Hepatocyte-specific CCAAT/enhancer binding protein α restricts liver fibrosis progression

Metabolic dysfunction-associated steatohepatitis (MASH) - previously described as nonalcoholic steatohepatitis (NASH) - is a major driver of liver fibrosis in humans, while liver fibrosis is a key determinant of all-cause mortality in liver disease independent of MASH occurrence. CCAAT/enhancer binding protein α (CEBPA), as a versatile ligand-independent transcriptional factor, has an important function in myeloid cells, and is under clinical evaluation for cancer therapy. CEBPA is also expressed in hepatocytes and regulates glucolipid homeostasis; however, the role of hepatocyte-specific CEBPA in modulating liver fibrosis progression is largely unknown. Here, hepatic CEBPA expression was found to be decreased during MASH progression both in humans and mice, and hepatic CEBPA mRNA was negatively correlated with MASH fibrosis in the human liver. CebpaΔHep mice had markedly enhanced liver fibrosis induced by a high-fat, high-cholesterol, high-fructose diet or carbon tetrachloride. Temporal and spatial hepatocyte-specific CEBPA loss at the progressive stage of MASH in CebpaΔHep,ERT2 mice functionally promoted liver fibrosis. Mechanistically, hepatocyte CEBPA directly repressed Spp1 transactivation to reduce the secretion of osteopontin, a fibrogenesis inducer of hepatic stellate cells. Forced hepatocyte-specific CEBPA expression reduced MASH-associated liver fibrosis. These results demonstrate an important role for hepatocyte-specific CEBPA in liver fibrosis progression, and may help guide the therapeutic discoveries targeting hepatocyte CEBPA for the treatment of liver fibrosis.

Brown Algae Dictyopteris divaricata Attenuates Adipogenesis by Modulating Adipocyte Differentiation and Promoting Lipolysis through Heme Oxygenase-1 Activation in 3T3-L1 Cells

The present study aims to explore the probable anti-adipogenesis effect of Dictyopteris divaricata (D. divaricata) in 3T3-L1 preadipocytes by regulating heme oxygenase-1 (HO-1). The extract of D. divaricata retarded lipid accretion and decreased triglyceride (TG) content in 3T3-L1 adipocytes but increased free glycerol levels. Treatment with the extract inhibited lipogenesis by inhibiting protein expressions of fatty acid synthase (FAS) and lipoprotein lipase (LPL), whereas lipolysis increased by activating phosphorylation of hormone-sensitive lipase (p-HSL) and AMP-activated protein kinase (p-AMPK). The extract inhibited adipocyte differentiation of 3T3-L1 preadipocytes through down-regulating adipogenic transcription factors, including peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα), and sterol regulatory element-binding protein 1 (SREBP1). This is attributed to the triggering of Wnt/β-catenin signaling. In addition, this study found that treatment with the extract activated HO-1 expression. Pharmacological approaches revealed that treatment with Zinc Protoporphyrin (ZnPP), an HO-1 inhibitor, resulted in an increase in lipid accumulation and a decrease in free glycerol levels. Finally, three adipogenic transcription factors, such as PPARγ, C/EBPα, and SREBP1, restored their expression in the presence of ZnPP. Analysis of chemical constituents revealed that the extract of D. divaricata is rich in 1,4-benzenediol, 7-tetradecenal, fucosterol, and n-hexadecanoic acid, which are known to have multiple pharmacological properties.

Positive Regulation of Acetate in Adipocyte Differentiation and Lipid Deposition in Obese Mice

Acetate is associated with adipocyte differentiation and lipid deposition. To further develop this scientific point, obese mice on a high-fat diet were given an intragastric administration of acetate for 8 weeks and mouse adipose mesenchymal stem cells (mAMSCs) were treated with acetate for 24 h. The results showed that the body weight, food intake, Lee's index, adipose tissue coefficient, liver index, blood lipid levels, insulin resistance, pro-inflammatory factors levels and fatty lesions in liver and adipose tissue in obese mice treated with acetate increased markedly, while anti-inflammatory factors levels and liver function decreased significantly (p < 0.05). The mRNA expression levels of PPAR-γ, C/EBP-α, SREBP, AFABP, FAS, ACC-1, SCD-1, LPL, LEPR, GPR41 and GPR43 genes in adipose tissue and mAMSCs were significantly increased, while the mRNA expression levels of HSL, CPT-1, CPT-2, AMPK, AdipoR1 and AdipoR2 genes were significantly reduced (p < 0.05). Except for AMPK-α signaling pathway proteins, the phosphorylation levels of p38 MAPK, ERK1/2, JNK and mTOR were significantly increased (p < 0.05) and these changes were dose-dependent. The findings indicated that acetate played a positive role in regulating adipocyte differentiation and lipid deposition by activating MAPKs and mTOR signaling pathways (the expression up-regulation of genes such as PPAR-γ, C/EBP-α and SREBP-1, etc.) and inhibiting the AMPK signaling pathway (the expression down-regulation of genes such as HSL, CPT-1 and AMPK-α, etc.).

The effect of homocysteine on the expression of CD36, PPARγ, and C/EBPα in adipose tissue of normal and obese mice

The purpose of this study was to investigate the effect of homocysteine (Hcy) on CD36, PPARγ, and C/EBPα gene and protein expression in adipose tissue obtained from normal and high-calorie diet obesity models. CD36, PPARγ, and C/EBPα gene expression and protein levels in adipose tissue specimens were determined using the RT-PCR and ELISA methods, respectively. Significantly increased CD36 gene expression was observed in adipose tissue from obese mice, while Hcy significantly reduced CD36 gene expression in adipose tissue from normal and obese mice. PPARγ and C/EBPα gene expression levels decreased significantly in all groups compared to the normal group. In addition, levels of both PPARγ and C/EBPα gene expression were lower with Hcy supplementation compared to their own controls. In conclusion, Hcy's reduction of CD36 gene expression in adipose tissue may be one probable factor in hyperhomocysteinemia representing an independent risk factor for cardiovascular diseases.

Galloyl Group in B-type Proanthocyanidin Dimers Was Responsible for Its Differential Inhibitory Activity on 3T3-L1 Preadipocytes due to the Strong Lipid Raft-Perturbing Potency

The effects of three B-type proanthocyanidin (PA) dimers covering procyanidin B2 (B-0g), procyanidin B2 3'-O-gallate (B-1g), and procyanidin B2 3,3'-di-O-gallate (B-2g) on 3T3-L1 preadipocyte differentiation and the underlying mechanisms were investigated. The results showed that digalloylated B-type PA dimers (B-2g) strongly inhibited 3T3-L1 preadipocyte differentiation through disrupting the integrity of the lipid raft structure and inhibiting the expression of peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer-binding protein alpha (C/EBPα) and then downregulating the expression of acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) factors, followed by B-1g, while B-0g had little effect. The different inhibitory effects were mainly due to the difference in the B-type PA dimer structure and the ability to interfere with lipid rafts. The greater the galloylation degree of B-type PA dimers, the stronger the ability to disrupt the lipid raft structure and oppose 3T3-L1 preadipocyte differentiation. In addition, galloylated B-type PA dimers had greater molecular hydrophobicity and topological polarity surface area and could penetrate into the lipid rafts to form multiple hydrogen bonds with the rafts by molecular dynamics simulation. These findings highlighted that the strong lipid raft-perturbing potency of galloylated B-type PA dimers was responsible for inhibition of 3T3-L1 preadipocyte differentiation.

[INFLUENCE OF BURN SERUM ON PROLIFERATION AND ADIPOSE DIFFERENTIATION OF 3T3-L1 PREADIPOCYTES]

OBJECTIVE

To investigate the effect of burn on the fat metabolism by observing the effect of burn serum on the proliferation and adipose differentiation of 3T3-L1 preadipocytes.

METHODS

Forty-eight male Sprague Dawley rats were randomly divided into sham burn group and burn at 1, 4, 7, 14, and 21 days groups, 8 rats in each group. The rats in burn groups were made the full-thickness thermal burns comprising 30% total body surface area. At 1, 4, 7, 14, and 21 days after burn, the serum of burn rats was collected. The rats in sham burn group were not treated as normal control. The proliferation activity of 3T3-L1 cells was detected using MTT method after treated by normal and burn serum. The burn serum having the highest proliferation inhibitory effect was chosen for subsequent study. The growth of 3T3-L1 cells in normal serum group (group A), burn serum group (group B), normal serum and adipogenic induction group (group C), burn serum and adipogenic induction group (group D) was observed using inverted microscope. After 7 days of treatment, the adipocytes was stained by oil red O and the absorbance (A) value was measured. The mRNA and protein levels of preoxisome proliferator-activated receptor γ (PPAR-γ) and lipoprotein lipase (LPL) were detected by real-time quantitative PCR and Western blot.

RESULTS

The proliferation ability of 3T3-L1 cells was significantly reduced in the group treated by 4- or 7-day burn serum (P < 0.05), especially 7-day burn serum treatment group (P < 0.05). Under inverted microscope, the cell morphology in group A and group B had no obvious change, but a large number of fat cells were observed in group C and a few were observed in group D. The positive or weak positive oil red O staining was observed in group C or group D, respectively. The cell counting and A value were significantly higher in group A than in group B, and in group C than in group D (P < 0.05). The mRNA level of PPAR-γ in group B was significantly reduced when compared with that in group A (P < 0.05). No significant difference was found in LPL mRNA levels and protein levels of PPAR-γ and LPL between group A and group B (P > 0.05). The mRNA and protein levels of PPAR-γ and LPL were significantly attenuated in group D when compared with those in group C (P < 0.05).

CONCLUSION

The adipose differentiation of 3T3-L1 preadipocytes can be significantly reduced after treated by 7-day burn serum of rat.

Illudins C2 and C3 stimulate lipolysis in 3T3-L1 adipocytes and suppress adipogenesis in 3T3-L1 preadipocytes

The secondary metabolites illudins C2 (1) and C3 (2), obtained from the culture broth of Coprinus atramentarius, have been shown to possess antimicrobial activity. In the present study, we discovered novel biological activities of 1 and 2 in lipolysis of differentiated 3T3-L1 adipocytes and adipogenesis of 3T3-L1 preadipocytes. Compounds 1 and 2 exhibit a dose-dependent increase in glycerol release and thereby reduce intracellular lipid accumulation. The stimulatory effects of 1 and 2 on lipolysis are prevented by cAMP-dependent protein kinase (PKA) and extracellular signal-regulated kinase (ERK) inhibitors. Compounds 1 and 2 down-regulated perilipin and also affected the mRNA and protein levels of adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL). However, 1 and 2 treatment leads to a significant increase in PKA-mediated phosphorylation of HSL at S563 and S660. In addition, 1 and 2 treatment in 3T3-L1 preadipocytes induces down-regulation of the critical transcription factors, CCAAT/enhancer binding protein α and β (C/EBPα and C/EBPβ), and peroxisome proliferator activated receptor γ (PPARγ), which are required for adipogenesis, and accordingly inhibits adipogenesis. These results suggest that 1 and 2 might be useful for treating obesity due to their modulatory effects on fat by affecting adipocyte differentiation and fat mobilization.

Characterization of the transcriptional and functional effects of fibroblast growth factor-1 on human preadipocyte differentiation

We recently established that fibroblast growth factor (FGF)-1 promotes adipogenesis of primary human preadipocytes (phPA). In the current report, we have characterized the adipogenic effects of FGF-1 in phPA and also in a human PA strain derived from an individual with Simpson-Golabi-Behmel syndrome (SGBS PA), which exhibit an intrinsic capacity to differentiate with high efficiency. In further studies, we compared these models with the well-characterized murine 3T3-L1 preadipocyte cell line (3T3-L1 PA). FGF-1 up-regulated the adipogenic program in phPA, with increased expression of peroxisome proliferator-activated receptor-gamma in confluent PA prior to induction of differentiation and increased expression of adipocyte markers during differentiation. Moreover, phPA differentiated in the presence of FGF-1 were more insulin responsive and secreted increased levels of adiponectin. FGF-1 treatment of SGBS PA further enhanced differentiation. For the most part, the adipogenic program in phPA paralleled that observed in 3T3-L1 PA; however, we found no evidence of mitotic clonal expansion in the phPA. Finally, we investigated a role for extracellular regulated kinase 1/2 (ERK1/2) in adipogenesis of phPA. FGF-1 induced robust phosphorylation of ERK1/2 in early differentiation and inhibition of ERK1/2 activity significantly reduced phPA differentiation. These data suggest that FGF-1 treated phPA represent a valuable in vitro model for the study of adipogenesis and insulin action and indicate that ERK1/2 activation is necessary for human adipogenesis in the absence of mitotic clonal expansion.

Overexpression of uncoupling protein 4 promotes proliferation and inhibits apoptosis and differentiation of preadipocytes

Uncoupling proteins are a family of mitochondrial proteins involved in energy metabolism. We previously showed that uncoupling protein 4 (UCP4) is differentially expressed in omental adipose tissue in diet-induced obese and normal rats. However, the effect of UCP4 on adipocytes is unclear. In this work, we established a stable preadipocyte cell line overexpressing UCP4 to observe the direct effect of UCP4 on adipocytes. Cells overexpressing UCP4 showed significantly attenuated differentiation of preadipocytes into adipocytes. During differentiation, expression of adipogenesis-associated markers such as fatty acid synthetase, peroxisome proliferator-activated receptor gamma, CCAAT enhancer binding protein alpha, adipocyte lipid binding protein and lipoprotein lipase were downregulated. Preadipoctes expressing UCP4 grew faster and more of them stayed in S phase compared to control cells. In addition, UCP4 overexpression protected preadipocytes from apoptosis induced by serum deprivation. Our results demonstrate that overexpression of UCP4 can promote proliferation and inhibit apoptosis and differentiation of preadipocytes.

Human neutrophil collagenase expression is C/EBP-dependent during myeloid development

OBJECTIVE

Human neutrophil collagenase (HNC) is one of several secondary granule proteins (SGP) expressed late in the myeloid maturation pathway. SGPs are encoded by unlinked and functionally diverse genes that are hypothesized to be coordinately regulated at the transcriptional level and demonstrate uniform dysregulation in leukemic cells. In support of the hypothesis that tissue and stage-specific expression of SGP genes is regulated by shared factor(s), we sought to identify factors responsible for positive regulation of the SGP genes.

METHODS

Using 5' deletion analysis, we identified a minimal HNC promoter located within the first 193 bp upstream of the transcription start site. Three CCAAT enhancer binding protein (C/EBP) sites were identified within this region and their functional importance was confirmed by mutational analysis, gel retardation, and oligonucleotide pulldown assays. Using chromatin immunoprecipitation (ChIP), we demonstrated that C/EBPalpha binds to the SGP gene promoters lactoferrin and HNC in nonexpressing cells. Upon induction of maturation, C/EBPalpha binds to these promoters and this binding correlates with the expression of both SGP genes.

CONCLUSION

We conclude that in the later stages of myeloid development, SGP genes are coordinately upregulated, and that members of the C/EBP family of transcription factors, in particular C/EBPalpha and C/EBPepsilon, play specific and unique roles in upregulating their expression.

The promoter region of the carbamoyl-phosphate synthetase III gene of Squalus acanthias

Carbamoyl-phosphate synthetase III (CPSase III) of Squalus acanthias (spiny dogfish) is a nuclear-encoded mitochondrial enzyme that catalyzes glutamine-dependent formation of carbamoyl phosphate for urea synthesis. In this paper we report the results of cloning a 10-kb segment of genomic DNA which includes the region flanking the 5' end of the spiny dogfish CPSase III gene. A total of 1,295 base pairs of sequence straddling the start codon was obtained. Primer extension experiments revealed that the transcription start site is the G located 114 residues upstream of the translation start codon ATG. The first exon has 240 base pairs, including the 5' untranslated region, the coding sequence for the signal peptide (38 amino acids), and the four N-terminal amino acids of the mature enzyme. The boundary of the first exon and the first intron of the CPSase III gene is concordant with that of rat and frog (Rana catesbeiana) CPSase I, which have been suggested to have evolved from CPSase III. The putative TATA box sequence, TACAAA, is located at position -31 with an uncommonly found C at the third position. Two C/EBP binding site sequences, ATTCTGCAAG (-405 to -397) and GTGCAGTAAG (-168 to -160), were identified in the promoter region, which suggests that spiny dogfish CPSase III might be subjected to transactivation of transcription by C/EBP-related proteins, as has been reported for rat CPSase I. The preparation and binding of a recombinant RcC/EBP-1 protein (the R. catesbeiana homolog of the mammalian C/EBP alpha) to the two spiny dogfish C/EBP binding sequences are described. Two putative heat-shock binding elements were also identified in the promoter region.

Stress-induced binding of the transcriptional factor CHOP to a novel DNA control element

CHOP (GADD153) is a mammalian nuclear protein that dimerizes with members of the C/EBP family of transcriptional factors. Absent under normal conditions, CHOP is induced by the stress encountered during nutrient deprivation, the acute-phase response, and treatment of cells with certain toxins. The basic region of CHOP deviates considerably in sequence from that of other C/EBP proteins, and CHOP-C/EBP heterodimers are incapable of binding to a common class of C/EBP sites. With respect to such sites, CHOP serves as an inhibitor of the activity of C/EBP proteins. However, recent studies indicate that certain functions of CHOP, such as the induction of growth arrest by overexpression of the wild-type protein and oncogenic transformation by the TLS-CHOP fusion protein, require an intact basic region, suggesting that DNA binding by CHOP may be implicated in these activities. In this study an in vitro PCR-based selection assay was used to identify sequences bound by CHOP-C/EBP dimers. These sequences were found to contain a unique core element PuPuPuTGCAAT(A/C)CCC. Competition in DNA-binding assays, DNase 1 footprint analysis, and methylation interference demonstrate that the binding is sequence specific. Deletions in the basic region of CHOP lead to a loss of DNA binding, suggesting that CHOP participates in this process. Stress induction in NIH 3T3 cells leads to the appearance of CHOP-containing DNA-binding activity. CHOP is found to contain a transcriptional activation domain which is inducible by cellular stress, lending further support to the notion that the protein can function as a positively acting transcription factor. We conclude that CHOP may serve a dual role both as an inhibitor of the ability of C/EBP proteins to activate some target genes and as a direct activator of others.

Three levels of functional interaction determine the activity of CCAAT/enhancer binding protein-alpha on the serum albumin promoter

We have studied the activation of the serum albumin promoter by transcription factor CCAAT/enhancer binding protein-alpha (C/EBP alpha) in the HepG2 hepatoma cell line. We find that three distinct mechanisms determine the ability of C/EBP alpha to activate this promoter in a cell-type-specific and cooperative manner. First, the trans-activating function of C/EBP alpha is generated through cooperation between three separate domains of the protein that we have named trans-activation elements (TE-I through TE-III). The TEs have little or no ability to activate transcription by themselves, but any two can cooperate to do so, both in the C/EBP alpha protein and when linked to the GAL4 DNA-binding domain. Second, TE-III was found to contain a negative regulatory subdomain, the function of which was alleviated when C/EBP alpha was bound in the environment of the albumin promoter. This formed the basis for cooperative activation of this promoter by C/EBP alpha. Finally, we demonstrate that the leucine zipper of C/EBP alpha participates in determining the cell type specificity of albumin promoter activation, as it exerts a strong negative effect on albumin promoter activation in the nonhepatic HeLa cell line but not in HepG2 cells. These findings shed new light on the mode of action of C/EBP alpha and show a novel function for leucine zipper in cell-type-specific gene expression.

Characterization and expression of C/EPB-like genes in the liver of Rana catesbeiana tadpoles during spontaneous and thyroid hormone-induced metamorphosis

Tissue-specific changes in gene expression occur in the liver of Rana catesbeiana tadpoles undergoing metamorphosis. Many of these changes can be induced precociously by administration of thyroid hormone (TH) to a tadpole or to cultured tadpole liver. While the precise molecular means by which TH exerts a tissue-specific response is unknown, recent studies suggest that the expression of genes which are liver-specific and characteristic of the adult liver phenotype may rely on TH-induction of tissue-specific transcription factors, as well as the thyroid hormone receptor proteins. Guided by this notion, we screened our Rana catesbeiana liver cDNA library and isolated clones, RcC/EBP-1 and -2, encoding Rana homologues of a mammalian transcription factor, C/EBP (CCAAT/enhancer core binding protein), implicated in the expression of liver-specific genes and terminal differentiation of hepatocytes. Gel mobility shift assays demonstrate that the proteins synthesized from these cDNAs bind specifically to the consensus binding site for C/EBP-related proteins. Characterization of the amino acid sequence in the bZIP DNA-binding domains of these proteins suggests that RcC/EBP-1 and -2 encode Rana homologues of C/EBP alpha and delta, respectively. Hybridization analyses demonstrate that the amount of RcC/EBP-2 mRNAs in tadpole liver remains constant throughout metamorphosis, whereas RcC/EBP-1 mRNAs are up-regulated during both spontaneous and TH-induced metamorphosis. The TH-induced up-regulation of RcC/EBP-1 mRNAs precedes the up-regulation of liver-specific urea cycle enzyme mRNAs by 6 to 12 hours. These results, coupled with in situ hybridization studies, suggest that RcC/EBP-1 mRNAs encode a transcription factor which may play an early role(s) in the terminal differentiation and/or reprogramming of gene expression in this tadpole's liver cells during both spontaneous and TH-induced metamorphosis.