RESEARCH LETTERS
Uncoupling protein-3 expression in skeletal muscle and free fatty acids in obesity Olivier Boss, Elisabetta Bobbioni-Harsch, Francoise Assimacopoulos-Jeannet, Patrick Muzzin, Robert Munger, Jean-Paul Giacobino, Alain Golay
The newly identified mitochondrial uncoupling proteins UCP2 and UCP3, by contrast with UCP1, are highly expressed in human beings,1,2 UCP2 being ubiquitous and UCP3 specific to skeletal muscle. Because of its tissue distribution, UCP3 might have an important role in wholebody energy homoeostasis in human beings. Variations in its degree of expression might contribute to the interindividual variability in resting energy expenditure and in the energybalance dysregulation found in obesity and type 2 diabetes. We investigated whether mRNA expression of UCP2 and UCP3 in human vastus lateralis muscle was correlated with variables related to fat or glucose metabolism and with resting energy expenditure in a mixed population of obese patients and obese patients with type 2 diabetes. Nine obese, 10 h fasted patients, including three with type 2 diabetes (untreated but dietetically controlled, fasting plasma glucose of 8·1 to 10·5 mmol/L, table), volunteered, with written consent, to participate, which was accepted by the local Human Investigation Committee. We measured lean body mass with bioelectrical impedance. Plasma glucose concentrations were determined with a Beckman Glucose Analyzer II (Beckman Instruments, CA, USA), and plasma free fatty acids and insulin concentrations with commercial kits (Wako Chemicals GmbH, Germany, and Abbott, IL). Glucose uptake was measured with a euglycaemic hyperinsulinaemic clamp, and glucose and lipid oxidation rates, as well as resting energy expenditure, were determined by indirect calorimetry.3 The concentrations of UCP2 and UCP3 mRNA in vastus lateralis biopsy fragments were measured by northern blot.2 The expression of UCP2 and UCP3 mRNA normalised to the respective concentrations of 18S rRNA were compared with 12 physical, biological, and metabolic variables and analysed (Simple Pearson ProductMoment correlations). The mRNA expression of UCP3 was positively and linearly correlated with circulating free fatty acids (r=0·83; p=0·005), whereas that of UCP2 was not (r=0·40). When adjustments were made for age, percentage of fat mass, body-mass index, lean body mass and bodyweight, the correlation between UCP3 mRNA and concentrations of free fatty acids was stronger (r=0·99; p0·05) was seen between UCP2 or UCP3 mRNA expression and age, percentage fat mass, body-mass index, lean body mass, resting energy expenditure per kg lean body mass, bodyweight, fasting plasma glucose, insulin concentrations, insulin-induced glucose uptake, glucose oxidation, and lipid oxidation. Patient (sex, age in years)
Percentage fat mass
BodyLean mass body index mass (kg/m2) (kg)
Free fatty acids (mmol/L)
Resting energy (kcal/ 24 h)
UCP2 UCP3 mRNA* mRNA*
Male, 55 Male, 33 Male, 62 Female, 40 Female, 65 Male, 46 Male, 60 Female, 64 Male, 61
29 31 36 34 47 32 31 44 38
34·4 44·1 26·9 24·3 36·7 35·8 30·4 40·9 33·4
1·01 0·87 1·16 0·67 0·96 1·32 0·38 0·97 0·96
1991 2866 1838 1621 1711 1838 1683 1758 1723
24·2 21·0 11·3 14·6 15·6 24·3 14·2 15·3 25·3
59·2 89·5 53·8 49·4 45·6 65·1 68·0 57·4 63·5
53·4 46·6 49·3 31·1 51·4 61·0 17·2 25·3 39·3
*Normalised for 18S rRNA levels (arbitrary units).
Physical, biological, and metabolic characteristics of patients
THE LANCET • Vol 351 • June 27, 1998
Free fatty acids might control muscle UCP3 expression. A 10-day severe calorie restriction increases muscle UCP2 and UCP3 mRNA expression,4 and in rodents infusion of free fatty acids increases muscle UCP3 mRNA.5 Our data suggest a role for muscle UCP3 in the metabolic adaptations to increases in fatty-acid supply, and, therefore, the involvement of UCP3 in a compensatory mechanism linking obesity to increased muscle thermogenesis. We thank Josiane Seydoux for help in the analysis of the results and for discussion. This work was supported by the Swiss National Science Foundation (grants 31-43405.95 and 32-45957.95), by the Ciba-GeigyJubiläums-Stiftung, the Fondation du Centenaire de la Société Suisse d’Assurances générales sur la vie humaine pour la santé publique et les recherches médicales, and the Foundation Berger. 1
Fleury C, Neverova M, Collins S, et al. Uncoupling protein-2: a novel gene linked to obesity and hyperinsulinemia. Nat Genet 1997; 15: 269–72. 2 Boss O, Samec S, Paoloni-Giacobino A, et al. Uncoupling protein-3: a new member of the mitochondrial carrier family with tissue-specific expression. FEBS Lett 1997; 408: 39–42. 3 Ferrannini E. The theoretical bases of indirect calorimetry: a review. Metabolism 1988; 37: 287–301. 4 Millet L, Vidal H, Andreelli F, et al. Increased uncoupling protein-2 and -3 mRNA expression during fasting in obese and lean humans. J Clin Invest 1997; 100: 2665–70. 5 Weigle DS, Selfridge LE, Schwartz MW, et al. Elevated free fatty acids induce uncoupling protein 3 expression in muscle. Diabetes 1998; 47: 298–302. Department of Medical Biochemistry (O Boss) and University Hospital, University of Geneva, 1211 Geneva 4, Switzerland (e-mail:
[email protected])
C282Y mutation in HFE (haemochromatosis) gene and type 2 diabetes Tim Frayling, Sian Ellard, Jane Grove, Mark Walker, Andrew T Hattersley
Patients with haemochromatosis may present with type 2 diabetes. It is uncertain whether the genetic predisposition to haemochromatosis has an important aetiological role in type 2 diabetes. An increased prevalence of haemochromatosis in patients with type 2 diabetes has been suggested.1 However, Turnbull and colleagues2 have suggested no increase in the frequency of haemochromatosis among patients with diabetes in northeast England (UK), based on screening with conventional biochemical tests for iron overload, serum ferritin, and transferrin. Understanding of the genetic susceptibility to haemochromatosis has advanced. A missense mutation at nucleotide 845 of the HFE gene that leads to the substitution of tyrosine for cysteine at codon 282 (C282Y) is strongly associated with haemochromatosis. 80–90% of haemochromatosis patients are homozygous for this mutation,3-5 for which the carrier frequency is estimated to be about 10% among northern Europeans.4,5 We determined the prevalence of the C282Y mutation among UK patients with type 2 diabetes with a previously described PCR restriction fragment length polymorphism assay with the enzyme RsaI.3 The presence of the mutation results in an additional RsaI restriction site. We screened 238 unrelated patients with type 2 diabetes (average age at diagnosis 55·0 years) and 215 age-matched normoglycaemic controls. One patient with type 2 diabetes and one control were homozygous for the mutant allele. The patient with diabetes was homozygous for C282Y and diagnosed aged 63 years. She had no clinical features of haemochromatosis and normal serum liver enzymes, but had substantially raised ferritin (>1000 g/L). The control homozygous for the C282Y mutation was a symptom-free menstruating woman
1933
