Graphislactone A, a Fungal Antioxidant Metabolite, Reduces Lipogenesis and Protects against Diet-Induced Hepatic Steatosis in Mice.

Graphislactone A (GPA), a secondary metabolite derived from a mycobiont found in the lichens of the genus Graphis, exhibits antioxidant properties. However, the potential biological functions and therapeutic applications of GPA at the cellular and animal levels have not yet been investigated. In the present study, we explored the therapeutic potential of GPA in mitigating non-alcoholic fatty liver disease (NAFLD) and its underlying mechanisms through a series of experiments using various cell lines and animal models. GPA demonstrated antioxidant capacity on a par with that of vitamin C in cultured hepatocytes and reduced the inflammatory response induced by lipopolysaccharide in primary macrophages. However, in animal studies using an NAFLD mouse model, GPA had a milder impact on liver inflammation while markedly attenuating hepatic steatosis. This effect was confirmed in an animal model of early fatty liver disease without inflammation. Mechanistically, GPA inhibited lipogenesis rather than fat oxidation in cultured hepatocytes. Similarly, RNA sequencing data revealed intriguing associations between GPA and the adipogenic pathways during adipocyte differentiation. GPA effectively reduced lipid accumulation and suppressed lipogenic gene expression in AML12 hepatocytes and 3T3-L1 adipocytes. In summary, our study demonstrates the potential application of GPA to protect against hepatic steatosis in vivo and suggests a novel role for GPA as an underlying mechanism in lipogenesis, paving the way for future exploration of its therapeutic potential.

Deletion of Jazf1 gene causes early growth retardation and insulin resistance in mice.

Single-nucleotide polymorphisms in the human juxtaposed with another zinc finger protein 1 (JAZF1) gene have repeatedly been associated with both type 2 diabetes (T2D) and height in multiple genome-wide association studies (GWAS); however, the mechanism by which JAZF1 causes these traits is not yet known. To investigate the possible functional role of JAZF1 in growth and glucose metabolism in vivo, we generated Jazf1 knockout (KO) mice and examined body composition and insulin sensitivity both in young and adult mice by using 1H-nuclear magnetic resonance and hyperinsulinemic-euglycemic clamp techniques. Plasma concentrations of insulin-like growth factor 1 (IGF-1) were reduced in both young and adult Jazf1 KO mice, and young Jazf1 KO mice were shorter in stature than age-matched wild-type mice. Young Jazf1 KO mice manifested reduced fat mass, whereas adult Jazf1 KO mice manifested increased fat mass and reductions in lean body mass associated with increased plasma growth hormone (GH) concentrations. Adult Jazf1 KO manifested muscle insulin resistance that was further exacerbated by high-fat diet feeding. Gene set enrichment analysis in Jazf1 KO liver identified the hepatocyte hepatic nuclear factor 4 alpha (HNF4α), which was decreased in Jazf1 KO liver and in JAZF1 knockdown cells. Moreover, GH-induced IGF-1 expression was inhibited by JAZF1 knockdown in human hepatocytes. Taken together these results demonstrate that reduction of JAZF1 leads to early growth retardation and late onset insulin resistance in vivo which may be mediated through alterations in the GH-IGF-1 axis and HNF4α.

Mechanisms linking gut microbial metabolites to insulin resistance.

Insulin resistance is the rate-limiting step in the development of metabolic diseases, including type 2 diabetes. The gut microbiota has been implicated in host energy metabolism and metabolic diseases and is recognized as a quantitatively important organelle in host metabolism, as the human gut harbors 10 trillion bacterial cells. Gut microbiota break down various nutrients and produce metabolites that play fundamental roles in host metabolism and aid in the identification of possible therapeutic targets for metabolic diseases. Therefore, understanding the various effects of bacterial metabolites in the development of insulin resistance is critical. Here, we review the mechanisms linking gut microbial metabolites to insulin resistance in various insulin-responsive tissues.

The essential role of fructose-1,6-bisphosphatase 2 enzyme in thermal homeostasis upon cold stress.

Skeletal muscle is a major organ for glucose disposal and thermogenesis. While hepatic fructose-1,6-bisphosphatase is well known as a key enzyme for gluconeogenesis, the role of muscle fructose-1,6-bisphosphatase 2 (Fbp2) in glucose disposal and thermogenesis is unknown. Here, using Fbp2 knockout (KO) mice, we assessed the physiological role of Fbp2 in energy and glucose metabolism and thermogenesis. In vivo assessments of energy metabolism, glucose metabolism, and thermogenesis were performed by indirect calorimetry, hyperinsulinemic-euglycemic clamp, and cold challenge studies, respectively. Under both feeding and fasting conditions, Fbp2 KO mice showed similar phenotypes regarding energy and glucose metabolism compared to wild-type (WT) mice. However, Fbp2 KO mice were severely intolerant to cold challenge under fasting conditions. Mechanistically, the cold-induced intramuscular conversion of lactate to glycogen (glyconeogenesis) is completely abolished in the KO muscle, which leads to a lack of glycogen source for thermogenesis in Fbp2 KO mice. The cold-intolerant phenotype of KO mice disappeared after feeding, and the KO mice were equally as cold tolerant as the WT mice and survived during the cold challenge for three weeks. Taken together, these data demonstrate that Fbp2 is essential for muscle thermogenesis by replenishing the intramuscular glycogen pool through glyconeogenesis when the exogenous glucose source is limited. These data imply the physiological importance of Fbp2 in thermal homeostasis and suggest a potential novel therapy targeted to increase glycogen replenishment upon cold stress.

A protective mechanism of probiotic Lactobacillus against hepatic steatosis via reducing host intestinal fatty acid absorption.

The gut microbiome has been known to contribute up to ~30% of the energy absorption of the host. Although various beneficial mechanisms of probiotics have been suggested for non-alcoholic fatty liver disease (NAFLD), whether and which probiotics impact the host's intestinal energy absorption have not yet been quantitatively studied. Here, we suggest a novel mechanism of probiotics against NAFLD, in which Lactobacillus rhamnosus GG, the most common probiotic, shares intestinal fatty acids and prevents the development of diet-induced hepatic steatosis. By using quantitative methods (radioactive tracers and LC-MS) under both in vitro and in vivo conditions, we found that bacteria and hosts competed for fatty acid absorption in the intestine, resulting in decreased weight gain, body fat mass, and hepatic lipid accumulation without differences in calorie intake and excretion in mice fed the probiotic bacteria.