ATF4 regulates lipid metabolism and thermogenesis

Activating transcription factor 4 （ATF4） has been shown to play key roles in many physiological processes. There are no reports, however, demonstrating a direct link between ATF4 and lipid metabolism. We noticed that Atf4- deficient mice are lean, suggesting a possible role for ATF4 in regulating lipid metabolism. The goal of our current study is to investigate the involvement of ATF4 in lipid metabolism and elucidate the underlying mechanisms. Studies using Atf4-deficient mice revealed increased energy expenditure, as measured by oxygen consumption. These mice also showed increases in lipolysis, expression of uncoupling protein 2 （UCP2） and p-oxidation genes and decreases in expression of lipogenic genes in white adipose tissue （WAT）, suggesting increased utilization and decreased synthesis of fatty acids, respectively. Expression of UCP1, 2 and 3 was also increased in brown adipose tissue （BAT）, suggesting increased thermogenesis. The effect of ATF4 deletion on expression of UCPs in BAT suggests that increased thermogenesis may underlie increased energy expenditure. Thus, our study identifies a possible new function for ATF4 in regulating lipid metabolism and thermogenesis.

Endocytosis of adiponectin receptor I through a clathrin- and Rab5-dependent pathway

In eukaryotic cells, receptor endocytosis is a key event regulating signaling transduction. Adiponectin receptors belong to a new receptor family that is distinct from G-protein-coupled receptors and has critical roles in the pathogenesis of diabetes and metabolic syndrome. Here, we analyzed the endocytosis of adiponectin and adiponectin receptor 1 （AdipoR1） and found that they are both internalized into transferrin-positive compartments that follow similar traffic routes. Blocking clathrin-mediated endocytosis by expressing Eps15 mutants or depleting K^＋ trapped AdipoR1 at the plasma membrane, and K^＋ depletion abolished adiponectin internalization, indicating that the endocytosis of AdipoR1 and adiponectin is clathrin-dependent. Depletion of K^＋ and overexpression of Eps15 mutants enhance adiponectin- stimulated AMP-activated protein kinase phosphorylation, suggesting that the endocytosis of AdipoR1 might down-regulate adiponectin signaling. In addition, AdipoR1 colocalizes with the small GTPase Rab5, and a dominant negative Rab5 abrogates AdipoR1 endocytosis. These data indicate that AdipoR1 is internalized through a clathrin- and Rab5- dependent pathway and that endocytosis may play a role in the regulation of adiponectin signaling.

Induction of CD4＋CD25＋Foxp3＋ regulatory T cell response by glatiramer acetate in type 1 diabetes

Glatiramer acetate （GA） is an immunomodulatory peptide drug used to treat multiple sclerosis. Its treatment effect has been expanded to other autoimmune conditions such as uveoretinitis, inflammatory bowel disease, graft re- jection and hepatic fibrosis. Here, we report that GA was effective in altering the clinical course of diabetes in cyclo- phosphamide （CY）-potentiated non-obese diabetic （CY-NOD） mice. Treatment with GA significantly reduced the dia- betic rate in the mice and ameliorated insulitis, which coincided with increased CD4＋CD25＋Foxp3＋ T cell response in treated mice. GA treatment led to increased expression of transcription factor Foxp3 and elevated production of interleukin-4 （IL-4） both in vivo and in vitro. It was evident that the effect of GA on up-regulation of Foxp3 was me- diated partially through IL-4. IL-4 was found to maintain Foxp3 expression and regulatory function of CD4＋CD25＋ regulatory T cells （Tregs）. This study provides new evidence that GA has treatment potential for type 1 diabetes through the induction of Tregs and that increased IL-4 production is partially responsible for the enhanced Treg＇s function in GA treatment.

抗性淀粉的代谢及对血糖的调节作用

目的 : 利用天然稳定同位素技术 ,探讨抗性淀粉吸收代谢的特点及对血糖调节的影响。方法 : 7名健康志愿者分别试食 40 g天然富1 3C的葡萄糖、可消化淀粉 ( DS)和抗性淀粉( RS) ,测定餐后 0～ 2 40 min血糖 ,1 3C-血糖、血胰岛素水平和餐后 3 0 h呼气中1 3CO2 转化率及累积转化率。结果 : 食用 RS后 ,血糖和 1 3C-血糖水平明显低于食用葡萄糖和 DS;以葡萄糖餐后 1 2 0min的血糖生成指数 ( GI)和 1 3C-GI为 1 0 0 % ,RS的 GI值和 1 3C-GI值分别为 2 3 .5 8%和 5 5 .5 6% ;RS餐后呼气中1 3CO2 转化率的峰值明显低于葡萄糖和 DS( P<0 .0 5 ) ,但是 3 0 h累积转化率可达94.0 % ,与葡萄糖 ( 96.9% )和 DS( 1 0 2 .0 % )接近 ( P>0 .0 5 ) ;RS使餐后胰岛素升高幅度、胰岛素 /葡萄糖比值明显低于葡萄糖和 DS( P<0 .0 5 )。结论 : 抗性淀粉吸收缓慢但较完全 ,与葡萄糖和DS相比 ,具有维持餐后血糖稳态 。

C/EBPα regulates SIRT1 expression during adipogenesis

SIRT1 plays an important role in adipogenesis, but how SIRT1 is regulated in adipogenesis is largely unknown. In this study, we show that both SIRT1 protein and mRNA levels were increased along with CCAAT/enhancer-binding protein a （C/EBPa） during adipocyte differentiation. C/EBPa, but not C/EBPap30, activated SIRT1 promoter in both HeLa cells and 3T3-L1 preadipocytes. Furthermore, C/EBPa upregulated SIRT1 mRNA and protein levels in HeLa cells and increased SIRT1 expression in a p53-independent manner in Soas2 cells. In preadipocytes, ectopic expression of C/EBPa upregulated SIRT1 protein level and knockdown of C/EBPa led to the decrease of SIRTI pro- tein level. Moreover, by promoter deletion analysis, gel shift assay and chromatin immunoprecipitation, we found that C/EBPa bound to the SIRT1 promoter at a consensus C/EBPα binding site. These data demonstrate that C/ EBPα regulates SIRT1 expression during adipogenesis by directly binding to the SIRT1 promoter.

Adipose tissue macrophage in immune regulation of metabolism

The prevalence of obesity and type 2 diabetes is escalating to an epidemic proportion worldwide. Obesity is known to be associated with a state of chronic, low-grade inflammation. Emerging lines of evidence have shown that both innate and adaptive immune responses play crucial roles in the control of metabolic homeostasis. Macrophages in adipose tissues are the essential effector cells in orchestrating metabolic inflammation, which is thought to promote the pathogenic progression of obesity mad obesity-related disorders. Here we discuss our current understanding of the distinct modes of activation of adipose tissue macrophages, which can sense the metabolic cues and exert profound effects upon adipose homeostasis. Targeting macrophages in adipose tissues may provide new avenues for developing immunomodulation-based therapeutics against obesity and obesity-associated metabolic diseases.

The steady-state level of CDK4 protein ms regulated by antagonistic actions between PAQR4 and SKP2 and involved in tumorigenesis

CDK4 is crucial for Gl-to-S transition of cell cycle. It is well established that ubiquitin-mediated degradations of CDK inhibitors and cycUns are pivotal for the timely and unidirectional progression of cell cycle. However, how CDK4 itself is modulated by ubiquitin-mediated degradation has been elusive. Here we report that the steady-state level of CDK4 is controlled by PAQR4, a member of the progestin and adipoQ receptor family, and SKP2, an E3 ubiquitin ligase. Knockdown of PAQR4 leads to reduction of cell proliferation, accompanied by reduced protein level of CDK4. PAQR4 reduces polyubiquitination and degradation of CDK4. PAQR4 interacts with the C-terminal lobe of CDK4. On the other hand, SKP2 also interacts with the C-terminal lobe of CDK4 and enhances polyubiquitination and degradation of CDK4. importantly, PAQR4 and SKP2 bind to the same region in CDK4, and PAQR4 competes with SKP2 for the binding, thereby abrogating SKP2-mediated ubiquitination of CDK4. Using a two-stage DMBA/TPA-induced skin cancer model, we find that PAQR4-deleted mice are resistant to chemical carcinogen-induced tumor formation. Collectively, our findings reveal that the steady-state level of CDK4 is controlled by the antagonistic actions between PAQR4 and SKP2, contributing to modulation of cell proliferation and tumorigenesis.

Neonatal lethality and recycling defect of transferrin receptor in mice with Syntaxin12/13 disruption

Dear Editor,Iron deficiency,documented by World Health Organization(WHO),is the most common nutritional deficiency,and accounts for-50%of anemia globally.Iron-deficiency anemia is notably and frequently associated with chronic heart failure,chronic kidney disease,cancer and inflammatory bowel disease.According to WHO Global Health Estimates 2014 Summary,iron-deficiency anemia is a major and prevalent public health problem worldwide,which contributes to 0.2% mortality,especially maternal and child mortality.

Chemotherapy drugs induce pyroptosis through caspase-3-dependent cleavage of GSDME

Chemotherapy drugs can induce cancer cell death via a series of regulated cell death（RCD）pathways including apoptosis and regulated necrosis（Vanden Berghe et al.,2014）.Characterized by activation of the caspase family of cystine proteases,the occurrence of apoptosis leads to cell shrinkage and formation of apoptotic bodies.

Whole-exome sequencing identifies a novel INS mutation causative of maturity-onset diabetes of the young 10

Monognnic diabetes is often misdiagnosed with type 2 diabetes due to overlapping characteristics. This study aimed to discover novel causative mutations of monogenic diabetes in patients with clinically diagnosed type 2 diabetes and to explore potential molecular mechanisms. Whole-exome sequencing was performed on 31 individuals clinically diagnosed with type 2 diabetes. One novel heterozygnus mutation （p^la2Thr） in INS was identified. It was further gnnotyped in an additional case-control population （6523 cases and 4635 controls）, and this variant was observed in 0.09% of cases. IntraceUular trafficking of insulin proteins was assessed in INSl-E and HEK293T cells, p.Ala2Thr preproinsuUn-GFP was markedly retained in the endoplasmic reticulum （ER） in INS1-E cells. Activation of the PERK-elF2a-ATF4, IREla-XBP1, and ATF6 pathways as well as upregulated ER chaperones were detected in INS1-E cells transfected with the p.Ala2Thr mutant. In conclusion, we identified a causative mutation in IN5 respon- sible for maturity-onset diabetes of the young 10 （MODYIO） in a Chinese population and demonstrated that this mutation affected 13 cell function by inducing ER stress.

Branched chain amino acids and metabolic regulation

Amino acids are fundamental nutrients required for protein synthesis. The branched chain amino acids (BCAAs) leucine, isoleucine, and valine are the most abundant of the essential amino acids. BCAAs have recently been recognized as having functions in processes other than simple nutrition. For example, metabolic diseases are characterized by higher levels of circulating BCAAs. Moreover, supplementation with or deficiency in BCAAs is closely related to the regulation of metabolic homeostasis. Indeed, leucine deprivation induces increased lipolysis and thermogenesis, which result in fat loss, as well as suppressed lipogenesis and enhanced insulin sensitivity in the liver. Accumulating evidence has indicated that several amino acid sensors, including GCN2, ATF4, mTOR, and AMPK, play pivotal roles in the regulation of lipid metabolism, glucose metabolism, and energy homeostasis. Furthermore, the hypothalamus is critical for sensing amino acid levels and mediates the metabolic adaptation of the body upon limitation of essential amino acids (EAAs) through regulating expression of the S6K1, MC4R, and CRH. In this review, we highlight recent studies investigating the cellular mechanisms linking amino acids, amino acid sensors, metabolic regulation, and metabolic diseases. Amino acid sensing and metabolic regulation have become research hotspots in the metabolic field.

Genome engineering of stem cell organoids for disease modeling

Precision medicine emerges as a new approach that takes into account individual variability. Successful realization of precision medicine requires disease models that are able to incorporate personalized dis- ease information and recapitulate disease development processes at the molecular, cellular and organ levels. With recent development in stem cell field, a variety of tissue organoids can be derived from patient specific pluripotent stem cells and adult stem cells. In combi- nation with the state-of-the-art genome editing tools, organoids can be further engineered to mimic disease- relevant genetic and epigenetic status of a patient. This has therefore enabled a rapid expansion of sophisticated in vitro disease models, offering a unique system for fundamental and biomedical research as well as the development of personalized medicine. Here we summarize some of the latest advances and future perspectives in engineering stem cell organoids for human disease modeling.

Cellular model of neuronal atrophy induced by DYNC111 deficiency reveals protective roles of RAS-RAF-MEK signaling

Neuronal atrophy is a common pathological feature occurred in aging and neurodegenerative diseases. A variety of abnormalities including motor protein mal- function and mitochondrial dysfunction contribute to the loss of neuronal architecture; however, less is known about the intracallular signaling pathways that can pro- tect against or delay this pathogenic process. Here, we show that the DYNClll deficiency, a neuron-specific dynein intermediate chain, causes neuronal atrophy in primary hippocampal neurons. With this cellular model, we are able to find that activation of RAS-RAF.MEK signaling protects against neuronal atrophy induced by DYNClll deficiency, which relies on MEK-dependent autophagy in neuron. Moreover, we further reveal that BRAF also protects against neuronal atrophy induced by mitochondrial impairment. These findings demon- strate protective roles of the RAS-RAF-MEK axis against neuronal atrophy, and imply a new therapeutic target for clinical intervention.

Wld^(S),Nmnats and axon degeneration-progress in the past two decades

A chimeric protein called Wallerian degeneration slow(Wld^(S))was first discovered in a spontaneous mutant strain of mice that exhibited delayed Wallerian degeneration.This provides a useful tool in elucidating the mechanisms of axon degeneration.Over-expression of WldS attenuates the axon degeneration that is associated with several neurodegenerative disease models,suggesting a new logic for developing a potential protective strategy.At molecular level,although Wld^(S)is a fusion protein,the nicotinamide mononucleotide adenylyl transferase 1(Nmnat1)is required and sufficient for the protective effects of Wld^(S),indicating a critical role of NAD biosynthesis and perhaps energy metabolism in axon degeneration.These findings challenge the proposed model in which axon degeneration is operated by an active programmed process and thus may have important implication in understanding the mechanisms of neurodegeneration.In this review,we will summarize these recent findings and discuss their relevance to the mechanisms of axon degeneration.

Sympathetic transmitters control thermogenic efficacy of brown adipocytes by modulating mitochondrial complex V

Obesity is a worldwide epidemic and results from excessive energy intake or inefficient energy expenditure.It is promising to utilize the thermogenic function of brown adipose tissue for obesity intervention.However,the mechanisms controlling the efficacy of norepinephrine-induced thermogenesis in brown adipocytes remain elusive.Here we demonstrate that norepinephrine(NE)induces low-efficacy thermogenesis,evoking both heterogeneous changes(ΔΨm andΔpH)and homogenous responses,one of which is that NE stimulation causes large amounts of ATP consumption in brown adipocytes.We reveal that the proton-ATPase activity of mitochondrial complex V is a key factor that antagonizes proton leakage by UCP1 and determines the efficacy of NE-induced thermogenesis in brown adipocytes.Furthermore,to avoid unnecessary and undesired heat production,we reveal that ATP is a necessary sympathetic cotransmitter for the high efficacy and specificity of NE-induced thermogenesis in brown adipocytes as it increases intracellular calcium concentrations and upregulates the ATP synthase activity of complex V.Thus,we demonstrate the modulation mechanism of thermogenic efficacy in brown adipocytes.These findings imply new strategies to partially or fully utilize the thermogenic capacity of brown adipocytes to identify therapeutic targets for the treatment of obesity and diabetes.

Quantitative detection of single amino acid polymorphisms by targeted proteomics

Single-nucleotide polymorphisms(SNPs)are recognized as one kind of major genetic variants in population scale.However,polymorphisms at the proteome level in population scale remain elusive.In the present study,we named amino acid variances derived from SNPs within coding regions as single amino acid polymorphisms(SAPs)at the proteome level,and developed a pipeline of nontargeted and targeted proteomics to identify and quantify SAP peptides in human plasma.The absolute concentrations of three selected SAP-peptide pairs among 290 Asian individuals were measured by selected reaction monitoring(SRM)approach,and their associations with both obesity and diabetes were further analyzed.This work revealed that heterozygotes and homozygotes with various SAPs in a population could have different associations with particular traits.In addition,the SRM approach allows us for the first time to separately measure the absolute concentration of each SAP peptide in the heterozygotes,which also shows different associations with particular traits.

Eplerenone inhibits atrial fibrosis in mutant TGF-β1 transgenic mices..

The purpose of the present study was to study the impacts of eplerenone （EPL）, an antagonist of mineralocorticoid receptors （MR）, on atrial fibrosis in a mouse model with selective fibrosis in the atrium, and to explore the possible mechanisms. Using mutant TGF-β1 transgenic （Tx） mice, we first demonstrated that EPL inhibited atrial fibrosis specifically and decreased mac- rophage accumulation in the atria of these mice. Results from immunohistochemistry and western blotting showed that EPL attenuated protein expression of fibrosis-related molecules such as connective tissue growth factor （CTGF） and fibronectin in the atria of Tx mice. In culture, EPL inhibited gene expression of fibrosis-related molecules such as fibronectin, ct-SMA, and CTGF in TGF-β1-stimulated atrial fibroblasts, Finally, using a co-culture system, we showed that TGF-β1 stimulated atrial fi- broblasts induced migration of macrophages and this was blocked by EPL. EPL also blocked TGF-β1 induced gene expression of intedeukin-6 （IL-6） in atrial fibroblasts. Therefore, we conclude that EPL attenuated atrial fibrosis and macrophage infiltra- tion in Tx mice. TGF-I31 and IL-6 were involved in the impacts of EPL on activation of atrial fibroblasts and interactions be- tween fibroblasts and macrophages.

Mineralocorticoid receptor: a critical player in vascular remodeling

Vascular remodeling is a pathological condition with structural changes of blood vessels.Both inside-out and outside-in hypothesis have been put forward to describe mechanisms of vascular remodeling.An integrated model of these two hypotheses emphasizes the importance of immune cells such as monocytes/macrophages,T cells,and dendritic cells.These immune cells are at the center stage to orchestrate cellular proliferation,migration,and interactions of themselves and other vascular cells including endothelial cells(ECs),vascular smooth muscle cells(VSMCs),and fibroblasts.These changes on vascular wall lead to inflammation and oxidative stress that are largely responsible for vascular remodeling.Mineralocorticoid receptor(MR)is a classic nuclear receptor.MR agonist promotes inflammation and oxidative stress and therefore exacerbates vascular remodeling.Conversely,MR antagonists have the opposite effects.MR has direct roles on vascular cells through non-genomic or genomic actions to modulate inflammation and oxidative stress.Recent studies using genetic mouse models have revealed that MR in myeloid cells,VSMCs and ECs all contribute to vascular remodeling.In conclusion,data in the past years have demonstrated that MR is a critical control point in modulating vascular remodeling.Studies will continue to provide evidence with more detailed mechanisms to support this notion.

Thyroid hormone action in metabolic regulation

Thyroid hormone plays pivotal roles in growth,differentiation,development and metabolic homeostasis via thyroid hormone receptors(TRs)by controlling the expression of TR target genes.The transcriptional activity of TRs is modulated by multiple factors including various TR isoforms,diverse thyroid hormone response elements,different heterodimeric partners,coregulators,and the cellular location of TRs.In the present review,we summarize recent advance in understanding the molecular mechanisms of thyroid hormone action obtained from human subject research,thyroid hormone mimetics application,TR isoform-specific knock-in mouse models,and mitochondrion study with highlights in metabolic regulations.Finally,as future perspectives,we share our thoughts about current challenges and possible approaches to promote our knowledge of thyroid hormone action in metabolism.

mRNA quality control at the 5' end

All eukaryotic mRNAs are capped at their 5＇ end. Capping of mRNAs takes place co-transcriptionally and involves three steps. The intermediates of the capping process, as well as the uncapped 5＇ tri-phosphate RNA, are resistant to decapping and degradation by known factors, leading to the assumption that the capping process always proceeds to completion. This view was recently drastically changed. A novel family of enzymes, including the yeast proteins Rail, Dxo1/Ydr370C, and the mammalian protein DXO/Dom3Z, has been identified. These enzymes catalyze the conversion of the improperly capped mRNAs to 5＇ mono-phosphate RNA, allowing them to be degraded by 5＇-3＇ exoribonucleases. Several of these enzymes also possess 5＇-3＇ exoribonuclease activities themselves, and can single-handedly clear the improperly capped mRNAs. Studying of these enzymes has led to the realization that mRNA capping does not always proceed to completion, and the identification of an mRNA capping quality control mechanism in eukaryotes. In this paper, we briefly review recent advances in this area.