Regulation of skeletal muscle physiology and metabolism by peroxisome proliferator-activated receptor delta

Transcriptional up-regulation of antioxidant genes by PPARδ inhibits angiotensin II-induced premature senescence in vascular smooth muscle cells

This study evaluated peroxisome proliferator-activated receptor (PPAR) δ as a potential target for therapeutic intervention in Ang II-induced senescence in human vascular smooth muscle cells (hVSMCs). Activation of PPARδ by GW501516, a specific agonist of PPARδ, significantly inhibited the Ang II-induced premature senescence of hVSMCs. Agonist-activated PPARδ suppressed the generation of Ang II-triggered reactive oxygen species (ROS) with a concomitant reduction in DNA damage. Notably, GW501516 up-regulated the expression of antioxidant genes, such as glutathione peroxidase 1, thioredoxin 1, manganese superoxide dismutase and heme oxygenase 1. siRNA-mediated down-regulation of these antioxidant genes almost completely abolished the effects of GW501516 on ROS production and premature senescence in hVSMCs treated with Ang II. Taken together, the enhanced transcription of antioxidant genes is responsible for the PPARδ-mediated inhibition of premature senescence through sequestration of ROS in hVSMCs treated with Ang II.

Nutritional modulation of training-induced skeletal muscle adaptations

Skeletal muscle displays remarkable plasticity, enabling substantial adaptive modifications in its metabolic potential and functional characteristics in response to external stimuli such as mechanical loading and nutrient availability. Contraction-induced adaptations are determined largely by the mode of exercise and the volume, intensity, and frequency of the training stimulus. However, evidence is accumulating that nutrient availability serves as a potent modulator of many acute responses and chronic adaptations to both endurance and resistance exercise. Changes in macronutrient intake rapidly alter the concentration of blood-borne substrates and hormones, causing marked perturbations in the storage profile of skeletal muscle and other insulin-sensitive tissues. In turn, muscle energy status exerts profound effects on resting fuel metabolism and patterns of fuel utilization during exercise as well as acute regulatory processes underlying gene expression and cell signaling. As such, these nutrient-exercise interactions have the potential to activate or inhibit many biochemical pathways with putative roles in training adaptation. This review provides a contemporary perspective of our understanding of the molecular and cellular events that take place in skeletal muscle in response to both endurance and resistance exercise commenced after acute and/or chronic alterations in nutrient availability (carbohydrate, fat, protein, and several antioxidants). Emphasis is on the results of human studies and how nutrient provision (or lack thereof) interacts with specific contractile stimulus to modulate many of the acute responses to exercise, thereby potentially promoting or inhibiting subsequent training adaptation.

The intricate role of growth hormone in metabolism

Growth hormone (GH), a master regulator of somatic growth, also regulates carbohydrate and lipid metabolism via complex interactions with insulin and insulin-like growth factor-1 (IGF-1). Data from human and rodent studies reveal the importance of GH in insulin synthesis and secretion, lipid metabolism and body fat remodeling. In this review, we will summarize the tissue-specific metabolic effects of GH, with emphasis on recent targets identified to mediate these effects. Furthermore, we will discuss what role GH plays in obesity and present possible mechanisms by which this may occur.

Upregulation of PPARgamma in tissue with gastric carcinoma

Here we have for the first time investigated the expression of peroxisome proliferator-activated receptor gamma (PPARgamma) in chronic gastritis, gastric mucosal dysplasia, and gastric carcinoma. Avidin-biotin peroxidase complex immunohistochemical methods were adopted to examine the expression of PPARgamma in 53 patients with gastric carcinoma, 18 with gastric mucosal dysplasia, 30 with chronic atrophic gastritis, and 31 with chronic non-atrophic gastritis. The positive rate of PPARgamma was 41.5% in gastric carcinoma, 27.8% in gastric mucosal dysplasia, 10.0% in chronic atrophic gastritis, and 6.5% in chronic non-atrophic gastritis, respectively. Compared with those in chronic gastritis, expression of PPARgamma in gastric mucosal dysplasia and gastric carcinoma was significantly enhanced (p < 0.05). In gastric carcinoma, expression of PPARgamma was not associated with tumor cell differentiation and metastasis to lymph nodes (p > 0.05). Taken together, overexpression of PPARgamma was apparent in human gastric cancer, which might be an early event in carcinogenesis.

Peroxisome proliferator-activated receptors, metabolic syndrome and cardiovascular disease

Metabolic syndrome (MetS) is a constellation of risk factors including insulin resistance, central obesity, dyslipidemia and hypertension that markedly increase the risk of Type 2 diabetes (T2DM) and cardiovascular disease (CVD). The peroxisome proliferators-activated receptor (PPAR) isotypes, PPARα, PPARδ/ß and PPARγ are ligand-activated nuclear transcription factors, which modulate the expression of an array of genes that play a central role in regulating glucose, lipid and cholesterol metabolism, where imbalance can lead to obesity, T2DM and CVD. They are also drug targets, and currently, PPARα (fibrates) and PPARγ (thiazolodinediones) agonists are in clinical use for treating dyslipidemia and T2DM, respectively. These metabolic characteristics of the PPARs, coupled with their involvement in metabolic diseases, mean extensive efforts are underway worldwide to develop new and efficacious PPAR-based therapies for the treatment of additional maladies associated with the MetS. This article presents an overview of the functional characteristics of three PPAR isotypes, discusses recent advances in our understanding of the diverse biological actions of PPARs, particularly in the vascular system, and summarizes the developmental status of new single, dual, pan (multiple) and partial PPAR agonists for the clinical management of key components of MetS, T2DM and CVD. It also summarizes the clinical outcomes from various clinical trials aimed at evaluating the atheroprotective actions of currently used fibrates and thiazolodinediones.

The Role of PPARα Activation in Liver and Muscle

PPARα is one of three members of the soluble nuclear receptor family called peroxisome proliferator-activated receptor (PPAR). It is a sensor for changes in levels of fatty acids and their derivatives that responds to ligand binding with PPAR target gene transcription, inasmuch as it can influence physiological homeostasis, including lipid and carbohydrate metabolism in various tissues. In this paper we summarize the involvement of PPARα in the metabolically active tissues liver and skeletal muscle and provide an overview of the risks and benefits of ligand activation of PPARα, with particular consideration to interspecies differences.

Metabolic and nonmetabolic regulatory functions of peroxisome proliferator-activated receptor beta

PURPOSE OF REVIEW

This review focuses on the emerging knowledge about peroxisome proliferator-activated receptor beta regulatory functions on metabolism, inflammation, and cellular stress.

RECENT FINDINGS

Recent publications have confirmed the important roles of peroxisome proliferator-activated receptor beta in adaptive metabolic responses of skeletal muscle and have also implicated the nuclear receptor in the regulation of inflammation and oxidative stress in various tissues. The mechanisms implicated in these effects have been partially elucidated.

SUMMARY

Peroxisome proliferator-activated receptors mediate the transcriptional effects of fatty acids and fatty acid derivatives and regulate many physiological functions, including metabolism and development. Use of potent and specific agonists revealed that activation of peroxisome proliferator-activated receptor beta efficiently reverses some metabolic syndrome-associated abnormalities by affecting metabolic, inflammatory, and oxidative stress responses in several tissues through both genomic and nongenomic modes of action.