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Abstract
Aberrant RNA splicing is tightly linked to diseases, including metabolic dysfunction-associated steatotic liver disease (MASLD). Here, we revealed that minor intron splicing, a unique and conserved RNA processing event, is largely disrupted upon the progression of metabolic dysfunction-associated steatohepatitis (MASH) in mice and humans. We demonstrated deficiency of minor intron splicing in the liver induces MASH transition upon obesity-induced insulin resistance and LXR activation. Mechanistically, inactivation of minor intron splicing leads to minor intron retention of Insig1 and Insig2, resulting in premature termination of translation, which drives proteolytic activation of SREBP1c. This mechanism is conserved in human patients with MASH. Notably, disrupted minor intron splicing activates glutamine reductive metabolism for de novo lipogenesis through the induction of Idh1, which causes the accumulation of ammonia in the liver, thereby initiating hepatic fibrosis upon LXR activation. Ammonia clearance or IDH1 inhibition blocks hepatic fibrogenesis and mitigates MASH progression. More importantly, the overexpression of Zrsr1 restored minor intron retention and ameliorated the development of MASH, indicating that dysfunctional minor intron splicing is an emerging pathogenic mechanism that drives MASH progression. Additionally, reductive carboxylation flux triggered by minor intron retention in hepatocytes serves as a crucial checkpoint and potential target for MASH therapy.
Authors
Yinkun Fu, Xin Peng, Hongyong Song, Xiaoyun Li, Yang Zhi, Jieting Tang, Yifan Liu, Ding Chen, Wenyan Li, Jing Zhang, Jing Ma, Ming He, Yimin Mao, Xu-Yun Zhao
Abstract
The interplay between intracellular and intravascular lipolysis is crucial for maintaining circulating lipid levels and systemic energy homeostasis. Adipose triglyceride lipase (ATGL) and lipoprotein lipase (LPL), the primary triglyceride (TG) lipases responsible for these two spatially separate processes, are highly expressed in adipose tissue. Yet, their coordinated regulation remains undetermined. Here, we demonstrate that genetic ablation of G0S2, a specific inhibitory protein of ATGL, completely abolishes diet-induced hypertriglyceridemia and significantly attenuates atherogenesis in mice. These effects are attributed to enhanced whole-body TG clearance, not altered hepatic TG secretion. Specifically, G0S2 deletion increases circulating LPL concentration and activity, predominantly through LPL production from white adipose tissue (WAT). Strikingly, transplantation of G0S2-deficient WAT normalizes plasma TG levels in mice with hypertriglyceridemia. In conjunction with improved insulin sensitivity and decreased ANGPTL4 expression, the absence of G0S2 enhances the stability of LPL protein in adipocytes, a phenomenon that can be reversed upon ATGL inhibition. Collectively, these findings highlight the pivotal role of adipocyte G0S2 in regulating both intracellular and intravascular lipolysis, and the possibility of targeting G0S2 as a viable pharmacological approach to reduce circulating TGs.
Authors
Yongbin Chen, Scott M. Johnson, Stephanie D. Burr, Davide Povero, Aaron M. Anderson, Cailin E. McMahon, Jun Liu
Maintenance of graft tissue-resident Foxp3+ cells is necessary for lung transplant tolerance in mice
Abstract
Mechanisms that mediate allograft tolerance differ between organs. We have previously shown that Foxp3+ T cell-enriched bronchus-associated lymphoid tissue (BALT) is induced in tolerant murine lung allografts and that these Foxp3+ cells suppress alloimmune responses locally and systemically. Here, we demonstrated that Foxp3+ cells that reside in tolerant lung allografts differed phenotypically and transcriptionally from those in the periphery and were clonally expanded. Using a mouse lung re-transplant model, we showed that recipient Foxp3+ cells were continuously recruited to the BALT within tolerant allografts. We identified distinguishing features of graft-resident and newly recruited Foxp3+ cells and showed that graft-infiltrating Foxp3+ cells acquired transcriptional profiles resembling those of graft-resident Foxp3+ cells over time. Allografts underwent combined antibody-mediated rejection (AMR) and acute cellular rejection (ACR) when recruitment of recipient Foxp3+ cells was prevented. Finally, we showed that local administration of IL-33 could expand and activate allograft-resident Foxp3+ cells providing a platform for the design of tolerogenic therapies for lung transplant recipients. Our findings establish graft-resident Foxp3+ cells as critical orchestrators of lung transplant tolerance and highlight the need to develop lung-specific immunosuppression.
Authors
Wenjun Li, Yuriko Terada, Yun Zhu Bai, Yuhei Yokoyama, Hailey M. Shepherd, Junedh M. Amrute, Amit I. Bery, Zhiyi Liu, Jason M. Gauthier, Marina Terekhova, Ankit Bharat, Jon H. Ritter, Varun Puri, Ramsey R. Hachem, Hēth R. Turnquist, Peter T. Sage, Alessandro Alessandrini, Maxim N. Artyomov, Kory J. Lavine, Ruben G. Nava, Alexander S. Krupnick, Andrew E. Gelman, Daniel Kreisel
Abstract
Aortic aneurysms are potentially fatal focal enlargements of the aortic lumen; the disease burden disease is increasing as the human population ages. Pathological oxidative stress is implicated in development of aortic aneurysms. We pursued a chemogenetic approach to create an animal model of aortic aneurysm formation using a transgenic mouse line DAAO-TGTie2 that expresses yeast D-amino acid oxidase (DAAO) under control of the endothelial Tie2 promoter. In DAAO-TGTie2 mice, DAAO generates the reactive oxygen species hydrogen peroxide (H2O2) in endothelial cells only when provided with D-amino acids. When DAAO-TGTie2 mice are chronically fed D-alanine, the animals become hypertensive and develop abdominal but not thoracic aortic aneurysms. Generation of H2O2 in the endothelium leads to oxidative stress throughout the vascular wall. Proteomic analyses indicate that the oxidant-modulated protein kinase JNK1 is dephosphorylated by the phophoprotein phosphatase DUSP3 in abdominal but not thoracic aorta, causing activation of KLF4-dependent transcriptional pathways that trigger phenotypic switching and aneurysm formation. Pharmacological DUSP3 inhibition completely blocks aneurysm formation caused by chemogenetic oxidative stress. These studies establish that regional differences in oxidant-modulated signaling pathways lead to differential disease progression in discrete vascular beds, and identify DUSP3 as a potential pharmacological target for the treatment of aortic aneurysms.
Authors
Apabrita Ayan Das, Markus Waldeck-Weiermair, Shambhu Yadav, Fotios Spyropoulos, Arvind Pandey, Tanoy Dutta, Taylor A. Covington, Thomas Michel
Abstract
Tissue regenerative responses involve complex interactions between resident structural and immune cells. Recent reports indicate that accumulation of senescent cells during injury repair contributes to pathological tissue fibrosis. Using tissue-based spatial transcriptomics and proteomics, we identified upregulation of the immune checkpoint protein, cytotoxic T-lymphocyte associated protein 4 (CTLA4) on CD8+ T cells adjacent to regions of active fibrogenesis in human idiopathic pulmonary fibrosis (IPF) and in a murine model of repetitive bleomycin lung injury model of persistent fibrosis. In humanized CTLA4 knock-in mice, treatment with ipilimumab, an FDA-approved drug that targets CTLA4, resulted in accelerated lung epithelial regeneration and diminished fibrosis from repetitive bleomycin injury. Ipilimumab treatment resulted in the expansion of Cd3e+ T cells, diminished accumulation of senescent cells, and robust expansion of type 2 alveolar epithelial cells, facultative progenitor cells of the alveolar epithelium. Ex-vivo activation of isolated CTLA4-expressing CD8+ cells from mice with established fibrosis resulted in enhanced cytolysis of senescent cells, suggesting that impaired immune-mediated clearance of these cells contribute to persistence of lung fibrosis in this murine model. Our studies support the concept that endogenous immune surveillance of senescent cells may be essential in promoting tissue regenerative responses that facilitate the resolution of fibrosis.
Authors
Santosh Yadav, Muralidharan Anbalagan, Shamima Khatun, Devadharshini Prabhakaran, Justin Manges, Yasuka Matsunaga, James B. McLachlan, Joseph A. Lasky, Jay Kolls, Victor J. Thannickal
Abstract
CD4+FOXP3+ regulatory T (Treg) cells maintain self-tolerance, suppress the immune response to cancer, and protect against tissue injury during acute inflammation. Treg cells require mitochondrial metabolism to function, but how Treg cells adapt their metabolic programs to optimize their function during an immune response occurring in a metabolically stressed microenvironment remains unclear. Here, we tested whether Treg cells require the energy homeostasis-maintaining enzyme AMPK to adapt to metabolically aberrant microenvironments caused by malignancy or lung injury, finding that AMPK is dispensable for Treg cell immune-homeostatic function but is necessary for full Treg cell function in B16 melanoma tumors and during influenza virus pneumonia. AMPK-deficient Treg cells had lower mitochondrial mass and exhibited an impaired ability to maximize aerobic respiration. Mechanistically, we found that AMPK regulates DNA methyltransferase 1 to promote transcriptional programs associated with mitochondrial function in the tumor microenvironment. During viral pneumonia, we found that AMPK sustains metabolic homeostasis and mitochondrial activity. Induction of DNA hypomethylation was sufficient to rescue mitochondrial mass in AMPK-deficient Treg cells, linking AMPK function to mitochondrial metabolism via DNA methylation. These results define AMPK as a determinant of Treg cell adaptation to metabolic stress and offer potential therapeutic targets in cancer and tissue injury.
Authors
Manuel A. Torres Acosta, Jonathan K. Gurkan, Qianli Liu, Nurbek Mambetsariev, Carla Reyes Flores, Kathryn A. Helmin, Anthony M. Joudi, Luisa Morales-Nebreda, Kathleen Cheng, Hiam Abdala-Valencia, Samuel E. Weinberg, Benjamin D. Singer
Abstract
BACKGROUND. Hyperinsulinemia and insulin resistance often accompany elevated serum urate levels (hyperuricemia), a highly heritable condition that triggers gout; however, the underlying mechanisms are unclear. METHODS. We evaluated the association between the index of hyperinsulinemia and the fractional excretion of urate (FEUA) in 162 outpatients. The underlying mechanisms were investigated through single-cell data analysis and kinase screening combined with cell culture experiments. In 377,358 participants of the UK Biobank (UKBB), we analyzed serum urate, hyperinsulinemia, and salt intake. We also examined gene-environment interactions using single nucleotide variants in SLC22A12, which encodes urate transporter 1 (URAT1). RESULTS. The index of hyperinsulinemia was inversely associated with FEUA independently of other covariates. Mechanistically, URAT1 cell-surface abundance and urate transport activity were regulated by URAT1-Thr408 phosphorylation, which was stimulated by hyperinsulinemia via AKT. Kinase screening and single-cell data analysis revealed that SGK1, induced by high salt, activated the same pathway, increasing URAT1. Arg405 was essential for these kinases to phosphorylate URAT1-Thr408. In UKBB participants, hyperinsulinemia and high salt intake were independently associated with increased serum urate levels. We found that SLC22A12 eQTL rs475688 synergistically enhanced the positive association between serum urate and hyperinsulinemia. CONCLUSION. URAT1 mediates the association between hyperinsulinemia and hyperuricemia. Our data provide evidence for the role of gene-environment interactions in determining serum urate levels, paving the way for personalized management of hyperuricemia. FUNDING. ACRO Research Grants of Teikyo University; JSPS; the Japanese Society of Gout and Uric & Nucleic Acids; Fuji Yakuhin; Nanken-Kyoten; Medical Research Center Initiative for High Depth Omics.
Authors
Wataru Fujii, Osamu Yamazaki, Daigoro Hirohama, Ken Kaseda, Emiko Kuribayashi-Okuma, Motonori Tsuji, Makoto Hosoyamada, Yuta Kochi, Shigeru Shibata
Abstract
Although refrigerated storage slows the metabolism of volunteer donor RBCs, which is essential in transfusion medicine, cellular aging still occurs throughout this in vitro process. Storage-induced microerythrocytes (SMEs) are morphologically-altered senescent RBCs that accumulate during storage and are cleared from circulation following transfusion. However, the molecular and cellular alterations that trigger clearance of this RBC subset remain to be identified. Using a staining protocol that sorts long-stored SMEs (i.e., CFSEhigh) and morphologically-normal RBCs (CFSElow), these in vitro aged cells were characterized. Metabolomics analysis identified depletion of energy, lipid-repair, and antioxidant metabolites in CFSEhigh RBCs. By redox proteomics, irreversible protein oxidation primarily affected CFSEhigh RBCs. By proteomics, 96 proteins, mostly in the proteostasis family, had relocated to CFSEhigh RBC membranes. CFSEhigh RBCs exhibited decreased proteasome activity and deformability; increased phosphatidylserine exposure, osmotic fragility, and endothelial cell adherence; and were cleared from the circulation during human spleen perfusion ex vivo. Conversely, molecular, cellular, and circulatory properties of long-stored CFSElow RBCs resembled those of short-stored RBCs. CFSEhigh RBCs are morphologically and metabolically altered, have irreversibly oxidized and membrane-relocated proteins, and exhibit decreased proteasome activity. In vitro aging during storage selectively alters metabolism and proteostasis in these storage-induced senescent RBCs targeted for clearance.
Authors
Sandy Peltier, Mickaël Marin, Monika Dzieciatkowska, Michaël Dussiot, Micaela Kalani Roy, Johanna Bruce, Louise Leblanc, Youcef Hadjou, Sonia Georgeault, Aurélie Fricot, Camille Roussel, Daniel Stephenson, Madeleine Casimir, Abdoulaye Sissoko, François Paye, Safi Dokmak, Papa Alioune Ndour, Philippe Roingeard, Emilie-Fleur Gautier, Steven L. Spitalnik, Olivier Hermine, Pierre A. Buffet, Angelo D’Alessandro, Pascal Amireault
Abstract
Osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs) has been recognized as the principal mechanism underlying vascular calcification (VC). Runt-related transcription factor 2 (RUNX2) in VSMCs plays a pivotal role because it constitutes an essential osteogenic transcription factor for bone formation. As a key DNA demethylation enzyme, ten-eleven translocation 2 (TET2) is crucial in maintaining the VSMC phenotype. However, whether TET2 involves in VC progression remains elusive. Here we identified a substantial downregulation of TET2 in calcified human and mouse arteries, as well as human primary VSMCs. In vitro gain- and loss-of function experiments demonstrated TET2 regulated VC. Subsequently, in vivo knockdown of TET2 significantly exacerbated VC in both vitamin D3 and adenine-diet-induced chronic kidney disease (CKD) mice models. Mechanistically, TET2 binds to and suppresses the activity of the P2 promoter within the RUNX2 gene, whereas an enzymatic loss-of-function mutation of TET2 has a comparable effect. Furthermore, TET2 forms a complex with histone deacetylases 1/2 (HDAC1/2 ) to deacetylate H3K27ac on the P2 promoter, thereby inhibiting its transcription. Moreover, SNIP1 is indispensable for TET2 to interact with HDAC1/2 to exert inhibitory effect on VC, and knockdown of SNIP1 accelerated VC in mice. Collectively, our findings imply that TET2 might serve as a potential therapeutic target for VC.
Authors
Dayu He, Jianshuai Ma, Ziting Zhou, Yanli Qi, Yaxin Lian, Feng Wang, Huiyong Yin, Huanji Zhang, Tingting Zhang, Hui Huang
Abstract
Biological targeting is crucial for effective cancer treatment with reduced toxicity but is limited by the availability of tumor surface markers. To overcome this, we developed a nanoparticle-based, Tumor-specific suRfACE maRker-independent (TRACER) targeting approach. Utilizing the unique biodistribution properties of nanoparticles, we encapsulated Ac4ManNAz to selectively label tumors with azide reactive groups. Surprisingly, while NP-delivered Ac4ManNAz was cleared by the liver, it did not label macrophages, potentially reducing off-target effects. To exploit this tumor-specific labeling, we functionalized anti-4-1BB antibodies with dibenzocyclooctyne (DBCO) to target azide-labeled tumor cells and activate the immune response. In syngeneic B16F10 melanoma and orthotopic 4T1 breast cancer models, TRACER enhanced anti-4-1BB’s therapeutic efficacy, increasing median survival time. Immunofluorescence analyses revealed increased tumor infiltration of CD8+ T and NK cells with TRACER. Importantly, TRACER reduced hepatotoxicity associated with anti-4-1BB, resulting in normal serum ALT and AST levels and decreased CD8+ T cell infiltration in the liver. Quantitative analysis confirmed a 4.5-fold higher tumor-to-liver ratio of anti-4-1BB accumulation with TRACER compared to conventional anti-4-1BB antibodies. Our work provides a promising approach for developing targeted cancer therapies that circumvent limitations imposed by the paucity of tumor-specific markers, potentially improving efficacy and reducing off-target effects to overcome liver toxicity associated with anti-4-1BB.
Authors
Hyesun Hyun, Bo Sun, Mostafa Yazdimamaghani, Albert Wielgus, Yue Wang, Stephanie Ann Montgomery, Tian Zhang, Jianjun Cheng, Jonathan S. Serody, Andrew Z. Wang
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ISSN: 0021-9738 (print), 1558-8238 (online)