Metformin attenuates triglyceride accumulation in HepG2 cells through decreasing stearyl-coenzyme A desaturase 1 expression.

BACKGROUND: The prevalence of nonalcoholic fatty liver disease (NAFLD) has increased worldwide. Metformin decreases triglyceride (TG) accumulation in hepatocytes in vivo and in vitro. Stearyl-coenzyme A desaturase 1 (SCD1) knockout mice also show decreased liver TG accumulation; however, whether SCD1 plays a role in the effect of metformin on TG accumulation is unknown. Therefore, the aim of this study was to investigate whether SCD1 mediated the effect of metformin on TG accumulation. METHODS: HepG2 and AML12 cells were exposed to high glucose and high insulin with or without metformin. An adenovirus was used for the SCD1 knockdown and overexpression. The triglyceride level in cells was detected. The expression of related genes was detected by Western blot and quantitative real-time PCR. A dual-luciferase reporter assay was used to determine the effect of metformin on the transcriptional activity of the SCD1 promoter. RESULTS: Metformin decreased TG accumulation to normal level in HepG2 cells exposed to high glucose and high insulin. The expression of SCD1 and fatty acid synthetase (FAS) was also decreased to normal level by metformin. Knockdown of SCD1 mimicked the effect of metformin on decreasing TG levels in AML12 cells, and the overexpression of SCD1 attenuated the effect of metformin on decreasing TG accumulation in HepG2 cells. The dual-luciferase reporter assay showed that the transcriptional activity of the SCD1 promoter (- 550/+ 199) after metformin treatment was 2-fold lower compared to control group in HepG2 cells. Additionally, the phosphorylation of AMPK after metformin treatment was 2-fold higher, and the expression of sterol regulatory element-binding protein-1c (SREBP-1c) after metformin treatment was about 2-fold lower compared to high glucose and high insulin group in HepG2 cells. CONCLUSIONS: Together, these results reveal that metformin reduces TG accumulation in HepG2 cells via inhibiting the expression of SCD1.

Role of stearyl-coenzyme A desaturase 1 in mediating the effects of palmitic acid on endoplasmic reticulum stress, inflammation, and apoptosis in goose primary hepatocytes.

OBJECTIVE: Unlike mammals, goose fatty liver shows a strong tolerance to fatty acids without obvious injury. Stearyl-coenzyme A desaturase 1 (SCD1) serves crucial role in desaturation of saturated fatty acids (SAFs), but its role in the SAFs tolerance of goose hepatocytes has not been reported. This study was conducted to explore the role of SCD1 in regulating palmitic acid (PA) tolerance of goose primary hepatocytes. METHODS: 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide was examined to reflect the effect of PA on hepatocytes viability, and quantitative polymerase chain reaction was used to detect the mRNA levels of several genes related to endoplasmic reticulum (ER) stress, inflammation, and apoptosis, and the role of SCD1 in PA tolerance of goose hepatocytes was explored using RNA interfere. RESULTS: Our results indicated that goose hepatocytes exhibited a higher tolerant capacity to PA than human hepatic cell line (LO2 cells). In goose primary hepatocytes, the mRNA levels of fatty acid desaturation-related genes (SCD1 and fatty acid desaturase 2) and fatty acid elongate enzyme-related gene (elongase of very long chain fatty acids 6) were significantly upregulated with 0.6 mM PA treatment. However, in LO2 cells, expression of ER stressrelated genes (x box-binding protein, binding immunoglobulin protein, and activating transcription factor 6), inflammatory response-related genes (interleukin-6 [IL-6], interleukin- 1ß [IL-1ß], and interferon-γ) and apoptosis-related genes (bcl-2-associated X protein, b-cell lymphoma 2, Caspase-3, and Caspase-9) was significantly enhanced with 0.6 mM PA treatment. Additionally, small interfering RNA (siRNA) mediated downregulation of SCD1 significantly reduced the PA tolerance of goose primary hepatocytes under the treatment of 0.6 mM PA; meanwhile, the mRNA levels of inflammatory-related genes (IL-6 and IL-1ß) and several key genes involved in the phosphoinositide 3-kinase (PI3K)/ protein kinase B (AKT), forkhead box O1 (FoxO1), mammalian target of rapamycin and AMPK pathways (AKT1, AKT2, FoxO1, and sirtuin 1), as well as the protein expression of cytochrome C and the apoptosis rate were upregulated. CONCLUSION: In conclusion, our data suggested that SCD1 was involved in enhancing the PA tolerance of goose primary hepatocytes by regulating inflammation- and apoptosisrelated genes expression.

Berberine attenuates nonalcoholic hepatic steatosis through the AMPK-SREBP-1c-SCD1 pathway.

BACKGROUND: Berberine (BBR), a natural compound extracted from Chinese herb, has been shown to effectively attenuate nonalcoholic fatty liver disease (NAFLD) in clinic. However, the mechanism underlying the effect of BBR is not fully understood. Stearyl-coenzyme A desaturase 1 (SCD1) mediates lipid metabolism in liver. Therefore, we hypothesized that SCD1 mediated the beneficial effect of BBR on NAFLD. METHODS: The expression of SCD1 was measured in the liver of NAFLD patients and ob/ob mice. The effect of BBR on NAFLD was evaluated in C57BL/6 J mice on high fat diet (HFD). The effect of BBR was also investigated in HepG2 and AML12 cells exposed to high glucose and palmitic acid. Oil red O staining was performed to detect triglyceride (TG) level. Quantitative real-time polymerase chain reaction and Western blot were used to detect the messenger ribonucleic acid (mRNA) and protein expression of target genes. The activity of SCD1 promoter was measured by dual-luciferase reporter assay. RESULTS: The expression of SCD1 was increased in the liver of NAFLD patients and ob/ob mice. BBR reduced hepatic TG accumulation and decreased the expressions of hepatic SCD1 and other TG synthesis related genes both in vivo and in vitro. Knockdown of SCD1 expression mimicked the effect of BBR decreasing TG level in steatotic hepatocytes, whereas overexpression of SCD1 attenuated the effect of BBR. Mechanistically, BBR promoted the phosphorylation of AMP-activated protein kinase (AMPK) and sterol regulatory element-binding protein-1c (SREBP-1c) in HepG2 cells and the liver of HFD-fed mice. Activation of the AMPK-SREBP-1c pathway and sterol regulatory element (SRE) motif in SCD1 promoter (-920/-550) was responsible for the BBR-induced suppression of SCD1. CONCLUSION: BBR reduces liver TG synthesis and attenuates hepatic steatosis through the activation of AMPK-SREBP-1c-SCD1 pathway.