The Ubiquitous Soil Terpene Geosmin Acts as a Warning Chemical.

Known as the smell of earth after rain, geosmin is an odorous terpene detectable by humans at picomolar concentrations. Geosmin production is heavily conserved in actinobacteria, myxobacteria, cyanobacteria, and some fungi, but its biological activity is poorly understood. We theorized that geosmin was an aposematic signal used to indicate the unpalatability of toxin-producing microbes, discouraging predation by eukaryotes. Consistent with this hypothesis, we found that geosmin altered the behavior of the bacteriophagous nematode Caenorhabditis elegans on agar plates in the absence of bacteria. Normal movement was restored in mutant worms lacking differentiated ASE (amphid neurons, single ciliated endings) neurons, suggesting that geosmin is a taste detected by the nematodal gustatory system. In a predation assay, geosmin and the related terpene 2-methylisoborneol reduced grazing on the bacterium Streptomyces coelicolor. Predation was restored by the removal of both terpene biosynthetic pathways or the introduction of C. elegans that lacked differentiated ASE taste neurons, leading to the apparent death of both bacteria and worms. While geosmin and 2-methylisoborneol appeared to be nontoxic, grazing triggered bacterial sporulation and the production of actinorhodin, a pigment coproduced with a number of toxic metabolites. In this system, geosmin thus appears to act as a warning signal indicating the unpalatability of its producers and reducing predation in a manner that benefits predator and prey. This suggests that molecular signaling may affect microbial predator-prey interactions in a manner similar to that of the well-studied visual markers of poisonous animal prey. IMPORTANCE One of the key chemicals that give soil its earthy aroma, geosmin is a frequent water contaminant produced by a range of unrelated microbes. Many animals, including humans, are able to detect geosmin at minute concentrations, but the benefit that this compound provides to its producing organisms is poorly understood. We found that geosmin repelled the bacterial predator Caenorhabditis elegans in the absence of bacteria and reduced contact between the worms and the geosmin-producing bacterium Streptomyces coelicolor in a predation assay. While geosmin itself appears to be nontoxic to C. elegans, these bacteria make a wide range of toxic metabolites, and grazing on them harmed the worms. In this system, geosmin thus appears to indicate unpalatable bacteria, reducing predation and benefiting both predator and prey. Aposematic signals are well known in animals, and this work suggests that metabolites may play a similar role in the microbial world.

Differences in Riverine and Pond Water Dissolved Organic Matter Composition and Sources in Canadian High Arctic Watersheds Affected by Active Layer Detachments.

Regional warming has caused permafrost thermokarst and disturbances, such as active layer detachments (ALDs), which may alter carbon feedback in Arctic ecosystems. However, it is currently unclear how these disturbances alter DOM biogeochemistry in rivers and ponds in Arctic ecosystems. Water samples from the main river channel, ALD-disturbed/undisturbed tributaries, and disturbed/undisturbed ponds within a catchment in the Canadian High Arctic were collected and analyzed using carbon isotopes and spectroscopic methods. Both river and pond samples had large variations in dissolved organic carbon (DOC) concentrations. Ponds, particularly ALD-disturbed ponds, had much older 14C DOC ages than rivers. Results from δ13C and absorption and fluorescence analyses indicate higher autochthonous contributions in ponds than rivers and increasing autochthonous contributions from upper to lower reaches of the main channel. The disturbed samples had less carbohydrates but more carboxyl-rich alicyclic molecules in 1H nuclear magnetic resonance spectra than undisturbed samples. These ALD-impacted samples also contained less terrestrial-humic-like but more oxidized-quinone-like components in the fluorescence spectra. Interestingly, the disturbed pond DOM displayed the greatest DOM oxidation with ALDs compared to undisturbed areas. Compared to Arctic rivers, small Arctic ponds have DOM predominantly from permafrost and microbial sources and may have a disproportionally stronger positive feedback on climate warming.

Preservation of organic matter in sediments promoted by iron.

The biogeochemical cycles of iron and organic carbon are strongly interlinked. In oceanic waters, organic ligands have been shown to control the concentration of dissolved iron. In soils, solid iron phases shelter and preserve organic carbon, but the role of iron in the preservation of organic matter in sediments has not been clearly established. Here we use an iron reduction method previously applied to soils to determine the amount of organic carbon associated with reactive iron phases in sediments of various mineralogies collected from a wide range of depositional environments. Our findings suggest that 21.5 ± 8.6 per cent of the organic carbon in sediments is directly bound to reactive iron phases. We further estimate that a global mass of (19-45) × 10(15) grams of organic carbon is preserved in surface marine sediments as a result of its association with iron. We propose that these associations between organic carbon and iron, which are formed primarily through co-precipitation and/or direct chelation, promote the preservation of organic carbon in sediments. Because reactive iron phases are metastable over geological timescales, we suggest that they serve as an efficient 'rusty sink' for organic carbon, acting as a key factor in the long-term storage of organic carbon and thus contributing to the global cycles of carbon, oxygen and sulphur.

Metaproteomics of aquatic microbial communities in a deep and stratified estuary.

Here we harnessed the power of metaproteomics to assess the metabolic diversity and function of stratified aquatic microbial communities in the deep and expansive Lower St. Lawrence Estuary, located in eastern Canada. Vertical profiling of the microbial communities through the stratified water column revealed differences in metabolic lifestyles and in carbon and nitrogen processing pathways. In productive surface waters, we identified heterotrophic populations involved in the processing of high and low molecular weight organic matter from both terrestrial (e.g. cellulose and xylose) and marine (e.g. organic compatible osmolytes) sources. In the less productive deep waters, chemosynthetic production coupled to nitrification by MG-I Thaumarchaeota and Nitrospina appeared to be a dominant metabolic strategy. Similar to other studies of the coastal ocean, we identified methanol oxidation proteins originating from the common OM43 marine clade. However, we also identified a novel lineage of methanol-oxidizers specifically in the particle-rich bottom (i.e. nepheloid) layer. Membrane transport proteins assigned to the uncultivated MG-II Euryarchaeota were also specifically detected in the nepheloid layer. In total, these results revealed strong vertical structure of microbial taxa and metabolic activities, as well as the presence of specific "nepheloid" taxa that may contribute significantly to coastal ocean nutrient cycling.

Methane baseline concentrations and sources in shallow aquifers from the shale gas-prone region of the St. Lawrence lowlands (Quebec, Canada).

Hydraulic fracturing is becoming an important technique worldwide to recover hydrocarbons from unconventional sources such as shale gas. In Quebec (Canada), the Utica Shale has been identified as having unconventional gas production potential. However, there has been a moratorium on shale gas exploration since 2010. The work reported here was aimed at defining baseline concentrations of methane in shallow aquifers of the St. Lawrence Lowlands and its sources using δ(13)C methane signatures. Since this study was performed prior to large-scale fracturing activities, it provides background data prior to the eventual exploitation of shale gas through hydraulic fracturing. Groundwater was sampled from private (n = 81), municipal (n = 34), and observation (n = 15) wells between August 2012 and May 2013. Methane was detected in 80% of the wells with an average concentration of 3.8 ± 8.8 mg/L, and a range of <0.0006 to 45.9 mg/L. Methane concentrations were linked to groundwater chemistry and distance to the major faults in the studied area. The methane δ(1)(3)C signature of 19 samples was > -50‰, indicating a potential thermogenic source. Localized areas of high methane concentrations from predominantly biogenic sources were found throughout the study area. In several samples, mixing, migration, and oxidation processes likely affected the chemical and isotopic composition of the gases, making it difficult to pinpoint their origin. Energy companies should respect a safe distance from major natural faults in the bedrock when planning the localization of hydraulic fracturation activities to minimize the risk of contaminating the surrounding groundwater since natural faults are likely to be a preferential migration pathway for methane.

Using 13C enriched acetate in isotope labelling incubation experiments: a note of caution.

Vapour-phase fumigation with HCl is routinely used to remove inorganic carbon in preparation for the measurement of the concentration and δ13C value of organic carbon in a sample using elemental analysis coupled to an isotope ratio mass spectrometer. Acidification of the sample to be analyzed can lead to the loss of low molecular weight conjugate bases as volatile organic acids during the acidification and/or the drying steps following fumigation, through protonation of the conjugate base and volatilization. Such loss could lead to a severe bias in incubation experiments where 13C-enriched compounds such as acetate are used to trace reaction pathways or metabolites in a cultivation medium or a mesocosm for example. In this work, we enriched a carbonate-free freshwater sediment with 1-13C sodium acetate by 5, 10 and 20 ‰ relative to the δ13C value of the natural organic carbon of the sediment, and then tested the effects of HCl fumigation, drying at 50 °C and drying at room temperature, alone or in combination, on the measured δ13C values. We found that fumigation and drying at 50 °C, alone or in combination, both lead to the loss of the majority of the 13C-enriched acetate spike.

Organic matter preservation through complexation with iron minerals in two basins of a dimictic boreal lake with contrasting deep water redox regimes.

The biogeochemical cycles of iron and organic carbon (OC) are closely interconnected in terrestrial and aquatic systems. In ocean waters, the concentration of reactive Fe is tightly controlled by soluble organic ligands. In soils, Fe stabilizes OC by forming aggregates that shield OC from degradation. In lake sediments however, the role of Fe in the preservation of OC has not been explored as extensively yet. We investigated Fe-OC interactions in sediment collected from Lake Tantaré, in which two basins are characterized by contrasting redox conditions. These contrasting redox conditions provide an opportunity to assess their importance in the formation of stable Fe-OC complexes. On average, 30.1 ± 6.4 % of total OC was liberated upon reductively dissolving reactive iron. The Fe-associated and the non-Fe-associated OC pools were characterized at the elemental (OC, TN), isotopic (δ13C, δ15N) and functional group (FTIR) levels. Large differences in OC:Fe and TN:Fe ratios between the two basins were found which were not linked to OM chemical composition but rather to differences in reactive iron concentrations stemming from the higher abundance of iron sulfides in the anoxic basin. Nevertheless, since the affinity of OM for iron sulfides is lower than that for iron hydroxides, using OC:Fe and TN:Fe ratios as a diagnostic tool for the type of OM-Fe interactions should be done with care in anoxic environment. Same caution should be considered for oxic sediments due to the variation of the proportion of iron hydroxides associated with OM from sample to sample.

HSDL2 links nutritional cues to bile acid and cholesterol homeostasis.

In response to energy and nutrient shortage, the liver triggers several catabolic processes to promote survival. Despite recent progress, the precise molecular mechanisms regulating the hepatic adaptation to fasting remain incompletely characterized. Here, we report the identification of hydroxysteroid dehydrogenase-like 2 (HSDL2) as a mitochondrial protein highly induced by fasting. We show that the activation of PGC1α-PPARα and the inhibition of the PI3K-mTORC1 axis stimulate HSDL2 expression in hepatocytes. We found that HSDL2 depletion decreases cholesterol conversion to bile acids (BAs) and impairs FXR activity. HSDL2 knockdown also reduces mitochondrial respiration, fatty acid oxidation, and TCA cycle activity. Bioinformatics analyses revealed that hepatic Hsdl2 expression positively associates with the postprandial excursion of various BA species in mice. We show that liver-specific HSDL2 depletion affects BA metabolism and decreases circulating cholesterol levels upon refeeding. Overall, our report identifies HSDL2 as a fasting-induced mitochondrial protein that links nutritional signals to BAs and cholesterol homeostasis.

DEPTOR loss impairs brown adipocyte development in vitro but has limited impacts in mice.

OBJECTIVES: The mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that regulates growth and metabolism. In mice, activation of mTOR controls cold adaptation by promoting the recruitment and the activation of brown adipose tissue (BAT). DEP-domain containing mTOR-interacting protein (DEPTOR) interacts with mTOR to modulate its activity. Whether DEPTOR levels are modulated by cold in BAT and whether this protein regulates brown adipocyte development and thermogenic activation has never been tested. METHODS: DEPTOR levels were measured in mouse tissues upon cold exposure and in brown preadipocytes following the induction of adipogenesis. Lentiviruses expressing short-hairpin RNA were used to repress DEPTOR expression in brown preadipocytes in vitro. Conditional deletion of DEPTOR in brown preadipocytes and in mature brown fat cells was achieved by crossing DEPTOR floxed mice with either Myf5-Cre or Ucp1-CreERT2 mice. These animals were exposed to cold and extensively phenotyped. RESULTS: DEPTOR is highly expressed in BAT and its levels are induced by chronic cold exposure, a condition that triggers BAT expansion and activation. Supporting a role for DEPTOR in brown fat cell recruitment, we found that DEPTOR is induced during brown adipocyte development and that its depletion impairs adipogenesis in vitro. This adipogenic lesion was associated with defects in both Akt activation and the expression of key adipogenic regulators. Conditional deletion of DEPTOR in brown preadipocytes or mature brown fat cells did not impact BAT recruitment and thermogenesis in mice but slightly reduced the expression of adipogenic and lipogenic genes. CONCLUSIONS: DEPTOR is highly expressed in BAT and its levels are dynamically regulated during brown fat cell development and upon cold exposure. Although DEPTOR depletion severely represses brown fat adipogenesis in vitro, its deletion is dispensable for BAT development, recruitment, and thermogenic activation in mice.

Pre- and post-industrial levels of polycyclic aromatic hydrocarbons in sediments from the Estuary and Gulf of St. Lawrence (eastern Canada).

The concentrations of 23 polycyclic aromatic hydrocarbons (PAHs; 16 parent PAHs and 7 alkyl-PAHs) were determined in 45 surface sediment and 7 basal sediment box core samples retrieved from the Estuary and Gulf of St. Lawrence in eastern Canada. The concentration sums of 16 priority PAHs (Σ16PAHs) in the surface sediments (representing modern times or at least younger than the last decade) ranged from 71 to 5672 ng g-1. Σ16PAHs in the basal sediments ranged from 93 to 172 ng g-1 among the pre-industrial samples (pre-1900 common era or CE) and from 1216 to 1621 ng g-1 among the early post-industrial samples (~1930s and ~1940s CE). The highest Σ16PAH values occurred in samples retrieved from the Baie-Comeau-Matane area, an area affected by intense industrial anthropogenic activities. Source-diagnostic PAH ratios suggest a predominance of pyrogenic sources via atmospheric deposition, with a minor contribution of petrogenic seabed pockmark sources. The PAH concentrations in the sediments from the study areas reveal low ecological risks to benthic or other organisms living near the water-sediment interface.

The transcription factor hepatocyte nuclear factor 4A acts in the intestine to promote white adipose tissue energy storage.

The transcription factor hepatocyte nuclear factor 4 A (HNF4A) controls the metabolic features of several endodermal epithelia. Both HNF4A and HNF4G are redundant in the intestine and it remains unclear whether HNF4A alone controls intestinal lipid metabolism. Here we show that intestinal HNF4A is not required for intestinal lipid metabolism per se, but unexpectedly influences whole-body energy expenditure in diet-induced obesity (DIO). Deletion of intestinal HNF4A caused mice to become DIO-resistant with a preference for fat as an energy substrate and energetic changes in association with white adipose tissue (WAT) beiging. Intestinal HNF4A is crucial for the fat-induced release of glucose-dependent insulinotropic polypeptide (GIP), while the reintroduction of a stabilized GIP analog rescues the DIO resistance phenotype of the mutant mice. Our study provides evidence that intestinal HNF4A plays a non-redundant role in whole-body lipid homeostasis and points to a non-cell-autonomous regulatory circuit for body-fat management.

Deep ocean microbial communities produce more stable dissolved organic matter through the succession of rare prokaryotes.

The microbial carbon pump (MCP) hypothesis suggests that successive transformation of labile dissolved organic carbon (DOC) by prokaryotes produces refractory DOC (RDOC) and contributes to the long-term stability of the deep ocean DOC reservoir. We tested the MCP by exposing surface water from a deep convective region of the ocean to epipelagic, mesopelagic, and bathypelagic prokaryotic communities and tracked changes in dissolved organic matter concentration, composition, and prokaryotic taxa over time. Prokaryotic taxa from the deep ocean were more efficient at consuming DOC and producing RDOC as evidenced by greater abundance of highly oxygenated molecules and fluorescent components associated with recalcitrant molecules. This first empirical evidence of the MCP in natural waters shows that carbon sequestration is more efficient in deeper waters and suggests that the higher diversity of prokaryotes from the rare biosphere holds a greater metabolic potential in creating these stable dissolved organic compounds.

ZNF768 links oncogenic RAS to cellular senescence.

RAS proteins are GTPases that lie upstream of a signaling network impacting cell fate determination. How cells integrate RAS activity to balance proliferation and cellular senescence is still incompletely characterized. Here, we identify ZNF768 as a phosphoprotein destabilized upon RAS activation. We report that ZNF768 depletion impairs proliferation and induces senescence by modulating the expression of key cell cycle effectors and established p53 targets. ZNF768 levels decrease in response to replicative-, stress- and oncogene-induced senescence. Interestingly, ZNF768 overexpression contributes to bypass RAS-induced senescence by repressing the p53 pathway. Furthermore, we show that ZNF768 interacts with and represses p53 phosphorylation and activity. Cancer genomics and immunohistochemical analyses reveal that ZNF768 is often amplified and/or overexpressed in tumors, suggesting that cells could use ZNF768 to bypass senescence, sustain proliferation and promote malignant transformation. Thus, we identify ZNF768 as a protein linking oncogenic signaling to the control of cell fate decision and proliferation.

Reburial of fossil organic carbon in marine sediments.

Marine sediments act as the ultimate sink for organic carbon, sequestering otherwise rapidly cycling carbon for geologic timescales. Sedimentary organic carbon burial appears to be controlled by oxygen exposure time in situ, and much research has focused on understanding the mechanisms of preservation of organic carbon. In this context, combustion-derived black carbon has received attention as a form of refractory organic carbon that may be preferentially preserved in soils and sediments. However, little is understood about the environmental roles, transport and distribution of black carbon. Here we apply isotopic analyses to graphitic black carbon samples isolated from pre-industrial marine and terrestrial sediments. We find that this material is terrestrially derived and almost entirely depleted of radiocarbon, suggesting that it is graphite weathered from rocks, rather than a combustion product. The widespread presence of fossil graphitic black carbon in sediments has therefore probably led to significant overestimates of burial of combustion-derived black carbon in marine sediments. It could be responsible for biasing radiocarbon dating of sedimentary organic carbon, and also reveals a closed loop in the carbon cycle. Depending on its susceptibility to oxidation, this recycled carbon may be locked away from the biologically mediated carbon cycle for many geologic cycles.

HNF4α is a novel regulator of intestinal glucose-dependent insulinotropic polypeptide.

Mutations in the HNF4A gene cause MODY1 and are associated with an increased risk of Type 2 diabetes mellitus. On the other hand, incretins are hormones that potentiate reductions in blood glucose levels. Given the established role of incretin-based therapy to treat diabetes and metabolic disorders, we investigated a possible regulatory link between intestinal epithelial HNF4α and glucose-dependent insulinotropic polypeptide (GIP), an incretin that is specifically produced by gut enteroendocrine cells. Conditional deletion of HNF4α in the whole intestinal epithelium was achieved by crossing Villin-Cre and Hnf4αloxP/loxP C57BL/6 mouse models. GIP expression was measured by qPCR, immunofluorescence and ELISA. Gene transcription was assessed by luciferase and electrophoretic mobility shift assays. Metabolic parameters were analyzed by indirect calorimetry and dual-energy X-ray absorptiometry. HNF4α specific deletion in the intestine led to a reduction in GIP. HNF4α was able to positively control Gip transcriptional activity in collaboration with GATA-4 transcription factor. Glucose homeostasis and glucose-stimulated insulin secretion remained unchanged in HNF4α deficient mice. Changes in GIP production in these mice did not impact nutrition or energy metabolism under normal physiology but led to a reduction of bone area and mineral content, a well described physiological consequence of GIP deficiency. Our findings point to a novel regulatory role between intestinal HNF4α and GIP with possible functional impact on bone density.

The Hepatokine TSK does not affect brown fat thermogenic capacity, body weight gain, and glucose homeostasis.

OBJECTIVES: Hepatokines are proteins secreted by the liver that impact the functions of the liver and various tissues through autocrine, paracrine, and endocrine signaling. Recently, Tsukushi (TSK) was identified as a new hepatokine that is induced by obesity and cold exposure. It was proposed that TSK controls sympathetic innervation and thermogenesis in brown adipose tissue (BAT) and that loss of TSK protects against diet-induced obesity and improves glucose homeostasis. Here we report the impact of deleting and/or overexpressing TSK on BAT thermogenic capacity, body weight regulation, and glucose homeostasis. METHODS: We measured the expression of thermogenic genes and markers of BAT innervation and activation in TSK-null and TSK-overexpressing mice. Body weight, body temperature, and parameters of glucose homeostasis were also assessed in the context of TSK loss and overexpression. RESULTS: The loss of TSK did not affect the thermogenic activation of BAT. We found that TSK-null mice were not protected against the development of obesity and did not show improvement in glucose tolerance. The overexpression of TSK also failed to modulate thermogenesis, body weight gain, and glucose homeostasis in mice. CONCLUSIONS: TSK is not a significant regulator of BAT thermogenesis and is unlikely to represent an effective target to prevent obesity and improve glucose homeostasis.

The hepatokine Tsukushi is released in response to NAFLD and impacts cholesterol homeostasis.

Nonalcoholic fatty liver disease (NAFLD) prevails in obesity and is linked to several health complications including dyslipidemia and atherosclerosis. How exactly NAFLD induces atherogenic dyslipidemia to promote cardiovascular diseases is still elusive. Here, we identify Tsukushi (TSK) as a hepatokine induced in response to NAFLD. We show that both endoplasmic reticulum stress and inflammation promote the expression and release of TSK in mice. In humans, hepatic TSK expression is also associated with steatosis, and its circulating levels are markedly increased in patients suffering from acetaminophen-induced acute liver failure (ALF), a condition linked to severe hepatic inflammation. In these patients, elevated blood TSK levels were associated with decreased transplant-free survival at hospital discharge, suggesting that TSK could have a prognostic significance. Gain- and loss-of-function studies in mice revealed that TSK impacts systemic cholesterol homeostasis. TSK reduces circulating HDL cholesterol, lowers cholesterol efflux capacity, and decreases cholesterol-to-bile acid conversion in the liver. Our data identify the hepatokine TSK as a blood biomarker of liver stress that could link NAFLD to the development of atherogenic dyslipidemia and atherosclerosis.

Coupling a high-temperature catalytic oxidation total organic carbon analyzer to an isotope ratio mass spectrometer to measure natural-abundance delta13C-dissolved organic carbon in marine and freshwater samples.

The stable isotope composition of dissolved organic carbon (delta(13)C-DOC) provides powerful information toward understanding carbon sources and cycling, but analytical limitations have precluded its routine measurement in natural samples. Recent interfacing of wet oxidation-based dissolved organic carbon analyzers and isotope ratio mass spectrometers has simplified the measurement of delta(13)C-DOC in freshwaters, but the analysis of salty estuarine/marine samples still proves difficult. Here we describe the coupling of the more widespread high-temperature catalytic oxidation-based total organic carbon analyzer to an isotope ratio mass spectrometer (HTC-IRMS) through cryogenic trapping of analyte gases exiting the HTC analyzer for routine analysis of delta(13)C-DOC in aquatic and marine samples. Targeted elimination of major sources of background CO2 originating from the HTC analyzer allows for the routine measurement of samples over the natural range of DOC concentrations (from 40 microM to over 2000 microM), and salinities (<0.1-36 g/kg). Because consensus reference natural samples for delta(13)C-DOC do not exist, method validation was carried out with water-soluble stable isotope standards as well as previously measured natural samples (IAEA sucrose, Suwannee River Fulvic Acids, Deep Sargasso Sea consensus reference material, and St. Lawrence River water) and result in excellent delta(13)C-DOC accuracy (+/-0.2 per thousand) and precision (+/-0.3 per thousand).

PPARγ is a major regulator of branched-chain amino acid blood levels and catabolism in white and brown adipose tissues.

OBJECTIVE: We investigated whether PPARγ modulates adipose tissue BCAA metabolism, and whether this mediates the attenuation of obesity-associated insulin resistance induced by pharmacological PPARγ activation. METHODS: Mice with adipocyte deletion of one or two PPARγ copies fed a chow diet and rats fed either chow, or high fat (HF) or HF supplemented with BCAA (HF/BCAA) diets treated with rosiglitazone (30 or 15 mg/kg/day, 14 days) were evaluated for glucose and BCAA homeostasis. RESULTS: Adipocyte deletion of one PPARγ copy increased mice serum BCAA and reduced inguinal white (iWAT) and brown (BAT) adipose tissue BCAA incorporation into triacylglycerol, as well as mRNA levels of branched-chain aminotransferase (BCAT)2 and branched-chain α-ketoacid dehydrogenase (BCKDH) complex subunits. Adipocyte deletion of two PPARγ copies induced lipodystrophy, severe glucose intolerance and markedly increased serum BCAA. Rosiglitazone abolished the increase in serum BCAA induced by adipocyte PPARγ deletion. In rats, HF increased serum BCAA, such levels being further increased by BCAA supplementation. Rosiglitazone, independently of diet, lowered serum BCAA and upregulated iWAT and BAT BCAT and BCKDH activities. This was associated with a reduction in mTORC1-dependent inhibitory serine phosphorylation of IRS1 in skeletal muscle and whole-body insulin resistance evaluated by HOMA-IR. CONCLUSIONS: PPARγ, through the regulation of both BAT and iWAT BCAA catabolism in lipoeutrophic mice and muscle insulin responsiveness and proteolysis in lipodystrophic mice, is a major determinant of circulating BCAA levels. PPARγ agonism, therefore, may improve whole-body and muscle insulin sensitivity by reducing blood BCAA, alleviating mTORC1-mediated inhibitory IRS1 phosphorylation.

Depot-specific modulation of rat intraabdominal adipose tissue lipid metabolism by pharmacological inhibition of 11beta-hydroxysteroid dehydrogenase type 1.

The metabolic consequences of visceral obesity have been associated with amplification of glucocorticoid action by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) in adipose tissue. This study aimed to assess in a rat model of diet-induced obesity the effects of pharmacological 11beta-HSD1 inhibition on the morphology and expression of key genes of lipid metabolism in intraabdominal adipose depots. Rats fed a high-sucrose, high-fat diet were treated or not with a specific 11beta-HSD1 inhibitor (compound A, 3 mg/kg.d) for 3 wk. Compound A did not alter food intake or body weight gain but specifically reduced mesenteric adipose weight (-18%) and adipocyte size, without significantly affecting those of epididymal or retroperitoneal depots. In mesenteric fat, the inhibitor decreased (to 25-50% of control) mRNA levels of genes involved in lipid synthesis (FAS, SCD1, DGAT1) and fatty acid cycling (lipolysis/reesterification, ATGL and PEPCK) and increased (30%) the activity of the fatty acid oxidation-promoting enzyme carnitine palmitoyltransferase 1. In striking contrast, in the epididymal depot, 11beta-HSD1 inhibition increased (1.5-5-fold) mRNA levels of those genes related to lipid synthesis/cycling and slightly decreased carnitine palmitoyltransferase 1 activity, whereas gene expression remained unaffected in the retroperitoneal depot. Compound A robustly reduced liver triacylglycerol content and plasma lipids. The study demonstrates that pharmacological inhibition of 11beta-HSD1, at a dose that does not alter food intake, reduces fat accretion specifically in the mesenterical adipose depot, exerts divergent intraabdominal depot-specific effects on genes of lipid metabolism, and reduces steatosis and lipemia.