Caenorhabditis elegansis a powerful model organism that is invaluable for experimental research because it can be used to recapitulate most human diseases at either the metabolic or genomic levelin vivo. This organism contains many key components related to metabolic and oxidative stress networks that could conceivably allow us to increase and integrate information to understand the causes and mechanisms of complex diseases. Oxidative stress is an etiological factor that influences numerous human diseases, including diabetes.C. elegansdisplays remarkably similar molecular bases and cellular pathways to those of mammals. Defects in the insulin/insulin-like growth factor-1 signaling pathway or increased ROS levels induce the conserved phase II detoxification response via the SKN-1 pathway to fight against oxidative stress. However, it is noteworthy that, aside from the detrimental effects of ROS, they have been proposed as second messengers that trigger the mitohormetic response to attenuate the adverse effects of oxidative stress. Herein, we briefly describe the importance ofC. elegansas an experimental model system for studying metabolic disorders related to oxidative stress and the molecular mechanisms that underlie their pathophysiology.

Cellular energy regulation relies on complex signaling pathways that respond to fuel availability and metabolic demands. Dysregulation of these networks is implicated in the development of human metabolic diseases such as obesity and metabolic syndrome. In Caenorhabditis elegans the AMP-activated protein kinase, AAK, has been associated with longevity and stress resistance; nevertheless its precise role in energy metabolism remains elusive. In the present study, we find an evolutionary conserved role of AAK in oxidative metabolism. Similar to mammals, AAK is activated by AICAR and metformin and leads to increased glycolytic and oxidative metabolic fluxes evidenced by an increase in lactate levels and mitochondrial oxygen consumption and a decrease in total fatty acids and lipid storage, whereas augmented glucose availability has the opposite effects. We found that these changes were largely dependent on the catalytic subunit AAK-2, since the aak-2 null strain lost the observed metabolic actions. Further results demonstrate that the effects due to AAK activation are associated to SBP-1 and NHR-49 transcriptional factors and MDT-15 transcriptional co-activator, suggesting a regulatory pathway that controls oxidative metabolism. Our findings establish C. elegans as a tractable model system to dissect the relationship between distinct molecules that play a critical role in the regulation of energy metabolism in human metabolic diseases.

Thiamine is one of several essential cofactors for ATP generation. Its deficiency, like in beriberi and in the Wernicke-Korsakoff syndrome, has been studied for many decades. However, its mechanism of action is still not completely understood at the cellular and molecular levels. Since it acts as a coenzyme for dehydrogenases of pyruvate, branched-chain keto acids, and ketoglutarate, its nutritional privation is partly a phenocopy of inborn errors of metabolism, among them maple syrup urine disease. In the present paper, we report metabolic and genomic findings in mice deprived of thiamine. They are similar to the ones we have previously found in biotin deficiency, another ATP generation cofactor. Here we show that thiamine deficiency substantially reduced the energy state in the liver and activated the energy sensor AMP-activated kinase. With this vitamin deficiency, several metabolic parameters changed: blood glucose was diminished and serum lactate was increased, but insulin, triglycerides, and cholesterol, as well as liver glycogen, were reduced. These results indicate a severe change in the energy status of the whole organism. Our findings were associated with modified hepatic levels of the mRNAs of several carbon metabolism genes: a reduction of transcripts for liver glucokinase and fatty acid synthase and augmentation of those for carnitine palmitoyl transferase 1 and phosphoenolpyruvate carboxykinase as markers for glycolysis, fatty acid synthesis, beta-oxidation, and gluconeogenesis, respectively. Glucose tolerance was initially increased, suggesting augmented insulin sensitivity, as we had found in biotin deficiency; however, in the case of thiamine, it was diminished from the 3rd week on, when the deficient animals became undernourished, and paralleled the changes in AKT and mTOR, 2 main proteins in the insulin signaling pathway. Since many of the metabolic and gene expression effects on mice deprived of thiamine are similar to those in biotin deficiency, it may be that they result from a more general impairment of oxidative phosphorylation due to a shortage of ATP generation cofactors. These findings may be relevant to energy-related disorders, among them several inborn errors of metabolism, as well as common energy disorders like obesity, diabetes, and neurodegenerative illnesses.

Background/Aim: Biotin affects the genetic expression of several glucose metabolism enzymes, besides being a cofactor of carboxylases. To explore how extensively biotin affects the expression of carbon metabolism genes, we studied the effects of biotin starvation and replenishment in 3 distantly related eukaryotes: yeast Saccharomyces cerevisiae, nematode Caenorhabditis elegans and rat Rattus norvegicus. Methods: Biotin starvation was produced in Wistar rats, in C. elegans N2 and S. cerevisiae W303A fed with abundant glucose. High-density oligonucleotide microarrays were used to find gene expression changes. Glucose consumption, lactate and ethanol were measured by conventional tests. Results: In spite of abundant glucose provision, the expression of fatty oxidation and gluconeogenic genes was augmented, and the transcripts for glucose utilization and lipogenesis were diminished in biotin starvation. These results were associated with diminished glucose consumption and glycolysis products (lactate and ethanol in yeast), which was consistent across 3 very different eukaryotes. Conclusion: The results point toward a strongly selected role of biotin in the control of carbon metabolism, and in adaptations to variable availability of carbon, conceivably mediated by signal transduction including soluble guanylate cyclase, cGMP and a cGMP-dependent protein kinase (PKG) and/or biotin-dependent processes.

Chronic exposure to elevated glucose levels leads to fatty acid accumulation, which promotes the development of metabolic diseases such as obesity and type 2 diabetes. MXL-3 is a conserved transcriptional factor that modulates the inhibition of lipolysis in Caenorhabditis elegans. However, the role of MXL-3 in lipid metabolism during nutrient excess remains unknown. We hypothesized that inhibition of MXL-3 prevents glucose-dependent fat accumulation. Nematodes from wild-type N2, MXL-3::GFP and sbp-1 or mxl-3 null strains were grown on standard, high glucose or high glucose plus metformin plates for 24 h. Using laser-scanning confocal microscopy, we monitored the glucose-induced activation of MXL-3 labeled with GFP (MXL-3::GFP). Lipid levels were determined by Oil Red O (ORO) staining and gas chromatography/mass spectrometry, and gene expression was assessed by qRT-PCR. We found that high glucose activated MXL-3 by increasing its rate of nuclear entry, which in turn increased lipid levels via sterol regulatory element-binding protein (SBP-1). This activated critical genes that synthesize long chain unsaturated fatty acids (MUFAs and PUFAs) and repress lipolytic genes. Interestingly, the anti-diabetic drug metformin inhibited MXL-3 activation and subsequently prevented glucose-dependent fat accumulation. These findings highlight the importance of the MXL-3/SBP-1 axis in the regulation of lipid metabolism during nutritional excess and provide new insight into the mechanism by which metformin prevents lipid accumulation. This study also suggests that inhibition of MXL-3 may serve as a potential target for the treatment of chronic metabolic diseases, including obesity, type 2 diabetes, and cardiovascular disease.