Anik Boudreau

Dietary methionine restriction enhances metabolic flexibility and increases uncoupled respiration in both fed and fasted states

Dietary methionine restriction (MR) is a mimetic of chronic dietary restriction (DR) in the sense that MR increases rodent longevity, but without food restriction. We report here that MR also persistently increases total energy expenditure (EE) and limits fat deposition despite increasing weight-specific food consumption. In Fischer 344 (F344) rats consuming control or MR diets for 3, 9, and 20 mo, mean EE was 1.5-fold higher in MR vs. control rats, primarily due to higher EE during the night at all ages. The day-to-night transition produced a twofold higher heat increment of feeding (3.0 degrees C vs. 1.5 degrees C) in MR vs. controls and an exaggerated increase in respiratory quotient (RQ) to values greater than 1, indicative of the interconversion of glucose to lipid by de novo lipogenesis. The simultaneous inhibition of glucose utilization and shift to fat oxidation during the day was also more complete in MR (RQ approximately 0.75) vs. controls (RQ approximately 0.85). Dietary MR produced a rapid and persistent increase in uncoupling protein 1 expression in brown (BAT) and white adipose tissue (WAT) in conjunction with decreased leptin and increased adiponectin levels in serum, suggesting that remodeling of the metabolic and endocrine function of adipose tissue may have an important role in the overall increase in EE. We conclude that the hyperphagic response to dietary MR is matched to a coordinated increase in uncoupled respiration, suggesting the engagement of a nutrient-sensing mechanism, which compensates for limited methionine through integrated effects on energy homeostasis.

Alternative mRNA Splicing Produces a Novel Biologically Active Short Isoform of PGC-1α

The transcriptional co-activator PGC-1α regulates functional plasticity in adipose tissue by linking sympathetic input to the transcriptional program of adaptive thermogenesis. We report here a novel truncated form of PGC-1α (NT-PGC-1α) produced by alternative 3′ splicing that introduces an in-frame stop codon into PGC-1α mRNA. The expressed protein includes the first 267 amino acids of PGC-1α and 3 additional amino acids from the splicing insert. NT-PGC-1α contains the transactivation and nuclear receptor interaction domains but is missing key domains involved in nuclear localization, interaction with other transcription factors, and protein degradation. Expression and subcellular localization of NT-PGC-1α are dynamically regulated in the context of physiological signals that regulate full-length PGC-1α, but the truncated domain structure conveys unique properties with respect to protein-protein interactions, protein stability, and recruitment to target gene promoters. Therefore, NT-PGC-1α is a co-expressed, previously unrecognized form of PGC-1α with functions that are both unique from and complementary to PGC-1α.

Role of β-adrenergic receptors in the hyperphagic and hypermetabolic responses to dietary methionine restriction

Dietary methionine restriction (MR) limits fat deposition and decreases plasma leptin, while increasing food consumption, total energy expenditure (EE), plasma adiponectin, and expression of uncoupling protein 1 (UCP1) in brown and white adipose tissue (BAT and WAT). beta-adrenergic receptors (beta-AR) serve as conduits for sympathetic input to adipose tissue, but their role in mediating the effects of MR on energy homeostasis is unclear. Energy intake, weight, and adiposity were modestly higher in beta(3)-AR(-/-) mice on the Control diet compared with wild-type (WT) mice, but the hyperphagic response to the MR diet and the reduction in fat deposition did not differ between the genotypes. The absence of beta(3)-ARs also did not diminish the ability of MR to increase total EE and plasma adiponectin or decrease leptin mRNA, but it did block the MR-dependent increase in UCP1 mRNA in BAT but not WAT. In a further study, propranolol was used to antagonize remaining beta-adrenergic input (beta(1)- and beta(2)-ARs) in beta(3)-AR(-/-) mice, and this treatment blocked >50% of the MR-induced increase in total EE and UCP1 induction in both BAT and WAT. We conclude that signaling through beta-adrenergic receptors is a component of the mechanism used by dietary MR to increase EE, and that beta(1)- and beta(2)-ARs are able to substitute for beta(3)-ARs in mediating the effect of dietary MR on EE. These findings are consistent with the involvement of both UCP1-dependent and -independent mechanisms in the physiological responses affecting energy balance that are produced by dietary MR.

Remodeling the Integration of Lipid Metabolism Between Liver and Adipose Tissue by Dietary Methionine Restriction in Rats

Dietary methionine restriction (MR) produces an integrated series of biochemical and physiological responses that improve biomarkers of metabolic health, limit fat accretion, and enhance insulin sensitivity. Using transcriptional profiling to guide tissue-specific evaluations of molecular responses to MR, we report that liver and adipose tissue are the primary targets of a transcriptional program that remodeled lipid metabolism in each tissue. The MR diet produced a coordinated downregulation of lipogenic genes in the liver, resulting in a corresponding reduction in the capacity of the liver to synthesize and export lipid. In contrast, the transcriptional response in white adipose tissue (WAT) involved a depot-specific induction of lipogenic and oxidative genes and a commensurate increase in capacity to synthesize and oxidize fatty acids. These responses were accompanied by a significant change in adipocyte morphology, with the MR diet reducing cell size and increasing mitochondrial density across all depots. The coordinated transcriptional remodeling of lipid metabolism between liver and WAT by dietary MR produced an overall reduction in circulating and tissue lipids and provides a potential mechanism for the increase in metabolic flexibility and enhanced insulin sensitivity produced by the diet.

Comparing the effects of nano-sized sugarcane fiber with cellulose and psyllium on hepatic cellular signaling in mice

Aim To compare the effects of dietary fibers on hepatic cellular signaling in mice. Methods Mice were randomly divided into four groups (n = 9/group): high-fat diet (HFD) control, cellulose, psyllium, and sugarcane fiber (SCF) groups. All mice were fed a HFD with or without 10% dietary fiber (w/w) for 12 weeks. Body weight, food intake, fasting glucose, and fasting insulin levels were measured. At the end of the study, hepatic fibroblast growth factor (FGF) 21, AMP-activated protein kinase (AMPK) and insulin signaling protein content were determined. Results Hepatic FGF21 content was significantly lowered, but βKlotho, fibroblast growth factor receptor 1, fibroblast growth factor receptor 3, and peroxisome proliferator-activated receptor alpha proteins were significantly increased in the SCF group compared with those in the HFD group (P < 0.01). SCF supplementation also significantly enhanced insulin and AMPK signaling, as well as decreased hepatic triglyceride and cholesterol in comparison with the HFD mice. The study has shown that dietary fiber, especially SCF, significantly attenuates lipid accumulation in the liver by enhancing hepatic FGF21, insulin, and AMPK signaling in mice fed a HFD. Conclusion This study suggests that the modulation of gastrointestinal factors by dietary fibers may play a key role in both enhancing hepatic multiple cellular signaling and reducing lipid accumulation.

Screening native botanicals for bioactivity: An interdisciplinary approach

OBJECTIVE Plant-based therapies have been used in medicine throughout recorded history. Information about the therapeutic properties of plants often can be found in local cultures as folk medicine is communicated from one generation to the next. The aim of this study was to identify native Louisiana plants from Creole folk medicine as a potential source of therapeutic compounds for the treatment of insulin resistance, type 2 diabetes, and related disorders. METHODS We used an interdisciplinary approach combining expertise in disciplines ranging from cultural anthropology and botany to biochemistry and endocrinology to screen native southwest Louisiana plants. Translation of accounts of Creole folk medicine yielded a list of plants with documented use in treating a variety of conditions, including inflammation. These plants were collected, vouchered, and catalogued before extraction of soluble components. Extracts were analyzed for bioactivity in regulating inflammatory responses in macrophages or fatty acid-induced insulin resistance in C2C12 skeletal muscle cells. RESULTS Several extracts altered gene expression of inflammatory markers in macrophages. Multiplex analysis of kinase activation in insulin-signaling pathways in skeletal muscle also identified a subset of extracts that alter insulin-stimulated protein kinase B phosphorylation in the presence of fatty-acid-induced insulin resistance. CONCLUSION An interdisciplinary approach to screening botanical sources of therapeutic agents can be successfully applied to identify native plants used in folk medicine as potential sources of therapeutic agents in treating insulin resistance in skeletal muscle or inflammatory processes associated with obesity-related insulin resistance.

Groundsel Bush (Baccharis halimifolia) Extract Promotes Adipocyte Differentiation In Vitro and Increases Adiponectin Expression in Mature Adipocytes

An ethanolic extract of Baccharis halimifolia (groundsel bush, GB), which is a native Louisiana plant with documented use in Creole folk medicine, has been shown to inhibit lipopolysaccharide (LPS)-induced inflammation in cultured macrophages. Here, we examine the effects of GB on adipocyte development and function, as these processes are attractive targets for intervention in insulin resistance. Oil Red O neutral lipid staining, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and immunoblotting were used to measure GB effects on lipid accumulation, gene expression, and protein abundance, respectively. In differentiating 3T3-L1 adipocytes, GB enhanced lipid accumulation and increased expression of several adipogenic genes (GLUT4, aP2, ADPN, CEBPα, FAS, and PPARγ). Protein levels of two of these adipogenic markers (aP2 and adiponectin) were examined and found to be induced by GB treatment. In mature adipocytes, GB reduced the gene expression of resistin, a pro-inflammatory endocrine factor, increased the adiponectin protein levels in a time-dependent manner, and substantially attenuated the TNF-alpha-induced reduction in adiponectin. In macrophages, GB reduced the expression of pro-inflammatory genes that were induced by LPS. GB produces metabolically favorable changes in differentiating adipocytes, mature adipocytes, and macrophages in vitro, suggesting its potential use as a dietary supplement or nutraceutical to support metabolic health and resiliency.

An ethanolic extract of Artemisia scoparia (SCO) inhibits lipolysis in vivo and has anti-lipolytic effects on murine adipocytes in vitro.

An ethanolic extract of Artemisia scoparia (SCO) has metabolically favorable effects on adipocyte development and function in vitro and in vivo. In diet-induced obese mice, SCO supplementation significantly reduced fasting glucose and insulin levels. Given the importance of adipocyte lipolysis in metabolic health, we hypothesized that SCO modulates lipolysis in vitro and in vivo. Free fatty acids and glycerol were measured in the sera of mice fed a high-fat diet with or without SCO supplementation. In cultured 3T3-L1 adipocytes, the effects of SCO on lipolysis were assessed by measuring glycerol and free fatty acid release. Microarray analysis, qPCR, and immunoblotting were used to assess gene expression and protein abundance. We found that SCO supplementation of a high-fat diet in mice substantially reduces circulating glycerol and free fatty acid levels, and we observed a cell-autonomous effect of SCO to significantly attenuate tumor necrosis factor-α (TNFα)-induced lipolysis in cultured adipocytes. Although several prolipolytic and antilipolytic genes were identified by microarray analysis of subcutaneous and visceral adipose tissue from SCO-fed mice, regulation of these genes did not consistently correlate with SCOs ability to reduce lipolytic metabolites in sera or cell culture media. However, in the presence of TNFα in cultured adipocytes, SCO induced antilipolytic changes in phosphorylation of hormone-sensitive lipase and perilipin. Together, these data suggest that the antilipolytic effects of SCO on adipose tissue play a role in the ability of this botanical extract to improve whole body metabolic parameters and support its use as a dietary supplement to promote metabolic resiliency.

TITIN IS A CANDIDATE GENE FOR STROKE VOLUME RESPONSE TO ENDURANCE TRAINING: THE HERITAGE FAMILY STUDY

A genome-wide linkage scan for endurance training-induced changes in submaximal exercise stroke volume (DeltaSV50) in the HERITAGE Family Study revealed two chromosomal regions (2q31-q32 and 10p11.2) with at least suggestive evidence of linkage among white families. Here we report a further characterization of the quantitative trait locus (QTL) in chromosome 2q31 and provide evidence that titin (TTN) is likely a candidate gene involved. The original linkage was detected with two markers (D2S335 and D2S1391), and the QTL covered approximately 25 million base pairs (Mb). We added 12 microsatellite markers resulting in an average marker density of one marker per 2.3 Mb. The evidence of linkage increased from P = 0.006 to P = 0.0002 and 0.00002 in the multi- and single-point analyses, respectively. The strongest evidence of linkage was seen with two markers in and near the TTN gene. Transmission/disequilibrium test (TDT) with the same marker set provided evidence for association with one of the TTN markers (D2S385; P = 0.004). TTN is a major contributor to the elasticity of cardiomyocytes and a key regulator of the Frank-Starling mechanism. Since TTN is the largest gene in the human genome, the challenge is to identify the DNA sequence variants contributing to the interindividual differences in cardiac adaptation to endurance training.