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Abstract
Hepatic myofibroblasts are activated in response to chronic liver injury of any etiology to produce a fibrous scar. Despite extensive studies, the origin of myofibroblasts in different types of fibrotic liver diseases is unresolved. To identify distinct populations of myofibroblasts and quantify their contribution to hepatic fibrosis of two different etiologies, collagen-α1(I)-GFP mice were subjected to hepatotoxic (carbon tetrachloride; CCl4) or cholestatic (bile duct ligation; BDL) liver injury. All myofibroblasts were purified by flow cytometry of GFP(+) cells and then different subsets identified by phenotyping. Liver resident activated hepatic stellate cells (aHSCs) and activated portal fibroblasts (aPFs) are the major source (>95%) of fibrogenic myofibroblasts in these models of liver fibrosis in mice. As previously reported using other methodologies, hepatic stellate cells (HSCs) are the major source of myofibroblasts (>87%) in CCl4 liver injury. However, aPFs are a major source of myofibroblasts in cholestatic liver injury, contributing >70% of myofibroblasts at the onset of injury (5 d BDL). The relative contribution of aPFs decreases with progressive injury, as HSCs become activated and contribute to the myofibroblast population (14 and 20 d BDL). Unlike aHSCs, aPFs respond to stimulation with taurocholic acid and IL-25 by induction of collagen-α1(I) and IL-13, respectively. Furthermore, BDL-activated PFs express high levels of collagen type I and provide stimulatory signals to HSCs. Gene expression analysis identified several novel markers of aPFs, including a mesothelial-specific marker mesothelin. PFs may play a critical role in the pathogenesis of cholestatic liver fibrosis and, therefore, serve as an attractive target for antifibrotic therapy.
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Xu J, Liu X, Koyama Y, Wang P, Lan T, Kim IG, Kim IH, Ma HY, Kisseleva T. The types of hepatic myofibroblasts contributing to liver fibrosis of different etiologies. Front Pharmacol 2014; 5:167. [PMID: 25100997 PMCID: PMC4105921 DOI: 10.3389/fphar.2014.00167] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Accepted: 06/25/2014] [Indexed: 01/18/2023] Open
Abstract
Liver fibrosis results from dysregulation of normal wound healing, inflammation, activation of myofibroblasts, and deposition of extracellular matrix (ECM). Chronic liver injury causes death of hepatocytes and formation of apoptotic bodies, which in turn, release factors that recruit inflammatory cells (neutrophils, monocytes, macrophages, and lymphocytes) to the injured liver. Hepatic macrophages (Kupffer cells) produce TGFβ1 and other inflammatory cytokines that activate Collagen Type I producing myofibroblasts, which are not present in the normal liver. Secretion of TGFβ1 and activation of myofibroblasts play a critical role in the pathogenesis of liver fibrosis of different etiologies. Although the composition of fibrogenic myofibroblasts varies dependent on etiology of liver injury, liver resident hepatic stellate cells and portal fibroblasts are the major source of myofibroblasts in fibrotic liver in both experimental models of liver fibrosis and in patients with liver disease. Several studies have demonstrated that hepatic fibrosis can reverse upon cessation of liver injury. Regression of liver fibrosis is accompanied by the disappearance of fibrogenic myofibroblasts followed by resorption of the fibrous scar. Myofibroblasts either apoptose or inactivate into a quiescent-like state (e.g., stop collagen production and partially restore expression of lipogenic genes). Resolution of liver fibrosis is associated with recruitment of macrophages that secrete matrix-degrading enzymes (matrix metalloproteinase, collagenases) and are responsible for fibrosis resolution. However, prolonged/repeated liver injury may cause irreversible crosslinking of ECM and formation of uncleavable collagen fibers. Advanced fibrosis progresses to cirrhosis and hepatocellular carcinoma. The current review will summarize the role and contribution of different cell types to populations of fibrogenic myofibroblasts in fibrotic liver.
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Affiliation(s)
- Jun Xu
- School of Medicine, University of California at San Diego La Jolla, CA, USA
| | - Xiao Liu
- School of Medicine, University of California at San Diego La Jolla, CA, USA
| | - Yukinori Koyama
- School of Medicine, University of California at San Diego La Jolla, CA, USA
| | - Ping Wang
- School of Medicine, University of California at San Diego La Jolla, CA, USA
| | - Tian Lan
- School of Medicine, University of California at San Diego La Jolla, CA, USA
| | - In-Gyu Kim
- School of Medicine, University of California at San Diego La Jolla, CA, USA
| | - In H Kim
- School of Medicine, University of California at San Diego La Jolla, CA, USA
| | - Hsiao-Yen Ma
- School of Medicine, University of California at San Diego La Jolla, CA, USA
| | - Tatiana Kisseleva
- School of Medicine, University of California at San Diego La Jolla, CA, USA
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Blackstock CD, Higashi Y, Sukhanov S, Shai SY, Stefanovic B, Tabony AM, Yoshida T, Delafontaine P. Insulin-like growth factor-1 increases synthesis of collagen type I via induction of the mRNA-binding protein LARP6 expression and binding to the 5' stem-loop of COL1a1 and COL1a2 mRNA. J Biol Chem 2014; 289:7264-74. [PMID: 24469459 PMCID: PMC3953245 DOI: 10.1074/jbc.m113.518951] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Revised: 01/15/2014] [Indexed: 12/27/2022] Open
Abstract
Collagen content in atherosclerotic plaque is a hallmark of plaque stability. Our earlier studies showed that insulin-like growth factor-1 (IGF-1) increases collagen content in atherosclerotic plaques of Apoe(-/-) mice. To identify mechanisms we investigated the effect of IGF-1 on the la ribonucleoprotein domain family member 6 (LARP6). LARP6 binds a stem-loop motif in the 5'-UTR of the mRNAs encoding the collagen type I α-subunits (α1(I) and α2(I)), and coordinates their translation into the heterotrimeric collagen type I molecule. In human aortic smooth muscle cells (SMCs), IGF-1 rapidly increased LARP6 expression and the rate of collagen synthesis and extracellular accumulation. IGF-1 increased both LARP6 and collagen type I expression via a post-transcriptional and translation-dependent mechanism involving PI3K/Akt/p70S6k-signaling. Immunoprecipitation of LARP6, followed by qPCR indicated that IGF-1 increased the level of COL1a1 and COL1a2 mRNA bound to LARP6. Mutation of the 5' stem-loop of Col1a1 mRNA, which inhibits binding of LARP6, abolished the ability of IGF-1 to increase synthesis of collagen type I. Furthermore, overexpression of a 5' stem-loop RNA molecular decoy that sequesters LARP6, prevented the ability of IGF-1 to increase pro-α1(I) and mature α1(I) expression in cultured medium. IGF-1 infusion in Apoe(-/-) mice increased expression of LARP6 and pro-α1(I) in aortic lysates, and SMC-specific IGF-1-overexpression robustly increased collagen fibrillogenesis in atherosclerotic plaque. In conclusion, we identify LARP6 as a critical mediator by which IGF-1 augments synthesis of collagen type I in vascular smooth muscle, which may play an important role in promoting atherosclerotic plaque stability.
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Affiliation(s)
- Christopher D. Blackstock
- From the Heart and Vascular Institute, and Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112 and
| | - Yusuke Higashi
- From the Heart and Vascular Institute, and Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112 and
| | - Sergiy Sukhanov
- From the Heart and Vascular Institute, and Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112 and
| | - Shaw-Yung Shai
- From the Heart and Vascular Institute, and Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112 and
| | - Branko Stefanovic
- the Department of Biomedical Science, College of Medicine, Florida State University, Tallahassee, Florida 32306
| | - A. Michael Tabony
- From the Heart and Vascular Institute, and Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112 and
| | - Tadashi Yoshida
- From the Heart and Vascular Institute, and Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112 and
| | - Patrice Delafontaine
- From the Heart and Vascular Institute, and Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112 and
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Stefanovic L, Longo L, Zhang Y, Stefanovic B. Characterization of binding of LARP6 to the 5' stem-loop of collagen mRNAs: implications for synthesis of type I collagen. RNA Biol 2014; 11:1386-401. [PMID: 25692237 PMCID: PMC4615758 DOI: 10.1080/15476286.2014.996467] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Accepted: 10/31/2014] [Indexed: 01/11/2023] Open
Abstract
Type I collagen is composed of 2 polypeptides, α1(I) and α2(I), which fold into triple helix. Collagen α1(I) and α2(I) mRNAs have a conserved stem-loop structure in their 5' UTRs, the 5'SL. LARP6 binds the 5'SL to regulate type I collagen expression. We show that 5 nucleotides within the single stranded regions of 5'SL contribute to the high affinity of LARP6 binding. Mutation of individual nucleotides abolishes the binding in gel mobility shift assay. LARP6 binding to 5'SL of collagen α2(I) mRNA is more stable than the binding to 5'SL of α1(I) mRNA, although the equilibrium binding constants are similar. The more stable binding to α2(I) mRNA may favor synthesis of the heterotrimeric type I collagen. LARP6 needs 2 domains to contact 5'SL, the La domain and the RRM. T133 in the La domain is critical for folding of the protein, while loop 3 in the RRM is critical for binding 5'SL. Loop 3 is also involved in the interaction of LARP6 and protein translocation channel SEC61. This interaction is essential for type I collagen synthesis, because LARP6 mutant which binds 5'SL but which does not interact with SEC61, suppresses collagen synthesis in a dominant negative manner. We postulate that LARP6 directly targets collagen mRNAs to the SEC61 translocons to facilitate coordinated translation of the 2 collagen mRNAs. The unique sequences of LARP6 identified in this work may have evolved to enable its role in type I collagen biosynthesis.
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Affiliation(s)
- Lela Stefanovic
- Department of Biomedical Sciences; College of Medicine; Florida State University; Tallahassee, FL USA
- Current affiliation: Molecular Biophysics; Florida State University; Tallahassee, FL USA
| | - Liam Longo
- Current affiliation: Molecular Biophysics; Florida State University; Tallahassee, FL USA
| | - Yujie Zhang
- Department of Biomedical Sciences; College of Medicine; Florida State University; Tallahassee, FL USA
- Current affiliation: Molecular Biophysics; Florida State University; Tallahassee, FL USA
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Vukmirovic M, Manojlovic Z, Stefanovic B. Serine-threonine kinase receptor-associated protein (STRAP) regulates translation of type I collagen mRNAs. Mol Cell Biol 2013; 33:3893-906. [PMID: 23918805 PMCID: PMC3811873 DOI: 10.1128/mcb.00195-13] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Accepted: 07/08/2013] [Indexed: 11/20/2022] Open
Abstract
Type I collagen is the most abundant protein in the human body and is composed of two α1(I) and one α2(I) polypeptides which assemble into a triple helix. For the proper assembly of the collagen triple helix, the individual polypeptides must be translated in coordination. Here, we show that serine-threonine kinase receptor-associated protein (STRAP) is tethered to collagen mRNAs by interaction with LARP6. LARP6 is a protein which directly binds the 5' stem-loop (5'SL) present in collagen α1(I) and α2(I) mRNAs, but it interacts with STRAP with its C-terminal domain, which is not involved in binding 5'SL. Being tethered to collagen mRNAs, STRAP prevents unrestricted translation, primarily that of collagen α2(I) mRNAs, by interacting with eukaryotic translation initiation factor 4A (eIF4A). In the absence of STRAP, more collagen α2(I) mRNA can be pulled down with eIF4A, and collagen α2(I) mRNA is unrestrictedly loaded onto the polysomes. This results in an imbalance of synthesis of α1(I) and α2(I) polypeptides, in hypermodifications of α1(I) polypeptide, and in inefficient assembly of the polypeptides into a collagen trimer and their secretion as monomers. These defects can be partially restored by supplementing STRAP. Thus, we discovered STRAP as a novel regulator of the coordinated translation of collagen mRNAs.
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Affiliation(s)
- Milica Vukmirovic
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, USA
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Manojlovic Z, Blackmon J, Stefanovic B. Tacrolimus (FK506) prevents early stages of ethanol induced hepatic fibrosis by targeting LARP6 dependent mechanism of collagen synthesis. PLoS One 2013; 8:e65897. [PMID: 23755290 PMCID: PMC3670911 DOI: 10.1371/journal.pone.0065897] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Accepted: 04/29/2013] [Indexed: 01/06/2023] Open
Abstract
Tacrolimus (FK506) is a widely used immunosuppressive drug. Its effects on hepatic fibrosis have been controversial and attributed to immunosuppression. We show that in vitro FK506, inhibited synthesis of type I collagen polypeptides, without affecting expression of collagen mRNAs. In vivo, administration of FK506 at a dose of 4 mg/kg completely prevented development of alcohol/carbon tetrachloride induced liver fibrosis in rats. Activation of hepatic stellate cells (HSCs) was absent in the FK506 treated livers and expression of collagen α2(I) mRNA was at normal levels. Collagen α1(I) mRNA was increased in the FK506 treated livers, but this mRNA was not translated into α1(I) polypeptide. No significant inflammation was associated with the fibrosis model used. FK506 binding protein 3 (FKBP3) is one of cellular proteins which binds FK506 with high affinity. We discovered that FKBP3 interacts with LARP6 and LARP6 is the major regulator of translation and stability of collagen mRNAs. In the presence of FK506 the interaction between FKBP3 and LARP6 is weakened and so is the pull down of collagen mRNAs with FKBP3. We postulate that FK506 inactivates FKBP3 and that lack of interaction of LARP6 and FKBP3 results in aberrant translation of collagen mRNAs and prevention of fibrosis. This is the first report of such activity of FK506 and may renew the interest in using this drug to alleviate hepatic fibrosis.
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Affiliation(s)
- Zarko Manojlovic
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, United States of America
| | - John Blackmon
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, United States of America
| | - Branko Stefanovic
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, United States of America
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Myofibroblasts revert to an inactive phenotype during regression of liver fibrosis. Proc Natl Acad Sci U S A 2012; 109:9448-53. [PMID: 22566629 DOI: 10.1073/pnas.1201840109] [Citation(s) in RCA: 580] [Impact Index Per Article: 48.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Myofibroblasts produce the fibrous scar in hepatic fibrosis. In the carbon tetrachloride (CCl(4)) model of liver fibrosis, quiescent hepatic stellate cells (HSC) are activated to become myofibroblasts. When the underlying etiological agent is removed, clinical and experimental fibrosis undergoes a remarkable regression with complete disappearance of these myofibroblasts. Although some myofibroblasts apoptose, it is unknown whether other myofibroblasts may revert to an inactive phenotype during regression of fibrosis. We elucidated the fate of HSCs/myofibroblasts during recovery from CCl(4)- and alcohol-induced liver fibrosis using Cre-LoxP-based genetic labeling of myofibroblasts. Here we demonstrate that half of the myofibroblasts escape apoptosis during regression of liver fibrosis, down-regulate fibrogenic genes, and acquire a phenotype similar to, but distinct from, quiescent HSCs in their ability to more rapidly reactivate into myofibroblasts in response to fibrogenic stimuli and strongly contribute to liver fibrosis. Inactivation of HSCs was associated with up-regulation of the anti-apoptotic genes Hspa1a/b, which participate in the survival of HSCs in culture and in vivo.
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Kisseleva T, Brenner DA. The phenotypic fate and functional role for bone marrow-derived stem cells in liver fibrosis. J Hepatol 2012; 56:965-72. [PMID: 22173163 PMCID: PMC3307836 DOI: 10.1016/j.jhep.2011.09.021] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/05/2011] [Revised: 08/12/2011] [Accepted: 09/04/2011] [Indexed: 12/13/2022]
Abstract
Liver fibrosis is an outcome of chronic liver injury of any etiology. It is manifested by extensive deposition of extracellular matrix (ECM) proteins that produce a fibrous scar in the injured liver. Bone marrow (BM) cells may play an important role in pathogenesis and resolution of liver fibrosis. BM cells contribute to the inflammatory response by TGF-β1 secretion and activation of liver resident myofibroblasts. Moreover, BM itself can serve as a source of collagen expressing cells, e.g. BM-derived fibrocytes and mesenchymal progenitors, which in turn, have a potential to in situ differentiate into fibrogenic myofibroblasts and facilitate fibrosis. Finally, BM cells play an active part in resolution of liver fibrosis after cessation of fibrogenic stimuli. While natural killer (NK) cells are implicated in apoptosis of activated hepatic stellate cells/myofibroblasts, cells of myelo-monocitic lineage secrete matrix metalloproteinases to actively degrade the fibrous scar. The focus of this review is on the current understanding of the role of different subsets of BM cells in the onset, development and resolution of liver fibrosis.
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Manojlovic Z, Stefanovic B. A novel role of RNA helicase A in regulation of translation of type I collagen mRNAs. RNA (NEW YORK, N.Y.) 2012; 18:321-34. [PMID: 22190748 PMCID: PMC3264918 DOI: 10.1261/rna.030288.111] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Accepted: 11/04/2011] [Indexed: 05/30/2023]
Abstract
Type I collagen is composed of two α1(I) polypeptides and one α2(I) polypeptide and is the most abundant protein in the human body. Expression of type I collagen is primarily controlled at the level of mRNA stability and translation. Coordinated translation of α(I) and α2(I) mRNAs is necessary for efficient folding of the corresponding peptides into the collagen heterotrimer. In the 5' untranslated region (5' UTR), collagen mRNAs have a unique 5' stem-loop structure (5' SL). La ribonucleoprotein domain family member 6 (LARP6) is the protein that binds 5' SL with high affinity and specificity and coordinates their translation. Here we show that RNA helicase A (RHA) is tethered to the 5' SL of collagen mRNAs by interaction with the C-terminal domain of LARP6. In vivo, collagen mRNAs immunoprecipitate with RHA in an LARP6-dependent manner. Knockdown of RHA prevents formation of polysomes on collagen mRNAs and dramatically reduces synthesis of collagen protein, without affecting the level of the mRNAs. A reporter mRNA with collagen 5' SL is translated three times more efficiently in the presence of RHA than the same reporter without the 5' SL, indicating that the 5' SL is the cis-acting element conferring the regulation. During activation of quiescent cells into collagen-producing cells, expression of RHA is highly up-regulated. We postulate that RHA is recruited to the 5' UTR of collagen mRNAs by LARP6 to facilitate their translation. Thus, RHA has been discovered as a critical factor for synthesis of the most abundant protein in the human body.
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Affiliation(s)
- Zarko Manojlovic
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306, USA
| | - Branko Stefanovic
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306, USA
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Luchsinger LL, Patenaude CA, Smith BD, Layne MD. Myocardin-related transcription factor-A complexes activate type I collagen expression in lung fibroblasts. J Biol Chem 2011; 286:44116-44125. [PMID: 22049076 DOI: 10.1074/jbc.m111.276931] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Pulmonary fibrosis is characterized by the excessive deposition of a collagen-rich extracellular matrix. The accumulation of collagen within the lung interstitium leads to impaired respiratory function. Furthermore, smooth muscle actin-positive myofibroblasts within the fibrotic lung contribute to disease progression. Because collagen and smooth muscle cell α-actin are coordinately expressed in the setting of fibrosis, the hypothesis was tested that specific transcriptional regulators of the myocardin family might also regulate collagen gene expression in myofibroblasts. Myocardin-related transcription factors (MRTFs), through their interaction with the serum-response factor (SRF) on CArG box regulatory elements (CC(A/T)6GG), are important regulators of myofibroblast differentiation. MRTF-A transactivated type I collagen gene reporters as much as 100-fold in lung myofibroblasts. Loss of functional MRTF-A using either a dominant negative MRTF-A isoform, shRNA targeting MRTF-A, or genetic deletion of MRTF-A in lung fibroblasts significantly disrupted type I collagen synthesis relative to controls. Analysis of the COL1A2 proximal promoter revealed a noncanonical CArG box (CCAAACTTGG), flanked by several Sp1 sites important for MRTF-A activation. Chromatin immunoprecipitation experiments confirmed the co-localization of MRTF-A, SRF, and Sp1 bound to the same region of the COL1A2 promoter. Mutagenesis of either the noncanonical CArG box or the Sp1 sites significantly disrupted MRTF-A activation of COL1A2. Together, our findings show that MRTF-A is an important regulator of collagen synthesis in lung fibroblasts and exhibits a dependence on both SRF and Sp1 function to enhance collagen expression.
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Affiliation(s)
- Larry L Luchsinger
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Cassandra A Patenaude
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Barbara D Smith
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.
| | - Matthew D Layne
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.
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Parker BJ, Moltke I, Roth A, Washietl S, Wen J, Kellis M, Breaker R, Pedersen JS. New families of human regulatory RNA structures identified by comparative analysis of vertebrate genomes. Genome Res 2011; 21:1929-43. [PMID: 21994249 DOI: 10.1101/gr.112516.110] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Regulatory RNA structures are often members of families with multiple paralogous instances across the genome. Family members share functional and structural properties, which allow them to be studied as a whole, facilitating both bioinformatic and experimental characterization. We have developed a comparative method, EvoFam, for genome-wide identification of families of regulatory RNA structures, based on primary sequence and secondary structure similarity. We apply EvoFam to a 41-way genomic vertebrate alignment. Genome-wide, we identify 220 human, high-confidence families outside protein-coding regions comprising 725 individual structures, including 48 families with known structural RNA elements. Known families identified include both noncoding RNAs, e.g., miRNAs and the recently identified MALAT1/MEN β lincRNA family; and cis-regulatory structures, e.g., iron-responsive elements. We also identify tens of new families supported by strong evolutionary evidence and other statistical evidence, such as GO term enrichments. For some of these, detailed analysis has led to the formulation of specific functional hypotheses. Examples include two hypothesized auto-regulatory feedback mechanisms: one involving six long hairpins in the 3'-UTR of MAT2A, a key metabolic gene that produces the primary human methyl donor S-adenosylmethionine; the other involving a tRNA-like structure in the intron of the tRNA maturation gene POP1. We experimentally validate the predicted MAT2A structures. Finally, we identify potential new regulatory networks, including large families of short hairpins enriched in immunity-related genes, e.g., TNF, FOS, and CTLA4, which include known transcript destabilizing elements. Our findings exemplify the diversity of post-transcriptional regulation and provide a resource for further characterization of new regulatory mechanisms and families of noncoding RNAs.
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Affiliation(s)
- Brian J Parker
- The Bioinformatics Centre, Department of Biology, University of Copenhagen, DK-2200 Copenhagen, Denmark.
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Thompson KJ, McKillop IH, Schrum LW. Targeting collagen expression in alcoholic liver disease. World J Gastroenterol 2011; 17:2473-81. [PMID: 21633652 PMCID: PMC3103805 DOI: 10.3748/wjg.v17.i20.2473] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Revised: 04/17/2011] [Accepted: 04/24/2011] [Indexed: 02/06/2023] Open
Abstract
Alcoholic liver disease (ALD) is a leading cause of liver disease and liver-related deaths globally, particularly in developed nations. Liver fibrosis is a consequence of ALD and other chronic liver insults, which can progress to cirrhosis and hepatocellular carcinoma if left untreated. Liver fibrosis is characterized by accumulation of excess extracellular matrix components, including type I collagen, which disrupts liver microcirculation and leads to injury. To date, there is no therapy for the treatment of liver fibrosis; thus treatments that either prevent the accumulation of type I collagen or hasten its degradation are desirable. The focus of this review is to examine the regulation of type I collagen in fibrogenic cells of the liver and to discuss current advances in therapeutics to eliminate excessive collagen deposition.
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Parsons CJ, Stefanovic B, Seki E, Aoyama T, Latour AM, Marzluff WF, Rippe RA, Brenner DA. Mutation of the 5'-untranslated region stem-loop structure inhibits α1(I) collagen expression in vivo. J Biol Chem 2010; 286:8609-8619. [PMID: 21193410 DOI: 10.1074/jbc.m110.189118] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Type I collagen is a heterotrimeric extracellular matrix protein consisting of two α1(I) chains and one α2(I) chain. During liver fibrosis, activated hepatic stellate cells (HSCs) are the major source of the type I collagen that accumulates in the damaged tissue. Expression of α1(I) and α2(I) collagen mRNA is increased 60-fold compared with quiescent stellate cells and is due predominantly to post-transcriptional message regulation. Specifically, a stem-loop structure in the 5'-untranslated region of α1(I) collagen mRNA may regulate mRNA expression in activated HSCs through its interaction with stem-loop binding proteins. The stem-loop may also be necessary for efficient production and folding of the type I collagen heterotrimer. To assess the role of the stem-loop in type I collagen expression in vivo, we generated a knock-in mouse harboring a mutation that abolished the stem-loop structure. Heterozygous and homozygous knock-in mice exhibited a normal phenotype. However, steady-state levels of α1(I) collagen mRNA decreased significantly in homozygous mutant MEFs as well as HSCs; intracellular and secreted type I collagen protein levels also decreased. Homozygous mutant mice developed less liver fibrosis. These results confirm an important role of the 5' stem-loop in regulating type I collagen mRNA and protein expression and provide a mouse model for further study of collagen-associated diseases.
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Affiliation(s)
| | - Branko Stefanovic
- the Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32306-4300, and
| | - Ekihiro Seki
- the Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093
| | - Tomonori Aoyama
- the Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093
| | | | | | - Richard A Rippe
- the Division of Gastroenterology and Hepatology, Department of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7080
| | - David A Brenner
- the Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093.
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Cai L, Fritz D, Stefanovic L, Stefanovic B. Nonmuscle myosin-dependent synthesis of type I collagen. J Mol Biol 2010; 401:564-78. [PMID: 20603131 DOI: 10.1016/j.jmb.2010.06.057] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Revised: 06/09/2010] [Accepted: 06/25/2010] [Indexed: 01/15/2023]
Abstract
Type I collagen, synthesized in all tissues as the heterotrimer of two alpha1(I) polypeptides and one alpha2(I) polypeptide, is the most abundant protein in the human body. Here we show that intact nonmuscle myosin filaments are required for the synthesis of heterotrimeric type I collagen. Conserved 5' stem-loop in collagen alpha1(I) and alpha2(I) mRNAs binds the RNA-binding protein LARP6. LARP6 interacts with nonmuscle myosin through its C-terminal domain and associates collagen mRNAs with the filaments. Dissociation of nonmuscle myosin filaments results in secretion of collagen alpha1(I) homotrimer, diminished intracellular colocalization of collagen alpha1(I) and alpha2(I) polypeptides (required for folding of the heterotrimer), and their increased intracellular degradation. Inhibition of the motor function of myosin has similar collagen-specific effects, while disruption of actin filaments has a general effect on protein secretion. Nonmuscle myosin copurifies with polysomes, and there is a subset of polysomes involved in myosin-dependent translation of collagen mRNAs. These results indicate that association of collagen mRNAs with nonmuscle myosin filaments is necessary to coordinately synthesize collagen alpha1(I) and alpha2(I) polypeptides. We postulate that LARP6/myosin-dependent mechanism regulates the synthesis of heterotrimeric type I collagen by coordinating the translation of collagen mRNAs.
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Affiliation(s)
- Le Cai
- Department of Biomedical Sciences, College of Medicine, Florida State University, 1115 West Call Street, Tallahassee, FL 32306, USA
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15
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Cai L, Fritz D, Stefanovic L, Stefanovic B. Binding of LARP6 to the conserved 5' stem-loop regulates translation of mRNAs encoding type I collagen. J Mol Biol 2010; 395:309-26. [PMID: 19917293 PMCID: PMC2826804 DOI: 10.1016/j.jmb.2009.11.020] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Revised: 11/05/2009] [Accepted: 11/09/2009] [Indexed: 10/20/2022]
Abstract
Type I collagen is the most abundant protein in the human body, produced by folding of two alpha1(I) polypeptides and one alpha2(I) polypeptide into the triple helix. A conserved stem-loop structure is found in the 5' untranslated region of collagen mRNAs, encompassing the translation start codon. We cloned La ribonucleoprotein domain family member 6 (LARP6) as the protein that binds the collagen 5' stem-loop in a sequence-specific manner. LARP6 has a distinctive bipartite RNA binding domain not found in other members of the La superfamily. LARP6 interacts with the two single-stranded regions of the 5' stem-loop. The K(d) for binding of LARP6 to the 5' stem-loop is 1.4 nM. LARP6 binds the 5' stem-loop in both the nucleus and the cytoplasm. In the cytoplasm, LARP6 does not associate with polysomes; however, overexpression of LARP6 blocks ribosomal loading on collagen mRNAs. Knocking down LARP6 by small interfering RNA also decreased polysomal loading of collagen mRNAs, suggesting that it regulates translation. Collagen protein is synthesized at discrete regions of the endoplasmic reticulum. Using collagen-GFP (green fluorescent protein) reporter protein, we could reproduce this focal pattern of synthesis, but only when the reporter was encoded by mRNA with the 5' stem-loop and in the presence of LARP6. When the reporter was encoded by mRNA without the 5' stem-loop, or in the absence of LARP6, it accumulated diffusely throughout the endoplasmic reticulum. This indicates that LARP6 activity is needed for focal synthesis of collagen polypeptides. We postulate that the LARP6-dependent mechanism increases local concentration of collagen polypeptides for more efficient folding of the collagen heterotrimer.
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Affiliation(s)
- Le Cai
- Department of Biomedical Sciences, College of Medicine, Tallahassee, FL 32306, USA
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16
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Cubero FJ, Nieto N. Ethanol and arachidonic acid synergize to activate Kupffer cells and modulate the fibrogenic response via tumor necrosis factor alpha, reduced glutathione, and transforming growth factor beta-dependent mechanisms. Hepatology 2008; 48:2027-2039. [PMID: 19003881 PMCID: PMC4477289 DOI: 10.1002/hep.22592] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
UNLABELLED Because of the contribution of ethanol and polyunsaturated fatty acids (PUFAs) to alcoholic liver disease, we investigated whether chronic ethanol administration and arachidonic acid (AA) could synergistically mediate Kupffer cell (KC) activation and modulate the stellate cell (HSC) fibrogenic response. RESULTS (1) the effects of ethanol and AA on KC and HSC were as follows: Cell proliferation, lipid peroxidation, H(2)O(2), O(2).(-), nicotinamide adenine dinucleotide phosphate reduced form (NADPH) oxidase activity, and tumor necrosis factor alpha (TNF-alpha) were higher in KC(ethanol) than in KC(control), and were enhanced by AA; HSC(ethanol) proliferated faster, increased collagen, and showed higher GSH than HSC(control), with modest effects by AA. (2) AA effects on the control co-culture: We previously reported the ability of KC to induce a pro-fibrogenic response in HSC via reactive oxygen species (ROS)-dependent mechanisms; we now show that AA further increases cell proliferation and collagen in the control co-culture. The latter was prevented by vitamin E (an antioxidant) and by diphenyleneiodonium (a NADPH oxidase inhibitor). (3) Ethanol effects on the co-cultures: Co-culture with KC(control) or KC(ethanol) induced HSC(control) and HSC(ethanol) proliferation; however, the pro-fibrogenic response in HSC(ethanol) was suppressed because of up-regulation of TNF-alpha and GSH, which was prevented by a TNF-alpha neutralizing antibody (Ab) and by L-buthionine-sulfoximine, a GSH-depleting agent. (4) Ethanol plus AA effects on the co-cultures: AA lowered TNF-alpha in the HSC(control) co-cultures, allowing for enhanced collagen deposition; furthermore, AA restored the pro-fibrogenic response in the HSC(ethanol) co-cultures by counteracting the up-regulation of TNF-alpha and GSH with a significant increase in GSSG and in pro-fibrogenic transforming growth factor beta (TGF-beta). CONCLUSION These results unveil synergism between ethanol and AA to the mechanism whereby KC mediate ECM remodeling and suggest that even if chronic ethanol consumption sensitizes HSC to up-regulate anti-fibrogenic signals, their effects are blunted by a second "hit" such as AA.
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Affiliation(s)
- Francisco Javier Cubero
- Department of Medicine, Division of Liver Diseases, Mount Sinai School of Medicine, Box 1123, 1425 Madison Avenue, Room 11-76, New York, NY 10029, USA
| | - Natalia Nieto
- Department of Medicine, Division of Liver Diseases, Mount Sinai School of Medicine, Box 1123, 1425 Madison Avenue, Room 11-76, New York, NY 10029, USA
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Chen WJ, Pang JHS, Lin KH, Yang SH. Propylthiouracil, independent of its antithyroid effect, decreases VSMC collagen expression. Basic Res Cardiol 2008; 104:60-8. [DOI: 10.1007/s00395-008-0746-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/11/2008] [Accepted: 08/20/2008] [Indexed: 11/24/2022]
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Pedersen JS, Bejerano G, Siepel A, Rosenbloom K, Lindblad-Toh K, Lander ES, Kent J, Miller W, Haussler D. Identification and classification of conserved RNA secondary structures in the human genome. PLoS Comput Biol 2006; 2:e33. [PMID: 16628248 PMCID: PMC1440920 DOI: 10.1371/journal.pcbi.0020033] [Citation(s) in RCA: 406] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2005] [Accepted: 03/06/2006] [Indexed: 12/28/2022] Open
Abstract
The discoveries of microRNAs and riboswitches, among others, have shown functional RNAs to be biologically more important and genomically more prevalent than previously anticipated. We have developed a general comparative genomics method based on phylogenetic stochastic context-free grammars for identifying functional RNAs encoded in the human genome and used it to survey an eight-way genome-wide alignment of the human, chimpanzee, mouse, rat, dog, chicken, zebra-fish, and puffer-fish genomes for deeply conserved functional RNAs. At a loose threshold for acceptance, this search resulted in a set of 48,479 candidate RNA structures. This screen finds a large number of known functional RNAs, including 195 miRNAs, 62 histone 3′UTR stem loops, and various types of known genetic recoding elements. Among the highest-scoring new predictions are 169 new miRNA candidates, as well as new candidate selenocysteine insertion sites, RNA editing hairpins, RNAs involved in transcript auto regulation, and many folds that form singletons or small functional RNA families of completely unknown function. While the rate of false positives in the overall set is difficult to estimate and is likely to be substantial, the results nevertheless provide evidence for many new human functional RNAs and present specific predictions to facilitate their further characterization. Structurally functional RNA is a versatile component of the cell that comprises both independent molecules and regulatory elements of mRNA transcripts. The many recent discoveries of functional RNAs, most notably miRNAs, suggests that many more are yet to be found. Computational identification of functional RNAs has traditionally been hampered by the lack of strong sequence signals. However, structural conservation over long evolutionary times creates a characteristic substitution pattern, which can be exploited with the advent of comparative genomics. The authors have devised a method for identification of functional RNA structures based on phylogenetic analysis of multiple alignments. This method has been used to screen the regions of the human genome that are under strong selective constraints. The result is a set of 48,479 candidate RNA structures. For some classes of known functional RNAs, such as miRNAs and histone 3′UTR stem loops, this set includes nearly all deeply conserved members. The initial large candidate set has been partitioned by size, shape, and genomic location and ranked by score to produce specific lists of top candidates for miRNAs, selenocysteine insertion sites, RNA editing hairpins, and RNAs involved in transcript auto regulation.
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Affiliation(s)
- Jakob Skou Pedersen
- Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, USA.
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19
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Abstract
Alcohol abuse is a main cause of liver fibrosis and cirrhosis in the western world. Although the major mechanisms of fibrogenesis are independent of the origin of liver injury, alcoholic liver fibrosis features distinctive characteristics, including the pronounced inflammatory response of immune cells due to elevated gut-derived endotoxin plasma levels, increased formation of reactive oxygen species (ROS), ethanol-induced pericentral hepatic hypoxia or formation of cell-toxic and pro-fibrogenic ethanol metabolites (e.g., acetaldehyde or lipid oxidation products). These factors are together responsible for increased hepatocellular cell death and activation of hepatic stellate cells (HSCs), the key cell type of liver fibrogenesis. To date, removing the causative agent is the most effective intervention to prevent the manifestation of liver cirrhosis. A novel experimental approach in fibrosis therapy is the selective induction of cell death in HSCs. Substances such as gliotoxin, anandamide or antibody against tissue inhibitor of metalloproteinase (TIMP)-1 can selectively induce cell death in activated HSCs. These new results in basic science are encouraging for the search of new antifibrotic treatment.
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Affiliation(s)
- Sören V Siegmund
- Department of Medicine, College of Physicians & Surgeons, Columbia University, New York, NY 10032, USA
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20
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Stefanovic L, Brenner DA, Stefanovic B. Direct hepatotoxic effect of KC chemokine in the liver without infiltration of neutrophils. Exp Biol Med (Maywood) 2005; 230:573-86. [PMID: 16118408 DOI: 10.1177/153537020523000809] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
KC is a mouse homolog of human chemokine gro-alpha (CXCL1), expression of which is increased in liver diseases. We show that activated, but not quiescent, hepatic stellate cells (HSCs) express KC. Hepatic stellate cells constitutively express the KC receptor, CXCR2. Addition of recombinant KC to HSCs undergoing activation in culture increases secretion and processing of Type I collagen. Overexpression of endogenous KC in the mouse liver could be achieved by an intraperitoneal injection of CCl(4), followed after 24 hrs by an injection of recombinant KC into circulation. This protocol resulted in about a 14-fold increase in concentration of KC protein in the liver. Overexpression of KC was associated with upregulation of the mRNA for CXCR2 and MIP-2 and with necrosis and increased synthesis of Type I collagen. This suggests that KC has a direct hepatotoxic effect, which led to a massive liver necrosis after 48 hrs. No accumulation of neutrophils was seen in the livers as judged by histology and reverse transcriptase-polymerase chain reaction analysis of myeloperoxidase mRNA. Autostimulation of KC and CXCR2 expression by recombinant KC protein in the mice with preexisting liver injury indicates a positive feedback regulation. Such regulation and direct hepatotoxicity of KC with increased collagen synthesis represent novel findings about the role of KC/ gro-alpha in liver pathology.
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Affiliation(s)
- Lela Stefanovic
- Department of Biomedical Science, Florida State University College of Medicine, Tallahassee, FL 32306, USA
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21
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Tsukada S, Parsons CJ, Rippe RA. Mechanisms of liver fibrosis. Clin Chim Acta 2005; 364:33-60. [PMID: 16139830 DOI: 10.1016/j.cca.2005.06.014] [Citation(s) in RCA: 275] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2005] [Revised: 06/07/2005] [Accepted: 06/08/2005] [Indexed: 01/18/2023]
Abstract
Liver fibrosis represents a significant health problem worldwide of which no acceptable therapy exists. The most characteristic feature of liver fibrosis is excess deposition of type I collagen. A great deal of research has been performed to understand the molecular mechanisms responsible for the development of liver fibrosis. The activated hepatic stellate cell (HSC) is the primary cell type responsible for the excess production of collagen. Following a fibrogenic stimulus, HSCs change from a quiescent to an activated, collagen-producing cell. Numerous changes in gene expression are associated with HSC activation including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses in understanding the molecular basis of collagen gene regulation have revealed a complex process offering the opportunity for multiple potential therapeutic strategies. However, further research is still needed to gain a better understanding of HSC activation and how this cell maintains its fibrogenic nature. In this review we describe many of the molecular events that occur following HSC activation and collagen gene regulation that contribute to the fibrogenic nature of these cells and provide a review of therapeutic strategies to treat this disease.
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Affiliation(s)
- Shigeki Tsukada
- Division of Gastroenterology and Hepatology, Department of Medicine, University of North Carolina at Chapel Hill, NC 27599-7032, USA
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22
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Luzina IG, Tsymbalyuk N, Choi J, Hasday JD, Atamas SP. CCL18-stimulated upregulation of collagen production in lung fibroblasts requires Sp1 signaling and basal Smad3 activity. J Cell Physiol 2005; 206:221-8. [PMID: 16021625 DOI: 10.1002/jcp.20452] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A CC chemokine CCL18 stimulates collagen production in pulmonary fibroblasts through an unknown signaling mechanism. In this study, involvement of Sp1 and Smad3 in CCL18 signaling in primary human pulmonary fibroblast cultures was investigated. Phosphorylation of Sp1, DNA-binding by Sp1, and the activity of an Sp1-dependent reporter were all increased in response to CCL18 stimulation. CCL18 did not stimulate a detectable increase in Smad3 phosphorylation or Smad3/4 DNA-binding activity, although some basal phosphorylation and DNA binding by Smad3/4 were noted. Transient overexpression of dominant negative mutants of Sp1 and Smad3 abrogated CCL18-dependent upregulation as well as basal production of collagen. These observations suggested that CCL18 activates collagen production in pulmonary fibroblasts through an Sp1-dependent pathway that also requires basal Smad3 activity. Possible involvement of autocrine TGF-beta in CCL18 signaling was considered. CCL18 stimulated increases in collagen mRNA and protein production without detectable changes in TGF-beta1, -beta2, and -beta3 mRNA or protein levels. Neutralizing anti-TGF-beta antibodies, latency-associated peptide, ALK5-specific inhibitor SD431542, and an inhibitor of the protease-dependent TGF-beta activation aprotinin, each failed to block CCL18-stimulated collagen production. These observations suggest that both CCL18 signaling in pulmonary fibroblasts and basal Smad3 activity are independent of autocrine TGF-beta.
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Affiliation(s)
- Irina G Luzina
- Department of Medicine, University of Maryland School of Medicine, Baltimore VA Medical Center, Baltimore, Maryland 21201, USA.
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23
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Stefanovic L, Stephens CE, Boykin D, Stefanovic B. Inhibitory effect of dicationic diphenylfurans on production of type I collagen by human fibroblasts and activated hepatic stellate cells. Life Sci 2005; 76:2011-26. [PMID: 15707883 DOI: 10.1016/j.lfs.2004.09.043] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2004] [Accepted: 09/23/2004] [Indexed: 11/19/2022]
Abstract
Excessive production of extracellular matrix is responsible for clinical manifestations of fibroproliferative disorders and drugs which can inhibit excessive synthesis of type I collagen are needed for the therapy. Several dicationic diphenylfurans were synthesized and were found to bind RNA. Two of these type compounds were able to reduce synthesis of type I collagen by human fibroblasts and human activated hepatic stellate cells (HSCs). Activated HSCs are responsible for collagen production in liver fibrosis. When added at 40 microM compound 588 reduced intracellular level and secretion of procollagen alpha1(I) by 50%, while compound 654 reduced these parameters by more than 80% at 20 microM. 654 also significantly reduced secretion of fibronectin. Toxic effects were observed at 80 microM for 588 and 40 microM for 654. 654 reduced expression of a reporter gene with collagen signal peptide, while expression of the same gene without signal peptide was unaffected. Also, expression of intracellular proteins tubulin and calnexin was unchanged. 654 accumulated inside the cell in the cytoplasm and did not change the steady-state level of collagen mRNAs. Treatment of cells with proteosome inhibitor MG132 did not change the inhibitory effect of 654, suggesting that 654 acts as suppressor of translation of proteins containing a signal peptide. Most secreted proteins of fibroblasts and activated HSCs are components of extracellular matrix. Therefore inhibition of their production, as shown here for procollagen alpha1(I) and fibronectin, may be a useful property of some of diphenylfurans, making these compounds a basis for development of antifibrotic drugs.
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Affiliation(s)
- Lela Stefanovic
- Department of Biomedical Science, Florida State University College of Medicine, Tallahassee, FL 32306, USA
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24
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Abstract
Alcohol abuse is a major cause of liver fibrosis and cirrhosis in developed countries. Before alcoholic liver fibrosis becomes evident, the liver undergoes several stages of alcoholic liver disease including steatosis and steatohepatitis. Although the main mechanisms of fibrogenesis are independent of the etiology of liver injury, alcoholic liver fibrosis is distinctively characterized by a pronounced inflammatory response due to elevated gut-derived endotoxin plasma levels, an augmented generation of oxidative stress with pericentral hepatic hypoxia and the formation of cell-toxic and profibrogenic ethanol metabolites (e.g. acetaldehyde or lipid oxidation products). These factors, based on a complex network of cytokine actions, together result in increased hepatocellular damage and activation of hepatic stellate cells, the key cell type of liver fibrogenesis. Although to date removal of the causative agent, i.e. alcohol, still represents the most effective intervention to prevent the manifestation of alcoholic liver disease, sophisticated molecular approaches are underway, aiming to specifically blunt profibrogenic signaling pathways in liver cells or specifically induce cell death in activated hepatic stellate cells to decrease the scarring of the liver.
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Affiliation(s)
- Soren V Siegmund
- Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
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25
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Thiele BJ, Doller A, Kähne T, Pregla R, Hetzer R, Regitz-Zagrosek V. RNA-binding proteins heterogeneous nuclear ribonucleoprotein A1, E1, and K are involved in post-transcriptional control of collagen I and III synthesis. Circ Res 2004; 95:1058-66. [PMID: 15514164 DOI: 10.1161/01.res.0000149166.33833.08] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Collagen types I and III, coded by COL1A1/COL1A2 and COL3A1 genes, are the major fibrillar collagens produced by fibroblasts, including cardiac fibroblasts of the adult heart. Characteristic for different cardiomyopathies is a remodeling process associated with an upregulation of collagen synthesis, which leads to fibrosis. We report identification of three mRNA-binding proteins, heterogeneous nuclear ribonucleoprote (hnRNP) A1, E1, and K, as positive effectors of collagen synthesis acting at the post-transcriptional level by interaction with the 3'-untranslated regions (3'-UTRs) of COL1A1, 1A2, and 3A1 mRNAs. In vitro, binding experiments (electromobility shift assay and UV cross-linking) reveal significant differences in binding to CU- and AU-rich binding motifs. Reporter gene cell transfection experiments and RNA stability assays show that hnRNPs A1, E1, and K stimulate collagen expression by stabilizing mRNAs. Collagen synthesis is activated via the angiotensin II type 1 (AT1) receptor. We demonstrate that transforming growth factor-beta1, a major product of stimulated AT1 receptor, does not activate solely collagen synthesis but synergistically the synthesis of hnRNP A1, E1, and K as well. Thus, post-transcriptional control of collagen synthesis at the mRNA level may substantially be caused by alteration of the expression of RNA-binding proteins. The pathophysiological impact of this finding was demonstrated by screening the expression of hnRNP E1 and K in cardiovascular diseases. In the heart muscle of patients experiencing aortic stenosis, ischemic cardiomyopathy, or dilatative cardiomyopathy, a significant increase in the expression of hnRNP E1, A1, and K was found between 1.5- and 4.5-fold relative to controls.
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26
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Stefanovic B, Stefanovic L, Schnabl B, Bataller R, Brenner DA. TRAM2 protein interacts with endoplasmic reticulum Ca2+ pump Serca2b and is necessary for collagen type I synthesis. Mol Cell Biol 2004; 24:1758-68. [PMID: 14749390 PMCID: PMC344171 DOI: 10.1128/mcb.24.4.1758-1768.2004] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cotranslational insertion of type I collagen chains into the lumen of the endoplasmic reticulum (ER) and their subsequent folding into a heterotrimeric helix is a complex process which requires coordinated action of the translation machinery, components of translocons, molecular chaperones, and modifying enzymes. Here we describe a role for the protein TRAM2 in collagen type I expression in hepatic stellate cells (HSCs) and fibroblasts. Activated HSCs are collagen-producing cells in the fibrotic liver. Quiescent HSCs produce trace amounts of type I collagen, while upon activation collagen synthesis increases 50- to 70-fold. Likewise, expression of TRAM2 dramatically increases in activated HSCs. TRAM2 shares 53% amino acid identity with the protein TRAM, which is a component of the translocon. However, TRAM2 has a C terminus with only a 15% identity. The C-terminal part of TRAM2 interacts with the Ca(2+) pump of the ER, SERCA2b, as demonstrated in a Saccharomyces cerevisiae two-hybrid screen and by immunoprecipitations in human cells. TRAM2 also coprecipitates with anticollagen antibody, suggesting that these two proteins interact. Deletion of the C-terminal part of TRAM2 inhibits type I collagen synthesis during activation of HSCs. The pharmacological inhibitor of SERCA2b, thapsigargin, has a similar effect. Depletion of ER Ca(2+) with thapsigargin results in inhibition of triple helical collagen folding and increased intracellular degradation. We propose that TRAM2, as a part of the translocon, is required for the biosynthesis of type I collagen by coupling the activity of SERCA2b with the activity of the translocon. This coupling may increase the local Ca(2+) concentration at the site of collagen synthesis, and a high Ca(2+) concentration may be necessary for the function of molecular chaperones involved in collagen folding.
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Affiliation(s)
- Branko Stefanovic
- Department of Biomedical Science, College of Medicine, Florida State University, Tallahassee, Florida 32306, USA.
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27
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Martin KA, Rzucidlo EM, Merenick BL, Fingar DC, Brown DJ, Wagner RJ, Powell RJ. The mTOR/p70 S6K1 pathway regulates vascular smooth muscle cell differentiation. Am J Physiol Cell Physiol 2004; 286:C507-17. [PMID: 14592809 DOI: 10.1152/ajpcell.00201.2003] [Citation(s) in RCA: 176] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Vascular smooth muscle cells (VSMC) in mature, normal blood vessels exhibit a differentiated, quiescent, contractile morphology, but injury induces a phenotypic modulation toward a proliferative, dedifferentiated, migratory phenotype with upregulated extracellular matrix protein synthesis (synthetic phenotype), which contributes to intimal hyperplasia. The mTOR (the mammalian target of rapamycin) pathway inhibitor rapamycin inhibits intimal hyperplasia in animal models and in human clinical trials. We report that rapamycin treatment induces differentiation in cultured synthetic phenotype VSMC from multiple species. VSMC treated with rapamycin assumed a contractile morphology, quantitatively reflected by a 67% decrease in cell area. Total protein and collagen synthesis were also inhibited by rapamycin. Rapamycin induced expression of the VSMC differentiation marker contractile proteins smooth muscle (SM) α-actin, calponin, and SM myosin heavy chain (SM-MHC), as observed by immunoblotting and immunohistochemistry. Notably, we detected a striking rapamycin induction of calponin and SM-MHC mRNA, suggesting a role for mTOR in transcriptional control of VSMC gene expression. Rapamycin also induced expression of the cyclin-dependent kinase inhibitors p21cipand p27kip, consistent with cell cycle withdrawal. Rapamycin inhibits mTOR, a signaling protein that regulates protein synthesis effectors, including p70 S6K1. Overexpression of p70 S6K1 inhibited rapamycin-induced contractile protein and p21cipexpression, suggesting that this kinase opposes VSMC differentiation. In conclusion, we report that regulation of VSMC differentiation is a novel function of the rapamycin-sensitive mTOR signaling pathway.
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MESH Headings
- Animals
- Aorta, Thoracic/cytology
- Biomarkers
- Cattle
- Cell Cycle Proteins/metabolism
- Cell Differentiation/drug effects
- Cell Differentiation/physiology
- Cells, Cultured
- Cyclin-Dependent Kinase Inhibitor p21
- Cyclin-Dependent Kinase Inhibitor p27
- Cyclins/metabolism
- Endothelium, Vascular/cytology
- Extracellular Matrix Proteins/metabolism
- Immunosuppressive Agents/pharmacology
- Muscle Contraction/drug effects
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Phenotype
- Protein Kinases/metabolism
- Ribosomal Protein S6 Kinases, 70-kDa/metabolism
- Signal Transduction/drug effects
- Signal Transduction/physiology
- Sirolimus/pharmacology
- TOR Serine-Threonine Kinases
- Tumor Suppressor Proteins/metabolism
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Affiliation(s)
- Kathleen A Martin
- Department of Surgery, Section of Vascular Surgery, Dartmouth Medical School, Lebanon, New Hampshire 03756, USA.
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28
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Lindquist JN, Parsons CJ, Stefanovic B, Brenner DA. Regulation of alpha1(I) collagen messenger RNA decay by interactions with alphaCP at the 3'-untranslated region. J Biol Chem 2004; 279:23822-9. [PMID: 14973140 DOI: 10.1074/jbc.m314060200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Liver fibrosis is characterized by an increased deposition of extracellular matrix proteins, including collagen type I, by activated hepatic stellate cells (HSCs). Previous studies have shown that this increase is mediated primarily by a post-transcriptional mechanism. In particular, the RNA-binding protein alphaCP binds to the alpha1(I) collagen 3'-untranslated region (UTR) and stabilizes this RNA in activated, but not quiescent, HSCs. This study examines the role of alphaCP in the decay of transcripts containing the collagen 3'-UTR in extracts obtained from NIH fibroblasts and quiescent and activated HSCs. Using an in vitro decay system, alphaCP binding activity was competed out with the addition of wild type oligonucleotides, but not with mutant oligonucleotides. Competition of alphaCP binding activity increased the rate of decay of wild type transcripts containing the alphaCP 3'-UTR binding site, but not of transcripts containing a mutated binding site. Quiescent HSC extracts contain no alphaCP binding activity and have no difference in the rate of decay of transcripts with wild type and mutant binding sites for alphaCP. The addition of recombinant alphaCP was sufficient to increase the half-life of the wild type transcript, whereas that of the mutant transcript was minimally changed. In vitro decay assays performed with activated HSC extracts that contain alphaCP binding activity demonstrate a markedly reduced decay rate of wild type compared with mutant transcripts. In vivo small interfering RNA experiments targeting alphaCP showed a reduction of the binding activity of alphaCP and a concomitant reduction in intracellular levels of alpha1(I) collagen messenger RNA. In conclusion, this study demonstrates the direct role of alphaCP in the stabilization of alpha1(I) collagen messenger RNA by blocking RNA degradation in activated HSCs.
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Affiliation(s)
- Jeffrey N Lindquist
- Biochemistry and Biophysics and Medicine, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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Bataller R, Gäbele E, Schoonhoven R, Morris T, Lehnert M, Yang L, Brenner DA, Rippe RA. Prolonged infusion of angiotensin II into normal rats induces stellate cell activation and proinflammatory events in liver. Am J Physiol Gastrointest Liver Physiol 2003; 285:G642-51. [PMID: 12773299 DOI: 10.1152/ajpgi.00037.2003] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Recent evidence indicates that angiotensin II (ANG II) plays an important role in liver fibrogenesis. However, the underlying mechanisms are largely unknown. In advanced chronic liver diseases, circulating levels of ANG II are frequently elevated. We investigated the hepatic effects of prolonged systemic infusion of ANG II in normal rats. Saline or ANG II at subpressor and pressor doses (15 and 50 ng.kg-1.min-1, respectively) were infused to normal rats for 4 wk through a subcutaneous osmotic pump. Infusion of ANG II resulted in liver injury, as assessed by elevated serum liver enzymes. Livers from ANG II-perfused rats showed activation of JNK and ERK as well as increased NF-kappaB and activating protein-1 DNA-binding activity. Moreover, ANG II perfusion induced oxidative stress, increased concentration of proinflammatory cytokines, and upregulated the inflammatory proteins inducible nitric oxide synthase and cyclooxygenase-2. Histological examination of the livers from ANG II-infused rats showed mild portal inflammation as well as thickening and thrombosis of small hepatic vessels. ANG II-treated livers showed accumulation of CD43-positive inflammatory cells and activated hepatic stellate cells (HSCs) at the pericentral areas. A slight increase in collagen synthesis was observed, as assessed by Sirius red staining and hepatic hydroxyproline. All of these effects were observed when ANG II was perfused at subpressor and pressor doses. ANG II also accelerated the activation of primary cultured rat HSCs. In conclusion, increased systemic ANG II can induce liver injury by promoting proinflammatory events and vascular damage. ANG II-induced hepatic effects are not dependent on increase in arterial pressure.
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Affiliation(s)
- Ramón Bataller
- Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7032, USA
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Schnabl B, Purbeck CA, Choi YH, Hagedorn CH, Brenner D. Replicative senescence of activated human hepatic stellate cells is accompanied by a pronounced inflammatory but less fibrogenic phenotype. Hepatology 2003; 37:653-64. [PMID: 12601363 DOI: 10.1053/jhep.2003.50097] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Limited proliferative capacity is a characteristic of most normal human cells and results in a growth-arrested state, called replicative senescence. Functional expression of the telomerase catalytic subunit (human telomerase reverse transcriptase; hTERT) in human activated hepatic stellate cells (HSCs) rescues them from death with immortalization and maintains an activated HSC phenotype. The aim of this study was to evaluate alterations in gene and protein expression of in vitro aged human activated HSCs and to define the pathway by which senescent-activated HSCs are eliminated in culture. Altered patterns of gene expression in senescent human HSCs were assessed using DNA microarray analysis and compared with early passage HSCs or hTERT immortalized HSCs. Senescent HSCs showed higher expression of inflammation and stress-associated genes as compared with early passage HSCs. Senescent HSCs expressed reduced levels of extracellular matrix proteins, including collagens, tenascin, and fibronectin. TUNEL staining of senescent HSCs showed approximately 21% positive cells, indicating DNA fragmentation and apoptosis. Apoptosis involved the mitochondrial pathway with decreased levels of Bcl-2 and Bcl-x(L) protein, release of cytochrome c, and increased caspase-3 activity. In contrast, 4% to 5% of early activated HSCs or telomerase positive HSCs were TUNEL positive. In conclusion, cultured human HSCs undergo a switch from a fibrogenic to an inflammatory phenotype, suggesting that senescent human HSCs might modulate chronic wound healing processes. Maintenance of telomere length represents an important survival factor for activated human HSCs.
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Affiliation(s)
- Bernd Schnabl
- Department of Medicine and Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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