Targeting YAP-mediated HSC death susceptibility and senescence for treatment of liver fibrosis.
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2023-06
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Abstract
Background and aims
Liver fibrosis results from the accumulation of myofibroblasts (MFs) derived from quiescent HSCs, and yes-associated protein (YAP) controls this state transition. Although fibrosis is also influenced by HSC death and senescence, whether YAP regulates these processes and whether this could be leveraged to treat liver fibrosis are unknown.Approach and results
YAP activity was manipulated in MF-HSCs to determine how YAP impacts susceptibility to pro-apoptotic senolytic agents or ferroptosis. Effects of senescence on YAP activity and susceptibility to apoptosis versus ferroptosis were also examined. CCl 4 -treated mice were treated with a ferroptosis inducer or pro-apoptotic senolytic to determine the effects on liver fibrosis. YAP was conditionally disrupted in MFs to determine how YAP activity in MF-HSC affects liver fibrosis in mouse models. Silencing YAP in cultured MF-HSCs induced HSC senescence and vulnerability to senolytics, and promoted ferroptosis resistance. Conversely, inducing HSC senescence suppressed YAP activity, increased sensitivity to senolytics, and decreased sensitivity to ferroptosis. Single-cell analysis of HSCs from fibrotic livers revealed heterogeneous sensitivity to ferroptosis, apoptosis, and senescence. In mice with chronic liver injury, neither the ferroptosis inducer nor senolytic improved fibrosis. However, selectively depleting YAP in MF-HSCs induced senescence and decreased liver injury and fibrosis.Conclusion
YAP determines whether MF-HSCs remain activated or become senescent. By regulating this state transition, Yap controls both HSC fibrogenic activity and susceptibility to distinct mechanisms for cell death. MF-HSC-specific YAP depletion induces senescence and protects injured livers from fibrosis. Clarifying determinants of HSC YAP activity may facilitate the development of novel anti-fibrotic therapies.Type
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Scholars@Duke
Kuo Du
Xiao-Fan Wang
The current research in the Wang laboratory mainly focuses on the elucidation of molecular nature and signaling mechanisms associated with the initiation of cellular senescence. In addition, we continue to study changes in tumor microenvironment that promotes tumor progression and metastasis, particularly how tumor cells interact with the immune system. Ultimately, we hope that our studies in these areas to lead to the development of novel therapeutics for the treatment of various types of human cancer.
Jen-Tsan Ashley Chi
We are using functional genomic approaches to investigate the nutrient signaling and stress adaptations of cancer cells when exposed to various nutrient deprivations and microenvironmental stress conditions. Recently, we focus on two areas. First, we are elucidating the genetic determinants and disease relevance of ferroptosis, a newly recognized form of cell death. Second, we have identified the mammalian stringent response pathway which is highly similar to bacterial stringent response, but with some very interesting twists and novel mechanisms.
A. The genetic determinants and disease relevance of ferroptosis
Ferroptosis is a newly recognized form of cell death that is characterized by iron dependency and lipid peroxidation. The importance of ferroptosis is being recognized in many human diseases, including cancers, ischemia injuries, and neurodegeneration. Previously, we have identified the profound cystine addiction of renal cell carcinoma (1), breast cancer cells (2, 3), and ovarian cancer cells (4). Based on the concept that cystine deprivation triggers the ferroptosis due to the unopposed oxidative stresses, we have performed functional genomic screens to identify many novel genetic determinants of ferroptosis. For example, we have found that DNA damage response and ATM kinase regulate ferroptosis via affecting iron metabolism (5). This finding supports the potential of ionizing radiation to trigger DNA damage response and synergize with ferroptosis to treat human cancers. In addition, we found that ferroptosis is highly regulated by cell density. When cells are grown at low density, they are highly susceptible to ferroptosis. In contrast, the same cells become resistant to ferroptosis when grown at high density and confluency. we have found the Hippo pathway effectors TAZ and YAP are responsible for the cell density-dependent ferroptosis (4, 6, 7). Right now, we are pursuing several other novel determinants of ferroptosis that will reveal surprising insights into this new form of cell death.
B. A new stress pathway – mammalian stress response
All living organisms encounter a wide variety of nutrient deprivations and environmental stresses. Therefore, all organisms have developed various mechanisms to respond and promote survival under stress. In bacteria, the main strategy is “stringent response” triggered by the accumulation of the alarmone (p)ppGpp (shortened to ppGpp below) via regulation of its synthetase RelA and its hydrolase SpoT (8). The ppGpp binds to the transcription factor DksA and RNA polymerase to orchestrate extensive transcriptional changes that repress proliferation and promote stress survival (8, 9). While highly conserved among bacteria, the stringent response had not been reported in metazoans. However, a recent study identified Drosophila and human MESH1 (Metazoan SpoT Homolog 1) as the homologs of the ppGpp hydrolase domain of the bacterial SpoT (10). Both MESH1 proteins exhibit ppGpp hydrolase activity, and the deletion of Mesh1 in Drosophila led to a transcriptional response reminiscent of the bacterial stringent response (10). Recently, we have found that the genetic removal of MESH1 in tumor cells triggers extensive transcriptional changes and confers protection against oxidative stress-induced ferroptosis (11). Importantly, MESH1 removal also triggers proliferative arrest and other robust anti-tumor effects. Therefore, MESH1 knockdown leads to both stress survival and proliferation arrest, two cardinal features highly reminiscent of the bacterial stringent response. Therefore, we termed this pathway as “mammalian stringent response” (12). We have found that NADPH is the relevant MESH1 in the contexts of ferroptosis (13). Now, we are investigating how MESH1 removal leads to proliferation of arrests and anti-tumor phenotypes. Furthermore, we have found several other substrates of MESH1. We are investigating their function using culture cells, MESH1 KO mice, and other model organisms.
C. Genomic and single cell RNA analysis of Red Blood Cells
Red blood cells (RBC) are responsible for oxygen delivery to muscles during vigorous exercise. Therefore, many doping efforts focus on increasing RBC number and function to boost athletic performance during competition. For many decades, RBC were thought to be merely identical “sacs of hemoglobin” with no discernable differences due to factors such as age or pre-transfusion storage time. Additionally, because RBC lose their nuclei during terminal differentiation, they were not believed to retain any genetic materials. These long-held beliefs have now been disproven and the results have significant implications for detecting autologous blood transfusion (ABT) doping in athletes. We were among the first to discover that RBCs contain abundant and diverse species of RNAs. Using this knowledge, we subsequently optimized protocols and performed genomic analysis of the RBC transcriptome in sickle cell disease; these results revealed that heterogeneous RBCs could be divided into several subpopulations, which had implications for the mechanisms of malaria resistance. As an extension of these studies, we used high resolution Illumina RNA-Seq approaches to identify hundreds of additional known and novel microRNAs, mRNAs, and other RNA species in RBCs. This dynamic RBC transcriptome represents a significant opportunity to assess the impact that environmental factors (such as pre-transfusion refrigerate storage) on the RBC transcriptome. We have now identified a >10-fold change in miR-720 as well as several other RNA transcripts whose levels are significantly altered by RBC storage (14) which gained significant press coverage. We are pursuing the genomic and single cell analysis of RNA transcriptome in the context of blood doping, sickle cell diseases and other red cell diseases.
1. Tang X, Wu J, Ding CK, Lu M, Keenan MM, Lin CC, et al. Cystine Deprivation Triggers Programmed Necrosis in VHL-Deficient Renal Cell Carcinomas. Cancer Res. 2016;76(7):1892-903.
2. Tang X, Ding CK, Wu J, Sjol J, Wardell S, Spasojevic I, et al. Cystine addiction of triple-negative breast cancer associated with EMT augmented death signaling. Oncogene. 2017;36(30):4379.
3. Lin CC, Mabe NW, Lin YT, Yang WH, Tang X, Hong L, et al. RIPK3 upregulation confers robust proliferation and collateral cystine-dependence on breast cancer recurrence. Cell Death Differ. 2020.
4. Yang WH, Huang Z, Wu J, Ding C-KC, Murphy SK, Chi J-T. A TAZ-ANGPTL4-NOX2 axis regulates ferroptotic cell death and chemoresistance in epithelial ovarian cancer. Molecular Cancer Research. 2019: molcanres.0691.2019.
5. Chen PH, Wu J, Ding CC, Lin CC, Pan S, Bossa N, et al. Kinome screen of ferroptosis reveals a novel role of ATM in regulating iron metabolism. Cell Death Differ. 2019.
6. Yang W-H, Chi J-T. Hippo pathway effectors YAP/TAZ as novel determinants of ferroptosis. Molecular & Cellular Oncology. 2019:1699375.
7. Yang WH, Ding CKC, Sun T, Hsu DS, Chi JT. The Hippo Pathway Effector TAZ Regulates Ferroptosis in Renal Cell Carcinoma Cell Reports. 2019;28(10):2501-8.e4.
8. Potrykus K, Cashel M. (p)ppGpp: still magical? Annu Rev Microbiol. 2008;62:35-51.
9. Kriel A, Bittner AN, Kim SH, Liu K, Tehranchi AK, Zou WY, et al. Direct regulation of GTP homeostasis by (p)ppGpp: a critical component of viability and stress resistance. Mol Cell. 2012;48(2):231-41.
10. Sun D, Lee G, Lee JH, Kim HY, Rhee HW, Park SY, et al. A metazoan ortholog of SpoT hydrolyzes ppGpp and functions in starvation responses. Nat Struct Mol Biol. 2010;17(10):1188-94.
11. Dixon SJ, Lemberg KM, Lamprecht MR, Skouta R, Zaitsev EM, Gleason CE, et al. Ferroptosis: an iron-dependent form of nonapoptotic cell death. Cell. 2012;149(5):1060-72.
12. Ding C-KC, Rose J, Wu J, Sun T, Chen K-Y, Chen P-H, et al. Mammalian stringent-like response mediated by the cytosolic NADPH phosphatase MESH1. bioRxiv. 2018.
13. Ding C-KC, Rose J, Sun T, Wu J, Chen P-H, Lin C-C, et al. MESH1 is a cytosolic NADPH phosphatase that regulates ferroptosis. Nature Metabolism. 2020.
14. Yang WH, Doss JF, Walzer KA, McNulty SM, Wu J, Roback JD, et al. Angiogenin-mediated tRNA cleavage as a novel feature of stored red blood cells. Br J Haematol. 2018.
Anna Mae Diehl
Our lab has a long standing interest in liver injury and repair. To learn more about the mechanisms that regulate this process, we study cultured cells, animal models of acute and chronic liver damage and samples from patients with various types of liver disease. Our group also conducts clinical trials in patients with chronic liver disease. We are particularly interested in fatty liver diseases, such as alcoholic fatty liver disease and nonalcoholic fatty liver disease (NAFLD).
Research by our group has advanced understanding in two main areas: 1) immune system regulation of liver injury and regeneration and 2)the role of fetal morphogens, such as the hedgehog pathway, in regulating fibrotic responses to liver damage. Our basic research programs have been enjoyed continuous NIH support since 1989. We welcome students, post-doctoral fellows and visiting scientists who have interests in this research area to contact us about training opportunities and potential collaborations.
Since 2001 we have also been an active participant in the NIDDK-funded Nonalcoholic Steatohepatitis Clinical Research Network (NASH CRN), a national consortium comprised of 8 university medical centers selected to generate a national registry for patients with NAFLD and to conduct multicenter treatment trials for this disorder. We are actively recruiting patients for this program, as well as a number of other industry-supported NAFLD studies.
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