Amplification of Glyceronephosphate O-Acyltransferase and Recruitment of USP30 Stabilize DRP1 to Promote Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide, and the underlying pathophysiology of HCC is highly complex. In this study, we report that, in a bioinformatic screen of 2,783 genes encoding metabolic enzymes, GNPAT, which encodes the enzyme glyceronephosphate O-acyltransferase, is amplified, upregulated, and highly correlated with poor clinical outcome in human patients with HCC. High GNPAT expression in HCC was due to its amplification and transcriptional activation by the c-Myc/KDM1A complex. GNPAT compensated the oncogenic phenotypes in c-Myc-depleted HCC cells. Mechanistically, GNPAT recruited the enzyme USP30, which deubiquitylated and stabilized dynamin-related protein 1 (DRP1), thereby facilitating regulation of mitochondrial morphology, lipid metabolism, and hepatocarcinogenesis. Inhibition of GNPAT and DRP1 dramatically attenuated lipid metabolism and hepatocarcinogenesis. Furthermore, DRP1 mediated the oncogenic phenotypes driven by GNPAT. Taken together, these results indicate that GNPAT and USP30-mediated stabilization of DRP1 play a critical role in the development of HCC.Significance: This study identifies and establishes the role of the enzyme GNPAT in liver cancer progression, which may serve as a potential therapeutic target for liver cancer. Cancer Res; 78(20); 5808-19. ©2018 AACR.

Role of DGAT enzymes in triacylglycerol metabolism

The esterification of a fatty acyl moiety to diacylglycerol to form triacylglycerol (TAG) is catalysed by two diacylglycerol O-acyltransferases (DGATs) encoded by genes belonging to two distinct gene families. The enzymes are referred to as DGAT1 and DGAT2 in order of their identification. Both proteins are transmembrane proteins localized in the endoplasmic reticulum. Their membrane topologies are however significantly different. This difference is hypothesized to give the two isozymes different abilities to interact with other proteins and organelles and access to different pools of fatty acids, thereby creating a distinction between the enzymes in terms of their role and contribution to lipid metabolism. DGAT1 is proposed to have dual topology contributing to TAG synthesis on both sides of the ER membrane and esterifying only the pre-formed fatty acids. There is evidence to suggest that DGAT2 translocates to the lipid droplet (LD), associates with other proteins, and synthesizes cytosolic and luminal apolipoprotein B associated LD-TAG from both endogenous and exogenous fatty acids. The aim of this review is to differentiate between the two DGAT enzymes by comparing the genes that encode them, their proposed topologies, the proteins they interact with, and their roles in lipid metabolism.

Bioactive Lipid Species and Metabolic Pathways in Progression and Resolution of Nonalcoholic Steatohepatitis

The prevalence of nonalcoholic steatohepatitis (NASH) is increasing worldwide, yet there are no effective treatments. A decade has passed since the initial lipidomics analyses of liver tissues from patients with nonalcoholic fatty liver disease. We have learned that liver cells from patients with NASH have an abnormal lipid composition and that the accumulation of lipids leads to organelle dysfunction, cell injury and death, and chronic inflammation, called lipotoxicity. We review the lipid species and metabolic pathways that contribute to the pathogenesis of NASH and potential therapeutic targets, including enzymes involved in fatty acid and triglyceride synthesis, bioactive sphingolipids and polyunsaturated-derived eicosanoids, and specialized pro-resolving lipid mediators. We discuss the concept that NASH is a disease that can resolve and the roles of lipid molecules in the resolution of inflammation and regression of fibrosis.

Lipid droplet and peroxisome biogenesis occur at the same ER subdomains

Nascent lipid droplet (LD) formation occurs in the endoplasmic reticulum (ER) membrane but it is not known how sites of biogenesis are determined. We previously identified ER domains in S. cerevisiae containing the reticulon homology domain (RHD) protein Pex30 that are regions where preperoxisomal vesicles (PPVs) form. Here, we show that Pex30 domains are also sites where most nascent LDs form. Mature LDs usually remain associated with Pex30 subdomains, and the same Pex30 subdomain can simultaneously associate with a LD and a PPV or peroxisome. We find that in higher eukaryotes multiple C2 domain containing transmembrane protein (MCTP2) is similar to Pex30: it contains an RHD and resides in ER domains where most nascent LD biogenesis occurs and that often associate with peroxisomes. Together, these findings indicate that most LDs and PPVs form and remain associated with conserved ER subdomains, and suggest a link between LD and peroxisome biogenesis.

Interplay of miRNAs and Canonical Wnt Signaling Pathway in Hepatocellular Carcinoma

Hepatocellular carcinoma is one of the leading causes of cancer death worldwide and the activation of canonical Wnt signaling pathway is universal in hepatocellular carcinoma patients. MicroRNAs are found to participate in the pathogenesis of hepatocellular carcinoma by activating or inhibiting components in the canonical Wnt signaling pathway. Meanwhile, transcriptional activation of microRNAs by canonical Wnt signaling pathway also contributes to the occurrence and progression of hepatocellular carcinoma. Pharmacological inhibition of hepatocellular carcinoma pathogenesis and other cancers by microRNAs are now in clinical trials despite the challenges of identifying efficient microRNAs candidates and safe delivery vehicles. The focus of this review is on the interplay mechanisms between microRNAs and canonical Wnt signaling pathway in hepatocellular carcinoma, and a deep understanding of the crosstalk will promote to develop a better management of this disease.

DGAT2 Inhibition Alters Aspects of Triglyceride Metabolism in Rodents but Not in Non-human Primates

Diacylglycerol acyltransferase 2 (DGAT2) catalyzes the final step in triglyceride (TG) synthesis and has been shown to play a role in regulating hepatic very-low-density lipoprotein (VLDL) production in rodents. To explore the potential of DGAT2 as a therapeutic target for the treatment of dyslipidemia, we tested the effects of small-molecule inhibitors and gene silencing both in vitro and in vivo. Consistent with prior reports, chronic inhibition of DGAT2 in a murine model of obesity led to correction of multiple lipid parameters. In contrast, experiments in primary human, rhesus, and cynomolgus hepatocytes demonstrated that selective inhibition of DGAT2 has only a modest effect. Acute and chronic inhibition of DGAT2 in rhesus primates recapitulated the in vitro data yielding no significant effects on production of plasma TG or VLDL apolipoprotein B. These results call into question whether selective inhibition of DGAT2 is sufficient for remediation of dyslipidemia.

Small but Heavy Role: MicroRNAs in Hepatocellular Carcinoma Progression

Hepatocellular carcinoma (HCC), which accounts for 85-90% of primary liver cancer, is the fifth most common malignant tumor and the third leading cause of cancer-related deaths worldwide, but the pathological mechanism of HCC is still not fully elucidated. miRNAs are evolutionarily endogenous small noncoding RNAs that negatively regulate gene expression via posttranscriptional inhibition or target mRNA degradation in several diseases, especially human cancer. Therefore, discovering the roles of miRNAs is appealing to scientific researchers. Emerging evidence has shown that the aberrant expressions of numerous miRNAs are involved in many HCC biological processes. In hepatocarcinogenesis, miRNAs with dysregulated expression can exert their function as oncogenes or tumor suppressors depending on their cellular target during the cell cycle, and in tumor development, differentiation, apoptosis, angiogenesis, metastasis, and progression of the tumor microenvironment. In this review, we summarize current findings on miRNAs and assess their functions to explore the molecular mechanisms of tumor progression in HCC.

The assembly of lipid droplets and their roles in challenged cells

Cytoplasmic lipid droplets are important organelles in nearly every eukaryotic and some prokaryotic cells. Storing and providing energy is their main function, but they do not work in isolation. They respond to stimuli initiated either on the cell surface or in the cytoplasm as conditions change. Cellular stresses such as starvation and invasion are internal insults that evoke changes in droplet metabolism and dynamics. This review will first outline lipid droplet assembly and then discuss how droplets respond to stress and in particular nutrient starvation. Finally, the role of droplets in viral and microbial invasion will be presented, where an unresolved issue is whether changes in droplet abundance promote the invader, defend the host, to try to do both. The challenges of stress and infection are often accompanied by changes in physical contacts between droplets and other organelles. How these changes may result in improving cellular physiology, an ongoing focus in the field, is discussed.

Converging cellular themes for the hereditary spastic paraplegias

Hereditary spastic paraplegias (HSPs) are neurologic disorders characterized by prominent lower-extremity spasticity, resulting from a length-dependent axonopathy of corticospinal upper motor neurons. They are among the most genetically-diverse neurologic disorders, with >80 distinct genetic loci and over 60 identified genes. Studies investigating the molecular pathogenesis underlying HSPs have emphasized the importance of converging cellular pathogenic themes in the most common forms of HSP, providing compelling targets for therapy. Most notably, these include organelle shaping and biogenesis as well as membrane and cargo trafficking.

miR-196b promotes lung cancer cell migration and invasion through the targeting of GATA6

MicroRNAs (miRNAs) have been proven to regulate gene expression at the protein translation level. miRNA abnormal expression has been associated with the development of lung cancer. In the present study, we aimed to investigate the mechanism of miR-196 in non-small cell lung cancer (NSCLC). The miR-196b and GATA-6 (GATA6) expression levels were examined in NSCLC by RT-qPCR and western blot analysis. Transwell assay was used to assess cell migration and invasion. Moreover, the specific target of miR-196b in NSCLC was verified by the luciferase reporter assay. The expression of miR-196b was higher in both NSCLC tissues and cells than the normal levels. Specifically, the miR-196b mimic group in NSCLC cells markedly promoted cell migration and invasion, while the miR-196b inhibitor group exhibited the opposite effect. Furthermore, GATA6 was verified as a specific target of miR-196b in NSCLC cells and GATA6 could attenuate the migratory and invasive ability of NSCLC cells regulated by miR-196b. In addition, the relationship between GATA6 and miR-196b expression was negatively correlated in NSCLC tissues. Thus, miR-196b enhanced NSCLC cell migration and invasion via the downregulation of GATA6, indicating its potential application in NSCLC diagnosis and therapy.

The deubiquitinase USP21 stabilizes MEK2 to promote tumor growth

Deubiquitinases (DUBs) play essential roles in normal cell proliferation and tumor growth. However, the molecular mechanisms of DUBs on hepatocellular carcinoma (HCC) remains largely unknown. In this study, based on analysis of several HCC datasets, we found that the USP21 gene, which encodes a member of the ubiquitin-specific protease family, is highly amplified and overexpressed in HCCs, with the extent of this up-regulation significantly correlating with poor clinical outcomes. Inhibition of USP21 in HCC cell lines decreased cell proliferation, anchorage-independent growth, cell cycle progression, and in vivo tumor growth. Conversely, ectopic expression of USP21 transformed the normal human hepatocyte line HL-7702 and increased the tumorigenicity of the HCC cell line MHCC97L. Mechanistically, USP21 stabilized MEK2 by decreasing its polyubiquitination at Lys48, thereby activating the ERK signaling pathway. Importantly, MEK2 partially mediated the optimal expression of USP21-mediated oncogenic phenotypes. These findings indicate that USP21-mediated deubiquitination and stabilization of MEK2 play a critical role in HCC development.

Stearate-to-palmitate ratio modulates endoplasmic reticulum stress and cell apoptosis in non-B non-C hepatoma cells

The increased prevalence of hepatocellular carcinoma (HCC) without viral infection, namely, NHCC, is a major public health issue worldwide. NHCC is frequently derived from non‐alcoholic fatty liver (NAFL) and non‐alcoholic steatohepatitis, which exhibit dysregulated fatty acid (FA) metabolism. This raises the possibility that NHCC evolves intracellular machineries to adapt to dysregulated FA metabolism. We herein aim to identify NHCC‐specifically altered FA and key molecules to achieve the adaptation. To analyze FA, imaging mass spectrometry (IMS) was performed on 15 HCC specimens. The composition of saturated FA (SFA) in NHCC was altered from that in typical HCC. The stearate‐to‐palmitate ratio (SPR) was significantly increased in NHCC. Associated with the SPR increase, the ELOVL6 protein level was upregulated in NHCC. The knockdown of ELOVL6 reduced SPR, and enhanced endoplasmic reticulum stress, inducing apoptosis of Huh7 and HepG2 cells. In conclusion, NHCC appears to adapt to an FA‐rich environment by modulating SPR through ELOVL6.

The large GTPase atlastin controls ER remodeling around a pathogen vacuole

The ubiquitous environmental bacterium Legionella pneumophila is the causative agent of Legionnaires' pneumonia and replicates in free-living protozoa and mammalian macrophages in a specific compartment, the Legionella-containing vacuole (LCV). LCVs communicate with the endosomal, retrograde and secretory vesicle trafficking pathway, and eventually tightly interact with the endoplasmic reticulum (ER). In Dictyostelium discoideum amoebae and macrophages, the ER tubule-resident large GTPase Sey1/atlastin3 (Atl3) accumulates on LCVs and promotes LCV expansion and intracellular replication of L. pneumophila. Fluorescence microscopy of D. discoideum infected with L. pneumophila indicated that Sey1 is involved in extensive ER remodeling around LCVs. An ultrastructural analysis confirmed these findings. Moreover, dominant negative Sey1_K154A compromises ER accumulation on LCVs and causes an aberrant ER morphology in uninfected D. discoideum as well as in amoebae infected with avirulent L. pneumophila that lack a functional type IV secretion system. Thus, the large, dynamin-like GTPase Sey1/Atl3 controls circumferential ER remodeling during LCV maturation.

Integration analysis of microRNA and mRNA paired expression profiling identifies deregulated microRNA-transcription factor-gene regulatory networks in ovarian endometriosis

BACKGROUND

The etiology and pathophysiology of endometriosis remain unclear. Accumulating evidence suggests that aberrant microRNA (miRNA) and transcription factor (TF) expression may be involved in the pathogenesis and development of endometriosis. This study therefore aims to survey the key miRNAs, TFs and genes and further understand the mechanism of endometriosis.

METHODS

Paired expression profiling of miRNA and mRNA in ectopic endometria compared with eutopic endometria were determined by high-throughput sequencing techniques in eight patients with ovarian endometriosis. Binary interactions and circuits among the miRNAs, TFs, and corresponding genes were identified by the Pearson correlation coefficients. miRNA-TF-gene regulatory networks were constructed using bioinformatic methods. Eleven selected miRNAs and TFs were validated by quantitative reverse transcription-polymerase chain reaction in 22 patients.

RESULTS

Overall, 107 differentially expressed miRNAs and 6112 differentially expressed mRNAs were identified by comparing the sequencing of the ectopic endometrium group and the eutopic endometrium group. The miRNA-TF-gene regulatory network consists of 22 miRNAs, 12 TFs and 430 corresponding genes. Specifically, some key regulators from the miR-449 and miR-34b/c cluster, miR-200 family, miR-106a-363 cluster, miR-182/183, FOX family, GATA family, and E2F family as well as CEBPA, SOX9 and HNF4A were suggested to play vital regulatory roles in the pathogenesis of endometriosis.

CONCLUSION

Integration analysis of the miRNA and mRNA expression profiles presents a unique insight into the regulatory network of this enigmatic disorder and possibly provides clues regarding replacement therapy for endometriosis.

Hereditary spastic paraplegia

The hereditary spastic paraplegias (HSPs) are a heterogeneous group of neurologic disorders with the common feature of prominent lower-extremity spasticity, resulting from a length-dependent axonopathy of corticospinal upper motor neurons. The HSPs exist not only in "pure" forms but also in "complex" forms that are associated with additional neurologic and extraneurologic features. The HSPs are among the most genetically diverse neurologic disorders, with well over 70 distinct genetic loci, for which about 60 mutated genes have already been identified. Numerous studies elucidating the molecular pathogenesis underlying HSPs have highlighted the importance of basic cellular functions - especially membrane trafficking, mitochondrial function, organelle shaping and biogenesis, axon transport, and lipid/cholesterol metabolism - in axon development and maintenance. An encouragingly small number of converging cellular pathogenic themes have been identified for the most common HSPs, and some of these pathways present compelling targets for future therapies.

microRNA-206 impairs c-Myc-driven cancer in a synthetic lethal manner by directly inhibiting MAP3K13

c-Myc (Myc) is one of the most frequently dysregulated oncogenic transcription factors in human cancer. By functionally screening a microRNA (miR) library, we identified miR-206 as being a synthetic lethal in Myc over-expressing human cancer cells. miR-206 inhibited MAP3K13, which resulted in Myc protein de-stabilization, and an inhibition of anchorage-independent growth and in vivo tumorigenesis by Myc over-expressing human cancer cells. Eliminating MAP3K13 by shRNA recapitulated the effects caused by miR-206, thus supporting the idea that miR-206's effect on Myc was mediated through MAP3K13. Conversely, enforced expression of MAP3K13 stabilized Myc by promoting its N-terminal phosphorylation and enhancing its transcriptional activity. Gene expression analyses of breast cancers expressing high levels of Myc indicated that low miR-206 expression and high MAP3K13 expression correlated with poor patient survival. The critical link between miR-206 and MAP3K13 in the development of Myc over-expressing human cancers suggests potential points of therapeutic intervention for this molecular sub-category.

Pharmacological inhibition of diacylglycerol acyltransferase-1 and insights into postprandial gut peptide secretion

AIM

To examine the role that enzyme Acyl-CoA:diacylglycerol acyltransferase-1 (DGAT1) plays in postprandial gut peptide secretion and signaling.

METHODS

The standard experimental paradigm utilized to evaluate the incretin response was a lipid challenge. Following a lipid challenge, plasma was collected via cardiac puncture at each time point from a cohort of 5-8 mice per group from baseline at time zero to 10 h. Incretin hormones [glucagon like peptide-1 (GLP-1), peptide tyrosine-tyrosine (PYY) and glucose dependent insulinotropic polypeptide (GIP)] were then quantitated. The impact of pharmacological inhibition of DGAT1 on the incretin effect was evaluated in WT mice. Additionally, a comparison of loss of DGAT1 function either by genetic ablation or pharmacological inhibition. To further elucidate the pathways and mechanisms involved in the incretin response to DGAT1 inhibition, other interventions [inhibitors of dipeptidyl peptidase-IV (sitagliptin), pancreatic lipase (Orlistat), GPR119 knockout mice] were evaluated.

RESULTS

DGAT1 deficient mice and wildtype C57/BL6J mice were lipid challenged and levels of both active and total GLP-1 in the plasma were increased. This response was further augmented with DGAT1 inhibitor PF-04620110 treated wildtype mice. Furthermore, PF-04620110 was able to dose responsively increase GLP-1 and PYY, but blunt GIP at all doses of PF-04620110 during lipid challenge. Combination treatment of PF-04620110 and Sitagliptin in wildtype mice during a lipid challenge synergistically enhanced postprandial levels of active GLP-1. In contrast, in a combination study with Orlistat, the ability of PF-04620110 to elicit an enhanced incretin response was abrogated. To further explore this observation, GPR119 knockout mice were evaluated. In response to a lipid challenge, GPR119 knockout mice exhibited no increase in active or total GLP-1 and PYY. However, PF-04620110 was able to increase total GLP-1 and PYY in GPR119 knockout mice as compared to vehicle treated wildtype mice.

CONCLUSION

Collectively, these data provide some insight into the mechanism by which inhibition of DGAT1 enhances intestinal hormone release.

miR-363-3p inhibits tumor growth by targeting PCNA in lung adenocarcinoma

Increasing evidence suggests that microRNAs play key roles in lung cancer. Our previous study demonstrated that microRNA 363-3p (miR-363-3p) is downregulated in lung cancer tissues. In this study, we demonstrated that overexpression of miR-363-3p inhibits the proliferation and colony formation of A549 and H441 cells, while silencing of miR-363-3p has the converse effects. The anti-oncogenic function of miR-363-3p was verified in a mouse tumor xenograft model. Furthermore, cell cycle analysis showed miR-363-3p can induce S phase arrest by downregulating Cyclin-D1 and upregulating Cyclin-dependent kinase-2 in lung adenocarcinoma cells. Additionally, miR-363-3p enhances cell apoptosis, whereas miR-363-3p inhibitor prevents apoptosis and leads to downregulation of Bax and Bak expression. The anti-proliferative function of miR-363-3p toward lung cancer cells may be explained by its ability to inhibit the activation of the mTOR and ERK signaling pathways. Using target prediction software and luciferase reporter assays, we identified PCNA as a specific target of miR-363-3p. miR-363-3p can decreased the accumulation of endogenous PCNA in lung adenocarcinoma cells. Moreover, exogenous expression of PCNA relieve the inhibition of miR-363-3p on cell proliferation, colony formation and mTOR and ERK signaling pathways. Taken together, our data indicate that miR-363-3p suppresses tumor growth by targeting PCNA in lung adenocarcinoma.

Identification of active miRNA promoters from nuclear run-on RNA sequencing

The genome-wide identification of microRNA transcription start sites (miRNA TSSs) is essential for understanding how miRNAs are regulated in development and disease. In this study, we developed mirSTP (mirna transcription Start sites Tracking Program), a probabilistic model for identifying active miRNA TSSs from nascent transcriptomes generated by global run-on sequencing (GRO-seq) and precision run-on sequencing (PRO-seq). MirSTP takes advantage of characteristic bidirectional transcription signatures at active TSSs in GRO/PRO-seq data, and provides accurate TSS prediction for human intergenic miRNAs at a high resolution. MirSTP performed better than existing generalized and experiment specific methods, in terms of the enrichment of various promoter-associated marks. MirSTP analysis of 27 human cell lines in 183 GRO-seq and 28 PRO-seq experiments identified TSSs for 480 intergenic miRNAs, indicating a wide usage of alternative TSSs. By integrating predicted miRNA TSSs with matched ENCODE transcription factor (TF) ChIP-seq data, we connected miRNAs into the transcriptional circuitry, which provides a valuable source for understanding the complex interplay between TF and miRNA. With mirSTP, we not only predicted TSSs for 72 miRNAs, but also identified 12 primary miRNAs with significant RNA polymerase pausing alterations after JQ1 treatment; each miRNA was further validated through BRD4 binding to its predicted promoter. MirSTP is available at http://bioinfo.vanderbilt.edu/mirSTP/.

Lipid and Carbohydrate Metabolism in Caenorhabditis elegans

Lipid and carbohydrate metabolism are highly conserved processes that affect nearly all aspects of organismal biology. Caenorhabditis elegans eat bacteria, which consist of lipids, carbohydrates, and proteins that are broken down during digestion into fatty acids, simple sugars, and amino acid precursors. With these nutrients, C. elegans synthesizes a wide range of metabolites that are required for development and behavior. In this review, we outline lipid and carbohydrate structures as well as biosynthesis and breakdown pathways that have been characterized in C. elegans We bring attention to functional studies using mutant strains that reveal physiological roles for specific lipids and carbohydrates during development, aging, and adaptation to changing environmental conditions.

A unifying mathematical model of lipid droplet metabolism reveals key molecular players in the development of hepatic steatosis

The liver responds to elevated plasma concentrations of free fatty acids (FFAs) with an enhanced uptake of FFAs and their esterification to triacylglycerol (TAG). On the long term, this may result in massive hepatic TAG accumulation called steatosis hepatitis. In hepatocytes, the poor water-soluble TAG is packed in specialized organelles: Lipid droplets (LDs) serving as transient cellular deposit and lipoproteins (LPs) transporting TAG and cholesterol esters to extra-hepatic tissues. The dynamics of these organelles is controlled by a variety of regulatory surface proteins (RSPs). Assembly and export of VLDLs are mainly regulated by the microsomal transfer protein (MTP) and apoprotein B100. Formation and lipolysis of LDs are regulated by several RSPs. The best studied regulators belong to the PAT (Perilipin/Adipophilin/TIP47) and CIDE families. Knockdown or overexpression of SRPs may significantly affect the total number and size distribution of LDs. Intriguingly, a large cell-to-cell heterogeneity with respect to the number and size of LDs has been found in various cell types including hepatocytes. These findings suggest that the extent of cellular lipid accumulation is determined not only by the imbalance between lipid supply and utilization but also by variations in the expression of RSPs and metabolic enzymes. To better understand the relative regulatory impact of individual processes involved in the cellular TAG turnover, we developed a comprehensive kinetic model encompassing the pathways of the fatty acid and triglyceride metabolism and the main molecular processes governing the dynamics of LDs. The model was parametrized such that a large number of experimental in vitro and in vivo findings are correctly recapitulated. A control analysis of the model revealed that variations in the activity of FFA uptake, diacylglycerol acyltransferase (DGAT) 2, and adipose triglyceride lipase (ATGL) have the strongest influence on the cellular TAG level. We used the model to simulate LD size distributions in human hepatoma cells and hepatocytes exposed to a challenge with FFAs. A random fold change by a factor of about two in the activity of RSPs was sufficient to reproduce the large diversity of droplet size distributions observed in individual cells. Under the premise that the same extent of variability of RSPs holds for the intact organ, our model predicts variations in the TAG content of individual hepatocytes by a factor of about 3-6 depending on the nutritional regime. Taken together, our modeling approach integrates numerous experimental findings on individual processes in the cellular TAG metabolism and LD dynamics metabolism to a consistent state-of-the-art dynamic network model that can be used to study how changes in the external conditions or systemic parameters will affect the TAG content of hepatocytes.

Lipid Droplet Biogenesis

Lipid droplets (LDs) are ubiquitous organelles that store neutral lipids for energy or membrane synthesis and act as hubs for metabolic processes. Cells generate LDs de novo, converting cells to emulsions with LDs constituting the dispersed oil phase in the aqueous cytoplasm. Here we review our current view of LD biogenesis. We present a model of LD formation from the ER in distinct steps and highlight the biology of proteins that govern this biophysical process. Areas of incomplete knowledge are identified, as are connections with physiology and diseases linked to alterations in LD biology.

Specific regulation of thermosensitive lipid droplet fusion by a nuclear hormone receptor pathway

Nuclear receptors play important roles in regulating fat metabolism and energy production in humans. The regulatory functions and endogenous ligands of many nuclear receptors are still unidentified, however. Here, we report that CYP-37A1 (ortholog of human cytochrome P450 CYP4V2), EMB-8 (ortholog of human P450 oxidoreductase POR), and DAF-12 (homolog of human nuclear receptors VDR/LXR) constitute a hormone synthesis and nuclear receptor pathway in Caenorhabditis elegans This pathway specifically regulates the thermosensitive fusion of fat-storing lipid droplets. CYP-37A1, together with EMB-8, synthesizes a lipophilic hormone not identical to Δ7-dafachronic acid, which represses the fusion-promoting function of DAF-12. CYP-37A1 also negatively regulates thermotolerance and lifespan at high temperature in a DAF-12-dependent manner. Human CYP4V2 can substitute for CYP-37A1 in C. elegans This finding suggests the existence of a conserved CYP4V2-POR-nuclear receptor pathway that functions in converting multilocular lipid droplets to unilocular ones in human cells; misregulation of this pathway may lead to pathogenic fat storage.

Reep1 null mice reveal a converging role for hereditary spastic paraplegia proteins in lipid droplet regulation

Hereditary spastic paraplegias (HSPs; SPG1-76 plus others) are length-dependent disorders affecting long corticospinal axons, and the most common autosomal dominant forms are caused by mutations in genes that encode the spastin (SPG4), atlastin-1 (SPG3A) and REEP1 (SPG31) proteins. These proteins bind one another and shape the tubular endoplasmic reticulum (ER) network throughout cells. They also are involved in lipid droplet formation, enlargement, or both in cells, though mechanisms remain unclear. Here we have identified evidence of partial lipoatrophy in Reep1 null mice in addition to prominent spastic paraparesis. Furthermore, Reep1-/- embryonic fibroblasts and neurons in the cerebral cortex both show lipid droplet abnormalities. The apparent partial lipodystrophy in Reep1 null mice, although less severe, is reminiscent of the lipoatrophy phenotype observed in the most common form of autosomal recessive lipodystrophy, Berardinelli-Seip congenital lipodystrophy. Berardinelli-Seip lipodystrophy is caused by autosomal recessive mutations in the BSCL2 gene that encodes an ER protein, seipin, that is also mutated in the autosomal dominant HSP SPG17 (Silver syndrome). Furthermore, REEP1 co-immunoprecipitates with seipin in cells. This strengthens the link between alterations in ER morphogenesis and lipid abnormalities, with important pathogenic implications for the most common forms of HSP.

MicroRNA-148a deficiency promotes hepatic lipid metabolism and hepatocarcinogenesis in mice

miRNAs are involved in many physiologic and disease processes by virtue of degrading specific mRNAs or inhibiting their translation. miR-148a has been implicated in the control of tumor growth and cholesterol and triglyceride homeostasis using in vitro or in vivo gene expression- and silencing-based approaches. Here miR-148a knockout (KO) mice were used to investigate the intrinsic role of miR-148a in liver physiology and hepatocarcinogenesis in mice. miR-148a downregulation was found to be correlated with poor clinical outcomes in hepatocellular carcinoma (HCC) patients. Under regular chow diet (RCD) or high fat diet (HFD), miR-148a deletion significantly accelerated DEN-induced hepatocarcinogenesis in mice. Mechanistically, miR-148a deletion promotes lipid metabolic disorders in mice. Moreover, restoration of miR-148a reversed these defects. Finally, miR-148a was found to directly inhibit several key regulators of hepatocarcinogenesis and lipid metabolism. These findings reveal crucial roles for miR-148a in the hepatic lipid metabolism and hepatocarcinogenesis. They further identify miR-148a as a potential therapeutic target for certain liver diseases, including cancer.

MiR-107 inhibits proliferation of lung cancer cells through regulating TP53 regulated inhibitor of apoptosis 1 (TRIAP1)

Aims

Accumulating evidence indicates that aberrant expression of miR-107 plays a crucial role in cancers. This study aims to display the function of miR-107 and its novel target genes in the progression of lung cancer.

Methods and Material

MiR-107 or miR-107 inhibitor was transfected into lung cancer cells A549. The levels of miR-107 and TP53 regulated inhibition of apoptosis 1 (TRIAP1) were examined by quantitative real-time Polymerase Chain Reaction (qRT-PCR) analysis and Western Blot. Functionally, MTT and colony formation assays were carried out to test the effect of miR-107 inhibitor and/or small interference RNA (siRNA) targeting TRIAP1 mRNA on proliferation of lung cancer cells. Levels of miR-107 or TRIAP1 were detected in clinical lung cancer samples by using qRT-PCR analysis.

Results

QRT-PCR analysis revealed that miR-107 inhibitor or miR-107 was successfully transfected into A549 cells. Western Blot indicated that miR-107 decreased the expression of TRIAP1 protein in the cells. In contrast, miR-107 inhibitor augmented the levels of TRIAP1 protein. Functionally, miR-107 inhibitor remarkably suppressed A549 cell proliferation, whereas, TRIAP1 siRNAs could abrogate the miR-107 inhibitor-induced proliferation of cells. Then, we validated that TRIAP1 was increased in clinical lung cancer samples. MiR-107 expression was negatively related to TRIAP1 expression in clinical lung cancer samples.

Conclusions

MiR-107 suppresses cell proliferation by targeting TRIAP1 in lung cancer. Our finding allows new insights into the mechanisms of lung cancer that is mediated by miR-107.

Mitochondrial morphology and cellular distribution are altered in SPG31 patients and are linked to DRP1 hyperphosphorylation

Hereditary spastic paraplegia, SPG31, is a rare neurological disorder caused by mutations in REEP1 gene encoding the microtubule-interacting protein, REEP1. The mechanism by which REEP1-dependent processes are linked with the disease is unclear. REEP1 regulates the morphology and trafficking of various organelles via interaction with the microtubules. In this study, we collected primary fibroblasts from SPG31 patients to investigate their mitochondrial morphology. We observed that the mitochondrial morphology in patient cells was highly tubular compared with control cells. We provide evidence that these morphological alterations are caused by the inhibition of mitochondrial fission protein, DRP1, due to the hyperphosphorylation of its serine 637 residue. This hyperphosphorylation is caused by impaired interactions between REEP1 and mitochondrial phosphatase PGAM5. Genetically or pharmacologically induced decrease of DRP1-S637 phosphorylation restores mitochondrial morphology in patient cells. Furthermore, ectopic expression of REEP1 carrying pathological mutations in primary neuronal culture targets REEP1 to the mitochondria. Mutated REEP1 proteins sequester mitochondria to the perinuclear region of the neurons and therefore, hamper mitochondrial transport along the axon. Considering the established role of mitochondrial distribution and morphology in neuronal health, our results support the involvement of a mitochondrial dysfunction in SPG31 pathology.

ER Membrane Phospholipids and Surface Tension Control Cellular Lipid Droplet Formation

Cells convert excess energy into neutral lipids that are made in the endoplasmic reticulum (ER) bilayer. The lipids are then packaged into spherical or budded lipid droplets (LDs) covered by a phospholipid monolayer containing proteins. LDs play a key role in cellular energy metabolism and homeostasis. A key unanswered question in the life of LDs is how they bud off from the ER. Here, we tackle this question by studying the budding of artificial LDs from model membranes. We find that the bilayer phospholipid composition and surface tension are key parameters of LD budding. Phospholipids have differential LD budding aptitudes, and those inducing budding decrease the bilayer tension. We observe that decreasing tension favors the egress of neutral lipids from the bilayer and LD budding. In cells, budding conditions favor the formation of small LDs. Our discovery reveals the importance of altering ER physical chemistry for controlled cellular LD formation.

Dgat1 and Dgat2 regulate enterocyte triacylglycerol distribution and alter proteins associated with cytoplasmic lipid droplets in response to dietary fat

Enterocytes, the absorptive cells of the small intestine, mediate efficient absorption of dietary fat (triacylglycerol, TAG). The digestive products of dietary fat are taken up by enterocytes, re-esterified into TAG, and packaged on chylomicrons (CMs) for secretion into blood or temporarily stored within cytoplasmic lipid droplets (CLDs). Altered enterocyte TAG distribution impacts susceptibility to high fat diet associated diseases, but molecular mechanisms directing TAG toward these fates are unclear. Two enzymes, acyl CoA: diacylglycerol acyltransferase 1 (Dgat1) and Dgat2, catalyze the final, committed step of TAG synthesis within enterocytes. Mice with intestine-specific overexpression of Dgat1 (Dgat1Int) or Dgat2 (Dgat2Int), or lack of Dgat1 (Dgat1-/-), were previously found to have altered intestinal TAG secretion and storage. We hypothesized that varying intestinal Dgat1 and Dgat2 levels alters TAG distribution in subcellular pools for CM synthesis as well as the morphology and proteome of CLDs. To test this we used ultrastructural and proteomic methods to investigate intracellular TAG distribution and CLD-associated proteins in enterocytes from Dgat1Int, Dgat2Int, and Dgat1-/- mice 2h after a 200μl oral olive oil gavage. We found that varying levels of intestinal Dgat1 and Dgat2 altered TAG pools involved in CM assembly and secretion, the number or size of CLDs present in enterocytes, and the enterocyte CLD proteome. Overall, these results support a model where Dgat1 and Dgat2 function coordinately to regulate the process of dietary fat absorption by preferentially synthesizing TAG for incorporation into distinct subcellular TAG pools in enterocytes.

MicroRNA-30a attenuates mutant KRAS-driven colorectal tumorigenesis via direct suppression of ME1

Frequent KRAS mutations contribute to multiple cancers including ~40% of human colorectal cancers (CRCs). Systematic screening of 1255 microRNAs (miRNAs) identified miR-30a as a synthetic lethal in KRAS-mutant CRC cells. miR-30a was downregulated in CRCs and repressed by P65. miR-30a directly targeted malic enzyme 1 (ME1) and KRAS, and inhibited anchorage-independent growth and in vivo tumorigenesis by KRAS-mutant CRC cells. ME1 was significantly upregulated in KRAS-mutant CRCs. Eliminating ME1 by short hairpin RNA (shRNA) resulted in obviously decreased NADPH production, levels of triglyceride and fatty acid, and an inhibition of tumorigenicity of KRAS-mutant CRCs. miR-30a overexpression and ME1 suppression attenuated AOM/DSS-induced colorectal tumorigenesis. The critical roles of miR-30a and ME1 in the development of KRAS-mutant CRCs indicate therapy potentials for this subtype of cancer.

Atlastin regulates store-operated calcium entry for nerve growth factor-induced neurite outgrowth

Homotypic membrane fusion of the endoplasmic reticulum (ER) is mediated by a class of dynamin-like GTPases known as atlastin (ATL). Depletion of or mutations in ATL cause an unbranched ER morphology and hereditary spastic paraplegia (HSP), a neurodegenerative disease characterized by axon shortening in corticospinal motor neurons and progressive spasticity of the lower limbs. How ER shaping is linked to neuronal defects is poorly understood. Here, we show that dominant-negative mutants of ATL1 in PC-12 cells inhibit nerve growth factor (NGF)-induced neurite outgrowth. Overexpression of wild-type or mutant ATL1 or depletion of ATLs alters ER morphology and affects store-operated calcium entry (SOCE) by decreasing STIM1 puncta formation near the plasma membrane upon calcium depletion of the ER. In addition, blockage of the STIM1-Orai pathway effectively abolishes neurite outgrowth of PC-12 cells stimulated by NGF. These results suggest that SOCE plays an important role in neuronal regeneration, and mutations in ATL1 may cause HSP, partly by undermining SOCE.

Loss of spatacsin function alters lysosomal lipid clearance leading to upper and lower motor neuron degeneration

Mutations in SPG11 account for the most common form of autosomal recessive hereditary spastic paraplegia (HSP), characterized by a gait disorder associated with various brain alterations. Mutations in the same gene are also responsible for rare forms of Charcot-Marie-Tooth (CMT) disease and progressive juvenile-onset amyotrophic lateral sclerosis (ALS). To elucidate the physiopathological mechanisms underlying these human pathologies, we disrupted the Spg11 gene in mice by inserting stop codons in exon 32, mimicking the most frequent mutations found in patients. The Spg11 knockout mouse developed early-onset motor impairment and cognitive deficits. These behavioral deficits were associated with progressive brain atrophy with the loss of neurons in the primary motor cortex, cerebellum and hippocampus, as well as with accumulation of dystrophic axons in the corticospinal tract. Spinal motor neurons also degenerated and this was accompanied by fragmentation of neuromuscular junctions and muscle atrophy. This new Spg11 knockout mouse therefore recapitulates the full range of symptoms associated with SPG11 mutations observed in HSP, ALS and CMT patients. Examination of the cellular alterations observed in this model suggests that the loss of spatacsin leads to the accumulation of lipids in lysosomes by perturbing their clearance from these organelles. Altogether, our results link lysosomal dysfunction and lipid metabolism to neurodegeneration and pinpoint a critical role of spatacsin in lipid turnover.

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Spg11 knockout mouse recapitulates the motor and cognitive symptoms observed in patients.

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Spg11 knockout mouse presents neurodegeneration in cortex, cerebellum, hippocampus and spinal cord.

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Loss of spatacsin, the product of Spg11, leads to early lysosomal dysfunction.

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Loss of spatacsin promotes lipid accumulation in lysosomes.

Diacylglycerol acyltransferase 2 links glucose utilization to fatty acid oxidation in the brown adipocytes

Brown adipose tissue uptake of glucose and fatty acids is very high during nonshivering thermogenesis. Adrenergic stimulation markedly increases glucose uptake, de novo lipogenesis, and FA oxidation simultaneously. The mechanism that enables this concerted response has hitherto been unknown. Here, we find that in primary brown adipocytes and brown adipocyte-derived cell line (IMBAT-1), acute inhibition and longer-term knockdown of DGAT2 links the increased de novo synthesis of fatty acids from glucose to a pool of TAG that is simultaneously hydrolyzed, providing FA for mitochondrial oxidation. DGAT1 does not contribute to this pathway, but uses exogenous FA and glycerol to synthesize a functionally distinct pool of TAG to which DGAT2 also contributes. The DGAT2-dependent channelling of 14C from glucose into TAG and CO2 was reproduced in β3-agonist-stimulated primary brown adipocytes. Knockdown of DGAT2 in IMBAT-1 affected the mRNA levels of UCP1 and genes important in FA activation and esterification. Therefore, in β3-agonist activated brown adipocytes, DGAT2 specifically enables channelling of de novo synthesized FA into a rapidly mobilized pool of TAG, which is simultaneously hydrolyzed to provide substrates for mitochondrial fatty acid oxidation.

Identification of microRNA profile specific to cancer stem-like cells directly isolated from human larynx cancer specimens

Background

Emerging evidences proposed that microRNAs are associated with regulation of distinct physio-pathological processes including development of normal stem cells and carcinogenesis. In this study we aimed to investigate microRNA profile of cancer stem-like cells (CSLCs) isolated form freshly resected larynx cancer (LCa) tissue samples.

Methods

CD133 positive (CD133⁺) stem-like cells were isolated from freshly resected LCa tumor specimens. MicroRNA profile of 12 pair of CD133⁺ and CD133⁻ cells was determined using microRNA microarray and differential expressions of selvected microRNAs were validated by quantitative real time PCR (qRT-PCR).

Results

MicroRNA profiling of CD133⁺ and CD133⁻ LCa samples with microarray revealed that miR-26b, miR-203, miR-200c, and miR-363-3p were significantly downregulated and miR-1825 was upregulated in CD133⁺ larynx CSLCs. qRT-PCR analysis in a total of 25 CD133⁺/CD133⁻ sample pairs confirmed the altered expressions of these five microRNAs. Expressions of miR-26b, miR-200c, and miR-203 were significantly correlated with miR-363-3p, miR-203, and miR-363-3p expressions, respectively. Furthermore, in silico analysis revealed that these microRNAs target both cancer and stem-cell associated signaling pathways.

Conclusions

Our results showed that certain microRNAs in CD133⁺ cells could be used as cancer stem cell markers. Based on these results, we propose that this panel of microRNAs might carry crucial roles in LCa pathogenesis through regulating stem cell properties of tumor cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2863-3) contains supplementary material, which is available to authorized users.

Modeling Axonal Defects in Hereditary Spastic Paraplegia with Human Pluripotent Stem Cells

BACKGROUND

Cortical motor neurons, also known as upper motor neurons, are large projection neurons whose axons convey signals to lower motor neurons to control the muscle movements. Degeneration of cortical motor neuron axons is implicated in several debilitating disorders, including hereditary spastic paraplegia (HSP) and amyotrophic lateral sclerosis (ALS). Since the discovery of the first HSP gene, SPAST that encodes spastin, over 70 distinct genetic loci associated with HSP have been identified. How the mutations of these functionally diverse genes result in axonal degeneration and why certain axons are affected in HSP remains largely unknown. The development of induced pluripotent stem cell (iPSC) technology has provided researchers an excellent resource to generate patient-specific human neurons to model human neuropathologic processes including axonal defects.

METHODS

In this article, we will frst review the pathology and pathways affected in the common forms of HSP subtypes by searching the PubMed database. We will then summurize the findings and insights gained from studies using iPSC-based models, and discuss the challenges and future directions.

RESULTS

HSPs, a heterogeneous group of genetic neurodegenerative disorders, are characterized by lower extremity weakness and spasticity that result from retrograde axonal degeneration of cortical motor neurons. Recently, iPSCs have been generated from several common forms of HSP including SPG4, SPG3A, and SPG11 patients. Neurons derived from HSP iPSCs exhibit disease-relevant axonal defects, such as impaired neurite outgrowth, increased axonal swellings, and reduced axonal transport.

CONCLUSION

These patient-derived neurons offer unique tools to study the pathogenic mechanisms and explore the treatments for rescuing axonal defects in HSP, as well as other diseases involving axonopathy.

C30F12.4 influences oogenesis, fat metabolism, and lifespan in C. elegans

Reproduction, fat metabolism, and longevity are intertwined regulatory axes; recent studies in C. elegans have provided evidence that these processes are directly coupled. However, the mechanisms by which they are coupled and the reproductive signals modulating fat metabolism and lifespan are poorly understood. Here, we find that an oogenesis-enriched gene, c30f12.4, is specifically expressed and located in germ cells and early embryos; when the gene is knocked out, oogenesis is disrupted and brood size is decreased. In addition to the reproductive phenotype, we find that the loss of c30f12.4 alters fat metabolism, resulting in decreased fat storage and smaller lipid droplets. Meanwhile, c30f12.4 mutant worms display a shortened lifespan. Our results highlight an important role for c30f12.4 in regulating reproduction, fat homeostasis, and aging in C. elegans, which helps us to better understand the relationship between these processes.

Spastin, atlastin, and ER relocalization are involved in axon but not dendrite regeneration

A Drosophila model system is used to show that the hereditary spastic paraplegia proteins spastin and atlastin help axons but not dendrites regenerate. The endoplasmic reticulum concentrates at tips of regenerating axons but not dendrites, and this depends on spastin and atlastin.

Mutations in >50 genes, including spastin and atlastin, lead to hereditary spastic paraplegia (HSP). We previously demonstrated that reduction of spastin leads to a deficit in axon regeneration in a Drosophila model. Axon regeneration was similarly impaired in neurons when HSP proteins atlastin, seipin, and spichthyin were reduced. Impaired regeneration was dependent on genetic background and was observed when partial reduction of HSP proteins was combined with expression of dominant-negative microtubule regulators, suggesting that HSP proteins work with microtubules to promote regeneration. Microtubule rearrangements triggered by axon injury were, however, normal in all genotypes. We examined other markers to identify additional changes associated with regeneration. Whereas mitochondria, endosomes, and ribosomes did not exhibit dramatic repatterning during regeneration, the endoplasmic reticulum (ER) was frequently concentrated near the tip of the growing axon. In atlastin RNAi and spastin mutant animals, ER accumulation near single growing axon tips was impaired. ER tip concentration was observed only during axon regeneration and not during dendrite regeneration. In addition, dendrite regeneration was unaffected by reduction of spastin or atlastin. We propose that the HSP proteins spastin and atlastin promote axon regeneration by coordinating concentration of the ER and microtubules at the growing axon tip.

A Genetic Screen for Mutants with Supersized Lipid Droplets in Caenorhabditis elegans

To identify genes that regulate the dynamics of lipid droplet (LD) size, we have used the genetically tractable model organism Caenorhabditis elegans, whose wild-type LD population displays a steady state of size with an upper limit of 3 μm in diameter. From a saturated forward genetic screen of 6.7 × 10⁵ mutagenized haploid genomes, we isolated 118 mutants with supersized intestinal LDs often reaching 10 μm. These mutants define nine novel complementation groups, in addition to four known genes (maoc-1, dhs-28, daf-22, and prx-10). The nine groups are named drop (lipid droplet abnormal) and categorized into four classes. Class I mutants drop-5 and drop-9, similar to prx-10, are up-regulated in ACS-22-DGAT-2-dependent LD growth, resistant to LD hydrolysis, and defective in peroxisome import. Class II mutants drop-2, drop-3, drop-6, and drop-7 are up-regulated in LD growth, are resistant to LD hydrolysis, but are not defective in peroxisome import. Class III mutants drop-1 and drop-8 are neither up-regulated in LD growth nor resistant to LD hydrolysis, but seemingly up-regulated in LD fusion. Class IV mutant drop-4 is cloned as sams-1 and, different to the other three classes, is ACS-22-independent and hydrolysis-resistant. These four classes of supersized LD mutants should be valuable for mechanistic studies of LD cellular processes including growth, hydrolysis, and fusion.

Investigating Connections between Metabolism, Longevity, and Behavior in Caenorhabditis elegans

An overview of Caenorhabditis elegans as an experimental organism for studying energy balance is presented. Some of the unresolved questions that complicate the interpretation of lipid measurements from C. elegans are highlighted. We review studies that show that both lipid synthesis and lipid breakdown pathways are activated and needed for the longevity of hermaphrodites that lack their germlines. These findings illustrate the heterogeneity of triglyceride-rich lipid particles in C. elegans and reveal specific lipid signals that promote longevity. Finally, we provide a brief overview of feeding behavioral responses of C. elegans to varying nutritional conditions and highlight an unanticipated metabolic pathway that allows the incorporation of experience in feeding behavior.

MicroRNA-based screens for synthetic lethal interactions with c-Myc

microRNAs (miRs) are small, non-coding RNAs, which play crucial roles in the development and progression of human cancer. Given that miRs are stable, easy to synthetize and readily introduced into cells, they have been viewed as having potential therapeutic benefit in cancer. c-Myc (Myc) is one of the most commonly deregulated oncogenic transcription factors and has important roles in the pathogenesis of cancer, thus making it an important, albeit elusive therapeutic target. Here we review the miRs that have been identified as being both positive and negative targets for Myc and how these participate in the complex phenotypes that arise as a result of Myc-driven transformation. We also discussseveral recent reports of Myc-synthetic lethal interactions with miRs.These highlight the importance and complexity of miRs in Myc-mediated biological functions and the opportunities for Myc-driven human cancer therapies.

Recent discoveries on absorption of dietary fat: Presence, synthesis, and metabolism of cytoplasmic lipid droplets within enterocytes

Dietary fat provides essential nutrients, contributes to energy balance, and regulates blood lipid concentrations. These functions are important to health, but can also become dysregulated and contribute to diseases such as obesity, diabetes, cardiovascular disease, and cancer. Within enterocytes, the digestive products of dietary fat are re-synthesized into triacylglycerol, which is either secreted on chylomicrons or stored within cytoplasmic lipid droplets (CLDs). CLDs were originally thought to be inert stores of neutral lipids, but are now recognized as dynamic organelles that function in multiple cellular processes in addition to lipid metabolism. This review will highlight recent discoveries related to dietary fat absorption with an emphasis on the presence, synthesis, and metabolism of CLDs within this process.

Expanding roles for lipid droplets

Lipid droplets are the intracellular sites for neutral lipid storage. They are critical for lipid metabolism and energy homeostasis, and their dysfunction has been linked to many diseases. Accumulating evidence suggests that the roles lipid droplets play in biology are significantly broader than previously anticipated. Lipid droplets are the source of molecules important in the nucleus: they can sequester transcription factors and chromatin components and generate the lipid ligands for certain nuclear receptors. Lipid droplets have also emerged as important nodes for fatty acid trafficking, both inside the cell and between cells. In immunity, new roles for droplets, not directly linked to lipid metabolism, have been uncovered, with evidence that they act as assembly platforms for specific viruses and as reservoirs for proteins that fight intracellular pathogens. Until recently, knowledge about droplets in the nervous system has been minimal, but now there are multiple links between lipid droplets and neurodegeneration: many candidate genes for hereditary spastic paraplegia also have central roles in lipid-droplet formation and maintenance, and mitochondrial dysfunction in neurons can lead to transient accumulation of lipid droplets in neighboring glial cells, an event that may, in turn, contribute to neuronal damage. As the cell biology and biochemistry of lipid droplets become increasingly well understood, the next few years should yield many new mechanistic insights into these novel functions of lipid droplets.

microRNA-129-5p, a c-Myc negative target, affects hepatocellular carcinoma progression by blocking the Warburg effect

Deregulation of microRNAs (miRNAs) and c-Myc (Myc) contributes to hepatocellular carcinoma (HCC) progression, but how miRNAs and Myc regulate each other in hepatocarcinogenesis is still poorly understood. Using a functional screen, we identified miR-129-5p as a miRNA that inhibits HCC cell growth. miR-129-5p targets the mitochondrial matrix protein pyruvate dehydrogenase kinase 4 (PDK4), which leads to decreased phosphorylation of the E1α subunit of pyruvate dehyrogenase (PDH) complex, inhibition of glycolysis, retarded tumor growth, and impaired lung colonization. Enforced expression of PDK4 refractory to inhibition by miR-129-5p rescued all of these phenotypes. Targeting PDK4 by shRNA recapitulated the effects caused by miR-129-5p. miR-129-5p is transcriptionally repressed by a complex comprised of Myc, histone deacetylase 3 (HDAC3), and enhancer of zeste 2 polycomb repressive complex 2 (EZH2). Levels of miR-129-5p negatively correlated with clinical stages in human HCC. Restoring miR-129-5p expression suppressed the diethylnitrosamine (DEN)-induced hepatocarcinogenesis in mice. Thus, we concluded that miR-129-5p, which is a negative target of Myc, blocks glycolysis to retard hepatocarcinogenesis via targeting PDK4. The critical link between miR-129-5p and PDK4 in the progression of HCC suggests potential points of therapeutic intervention for this disease.

Tipping the Balance: Hepatotoxicity and the 4 Apical Key Events of Hepatic Steatosis

Hepatic steatosis is a condition were fat accumulates in the liver and it is associated with extra-hepatic diseases related to metabolic syndrome and systemic energy metabolism. If not reversed, steatosis can progress to steatohepatitis and irreversible stages of liver disease including fibrosis, cirrhosis, hepatocellular carcinoma, and death. From a public health standpoint, identifying chemical exposures that may be factors in steatosis etiology are important for preventing hepatotoxicity and liver disease progression. It is therefore important to identify the biological events that are key for steatosis pathology mediated by chemical exposure. In this review, we give a current overview of the complex biological cascades that can disrupt lipid homeostasis in hepatocytes in the context of 4 apical key events central to hepatic lipid retention: hepatic fatty acid (FA) uptake,de novoFA and lipid synthesis, FA oxidation, and lipid efflux. Our goal is to review these key cellular events and visually summarize them using a network for application in pathway-based toxicity testing. This effort provides a foundation to improve next-generation chemical screening efforts that may be used to prevent and ultimately reverse the growing incidence of fatty liver disease in our population.

MiR-30e suppresses proliferation of hepatoma cells via targeting prolyl 4-hydroxylase subunit alpha-1 (P4HA1) mRNA

Aberrant microRNA expression has been shown to be characteristic of many cancers. It has been reported that the expression levels of miR-30e are decreased in liver cancer tissues. However, the role of miR-30e in hepatocellular carcinoma remains poorly understood. In the present study, we investigated the significance of miR-30e in hepatocarcinogenesis. Bioinformatics analysis reveals a putative target site of miR-30e in the 3'-untranslated region (3'UTR) of prolyl 4-hydroxylase subunit alpha-1 (P4HA1) mRNA. Moreover, luciferase reporter gene assays verified that miR-30e directly targeted 3'UTR of P4HA1 mRNA. Then, we demonstrated that miR-30e was able to reduce the expression of P4HA1 at the levels of mRNA and protein using reverse transcription-polymerase chain reaction and Western blot analysis. Enforced expression of miR-30e suppressed proliferation of HepG2 cells by 5-ethynyl-2-deoxyuridine (EdU) assay and reduced colony formation of these cells by colony formation analysis. Conversely, anti-miR-30e enhanced the proliferation of hepatoma cells in vitro. Interestingly, the ectopic expression of P4HA1 could efficiently rescue the inhibition of cell proliferation mediated by miR-30e in HepG2 cells. Meanwhile, silencing of P4HA1 abolished the anti-miR-30e-induced proliferation of cells. Clinically, quantitative real-time PCR showed that miR-30e was down-regulated in liver tumor tissues relative to their peritumor tissues. The expression levels of miR-30e were negatively correlated to those of P4HA1 mRNA in clinical liver tumor tissues. Thus, we conclude that miR-30e suppresses proliferation of hepatoma cells through targeting P4HA1 mRNA. Our finding provides new insights into the mechanism of hepatocarcinogenesis.

microRNA changes in liver tissue associated with fibrosis progression in patients with hepatitis C

BACKGROUND & AIMS

Accumulating evidence indicates that microRNAs play a role in a number of disease processes including the pathogenesis of liver fibrosis in hepatitis C infection. Our goal is to add to the accruing information regarding microRNA deregulation in liver fibrosis to increase our understanding of the underlying mechanisms of pathology and progression.

METHODS

We used next generation sequencing to profile all detectable microRNAs in liver tissue and serum from patients with hepatitis C, stages F1-F4 of fibrosis.

RESULTS

We found altered expression of several microRNAs, in particular, miR-182, miR199a-5p, miR-200a-5p and miR-183 were found to be significantly upregulated in tissue from liver biopsies of hepatitis C patients with advanced fibrosis, stage F3 and F4, when compared with liver biopsies from patients with early fibrosis, stages F1 and F2. We also found miR-148-5p, miR-1260b, miR-122-3p and miR-378i among the microRNAs most significantly down-regulated from early to advanced fibrosis of the liver. We also sequenced the serum microRNAs; however, we were not able to detect significant changes in circulating microRNAs associated with fibrosis stage after adjusting for multiple tests.

CONCLUSIONS

Adding measurements of tissue microRNAs acquired during routine biopsies will continue to increase our knowledge of underlying mechanisms of fibrosis. Our goal is that these data, in combination with studies from other researchers and future long-term studies, could be used to enhance the staging accuracy of liver biopsies and expand the surveillance of patients at increased risk for cancer and progression to advanced fibrosis.

The role of MicroRNAs in human cancer

MicroRNAs (miRNAs) are endogenous, small non-coding RNAs that function in regulation of gene expression. Compelling evidences have demonstrated that miRNA expression is dysregulated in human cancer through various mechanisms, including amplification or deletion of miRNA genes, abnormal transcriptional control of miRNAs, dysregulated epigenetic changes and defects in the miRNA biogenesis machinery. MiRNAs may function as either oncogenes or tumor suppressors under certain conditions. The dysregulated miRNAs have been shown to affect the hallmarks of cancer, including sustaining proliferative signaling, evading growth suppressors, resisting cell death, activating invasion and metastasis, and inducing angiogenesis. An increasing number of studies have identified miRNAs as potential biomarkers for human cancer diagnosis, prognosis and therapeutic targets or tools, which needs further investigation and validation. In this review, we focus on how miRNAs regulate the development of human tumors by acting as tumor suppressors or oncogenes.