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Abstract

Epidemiologic and animal studies implicate overconsumption of fructose in the development of nonalcoholic fatty liver disease, but the molecular mechanisms underlying fructose-induced chronic liver diseases remain largely unknown. Here, we have presented evidence supporting the essential function of the lipogenic transcription factor carbohydrate response element–binding protein (ChREBP) in mediating adaptive responses to fructose and protecting against fructose-induced hepatotoxicity. In WT mice, a high-fructose diet (HFrD) activated hepatic lipogenesis in a ChREBP-dependent manner; however, in Chrebp-KO mice, a HFrD induced steatohepatitis. In Chrebp-KO mouse livers, a HFrD reduced levels of molecular chaperones and activated the C/EBP homologous protein–dependent (CHOP-dependent) unfolded protein response, whereas administration of a chemical chaperone or Chop shRNA rescued liver injury. Elevated expression levels of cholesterol biosynthesis genes in HFrD-fed Chrebp-KO livers were paralleled by an increased nuclear abundance of sterol regulatory element–binding protein 2 (SREBP2). Atorvastatin-mediated inhibition of hepatic cholesterol biosynthesis or depletion of hepatic Srebp2 reversed fructose-induced liver injury in Chrebp-KO mice. Mechanistically, we determined that ChREBP binds to nuclear SREBP2 to promote its ubiquitination and destabilization in cultured cells. Therefore, our findings demonstrate that ChREBP provides hepatoprotection against a HFrD by preventing overactivation of cholesterol biosynthesis and the subsequent CHOP-mediated, proapoptotic unfolded protein response. Our findings also identified a role for ChREBP in regulating SREBP2-dependent cholesterol metabolism.

Authors

Deqiang Zhang, Xin Tong, Kyle VanDommelen, Neil Gupta, Kenneth Stamper, Graham F. Brady, Zhuoxian Meng, Jiandie Lin, Liangyou Rui, M. Bishr Omary, Lei Yin

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Abstract

Obesity increases sympathetic nerve activity (SNA) via activation of proopiomelanocortin neurons in the arcuate nucleus (ArcN), and this action requires simultaneous withdrawal of tonic neuropeptide Y (NPY) sympathoinhibition. However, the sites and neurocircuitry by which NPY decreases SNA are unclear. Here, using designer receptors exclusively activated by designer drugs (DREADDs) to selectively activate or inhibit ArcN NPY neurons expressing agouti-related peptide (AgRP) in mice, we have demonstrated that this neuronal population tonically suppresses splanchnic SNA (SSNA), arterial pressure, and heart rate via projections to the paraventricular nucleus (PVN) and dorsomedial hypothalamus (DMH). First, we found that ArcN NPY/AgRP fibers closely appose PVN and DMH presympathetic neurons. Second, nanoinjections of NPY or an NPY receptor Y1 (NPY1R) antagonist into PVN or DMH decreased or increased SSNA, respectively. Third, blockade of DMH NPY1R reversed the sympathoinhibition elicited by selective, DREADD-mediated activation of ArcN NPY/AgRP neurons. Finally, stimulation of ArcN NPY/AgRP terminal fields in the PVN and DMH decreased SSNA. Considering that chronic obesity decreases ArcN NPY content, we propose that the ArcN NPY neuropathway to the PVN and DMH is pivotal in obesity-induced elevations in SNA.

Authors

Zhigang Shi, Christopher J. Madden, Virginia L. Brooks

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Abstract

Huntington’s disease is a neurodegenerative disorder caused by a polyglutamine repeat in the Huntingtin gene (HTT). Although suppressing the expression of mutant HTT (mHTT) has been explored as a therapeutic strategy to treat Huntington’s disease, considerable efforts have gone into developing allele-specific suppression of mHTT expression, given that loss of Htt in mice can lead to embryonic lethality. It remains unknown whether depletion of HTT in the adult brain, regardless of its allele, could be a safe therapy. Here, we report that permanent suppression of endogenous mHTT expression in the striatum of mHTT-expressing mice (HD140Q-knockin mice) using CRISPR/Cas9-mediated inactivation effectively depleted HTT aggregates and attenuated early neuropathology. The reduction of mHTT expression in striatal neuronal cells in adult HD140Q-knockin mice did not affect viability, but alleviated motor deficits. Our studies suggest that non–allele-specific CRISPR/Cas9-mediated gene editing could be used to efficiently and permanently eliminate polyglutamine expansion–mediated neuronal toxicity in the adult brain.

Authors

Su Yang, Renbao Chang, Huiming Yang, Ting Zhao, Yan Hong, Ha Eun Kong, Xiaobo Sun, Zhaohui Qin, Peng Jin, Shihua Li, Xiao-Jiang Li

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Abstract

Preferentially expressed antigen in melanoma (PRAME) is a cancer-testis antigen that is expressed in many cancers and leukemias. In healthy tissue, PRAME expression is limited to the testes and ovaries, making it a highly attractive cancer target. PRAME is an intracellular protein that cannot currently be drugged. After proteasomal processing, the PRAME300–309 peptide ALYVDSLFFL (ALY) is presented in the context of human leukocyte antigen HLA-A*02:01 molecules for recognition by the T cell receptor (TCR) of cytotoxic T cells. Here, we have described Pr20, a TCR mimic (TCRm) human IgG1 antibody that recognizes the cell-surface ALY peptide/HLA-A2 complex. Pr20 is an immunological tool and potential therapeutic agent. Pr20 bound to PRAME+HLA-A2+ cancers. An afucosylated Fc form (Pr20M) directed antibody-dependent cellular cytotoxicity against PRAME+HLA-A2+ leukemia cells and was therapeutically effective against mouse xenograft models of human leukemia. In some tumors, Pr20 binding markedly increased upon IFN-γ treatment, mediated by induction of the immunoproteasome catalytic subunit β5i. The immunoproteasome reduced internal destructive cleavages within the ALY epitope compared with the constitutive proteasome. The data provide rationale for developing TCRm antibodies as therapeutic agents for cancer, offer mechanistic insight on proteasomal regulation of tumor-associated peptide/HLA antigen complexes, and yield possible therapeutic solutions to target antigens with ultra-low surface presentation.

Authors

Aaron Y. Chang, Tao Dao, Ron S. Gejman, Casey A. Jarvis, Andrew Scott, Leonid Dubrovsky, Melissa D. Mathias, Tatyana Korontsvit, Victoriya Zakhaleva, Michael Curcio, Ronald C. Hendrickson, Cheng Liu, David A. Scheinberg

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Abstract

The mechanisms that regulate cell death and inflammation play an important role in liver disease and cancer. Receptor-interacting protein kinase 1 (RIPK1) induces apoptosis and necroptosis via kinase-dependent mechanisms and exhibits kinase-independent prosurvival and proinflammatory functions. Here, we have used genetic mouse models to study the role of RIPK1 in liver homeostasis, injury, and cancer. While ablating either RIPK1 or RelA in liver parenchymal cells (LPCs) did not cause spontaneous liver pathology, mice with combined deficiency of RIPK1 and RelA in LPCs showed increased hepatocyte apoptosis and developed spontaneous chronic liver disease and cancer that were independent of TNF receptor 1 (TNFR1) signaling. In contrast, mice with LPC-specific knockout of Ripk1 showed reduced diethylnitrosamine-induced (DEN-induced) liver tumorigenesis that correlated with increased DEN-induced hepatocyte apoptosis. Lack of RIPK1 kinase activity did not inhibit DEN-induced liver tumor formation, showing that kinase-independent functions of RIPK1 promote DEN-induced hepatocarcinogenesis. Moreover, mice lacking both RIPK1 and TNFR1 in LPCs displayed normal tumor formation in response to DEN, demonstrating that RIPK1 deficiency decreases DEN-induced liver tumor formation in a TNFR1-dependent manner. Therefore, these findings indicate that RIPK1 cooperates with NF-κB signaling to prevent TNFR1-independent hepatocyte apoptosis and the development of chronic liver disease and cancer, but acts downstream of TNFR1 signaling to promote DEN-induced liver tumorigenesis.

Authors

Trieu-My Van, Apostolos Polykratis, Beate Katharina Straub, Vangelis Kondylis, Nikoletta Papadopoulou, Manolis Pasparakis

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Abstract

Mutations in WNT1 cause osteogenesis imperfecta (OI) and early-onset osteoporosis, identifying it as a key Wnt ligand in human bone homeostasis. However, how and where WNT1 acts in bone are unclear. To address this mechanism, we generated late-osteoblast-specific and osteocyte-specific WNT1 loss- and gain-of-function mouse models. Deletion of Wnt1 in osteocytes resulted in low bone mass with spontaneous fractures similar to that observed in OI patients. Conversely, Wnt1 overexpression from osteocytes stimulated bone formation by increasing osteoblast number and activity, which was due in part to activation of mTORC1 signaling. While antiresorptive therapy is the mainstay of OI treatment, it has limited efficacy in WNT1-related OI. In this study, anti-sclerostin antibody (Scl-Ab) treatment effectively improved bone mass and dramatically decreased fracture rate in swaying mice, a model of global Wnt1 loss. Collectively, our data suggest that WNT1-related OI and osteoporosis are caused in part by decreased mTORC1-dependent osteoblast function resulting from loss of WNT1 signaling in osteocytes. As such, this work identifies an anabolic function of osteocytes as a source of Wnt in bone development and homoeostasis, complementing their known function as targets of Wnt signaling in regulating osteoclastogenesis. Finally, this study suggests that Scl-Ab is an effective genotype-specific treatment option for WNT1-related OI and osteoporosis.

Authors

Kyu Sang Joeng, Yi-Chien Lee, Joohyun Lim, Yuqing Chen, Ming-Ming Jiang, Elda Munivez, Catherine Ambrose, Brendan H. Lee

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Abstract

HIV-1 causes a chronic, incurable disease due to its persistence in CD4+ T cells that contain replication-competent provirus, but exhibit little or no active viral gene expression and effectively resist combination antiretroviral therapy (cART). These latently infected T cells represent an extremely small proportion of all circulating CD4+ T cells but possess a remarkable long-term stability and typically persist throughout life, for reasons that are not fully understood. Here we performed massive single-genome, near-full-length next-generation sequencing of HIV-1 DNA derived from unfractionated peripheral blood mononuclear cells, ex vivo-isolated CD4+ T cells, and subsets of functionally polarized memory CD4+ T cells. This approach identified multiple sets of independent, near-full-length proviral sequences from cART-treated individuals that were completely identical, consistent with clonal expansion of CD4+ T cells harboring intact HIV-1. Intact, near-full-genome HIV-1 DNA sequences that were derived from such clonally expanded CD4+ T cells constituted 62% of all analyzed genome-intact sequences in memory CD4 T cells, were preferentially observed in Th1-polarized cells, were longitudinally detected over a duration of up to 5 years, and were fully replication- and infection-competent. Together, these data suggest that clonal proliferation of Th1-polarized CD4+ T cells encoding for intact HIV-1 represents a driving force for stabilizing the pool of latently infected CD4+ T cells.

Authors

Guinevere Q. Lee, Nina Orlova-Fink, Kevin Einkauf, Fatema Z. Chowdhury, Xiaoming Sun, Sean Harrington, Hsiao-Hsuan Kuo, Stephane Hua, Hsiao-Rong Chen, Zhengyu Ouyang, Kavidha Reddy, Krista Dong, Thumbi Ndung’u, Bruce D. Walker, Eric S. Rosenberg, Xu G. Yu, Mathias Lichterfeld

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Abstract

BACKGROUND. The risk of advanced fibrosis in first-degree relatives of patients with nonalcoholic fatty liver disease and cirrhosis (NAFLD-cirrhosis) is unknown and needs to be systematically quantified. We aimed to prospectively assess the risk of advanced fibrosis in first-degree relatives of probands with NAFLD-cirrhosis. METHODS. This is a cross-sectional analysis of a prospective cohort of 26 probands with NAFLD-cirrhosis and 39 first-degree relatives. The control population included 69 community-dwelling twin, sib-sib, or parent-offspring pairs (n = 138), comprising 69 individuals randomly ascertained to be without evidence of NAFLD and 69 of their first-degree relatives. The primary outcome was presence of advanced fibrosis (stage 3 or 4 fibrosis). NAFLD was assessed clinically and quantified by MRI proton density fat fraction (MRI-PDFF). Advanced fibrosis was diagnosed by liver stiffness greater than 3.63 kPa using magnetic resonance elastography (MRE). RESULTS. The prevalence of advanced fibrosis in first-degree relatives of probands with NAFLD-cirrhosis was significantly higher than that in the control population (17.9% vs. 1.4%, P = 0.0032). Compared with controls, the odds of advanced fibrosis among the first-degree relatives of probands with NAFLD-cirrhosis were odds ratio 14.9 (95% CI, 1.8–126.0, P = 0.0133). Even after multivariable adjustment by age, sex, Hispanic ethnicity, BMI, and diabetes status, the risk of advanced fibrosis remained both statistically and clinically significant (multivariable-adjusted odds ratio 12.5; 95% CI, 1.1–146.1, P = 0.0438). CONCLUSION. Using a well-phenotyped familial cohort, we demonstrated that first-degree relatives of probands with NAFLD-cirrhosis have a 12 times higher risk of advanced fibrosis. Advanced fibrosis screening may be considered in first-degree relatives of NAFLD-cirrhosis patients. TRIAL REGISTRATION. UCSD IRB: 140084. FUNDING. National Institute of Diabetes and Digestive and Kidney Diseases and National Institute of Environmental Health Sciences, NIH.

Authors

Cyrielle Caussy, Meera Soni, Jeffrey Cui, Ricki Bettencourt, Nicholas Schork, Chi-Hua Chen, Mahdi Al Ikhwan, Shirin Bassirian, Sandra Cepin, Monica P. Gonzalez, Michel Mendler, Yuko Kono, Irine Vodkin, Kristin Mekeel, Jeffrey Haldorson, Alan Hemming, Barbara Andrews, Joanie Salotti, Lisa Richards, David A. Brenner, Claude B. Sirlin, Rohit Loomba, the Familial NAFLD Cirrhosis Research Consortium

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Abstract

Overconsumption of fructose and other sugars has been linked to nonalcoholic fatty liver disease (NAFLD); however, the sugar-associated effects that lead to disease are poorly defined. In this issue of the JCI, Zhang and colleagues show that the carbohydrate response element–binding protein (ChREBP) coordinates an adaptive response to a high-fructose diet in mice and that loss of this transcription factor leads to hepatic inflammation and early signs of fibrosis. Intriguingly, ChREBP-dependent effects were due to an exaggerated activation of the proapoptotic arms of the endoplasmic reticulum stress response that is probably secondary to inappropriate derepression of cholesterol biosynthesis. These findings suggest that a previously unknown link exists between ChREBP and the regulation of cholesterol synthesis that affects liver injury.

Authors

Angela M. Hall, Brian N. Finck

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Abstract

While antiretroviral therapy (ART) can reduce HIV-1 to undetectable levels, the virus generally reappears if treatment is stopped. Resurgence of the virus is due to the reactivation of T cells harboring latent integrated provirus, and recent studies indicate that proliferation of these latently infected cells helps maintain the HIV-1 reservoir. In this issue of the JCI, Lee et al. evaluated CD4+ T cell subsets to determine whether certain populations are more likely to harbor full-length, replication-competent provirus. The authors identified an enrichment of clonally expanded Th1 cells containing intact HIV-1 proviruses, suggesting that this polarized subset contributes to the persistence of the reservoir. Strategies to target these provirus-harboring cells need to be considered for future therapies aimed toward HIV-1 cure.

Authors

Kyungyoon J. Kwon, Robert F. Siliciano

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Abstract

WNT proteins drive the development and maintenance of many tissues, including bone. It is less clear which of the many WNT proteins act on bone or where these WNTs act in the skeleton; however, loss-of-function mutations in WNT1 cause bone fragility in children and adults. In this issue of the JCI, Joeng and colleagues demonstrate that bone formation is under the control of WNT1 produced by osteocytes, the cells that reside deep in the bone matrix and form dendritic networks. The implication of WNT1 in the control of bone formation identifies a potential new target for the treatment of low bone mass disorders, such as osteoporosis.

Authors

Frank Rauch

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June 2017

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June 2017 Issue

On the cover:
Coordinating apoptosis in activated neutrophils

Ebner et al. report that TTP regulates the timing of apoptosis in activated neutrophils via destabilization of the mRNA for the anti-apoptotic protein MCL-1. The cover image evokes the ephemeral nature of neutrophil engagement, depicting a neutrophil melting through an hourglass as it undergoes TTP-regulated apoptosis. Image credit: Florian Ebner.

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Jci tm 2017 06

June 2017 JCI This Month

JCI This Month is a digest of the research, reviews, and other features published each month.

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Review Series - More

Nuclear Receptors

Series edited by Mitchell A. Lazar

Nuclear receptors are a class of intracellular proteins that sense and respond to a variety of endogenous hormones, vitamins, and xenobiotic endocrine disruptors by modulating gene expression. These proteins have well-established roles in the regulation of energy balance and the skeletal system, and they are emerging as important players in other areas of human physiology and disease. Humans have 48 nuclear receptors that all possess an N-terminal transactivation domain, a highly conserved central region DNA-binding domain, and a C-terminal ligand-binding domain. Ligand binding results in the transactivation of specific genes within a given tissue. Notably, a number of nuclear receptors do not have a known endogenous ligand and structural studies indicate that they may not bind ligands at all, but instead recruit other nuclear receptors or chromatin modifiers to control gene expression. Nuclear receptor activity can be modulated through interactions with other nuclear receptors or transcriptional coactivator or corepressor proteins, as well as through modulation by numerous growth factor and cytokine signaling cascades that induce various posttranslational modifications. Reviews in this series examine the role of nuclear receptors in metabolic syndrome, cardiovascular disease, liver function, hormone-dependent cancers, responses to common therapeutic agents, genetic disorders, the effects of vitamin D, and parasitic disease.

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