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1.  Genetic architecture of human fibrotic diseases: disease risk and disease progression 
Genetic studies of human diseases have identified multiple genetic risk loci for various fibrotic diseases. This has provided insights into the myriad of biological pathways potentially involved in disease pathogenesis. These discoveries suggest that alterations in immune responses, barrier function, metabolism and telomerase activity may be implicated in the genetic risks for fibrotic diseases. In addition to genetic disease-risks, the identification of genetic disease-modifiers associated with disease complications, severity or prognosis provides crucial insights into the biological processes implicated in disease progression. Understanding the biological processes driving disease progression may be critical to delineate more effective strategies for therapeutic interventions. This review provides an overview of current knowledge and gaps regarding genetic disease-risks and genetic disease-modifiers in human fibrotic diseases.
PMCID: PMC3866586  PMID: 24391588
fibrosis; auto-immunity; genetics; GWAS; disease progression
2.  Deletion of Fn14 receptor protects from right heart fibrosis and dysfunction 
Basic Research in Cardiology  2013;108(2):325.
Pulmonary arterial hypertension (PAH) is a fatal disease for which no cure is yet available. The leading cause of death in PAH is right ventricular (RV) failure. Previously, the TNF receptor superfamily member fibroblast growth factor-inducible molecule 14 (Fn14) has been associated with different fibrotic diseases. However, so far there is no study demonstrating a causal role for endogenous Fn14 signaling in RV or LV heart disease. The purpose of this study was to determine whether global ablation of Fn14 prevents RV fibrosis and remodeling improving heart function. Here, we provide evidence for a causative role of Fn14 in pulmonary artery banding (PAB)-induced RV fibrosis and dysfunction in mice. Fn14 expression was increased in the RV after PAB. Mice lacking Fn14 (Fn14−/−) displayed substantially reduced RV fibrosis and dysfunction following PAB compared to wild-type littermates. Cell culture experiments demonstrated that activation of Fn14 induces collagen expression via RhoA-dependent nuclear translocation of myocardin-related transcription factor-A (MRTF-A)/MAL. Furthermore, activation of Fn14 in vitro caused fibroblast proliferation and myofibroblast differentiation, which corresponds to suppression of PAB-induced RV fibrosis in Fn14−/− mice. Moreover, our findings suggest that Fn14 expression is regulated by endothelin-1 (ET-1) in cardiac fibroblasts. We conclude that Fn14 is an endogenous key regulator in cardiac fibrosis and suggest this receptor as potential new target for therapeutic interventions in heart failure.
Electronic supplementary material
The online version of this article (doi:10.1007/s00395-012-0325-x) contains supplementary material, which is available to authorized users.
PMCID: PMC3597271  PMID: 23325387
Right heart disease; Fibrosis; Fn14; MAL; Cardiac fibroblasts
3.  TWEAK and Fn14 expression in the pathogenesis of joint inflammation and bone erosion in rheumatoid arthritis 
TNF-like weak inducer of apoptosis (TWEAK) has been proposed as a mediator of inflammation and bone erosion in rheumatoid arthritis (RA). This study aimed to investigate TWEAK and TWEAK receptor (Fn14) expression in synovial tissue from patients with active and inactive rheumatoid arthritis (RA), osteoarthritis (OA) and normal controls and assess soluble (s)TWEAK levels in the synovial fluids from patients with active RA and OA. Effects of sTWEAK on osteoclasts and osteoblasts were investigated in vitro.
TWEAK and Fn14 expression were detected in synovial tissues by immunohistochemistry (IHC). Selected tissues were dual labelled with antibodies specific for TWEAK and lineage-selective cell surface markers CD68, Tryptase G, CD22 and CD38. TWEAK mRNA expression was examined in human peripheral blood mononuclear cells (PBMC) sorted on the basis of their expression of CD22. sTWEAK was detected in synovial fluid from OA and RA patients by ELISA. The effect of sTWEAK on PBMC and RAW 264.7 osteoclastogenesis was examined. The effect of sTWEAK on cell surface receptor activator of NF Kappa B Ligand (RANKL) expression by human osteoblasts was determined by flow cytometry.
TWEAK and Fn14 expression were significantly higher in synovial tissue from all patient groups compared to the synovial tissue from control subjects (P < 0.05). TWEAK was significantly higher in active compared with inactive RA tissues (P < 0.05). TWEAK expression co-localised with a subset of CD38+ plasma cells and with CD22+ B-lymphocytes in RA tissues. Abundant TWEAK mRNA expression was detected in normal human CD22+ B cells. Higher levels of sTWEAK were observed in synovial fluids isolated from active RA compared with OA patients. sTWEAK did not stimulate osteoclast formation directly from PBMC, however, sTWEAK induced the surface expression of RANKL by human immature, STRO-1+ osteoblasts.
The expression of TWEAK by CD22+ B cells and CD38+ plasma cells in RA synovium represents a novel potential pathogenic pathway. High levels of sTWEAK in active RA synovial fluid and of TWEAK and Fn14 in active RA tissue, together with the effect of TWEAK to induce osteoblastic RANKL expression, is consistent with TWEAK/Fn14 signalling being important in the pathogenesis of inflammation and bone erosion in RA.
PMCID: PMC3132040  PMID: 21435232
4.  A Novel Role for Tumor Necrosis Factor–like Weak Inducer of Apoptosis (TWEAK) in the Development of Cardiac Dysfunction and Failure 
Circulation  2009;119(15):2058-2068.
Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK), a member of the TNF superfamily, is a multifunctional cytokine known to regulate cellular functions in contexts of injury and disease through its receptor FGF-inducible molecule 14 (Fn14). While many of the processes and downstream signals regulated by the TWEAK/Fn14 pathway have been implicated in the development of cardiac dysfunction, the role of TWEAK in the cardiovascular system is completely unknown.
Methods and Results
Herein, we demonstrate that mouse and human cardiomyocytes express the TWEAK receptor Fn14. Furthermore, we determine that elevated circulating levels of TWEAK, induced via transgenic or adenoviral mediated gene expression in mice, results in a dilated cardiomyopathy (DCM) with subsequent severe cardiac dysfunction. This phenotype was mediated exclusively by the Fn14 receptor, independent of TNF-α, and was associated with cardiomyocyte elongation and cardiac fibrosis, but not cardiomyocyte apoptosis. Moreover, we find that circulating TWEAK levels were differentially upregulated in patients with idiopathic DCM as compared to other forms of heart disease and normal control subjects.
Our data suggest that TWEAK/Fn14 may be important in regulating myocardial structural remodeling and function, and may play a role in the pathogenesis of DCM.
PMCID: PMC2924152  PMID: 19349318
TWEAK; Fn14; Cardiomyocytes; Hypertrophy; Heart Failure
5.  Caspase-6 Regulates B Cell Activation and Differentiation into Plasma Cells1 
Caspase (Casp) family proteases regulate not only lymphocyte apoptosis but also lymphocyte activation and development. In this study, we show that Casp6 regulates B cell activation and differentiation into plasma cells by modifying cell cycle entry. B cells from Casp6 knockout (Casp6 KO) mice examined ex vivo have more cells in G1 than wild-type B cells, and mitogen-induced G1 entry of Casp6 KO B cells is much faster than that of wild-type B cells. Even so, S phase entry and proliferation are not increased in Casp6 KO B cells. Rather than proliferating, activated Casp6 KO B cells preferentially differentiate into syndecan-1+ plasma cells and produce Abs. In Casp6 KO mice compared with WT mice, serum levels of IgG1, IgG2a, and IgG2b are increased and Ag-specific Ab responses are also enhanced along with increased percentages of syndecan-1+ plasma cells. Casp6 may regulate both B cell activation and differentiation by modifying requirements for G0 B cells to enter G1.
PMCID: PMC2728076  PMID: 18981099
6.  TL1A–DR3 interaction regulates Th17 cell function and Th17-mediated autoimmune disease 
The Journal of Experimental Medicine  2008;205(5):1049-1062.
T helper type 17 (Th17) cells play an important pathogenic function in autoimmune diseases; their regulation, however, is not well understood. We show that the expression of a tumor necrosis factor receptor family member, death receptor 3 (DR3; also known as TNFRSF25), is selectively elevated in Th17 cells, and that TL1A, its cognate ligand, can promote the proliferation of effector Th17 cells. To further investigate the role of the TL1A–DR3 pathway in Th17 regulation, we generated a TL1A-deficient mouse and found that TL1A−/− dendritic cells exhibited a reduced capacity in supporting Th17 differentiation and proliferation. Consistent with these data, TL1A−/− animals displayed decreased clinical severity in experimental autoimmune encephalomyelitis (EAE). Finally, we demonstrated that during EAE disease progression, TL1A was required for the optimal differentiation as well as effector function of Th17 cells. These observations thus establish an important role of the TL1A–DR3 pathway in promoting Th17 cell function and Th17-mediated autoimmune disease.
PMCID: PMC2373838  PMID: 18411337
8.  TWEAK induces liver progenitor cell proliferation 
Journal of Clinical Investigation  2005;115(9):2330-2340.
Progenitor (“oval”) cell expansion accompanies many forms of liver injury, including alcohol toxicity and submassive parenchymal necrosis as well as experimental injury models featuring blocked hepatocyte replication. Oval cells can potentially become either hepatocytes or biliary epithelial cells and may be critical to liver regeneration, particularly when hepatocyte replication is impaired. The regulation of oval cell proliferation is incompletely understood. Herein we present evidence that a TNF family member called TWEAK (TNF-like weak inducer of apoptosis) stimulates oval cell proliferation in mouse liver through its receptor Fn14. TWEAK has no effect on mature hepatocytes and thus appears to be selective for oval cells. Transgenic mice overexpressing TWEAK in hepatocytes exhibit periportal oval cell hyperplasia. A similar phenotype was obtained in adult wild-type mice, but not Fn14-null mice, by administering TWEAK-expressing adenovirus. Oval cell expansion induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) was significantly reduced in Fn14-null mice as well as in adult wild-type mice with a blocking anti-TWEAK mAb. Importantly, TWEAK stimulated the proliferation of an oval cell culture model. Finally, we show increased Fn14 expression in chronic hepatitis C and other human liver diseases relative to its expression in normal liver, which suggests a role for the TWEAK/Fn14 pathway in human liver injury. We conclude that TWEAK has a selective mitogenic effect for liver oval cells that distinguishes it from other previously described growth factors.
PMCID: PMC1187931  PMID: 16110324

Results 1-8 (8)