PI3K/Akt 及其靶蛋白FOXO1 与非酒精性脂肪性肝病

FOXO转录因子是Forkhead蛋白大家族的一个亚群,在人类的4个同源基因中包括FoxO1、FoxO2、FoxO3a和FoxO4。FoxO蛋白质通过丝氨酸或苏氨酸以及赖氨酸残基的磷酸化和乙酰化等后转录修饰后而发挥作用。其中Foxo1是含有高度保守DNA结合位点的核转录蛋白,其主要功能是磷脂酰肌醇3-激酶(PI3K)/蛋白激酶B(Akt)的底物,在胰岛素信号转导中起负性调节作用,Foxo1通过介导胰岛素依赖性微粒体甘油三酯转运蛋白(MTP)的表达,影响肝脏装配和分泌极低密度脂蛋白(VLDL),维持脂代谢稳定。在胰岛素抵抗和脂肪肝状态下,肝细胞核内Foxo1表达明显升高,引起高甘油三酯血症和脂肪肝。有针对性的干预PI3K/Akt及Foxo1的表达,可能从分子机制上为非酒精性脂肪肝的防治提供广阔前景。     

Long noncoding RNA THRIL promotes foam cell formation and inflammation in macrophages

Tumor necrosis factor-α (TNF-α) and heterogenous nuclear ribonucleoprotein L (hnRNPL)-related immunoregulatory lincRNA (THRIL) is a long noncoding RNA (lncRNA) involved in various inflammatory diseases. However, its role in atherosclerosis is not known. In this study, we aimed to investigate the function of THRIL in mediating macrophage inflammation and foam cell formation. The expression of THRIL was quantified in THP-1 macrophages after treatment with oxidized low-density lipoprotein (oxLDL). The effect of THRIL overexpression and knockdown on oxLDL-induced inflammatory responses and lipid accumulation was determined. THRIL-associated protein partners were identified by RNA pull-down and RNA immunoprecipitation assays. We show that THRIL is upregulated in macrophages after oxLDL treatment. Knockdown of THRIL blocks oxLDL-induced expression of interleukin-1β (IL-1β), IL-6, and TNF-α and lipid accumulation. Conversely, ectopic expression of THRIL enhances inflammatory gene expression and lipid deposition in oxLDL-treated macrophages. Moreover, THRIL depletion increases cholesterol efflux from macrophages and the expression of ATP-binding cassette transporter (ABC) A1 and ABCG1. FOXO1 is identified as a protein partner of THRIL and promotes macrophage inflammation and lipid accumulation. Furthermore, overexpression of FOXO1 restores lipid accumulation and inflammatory cytokine production in THRIL-depleted macrophages. In conclusion, our data suggest a model where THRIL interacts with FOXO1 to promote macrophage inflammation and foam cell formation. THRIL may represent a therapeutic target for atherosclerosis.     

A genome-wide survey of maize lipid-related genes: candidate genes mining,digital gene expression profiling and co-location with QTL for maize kernel oil

Lipids play an important role in plants due to their abundance and their extensive participation in many metabolic processes. Genes involved in lipid metabolism have been extensively studied in Arabidopsis and other plant species. In this study, a total of 1003 maize lipid-related genes were cloned and annotated, including 42 genes with experimental validation, 732 genes with full-length cDNA and protein sequences in public databases and 229 newly cloned genes. Ninety-seven maize lipid-related genes with tissue-preferential expression were discovered by in silico gene expression profiling based on 1984483 maize Expressed Sequence Tags collected from 182 cDNA libraries. Meanwhile, 70 QTL clusters for maize kernel oil were identified, covering 34.5% of the maize genome. Fifty-nine (84%) QTL clusters co-located with at least one lipid-related gene, and the total number of these genes amounted to 147. Interestingly, thirteen genes with kernel-preferential expression profiles fell within QTL clusters for maize kernel oil content. All the maize lipid-related genes identified here may provide good targets for maize kernel oil QTL cloning and thus help us to better understand the molecular mechanism of maize kernel oil accumulation.     

P13K／Akt及其靶蛋白FOXO1与非酒精性脂肪性肝病

FOXO转录因子是Forkhead蛋白大家族的一个亚群,在人类的4个同源基因中包括Fox01、Fox02、Fox03a和Fox04。FoxO蛋白质通过丝氨酸或苏氨酸以及赖氨酸残基的磷酸化和乙酰化等后转录修饰后而发挥作用。其中Foxol是含有高度保守DNA结合位点的核转录蛋白,其主要功能是磷脂酰肌醇3。激酶（P13K）／蛋白激酶B（Ala）的底物,在胰岛素信号转导中起负性调节作用,Foxol通过介导胰岛素依赖性微粒体甘油三酯转运蛋白（MTP）的表达,影响肝脏装配和分泌极低密度脂蛋白（VLDL）,维持脂代谢稳定。在胰岛素抵抗和脂肪肝状态下,肝细胞核内Foxol表达明显升高,引起高甘油三酯血症和脂肪肝。有针对性的干预P13姒啵t及Foxol的表达,可能从分子机制上为非酒精性脂肪肝的防治提供广阔前景。     

PERK signaling pathway in bone metabolism: Friend or foe?

Osteoblasts and osteoclasts participate in the process of bone remodelling to meet the needs of normal growth and development or repair pathological damage. Endoplasmic reticulum stress (ER stress) can break the intracellular homeostasis of osteoclasts and osteoblasts, which is closely related to abnormal bone remodelling. The double‐stranded RNA‐dependent protein kinase (PKR)‐like ER kinase (PERK) is a key transmembrane protein that regulates ER stress, and growing evidence suggests that the PERK pathway plays a crucial role in regulating bone metabolism under both physiological and pathological conditions. Based on the current findings, we summarized the main mechanisms involved in bone metabolism downstream of the PERK pathway, among which elF2α, FOXO1, CaN, Nrf2 and DAG play a role in regulating the differentiation of osteoblasts and osteoclasts. Importantly, strategies by the regulation of PERK pathway exert beneficial effects in preclinical trials of several bone‐related diseases. Given the importance and novelty of PERK pathway, we provide an overview and discuss the roles of PERK pathway in regulating bone metabolism and its impact on bone‐related diseases. We hope that the development of research in this field will bring a bright future for the treatment of bone‐related diseases.

Effects of downstream changes caused by activation of PERK on osteoblastogenesis and osteoclastogenesis. Phosphorylated elF2a, Nrf2, DAG, FOXO1 and enhanced activity of CaN have different impacts on osteogenic and osteoclast differentiation, respectively. Green squares indicate the expression of the genes.     

Inhibition of AMP Kinase by the Protein Phosphatase 2A Heterotrimer,PP2APpp2r2d

AMP kinase is a heterotrimeric serine/threonine protein kinase that regulates a number of metabolic processes, including lipid biosynthesis and metabolism. AMP kinase activity is regulated by phosphorylation, and the kinases involved have been uncovered. The particular phosphatases counteracting these kinases remain elusive. Here we discovered that the protein phosphatase 2A heterotrimer, PP2A^Ppp2r2d, regulates the phosphorylation state of AMP kinase by dephosphorylating Thr-172, a residue that activates kinase activity when phosphorylated. Co-immunoprecipitation and co-localization studies indicated that PP2A^Ppp2r2d directly interacted with AMP kinase. PP2A^Ppp2r2d dephosphorylated Thr-172 in rat aortic and human vascular smooth muscle cells. A positive correlation existed between decreased phosphorylation, decreased acetyl-CoA carboxylase Acc1 phosphorylation, and sterol response element-binding protein 1c-dependent gene expression. PP2A^Ppp2r2d protein expression was up-regulated in the aortas of mice fed a high fat diet, and the increased expression correlated with increased blood lipid levels. Finally, we found that the aortas of mice fed a high fat diet had decreased AMP kinase Thr-172 phosphorylation, and contained an Ampk-PP2A^Ppp2r2d complex. Thus, PP2A^Ppp2r2d may antagonize the aortic AMP kinase activity necessary for maintaining normal aortic lipid metabolism. Inhibiting PP2A^Ppp2r2d or activating AMP kinase represents a potential pharmacological treatment for many lipid-related diseases.     

Peroxisomes,lipid metabolism and lipotoxicity

Peroxisomes play an essential role in cellular lipid metabolism as exemplified by the existence of a number of genetic diseases in humans caused by the impaired function of one of the peroxisomal enzymes involved in lipid metabolism. Key pathways in which peroxisomes are involved include: (1.) fatty acid beta-oxidation; (2.) etherphospholipid biosynthesis, and (3.) fatty acid alpha-oxidation. In this paper we will describe these different pathways in some detail and will provide an overview of peroxisomal disorders of metabolism and in addition discuss the toxicity of the intermediates of peroxisomal metabolism as they accumulate in the different peroxisomal deficiencies.     

Activity based subcellular resolution imaging of lipases

Lipases play a key role in whole body energy homeostasis. Dysregulation of lipolytic activities affects lipid absorption, mobilization, and transport, and is causative for lipid-related diseases. Regulation of enzymes involved in lipid metabolism is governed by a complex network of protein-protein and protein-small molecule interactions. Thus these enzymes have to be studied under the physiologically most relevant conditions, that is, in vivo. Our latest generation of activity based probes designed for capturing of lipases employs bioorthogonal chemical linker groups, which are membrane permeable and thus allow studying protein activity in living cells. Another advantage is the virtually unlimited choice of reporter tags. Here we report on a novel method combining in vivo activity based labeling of lipases with in situ detection of lipolytic activities by on slide click chemistry and imaging by fluorescence microscopy. We demonstrate that cytosolic as well as organelle resident lipases are specifically labeled in intact living cells. This method will shed light on the (sub)cellular localization of lipolytic proteomes of cells and tissues in health and disease directly at enzymatic activity level without the need of prior knowledge of the identities of the responsible enzymes or dependence on the availability of specific antibodies.     

Leptin induces macrophage lipid body formation by a phosphatidylinositol 3-kinase- and mammalian target of rapamycin-dependent mechanism

Leptin is an adipocyte-derived hormone/cytokine that links nutritional status with neuroendocrine and immune functions. Lipid bodies (lipid droplets) are emerging as dynamic organelles with roles in lipid metabolism and inflammation. Here we investigated the roles of leptin in signaling pathways involved in cytoplasmic lipid body biogenesis and leukotriene B(4) synthesis in macrophages. Our results demonstrated that leptin directly activated macrophages and induced the formation of adipose differentiation-related protein-enriched lipid bodies. Newly formed lipid bodies were sites of 5-lipoxygenase localization and correlated with an enhanced capacity of leukotriene B(4) production. We demonstrated that leptin-induced macrophage activation was dependent on phosphatidylinositol 3-kinase (PI3K) activity, since the lipid body formation was inhibited by LY294002 and was absent in the PI3K knock-out mice. Leptin induces phosphorylation of p70(S6K) and 4EBP1 key downstream signaling intermediates of the mammalian target of rapamycin (mTOR) pathway in a rapamycin-sensitive mechanism. The mTOR inhibitor, rapamycin, inhibited leptin-induced lipid body formation, both in vivo and in vitro. In addition, rapamycin inhibited leptin-induced adipose differentiation-related protein accumulation in macrophages and lipid body-dependent leukotriene synthesis, demonstrating a key role for mTOR in lipid body biogenesis and function. Our results establish PI3K/mTOR as an important signaling pathway for leptin-induced cytoplasmic lipid body biogenesis and adipose differentiation-related protein accumulation. Furthermore, we demonstrate a previously unrecognized link between intracellular (mTOR) and systemic (leptin) nutrient sensors in macrophage lipid metabolism. Leptin-induced increased formation of cytoplasmic lipid bodies and enhanced inflammatory mediator production in macrophages may have implications for obesity-related cardiovascular diseases.