Katja Kannisto

Evidence That Peroxisome Proliferator–Activated Receptor Delta Influences Cholesterol Metabolism in Men

Objective—The objective of this work was to explore the role of peroxisome proliferator–activated receptor delta (PPARD) in lipid metabolism in humans. Methods and Results—PPARD is a nuclear receptor involved in lipid metabolism in primates and mice. We screened the 5′-region of the human gene for polymorphisms to be used as tools in association studies. Four polymorphisms were detected: −409C/T in the promoter region, +73C/T in exon 1, +255A/G in exon 3, and +294T/C in exon 4. The frequencies of the rare alleles were 4.2%, 4.2%, 1.2% and 15.6%, respectively, in a population-based group of 543 healthy men. Only the +294T/C polymorphism showed significant association with a metabolic trait. Homozygotes for the rare C allele had a higher plasma LDL–cholesterol concentration than homozygotes for the common T allele, which was verified in an independent cohort consisting of 282 healthy men. Transfection studies showed that the rare C allele had higher transcriptional activity than the common T allele. Electrophoretic mobility shift assays demonstrated that the +294T/C polymorphism influenced binding of Sp-1. An interaction with the PPAR alpha L162V polymorphism was also detected for several lipid parameters. Conclusions—These findings suggest that PPARD plays a role in cholesterol metabolism in humans.

Insulin action in cultured human skeletal muscle cells during differentiation: assessment of cell surface GLUT4 and GLUT1 content

Abstract: In mature human skeletal muscle, insulin-stimulated glucose transport is mediated primarily via the GLUT4 glucose transporter. However, in contrast to mature skeletal muscle, cultured muscle expresses significant levels of the GLUT1 glucose transporter. To assess the relative contribution of these two glucose transporters, we used a novel photolabelling techniques to assess the cell surface abundance of GLUT1 and GLUT4 specifically in primary cultures of human skeletal muscle. We demonstrate that insulin-stimulated glucose transport in cultured human skeletal muscle is mediated by GLUT4, as no effect on GLUT1 appearance at the plasma membrane was noted. Furthermore, GLUT4 mRNA and protein increased twofold (p < 0.05), after differentiation, whereas GLUT1 mRNA and protein decreased 55% (p < 0.005). Incubation of differentiated human skeletal muscle cells with a non-peptide insulin mimetic significantly (p < 0.05) increased glucose uptake and glycogen synthesis. Thus, cultured myotubes are a useful tool to facilitate biological and molecular validation of novel pharmacological agents aimed to improve glucose metabolism in skeletal muscle.

Regulation of Plasma PAI-1 Concentrations in HAART-Associated Lipodystrophy During Rosiglitazone Therapy

Objective—Patients with highly active antiretroviral therapy–associated lipodystrophy (HAART+LD+) have high plasminogen activator inhibitor-1 (PAI-1) concentrations for unknown reasons. We determined whether (1) plasma PAI-1 antigen concentrations are related to liver fat content (LFAT) independently of the size of other fat depots and (2) rosiglitazone decreases PAI-1 and LFAT in these patients. Methods and Results—In the cross-sectional study, 3 groups were investigated: 30 HIV-positive patients with HAART+LD+, 13 HIV-positive patients without lipodystrophy (HAART+LD−), and 15 HIV-negative subjects (HIV−). In the treatment study, the HAART+LD+ group received either rosiglitazone (8 mg, n=15) or placebo (n=15) for 24 weeks. Plasma PAI-1 was increased in HAART+LD+ (28±2 ng/mL) compared with the HAART+LD− (18±3, P <0.02) and HIV− (10±3, P <0.001) groups. LFAT was higher in HAART+LD+ (7.6±1.7%) than in the HAART+LD− (2.1±1.1%, P <0.001) and HIV− (3.6±1.2%, P <0.05) groups. Within the HAART+LD+ group, plasma PAI-1 was correlated with LFAT (r =0.49, P <0.01) but not with subcutaneous or intra-abdominal fat or serum insulin or triglycerides. In subcutaneous adipose tissue, PAI-1 mRNA was 2- to 3-fold higher in the HAART+LD+ group than in either the HAART+LD− or HIV− group. Rosiglitazone decreased LFAT, serum insulin, and plasma PAI-1 and increased serum triglycerides but had no effect on intra-abdominal or subcutaneous fat mass or PAI-1 mRNA. Conclusions—Plasma PAI-1 concentrations are increased in direct proportion to LFAT in HAART+LD+ patients. Rosiglitazone decreases LFAT, serum insulin, and plasma PAI-1 without changing the size of other fat depots or PAI-1 mRNA in subcutaneous fat. These data suggest that liver fat contributes to plasma PAI-1 concentrations in these patients.

Adipose tissue inflammation and liver fat in patients with highly active antiretroviral therapy-associated lipodystrophy

In this cross-sectional study, we sought to determine whether gene expression of macrophage markers and inflammatory chemokines in lipoatrophic subcutaneous abdominal adipose tissue and liver fat content are increased and interrelated in human immunodeficiency virus (HIV)-1-positive, highly active antiretroviral therapy (HAART)-treated patients with lipodystrophy (HAART+LD+; n = 27) compared with those without (HAART+LD-; n = 13). The study groups were comparable with respect to age, gender, and body mass index. The HAART+LD+ group had twofold more intra-abdominal (P = 0.01) and 1.5-fold less subcutaneous (P = 0.091) fat than the HAART+LD- group. As we have reported previously, liver fat was 10-fold higher in the HAART+LD+ compared with the HAART+LD- group (P = 0.00003). Inflammatory gene expression was increased in HAART-lipodystrophy: CD68 4.5-fold (P = 0.000013), tumor necrosis factor (TNF)-alpha 2-fold (P = 0.0094), chemokine (C-C motif) ligand (CCL) 2 2.5-fold (P = 0.0024), CCL3 7-fold (P = 0.0000017), integrin alphaM (ITGAM) 3-fold (P = 0.00067), epidermal growth factor-like module containing, mucin-like, hormone receptor-like (EMR)1 2.5-fold (P = 0.0038), and a disintegrin and metalloproteinase domain (ADAM)8 3.5-fold (P = 0.00057) higher in the HAART+LD+ compared with the HAART+LD- group. mRNA concentration of CD68 (r = 0.37, P = 0.019), ITGAM (r = 0.35, P = 0.025), CCL2 (r = 0.39, P = 0.012), and CCL3 (r = 0.54, P = 0.0003) correlated with liver fat content. In conclusion, gene expression of markers of macrophage infiltration and adipose tissue inflammation is increased in lipoatrophic subcutaneous abdominal adipose tissue of patients with HAART-associated lipodystrophy compared with those without. CD68, ITGAM, CCL2, and CCL3 expression is significantly associated with accumulation of liver fat.