotype-specific lipoprotein effects of exercise training that favored the CC group for increases in HDL-C and HDL₃-C and decreases in VLDL-TG, medium VLDL, and total VLDL (P values = 0.01–0.05; Tables 1, 2). There were significant sex×genotype interactions for HDL-C (P = 0.01) and HDL₃-C (P = 0.02) that favored the CC men, such that the increase in HDL-C and HDL₃-C were greater in the CC than CT men (P values <0.05), but not the women. In contrast, the lipoprotein changes in the CT group were minimal. There was an increase in postheparin LPL activity in the entire population due to a 23% increase (P < 0.01) in the CC homozygotes, with no change in the CT group (−6%, P = 0.60). There was a significantly greater increase in LPL activity in the CC compared with the CT women (P < 0.04), but there was no difference between the CC and CT men (P = 0.47) or a sex×genotype interaction. HL activity decreased 24% (P < 0.01) in the CT group, but did not change in the CC homozygotes or the entire population, and there was no sex×genotype effect (Fig. 1). Overall, the exercise training intervention reversed the lipoprotein profiles of the CC homozygotes to levels comparable to the baseline lipoprotein profiles of the CT group (data not shown).

Fig. 1.

The absolute changes in postheparin lipoprotein lipase (LPL) and hepatic lipase (HL) activity after aerobic exercise training overall and by genotype group. *P ≤ 0.05, †P ≤ 0.01.

Associations between changes in lipoproteins and lipase activities after exercise training.

In the entire population, the absolute change in LPL activity with exercise training correlated with relative (%) changes in the primary endpoints of plasma TG (r = −0.25, P < 0.05), VLDL-TG (r = −0.41, P = 0.001), HDL-C (r = 0.26, P < 0.05), HDL₃ -C (r = 0.33, P = 0.01), and several VLDL and HDL subclasses. This was primarily due to significant associations for LPL changes with TG (r = −0.34, P = 0.02), VLDL-TG (r = −0.51, P < 0.001), medium VLDL (r = −0.38, P = 0.02), VLDL size (r = −0.45, P = 0.003), HDL₃-C (r = 0.38, P < 0.02), and small HDL (r = 0.33, P = 0.03), with a trend for HDL-C (r = 0.28, P = 0.08) only in the CC, but not the CT group. For HL activity, there were only significant associations with percent change in large LDL in the CC (r = −0.33, P < 0.04) and CT (r = −0.28, P < 0.02) groups and HDL-C (r = −0.42, P < 0.05) in the CT group. There was no association between changes in the lipoproteins or lipases and changes in body weight or visceral fat area.

DISCUSSION

The magnitude of the anti-atherogenic effects of exercise training on VLDL, HDL, and LDL subclasses (16, 18) is affected by metabolic, lifestyle (exercise, weight loss, diet, smoking, etc.), and genetic factors (5, 15, 23, 25). The results of this study show that the LIPC -514C>T polymorphism influences exercise training-induced reductions in plasma VLDL and VLDL-TG and increases in HDL particle number and that the increases in HDL are genotype and sex specific, favoring the CC male homozygotes. Additionally, we found significant associations between the changes in LPL and the changes in TG, most of the VLDL subfractions, HDL₃-C, and small HDL particle number only in the CC homozygote subjects. In contrast, the changes in TG, VLDL, and HDL lipoprotein particles in subjects carrying the -514T allele correlate poorly with changes in HL and LPL activity. Thus, contrary to the strong associations between LIPC polymorphisms and changes in HL activity and lipoproteins with drug (13, 28) and dietary (21, 22) therapy in the CC genotype, the -514C>T genotype-specific effect of exercise training on lipoprotein metabolism occurs only in CC homozygotes and appears to be mediated by an increase in LPL activity.

The TG lipase gene family of HL, LPL, endothelial lipase (EL), and pancreatic lipase (PL) affect TG metabolism and, except for PL, also affect HDL metabolism (20, 27). Our results confirm that the -514T allele is associated with higher baseline levels of HDL-C, HDL₂-C, large HDL and large LDL subclasses (9), higher LPL in women, and a trend for lower HL activity (11, 29). This suggests that the lipoprotein phenotype in the CT subjects may be mediated by higher LPL activity and lower HL activity. The training-induced improvements in the lipoprotein phenotype of the CC homozygotes correlated with changes in LPL, but not HL, activity. However, the LPL gene is on chromosome 8 and the HL gene is on 15; thus the -514C>T variant may contribute to the training-induced increase in LPL activity through trans effects on functional polymorphisms located on other chromosomes (11, 14, 26, 29). This is consistent with the theory that this polymorphism is associated with lower HL by directly affecting HL expression or through linkage disequilibrium with functional polymorphisms on other genes that regulate the effects of HL and LPL on lipoprotein metabolism (14).

The exercise training-induced increase in LPL was associated with reductions in plasma TG, VLDL-TG, VLDL particle numbers and increases in HDL₃-C and some HDL subclass particle numbers measured by NMR technology only in the CC homozygotes, but again there were minimal lipoprotein changes in CT heterozygotes. These improvements in TG and HDL lipoproteins correlated with changes in LPL only in the CC homozygotes and not with HL activity in CT or CC subjects. In a recent study, Seip et al. (24) showed the APOE haplotypes ϵ2/ϵ3 and ϵ3/ϵ4 were associated with an exercise training-induced increase in LPL activity, and the ϵ3/ϵ3 haplotype was associated with a decrease in LPL that was independent of sex, while the ϵ2/ϵ3 haplotype was associated with a higher HL activity in men, but not in women, regardless of training status. This suggests the APOE genotype interacts with sex to affect postheparin lipase activities, lipoprotein lipids, and their responses to exercise training. Similar to our findings, training-induced changes in LPL, but not HL, correlated inversely with changes in TG and directly with HDL in the Heritage Family Study (4, 25), but only HDL₂-C increased in black subjects while TG, total cholesterol, and ApoB decreased and HDL-C and HDL₃-C increased significantly in white subjects. There also was a greater increase in insulin sensitivity with exercise training in CC homozygotes than in the CT subjects in the Heritage Study (25). Collectively, our results and the Heritage Family Study suggest that genotype-specific responses to exercise training may reduce the dyslipidemia, insulin resistance, and glucose intolerance observed in older sedentary, overweight/obese CC homozygotes. Similar to findings in our study, lipid-lowering therapy in the Familial Atherosclerosis Treatment Study (28) produced larger increases in HDL-C levels, LDL particle buoyancy, and LDL particle size in CC homozygotes, but these changes correlated with decreases in HL activity, not increases in LPL, a finding that is opposite to the association between the changes in lipoproteins and LPL observed in our study. Other studies also demonstrate that the LIPC genotype affects HL activity to modulate HDL and LDL subclass distribution and catabolism (8, 11, 14, 29), as well as dyslipidemia associated with central obesity (7) and androgen therapy (13). These metabolic effects could be altered by changes in body weight and/or dietary fat intake during training, as lower fat diets in CT subjects are associated with higher HDL and HDL particle size (21, 22). Central obesity, hormone therapy, and sex in our study subjects also could have affected the lipoprotein, HL, and LPL responses to exercise training (11, 23, 29), but a strength of our study is that the subjects were their own controls and their medications, diet, and body weight were carefully monitored for consistency during the exercise training program, and changes in these variables were controlled in the analyses. The diet standardization and weight stability prior to and throughout the study and the progressive, standardized training program minimized the confounding effects of differences in diet composition, body weight, and regional fat distribution between genotype groups on lipid metabolism.

A limitation of this study is the small sample, which probably reduced the statistical power to detect all potential genotype interactions with lipid metabolism, exercise training and sex contributed to the absence of TT homozygotes, and prevented the assessment of whether the genotype-specific lipoprotein responses to exercise training are dominant, recessive, or dose dependent. Despite these constraints, the results support our hypothesis that exercise training would elicit significant anti-atherogenic, genotype-specific effects on postheparin lipase activities to lower VLDL-TG and total VLDL and raise HDL-C and HDL₃-C consistent with the strong associations between LPL activity and plasma TG and HDL observed after exercise training (4) and in endurance-trained athletes (12). Furthermore, the improvements in HDL-C were greatest in the men, independent of age and changes in body composition.

Thus the LIPC -514C>T polymorphism contributes to baseline heterogeneity in plasma lipoprotein-lipid levels and postheparin lipase activities among men and women and is associated with lipoprotein responses to exercise training in older, overweight to obese, sedentary, Caucasian adults. These training-induced lipid responses occur only in -514 CC homozygotes through mechanisms involving LPL, but not HL, on TG and HDL metabolism. Furthermore, exercise training ameliorated the atherogenic effect of the -514C allele on lipid metabolism, improving the CC group's lipid profiles to levels comparable to those of the CT subjects and resulting in greater sex×genotype-specific improvements for HDL, primarily in the CC men. These findings support the potential for genetic screening to target CC men for personalized exercise therapy that may reduce risk for CHD by raising HDL and reversing their dyslipidemia.

GRANTS

This research was supported by National Institutes of Health Grants AG-17474, AG-15389, AG-00268, DK-46204, AG-18408, AG-20116, P30 AG-028747, P30 DK-072488; the Baltimore VA Geriatric Research, Education and Clinical Center; and the Medical Research Service of the Department of Veterans Affairs.

DISCLOSURES

No conflicts of interest, financial or otherwise, are declared by the authors.

AUTHOR CONTRIBUTIONS

Author contributions: T.E.B., A.H., D.A.P., R.E.F., J.M.H., and A.P.G. conception and design of research; T.E.B., A.H., D.A.P., R.E.F., and J.M.H. performed experiments; T.E.B., A.H., R.L.P., J.M.H., and A.P.G. analyzed data; T.E.B., A.H., D.A.P., R.E.F., R.L.P., J.M.H., and A.P.G. interpreted results of experiments; T.E.B., A.H., D.A.P., R.L.P., J.M.H., and A.P.G. drafted manuscript; T.E.B., A.H., D.A.P., R.L.P., J.M.H., and A.P.G. edited and revised manuscript; T.E.B., A.H., D.A.P., R.E.F., R.L.P., J.M.H., and A.P.G. approved final version of manuscript; R.L.P. prepared figures.