Thiazolidenediones such as pioglitazone improve insulin sensitivity in diabetic patients by several mechanisms, including increased uptake and metabolism of free fatty acids in adipose tissue. The purpose of the present study was to determine the effect of pioglitazone on mitochondrial biogenesis and expression of genes involved in fatty acid oxidation in subcutaneous fat. Patients with type 2 diabetes were randomly divided into two groups and treated with placebo or pioglitazone (45 mg/day) for 12 weeks. Mitochodrial DNA copy number and expression of genes involved in mitochondrial biogenesis were quantified by real-time PCR. Pioglitazone treatment significantly increased mitochondrial copy number and expression of factors involved in mitochondrial biogenesis, including peroxisome proliferator–activated receptor (PPAR)-γ coactivator-1α and mitochondrial transcription factor A. Treatment with pioglitazone stimulated the expression of genes in the fatty acid oxidation pathway, including carnitine palmitoyltransferase-1, malonyl-CoA decarboxylase, and medium-chain acyl-CoA dehydrogenase. The expression of PPAR-α, a transcriptional regulator of genes encoding mitochondrial enzymes involved in fatty acid oxidation, was higher after pioglitazone treatment. Finally, the increased mitochondrial copy number and the higher expression of genes involved in fatty acid oxidation in human adipocytes may contribute to the hypolipidemic effects of pioglitazone.

OBJECTIVE—Pioglitazone is a member of the thiazolidinediones (TZDs), insulin-sensitizing agents used to treat type 2 diabetes. The aim of this study was to define the effect of pioglitazone on the expression of genes related to carbohydrate and lipid metabolism in subcutaneous fat obtained from type 2 diabetic patients. RESEARCH DESIGN AND METHODS—Forty-eight volunteers with type 2 diabetes were divided into two groups treated for 12 weeks with placebo or pioglitazone (30 mg/day). The expression of several genes was quantified by real-time RT-PCR. RESULTS—Pioglitazone treatment increased the expression of genes involved in glycerol-3-phosphate synthesis. The mRNA expression of PEPCK-C and glycerol-3-phosphate dehydrogenase (GPDH) increased (P < 0.01) in patients treated with pioglitazone. There was no difference in glycerol kinase (GyK) mRNA levels. The expression of genes that regulate fatty acid availability in adipocytes, including lipoprotein lipase (LPL) and acetyl-CoA synthetase (ACS), was higher (P < 0.01) in pioglitazone-treated patients. Pioglitazone stimulated (P < 0.0001) expression of c-Cbl-associated protein (CAP), whereas tumor necrosis factor-α, leptin, resistin, angiopoietin like-4, and 11-β-hydroxysteroid dehydrogenase type 1 (11β HSD 1) were not affected by pioglitazone. The baseline peroxisome proliferator-activated receptor (PPAR)-γ1 mRNA was significantly correlated with mRNA for LPL, CAP, ACS, 11β HSD 1, GyK, fatty acid synthase, leptin, and GPDH, whereas PPAR-γ2 mRNA was correlated with CAP, PEPCK-C, leptin, and GPDH. CONCLUSIONS—Treatment with pioglitazone increased body weight, and this is associated with upregulation of some, but not all, genes previously demonstrated as “TZD responsive” in subcutaneous fat. The results suggest that TZDs might increase body weight through the upregulation of genes facilitating adipocyte lipid storage in vivo.

Insulin resistance is associated with metabolic inflexibility, impaired switching of substrate oxidation from fatty acids to glucose in response to insulin. Impaired switching to fat oxidation in response to a high-fat diet (HFD) is hypothesized to contribute to insulin resistance. The objective of this study was to test the hypothesis that defects in substrate switching in response to insulin and a HFD are linked to reduced mitochondrial biogenesis and occur before the development of diabetes. Metabolic flexibility was measured in young sedentary men with (n = 16) or without (n = 34) a family history of diabetes by euglycemic-hyperinsulinemic clamp. Flexibility correlated with fat oxidation measured in a respiratory chamber after a 3-day HFD. Muscle mitochondrial content was higher in flexible subjects with high fat oxidation after a HFD and contributed 49% of the variance. Subjects with a family history of diabetes were inflexible and had reduced HFD-induced fat oxidation and muscle mitochondrial content but did not differ in the amount of body or visceral fat. Metabolic inflexibility, lower adaptation to a HFD, and reduced muscle mitochondrial mass cluster together in subjects with a family history of diabetes, supporting the role of an intrinsic metabolic defect of skeletal muscle in the pathogenesis of insulin resistance.

Mitochondrial biogenesis is a complex process, and several factors and signaling pathways regulate this process in muscle or brown adipocytes. The aim of the study was to explore pathways affecting mitochondrial biogenesis and fatty acid oxidation (FAO) in human white adipocytes. Human preadipocytes obtained from liposuction samples were differentiated in vitro. On the 10th day of differentiation, 4 microM forskolin and 1 microM peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist (pioglitazone, rosiglitazone, or GW 929) or 10 microM PPARalpha agonist (WY-14,643) were added to the media for 96 h. Quantitative real-time PCR was used to determine gene expression/mitochondrial copy number and 14C-labeled palmitate to measure direct energy dissipation. The treatment of adipocytes with forskolin increased mitochondrial copy number and the expression of genes involved in mitochondrial biogenesis (PPARgamma coactivator 1alpha and transcriptional factor A) and fatty acid oxidation (PPARalpha and medium-chain acyl-coenzyme A dehydrogenase). The end (CO2) and intermediate products (14C-labeled acid-soluble products) of FAO were also increased after forskolin treatment. PPARgamma and PPARalpha agonists increased mitochondrial copy number, uncoupling protein 1, medium-chain acyl-coenzyme A dehydrogenase, and carnitine palmitoyltransferase 1, but did not change PPARalpha, PPARgamma coactivator 1alpha, or transcriptional factor A mRNA levels. FAO was higher after rosiglitazone, GW 929, and WY-14,643 but not after pioglitazone treatment. Pharmacological activation of the cAMP or PPARgamma pathway pushes the white adipocyte down the oxidative continuum. The direct energy-dissipating effects could be significant tools to treat obesity and to improve insulin resistance in type 2 diabetic patients by reduction of fat accumulation in adipocytes or by reprogramming fatty acid metabolism.

Peroxisome proliferator-activated receptors (PPARs) belong to a ligand-dependent nuclear receptor family. In the past decade, numerous studies have revealed the presence and significance of PPARs in the reproductive system. PPARs are expressed at different levels of hypothalamic-pituitary-gonadal (HPG) axis. They are also present in the uterus as well as in the placenta and embryonic tissues of different species. PPARs significance has been reported during the estrous/menstrual cycle and pregnancy with the gamma isoform studied most frequently. Several studies indicate that PPARs regulate proliferation of ovarian cells, tissue remodeling and steroidogenesis. In the endometrium, PPARs are engaged in the regulation of prostaglandins, steroids and cytokines synthesis. The role of PPARs in the trophoblast differentiation, maturation and invasion as well as in the embryo development has also been demonstrated. In this review, we summarize current findings concerning the role of PPARs in the regulation of reproductive functions at different levels of the HPG axis during various physiological statuses of females. In addition, the role of PPARs in the modulation of uterine functions as well as the placenta and embryo development has also been discussed.