GSK3β inhibition suppresses the hepatic lipid accumulation in Schizothorax prenanti

Phosphorus Overload Promotes Hepatic Lipolysis by Suppressing GSK3β-Dependent Phosphorylation of PPARα at Ser84 and Thr265 in a Freshwater Teleost

Excessive phosphorus (Pi) contributes to eutrophication in an aquatic environment, which threatens human and fish health. However, the mechanisms by which Pi overload influences aquatic animals remain largely unexplored. In the present study, Pi supplementation increased the Pi content, inhibited lipid accumulation and lipogenesis, and stimulated lipolysis in the liver. Pi supplementation increased the phosphorylation of glycogen synthase kinase-3 β (GSK3β) at serine 9 (S9) but inhibited the phosphorylation of GSK3α at tyrosine 279 (Y279), GSK3β at tyrosine 216 (Y216), and peroxisome proliferator-activated receptor α (PPARα) at serine 84 (S84) and threonine 265 (T265). Pi supplementation also upregulated PPARα protein expression and stimulated its transcriptional activity, thereby inducing lipolysis. Pi suppressed GSK3β activity and prevented GSK3β, but not GSK3α, from interacting with PPARα, which in turn alleviated PPARα phosphorylation. GSK3β-induced phosphorylation of PPARα was dependent on GSK3β S9 dephosphorylation rather than Y216 phosphorylation. Mechanistically, underphosphorylation of PPARα mediated Pi-induced lipid degradation through transcriptionally activating adipose triglyceride lipase (atgl) and very long-chain-specific acyl-CoA dehydrogenase (acadvl). Collectively, our findings uncovered a new mechanism by which Pi facilitates lipolysis via the GSK3β-PPARα pathway and highlighted the importance of S84 and T265 phosphorylation in PPARα action.

Characterization and functional analysis of GSK3β from Epinephelus coioides in Singapore grouper iridovirus infection

Glycogen synthase kinase 3β (GSK3β), a serine/threonine protein kinase, is a crucial regulator of several signaling pathways and plays a vital role in cell proliferation, growth, apoptosis, and immune responses. However, the role of GSK3β during viral infection in teleosts remains largely unknown. In the present study, a GSK3β homologue from Epinephelus coioides (EcGSK3β) was cloned and characterized. The open reading frame of EcGSK3β consists of 1323 bp, encoding a 440 amino acid protein, with a predicted molecular mass of 48.23 kDa. Similar to its mammalian counterpart, EcGSK3β contains an S_TKc domain. EcGSK3β shares 99.77% homology with the giant grouper (Epinephelus lanceolatus). Quantitative real-time PCR analysis indicated that EcGSK3β mRNA was broadly expressed in all tested tissues, with abundant expression in the skin, blood, and intestines. Additionally, the expression of EcGSK3β increased after Singapore grouper iridovirus (SGIV) infection in grouper spleen (GS) cells. Intracellular localization analysis demonstrated that EcGSK3β is mainly distributed in the cytoplasm. EcGSK3β overexpression promoted SGIV replication during viral infection in vitro. In contrast, silencing of EcGSK3β inhibited SGIV replication. EcGSK3β significantly downregulated the activities of interferon-β, interferon-sensitive response element, and NF-κB. Taken together, these findings are important for a better understanding of the function of GSK3β in fish and reveal its involvement in the host response to viral immune challenge.

Toxicological impacts of excessive lithium on largemouth bass (Micropterus salmoides): Body weight, hepatic lipid accumulation, antioxidant defense and inflammation response

The unreasonably anthropogenic activities make lithium a widespread pollutant in aquatic environment, and this metallic element can enter the food chain to influence humans. Therefore, the study was designed to explore the influence of dietary lithium supplementation on body weight, lipid deposition, antioxidant capacity and inflammation response of largemouth bass. Multivariate statistical analysis confirmed the toxicological impacts of excessive lithium on largemouth bass. Specifically, excessive dietary lithium (≥87.08 mg/kg) significantly elevated weight gain and feed intake of largemouth bass. Meanwhile, overload lithium inclusion aggravated the accumulation of hepatic lipid and serum lithium. Gene expression results showed that lithium inclusion, especially overload lithium, promoted the transcription of lipogenesis related genes, PPARγ, ACC and FAS, inhibited the expression of fatty acid oxidation related genes, PPARα and ACO, and lipolysis related genes, HSL and MGL. Meanwhile, high lithium inclusion caused the oxidative stress, which was partly through the inhibition of Nrf2/Keap1 pathway. Moreover, dietary lithium inclusion significantly depressed the activity of hepatic lysozyme, and promoted the transcription of proinflammation factors, TNF-α, 5-LOX, IL-1β and IL-8, which was suggested to be regulated by the p38 MAPK pathway. Our findings suggested that overload lithium resulted in increased body weight, hepatic lipid deposition, oxidative stress and inflammation response. The results obtained here provided novel insights on the toxicological impacts of excessive lithium on aquatic animals.

High dose lithium chloride causes colitis through activating F4/80 positive macrophages and inhibiting expression of Pigr and Claudin-15 in the colon of mice

OBJECTIVE

Lithium chloride (LiCl) was a mood stabilizer for bipolar affective disorders and it could activate Wnt/β-catenin signaling pathway both in vivo and in vitro. Colon is one of a very susceptible tissues to Wnt signaling pathway, and so it would be very essential to explore the toxic effect of a high dose of LiCl on colon.

METHODS

C57BL/6 mice were injected intraperitoneally with 200 mg/kg LiCl one dose a day for 5 days to activate Wnt signal pathway in intestines. H&E staining was used to assess the colonic tissues of mice treated with high dose of LiCl. The expression of inflammation-associated genes and tight junction-associated genes in colons was measured using qPCR, Western blot and immunostaining methods. The gut microbiome was tested through 16S rDNA gene analysis.

RESULTS

The differentiation of enteroendocrine cells in colon was inhibited by treatment of 200 mg/kg LiCl. The F4/80 positive macrophages in colon were activated by high dose of LiCl, and migrated from the submucosa to the lamina propria. The expression of pro-inflammatory genes TNFα and IL-1β was increased in the colon of high dose of LiCl treated mice. Clostridium_sp_k4410MGS_306 and Prevotellaceae_UCG_001 were specific and predominant for the high dose of LiCl treated mice. The expression of IgA coding genes, Pigr and Claudin-15 was significantly decreased in the colon tissues of the high dose of LiCl treated mice.

CONCLUSION

200 mg/kg LiCl might cause the inflammation in colon of mice through activating F4/80 positive macrophages and inhibiting the expression of IgA coding genes in plasma cells and the expression of Pigr and Claudin-15 in colonic epithelial cells, providing evidences for the toxic effects of high dose of LiCl on colon.