Biomedical subjects

Alexander A Soukas

Publications and source records attributed to Alexander A Soukas.

6 recordsLinked to original sources

PubMed2026

A lipid-sensitive food choice behavior influences aging outcomes from a longevity-promoting diet.

Organisms utilize sophisticated neurocircuitry to select optimal food sources. Methylobacterium is a lifespan-promoting diet for C. elegans that drives faster development and longevity; however, after ingestion, C. elegans consistently choose any other food option available. A screen for genetic regulators of this avoidance behavior toward Methylobacterium identified the AWB/AWC sensory neurons and the odr-1 guanylate cyclase expressed in those four ciliated neurons as mediators of the aversive response. Metabolic profiling of the Methylobacterium diet reveals enrichment for saturated fats, and here, we show that C. elegans sense and integrate signals related to these ingested lipids that subsequently cue food-related behaviors. Moreover, disruption of endogenous lipid metabolism modifies the intensity of the avoidance from Methylobacterium, suggesting the current state of lipid homeostasis influences food preference. Taken together, our work reveals that C. elegans modify food choice contemporaneously based in part on the chemosensory capacity to detect and utilize dietary lipids, which has longevity-promoting consequences.

AWB↗

PubMed2025

A consensus guide to preclinical indirect calorimetry experiments.

Understanding the complex factors influencing mammalian metabolism and body weight homeostasis is a long-standing challenge requiring knowledge of energy intake, absorption and expenditure. Using measurements of respiratory gas exchange, indirect calorimetry can provide non-invasive estimates of whole-body energy expenditure. However, inconsistent measurement units and flawed data normalization methods have slowed progress in this field. This guide aims to establish consensus standards to unify indirect calorimetry experiments and their analysis for more consistent, meaningful and reproducible results. By establishing community-driven standards, we hope to facilitate data comparison across research datasets. This advance will allow the creation of an in-depth, machine-readable data repository built on shared standards. This overdue initiative stands to markedly improve the accuracy and depth of efforts to interrogate mammalian metabolism. Data sharing according to established best practices will also accelerate the translation of basic findings into clinical applications for metabolic diseases afflicting global populations.

Calorimetry, Indirect↗

PubMed2025

Hormetic nutrient stress promotes longevity by orchestrating histone acetylation on key lipid catabolism and antioxidant defense genes.

Exposure to low levels of environmental challenges, known as hormetic stress, such as nutrient deprivation and heat shock, fosters subsequent stress resistance and promotes healthy aging in later life. However, specific mechanisms governing transcriptional reprogramming upon hormetic nutrient stress remain elusive. In this study, we identified histone H3 lysine 27 acetylation (H3K27ac) as a crucial driver of transcriptomic adaptation to hormetic fasting. Beyond its immediate function of enhancing lipid catabolism for alternative energy sources, stress-induced H3K27ac activates lifelong antioxidant defenses, thereby reducing reactive oxygen species (ROS) produced by stress-induced fatty acid oxidation and their accumulation during aging. The increase in H3K27ac, mediated by pioneer factor PHA-4/FOXA and cooperating transcription factor NHR-49/HNF4, is crucial for lifespan extension under hermetic nutrient stress in Caenorhabditis elegans. Our findings establish H3K27ac as a key transcriptional switch that bridges nutrient status with transcriptomic reprogramming, underpinning the pro-longevity effects of hormetic fasting through orchestrating lipid catabolism and antioxidative defenses.

Journal Article↗

PubMed2005

Induction of leptin receptor expression in the liver by leptin and food deprivation.

Leptin resistance is a common feature of obesity and the metabolic syndrome. However, the regulated expression of the leptin receptor (Ob-R) has not been studied in detail. Expression profiling of liver mRNA in leptin-treated wild-type mice revealed a marked increase in leptin receptor mRNA levels, which had not previously been described. This was confirmed by isoform-specific real-time PCR, which showed a >25-fold increase in the mRNAs encoding the short forms (Ob-Ra, Ob-Rc) and a >10-fold increase in the mRNA encoding the long (Ob-Rb) form of the leptin receptor in liver. In parallel, we also observed induction of plasma-soluble leptin receptor (SLR) protein by leptin administration, pair feeding, and short term food restriction. However, induction of SLR by leptin is abolished in mice with selective deletion of Ob-R from liver using Cre-LoxP technology. These data suggest that the liver is a major source of Ob-R mRNA expression under conditions of negative energy balance. Membrane-bound Ob-R is then shed into the circulation as SLR. Our study thus reveals an unexpected role of the liver in modulating total circulating leptin levels and possibly its biological activity.

Animals↗

PubMed2004

Site and mechanism of leptin action in a rodent form of congenital lipodystrophy.

Lipodystrophy is characterized by the complete or partial absence of adipose tissue, insulin resistance, hepatic steatosis, and leptin deficiency. Here, we show that low-dose central leptin corrects the insulin resistance and fatty liver of lipodystrophic aP2-nSREBP-1c mice, while the same dose given peripherally does not. Central leptin also repressed stearoyl-CoA desaturase-1 (SCD-1) RNA and enzymatic activity, which were increased in livers of lipodystrophic mice. aP2-nSREBP-1c mice homozygous for an SCD-1 deletion had markedly reduced hepatic steatosis, increased saturated fatty acids, decreased acetyl-CoA carboxylase activity, and decreased malonyl-CoA levels in the liver. Despite the reduction in hepatic steatosis, these mice remained diabetic. A leptin dose-response curve showed that subcutaneous leptin improved hyperglycemia and hyperinsulinemia in aP2-nSREBP-1c mice at doses that did not substantially alter hepatic steatosis or hepatic SCD enzymatic activity. Leptin treatment at this dose improved insulin-stimulated insulin receptor and insulin receptor substrate 2 (IRS-2) phosphorylation, IRS-2-associated PI3K activity, and Akt activity in liver. Together, these data suggest that CNS-mediated repression of SCD-1 contributes to leptin's antisteatotic actions. Intracerebroventricular leptin improves glucose homeostasis by improving insulin signal transduction in liver, but in this case the effect appears to be independent of SCD-1.

Animals↗

PubMed2002

Role for stearoyl-CoA desaturase-1 in leptin-mediated weight loss.

Leptin elicits a metabolic response that cannot be explained by its anorectic effects alone. To examine the mechanism underlying leptin's metabolic actions, we used transcription profiling to identify leptin-regulated genes in ob/ob liver. Leptin was found to specifically repress RNA levels and enzymatic activity of hepatic stearoyl-CoA desaturase-1 (SCD-1), which catalyzes the biosynthesis of monounsaturated fatty acids. Mice lacking SCD-1 were lean and hypermetabolic. ob/ob mice with mutations in SCD-1 were significantly less obese than ob/ob controls and had markedly increased energy expenditure. ob/ob mice with mutations in SCD-1 had histologically normal livers with significantly reduced triglyceride storage and VLDL (very low density lipoprotein) production. These findings suggest that down-regulation of SCD-1 is an important component of leptin's metabolic actions.

Animals↗