The adipocyte-expressed forkhead transcription factor Foxc2 regulates metabolism through altered mitochondrial function.

OBJECTIVE: Previous findings demonstrate that enhanced expression of the forkhead transcription factor Foxc2 in adipose tissue leads to a lean and insulin-sensitive phenotype. These findings prompted us to further investigate the role of Foxc2 in the regulation of genes of fundamental importance for metabolism and mitochondrial function. RESEARCH DESIGN AND METHODS: The effects of Foxc2 on expression of genes involved in mitochondriogenesis and mitochondrial function were assessed by quantitative real-time PCR. The potential of a direct transcriptional regulation of regulated genes was tested in promoter assays, and mitochondrial morphology was investigated by electron microscopy. Mitochondrial function was tested by measuring oxygen consumption and extracellular acidification rates as well as palmitate oxidation. RESULTS: Enhanced expression of FOXC2 in adipocytes or in cells with no endogenous Foxc2 expression induces mitochondriogenesis and an elongated mitochondrial morphology. Together with increased aerobic metabolic capacity, increased palmitate oxidation, and upregulation of genes encoding respiratory complexes and of brown fat-related genes, Foxc2 also specifically induces mitochondrial fusion genes in adipocytes. Among tested forkhead genes, Foxc2 is unique in its ability to trans-activate the nuclear-encoded mitochondrial transcription factor A (mtTFA/Tfam) gene--a master regulator of mitochondrial biogenesis. In human adipose tissue the expression levels of mtTFA/Tfam and of fusion genes also correlate with that of Foxc2. CONCLUSIONS: We previously showed that a high-calorie diet and insulin induce Foxc2 in adipocytes; the current findings identify a previously unknown role for Foxc2 as an important metabo-regulator of mitochondrial morphology and metabolism.

Viscoelastic sensing of conformational changes in plasminogen induced upon binding of low molecular weight compounds.

Plasminogen is a precursor to the fibrinolytic enzyme plasmin and is known to undergo large conformational changes when subjected to low molecular lysine analogues such as tranexamic acid (TA) or ε-amino-n-caproic acid (EACA). Here, we demonstrate how well-controlled surface immobilization of biotinylated plasminogen allows for monitoring of the interaction between TA and EACA with plasminogen. The interaction was studied by the quartz crystal microbalance with dissipation monitoring (QCM-D) technique as well as by surface plasmon resonance (SPR) based sensing. QCM-D measures changes in acoustically coupled mass (by detection of changes in the resonance frequency of the crystal, Δf) and is sensitive to changes in mass adsorbed on the sensor surface including how liquid medium is associated with this material. Through the dissipation factor (i.e., changes in the energy dissipation of the crystal oscillation, ΔD), QCM-D is also sensitive to the viscoelastic properties of material adsorbed to the sensor surface. Upon binding of TA or EACA, changes in the plasminogen structure were recorded as distinct, although small, ΔD responses which were used to determine affinity constants. By comparing native and truncated plasminogen, we conclude that the observed dissipation shifts were caused by conformational changes in the proteins leading to changes in the viscoelastic properties of the protein layer on the surface. These results demonstrate a novel application of the QCM-D technique, paving the way for a whole new approach to screening of this target for novel lead structures.

Anti-inflammatory properties of the short-chain fatty acids acetate and propionate: a study with relevance to inflammatory bowel disease.

AIM: To compare the anti-inflammatory properties of butyrate with two other SCFAs, namely acetate and propionate, which have less well-documented effects on inflammation. METHODS: The effect of SCFAs on cytokine release from human neutrophils was studied with ELISA. SCFA-dependent modulation of NF-kappaB reporter activity was assessed in the human colon adenocarcinoma cell line, Colo320DM. Finally, the effect of SCFAs on gene expression and cytokine release, measured with RT-PCR and ELISA, respectively, was studied in mouse colon organ cultures established from colitic mice. RESULTS: Acetate, propionate and butyrate at 30 mmol/L decreased LPS-stimulated TNFalpha release from neutrophils, without affecting IL-8 protein release. All SCFAs dose dependently inhibited NF-kappaB reporter activity in Colo320DM cells. Propionate dose-dependently suppressed IL-6 mRNA and protein release from colon organ cultures and comparative studies revealed that propionate and butyrate at 30 mmol/L caused a strong inhibition of immune-related gene expression, whereas acetate was less effective. A similar inhibition was achieved with the proteasome inhibitor MG-132, but not the p38 MAPK inhibitor SB203580. All SCFAs decreased IL-6 protein release from organ cultures. CONCLUSION: In the present study propionate and butyrate were equipotent, whereas acetate was less effective, at suppressing NF-kappaB reporter activity, immune-related gene expression and cytokine release in vitro. Our findings suggest that propionate and acetate, in addition to butyrate, could be useful in the treatment of inflammatory disorders, including IBD.