Diet and Exercise Drive Progressive, Depot-Specific Remodeling of Adipose Lipid Droplet Cargo

Physiology · 2026-05-01

Adipose tissue, broadly classified into white (WAT) and brown adipose tissue (BAT), is an endocrine tissue with a wide-ranging capacity for energy storage and thermogenesis. Within adipocytes, excess energy is stored within large, unilocular lipid droplets (LDs) in WAT or small, multilocular LDs in BAT. While numerous studies have focused on whole-adipose depot characterization, we and others have demonstrated that LDs can be dramatically altered by obesogenic diets, altering both their lipid cargo and biophysical properties. Here, we characterized how diet and exercise progressively reshape LD cargo across WAT and BAT using liquid chromatography-mass spectrometry (LC-MS) based lipidomics. We utilized 8-week-old C57BL/6 male mice that were endurance exercise-trained (4-week voluntary wheel running) or sedentary (static cages) and fed a control (CD; 10% Kcal fat) or high-fat diet (HFD; 45% Kcal fat). First, we contrasted the whole-tissue and LD lipidomes across (four) WAT and BAT and confirmed the biased enrichment of triacylglycerols (TG) in LDs across depots, whereas acylcarnitines (CAR) were enriched in whole tissues. Further, we show that regardless of diet, inguinal WAT (ingWAT) from sedentary mice exhibited progressive increases in LD lipid variance (~220 lipids) across 12 weeks (12- vs. 4-wks; p< 0.01) supporting tight lipid packing. This was not observed for iBAT LDs (~360 lipids), remaining stable throughout 12 weeks. Conversely, regardless of diet, 4-week endurance training prevented fat mass gain and heightened ingWAT LD lipid variability, and only CD-fed mice reduced the long-chain ( >50 carbons) TG species with variable degrees of unsaturation, indicating widespread lipid remodeling. For iBAT LDs, 4-week training in CD-fed mice reduced and in HFD-fed mice heightened LD cargo variability, compared to diet-matched controls, and HFD-fed trained mice reduced long-chain, unsaturated TG. To demonstrate if the effects of exercise on LD cargo persist once training stops, we profiled LD lipids after 4 weeks of detraining (8wk) followed by 4-week retraining (12wk). Detraining produced similar ingWAT LD lipid variability across all groups, reflecting the catch-up adiposity observed in previously trained groups, although variability remained lower than the training period (8- vs. 4-wks; p< 0.0001). Retraining reversed this pattern: adiposity decreased and ingWAT LD lipid variance increased relative to detraining (12- vs. 8-wks; p< 0.001), though variance did not reach that of diet-matched controls. Only a small number of lipids decreased with retraining, all of which were saturated TG (~50 carbons), pointing to flexible LD lipid packing. Together, findings show that diet and exercise dynamically reshape LD composition across adipose depots, altering lipid packing flexibility that may determine metabolic adaptations and thermogenic function. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

MetaboMiNR: a redstone MiNRcraft tool for nuclear receptors and metabolism

Endocrinology · 2026-03-06

Constitutive Androstane Receptor induces Ribonucleotide Reductase-M2 expression and maintains hepatocyte ploidy in mice

bioRxiv (Cold Spring Harbor Laboratory) · 2025-05-02 · 1 citations

Abstract The nuclear receptor Constitutive Androstane Receptor (CAR/NR1i3) is known for regulating various liver functions, including detoxification, nutrient metabolism, and hepatocyte proliferation. While CAR activation has been previously linked to higher ploidy, the underlying mechanisms are not fully known. Here, we uncover a basal role for CAR in maintaining hepatocyte ploidy, such that CAR deletion increases the number of diploid (2c) hepatocytes with a concomitant reduction in tetraploid (4c) hepatocytes. We demonstrate that CAR controls the de novo dNTP synthesis by directly transactivating the Ribonucleotide Reductase-M2 ( RRM2 ) gene, which encodes the rate-limiting catalytic subunit of the enzyme, ribonucleotide reductase. Further, we find that the ligand-dependent CAR activation is sufficient to induce several genes involved in the de novo dNTP synthesis pathways, resulting in higher hepatic dATP and dTTP levels within the liver. Importantly, overexpressing RRM2 levels in CAR knockouts led to increased DNA synthesis and tetraploid (4c) hepatocytes compared to the control mice. Importantly, we demonstrate that CAR-mediated DNA synthesis in liver cells is dependent on catalytically active RRM2 function. Taken together, these findings reveal that the CAR-mediated RRM2 regulation contributes towards DNA synthesis and thereby maintains hepatocyte ploidy.

Adipose Farnesoid X Receptor Deletion Results in Hepatic Fat Accumulation upon Diet Induced Obesity

Endocrinology · 2025-04-01

Abstract Text The nutrient sensor farnesoid X receptor (FXR) transcriptionally regulates whole-body lipid and glucose homeostasis. Several studies examined FXR modulation as a modality to treat obesity with varying conflicting results, emphasizing the need to study tissue-specific roles of FXR. We show that deletion of adipocyte Fxr is sufficient to mimic high fat diet-induced responses, including adipocyte hypertrophy, glucose intolerance, increased triacylglycerol tail length and abundance, and suppression of several metabolic genes. Moreover, these effects are exacerbated in adipocyte-specific Fxr knockout (Ad-FxrKO) mice upon high fat diet challenge. We uncover that adipose FXR deletion leads to excessive fat accumulation in the liver. Taken together, we find that dysregulation of adipose FXR axis may contribute to the pathogenesis of metabolic diseases. Date of Presentation October 16, 2024

Deleting adipose FXR exacerbates metabolic defects and induces endocannabinoid lipid, 2-oleoyl glycerol, in obesity

Journal of Lipid Research · 2025-02-10 · 5 citations

The nutrient sensor farnesoid X receptor (FXR) transcriptionally regulates whole-body lipid and glucose homeostasis. Several studies examined targeting FXR as a modality to treat obesity with varying conflicting results, emphasizing the need to study tissue-specific roles of FXR. We show that deletion of adipocyte Fxr results in increased adipocyte hypertrophy and suppression of several metabolic genes that is akin to some of the changes noted in high-fat diet (HFD)-fed control mice. Moreover, upon HFD challenge, these effects are worsened in adipocyte-specific Fxr knockout mice. We uncover that FXR regulates fatty acid amide hydrolase (Faah) such that its deletion lowers Faah expression. Conversely, FXR activation by its ligand, chenodeoxycholic acid, induces Faah transcription. Notably, HFD results in the reduction of adipose Faah expression in control mice and that Faah inhibition or deletion is linked to obesity. We report that the adipocyte FXR-Faah axis controls local 2-oleoyl glycerol and systemic N-acyl ethanolamine levels. Taken together, these findings show that loss of adipose FXR may contribute to the pathogenesis of obesity and subsequent metabolic defects.

Author response: Sex differences in bile acid homeostasis and excretion underlie the disparity in liver cancer incidence between males and females

2025-07-25

Hepatocellular carcinoma (HCC), the most common liver cancer, exhibits a higher incidence in males. Here, we report that mice lacking the bile acid regulators, Farnesoid X Receptor (FXR) and Small Heterodimer Partner (SHP), recapitulate the sex difference in liver cancer risk. Since few therapeutic options are available, we focused on understanding the intrinsic protection afforded to female livers. Transcriptomic analysis in control and FXR and SHP double knockout livers identified female-specific changes in metabolism, including amino acids, lipids, and steroids. We examined if the obtained transcriptomic signatures correlate with the survival outcomes for HCC patients to assess the translational potential of this murine HCC model. Gene signatures that are unique to the knockout females correspond with low-grade tumors and better survival. Ovariectomy blunts the metabolic changes in female livers and promotes tumorigenesis that, intriguingly, coincides with increases in serum bile acid (BA) levels. Despite similar genetics, we found higher serum BA concentrations in males, whereas female knockout mice excreted more BAs. Decreasing enterohepatic BA recirculation using cholestyramine, an FDA-approved resin, dramatically reduced the liver cancer burden in male mice. Overall, we reveal that sex-specific BA metabolism leading to lower circulating BA concentration protects female livers from developing cancer. Thus, targeting BA excretion may be a promising therapeutic strategy against HCC.We show that female-specific gene profiles identified in Fxr-/-, Shp-/- double knockout (DKO) mice correlate with better outcomes for HCC patients and uncover sex differences in circulation and excretion of bile acid. Overall, we demonstrate that increasing (ovariectomy or chemical injury) or decreasing (pharmacologically with FDA-approved resin) serum bile acids, not hepatic bile acids, promoted or alleviated liver cancer burden.

Portal bile acid composition and microbiota along the <i>murine</i> intestinal tract exhibit sex differences in physiology

Gut Microbes · 2025-08-04 · 7 citations

Microbes in the intestine transform bile acids during transit, altering their functional and signaling capacities before recirculation via the portal vein. Sex differences in the gut microbiota have been noted, but their consequence on bile acid composition is unclear. Here, we investigated the composition and functional potential of microbes in the small and large intestines together with portal and systemic bile acid levels. Female and male mice exhibit distinct microbial diversity throughout the length of the intestine, leading to dimorphism in genes related to bile acid transformation. Of note, genes linked to bacterial oxidative properties were abundant in males, and consistently, we found 3X higher oxo-bile acids in portal circulation in males than females. Conversely, conjugated primary bile acids were 1.8X more abundant in the portal bile acid pool of female mice. Oxidized and deconjugated bile acids were absent in germ-free mice consistent with microbe-mediated bile acid transformation. More importantly, gnotobiotic mice do not show sex differences in portal bile acids. Taken together, we demonstrate that sex differences in gut microbiota with subsequent changes in microbially transformed bile acid levels contribute to distinct sex-specific bile acid pools within the enterohepatic loop.

Serum cholic acid and cecal Faecalibaculum increase in a male-specific manner in a murine hepatocellular carcinoma model

Journal of Lipid Research · 2025-11-28 · 1 citations

Hepatocellular carcinoma (HCC) has a higher incidence in males and is a leading cause of cancer-related deaths, which lacks effective therapies and surveillance markers. Using a murine model of bile acid excess (farnesoid X receptor and small heterodimer partner double knockout, DKO), which phenocopies many aspects of HCC, including sex differences, we investigated the links between sex, bile acid metabolism, and microbial composition. Unexpectedly, the increase in the ratios of carcinogenic deoxycholic acid (DCA) was similar between DKO males with HCC and cancer-resistant DKO females. However, both taurine-conjugated and free cholic acid (CA) sharply increased in the serum of DKO males, with free-CA comprising 65% of the bile acid pool, whereas DKO female serum was mostly comprised of conjugated bile acids. Unlike such sex differences in DKO serum composition, conjugated bile acids were predominant in the hepatic BA pool irrespective of the sex or genotype, as expected. Fecal and cecal microbiota-many of which harbor bile acid transformation/deconjugation capacity-were altered in DKO mice in a sex-specific manner. Untargeted fecal metabolite analysis showed differences in bile acids, phospholipids, and oxidized fatty acids between the genotypes, with DKO females excreting more sulphated and oxidized CA than tumor-bearing DKO males. Further analysis revealed a direct correlation between unconjugated CA levels with the abundance of the microbial genus Faecalibaculum in the DKO HCC model. These findings suggest distinct sex-specific changes in cecal and fecal microbiota, and BA composition may be leveraged in combination as a potential tool for HCC surveillance.

Sex differences in bile acid homeostasis and excretion underlie the disparity in liver cancer incidence between males and females

eLife · 2025-12-29

Hepatocellular carcinoma (HCC), the common liver cancer, exhibits higher incidence in males. Here, we report that mice lacking bile acid (BA) regulators, Farnesoid X Receptor (FXR also termed NR1H4) and Small Heterodimer Partner (SHP also termed NR0B2), recapitulate the sex difference in liver cancer risk. Since few therapeutic options are available, we focused on understanding the intrinsic protection afforded to female livers. Transcriptomic analysis in control and NR1H4 and NR0B2 double knockout livers identified female-specific changes in metabolism, including amino acids, lipids, and steroids. To assess translational relevance, we examined if transcriptomic signatures obtained from this murine HCC model correlate with survival outcomes for HCC patients. Gene signatures unique to the knockout females correspond with low-grade tumors and better survival. Ovariectomy blunts the metabolic changes and promotes liver tumorigenesis in females that, intriguingly, coincides with increased serum bile acid (BA) levels. Despite similar genetics, knockout male mice displayed higher serum BA concentrations, while female knockouts excreted more BAs. Decreasing enterohepatic BA recirculation using cholestyramine, an FDA-approved resin, dramatically reduced the liver cancer burden in male mice. Overall, we reveal that sex-specific BA metabolism leading to lower circulating BA concentration protects female livers from developing cancer. Thus, targeting BA excretion may be a promising therapeutic strategy against HCC.

Author response: Sex differences in bile acid homeostasis and excretion underlie the disparity in liver cancer incidence between males and females

2025-12-29

Transcriptomic and metabolite analysis reveal sex differences in circulation and excretion of bile acids in a mouse- model of hepatocellular carcinoma (HCC), and the identified female-specific gene profile correlates with better HCC survival.