Myoung Sook Han, Yu-Mi Lim, Wenying Quan, Jung Ran Kim, Kun Wook Chung, Mira Kang, Sunshin Kim, Sun Young Park, Joong-Soo Han, Shin-Young Park, Hyae Gyeong Cheon, Sang Dal Rhee, Tae-Sik Park, Myung-Shik Lee

Targeting the gut-liver axis by modulating the gut-microbiome can be a promising therapeutic approach in nonalcoholic fatty liver disease (NAFLD). The aim of this study was to evaluate the effects of single species and a combination of Lactobacillus and Pediococcus in NAFLD mice model. Six-week male C57BL/6J mice were divided into 9 groups (n = 10/group; normal, Western diet, and 7 Western diet-strains [10⁹ CFU/g, 8 weeks]). The strains used were L. bulgaricus, L. casei, L. helveticus, P. pentosaceus KID7, and three combinations (1: L. casei+L. helveticus, 2: L. casei+L. helveticus+P. pentosaceus KID7, and 3: L. casei+L. helveticus+L. bulgaricus). Liver/Body weight ratio, serum and stool analysis, liver pathology, and metagenomics by 16S rRNA-sequencing were examined. In the liver/body ratio, L. bulgaricus (5.1 ± 0.5), L. helveticus (5.2 ± 0.4), P. pentosaceus KID7 (5.5 ± 0.5), and combination1 and 2 (4.2 ± 0.6 and 4.8 ± 0.7) showed significant reductions compared with Western (6.2 ± 0.6)(p < 0.001). In terms of cholesterol and steatosis/inflammation/NAFLD activity, all groups except for L. casei were associated with an improvement (p < .05). The elevated level of tumor necrosis factor-α/interleukin-1β (pg/ml) in Western (65.8 ± 7.9/163.8 ± 12.2) was found to be significantly reduced in L. bulgaricus (24.2 ± 1.0/58.9 ± 15.3), L. casei (35.6 ± 2.1/62.9 ± 6.0), L. helveticus (43.4 ± 3.2/53.6 ± 7.5), and P. pentosaceus KID7 (22.9 ± 3.4/59.7 ± 12.2)(p < 0.01). Cytokines were improved in the combination groups. In metagenomics, each strains revealed a different composition and elevated Firmicutes/Bacteroidetes ratio in the western (47.1) was decreased in L. bulgaricus (14.5), L. helveticus (3.0), and P. pentosaceus KID7 (13.3). L. bulgaricus, L. casei, L. helveticus, and P. pentosaceus KID7 supplementation can improve NAFLD-progression by modulating gut-microbiome and inflammatory pathway.

The endoplasmic reticulum (ER) is the principal organelle in the cell for protein folding and trafficking, lipid synthesis, and cellular calcium homeostasis. Perturbation of ER function results in activation of the unfolded protein response (UPR) and is implicated in abnormal lipid biosynthesis and development of insulin resistance. In this study, we investigated whether transcription of sphingosine kinase (Sphk)2 is regulated by ER stress‐mediated UPR pathways. Sphk2, a major isotype of sphingosine kinase in the liver, was transcriptionally up‐regulated by tunicamycin and lipopolysaccharides. Transcriptional regulation of Sphk2 was mediated by activation of activating transcription factor (ATF)4 as demonstrated by promoter assays, immunoblotting, and small interfering RNA analyses. In primary hepatocytes, adenoviral Sphk2 expression elevated cellular sphingosine 1 phosphate (S1P) and activated protein kinase B phosphorylation, with no alteration of insulin receptor substrate phosphorylation. Hepatic overexpression of Sphk2 in mice fed a high‐fat diet (HFD) led to elevated S1P and reduced ceramide, sphingomyelin, and glucosylceramide in plasma and liver. Hepatic accumulation of lipid droplets by HFD feeding was reduced by Sphk2‐mediated up‐regulation of fatty acid (FA) oxidizing genes and increased FA oxidation in liver. In addition, glucose intolerance and insulin resistance were ameliorated by improved hepatic insulin signaling through Sphk2 up‐regulation.Conclusion:Sphk2 is transcriptionally up‐regulated by acute ER stress through activation of ATF4 and improves perturbed hepatic glucose and FA metabolism. (Hepatology2015;62:135‐146)

The role of serine palmitoyltransferase (SPT) and de novo ceramide biosynthesis in cardiac ceramide and sphingomyelin metabolism is unclear. To determine whether the de novo synthetic pathways, rather than ceramide uptake from circulating lipoproteins, is important for heart ceramide levels, we created cardiomyocyte-specific deficiency of Sptlc2, a subunit of SPT. Heart-specific Sptlc2-deficient (hSptlc2 KO) mice had a >35% reduction in ceramide, which was limited to C18:0 and very long chain ceramides. Sphingomyelinase expression, and levels of sphingomyelin and diacylglycerol were unchanged. But surprisingly phospholipids and acyl CoAs contained increased saturated long chain fatty acids. hSptlc2 KO mice had decreased fractional shortening and thinning of the cardiac wall. While the genes regulating glucose and fatty acid metabolism were not changed, expression of cardiac failure markers and the genes involved in the formation of extracellular matrices were up-regulated in hSptlc2 KO hearts. In addition, ER-stress markers were up-regulated leading to increased apoptosis. These results suggest that Sptlc2-mediated de novo ceramide synthesis is an essential source of C18:0 and very long chain, but not of shorter chain, ceramides in the heart. Changes in heart lipids other than ceramide levels lead to cardiac toxicity.

Non-alcoholic fatty liver disease (NAFLD) arises from mitochondrial dysfunction under sustained imbalance between energy intake and expenditure, but the underlying mechanisms controlling mitochondrial respiration have not been entirely understood. Heterotrimeric G proteins converge signals from activated GPCRs, and modulate cell signaling pathways to maintain metabolic homeostasis. Here, we investigated the regulatory role of Gα₁₂ on hepatic lipid metabolism and whole-body energy expenditure in mice. Fasting increased Gα₁₂ level in mouse liver. Gα₁₂ ablation markedly augmented fasting-induced hepatic fat accumulation. cDNA microarray analysis from Gna12 KO liver revealed that Gα₁₂ signaling pathway regulated sirtuin 1 (SIRT1) and PPARα responsible for mitochondrial respiration. Defective induction of SIRT1 upon fasting was observed in the liver of Gna12 KO mice, which was reversed by lentivirus-mediated Gα₁₂ overexpression in hepatocytes. Mechanistically, Gα₁₂ stabilized SIRT1 protein through transcriptional induction of USP22 via HIF-1α increase. Gα₁₂ levels were markedly diminished in liver biopsies from NAFLD patients. Consistently, Gna12 KO mice fed high-fat diet displayed greater susceptibility to diet-induced liver steatosis and obesity due to decrease in energy expenditure. Our results demonstrate that Gα₁₂ regulates SIRT1-dependent mitochondrial respiration through HIF-1α-dependent USP22 induction, identifying Gα₁₂ as an upstream molecule that contributes to the regulation of mitochondrial energy expenditure.