Adiponectin expression is induced by vitamin E via a peroxisome proliferator-activated receptor gamma-dependent mechanism

Adiponectin is a well-known adipokine secreted by adipocytes that presents insulin-sensitizing properties. The regulation of expression of this adipokine by micronutrients is largely unknown. We demonstrate here that adiponectin expression is induced in adipocytes after exposure to tocopherols via the peroxisome proliferator-activated receptor gamma (PPARgamma) pathway. Vitamin E force feeding resulted in an induction of adiponectin in mice at both mRNA and protein levels. Adiponectin mRNA and protein secretion were also increased by vitamin E (alpha- and gamma-tocopherol) in 3T3-L1 cells, together with PPARgamma mRNA, independent of an antioxidant effect. In transient transfections, both alpha- and gamma-vitamers induced the luciferase gene reporter under the control of a human adiponectin promoter via a PPAR-responsive element. The induction of adiponectin by tocopherols seems to be PPARgamma dependent, because it was blocked by the specific antagonist GW9662. Finally, we showed that intracellular concentrations of a PPARgamma endogenous ligand, 15-deoxy-Delta12,14-prostaglandin J2, increased after treatment with tocopherols in 3T3-L1 cells. In summary, vitamin E up-regulates adiponectin expression via a mechanism that implicates PPARgamma together with its endogenous ligand 15-deoxy-Delta12,14-prostaglandin J2. The induction of adiponectin via an original molecular mechanism could be considered as the basis for the beneficial effect of vitamin E on insulin sensitivity.

Phloretin enhances adipocyte differentiation and adiponectin expression in 3T3-L1 cells

Adipocyte dysfunction is strongly associated with the development of cardiovascular risk factors and diabetes. It is accepted that the regulation of adipogenesis or adipokines expression, notably adiponectin, is able to prevent these disorders. In this report, we show that phloretin, a dietary flavonoid, enhances 3T3-L1 adipocyte differentiation as evidenced by increased triglyceride accumulation and GPDH activity. At a molecular level, mRNA expression levels of both PPARgamma and C/EBPalpha, the master adipogenic transcription factors, are markedly increased by phloretin. Moreover, mRNA levels of PPARgamma target genes such as LPL, aP2, CD36 and LXRalpha are up-regulated by phloretin. We also show that phloretin enhances the expression and secretion of adiponectin. Co-transfection studies suggest the induction of PPARgamma transcriptional activity as a possible mechanism underlying the phloretin-mediated effects. Taken together, these results suggest that phloretin may be beneficial for reducing insulin resistance through its potency to regulate adipocyte differentiation and function.

CD36 is involved in lycopene and lutein uptake by adipocytes and adipose tissue cultures

SCOPE

Carotenoids are mainly stored in adipose tissue. However, nothing is known regarding the uptake of carotenoids by adipocytes. Thus, our study explored the mechanism by which lycopene and lutein, two major human plasma carotenoids, are transported.

METHODS AND RESULTS

CD36 was a putative candidate for this uptake, 3T3-L1 cells were treated with sulfosuccinimidyl oleate, a CD36-specific inhibitor. sulfosuccinimidyl oleate-treated cells showed a significant decrease in both lycopene and lutein uptake as compared to control cells. Their uptake was also decreased by partial inhibition of CD36 expression using siRNA, whereas the overexpression of CD36 in Cos-1 cells increased their uptake. Finally, the effect of CD36 on carotenoid uptake was confirmed ex vivo in cultures of adipose tissue explants from CD36(-/-) mice, which exhibited reduced carotenoid uptake as compared to wild-type mice explants.

CONCLUSION

For the first time, we report the involvement of a transporter, CD36, in carotenoid uptake by adipocytes and adipose tissue.

Vitamin E decreases endogenous cholesterol synthesis and apo-AI-mediated cholesterol secretion in Caco-2 cells

Intestine is the gateway for newly absorbed tocopherols. This organ also plays a crucial role in cholesterol metabolism. Because tocopherols are known to impact cholesterol metabolism in the liver, we hypothesized that tocopherols could also modulate cholesterol metabolism in the intestine. This study aimed to verify this hypothesis and to unveil the mechanisms involved, using Caco-2 cells as a model of the human intestinal cell. Both α- and γ-tocopherol significantly (P<.05) decreased endogenous cholesterol synthesis and apo-AI-mediated cholesterol secretion in Caco-2 cells. Tocopherols down-regulated (P<.05) up to half of the genes involved in the cholesterol synthesis pathway, together with CYP27A1, which is involved in oxysterol production. The activity of this enzyme, as well as the levels of intracellular oxysterols, was significantly diminished by tocopherols. Finally, tocopherols significantly reduced ABCA1 mRNA levels in Caco-2 cells. We conclude that tocopherols impair the endogenous synthesis and apo-AI-mediated secretion of cholesterol in Caco-2 cells. This effect involves a down-regulation of genes involved in the cholesterol synthesis pathway, resulting in down-regulation of CYP27A1 which, in turn, diminishes oxysterol concentrations. The outcome is a decrease of LXR activity, resulting in down-regulation of ABCA1. These data reinforce the effect of α- and γ-tocopherol on cholesterol metabolism via gene expression regulation.

Purified low-density lipoprotein and bovine serum albumin efficiency to internalise lycopene into adipocytes

Epidemiological studies have suggested that lycopene has protective effects against various diseases including cardiovascular diseases. However, mechanistic studies to understand these effects are difficult due to the insolubility of lycopene in aqueous culture medium. The objective of the present study was to use LDL or BSA as physiological vehicles for lycopene and to compare them with various classical vehicles. Among tested vehicles, only LDL, BSA, THF/BHT, beadlets, and liposomes were able to solubilise lycopene. No cytotoxicity was observed with these vehicles. LDL and BSA allowed good stability of lycopene during incubation (52% and 43% for 2microM lycopene solutions), but remained less efficient than THF/BHT or beadlets (67% and 62%). Incubation of adipocytes (3T3-L1) with the different vehicles for 24 and 48h showed that beadlets best delivered lycopene to cells. Finally, whatever the vehicle used, intracellular localization of lycopene was the same: lipid droplets (32-51%), plasma membrane (32-37%) and nuclear membrane (19-29%). As a conclusion, LDL or BSA display comparable properties to THF/BHT or beadlets. It is the first time that lycopene carried by physiological vehicles is shown to reach different subcellular compartments supporting molecular effects in adipocyte, such as cell signaling or nuclear receptor interacting.

The plasminogen activation system modulates differently adipogenesis and myogenesis of embryonic stem cells

Regulation of the extracellular matrix (ECM) plays an important functional role either in physiological or pathological conditions. The plasminogen activation (PA) system, comprising the uPA and tPA proteases and their inhibitor PAI-1, is one of the main suppliers of extracellular proteolytic activity contributing to tissue remodeling. Although its function in development is well documented, its precise role in mouse embryonic stem cell (ESC) differentiation in vitro is unknown. We found that the PA system components are expressed at very low levels in undifferentiated ESCs and that upon differentiation uPA activity is detected mainly transiently, whereas tPA activity and PAI-1 protein are maximum in well differentiated cells. Adipocyte formation by ESCs is inhibited by amiloride treatment, a specific uPA inhibitor. Likewise, ESCs expressing ectopic PAI-1 under the control of an inducible expression system display reduced adipogenic capacities after induction of the gene. Furthermore, the adipogenic differentiation capacities of PAI-1(-/-) induced pluripotent stem cells (iPSCs) are augmented as compared to wt iPSCs. Our results demonstrate that the control of ESC adipogenesis by the PA system correspond to different successive steps from undifferentiated to well differentiated ESCs. Similarly, skeletal myogenesis is decreased by uPA inhibition or PAI-1 overexpression during the terminal step of differentiation. However, interfering with uPA during days 0 to 3 of the differentiation process augments ESC myotube formation. Neither neurogenesis, cardiomyogenesis, endothelial cell nor smooth muscle formation are affected by amiloride or PAI-1 induction. Our results show that the PA system is capable to specifically modulate adipogenesis and skeletal myogenesis of ESCs by successive different molecular mechanisms.

Mesenchymal stem cells derived from patients with premature aging syndromes display hallmarks of physiological aging

Progeroid syndromes are rare genetic diseases with most of autosomal dominant transmission, the prevalence of which is less than 1/10,000,000. These syndromes caused by mutations in the <i>LMNA</i> gene encoding A-type lamins belong to a group of disorders called laminopathies. Lamins are implicated in the architecture and function of the nucleus and chromatin. Patients affected with progeroid laminopathies display accelerated aging of mesenchymal stem cells (MSCs)-derived tissues associated with nuclear morphological abnormalities. To identify pathways altered in progeroid patients' MSCs, we used induced pluripotent stem cells (hiPSCs) from patients affected with classical Hutchinson-Gilford progeria syndrome (HGPS, c.1824C&gt;T-p.G608G), HGPS-like syndrome (HGPS-L; c.1868C&gt;G-p.T623S) associated with farnesylated prelamin A accumulation, or atypical progeroid syndromes (APS; homozygous c.1583C&gt; T-p.T528M; heterozygous c.1762T&gt;C-p.C588R; compound heterozygous c.1583C&gt;T and c.1619T&gt;C-p.T528M and p.M540T) without progerin accumulation. By comparative analysis of the transcriptome and methylome of hiPSC-derived MSCs, we found that patient's MSCs display specific DNA methylation patterns and modulated transcription at early stages of differentiation. We further explored selected biological processes deregulated in the presence of <i>LMNA</i> variants and confirmed alterations of age-related pathways during MSC differentiation. In particular, we report the presence of an altered mitochondrial pattern; an increased response to double-strand DNA damage; and telomere erosion in HGPS, HGPS-L, and APS MSCs, suggesting converging pathways, independent of progerin accumulation, but a distinct DNA methylation profile in HGPS and HGPS-L compared with APS cells.

Transcriptome and acetylome profiling identify crucial steps of neuronal differentiation in Rubinstein-Taybi syndrome

Rubinstein-Taybi syndrome (RTS) is a rare and severe genetic developmental disorder characterized by multiple congenital anomalies and intellectual disability. CREBBP and EP300, the two genes known to cause RTS encode transcriptional coactivators with a catalytic lysine acetyltransferase (KAT) activity. Loss of CBP or p300 function results in a deficit in protein acetylation, in particular at histones. In RTS, nothing is known on the consequences of the loss of histone acetylation on the transcriptomic profiles during neuronal differentiation. To address this question, we differentiated induced pluripotent stem cells from RTS patients carrying a recurrent CREBBP mutation that inactivates the KAT domain into cortical and pyramidal neurons. By comparing their acetylome and their transcriptome at different neuronal differentiation time points, we identified 25 specific acetylated histone residues altered in RTS. We also identified the transition between neural progenitors and immature neurons as a critical step of the differentiation process, with a delayed neuronal maturation in RTS. Overall, this study opens new perspectives in the definition of epigenetic biomarkers for RTS, whose methodology could be extended to other chromatinopathies.