Even effect of milk protein and carbohydrate intake but no further effect of heavy resistance exercise on myofibrillar protein synthesis in older men.

PURPOSE: The responsiveness of older individuals' skeletal muscle to anabolic strategies may be impaired. However, direct comparisons within the same experimental setting are sparse. The aim of this study was to assess the resting and post-resistance exercise muscle protein synthesis rates in response to two types of milk protein and carbohydrate using a unilateral exercise leg model. METHODS: Twenty-seven older (69 ± 1 year, mean ± SE) men were randomly assigned one of three groups: Whey hydrolysate (WH), caseinate (CAS), or carbohydrate (CHO). By applying stable isotope tracer techniques (L-[15N]phenylalanine), the fasted-rested (basal) myofibrillar fractional synthesis rate (FSR) was measured. Hereafter, FSR was measured in the postprandial phase (0.45 g nutrient/kg LBM) in both legs, one rested (fed-rest) and one exercised (10 × 8 reps at 70% 1RM; fed-exercise). In addition, the activity of p70S6K and venous plasma insulin, phenylalanine, and leucine concentrations were measured. RESULTS: Insulin, phenylalanine, and leucine concentrations differed markedly after intake of the different study drinks. The basal FSR in WH, CAS, and CHO were 0.027 ± 0.003, 0.030 ± 0.003, and 0.030 ± 0.004%/h, the fed-rested FSR were 0.043 ± 0.004, 0.045 ± 0.003, and 0.035 ± 0.004%/h, and the fed-exercised FSR were 0.041 ± 0.004, 0.043 ± 0.004, and 0.034 ± 0.004%/h, respectively. No significant differences were observed at any state between the groups. Fed-rested- and fed-exercised FSR were higher than basal (P < 0.001). 3 h after exercise and feeding, no significant group differences were detected in the activity of p70S6K. CONCLUSIONS: Milk protein and carbohydrate supplementation stimulate myofibrillar protein synthesis in older men, with no further effect of heavy resistance exercise within 0-3 h post exercise.

Synthesis and biological evaluation of dihydropyrano-[2,3-c]pyrazoles as a new class of PPARγ partial agonists.

Peroxisome proliferator-activated receptor γ (PPARγ) is a well-known target for thiazolidinedione antidiabetic drugs. In this paper, we present the synthesis and biological evaluation of a series of dihydropyrano[2,3-c]pyrazole derivatives as a novel family of PPARγ partial agonists. Two analogues were found to display high affinity for PPARγ with potencies in the micro molar range. Both of these hits were selective against PPARγ, since no activity was measured when tested against PPARα, PPARδ and RXRα. In addition, a novel modelling approach based on multiple individual flexible alignments was developed for the identification of ligand binding interactions in PPARγ. In combination with cell-based transactivation experiments, the flexible alignment model provides an excellent analytical tool to evaluate and visualize the effect of ligand chemical structure with respect to receptor binding mode and biological activity.

Design and synthesis of novel Y-shaped barbituric acid derivatives as PPARγ activators.

Novel Y-shaped barbituric acid (BA) derivatives have been designed using rational methods including molecular docking. Fourteen novel compounds were synthesized using hydroxyl group protection-deprotection strategies for PPARγ activation. Competitive binding analysis of the synthesized molecules using time-resolved fluorescence resonance energy transfer (FRET) method was carried out, and the IC50 values were determined. The symmetrically substituted derivatives have shown greater binding affinity than unsymmetrically substituted derivatives. Nitrobenzyl and cyanophenyl substituted derivatives have shown reasonable binding affinities (10.1 and 6.5 µM, respectively), while mono and diacetate derivatives were found inactive. Molecular dynamics simulations show that the designed compounds have interaction profiles similar to partial agonists. The most significant finding of our study is that BA derivatives with symmetrically substituted weakly polar side chains result in the desired moderate level of PPARγ binding affinities.

The elusive endogenous adipogenic PPARγ agonists: Lining up the suspects.

The nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) is the key decisive factor controlling the development of adipocytes. Ligand-mediated activation of PPARγ occurs early during adipogenesis and is thought to prime adipose conversion. Although several fatty acids and their derivatives are known to bind to and activate PPARγ, the identity of the ligand(s) responsible for initiating adipocyte differentiation is still a matter of debate. Here we review recent data on pathways involved in ligand production as well as possible endogenous, adipogenic PPARγ agonists.

Activity of dietary fatty acids on FFA1 and FFA4 and characterisation of pinolenic acid as a dual FFA1/FFA4 agonist with potential effect against metabolic diseases.

Various foods are associated with effects against metabolic diseases such as insulin resistance and type 2 diabetes; however, their mechanisms of action are mostly unclear. Fatty acids may contribute by acting as precursors of signalling molecules or by direct activity on receptors. The medium- and long-chain NEFA receptor FFA1 (free fatty acid receptor 1, previously known as GPR40) has been linked to enhancement of glucose-stimulated insulin secretion, whereas FFA4 (free fatty acid receptor 4, previously known as GPR120) has been associated with insulin-sensitising and anti-inflammatory effects, and both receptors are reported to protect pancreatic islets and promote secretion of appetite and glucose-regulating hormones. Hypothesising that FFA1 and FFA4 mediate therapeutic effects of dietary components, we screened a broad selection of NEFA on FFA1 and FFA4 and characterised active compounds in concentration-response curves. Of the screened compounds, pinolenic acid, a constituent of pine nut oil, was identified as a relatively potent and efficacious dual FFA1/FFA4 agonist, and its suitability for further studies was confirmed by additional in vitro characterisation. Pine nut oil and free and esterified pure pinolenic acid were tested in an acute glucose tolerance test in mice. Pine nut oil showed a moderately but significantly improved glucose tolerance compared with maize oil. Pure pinolenic acid or ethyl ester gave robust and highly significant improvements of glucose tolerance. In conclusion, the present results indicate that pinolenic acid is a comparatively potent and efficacious dual FFA1/FFA4 agonist that exerts antidiabetic effects in an acute mouse model. The compound thus deserves attention as a potential active dietary ingredient to prevent or counteract metabolic diseases.

Isomeric C12-alkamides from the roots of Echinacea purpurea improve basal and insulin-dependent glucose uptake in 3T3-L1 adipocytes.

Echinacea purpurea has been used in traditional medicine as a remedy for the treatment and prevention of upper respiratory tract infections and the common cold. Recent investigations have indicated that E. purpurea also has an effect on insulin resistance. A dichloromethane extract of E. purpurea roots was found to enhance glucose uptake in adipocytes and to activate peroxisome proliferator-activated receptor γ. The purpose of the present study was to identify the bioactive compounds responsible for the potential antidiabetic effect of the dichloromethane extract using a bioassay-guided fractionation approach. Basal and insulin-dependent glucose uptake in 3T3-L1 adipocytes were used to assess the bioactivity of extract, fractions and isolated metabolites. A peroxisome proliferator-activated receptor γ transactivation assay was used to determine the peroxisome proliferator-activated receptor γ activating properties of the extract, active fractions and isolated metabolites. Two novel isomeric dodeca-2E,4E,8Z,10E/Z-tetraenoic acid 2-methylbutylamides together with two known C12-alkamides and α-linolenic acid were isolated from the active fractions. The isomeric C12-alkamides were found to activate peroxisome proliferator-activated receptor γ, to increase basal and insulin-dependent glucose uptake in adipocytes in a dose-dependent manner, and to exhibit characteristics of a peroxisome proliferator-activated receptor γ partial agonist.

Clinical impact of FDG-PET/CT on colorectal cancer staging and treatment strategy.

FDG-PET/CT is rarely used for initial staging of patients with colorectal cancer (CRC). Surgical resection of primary tumor and isolated metastases may result in long-term survival or presumed cure, whereas disseminated disease contraindicates operation. We analyzed a retrospective material to elucidate the potential value of FDG-PET/CT for staging of CRC. Data were retrieved from 67 consecutive patients (24-84 years) with histopathologically proven CRC who had undergone FDG-PET/CT in addition to conventional imaging for initial staging. Treatment plans before and after FDG-PET/CT were compared and patients divided as follows: (A) Patients with a change in therapy following FDG-PET/CT and (B) Patients without a change following FDG-PET/CT. Sixty-two patients had colon and five had rectal cancer. Of these, 20 (30%; CI 20.2-41.7) belonged to group A, whereas 47 (70%; CI 58.3-79.8) fell in group B. In conclusion, FDG-PET/CT changed treatment plan in 30% of cases. In ⅓ of these there was either a change from intended curative to palliative therapy or vice versa, while in the remaining ⅔ the pattern was more mixed. Thus, even in a retrospective routine material there were substantial changes in management strategy following FDG-PET/CT for staging in CRC.

Discovery of new PPARγ agonists based on arylopeptoids.

In this study we present the design, synthesis and biological evaluation of a small, first-generation library of small molecule aromatic amides based on the arylopeptoid skeleton. The compounds were efficiently synthesized using a highly convenient submonomer solid-phase methodology which potentially allows for access to great product diversity. The synthesized compounds were tested for their ability to activate peroxisome proliferator-activated receptors (PPARs) and they all acted as PPARγ agonists in the µM range spanning from 2.5- to 14.7-fold activation of the receptor. This is the first discovery of bioactive molecules based on the arylopeptoid architecture.

Discovery of a novel selective PPARγ ligand with partial agonist binding properties by integrated in silico/in vitro work flow.

Full agonists to the peroxisome proliferator-activated receptor (PPAR)γ, such as Rosiglitazone, have been associated with a series of undesired side effects, such as weight gain, fluid retention, cardiac hypertrophy, and hepatotoxicity. Nevertheless, PPARγ is involved in the expression of genes that control glucose and lipid metabolism and is an important target for drugs against type 2 diabetes, dyslipidemia, atherosclerosis, and cardiovascular disease. In an effort to identify novel PPARγ ligands with an improved pharmacological profile, emphasis has shifted to selective ligands with partial agonist binding properties. Toward this end we applied an integrated in silico/in vitro workflow, based on pharmacophore- and structure-based virtual screening of the ZINC library, coupled with competitive binding and transactivation assays, and adipocyte differentiation and gene expression studies. Hit compound 9 was identified as the most potent ligand (IC50 = 0.3 µM) and a relatively poor inducer of adipocyte differentiation. The binding mode of compound 9 was confirmed by molecular dynamics simulation, and the calculated free energy of binding was -8.4 kcal/mol. A novel functional group, the carbonitrile group, was identified to be a key substituent in the ligand-protein interactions. Further studies on the transcriptional regulation properties of compound 9 revealed a gene regulatory profile that was to a large extent unique, however functionally closer to that of a partial agonist.

High-glycemic index carbohydrates abrogate the antiobesity effect of fish oil in mice.

Fish oil rich in n-3 polyunsaturated fatty acids is known to attenuate diet-induced obesity and adipose tissue inflammation in rodents. Here we aimed to investigate whether different carbohydrate sources modulated the antiobesity effects of fish oil. By feeding C57BL/6J mice isocaloric high-fat diets enriched with fish oil for 6 wk, we show that increasing amounts of sucrose in the diets dose-dependently increased energy efficiency and white adipose tissue (WAT) mass. Mice receiving fructose had about 50% less WAT mass than mice fed a high fish oil diet supplemented with either glucose or sucrose, indicating that the glucose moiety of sucrose was responsible for the obesity-promoting effect of sucrose. To investigate whether the obesogenic effect of sucrose and glucose was related to stimulation of insulin secretion, we combined fish oil with high and low glycemic index (GI) starches. Mice receiving the fish oil diet containing the low-GI starch had significantly less WAT than mice fed high-GI starch. Moreover, inhibition of insulin secretion by administration of nifedipine significantly reduced WAT mass in mice fed a high-fish oil diet in combination with sucrose. Our data show that the macronutrient composition of the diet modulates the effects of fish oil. Fish oil combined with sucrose, glucose, or high-GI starch promotes obesity, and the reported anti-inflammatory actions of fish oil are abrogated. In conclusion, our data indicate that glycemic control of insulin secretion modulates metabolic effects of fish oil by demonstrating that high-GI carbohydrates attenuate the antiobesity effects of fish oil.

Pharmacophore-driven identification of PPARγ agonists from natural sources.

In a search for more effective and safe anti-diabetic compounds, we developed a pharmacophore model based on partial agonists of PPARγ. The model was used for the virtual screening of the Chinese Natural Product Database (CNPD), a library of plant-derived natural products primarily used in folk medicine. From the resulting hits, we selected methyl oleanonate, a compound found, among others, in Pistacia lentiscus var. Chia oleoresin (Chios mastic gum). The acid of methyl oleanonate, oleanonic acid, was identified as a PPARγ agonist through bioassay-guided chromatographic fractionations of Chios mastic gum fractions, whereas some other sub-fractions exhibited also biological activity towards PPARγ. The results from the present work are two-fold: on the one hand we demonstrate that the pharmacophore model we developed is able to select novel ligand scaffolds that act as PPARγ agonists; while at the same time it manifests that natural products are highly relevant for use in virtual screening-based drug discovery.

UCP1 induction during recruitment of brown adipocytes in white adipose tissue is dependent on cyclooxygenase activity.

BACKGROUND: The uncoupling protein 1 (UCP1) is a hallmark of brown adipocytes and pivotal for cold- and diet-induced thermogenesis. METHODOLOGY/PRINCIPAL FINDINGS: Here we report that cyclooxygenase (COX) activity and prostaglandin E(2) (PGE(2)) are crucially involved in induction of UCP1 expression in inguinal white adipocytes, but not in classic interscapular brown adipocytes. Cold-induced expression of UCP1 in inguinal white adipocytes was repressed in COX2 knockout (KO) mice and by administration of the COX inhibitor indomethacin in wild-type mice. Indomethacin repressed beta-adrenergic induction of UCP1 expression in primary inguinal adipocytes. The use of PGE(2) receptor antagonists implicated EP(4) as a main PGE(2) receptor, and injection of the stable PGE(2) analog (EP(3/4) agonist) 16,16 dm PGE(2) induced UCP1 expression in inguinal white adipose tissue. Inhibition of COX activity attenuated diet-induced UCP1 expression and increased energy efficiency and adipose tissue mass in obesity-resistant mice kept at thermoneutrality. CONCLUSIONS/SIGNIFICANCE: Our findings provide evidence that induction of UCP1 expression in white adipose tissue, but not in classic interscapular brown adipose tissue is dependent on cyclooxygenase activity. Our results indicate that cyclooxygenase-dependent induction of UCP1 expression in white adipose tissues is important for diet-induced thermogenesis providing support for a surprising role of COX activity in the control of energy balance and obesity development.

Quercetin enhances adiponectin secretion by a PPAR-gamma independent mechanism.

To study possible insulin sensitizing, anti-inflammatory and anti-oxidative effects of the flavonol quercetin, rats were fed a high-fat diet (19%, w/w) with (HFQ) or without (HF) 0.03% quercetin or a flavonoid-poor low-fat (5%, w/w) maintenance diet (LF) over 4 weeks. Body weight was measured weekly, and plasma concentrations of adiponectin, leptin, insulin, glucose, triacylglycerols, total cholesterol, as well as of markers of inflammation and oxidative stress were measured (12h fasted) at the end of the feeding period. Adiponectin and peroxisome-proliferator-activated-receptor (PPAR)-gamma mRNA were measured in adipose tissue (WAT) by real-time RT-PCR. PPAR-gamma transactivation was investigated by means of a reporter gene assay. HF feeding resulted in elevated fasted plasma glucose concentrations, while HFQ did not differ from LF feeding. In the HFQ group plasma concentrations and WAT mRNA levels of adiponectin were elevated compared with the HF group, however, PPAR-gamma mRNA concentration in WAT was decreased (HFQ vs. HF). Compared to both other groups quercetin feeding significantly reduced oxidative stress, measured by plasma 8-iso-PGF(2alpha), while body weight gain, body composition and plasma leptin levels were not affected. Neither quercetin nor its metabolites induced PPAR-gamma-mediated transactivation in vitro. Adiponectin stimulating effects of quercetin are PPAR-gamma-independent and prevent impairment of insulin sensitivity without affecting body weight and composition.

Epidermis-type lipoxygenase 3 regulates adipocyte differentiation and peroxisome proliferator-activated receptor gamma activity.

The nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR gamma) is essential for adipogenesis. Although several fatty acids and their derivatives are known to bind and activate PPAR gamma, the nature of the endogenous ligand(s) promoting the early stages of adipocyte differentiation has remained enigmatic. Previously, we showed that lipoxygenase (LOX) activity is involved in activation of PPAR gamma during the early stages of adipocyte differentiation. Of the seven known murine LOXs, only the unconventional LOX epidermis-type lipoxygenase 3 (eLOX3) is expressed in 3T3-L1 preadipocytes. Here, we show that forced expression of eLOX3 or addition of eLOX3 products stimulated adipogenesis under conditions that normally require an exogenous PPAR gamma ligand for differentiation. Hepoxilins, a group of oxidized arachidonic acid derivatives produced by eLOX3, bound to and activated PPAR gamma. Production of hepoxilins was increased transiently during the initial stages of adipogenesis. Furthermore, small interfering RNA-mediated or retroviral short hairpin RNA-mediated knockdown of eLOX3 expression abolished differentiation of 3T3-L1 preadipocytes. Finally, we demonstrate that xanthine oxidoreductase (XOR) and eLOX3 synergistically enhanced PPAR gamma-mediated transactivation. Collectively, our results indicate that hepoxilins produced by the concerted action of XOR and eLOX3 may function as PPAR gamma activators capable of promoting the early PPAR gamma-dependent steps in the conversion of preadipocytes into adipocytes.

Identification of bioactive compounds from flowers of black elder (Sambucus nigra L.) that activate the human peroxisome proliferator-activated receptor (PPAR) gamma.

Obesity is one of the predisposing factors for the development of overt Type 2 diabetes (T2D). T2D is caused by a combination of insulin resistance and beta-cell failure and can be treated with insulin sensitizing drugs that target the nuclear receptor peroxisome proliferator-activated receptor (PPAR) gamma. Extracts of elderflowers (Sambucus nigra) have been found to activate PPARgamma and to stimulate insulin-dependent glucose uptake suggesting that they have a potential use in the prevention and/or treatment of insulin resistance. Bioassay-guided chromatographic fractionation of a methanol extract of elderflowers resulted in the identification of two well-known PPARgamma agonists; alpha-linolenic acid and linoleic acid as well as the flavanone naringenin. Naringenin was found to activate PPARgamma without stimulating adipocyte differentiation. However, the bioactivities of these three metabolites were not able to fully account for the observed PPARgamma activation of the crude elderflower extracts and further studies are needed to determine whether this is due synergistic effects and/or other ligand-independent mechanisms. Elderflower metabolites such as quercetin-3-O-rutinoside, quercetin-3-O-glucoside, kaempferol-3-O-rutinoside, isorhamnetin-3-O-rutinoside, isorhamnetin-3-O-glucoside, and 5-O-caffeoylquinic acid were unable to activate PPARgamma. These findings suggest that flavonoid glycosides cannot activate PPARgamma, whereas some of their aglycones are potential agonists of PPARgamma.

ADD1/SREBP1c activates the PGC1-alpha promoter in brown adipocytes.

Cold adaptation elicits a paradoxical simultaneous induction of fatty acid synthesis and beta-oxidation in brown adipose tissue. We show here that cold exposure coordinately induced liver X receptor alpha (LXRalpha), adipocyte determination and differentiation-dependent factor 1 (ADD1)/sterol regulatory element-binding protein-1c (SREBP1c) and peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC1alpha) in brown and inguinal white adipose tissues, but not in epididymal white adipose tissue. Using in vitro models of white and brown adipocytes we demonstrate that beta-adrenergic stimulation induced expression of LXRalpha, ADD1/SREBP1c and PGC1alpha in cells with a brown-like adipose phenotype. We demonstrate that ADD1/SREBP1c is a powerful inducer of PGC1alpha expression via a conserved E box in the proximal promoter and that beta-adrenergic stimulation led to recruitment of ADD1/SREBP1c to this E box. The ability of ADD1/SREBP1c to activate the PGC1alpha promoter exhibited a striking cell type dependency, suggesting that additional cell type-restricted factors contribute to ADD1/SREBP1c-mediated activation. In conclusion, our data demonstrate a novel role of ADD1/SREBP1c as a regulator of PGC1alpha expression in brown adipose tissue.

Activation of PPARgamma by metabolites from the flowers of purple coneflower (Echinacea purpurea).

Thiazolidinediones are insulin sensitizing drugs that target the peroxisome proliferator-activated receptor (PPAR) gamma. An n-hexane extract of the flowers of Echinacea purpurea was found to activate PPARgamma without stimulating adipocyte differentiation. Bioassay-guided fractionations yielded five alkamides, of which one was new, and three fatty acids that all activated PPARgamma. The new alkamide hexadeca-2E,9Z,12Z,14E-tetraenoic acid isobutylamide (5) was identified by analysis of spectroscopic data and found to activate PPARgamma with no concurrent stimulation of adipocyte differentiation. Compound 5 was further shown to increase insulin-stimulated glucose uptake. The data suggest that flowers of E. purpurea contain compounds with potential to manage insulin resistance and type 2 diabetes.

Discovery of novel PPAR ligands by a virtual screening approach based on pharmacophore modeling, 3D shape, and electrostatic similarity screening.

Peroxisome proliferator-activated receptors (PPARs) are important targets for drugs used in the treatment of atherosclerosis, dyslipidaemia, obesity, type 2 diabetes, and other diseases caused by abnormal regulation of the glucose and lipid metabolism. We applied a virtual screening workflow based on a combination of pharmacophore modeling with 3D shape and electrostatic similarity screening techniques to discover novel scaffolds for PPAR ligands. From the resulting 10 virtual screening hits, five tested positive in human PPAR ligand-binding domain (hPPAR-LBD) transactivation assays and showed affinities for PPAR in a competitive binding assay. Compounds 5, 7, and 8 were identified as PPAR-alpha agonists, whereas compounds 2 and 9 showed agonistic activity for hPPAR-gamma. Moreover, compound 9 was identified as a PPAR-delta antagonist. These results demonstrate that our virtual screening protocol is able to enrich novel scaffolds for PPAR ligands that could be useful for drug development in the area of atherosclerosis, dyslipidaemia, and type 2 diabetes.

Activation of liver X receptors prevents statin-induced death of 3T3-L1 preadipocytes.

The biological functions of liver X receptors (LXRs) alpha and beta have primarily been linked to pathways involved in fatty acid and cholesterol homeostasis. Here we report a novel role of LXR activation in protecting cells from statin-induced death. When 3T3-L1 preadipocytes were induced to differentiate by standard isobutylmethylxanthine/dexamethasone/insulin treatment in the presence of statins, they failed to differentiate and underwent massive apoptosis. The simultaneous addition of selective LXR agonists prevented the statin-induced apoptosis. By using mouse embryo fibroblasts from wild-type (LXRalpha+/+/LXRbeta+/+), LXRalpha knock-out mice (LXRalpha(-/-)/LXRbeta+/+), LXRbeta knock-out mice (LXRalpha+/-/LXRbeta(-/-)), and LXR double knock-out mice (LXRalpha(-/-)/LXRbeta(-/-)) as well as 3T3-L1 cells transduced with retroviruses expressing either wild-type LXRalpha or a dominant negative version of LXRalpha, we demonstrate that the response to LXR agonists is LXR-dependent. Interestingly, LXR-mediated rescue of statin-induced apoptosis was not related to up-regulation of genes previously shown to be involved in the antiapoptotic action of LXR. Furthermore, forced expression of Bcl-2 did not prevent statin-induced apoptosis; nor did LXR action depend on protein kinase B, whose activation by insulin was impaired in statin-treated cells. Rather, LXR-dependent rescue of statin-induced apoptosis in 3T3-L1 preadipocytes required NF-kappaB activity, since expression of a dominant negative version of IkappaBalpha prevented LXR agonist-dependent rescue of statin-induced apoptosis. Thus, the results presented in this paper provide novel insight into the action of statins on and LXR-dependent inhibition of apoptosis.

Peroxisome proliferator-activated receptor gamma recruits the positive transcription elongation factor b complex to activate transcription and promote adipogenesis.

Positive transcription elongation factor b (P-TEFb) phosphorylates the C-terminal domain of RNA polymerase II, facilitating transcriptional elongation. In addition to its participation in general transcription, P-TEFb is recruited to specific promoters by some transcription factors such as c-Myc or MyoD. The P-TEFb complex is composed of a cyclin-dependent kinase (cdk9) subunit and a regulatory partner (cyclin T1, cyclin T2, or cyclin K). Because cdk9 has been shown to participate in differentiation processes, such as muscle cell differentiation, we studied a possible role of cdk9 in adipogenesis. In this study we show that the expression of the cdk9 p55 isoform is highly regulated during 3T3-L1 adipocyte differentiation at RNA and protein levels. Furthermore, cdk9, as well as cyclin T1 and cyclin T2, shows differences in nuclear localization at distinct stages of adipogenesis. Overexpression of cdk9 increases the adipogenic potential of 3T3-L1 cells, whereas inhibition of cdk9 by specific cdk inhibitors, and dominant-negative cdk9 mutant impairs adipogenesis. We show that the positive effects of cdk9 on the differentiation of 3T3-L1 cells are mediated by a direct interaction with and phosphorylation of peroxisome proliferator-activated receptor gamma (PPARgamma), which is the master regulator of this process, on the promoter of PPARgamma target genes. PPARgamma-cdk9 interaction results in increased transcriptional activity of PPARgamma and therefore increased adipogenesis.