技术资料

Incubation of skeletal muscle with 5-aminoimidazole-4carboxamide ribonucleoside (AICAR),a compound that activates 5'-AMP-activated protein kinase (AMPK),has been demonstrated to stimulate glucose transport and GLUT4 translocation to the plasma membrane. In this study,we characterized the AMPK cascade in 3T3-L1 adipocytes and the response of glucose transport to incubation with AICAR. Both isoforms of the catalytic alpha-subunit of AMPK are expressed in 3T3-L1 adipocytes,in which AICAR stimulated AMPK activity in a time- and dose-dependent fashion. AICAR stimulated 2-deoxy-D-glucose transport twofold and reduced insulin-stimulated uptake to 62% of the control transport rate dose-dependently,closely correlating with the activation of AMPK. AICAR also inhibited insulin-stimulated GLUT4 translocation,assessed using the plasma membrane lawn assay. The effects of AICAR on insulin-stimulated glucose transport are not mediated by either adenosine receptors or nitric oxide synthase and are mediated downstream of phosphatidylinositol 3'-kinase stimulation. We propose that in contrast to skeletal muscle,in which AMPK stimulation promotes glucose transport to provide ATP as a fuel,AMPK stimulation inhibits insulin-stimulated glucose transport in adipocytes,inhibiting triacylglycerol synthesis,to conserve ATP under conditions of cellular stress. Investigation of the mode of action of AICAR and AMPK may,therefore,give insight into the mechanism of insulin action. View Publication

The AMP-activated protein kinase (AMPK) is believed to protect cells against environmental stress (e.g. heat shock) by switching off biosynthetic pathways,the key signal being elevation of AMP. Identification of novel targets for the kinase cascade would be facilitated by development of a specific agent for activating the kinase in intact cells. Incubation of rat hepatocytes with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) results in accumulation of the monophosphorylated derivative (5-aminoimidazole-4-carboxamide ribonucleoside; ZMP) within the cell. ZMP mimics both activating effects of AMP on AMPK,i.e. direct allosteric activation and promotion of phosphorylation by AMPK kinase. Unlike existing methods for activating AMPK in intact cells (e.g. fructose,heat shock),AICAR does not perturb the cellular contents of ATP,ADP or AMP. Incubation of hepatocytes with AICAR activates AMPK due to increased phosphorylation,causes phosphorylation and inactivation of a known target for AMPK (3-hydroxy-3-methylglutaryl-CoA reductase),and almost total cessation of two of the known target pathways,i.e. fatty acid and sterol synthesis. Incubation of isolated adipocytes with AICAR antagonizes isoprenaline-induced lipolysis. This provides direct evidence that the inhibition by AMPK of activation of hormone-sensitive lipase by cyclic-AMP-dependent protein kinase,previously demonstrated in cell-free assays,also operates in intact cells. AICAR should be a useful tool for identifying new target pathways and processes regulated by the protein kinase cascade. View Publication

Molecular mechanisms of how energy metabolism affects embryonic stem cell (ESC) pluripotency remain unclear. AMP-activated protein kinase (AMPK),a key regulator for controlling energy metabolism,is activated in response to ATP-exhausting stress. We investigated whether cellular energy homeostasis is associated with maintenance of self-renewal and pluripotency in mouse ESCs (mESCs) by using 5-aminoimidazole-4-carboxyamide ribonucleoside (AICAR) as an activator of AMPK. We demonstrate that AICAR treatment activates the p53/p21 pathway and markedly inhibits proliferation of R1 mESCs by inducing G(1) /S-phase cell cycle arrest,without influencing apoptosis. Treatment with AICAR also significantly reduces pluripotent stem cell markers,Nanog and stage-specific embryonic antigen-1,in the presence of leukemia inhibitory factor,without affecting expression of Oct4. H9 human ESCs also responded to AICAR with induction of p53 activation and repression of Nanog expression. AICAR reduced Nanog mRNA levels in mESCs transiently,an effect not due to expression of miR-134 which can suppress Nanog expression. AICAR induced Nanog degradation,an effect inhibited by MG132,a proteasome inhibitor. Although AICAR reduced embryoid body formation from mESCs,it increased expression levels of erythroid cell lineage markers (Ter119,GATA1,Klf1,Hbb-b,and Hbb-bh1). Although erythroid differentiation was enhanced by AICAR,endothelial lineage populations were remarkably reduced in AICAR-treated cells. Our results suggest that energy metabolism regulated by AMPK activity may control the balance of self-renewal and differentiation of ESCs. View Publication

5-Azacytidine was first synthesized almost 40 years ago. It was demonstrated to have a wide range of anti-metabolic activities when tested against cultured cancer cells and to be an effective chemotherapeutic agent for acute myelogenous leukemia. However,because of 5-azacytidine's general toxicity,other nucleoside analogs were favored as therapeutics. The finding that 5-azacytidine was incorporated into DNA and that,when present in DNA,it inhibited DNA methylation,led to widespread use of 5-azacytidine and 5-aza-2'-deoxycytidine (Decitabine) to demonstrate the correlation between loss of methylation in specific gene regions and activation of the associated genes. There is now a revived interest in the use of Decitabine as a therapeutic agent for cancers in which epigenetic silencing of critical regulatory genes has occurred. Here,the current status of our understanding of the mechanism(s) by which 5-azacytosine residues in DNA inhibit DNA methylation is reviewed with an emphasis on the interactions of these residues with bacterial and mammalian DNA (cytosine-C5) methyltransferases. The implications of these mechanistic studies for development of less toxic inhibitors of DNA methylation are discussed. View Publication

RNA functions at enhancers remain mysterious. Here we show that the 7SK small nuclear RNA (snRNA) inhibits enhancer transcription by modulating nucleosome position. 7SK occupies enhancers and super enhancers genome wide in mouse and human cells,and it is required to limit enhancer-RNA initiation and synthesis in a manner distinct from promoter pausing. Clustered elements at super enhancers uniquely require 7SK to prevent convergent transcription and DNA-damage signaling. 7SK physically interacts with the BAF chromatin-remodeling complex,recruits BAF to enhancers and inhibits enhancer transcription by modulating chromatin structure. In turn,7SK occupancy at enhancers coincides with that of Brd4 and is exquisitely sensitive to the bromodomain inhibitor JQ1. Thus,7SK uses distinct mechanisms to counteract the diverse consequences of pervasive transcription that distinguish super enhancers,enhancers and promoters. View Publication

In a number of cell types,elevation of intracellular cAMP concentrations antagonizes growth factor-induced mitogenesis by abrogating the downstream signaling of RasGTP to extracellular-signal-regulated kinases (Erk 1,2). We studied the effect of elevation of cAMP concentrations on the IL-3-induced mitogenic response in the leukemic cell line AML193. We observed that 8-bromo-cAMP (8-Br-cAMP) had no inhibitory effect on the magnitude of this response. On the contrary. 8-Br-cAMP alone induced a proliferative response in these cells. 8-Br-cAMP activated Erk 1,2 in these cells without involvement of Shc phosphorylation. These findings suggest the presence of a novel cAMP-dependent signaling pathway in AML193 cells,which activates Erk 1,2 via a Shc-independent pathway and leads to the generation of a mitogenic response. View Publication

AbstractA basic assumption underlying induced pluripotent stem cell (iPSC) models of neurodegeneration is that disease-relevant pathologies present in brain tissue are also represented in donor-matched cells differentiated from iPSCs. However,few studies have tested this hypothesis in matched iPSCs and neuropathologically characterized donated brain tissues. To address this,we assessed iPSC-neuron production of ?-amyloid (A?) A?40,A?42,and A?43 in 24 iPSC lines matched to donor brains with primary neuropathologic diagnoses of sporadic AD (sAD),familial AD (fAD),control,and other neurodegenerative disorders. Our results demonstrate a positive correlation between A?43 production by fAD iPSC-neurons and A?43 accumulation in matched brain tissues but do not reveal a substantial correlation in soluble A? species between control or sAD iPSC-neurons and matched brains. However,we found that the ApoE4 genotype is associated with increased A? production by AD iPSC-neurons. Pathologic tau phosphorylation was found to be increased in AD and fAD iPSC-neurons compared to controls and positively correlated with the relative abundance of longer-length A? species produced by these cells. Taken together,our results demonstrate that sAD-predisposing genetic factors influence iPSC-neuron phenotypes and that these cells are capturing disease-relevant and patient-specific components of the amyloid cascade. View Publication

Background?-catenin,acting as the core effector of canonical Wnt signaling pathway,plays a pivotal role in controlling lineage commitment and the formation of definitive endoderm (DE) during early embryonic development. Despite extensive studies using various animal and cell models,the ?-catenin-centered regulatory mechanisms underlying DE formation remain incompletely understood,partly due to the rapid and complex cell fate transitions during early differentiation.ResultsIn this study,we generated new CTNNB1-/- human ES cells (hESCs) using CRISPR-based insertional gene disruption approach and systematically rescued the DE defect in these cells by introducing various truncated or mutant forms of ?-catenin. Our analysis showed that a truncated ?-catenin lacking both N- and C-terminal domains (?N148C) could robustly rescue the DE formation,whereas hyperactive ?-catenin mutants with S33Y mutation or N-terminal deletion (?N90) had limited ability to induce DE lineage. Notably,the ?N148C mutant exhibited significant nuclear translocation that was positively correlated with successful DE rescue. Transcriptomic analysis further uncovered that two weak ?-catenin mutants lacking the C-terminal transactivation domain (CTD) activated primitive streak (PS) genes,whereas the hyperactive ?-catenin mutants activated mesoderm genes.ConclusionOur study uncovered an unconventional regulatory function of ?-catenin through weak transactivation,indicating that the levels of ?-catenin activity determine the lineage bifurcation from mesendoderm into endoderm and mesoderm.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13578-024-01279-5. View Publication

The emergence of the primitive streak,representing an organizing center for gastrulation,marks the mesendodermal lineage specification from epiblast,in which the epiblast cells undergo highly organized collective behaviors to form mesendodermal cells properly. Cell death is observed at the peri-gastrulation stage,especially in the primitive streak region. However,the dynamic and regulatory mechanism of cell death in the primitive streak formation is unclear. Here,we observed that a quick inhibition of the fast elevated cell death is coinciding with an accumulation of ?-catenin during the early stage of primitive streak induction from human embryonic stem cells (hESCs). Deficiency of ?-catenin in hESCs does not affect their self-renewal but cause robust cell death after primitive streak induction,while neuroectodermal differentiation remains unchanged. Overexpression of full-length ?-catenin in ?-catenin-deficient hESCs restores the cell death restriction during induction of primitive streak. Mechanistically,the ?-catenin-restricted cell death during primitive streak is transcription-independent. The accumulated ?-catenin traps casein kinase-1 in ?-catenin destruction complex following WNT activation via its ARM repeat domain,resulting in the inhibition of mTORC1 by stabilizing DEPTOR,subsequently attenuates mitochondrial translocation of p53 and enhances mitophagy to promote cell survival. Consistently,mTORC1 inhibition by rapamycin or RAD001 attenuates the cell death in ?-catenin-deficient cells during induction of primitive streak. In addition,only the ?-catenin retains activations of cell death restriction and transcriptional activity can promote hESCs to successfully differentiate into primitive streak and cardiomyocytes,suggesting that ?-catenin-restricted cell death safeguards the fate transition during the primitive streak induction via offering a crucial window for the accumulation of ?-catenin to induce lineage-specific genes. These findings provide new insights into the function and mechanisms by which ?-catenin coordinates the cell death and early lineage commitment. View Publication

β-propeller protein-associated neurodegeneration (BPAN) is a rare X-linked neurodegenerative disorder caused by mutations in the WDR45 gene,yet its molecular mechanisms remain poorly understood. Here,we identify a role for WDR45 in stress granule (SG) disassembly,mediated through its phase separation with Caprin-1. We demonstrate that WDR45 forms gel-like condensates via its WD5 domain,which competitively displaces G3BP1 from Caprin-1 to promote SG disassembly. BPAN-associated WDR45 mutations impair condensate formation and Caprin-1 interaction,leading to delayed SG disassembly,which correlates with earlier disease onset. WDR45 depletion also exacerbates amyotrophic lateral sclerosis-associated pathological SGs,highlighting its broader relevance to neurodegenerative diseases. Using iPSC-derived midbrain neurons from a BPAN patient,we demonstrate delayed SG recovery,directly linking WDR45 dysfunction to neurodegeneration. These findings establish WDR45 as a critical regulator of SG dynamics,uncover a potential molecular basis of BPAN pathogenesis,and identify therapeutic targets for neurodegenerative diseases associated with SG dysregulation. BPAN is a rare neurodegenerative disease caused by WDR45 mutations. Here,the authors discover that WDR45 can competitively displace G3BP1 from Caprin-1 to promote stress granule disassembly,a function that is disrupted by BPAN-associated WDR45 mutations. View Publication

BACKGROUND: The collagen gel contraction assay measures gel size to assess the contraction of cells embedded in collagen gel matrices. Using the assay with lung fibroblasts is useful in studying the lung tissue remodeling process in wound healing and disease development. However,the involvement of bronchial epithelial cells in this process should also be investigated. METHODS: We applied a layer of mucociliary differentiated bronchial epithelial cells onto collagen gel matrices with lung fibroblasts. This co-culture model enables direct contact between epithelial and mesenchymal cells. We stimulated the culture with transforming growth factor (TGF) beta1 as an inducer of tissue remodeling for 21 days,and measured gel size,histological changes,and expression of factors related to extracellular matrix homeostasis. RESULTS: TGF-beta1 exerted a concentration-dependent effect on collagen gel contraction and on contractile myofibroblasts in the mesenchymal collagen layer. TGF-beta1 also induced expression of the mesenchymal marker vimentin in the basal layer of the epithelium,suggesting the induction of epithelial-mesenchymal transition. In addition,the expression of various genes encoding extracellular matrix proteins was upregulated. Fibrotic tenascin-C accumulated in the sub-epithelial region of the co-culture model. CONCLUSION: Our findings indicate that TGF-beta1 can affect both epithelial and mesenchymal cells,and induce gel contraction and structural changes. Our novel in vitro co-culture model will be a useful tool for investigating the roles of epithelial cells,fibroblasts,and their interactions in the airway remodeling process. View Publication

Background: Alzheimer's disease (AD) is characterized by progressive amyloid beta (Aβ) deposition in the brain,with eventual widespread neurodegeneration. While the cell-specific molecular signature of end-stage AD is reasonably well characterized through autopsy material,less is known about the molecular pathways in the human brain involved in the earliest exposure to Aβ. Human model systems that not only replicate the pathological features of AD but also the transcriptional landscape in neurons,astrocytes and microglia are crucial for understanding disease mechanisms and for identifying novel therapeutic targets. Methods: In this study,we used a human 3D iPSC-derived neurosphere model to explore how resident neurons,microglia and astrocytes and their interplay are modified by chronic amyloidosis induced over 3-5 weeks by supplementing media with synthetic Aβ1 - 42 oligomers. Neurospheres under chronic Aβ exposure were grown with or without microglia to investigate the functional roles of microglia. Neuronal activity and oxidative stress were monitored using genetically encoded indicators,including GCaMP6f and roGFP1,respectively. Single nuclei RNA sequencing (snRNA-seq) was performed to profile Aβ and microglia driven transcriptional changes in neurons and astrocytes,providing a comprehensive analysis of cellular responses. Results: Microglia efficiently phagocytosed Aβ inside neurospheres and significantly reduced neurotoxicity,mitigating amyloidosis-induced oxidative stress and neurodegeneration following different exposure times to Aβ. The neuroprotective effects conferred by the presence of microglia was associated with unique gene expression profiles in astrocytes and neurons,including several known AD-associated genes such as APOE. These findings reveal how microglia can directly alter the molecular landscape of AD. Conclusions: Our human 3D neurosphere culture system with chronic Aβ exposure reveals how microglia may be essential for the cellular and transcriptional responses in AD pathogenesis. Microglia are not only neuroprotective in neurospheres but also act as key drivers of Aβ-dependent APOE expression suggesting critical roles for microglia in regulating APOE in the AD brain. This novel,well characterized,functional in vitro platform offers unique opportunities to study the roles and responses of microglia to Aβ modelling key aspects of human AD. This tool will help identify new therapeutic targets,accelerating the transition from discovery to clinical applications. View Publication