Less pronounced response to exercise in healthy relatives to type 2 diabetic subjects compared with controls

Abstract

Healthy first-degree relatives with heredity of type 2 diabetes (FH+) are known to have metabolic inflexibility compared with subjects without heredity for diabetes (FH−). In this study, we aimed to test the hypothesis that FH+ individuals have an impaired response to exercise compared with FH−. Sixteen FH+ and 19 FH− insulin-sensitive men similar in age, peak oxygen consumption (V̇o_{2 peak}), and body mass index completed an exercise intervention with heart rate monitored during exercise for 7 mo. Before and after the exercise intervention, the participants underwent a physical examination and tests for glucose tolerance and exercise capacity, and muscle biopsies were taken for expression analysis. The participants attended, on average, 39 training sessions during the intervention and spent 18.8 MJ on exercise. V̇o_{2 peak}/kg increased by 14%, and the participants lost 1.2 kg of weight and 3 cm waist circumference. Given that the FH+ group expended 61% more energy during the intervention, we used regression analysis to analyze the response in the FH+ and FH− groups separately. Exercise volume had a significant effect on V̇o_{2 peak}, weight, and waist circumference in the FH− group, but not in the FH+ group. After exercise, expression of genes involved in metabolism, oxidative phosphorylation, and cellular respiration increased more in the FH− compared with the FH+ group. This suggests that healthy, insulin-sensitive FH+ and FH− participants with similar age, V̇o_{2 peak}, and body mass index may respond differently to an exercise intervention. The FH+ background might limit muscle adaptation to exercise, which may contribute to the increased susceptibility to type 2 diabetes in FH+ individuals.

type 2 diabetes is a disease characterized by peripheral insulin resistance and failure of the pancreatic β-cells to compensate for the increased insulin need. Despite the identification of many loci linked to type 2 diabetes, they explain <20% of the observed heredity (9). Notably, individuals with a first-degree family history of type 2 diabetes (FH+) have a threefold higher risk of developing the disease compared with those individuals without a history (FH−) (19). FH+ individuals have reduced basal energy expenditure and decreased insulin sensitivity long before developing signs of clinical diabetes (8). FH+ individuals are further characterized by metabolic inflexibility (32), having lower carbohydrate oxidation in response to insulin and lower fat oxidation during a high-fat diet (10, 40).

These metabolic differences have been proposed to be dependent on primary defects in mitochondria (37), muscle fiber composition (22), lack of physical activity (41), and/or a sedentary lifestyle (11). Skeletal muscle is the main organ for insulin-mediated glucose disposal (4, 29), and regular exercise can prevent or postpone the development of type 2 diabetes in high-risk populations (5, 17, 18). Exercise increases insulin sensitivity (29), reducing the need for glucose-lowering drugs (2, 28), and is further known to increase skeletal muscle mitochondrial content and function in both nondiabetic and diabetic subjects (26). Interestingly, fat oxidation is related to insulin sensitivity in FH+ subjects (15). Fat oxidation does not increase after weight loss induced by low-calorie diet (3), but increases after an exercise intervention (7) in diabetic patients and overweight subjects. However, despite exercise intervention, differences in muscle ATPase activity (13), and glucose metabolism (25) remain in diabetic subjects, indicating that metabolic perturbations are difficult to reverse completely with exercise.

Our laboratory has previously reported decreased expression of mitochondrial genes and genes involved in fatty acid metabolism in skeletal muscle in insulin-sensitive FH+ individuals compared with FH− of a similar age, body mass index (BMI), and peak oxygen consumption (V̇o_{2 peak}) (6). In the present study, we aimed to test the hypothesis that a FH+ background impairs the response to an exercise intervention compared with FH− controls.

MATERIALS AND METHODS

Study cohort.

Fifty sedentary men (age 30-45 yr) were recruited, 24 with (FH+) and 26 without a first-degree relative with type 2 diabetes (FH−), as described earlier (6, 33). Briefly, before enrollment, all subjects underwent a physical examination, a 75-g oral glucose tolerance test (OGTT), and a maximal exercise test. The FH+ and FH− groups were similar in age, BMI, V̇o_{2 peak}, habitual activity, and glucose tolerance and insulin sensitivity (all with normal fasting glucose, OGTT, and homeostatic model assessment-insulin resistance). The study was approved by the local ethics committee at Lund University, and written, informed consent was obtained from all participants. Clinical characteristics of the study participants are given in Table 1. Of the included individuals, 17 FH+ and 19 FH− individuals completed the training program. The 14 participants not able to complete the study reported lack of time as the main reason for noncompliance (n = 12), in addition to minor injuries (n = 1) and moving from the area (n = 1). One FH+ individual was excluded from the analysis due to being >4 SD from the rest of the group in weight change. The FH− group included one and the FH+ group included two active smokers. Actiheart devices were used by 17 of the participants (9 FH+, 8 FH−) for 5 days to monitor physical activity level before the initiation of the intervention, as described earlier (6).

Table 1.

The clinical characteristics of the participants at the initiation of the study

	All		FH−		FH+
	Mean	SD	Mean	SD	Mean	SD	MWU P value
Age, yr	38.1	4.3	37.8	4.7	38.4	3.9	0.683
Weight, kg	93.7	11.4	94.8	10.2	92.4	12.8	0.271
BMI, kg/m2	28.7	2.9	29.0	2.9	28.4	2.8	0.367
Waist circumference, cm	99.6	8.0	101.0	7.8	98.1	8.2	0.161
Hip circumference, cm	105.0	5.6	106.1	4.9	103.8	6.3	0.082
Waist/hip ratio	0.95	0.04	0.95	0.05	0.95	0.04	0.832
FFM, %	76.7	5.3	75.7	4.6	78.0	5.8	0.172
V̇o2peak/kg, ml·kg−1·min−1	31.4	4.7	30.5	4.7	32.5	4.6	0.286
V̇o2peak/FFM, ml·kg FFM−1·min−1	41.0	5.0	40.4	5.3	41.7	4.6	0.481
Fasting plasma glucose, mM	4.3	0.5	4.3	0.6	4.3	0.4	0.707
2-h Glucose tolerance, mM	5.8	1.3	5.8	1.4	5.8	1.2	0.883
HbA1c, %	4.3	0.3	4.3	0.3	4.3	0.4	0.781
Fasting insulin, mU/ml	7.5	3.2	7.4	3.0	7.7	3.6	1.000
HOMA-IR ratio	1.44	0.65	1.43	0.65	1.45	0.67	1.000
HOMA-β, %	309.8	376.2	354.4	483.6	242.9	175.5	0.708
mtDNA/nDNA ratio	2,509	727	2,443	835	2,587	590	0.735

The P value describes the significance of difference between the participants without and with first-degree heredity of type 2 diabetes (FH− and FH+ groups, respectively) using the Mann-Whitney U-test (MWU). BMI, body mass index; FFM, fat-free mass; V̇o_2peak, peak oxygen consumption; HbA1c, glycosylated hemoglobin; HOMA-IR, homeostasis model assessment of insulin resistance; HOMA-β, homeostasis model of β-cell function; mtDNA, mitochondrial DNA; nDNA, nuclear DNA.

Exercise intervention.

The exercise intervention lasted 216 days (SD 26 days) and has been described earlier (30, 31). Briefly, the subjects were offered combined supervised group training 3 times per week for the entire intervention. One session of 1-h spinning class and two sessions of 1-h aerobics class were given weekly. During the spinning class, a specially designed cycle ergometer (Pulse, Pulse Fitness, Congleton, UK) was used, and the sessions were led by a certified instructor. The workload was individually adjusted by braking the wheel during cycling. The aerobics classes were conducted to music and led by certified instructors. The classes included a warm-up period (10 min), rhythmic aerobic training (15 min) mixed with strength exercises for arm, leg, abdominal, and back muscles (15 min), cool-down, and stretching exercises (10 min). Strength training was performed with the subject's own body weight as resistance, such as push-ups, crunches, sit-ups, and back extensions. Heart rate was monitored continuously during the spinning and aerobics classes by a Polar belt (Polar Fitness F1, POLAR), which was used to calculate exercise intensity and total energy expenditure, using the flex-heart rate method (16). In this method, we use the relation between the heart rate and the intensity of the training. The exercise volume (reported in MJ) was calculated by multiplying the intensity (in W) with time spent on exercise. The relative intensity of exercise was measured with heart rate reserve (HRR), in which the intensity is described in percentage of individual maximal working capacity. The participants were told to adhere to their normal diets during the study.

Muscle biopsy and sampling.

Muscle biopsies were taken before and after the exercise intervention from the right vastus lateralis muscle under local anesthesia (lidocaine 1%), using a 6-mm Bergström needle (Stille). The participants were instructed not to perform any vigorous exercise within 48 h before the biopsy and to fast from 10 PM the previous day. RNA was isolated using the RNeasy Fibrous Tissue Kit (Qiagen). Concentration and purity were measured using a NanoDrop ND-1000 spectrophotometer (ratio of 260- to 280-nm absorbance > 1.8 and ratio of 260- to 230-nm absorbance > 1.0) (NanoDrop Technologies, Wilmington, DE). No major signs of degradation were observed using agarose gel electrophoresis and Experion DNA 1K gel chips (Bio-Rad). Mitochondrial DNA content (mtDNA) was quantified using quantitative PCR, comparing the mitochondrial 16S and ND6 genes with the nuclear RNaseP gene. Plasma glucose was measured with the hexokinase method (Beckman Syncron CX System Chemistry), insulin with ELISA (Dako), and HbA1c was measured with HPLC (Mono S, GE Healthcare), as described earlier (6).

Expression analysis.

Synthesis of biotin-labeled cRNA and hybridization to the Affymetrix Custom Array NuGO-Hs1a520180 GeneChip (http://www.nugo.org) were performed according to the manufacturer's recommendation. The GeneChip contains 23,941 probe sets for interrogation. Images were analyzed using the GeneChip Operating System (Affymetrix) software. We used ENTREZ custom chip definition files (http://brainarray.mbni.med.umich.edu) for regrouping the individual probes into consistent probe sets and remap them to the sets of genes for Affymetrix Custom Array (NuGO-Hs1a520180), which resulted in a total of 16,313 genes. The data were filtered based on the MAS5.0 present/absent calls, which classifies each gene as expressed above background (present call) or not (marginal or absent call). The expression data were normalized using robust multiarray average (12). Data were analyzed for FH+ and FH− separately due to the difference in amount of exercise performed. A regression model was used to identify expression changes dependent on exercise volume. Genes with P < 0.05 were considered for further analysis. False discovery rate analysis was made in R (27) using the q-value package (36) with a false discovery rate acceptance of < 0.05.

Incremental maximal exercise test.

An incremental maximal exercise test was performed before and after the exercise intervention on a bicycle ergometer (Marquette Hellige Medical Systems 900 ERG, Milwaukee, WI). The initial workload was 50 W and increased by 15 W/min; pedaling rate was maintained at 60 rpm using both visual feedback and verbal encouragement. O₂ consumption, CO₂ production, and ventilation were measured breath by breath (Oxycon Mobile, Jaeger, Hoechberg, Germany). Heart rate was continuously monitored throughout the test (Polar T 61, POLAR, Oulu, Finland). The subjects were encouraged to exercise to exhaustion, and V̇o_{2 peak} was reached when the respiratory exchange ratio exceeded 1.10. The gas sensors were calibrated before each test with a certified gas mixture, and air flow was calibrated using a calibration syringe.

Statistics.

Differences between the groups were analyzed using nonparametric Mann-Whitney U-tests and Wilcoxon rank test, and P < 0.05 was considered statistically significant. Linear regression was used with starting value and exercise volume as predictors of the end value. For comparison of gene expression on the pathway level, the mean centroid method was used, estimating the mean expression of all genes in a pathway (20). Data were analyzed with SPSS 19.0 (SPSS, Chicago, IL) and Graphpad 5 (Graphpad software, La Jolla, CA). For pathway analysis, Webgestalt (42) was used, utilizing the Gene Ontology (GO) (1) and Kyoto Encyclopedia of Genes and Genomes (KEGG) (14) annotation databases.

RESULTS

Exercise increase V̇o_{2 peak} and decrease body weight and waist circumference.

During the 216 days of the exercise intervention, the average participant attended 39 training sessions of 1-h duration (range 11–107 sessions), expending 18.8 MJ by exercise (range 5.3–42.1 MJ). During the intervention, both V̇o_{2 peak}/kg and V̇o_{2 peak}/kg fat-free mass increased by 14% and 13% (both P < 0.001), respectively, for the group as a whole. The participants lost 1.2 kg of weight and 3 cm of waist circumference (P = 0.025 and P < 0.001, respectively), and increased their skeletal muscle mtDNA content by 45% (P = 0.003, Table 2). Unexpectedly, there was an increase in fasting glucose at the end of the study. However, this was not associated with concomitant increase in glucose tolerance (2 h glucose during OGTT or HbA1c, Table 2). The intensity during the exercise was similar between the groups, having an average effect of 121 W and 130 W (P = 0.286, Fig. 1A) and a HRR of 62% and 63% (P = 0.418) in FH− and FH+, respectively. The FH+ group participated in 59% more exercise sessions and expended 61% more energy than the FH− group (Fig. 1B). This was due to both higher amount of exercise per month in the FH+ group (Fig. 1C) and a shorter period of active exercise in the FH− group (Fig. 1D). The changes in weight and waist circumference were more pronounced in the FH+ group, which could be related to the volume of exercise.

Table 2.

The changes during the 216-day intervention period

	All					FH−					FH+
	Before		After			Before		After			Before		After
	Mean	SD	Mean	SD	Wilcoxon P value	Mean	SD	Mean	SD	Wilcoxon P value	Mean	SD	Mean	SD	Wilcoxon P value
Weight, kg	93.7	11.4	92.5	11.5	0.025	94.8	10.2	94.3	10.5	0.647	92.4	12.8	90.4	12.6	0.009
BMI, kg/m2	28.7	2.9	28.3	3.0	0.025	29.0	2.9	28.8	3.0	0.616	28.4	2.8	27.8	2.9	0.009
Waist circumference, cm	99.6	8.0	96.9	7.9	<0.001	101.0	7.8	99.2	7.8	0.036	98.1	8.2	94.3	7.3	0.001
Hip circumference, cm	105.0	5.6	104.1	5.8	0.010	106.1	4.9	105.5	5.4	0.208	103.8	6.3	102.6	6.1	0.015
Waist/hip ratio	0.95	0.04	0.93	0.05	<0.001	0.95	0.05	0.94	0.05	0.142	0.95	0.04	0.92	0.05	0.001
FFM, %	76.7	5.3	76.6	5.8	0.806	75.7	4.6	75.2	5.5	0.546	78.0	5.8	78.4	5.7	0.535
V̇o2peak/kg, ml·kg−1·min−1	31.4	4.7	35.7	5.6	<0.001	30.5	4.7	34.6	5.5	0.003	32.5	4.6	36.9	5.7	0.003
V̇o2peak/FFM, ml·kg FFM−1·min−1	41.0	5.0	46.5	5.8	<0.001	40.4	5.3	45.7	5.7	0.001	41.7	4.6	47.3	6.0	0.003
Fasting plasma glucose, mM	4.3	0.5	4.7	0.6	<0.001	4.3	0.6	4.6	0.4	0.029	4.3	0.4	4.9	0.7	0.001
2-h Glucose tolerance, mM	5.8	1.3	5.5	1.5	0.245	5.8	1.4	5.7	1.7	0.717	5.8	1.2	5.4	1.3	0.175
HbA1c, %	4.3	0.3	4.3	0.3	0.196	4.3	0.3	4.3	0.3	0.178	4.3	0.4	4.3	0.4	0.685
Fasting insulin, mU/ml	7.5	3.2	8.8	5.7	0.097	7.4	3.0	7.5	2.7	0.586	7.7	3.6	10.3	7.7	0.066
HOMA-IR ratio	1.44	0.65	1.86	1.35	0.005	1.43	0.65	1.54	0.55	0.159	1.45	0.67	2.25	1.86	0.013
HOMA-β, %	309.8	376.2	170.7	123.7	0.005	354.4	483.6	166.4	123.9	0.035	242.9	175.5	175.9	127.4	0.053
mtDNA/nDNA ratio	2,509	727	3,636	1,598	0.003	2,443	835	3,323	991	0.158	2,587	590	3,904	1,977	0.053

The P value describes the significance of difference in each group before and after the intervention using Wilcoxon signed-rank test. Significant differences (P < 0.05) are in bold.

Fig. 1.

A: the average intensity of exercise during the training session measured in Watts (W) in participants without (FH−; ●) and with first-degree heredity of type 2 diabetes (FH+; ■). Each dot represents one individual, and the line indicates the median, P = 0.441. B: the exercise volume in the FH− and FH+ groups during the intervention. Each dot represents one individual, and the line indicates the median, P < 0.001. C: the mean exercise volume monthly by the active participants during the exercise intervention. Active is defined as not yet having recorded their last session. D: Kaplan-Meier graph of the percentage of participants actively taking part in the exercise intervention. Using the Mantel-Cox test, P = 0.012. ns, Nonsignificant. ***Significant difference: P < 0.001.

Due to the large difference in exercise volume between the groups, we used multiple regression to evaluate the effects of exercise in the FH− and FH+ groups separately. The exercise volume predicted decrease in weight and waist circumference and increase in V̇o_{2 peak}/kg stronger in the FH− group (P = 0.018, P = 0.008, and P = 0.001, respectively), compared with the FH+ group (P = 0.249, P = 0.087, and P = 0.068, respectively). Exercise volume did not predict increase in mtDNA in FH− nor in FH+ in a significant way (P = 0.601 and P = 0.105, respectively, Table 3). When plotting change in weight, waist circumference, and V̇o_{2 peak}/kg to exercise volume, the FH− group has a stronger relation compared with the FH+ (Fig. 2). The relative intensity in %HRR did not have any strong effects on these variables (Supplemental Table S1; Supplemental material for this article is available online at the journal website).

Table 3.

Univariate regression analysis of variables in their relation to exercise in megajoules

	FH−			FH+
	β	SE	P value	β	SE	P value
Age, yr	−0.255	0.097	0.018	−0.076	0.063	0.249
Weight, kg	−0.074	0.029	0.023	−0.022	0.019	0.272
BMI, kg/m2	−0.313	0.103	0.008	−0.127	0.068	0.087
Waist circumference, cm	−0.011	0.078	0.889	−0.081	0.039	0.061
Hip circumference, cm	−0.003	0.001	0.007	0.000	0.001	0.674
Waist/hip ratio	0.443	0.140	0.006	0.069	0.067	0.322
FFM, %	0.492	0.111	0.001	0.187	0.093	0.068
V̇o2peak/kg, ml·kg−1·min−1	0.446	0.167	0.018	0.118	0.134	0.397
V̇o2peak/FFM, ml·kg FFM−1·min−1	0.019	0.014	0.184	0.018	0.016	0.279
Fasting plasma glucose, mM	0.049	0.056	0.393	−0.031	0.031	0.341
2-h Glucose tolerance, mM	−0.008	0.007	0.295	0.007	0.005	0.181
HbA1c, %	−0.113	0.095	0.250	−0.082	0.150	0.593
Fasting insulin, mU/ml	−0.017	0.018	0.371	−0.01	0.037	0.787
HOMA-IR ratio	−2.668	4.190	0.534	−2.601	2.468	0.315
HOMA-β, %	34.4	63.6	0.601	108.0	60.0	0.105

Significant differences (P < 0.05) are in bold.

Fig. 2.

A–C: the relation between energy expenditure and change in weight (A), waist circumference (B), and peak oxygen consumption (V̇o_{2 peak})/kg (C) in the FH− group (●). D–F: relation between energy expenditure and weight (D), waist circumference (E), and V̇o_{2 peak}/kg (F) in the FH+ group (■). Spearman's r is given for each correlation.

Gene expression in skeletal muscle in relation to exercise volume and FH status.

First, we investigated the effects of exercise on the change in mean centroid value (a representation of the expression of all genes included in a defined pathway) of a number of pathways that were identified in the baseline study (6). Genes involved in metabolism and glycolysis (GO: 0008152 and GO: 0006096) increased significantly (P = 0.045 and P = 0.007, respectively) due to exercise in the FH− group, but no such change could be observed in the FH+ group (P = 0.418 and P = 0.639, respectively) (Table 4). Relative intensity in %HRR did not affect the expression of these pathways (Supplemental Table S2).

Table 4.

Regression analysis of mean centroid of selected pathways influenced by exercise

	FH−			FH+
	β	SE	P value	β	SE	P value
Metabolism	0.306	0.141	0.045	−0.082	0.098	0.418
Mitochondrion	−0.104	0.14	0.466	0.031	0.071	0.666
TCA cycle	0.613	0.382	0.128	−0.059	0.412	0.889
Glycolysis	0.597	0.191	0.007	0.095	0.197	0.639
Oxidative phosphorylation	0.616	0.328	0.079	−0.433	0.263	0.129
Regulation of FA oxidation	−0.653	0.320	0.058	0.157	0.31	0.622
FA metabolism	0.744	0.373	0.063	−0.257	0.279	0.377
FA oxidation	0.314	0.316	0.335	−0.141	0.294	0.641

β and SE values are for gigajoules of exercise. FA, fatty acid.

Second, we used a regression model to test the impact of the intervention on gene expression where the expression level after the intervention of each gene was predicted using the exercise volume and the gene expression at the baseline level. In this model, the expression of 1,066 genes in the FH− group and 365 genes in the FH+ group changed in response to exercise with nominal significance. Two hundred genes in the FH− and 96 genes in the FH+ group increased with exercise (complete gene list can be found in the supplemental file). Next, the 200 (FH−) and 96 (FH+) nominally significant genes that increased with exercise were analyzed using Webgestalt to evaluate if the genes upregulated by exercise are overrepresented in certain pathways. For the FH− group, 30 GO pathways were associated with these genes: a majority represented metabolic pathways, including mitochondria, cellular respiration, oxidative phosphorylation, electron transport chain, and mitochondrial ATP synthesis. In the FH+ group, 22 GO pathways changed significantly in response to exercise (Table 5). These pathways are not clearly linked to those implicated for the FH− group, and the statistical association is lower. Using the KEGG database, expression of 10 pathways increased significantly in the FH− group, including oxidative phosphorylation, metabolic pathways, and TCA cycle. No KEGG pathways were significantly increased for the FH+ group (Table 5). The relative intensity of exercise was evaluated similarly, and 33 and 54 nominally significant genes increased with increased %HRR for the FH− and FH+ participants, but the response on pathway level had a low statistical association compared with exercise volume (Supplemental Table S3).

Table 5.

GO and KEGG Pathways overrepresented among genes showing increased expression with exercise in the FH− and the FH+ groups

	C	O	R	Adj P	Pathway ID	Description
GO FH−
Biological process	129	24	14.34	1.74e-18	GO:0045333	Cellular respiration
Biological process	87	20	17.72	2.64e-17	GO:0022904	Respiratory electron transport chain
Biological process	470	36	5.90	4.57e-16	GO:0055114	Oxidation-reduction process
Biological process	117	21	13.84	4.57e-16	GO:0022900	Electron transport chain
Biological process	277	28	7.79	2.89e-15	GO:0015980	Energy derivation by oxidation of organic compounds
Biological process	380	31	6.29	1.75e-14	GO:0006091	Generation of precursor metabolites and energy
Biological process	53	11	16.00	7.61e-09	GO:0006119	Oxidative phosphorylation
Biological process	44	10	17.52	1.74e-08	GO:0042773	ATP synthesis coupled electron transport
Biological process	44	10	17.52	1.74e-08	GO:0042775	Mitochondrial ATP synthesis coupled electron transport
Biological process	35	9	19.82	3.99e-08	GO:0006120	Mitochondrial electron transport, NADH to ubiquinone
Molecular function	552	31	4.44	3.28e-10	GO:0016491	Oxidoreductase activity
Molecular function	48	11	18.12	6.11e-10	GO:0016655	Oxidoreductase activity, acting on NADH or NADPH, quinone or similar
Molecular function	36	10	21.96	6.11e-10	GO:0003954	NADH dehydrogenase activity
Molecular function	36	10	21.96	6.11e-10	GO:0008137	NADH dehydrogenase (ubiquinone) activity
Molecular function	36	10	21.96	6.11e-10	GO:0050136	NADH dehydrogenase (quinone) activity
Molecular function	78	11	11.15	1.19e-07	GO:0016651	Oxidoreductase activity, acting on NADH or NADPH
Molecular function	4,368	85	1.54	1.86e-05	GO:0003824	Catalytic activity
Molecular function	4	3	59.30	0.0002	GO:0004470	Malic enzyme activity
Molecular function	231	13	4.45	0.0002	GO:0048037	Cofactor binding
Molecular function	132	10	5.99	0.0002	GO:0009055	Electron carrier activity
Cellular component	1,240	76	4.98	1.99e-33	GO:0005739	Mitochondrion
Cellular component	612	49	6.51	4.32e-25	GO:0044429	Mitochondrial part
Cellular component	285	31	8.84	3.85e-19	GO:0005743	Mitochondrial inner membrane
Cellular component	307	31	8.21	2.64e-18	GO:0019866	Organelle inner membrane
Cellular component	430	33	6.24	5.41e-16	GO:0005740	Mitochondrial envelope
Cellular component	62	16	20.98	6.04e-16	GO:0070469	Respiratory chain
Cellular component	411	32	6.33	8.40e-16	GO:0031966	Mitochondrial membrane
Cellular component	240	24	8.13	3.69e-14	GO:0005759	Mitochondrial matrix
Cellular component	5,512	117	67.80	5.63e-14	GO:0044444	Cytoplasmic part
Cellular component	116	18	12.62	5.63e-14	GO:0044455	Mitochondrial membrane part
GO FH+
Biological process	6	2	59.18	0.0458	GO:0019368	Fatty acid elongation, unsaturated fatty acid
Biological process	255	7	4.87	0.0458	GO:0046486	Glycerolipid metabolic process
Biological process	3	2	118.36	0.0458	GO:0031642	Negative regulation of myelination
Biological process	7	2	50.73	0.0458	GO:0030497	Fatty acid elongation
Biological process	63	4	11.27	0.0458	GO:0008033	tRNA processing
Biological process	6	2	59.18	0.0458	GO:0042761	Very-long-chain fatty acid biosynthetic process
Biological process	103	5	8.62	0.0458	GO:0006399	tRNA metabolic process
Biological process	187	6	5.70	0.0458	GO:0045017	Glycerolipid biosynthetic process
Biological process	4	2	88.77	0.0458	GO:0034625	Fatty acid elongation, monounsaturated fatty acid
Molecular function	4	2	100.82	0.0106	GO:0009922	Fatty acid elongase activity
Molecular function	1,403	17	2.44	0.0159	GO:0016740	Transferase activity
Molecular function	7	2	57.61	0.0177	GO:0004312	Fatty acid synthase activity
Cellular component	1,913	23	2.29	0.0064	GO:0031090	Organelle membrane
Cellular component	614	11	3.42	0.0073	GO:0042175	Nuclear outer membrane-endoplasmic reticulum membrane network
Cellular component	601	11	3.49	0.0073	GO:0005789	Endoplasmic reticulum membrane
Cellular component	1,444	18	2.38	0.0073	GO:0012505	Endomembrane system
Cellular component	5,404	42	1.48	0.0136	GO:0044446	Intracellular organelle part
Cellular component	5,472	42	1.47	0.0146	GO:0044422	Organelle part
Cellular component	11	2	34.71	0.0151	GO:0031231	Intrinsic to peroxisomal membrane
Cellular component	11	2	34.71	0.0151	GO:0005779	Integral to peroxisomal membrane
Cellular component	729	11	2.88	0.0151	GO:0044432	Endoplasmic reticulum part
Cellular component	47	3	12.18	0.0184	GO:0005884	Actin filament
KEGG FH−
KEGG pathway	103	19	13.87	2.59e-15	190	Oxidative phosphorylation
KEGG pathway	101	18	13.40	1.64e-14	5012	Parkinson's disease
KEGG pathway	142	19	10.06	3.07e-13	5010	Alzheimer's disease
KEGG pathway	160	20	9.40	3.07e-13	5016	Huntington's disease
KEGG pathway	969	39	3.03	2.17e-09	1100	Metabolic pathways
KEGG pathway	38	7	13.85	2.94e-06	280	Valine, leucine and isoleucine degradation
KEGG pathway	16	4	18.80	0.0002	630	Glyoxylate and dicarboxylate metabolism
KEGG pathway	6	3	37.59	0.0002	62	Fatty acid elongation in mitochondria
KEGG pathway	26	4	11.57	0.0013	20	Citrate cycle (TCA cycle)
KEGG pathway	37	4	8.13	0.0042	71	Fatty acid metabolism

GO, Gene Ontology; KEGG, Kyoto Encyclopedia of Genes and Genomes; C, no. of genes in category, O, no. of observed genes in category, R, ratio of enrichment to expected genes, Adj P, P value adjusted for multiple comparisons.

DISCUSSION

In this study, we have evaluated the response to an exercise intervention in healthy, glucose-tolerant FH− and FH+ subjects with the two groups similar in regard to age, BMI, and V̇o_{2 peak}. Notably, the FH+ individuals spent more time exercising than those in the FH− group, expending 61% more energy on exercise during the intervention period. It is possible that the exposure of FH+ participants to the consequences of diabetes in the family motivated them to increase their exercise to a greater extent during the study compared with the FH− participants. The observed difference in exercise volume led us to analyze the data in the FH− and FH+ groups separately, to avoid misinterpretation between the effects of exercise and FH background. In the regression analysis, the FH+ group responded less to exercise in terms of weight, waist circumference, and V̇o_{2 peak}. Although this difference between the groups was not formally tested, it indicated that the FH+ background may limit the response to exercise. The individual intensity of the exercise was not a major determinant for exercise response in this study.

Several studies describe the exercise response in type 2 diabetic patients and have reported increased mitochondrial volume and increased activity of oxidative enzymes after exercise (21, 34, 35, 39, 41). In agreement, our analysis show increased mitochondrial density in both the FH− and FH+ groups (by 45%) after the intervention and also an increased expression of genes in the oxidative phosphorylation pathway in the FH− group. However, in this study, we also investigated the effect of exercise volume in relation to benefits gained. This analysis indicated that there is lesser gain per volume of exercise in the FH+ group vs. FH−, but no formal statistical test of this observation was done due to the difference in performed exercise between the groups. Further studies are clearly needed to determine the optimal, frequency, intensity, and type of exercise for this group at risk of metabolic disease.

Before the start of the exercise intervention, expression of genes in fatty acid oxidation and mitochondrial genes was decreased in FH+ compared with FH− individuals (6). The expression data, both from comparing mean centroid expression and when comparing overrepresented pathways in upregulated genes (GO and KEGG defined pathways), indicate that the FH− group has a stronger response to the exercise compared with FH+, suggesting that the FH+ background limits the beneficial effects of exercise on the gene expression level. The lower upregulation of those pathways in the FH+ group further emphasizes the reduced muscular adaptation to exercise and could possibly explain the lower basal expression of mitochondrial genes observed before the intervention, despite a similar habitual activity (6). Genes involved in oxidative phosphorylation were more strongly upregulated in the FH− compared with the FH+ group, indicating that lower expression of genes involved in oxidative phosphorylation in diabetic muscle (20, 24) can be attributed, at least partly, to the genetic background of FH+ rather than merely to activity levels (41). The adaptation to exercise is to some extent determined by genetic factors (38), and we speculate that the genetic variants responsible for low exercise response might be overrepresented in in the FH+ population and might be of importance for the development of type 2 diabetes.

The difference in exercise volume between the FH− and FH+ groups is a limitation of the study: it is, for example, not possible to know if FH− participants would gain less per megajoule of work performed at higher exercise volumes and thus have a more similar exercise response as the FH− group at these levels of exercise. However, our data support earlier findings with smaller increase in V̇o_{2 peak} (23) and lower upregulation of muscle ATP production (13) and glucose metabolism (25) in FH+ participants and add a new level of observations in terms of a more detailed description of muscle expression.

In conclusion, even a relatively modest increase in physical activity during 7 mo improves physical fitness and thereby some cardiometabolic risk factors. Although no formal statistical test was done between the groups, this study indicates that individuals with a family history of diabetes seem to gain less by increasing the volume of exercise, in terms of gene expression, weight loss, waist circumference, and V̇o_{2 peak}, indicating that the genetic background can influence the response in this group.

GRANTS

This study was supported by the Swedish Research Council Linnaeus grant: Lund University Diabetes Centre (Dnr 349-2006-237) and SFO Exodiab (Dnr 2009-1039); European Research Council Advanced Researcher Grant (GA 269045); NuGo; ALF; the Crafoord Foundation; SV Skånes Diabetes Förening; the Wallenberg Foundation; the Novo Nordisk Foundation; EXGENESIS; UMAS Fonder, Magn. Bergvalls Stiftelse; Syskonen Svenssons Fond; the Swedish Diabetes Research Foundation (2009-060); and the European Community's Seventh Framework Programme (FP7/2007–2013).

DISCLOSURES

No conflicts of interest, financial or otherwise, are declared by the author(s).

AUTHOR CONTRIBUTIONS

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