TAZ/WWTR1 mediates liver mesothelial-mesenchymal transition induced by stiff extracellular environment, TGF-ß1, and lysophosphatidic acid.

Mesothelial cells cover the surface of the internal organs and the walls of body cavities, facilitating the movement between organs by secretion of a lubricating fluid. Upon injury, mesothelial cells undergo a mesothelial-mesenchymal transition (MMT) and give rise to myofibroblasts during organ fibrosis, including in the liver. Although transforming growth factor-ß1 (TGF-ß1) was shown to induce MMT, molecular and cellular mechanisms underlying MMT remain to be clarified. In the present study, we examined how the extracellular environment, soluble factors, and cell density control the phenotype of liver mesothelial cells by culturing them at different cell densities or on hydrogels of different stiffness. We found that TGF-ß1 does not fully induce MMT in mesothelial cells cultured at high cell density or in the absence of fetal bovine serum. Extracellular lysophosphatidic acid (LPA) synergistically induced MMT in the presence of TGF-ß1 in mesothelial cells. LPA induced nuclear localization of WW domain-containing transcription regulator1 (WWTR1/TAZ) and knockdown of Taz, which suppressed LPA-induced MMT. Mesothelial cells cultured on stiff hydrogels upregulated nuclear localization of TAZ and myofibroblastic differentiation. Knockdown of Taz suppressed MMT of mesothelial cells cultured on stiff hydrogels, but inhibition of TGF-ß1 signaling failed to suppress MMT. Our data indicate that TAZ mediates MMT induced by TGF-ß1, LPA, and a stiff matrix. The microenvironment of a stiff extracellular matrix is a strong inducer of MMT.

Lung-restricted ALK5 inhibition avoids systemic toxicities associated with TGFß pathway inhibition.

Systemic therapies targeting transforming growth factor beta (TGFß) or TGFßR1 kinase (ALK5) have been plagued by toxicities including cardiac valvulopathy and bone physeal dysplasia in animals, posing a significant challenge for clinical development in pulmonary indications. The current work aims to demonstrate that systemic ALK5-associated toxicities can be mitigated through localized lung delivery. Lung-selective (THRX-144644) and systemically bioavailable (galunisertib) ALK5 inhibitors were compared to determine whether lung selectivity is sufficient to maintain local tissue concentrations while mitigating systemic exposure and consequent pathway-related findings. Both molecules demonstrated potent ALK5 activity in rat precision cut lung slices (PCLS; p-SMAD3 half-maximal inhibitory concentration [IC50], 141 nM and 1070 nM for THRX-144644 and galunisertib, respectively). In 14-day repeat-dose studies in rats, dose-related cardiac valvulopathy was recapitulated with oral galunisertib at doses ≥150 mg/kg/day. In contrast, inhaled nebulized THRX-144644 did not cause similar systemic findings up to the maximally tolerated doses in rats or dogs (10 and 1.5 mg/kg/day, respectively). THRX-144644 lung-to-plasma ratios ranged from 100- to 1200-fold in rats and dogs across dose levels. THRX-144644 lung trough (24 h) concentrations in rats and dogs ranged from 3- to 17-fold above the PCLS IC50 across tolerated doses. At a dose level exceeding tolerability (60 mg/kg/day; 76-fold above PCLS IC50) minimal heart and bone changes were observed when systemic drug concentrations reached pharmacologic levels. In conclusion, the current preclinical work demonstrates that localized pulmonary delivery of an ALK5 inhibitor leads to favorable TGFß pathway pharmacodynamic inhibition in lung while minimizing key systemic toxicities.

Loss of lysophosphatidic acid receptor 1 in hepatocytes reduces steatosis via down-regulation of CD36.

Nonalcoholic steatohepatitis is a major public health concern and is characterized by the accumulation of triglyceride in hepatocytes and inflammation in the liver. Steatosis is caused by dysregulation of the influx and efflux of lipids, lipogenesis, and mitochondrial ß-oxidation. Extracellular lysophosphatidic acid (LPA) regulates a broad range of cellular processes in development, tissue injury, and cancer. In the present study, we examined the roles of LPA in steatohepatitis induced by a methionine-choline-deficient (MCD) diet in mice. Hepatocytes express LPA receptor (Lpar) 1-3 mRNAs. Steatosis developed in mice fed the MCD diet was reduced by treatment with inhibitors for pan-LPAR or LPAR1. Hepatocyte-specific deletion of the Lpar1 gene also reduced the steatosis in the MCD model. Deletion of the Lpar1 gene in hepatocytes reduced expression of Cd36, a gene encoding a fatty acid transporter. Although LPA/LPAR1 signaling induces expression of Srebp1 mRNA in hepatocytes, LPA does not fully induce expression of SREBP1-target genes involved in lipogenesis. Human hepatocytes repopulated in chimeric mice are known to develop steatosis and treatment with an LPAR1 inhibitor reduces expression of CD36 mRNA and steatosis. Our data indicate that antagonism of LPAR1 reduces steatosis in mouse and human hepatocytes by down-regulation of Cd36.

Isolation of a unique hepatic stellate cell population expressing integrin α8 from embryonic mouse livers.

BACKGROUND: Hepatic stellate cells (HSCs) play an important role in liver fibrogenesis. However, little is known about their phenotype and role in liver development. The aim of this study is to identify specific markers for embryonic HSCs. RESULTS: Using antibodies against ALCAM and PDPN, we separated mesothelial cells (MCs) and HSCs from developing livers and identified integrin α8 (ITGA8) as a marker for embryonic desmin+ HSCs that are preferentially localized near the developing liver surface and α-smooth muscle actin+ perivascular mesenchymal cells around the vein. A cell lineage-tracing study revealed that upon differentiation, MC-derived HSCs or perivascular mesenchymal cells express ITGA8 during liver development. Using anti-ITGA8 antibodies, we succeeded in isolating MC-derived HSCs and perivascular mesenchymal cells from embryonic livers. In direct co-culture, ITGA8+ mesenchymal cells promoted the expression of hepatocyte and cholangiocyte markers in hepatoblasts. In the normal adult liver, expression of ITGA8 was restricted to portal fibroblasts in the portal triad. Upon liver injury, myofibroblasts increased the expression of ITGA8. CONCLUSIONS: ITGA8 is a specific cell surface marker of MC-derived HSCs and perivascular mesenchymal cells in the developing liver. Our data suggest that ITGA8+ mesenchymal cells maintain the phenotype of hepatoblast in liver development. Developmental Dynamics 247:867-881, 2018. © 2018 Wiley Periodicals, Inc.

Characterization of hepatic stellate cells, portal fibroblasts, and mesothelial cells in normal and fibrotic livers.

BACKGROUND & AIMS: Contribution of hepatic stellate cells (HSCs), portal fibroblasts (PFs), and mesothelial cells (MCs) to myofibroblasts is not fully understood due to insufficient availability of markers and isolation methods. The present study aimed to isolate these cells, characterize their phenotypes, and examine their contribution to myofibroblasts in liver fibrosis. METHODS: Liver fibrosis was induced in Collagen1a1-green fluorescent protein (Col1a1(GFP)) mice by bile duct ligation (BDL), 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet, or CCl4 injections. Combining vitamin A (VitA) lipid autofluorescence and expression of GFP and glycoprotein M6a (GPM6A), we separated HSCs, PFs, and MCs from normal and fibrotic livers by fluorescence-activated cell sorting (FACS). RESULTS: Normal Col1a1(GFP) livers broadly expressed GFP in HSCs, PFs, and MCs. Isolated VitA+ HSCs expressed reelin, whereas VitA-GFP+GPM6A- PFs expressed ectonucleoside triphosphate diphosphohydrolase-2 and elastin. VitA-GFP+GPM6A+ MCs expressed keratin 19, mesothelin, and uroplakin 1b. Transforming growth factor (TGF)-ß1 treatment induced the transformation of HSCs, PFs, and MCs into myofibroblasts in culture. TGF-ß1 suppressed cyclin D1 mRNA expression in PFs but not in HSCs and MCs. In biliary fibrosis, PFs adjacent to the bile duct expressed α-smooth muscle actin. FACS analysis revealed that HSCs are the major source of GFP+ myofibroblasts in the injured Col1a1(GFP) mice after DDC or CCl4 treatment. Although PFs partly contributed to GFP+ myofibroblasts in the BDL model, HSCs were still dominant source of myofibroblasts. CONCLUSION: HSCs, PFs, and MCs have distinct phenotypes, and PFs partly contribute to myofibroblasts in the portal triad in biliary fibrosis.

Role of TGF-ß signaling in differentiation of mesothelial cells to vitamin A-poor hepatic stellate cells in liver fibrosis.

Mesothelial cells (MCs) form a single layer of the mesothelium and cover the liver surface. A previous study demonstrated that, upon liver injury, MCs migrate inward from the liver surface and give rise to hepatic stellate cells (HSCs) in biliary fibrosis induced by bile duct ligation (BDL) or myofibroblasts in CCl4-induced fibrosis. The present study analyzed the role of transforming growth factor-ß (TGF-ß) signaling in mesothelial-mesenchymal transition (MMT) and the fate of MCs during liver fibrosis and its regression. Deletion of TGF-ß type II receptor (Tgfbr2) gene in cultured MCs suppressed TGF-ß-mediated myofibroblastic conversion. Conditional deletion of Tgfbr2 gene in MCs reduced the differentiation of MCs to HSCs and myofibroblasts in the BDL and CCl4 models, respectively, indicating that the direct TGF-ß signaling in MCs is responsible to MMT. After BDL and CCl4 treatment, MC-derived HSCs and myofibroblasts were distributed near the liver surface and the thickness of collagen was increased in Glisson's capsule beneath the liver surface. Fluorescence-activated cell sorting analysis revealed that MC-derived HSCs and myofibroblasts store little vitamin A lipids and have fibrogenic phenotype in the fibrotic livers. MCs contributed to 1.4 and 2.0% of activated HSCs in the BDL and CCl4 models, respectively. During regression of CCl4-induced fibrosis, 20% of MC-derived myofibroblasts survived in the liver and deactivated to vitamin A-poor HSCs. Our data indicate that MCs participate in capsular fibrosis by supplying vitamin A-poor HSCs during a process of liver fibrosis and regression.

Myofibroblastic Conversion and Regeneration of Mesothelial Cells in Peritoneal and Liver Fibrosis.

Mesothelial cells (MCs) form a single epithelial layer and line the surface of body cavities and internal organs. Patients who undergo peritoneal dialysis often develop peritoneal fibrosis that is characterized by the accumulation of myofibroblasts in connective tissue. Although MCs are believed to be the source of myofibroblasts, their contribution has remained obscure. We determined the contribution of peritoneal MCs to myofibroblasts in chlorhexidine gluconate (CG)-induced fibrosis compared with that of phenotypic changes of liver MCs. CG injections resulted in disappearance of MCs from the body wall and the accumulation of myofibroblasts in the connective tissue. Conditional linage tracing with Wilms tumor 1 (Wt1)-CreERT2 and Rosa26 reporter mice found that 17% of myofibroblasts were derived from MCs in peritoneal fibrosis. Conditional deletion of transforming growth factor-ß type II receptor in Wt1(+) MCs substantially reduced peritoneal fibrosis. The CG treatment also induced myofibroblastic conversion of MCs in the liver. Lineage tracing with Mesp1-Cre mice revealed that Mesp1(+) mesoderm gave rise to liver MCs but not peritoneal MCs. During recovery from peritoneal fibrosis, peritoneal MCs, but not liver MCs, contribute to the regeneration of the peritoneal mesothelium, indicating an inherent difference between parietal and visceral MCs. In conclusion, MCs partially contribute to myofibroblasts in peritoneal and liver fibrosis, and protection of the MC layer leads to reduced development of fibrous tissue.

Mesodermal mesenchymal cells give rise to myofibroblasts, but not epithelial cells, in mouse liver injury.

UNLABELLED: Hepatic stellate cells (HSCs) and portal fibroblasts (PFs) are believed to be the major source of myofibroblasts that participate in fibrogenesis by way of synthesis of proinflammatory cytokines and extracellular matrices. Previous lineage tracing studies using MesP1(Cre) and Rosa26lacZ(flox) mice demonstrated that MesP1+ mesoderm gives rise to mesothelial cells (MCs), which differentiate into HSCs and PFs during liver development. In contrast, several in vivo and in vitro studies reported that HSCs can differentiate into other cell types, including hepatocytes, cholangiocytes, and progenitor cell types known as oval cells, thereby acting as stem cells in the liver. To test whether HSCs give rise to epithelial cells in adult liver, we determined the hepatic lineages of HSCs and PFs using MesP1(Cre) and Rosa26mTmG(flox) mice. Genetic cell lineage tracing revealed that the MesP1+ mesoderm gives rise to MCs, HSCs, and PFs, but not to hepatocytes or cholangiocytes, in the adult liver. Upon carbon tetrachloride injection or bile duct ligation surgery-mediated liver injury, mesodermal mesenchymal cells, including HSCs and PFs, differentiate into myofibroblasts but not into hepatocytes or cholangiocytes. Furthermore, differentiation of the mesodermal mesenchymal cells into oval cells was not observed. These results indicate that HSCs are not sufficiently multipotent to produce hepatocytes, cholangiocytes, or oval cells by way of mesenchymal-epithelial transition in vivo. CONCLUSION: Cell lineage tracing demonstrated that mesodermal mesenchymal cells including HSCs are the major source of myofibroblasts but do not differentiate into epithelial cell types such as hepatocytes, cholangiocytes, and oval cells.

Human pituitary tumor-transforming gene 1 overexpression reinforces oncogene-induced senescence through CXCR2/p21 signaling in breast cancer cells.

INTRODUCTION: hPTTG1 (human pituitary tumor-transforming gene 1) is an oncogene overexpressed in breast cancer and several other types of cancer. Increased hPTTG1 expression has been shown to be associated with poor patient outcomes in breast cancer. Although hPTTG1 overexpression plays important roles in promoting the proliferation, invasion, and metastasis of cancer cells, it also has been suggested to induce cellular senescence. Deciphering the mechanism by which hPTTG1 overexpression induces these contradictory actions in breast cancer cells is critical to our understanding of the role of hPTTG1 in breast cancer development. METHODS: MCF-10A and MCF-7 cells were used to identify the mechanism of hPTTG1-induced senescence. The interplay between hPTTG1 overexpression and chemokine C-X-C motif receptor 2 (CXCR2)/p21-dependent senescence in tumor growth and metastasis of MCF-7 cells was investigated by orthotopic transplantation of severe combined immunodeficiency (SCID) mice. Additionally, human invasive ductal carcinoma (IDC) tissue arrays were used to confirm the hPTTG1/CXCR2/p21 axis established in vitro. RESULTS: In this study, we investigated the mechanism of hPTTG1-induced senescence as well as its role in breast cancer progression and metastasis. Herein, we showed that hPTTG1 overexpression reinforced senescence through the CXCR2/p21 signaling. Furthermore, hPTTG1 overexpression activated NF-κB signaling to transactivate the expression of interleukin (IL)-8 and growth-regulated oncogene alpha (GROα) to execute CXCR2 signaling in MCF-7 cells. When CXCR2 expression was knocked down in hPTTG1-overexpressing MCF-7 cells, hPTTG1-induced senescence was abrogated by alleviating CXCR2-induced p21 expression. In a mouse model, CXCR2-mediated senescence limited hPTTG1-induced tumor growth and metastasis. Moreover, CXCR2 knockdown in hPTTG1-overexpressing MCF-7 tumors dramatically accelerated tumor growth and metastasis. Our in vitro and in vivo results demonstrated that hPTTG1 overexpression reinforces senescence through CXCR2 signaling, and the evasion of CXCR2/p21-dependent senescence was critical to hPTTG1 exerting its oncogenic potential. Interestingly, although CXCR2-dependent senescence restrained hPTTG1-induced tumor progression, when MCF-7 cells and hPTTG1-overexpressing MCF-7 cells were co-transplanted into the mammary fat pads of SCID mice, hPTTG1-overexpressing senescent cells created a metastasis-promoting microenvironment that promoted lung metastasis of the MCF-7 cells. Immunohistochemical analysis of human breast tumor samples also confirmed the importance of the hPTTG1/CXCR2 axis in promoting breast cancer metastasis. CONCLUSIONS: Our findings provide novel molecular insights into hPTTG1-induced senescence and identify a novel mechanism by which hPTTG1 promotes metastasis by regulating the senescence-associated microenvironment.

Hepatic Prominin-1 expression is associated with biliary fibrosis.

BACKGROUND: Intrahepatic biliary fibrosis, as seen with cholestatic liver injuries such as biliary atresia, is mechanistically distinct from fibrosis caused by hepatocyte toxicity. We previously demonstrated the expansion of cells expressing the stem/progenitor cell marker Prominin-1, within regions of developing fibrosis in biliary atresia. Thus, we hypothesized that Prominin-1 expression is biliary fibrosis-specific. METHODS: Gene expression of Prominin-1 was analyzed in adult mice undergoing either cholestatic bile duct ligation or hepatotoxic carbon tetrachloride administration by quantitative polymerase chair reaction. Lineage tracing of Prominin-1-expressing cells and Collagen-1α-expressing cells was performed after bile duct ligation in Prominin-1cre-ert2-lacz;Gfplsl and Collagen-1αGfp transgenic mice, respectively. RESULTS: Prominin-1 expression increased significantly after bile duct ligation compared with sham (6.6 ± 0.9-fold change at 2 weeks, P < .05) but not with carbon tetrachloride (-0.7 ± 0.5-fold change, not significant). Upregulation of Prominin-1 was observed histologically throughout the liver as early as 5 days after bile duct ligation in Prominin-1cre-ert2-lacz mice by LacZ staining in nonhepatocyte cells. Lineage tracing of Prominin-1-expressing cells labeled prior to bile duct ligation in Prominin-1cre-ert2-lacz;Gfplsl mice, demonstrated increasing colocalization of GREEN FLUORESCENT PROTEIN with biliary marker CYTOKERATIN-19 within ductular reactions up to 5 weeks after bile duct ligation consistent with biliary transdifferentiation. In contrast, rare colocalization of GREEN FLUORESCENT PROTEIN with mesenchymal marker α-SMOOTH MUSCLE ACTIN in Prominin-1cre-ert2-lacz;Gfplsl mice and some colocalization of GREEN FLUORESCENT PROTEIN with PROMININ-1 in Collagen-1αGfp mice, indicate minimal contribution of Prominin-1 progenitor cells to the pool of collagen-producing myofibroblasts. CONCLUSION: During biliary fibrosis Prominin-1-expressing progenitor cells transdifferentiate into cells within ductular reactions. This transdifferentiation may promote fibrosis.

The Role of Mesothelial Cells in Liver Development, Injury, and Regeneration.

Mesothelial cells (MCs) cover the surface of visceral organs and the parietal walls of cavities, and they synthesize lubricating fluids to create a slippery surface that facilitates movement between organs without friction. Recent studies have indicated that MCs play active roles in liver development, fibrosis, and regeneration. During liver development, the mesoderm produces MCs that form a single epithelial layer of the mesothelium. MCs exhibit an intermediate phenotype between epithelial cells and mesenchymal cells. Lineage tracing studies have indicated that during liver development, MCs act as mesenchymal progenitor cells that produce hepatic stellate cells, fibroblasts around blood vessels, and smooth muscle cells. Upon liver injury, MCs migrate inward from the liver surface and produce hepatic stellate cells or myofibroblast depending on the etiology, suggesting that MCs are the source of myofibroblasts in capsular fibrosis. Similar to the activation of hepatic stellate cells, transforming growth factor ß induces the conversion of MCs into myofibroblasts. Further elucidation of the biological and molecular changes involved in MC activation and fibrogenesis will contribute to the development of novel approaches for the prevention and therapy of liver fibrosis.

MACS Isolation and Culture of Mouse Liver Mesothelial Cells.

Mesothelial cells (MCs) form a single squamous epithelial cell layer and cover the surfaces of the internal organs, as well as the walls of cavities. The isolation of MCs is of great importance to study their function and characteristics for the understanding of physiology and pathophysiology of the liver. Glycoprotein M6a (GPM6A) was originally identified as a cell surface protein expressed in neurons and recently its expression was reported in epicardium and liver MCs (Wu et al., 2001; Bochmann et al., 2010; Li et al., 2012). Here we describe a method to isolate MCs from the adult mouse liver with anti-GPM6A antibodies. Under the low glucose and serum concentration, primary MCs grow and form epithelial colonies (Figure 1).

Replacing immunoassays for mephedrone, ketamines and six amphetamine-type stimulants with flow injection analysis tandem mass spectrometry.

A screening procedure was developed for the simultaneous detection of mephedrone, six amphetamine-type stimulants (ATS), ketamine and its two metabolites with electrospray ionization flow injection analysis tandem mass spectrometry (FIA-MS-MS). Urine samples were fortified with deuterated analogues as internal standards, extracted with ethyl acetate and analyzed with FIA-MS-MS. The mass analyzer was operated in multiple reaction monitoring mode. Two product ions were monitored for each drug and internal standards. For each analyte, the limit of detection was less than 4 µg/L, within-day and between-day precisions (percent coefficient of variation) at three different concentrations were less than 7.3% and bias was between -17.3 and 11.8%. Total analysis time with FIA-MS-MS is 1.8 min per sample. A group of 215 urine samples were screened with immunoassay for ATS and analyzed with FIA-MS-MS and gas chromatography-mass spectrometry (GC-MS) for ketamines and ATS. The analysis of ATS by immunoassay and GC-MS was 96.7% concordant. The analysis of three ketamines and seven ATS by FIA-MS-MS and GC-MS was 97.2% concordant. The FIA-MS-MS procedure is efficient, accurate, flexible and capable of detecting analytes of different chemical groups. It can replace immunoassays for the screening of new designer drugs when commercial immunoassays are unavailable.

The anti-motility signaling mechanism of TGFß3 that controls cell traffic during skin wound healing.

When skin is wounded, migration of epidermal keratinocytes at the wound edge initiates within hours, whereas migration of dermal fibroblasts toward the wounded area remains undetectable until several days later. This "cell type traffic" regulation ensures proper healing of the wound, as disruptions of the regulation could either cause delay of wound healing or result in hypertrophic scars. TGFß3 is the critical traffic controller that selectively halts migration of the dermal, but not epidermal, cells to ensure completion of wound re-epithelialization prior to wound remodeling. However, the mechanism of TGFß3's anti-motility signaling has never been investigated. We report here that activated TßRII transmits the anti-motility signal of TGFß3 in full to TßRI, since expression of the constitutively activated TßRI-TD mutant was sufficient to replace TGFß3 to block PDGF-bb-induced dermal fibroblast migration. Second, the three components of R-Smad complex are all required. Individual downregulation of Smad2, Smad3 or Smad4 prevented TGFß3 from inhibiting dermal fibroblast migration. Third, Protein Kinase Array allowed us to identify the protein kinase A (PKA) as a specific downstream effector of R-Smads in dermal fibroblasts. Activation of PKA alone blocked PDGF-bb-induced dermal fibroblast migration, just like TGFß3. Downregulation of PKA's catalytic subunit nullified the anti-motility signaling of TGFß3. This is the first report on anti-motility signaling mechanism by TGFß family cytokines. Significance of this finding is not only limited to wound healing but also to other human disorders, such as heart attack and cancer, where the diseased cells have often managed to avoid the anti-motility effect of TGFß.