Inhibition of mitochondrial citrate shuttle alleviates metabolic syndromes induced by high-fat diet.

The mitochondrial citrate shuttle, which relies on the solute carrier family 25 member 1 (SLC25A1), plays a pivotal role in transporting citrate from the mitochondria to the cytoplasm. This shuttle supports glycolysis, lipid biosynthesis, and protein acetylation. Previous research has primarily focused on Slc25a1 in pathological models, particularly high-fat diet (HFD)-induced obesity. However, the impact of Slc25a1 inhibition on nutrient metabolism under HFD remains unclear. To address this gap, we used zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus) to evaluate the effects of inhibiting Slc25a1. In zebrafish, we administered Slc25a1-specific inhibitors (CTPI-2) for four weeks, while Nile tilapia received intraperitoneal injections of dsRNA to knockdown slc25a1b for seven days. Inhibition of the mitochondrial citrate shuttle effectively protected zebrafish from HFD-induced obesity, hepatic steatosis, and insulin resistance. Notably, glucose tolerance was unaffected. Inhibition of Slc25a1 altered hepatic protein acetylation patterns, with decreased cytoplasmic acetylation and increased mitochondrial acetylation. Under HFD conditions, Slc25a1 inhibition promoted fatty acid oxidation and reduced hepatic triglyceride accumulation by deacetylating Cpt1a. Additionally, Slc25a1 inhibition triggered acetylation-induced inactivation of Pdhe1α, leading to a reduction in glucose oxidative catabolism. This was accompanied by enhanced glucose uptake and storage in zebrafish livers. Furthermore, Slc25a1 inhibition under HFD conditions activated the SIRT1/PGC1α pathway, promoting mitochondrial proliferation and enhancing oxidative phosphorylation for energy production. Our findings provide new insights into the role of non-histone protein acetylation via the mitochondrial citrate shuttle in the development of hepatic lipid deposition and hyperglycemia caused by HFD.

Inhibiting mitochondrial citrate shuttling induces hepatic triglyceride deposition in Nile tilapia (Oreochromis niloticus) through lipid anabolic remodeling.

The solute carrier family 25 member 1 (Slc25a1)-dependent mitochondrial citrate shuttle is responsible for exporting citrate from the mitochondria to the cytoplasm for supporting lipid biosynthesis and protein acetylation. Previous studies on Slc25a1 concentrated on pathological models. However, the importance of Slc25a1 in maintaining metabolic homeostasis under normal nutritional conditions remains poorly understood. Here, we investigated the mechanism of mitochondrial citrate shuttle in maintaining lipid metabolism homeostasis in male Nile tilapia (Oreochromis niloticus). To achieve the objective, we blocked the mitochondrial citrate shuttle by inhibiting Slc25a1 under normal nutritional conditions. Slc25a1 inhibition was established by feeding Nile tilapia with 250 mg/kg 1,2,3-benzenetricarboxylic acid hydrate for 6 weeks or intraperitoneal injecting them with dsRNA to knockdown slc25a1b for 7 days. The Nile tilapia with Slc25a1 inhibition exhibited an obesity-like phenotype accompanied by fat deposition, liver damage and hyperglycemia. Moreover, Slc25a1 inhibition decreased hepatic citrate-derived acetyl-CoA, but increased hepatic triglyceride levels. Furthermore, Slc25a1 inhibition replenished cytoplasmic acetyl-CoA through enhanced acetate pathway, which led to hepatic triglycerides accumulation. However, acetate-derived acetyl-CoA caused by hepatic Slc25a1 inhibition did not activate de novo lipogenesis, but rather modified protein acetylation. In addition, hepatic Slc25a1 inhibition enhanced fatty acids esterification through acetate-derived acetyl-CoA, which increased Lipin1 acetylation and its protein stability. Collectively, our results illustrate that inhibiting mitochondrial citrate shuttle triggers lipid anabolic remodeling and results in lipid accumulation, indicating the importance of mitochondrial citrate shuttle in maintaining lipid metabolism homeostasis.

High cholesterol intake remodels cholesterol turnover and energy homeostasis in Nile tilapia (Oreochromis niloticus).

The roles of dietary cholesterol in fish physiology are currently contradictory. The issue reflects the limited studies on the metabolic consequences of cholesterol intake in fish. The present study investigated the metabolic responses to high cholesterol intake in Nile tilapia (Oreochromis niloticus), which were fed with four cholesterol-contained diets (0.8, 1.6, 2.4 and 3.2%) and a control diet for eight weeks. All fish-fed cholesterol diets showed increased body weight, but accumulated cholesterol (the peak level was in the 1.6% cholesterol group). Then, we selected 1.6% cholesterol and control diets for further analysis. The high cholesterol diet impaired liver function and reduced mitochondria number in fish. Furthermore, high cholesterol intake triggered protective adaptation via (1) inhibiting endogenous cholesterol synthesis, (2) elevating the expression of genes related to cholesterol esterification and efflux, and (3) promoting chenodeoxycholic acid synthesis and efflux. Accordingly, high cholesterol intake reshaped the fish gut microbiome by increasing the abundance of Lactobacillus spp. and Mycobacterium spp., both of which are involved in cholesterol and/or bile acids catabolism. Moreover, high cholesterol intake inhibited lipid catabolic activities through mitochondrial ß-oxidation, and lysosome-mediated lipophagy, and depressed insulin signaling sensitivity. Protein catabolism was elevated as a compulsory response to maintain energy homeostasis. Therefore, although high cholesterol intake promoted growth, it led to metabolic disorders in fish. For the first time, this study provides evidence for the systemic metabolic response to high cholesterol intake in fish. This knowledge contributes to an understanding of the metabolic syndromes caused by high cholesterol intake or deposition in fish. Supplementary Information: The online version contains supplementary material available at 10.1007/s42995-022-00158-7.

The dysfunction of hormone-sensitive lipase induces lipid deposition and reprogramming of nutrient metabolism in fish.

Hormone-sensitive lipase (HSL) is one of the rate-determining enzymes in the hydrolysis of TAG, playing a crucial role in lipid metabolism. However, the role of HSL-mediated lipolysis in systemic nutrient homoeostasis has not been intensively understood. Therefore, we used CRISPR/Cas9 technique and Hsl inhibitor (HSL-IN-1) to establish hsla-deficient (hsla-/-) and Hsl-inhibited zebrafish models, respectively. As a result, the hsla-/- zebrafish showed retarded growth and reduced oxygen consumption rate, accompanied with higher mRNA expression of the genes related to inflammation and apoptosis in liver and muscle. Furthermore, hsla-/- and HSL-IN-1-treated zebrafish both exhibited severe fat deposition, whereas their expressions of the genes related to lipolysis and fatty acid oxidation were markedly reduced. The TLC results also showed that the dysfunction of Hsl changed the whole-body lipid profile, including increasing the content of TG and decreasing the proportion of phospholipids. In addition, the systemic metabolic pattern was remodelled in hsla-/- and HSL-IN-1-treated zebrafish. The dysfunction of Hsl lowered the glycogen content in liver and muscle and enhanced the utilisation of glucose plus the expressions of glucose transporter and glycolysis genes. Besides, the whole-body protein content had significantly decreased in the hsla-/- and HSL-IN-1-treated zebrafish, accompanied with the lower activation of the mTOR pathway and enhanced protein and amino acid catabolism. Taken together, Hsl plays an essential role in energy homoeostasis, and its dysfunction would cause the disturbance of lipid catabolism but enhanced breakdown of glycogen and protein for energy compensation.

Biosynthesis of silver nanoparticles with antimicrobial and anticancer properties using two novel yeasts.

AgNPs are nanomaterials with many potential biomedical applications. In this study, the two novel yeast strains HX-YS and LPP-12Y capable of producing biological silver nanoparticles were isolated. Sequencing of ribosomal DNA-ITS fragments, as well as partial D1/D2 regions of 26S rDNA indicated that the strains are related to species from the genus Metschnikowia. The BioAgNPs produced by HX-YS and LPP-12Y at pH 5.0-6.0 and 26 °C ranged in size from 50 to 500 nm. The antibacterial activities of yeast BioAgNPs against five pathogenic bacteria were determined. The highest antibacterial effect was observed on P. aeruginosa, with additional obvious effects on E. coli ATCC8099 and S. aureus ATCC10231. Additionally, the BioAgNPs showed antiproliferative effects on lung cancer cell lines H1975 and A579, with low toxicity in Beas 2B normal lung cells. Therefore, the AgNPs biosynthesized by HX-YS and LPP-12Y may have potential applications in the treatment of bacterial infections and cancer.

Lipolysis and lipophagy play individual and interactive roles in regulating triacylglycerol and cholesterol homeostasis and mitochondrial form in zebrafish.

Neutral lipases-mediated lipolysis and acid lipases-moderated lipophagy are two main processes for degradation of lipid droplets (LDs). However, the individual and interactive roles of these metabolic pathways are not well known across vertebrates. This study explored the roles of lipolysis and lipophagy from the aspect of neutral and acid lipases in zebrafish. We established zebrafish strains deficient in either adipose triglyceride lipase (atgl-/-; AKO fish) or lysosomal acid lipase (lal-/-; LKO fish) respectively, and then inhibited lipolysis in the LKO fish and lipophagy in the AKO fish by feeding diets supplemented with the corresponding inhibitors Atglistatin and 3-Methyladenine, respectively. Both the AKO and LKO fish showed reduced growth, swimming activity, and oxygen consumption. The AKO fish did not show phenotypes in adipose tissue, but mainly accumulated triacylglycerol (TAG) in liver, also, they had large LDs in the hepatocytes, and did not stimulate lipophagy as a compensation response but maintained basal lipophagy. The LKO fish reduced total lipid accumulation in the body but had high cholesterol content in liver; also, they accumulated small LDs in the hepatocytes, and showed increased lipolysis, especially Atgl expression, as a compensatory mechanism. Simultaneous inhibition of lipolysis and lipophagy in zebrafish resulted in severe liver damage, with the potential to trigger mitophagy. Overall, our study illustrates that lipolysis and lipophagy perform individual and interactive roles in maintaining homeostasis of TAG and cholesterol metabolism. Furthermore, the interactive roles of lipolysis and lipophagy may be essential in regulating the functions and form of mitochondria.

Optimal Factors of Diffusion Tensor Imaging Predicting Corticospinal Tract Injury in Patients with Brain Tumors.

OBJECTIVE: To identify the optimal factors in diffusion tensor imaging for predicting corticospinal tract (CST) injury caused by brain tumors. MATERIALS AND METHODS: This prospective study included 33 patients with motor weakness and 64 patients with normal motor function. The movement of the CST, minimum distance between the CST and the tumor, and relative fractional anisotropy (rFA) of the CST on diffusion tensor imaging, were compared between patients with motor weakness and normal function. Logistic regression analysis was used to obtain the optimal factor predicting motor weakness. RESULTS: In patients with motor weakness, the displacement (8.44 ± 6.64 mm) of the CST (p = 0.009), minimum distance (3.98 ± 7.49 mm) between the CST and tumor (p < 0.001), and rFA (0.83 ± 0.11) of the CST (p < 0.001) were significantly different from those of the normal group (4.64 ± 6.65 mm, 14.87 ± 12.04 mm, and 0.98 ± 0.05, respectively) (p = 0.009, p < 0.001, and p < 0.001). The frequencies of patients with the CST passing through the tumor (6%, p = 0.002), CST close to the tumor (23%, p < 0.001), CST close to a malignant tumor (high grade glioma, metastasis, or lymphoma) (19%, p < 0.001), and CST passing through infiltrating edema (19%, p < 0.001) in the motor weakness group, were significantly different from those of the patients with normal motor function (0, 8, 1, and 10%, respectively). Logistic regression analysis showed that decreased rFA and CST close to a malignant tumor were effective variables related to motor weakness. CONCLUSION: Decreased fractional anisotropy, combined with closeness of a malignant tumor to the CST, is the optimal factor in predicting CST injury caused by a brain tumor.