Enhanced myofibroblastic differentiation and survival in Thy-1(-) lung fibroblasts

Epithelial-mesenchymal cell competition coordinates fate transitions across tissue compartments during lung development and fibrosis

Morphogenesis and cell state transitions must be coordinated in time and space to produce a functional tissue. In this study, we reveal that lung mesenchymal Yap levels and fitness antagonize epithelial Yap levels and stemness during lung development and repair following bleomycin injury. Elevated mesenchymal Yap signaling and fitness antagonize epithelial Yap levels and stemness, accelerating alveolar epithelial differentiation while impairing branching during lung development or bronchiolization after bleomycin injury. Conversely, mesenchymal Snail/Slug sequesters Yap/Taz to direct an adipogenic differentiation program towards alveolar fibroblast 1 (AF1) during both lung development and the resolution of pulmonary fibrosis. On the other hand, Yap/Myc-Tead binding instructs a myogenic differentiation program. Through our experiments and modeling, we identify tissue-scale mechanical cooperation as a pivotal factor in orchestrating organ formation and regeneration.

Thy-1 restricts steatosis and liver fibrosis in steatotic liver disease

BACKGROUND AND AIMS

Steatotic liver disease (SLD) is generally considered to represent a hepatic manifestation of metabolic syndrome and includes a disease spectrum comprising isolated steatosis, metabolic dysfunction-associated steatohepatitis, liver fibrosis and ultimately cirrhosis. A better understanding of the detailed underlying pathogenic mechanisms of this transition is crucial for the design of new and efficient therapeutic interventions. Thymocyte differentiation antigen (Thy-1, also known as CD90) expression on fibroblasts controls central functions relevant to fibrogenesis, including proliferation, apoptosis, cytokine responsiveness, and myofibroblast differentiation.

METHODS

The impact of Thy-1 on the development of SLD and progression to fibrosis was investigated in high-fat diet (HFD)-induced SLD wild-type and Thy-1-deficient mice. In addition, the serum soluble Thy-1 (sThy-1) concentration was analysed in patients with metabolic dysfunction-associated SLD stratified according to steatosis, inflammation, or liver fibrosis using noninvasive markers.

RESULTS

We demonstrated that Thy-1 attenuates the development of fatty liver and the expression of profibrogenic genes in the livers of HFD-induced SLD mice. Mechanistically, Thy-1 directly inhibits the profibrotic activation of nonparenchymal liver cells. In addition, Thy-1 prevents palmitic acid-mediated amplification of the inflammatory response of myeloid cells, which might indirectly contribute to the pronounced development of liver fibrosis in Thy-1-deficient mice. Serum analysis of patients with metabolically associated steatotic liver disease syndrome revealed that sThy-1 expression is correlated with liver fibrosis status, as assessed by liver stiffness, the Fib4 score, and the NAFLD fibrosis score.

CONCLUSION

Our data strongly suggest that Thy-1 may function as a fibrosis-protective factor in mouse and human SLD.

A Thy-1-negative immunofibroblast population emerges as a key determinant of fibrotic outcomes to biomaterials

Fibrosis-associated fibroblasts have been identified across various fibrotic disorders, but not in the context of biomaterials, fibrotic encapsulation, and the foreign body response. In other fibrotic disorders, a fibroblast subpopulation defined by Thy-1 loss is strongly correlated with fibrosis yet we do not know what promotes Thy-1 loss. We have previously shown that Thy-1 is an integrin regulator enabling normal fibroblast mechanosensing, and here, leveraging nonfibrotic microporous annealed particle (MAP) hydrogels versus classical fibrotic bulk hydrogels, we demonstrate that Thy1-/- mice mount a fibrotic response to MAP gels that includes inflammatory signaling. We found that a distinct and cryptic α-smooth muscle actin-positive Thy-1- fibroblast population emerges in response to interleuklin-1β (IL-1β) and tumor necrosis factor-α (TNFα). Furthermore, IL-1β/TNFα-induced Thy-1- fibroblasts consist of two distinct subpopulations that are strongly proinflammatory. These findings illustrate the emergence of a unique proinflammatory, profibrotic fibroblast subpopulation that is central to fibrotic encapsulation of biomaterials.

O-GlcNAc regulates anti-fibrotic genes in lung fibroblasts through EZH2

Epigenetic modifications are involved in fibrotic diseases, such as idiopathic pulmonary fibrosis (IPF), and contribute to the silencing of anti-fibrotic genes. H3K27me3, a key repressive histone mark, is catalysed by the methyltransferase enhancer of Zeste homologue 2 (EZH2), which is regulated by the post-translational modification, O-linked N-Acetylglucosamine (O-GlcNAc). In this study, we explored the effects of O-GlcNAc and EZH2 on the expression of antifibrotic genes, cyclooxygenase-2 (Cox2) and Heme Oxygenase (Homx1). The expression of Cox2 and Hmox1 was examined in primary IPF or non-IPF lung fibroblasts with or without EZH2 inhibitor EZP6438, O-GlcNAc transferase (OGT) inhibitor (OSMI-1) or O-GlcNAcase (OGA) inhibitor (thiamet G). Non-IPF cells were also subjected to TGF-β1 with or without OGT inhibition. The reduced expression of Cox2 and Hmox1 in IPF lung fibroblasts is restored by OGT inhibition. In non-IPF fibroblasts, TGF-β1 treatment reduces Cox2 and Hmox1 expression, which was restored by OGT inhibition. ChIP assays demonstrated that the association of H3K27me3 is reduced at the Cox2 and Hmox1 promoter regions following OGT or EZH2 inhibition. EZH2 levels and stability were decreased by reducing O-GlcNAc. Our study provided a novel mechanism of O-GlcNAc modification in regulating anti-fibrotic genes in lung fibroblasts and in the pathogenesis of IPF.

Retrospective identification of cell-intrinsic factors that mark pluripotency potential in rare somatic cells

Pluripotency can be induced in somatic cells by the expression of OCT4, KLF4, SOX2, and MYC. Usually only a rare subset of cells reprogram, and the molecular characteristics of this subset remain unknown. We apply retrospective clone tracing to identify and characterize the rare human fibroblasts primed for reprogramming. These fibroblasts showed markers of increased cell cycle speed and decreased fibroblast activation. Knockdown of a fibroblast activation factor identified by our analysis increased the reprogramming efficiency. We provide evidence for a unified model in which cells can move into and out of the primed state over time, explaining how reprogramming appears deterministic at short timescales and stochastic at long timescales. Furthermore, inhibiting the activity of LSD1 enlarged the pool of cells that were primed for reprogramming. Thus, even homogeneous cell populations can exhibit heritable molecular variability that can dictate whether individual rare cells will reprogram or not.

Inositol possesses antifibrotic activity and mitigates pulmonary fibrosis

BACKGROUND

Myo-inositol (or inositol) and its derivatives not only function as important metabolites for multiple cellular processes but also act as co-factors and second messengers in signaling pathways. Although inositol supplementation has been widely studied in various clinical trials, little is known about its effect on idiopathic pulmonary fibrosis (IPF). Recent studies have demonstrated that IPF lung fibroblasts display arginine dependency due to loss of argininosuccinate synthase 1 (ASS1). However, the metabolic mechanisms underlying ASS1 deficiency and its functional consequence in fibrogenic processes are yet to be elucidated.

METHODS

Metabolites extracted from primary lung fibroblasts with different ASS1 status were subjected to untargeted metabolomics analysis. An association of ASS1 deficiency with inositol and its signaling in lung fibroblasts was assessed using molecular biology assays. The therapeutic potential of inositol supplementation in fibroblast phenotypes and lung fibrosis was evaluated in cell-based studies and a bleomycin animal model, respectively.

RESULTS

Our metabolomics studies showed that ASS1-deficient lung fibroblasts derived from IPF patients had significantly altered inositol phosphate metabolism. We observed that decreased inositol-4-monophosphate abundance and increased inositol abundance were associated with ASS1 expression in fibroblasts. Furthermore, genetic knockdown of ASS1 expression in primary normal lung fibroblasts led to the activation of inositol-mediated signalosomes, including EGFR and PKC signaling. Treatment with inositol significantly downregulated ASS1 deficiency-mediated signaling pathways and reduced cell invasiveness in IPF lung fibroblasts. Notably, inositol supplementation also mitigated bleomycin-induced fibrotic lesions and collagen deposition in mice.

CONCLUSION

These findings taken together demonstrate a novel function of inositol in fibrometabolism and pulmonary fibrosis. Our study provides new evidence for the antifibrotic activity of this metabolite and suggests that inositol supplementation may be a promising therapeutic strategy for IPF.

Cardiac PDGFRα+ interstitial cells generate spontaneous inward currents that contribute to excitability in the heart

The cell types and conductance that contribute to normal cardiac functions remain under investigation. We used mice that express an enhanced green fluorescent protein (eGFP)-histone 2B fusion protein driven off the cell-specific endogenous promoter for Pdgfra to investigate the distribution and functional role of PDGFRα+ cells in the heart. Cardiac PDGFRα+ cells were widely distributed within the endomysium of atria, ventricle, and sino-atrial node (SAN) tissues. PDGFRα+ cells formed a discrete network of cells, lying in close apposition to neighboring cardiac myocytes in mouse and Cynomolgus monkey (Macaca fascicularis) hearts. Expression of eGFP in nuclei allowed unequivocal identification of these cells following enzymatic dispersion of muscle tissues. FACS purification of PDGFRα+ cells from the SAN and analysis of gene transcripts by qPCR revealed that they were a distinct population of cells that expressed gap junction transcripts, Gja1 and Gjc1. Cardiac PDGFRα+ cells generated spontaneous transient inward currents (STICs) and spontaneous transient depolarizations (STDs) that reversed at 0 mV. Reversal potential was maintained when ECl  = -40 mV. [Na+ ]o replacement and FTY720 abolished STICs, suggesting they were due to a non-selective cation conductance (NSCC) carried by TRPM7. PDGFRα+ cells also express β2 -adrenoceptor gene transcripts, Adrb2. Zinterol, a selective β2 -receptor agonist, increased the amplitude and frequency of STICs, suggesting these cells could contribute to adrenergic regulation of cardiac excitability. PDGFRα+ cells in cardiac muscles generate inward currents via an NSCC. STICs generated by these cells may contribute to the integrated membrane potentials of cardiac muscles, possibly affecting the frequency of pacemaker activity.

Mesenchymal cells in the Lung: Evolving concepts and their role in fibrosis

Mesenchymal cells in the lung are crucial during development, but also contribute to the pathogenesis of fibrotic disorders, including idiopathic pulmonary fibrosis (IPF), the most common and deadly form of fibrotic interstitial lung diseases. Originally thought to behave as supporting cells for the lung epithelium and endothelium with a singular function of producing basement membrane, mesenchymal cells encompass a variety of cell types, including resident fibroblasts, lipofibroblasts, myofibroblasts, smooth muscle cells, and pericytes, which all occupy different anatomic locations and exhibit diverse homeostatic functions in the lung. During injury, each of these subtypes demonstrate remarkable plasticity and undergo varying capacity to proliferate and differentiate into activated myofibroblasts. Therefore, these cells secrete high levels of extracellular matrix (ECM) proteins and inflammatory cytokines, which contribute to tissue repair, or in pathologic situations, scarring and fibrosis. Whereas epithelial damage is considered the initial trigger that leads to lung injury, lung mesenchymal cells are recognized as the ultimate effector of fibrosis and attempts to better understand the different functions and actions of each mesenchymal cell subtype will lead to a better understanding of why fibrosis develops and how to better target it for future therapy. This review summarizes current findings related to various lung mesenchymal cells as well as signaling pathways, and their contribution to the pathogenesis of pulmonary fibrosis.

Retrospective identification of intrinsic factors that mark pluripotency potential in rare somatic cells

Pluripotency can be induced in somatic cells by the expression of the four "Yamanaka" factors OCT4, KLF4, SOX2, and MYC. However, even in homogeneous conditions, usually only a rare subset of cells admit reprogramming, and the molecular characteristics of this subset remain unknown. Here, we apply retrospective clone tracing to identify and characterize the individual human fibroblast cells that are primed for reprogramming. These fibroblasts showed markers of increased cell cycle speed and decreased fibroblast activation. Knockdown of a fibroblast activation factor identified by our analysis led to increased reprogramming efficiency, identifying it as a barrier to reprogramming. Changing the frequency of reprogramming by inhibiting the activity of LSD1 led to an enlarging of the pool of cells that were primed for reprogramming. Our results show that even homogeneous cell populations can exhibit heritable molecular variability that can dictate whether individual rare cells will reprogram or not.

Role and mechanism of CD90+ fibroblasts in inflammatory diseases and malignant tumors

Fibroblasts are highly heterogeneous mesenchymal stromal cells, and different fibroblast subpopulations play different roles. A subpopulation of fibroblasts expressing CD90, a 25-37 kDa glycosylphosphatidylinositol anchored protein, plays a dominant role in the fibrotic and pro-inflammatory state. In this review, we focused on CD90⁺ fibroblasts, and their roles and possible mechanisms in disease processes. First, the main biological functions of CD90⁺ fibroblasts in inducing angiogenesis and maintaining tissue homeostasis are described. Second, the role and possible mechanism of CD90⁺ fibroblasts in inducing pulmonary fibrosis, inflammatory arthritis, inflammatory skin diseases, and scar formation are introduced, and we discuss how CD90⁺ cancer-associated fibroblasts might serve as promising cancer biomarkers. Finally, we propose future research directions related to CD90⁺ fibroblasts. This review will provide a theoretical basis for the diagnosis and treatment CD90⁺ fibroblast-related disease.

Antifibrotic Soluble Thy-1 Correlates with Renal Dysfunction in Chronic Kidney Disease

Kidney fibrosis is a major culprit in the development and progression of chronic kidney disease (CKD), ultimately leading to the irreversible loss of organ function. Thymocyte differentiation antigen-1 (Thy-1) controls many core functions of fibroblasts relevant to fibrogenesis but is also found in a soluble form (sThy-1) in serum and urine. We investigated the association of sThy-1 with clinical parameters in patients with CKD receiving hemodialysis treatment compared to individuals with a preserved renal function. Furthermore, Thy-1 tissue expression was detected in a mouse model of diabetic CKD (eNOS-/-; db/db) and non-diabetic control mice (eNOS-/-). Serum and urinary sThy-1 concentrations significantly increased with deteriorating renal function, independent of the presence of diabetes. Serum creatinine is the major, independent, and inverse predictor of serum sThy-1 levels. Moreover, sThy-1 is not only predicted by markers of renal function but is also itself an independent and strong predictor of markers of renal function, i.e., serum creatinine. Mice with severe diabetic CKD show increased Thy-1 mRNA and protein expression in the kidney compared to control animals, as well as elevated urinary sThy-1 levels. Pro-fibrotic mediators, such as interleukin (IL)-4, IL-13, IL-6 and transforming growth factor β, increase Thy-1 gene expression and release of sThy-1 from fibroblasts. Our data underline the role of Thy-1 in the control of kidney fibrosis in CKD and raise the opportunity that Thy-1 may function as a renal antifibrotic factor.

Epigenetic regulation of IPF fibroblast phenotype by glutaminolysis

OBJECTIVE

Excessive extra-cellular-matrix production and uncontrolled proliferation of the fibroblasts are characteristics of many fibrotic diseases, including idiopathic pulmonary fibrosis (IPF). The fibroblasts have enhanced glutaminolysis with up-regulated glutaminase, GLS1, which converts glutamine to glutamate. Here, we investigated the role of glutaminolysis and glutaminolysis-derived metabolite α-ketoglutarate (α-KG) on IPF fibroblast phenotype and gene expression.

METHODS

Reduced glutamine conditions were carried out either using glutamine-free culture medium or silencing the expression of GLS1 with siRNA, with or without α-KG compensation. Cell phenotype has been characterized under these different conditions, and gene expression profile was examined by RNA-Seq. Specific profibrotic genes (Col3A1 and PLK1) expression were examined by real-time PCR and western blots. The levels of repressive histone H3K27me3, which demethylase activity is affected by glutaminolysis, were examined and H3K27me3 association with promoter region of Col3A1 and PLK1 were checked by ChIP assays. Effects of reduced glutaminolysis on fibrosis markers were checked in an animal model of lung fibrosis.

RESULTS

The lack of glutamine in the culture medium alters the profibrotic phenotype of activated fibroblasts. The addition of exogenous and glutaminolysis-derived metabolite α-KG to glutamine-free media barely restores the pro-fibrotic phenotype of activated fibroblasts. Many genes are down-regulated in glutamine-free medium, α-KG supplementation only rescues a limited number of genes. As α-KG is a cofactor for histone demethylases of H3K27me3, the reduced glutaminolysis alters H3K27me3 levels, and enriches H3K27me3 association with Col3A1 and PLK1 promoter region. Adding α-KG in glutamine-free medium depleted H3K27me3 association with Col3A1 promoter region but not that of PLK1. In a murine model of lung fibrosis, mice with reduced glutaminolysis showed markedly reduced fibrotic markers.

CONCLUSIONS

This study indicates that glutamine is critical for supporting pro-fibrotic fibroblast phenotype in lung fibrosis, partially through α-KG-dependent and -independent mechanisms, and supports targeting fibroblast metabolism as a therapeutic method for fibrotic diseases.

The Genetic and Epigenetic Footprint in Idiopathic Pulmonary Fibrosis and Familial Pulmonary Fibrosis: A State-of-the-Art Review

Idiopathic pulmonary fibrosis (IPF) is a rare disease of the lung with a largely unknown etiology and a poor prognosis. Intriguingly, forms of familial pulmonary fibrosis (FPF) have long been known and linked to specific genetic mutations. There is little evidence of the possible role of genetics in the etiology of sporadic IPF. We carried out a non-systematic, narrative literature review aimed at describing the main known genetic and epigenetic mechanisms that are involved in the pathogenesis and prognosis of IPF and FPF. In this review, we highlighted the mutations in classical genes associated with FPF, including those encoding for telomerases (TERT, TERC, PARN, RTEL1), which are also found in about 10-20% of cases of sporadic IPF. In addition to the Mendelian forms, mutations in the genes encoding for the surfactant proteins (SFTPC, SFTPA1, SFTPA2, ABCA3) and polymorphisms of genes for the mucin MUC5B and the Toll-interacting protein TOLLIP are other pathways favoring the fibrogenesis that have been thoroughly explored. Moreover, great attention has been paid to the main epigenetic alterations (DNA methylation, histone modification and non-coding RNA gene silencing) that are emerging to play a role in fibrogenesis. Finally, a gaze on the shared mechanisms between cancer and fibrogenesis, and future perspectives on the genetics of pulmonary fibrosis have been analyzed.

The Role of Mesothelin in Activation of Portal Fibroblasts in Cholestatic Liver Injury

Fibrosis is a common consequence of abnormal wound healing, which is characterized by infiltration of myofibroblasts and formation of fibrous scar. In liver fibrosis, activated Hepatic Stellate Cells (aHSCs) and activated Portal Fibroblasts (aPFs) are the major contributors to the origin of hepatic myofibroblasts. aPFs are significantly involved in the pathogenesis of cholestatic fibrosis, suggesting that aPFs may be a primary target for anti-fibrotic therapy in cholestatic injury. aPFs are distinguishable from aHSCs by specific markers including mesothelin (Msln), Mucin 16 (Muc16), and Thymus cell antigen 1 (Thy1, CD90) as well as fibulin 2, elastin, Gremlin 1, ecto-ATPase nucleoside triphosphate diphosphohydrolase 2. Msln plays a critical role in activation of PFs, via formation of Msln-Muc16-Thy1 complex that regulates TGFβ1/TGFβRI-mediated fibrogenic signaling. The opposing pro- and anti-fibrogenic effects of Msln and Thy1 are key components of the TGFβ1-induced activation pathway in aPFs. In addition, aPFs and activated lung and kidney fibroblasts share similarities across different organs with expression of common markers and activation cascade including Msln-Thy1 interaction. Here, we summarize the potential function of Msln in activation of PFs and development of cholestatic fibrosis, offering a novel perspective for anti-fibrotic therapy targeting Msln.

Thy-1-Integrin Interactions in cis and Trans Mediate Distinctive Signaling

Thy-1 is a cell surface glycosylphosphatidylinositol (GPI)-anchored glycoprotein that bears a broad mosaic of biological roles across various cell types. Thy-1 displays strong physiological and pathological implications in development, cancer, immunity, and tissue fibrosis. Quite uniquely, Thy-1 is capable of mediating integrin-related signaling through direct trans- and cis-interaction with integrins. Both interaction types have shown distinctive roles, even when interacting with the same type of integrin, where binding in trans or in cis often yields divergent signaling events. In this review, we will revisit recent progress and discoveries of Thy-1–integrin interactions in trans and in cis, highlight their pathophysiological consequences and explore other potential binding partners of Thy-1 within the integrin regulation/signaling paradigm.

Modulation of H4K16Ac levels reduces pro-fibrotic gene expression and mitigates lung fibrosis in aged mice

Histone H4 lysine16 acetylation (H4K16Ac) modulates chromatin structure by serving as a switch from a repressive to a transcriptionally active state. This euchromatin mark is associated with active transcription. In this study, we investigated the effects of H4K16Ac on the expression of pro-fibrotic genes in lung fibroblasts from patients with idiopathic pulmonary fibrosis (IPF) and in an aging murine model of lung fibrosis. Methods: The lung tissues and fibroblasts from human IPF/non-IPF donors and from aged mice with/without bleomycin induced lung fibrosis were used in this study. The H4K16Ac levels were examined by immunohistochemistry or western blots. RNA silencing of H4K16Ac acetyltransferase Mof was used to reduce H4K16Ac levels in IPF fibroblasts. The effects of reduced H4K16Ac on pro-fibrotic gene expression were examined by western blots and real-time PCR. The association of H4K16Ac with these genes' promoter region were evaluated by ChIP assays. The gene expression profile in siRNA Mof transfected IPF cells were determined by RNA-Seq. The impact of H4K16Ac levels on lung fibrosis was evaluated in an aging murine model. Results: Aged mice with bleomycin induced lung fibrosis showed increased H4K16Ac levels. Human lung fibroblasts with siRNA Mof silencing demonstrated reduced H4K16Ac, and significantly down-regulated profibrotic genes, such as α-smooth muscle actin (α-SMA), collagen I, Nox4, and survivin. ChIP assays confirmed the associations of these pro-fibrotic genes' promoter region with H4K16Ac, while in siRNA Mof transfected cells the promoter/H4K16Ac associations were depleted. RNA-seq data demonstrated that Mof knockdown altered gene expression and cellular pathways, including cell damage and repair. In the aging mice model of persistent lung fibrosis, 18-month old mice given intra-nasal siRNA Mof from week 3 to 6 following bleomycin injury showed improved lung architecture, decreased total hydroxyproline content and lower levels of H4K16Ac. Conclusions: These results indicate a critical epigenetic regulatory role for histone H4K16Ac in the pathogenesis of pulmonary fibrosis, which will aid in the development of novel therapeutic strategies for age-related diseases such as IPF.

The role of Mesothelin signaling in Portal Fibroblasts in the pathogenesis of cholestatic liver fibrosis

Liver fibrosis develops in response to chronic toxic or cholestatic injury, and is characterized by apoptosis of damaged hepatocytes, development of inflammatory responses, and activation of Collagen Type I producing myofibroblasts that make liver fibrotic. Two major cell types, Hepatic Stellate Cells (HSCs) and Portal Fibroblasts (PFs) are the major source of hepatic myofibroblasts. Hepatotoxic liver injury activates Hepatic Stellate Cells (aHSCs) to become myofibroblasts, while cholestatic liver injury activates both aHSCs and Portal Fibroblasts (aPFs). aPFs comprise the major population of myofibroblasts at the onset of cholestatic injury, while aHSCs are increasingly activated with fibrosis progression. Here we summarize our current understanding of the role of aPFs in the pathogenesis of cholestatic fibrosis, their unique features, and outline the potential mechanism of targeting aPFs in fibrotic liver.

Interrelation Between Fibroblasts and T Cells in Fibrosing Interstitial Lung Diseases

Interstitial lung diseases (ILDs) are a heterogeneous group of diseases characterized by varying degrees of inflammation and fibrosis of the pulmonary interstitium. The interrelations between multiple immune cells and stromal cells participate in the pathogenesis of ILDs. While fibroblasts contribute to the development of ILDs through secreting extracellular matrix and proinflammatory cytokines upon activation, T cells are major mediators of adaptive immunity, as well as inflammation and autoimmune tissue destruction in the lung of ILDs patients. Fibroblasts play important roles in modulating T cell recruitment, differentiation and function and conversely, T cells can balance fibrotic sequelae with protective immunity in the lung. A more precise understanding of the interrelation between fibroblasts and T cells will enable a better future therapeutic design by targeting this interrelationship. Here we highlight recent work on the interactions between fibroblasts and T cells in ILDs, and consider the implications of these interactions in the future development of therapies for ILDs.

Categorization of lung mesenchymal cells in development and fibrosis

Pulmonary mesenchymal cells are critical players in both the mouse and human during lung development and disease states. They are increasingly recognized as highly heterogeneous, but there is no consensus on subpopulations or discriminative markers for each subtype. We completed scRNA-seq analysis of mesenchymal cells from the embryonic, postnatal, adult and aged fibrotic lungs of mice and humans. We consistently identified and delineated the transcriptome of lipofibroblasts, myofibroblasts, smooth muscle cells, pericytes, mesothelial cells, and a novel population characterized by Ebf1 expression. Subtype selective transcription factors and putative divergence of the clusters during development were described. Comparative analysis revealed orthologous subpopulations with conserved transcriptomic signatures in murine and human lung mesenchymal cells. All mesenchymal subpopulations contributed to matrix gene expression in fibrosis. This analysis would enhance our understanding of mesenchymal cell heterogeneity in lung development, homeostasis and fibrotic disease conditions.

Immune Stroma in Lung Cancer and Idiopathic Pulmonary Fibrosis: A Common Biologic Landscape?

Idiopathic pulmonary fibrosis (IPF) identifies a specific entity characterized by chronic, progressive fibrosing interstitial pneumonia of unknown cause, still lacking effective therapies. Growing evidence suggests that the biologic processes occurring in IPF recall those which orchestrate cancer onset and progression and these findings have already been exploited for therapeutic purposes. Notably, the incidence of lung cancer in patients already affected by IPF is significantly higher than expected. Recent advances in the knowledge of the cancer immune microenvironment have allowed a paradigm shift in cancer therapy. From this perspective, recent experimental reports suggest a rationale for immune checkpoint inhibition in IPF. Here, we recapitulate the most recent knowledge on lung cancer immune stroma and how it can be translated into the IPF context, with both diagnostic and therapeutic implications.

Urinary soluble CD90 predicts renal prognosis in patients with diabetic kidney disease

Background

Diabetic kidney disease (DKD), the major cause of chronic kidney disease, is associated with progressive renal fibrosis. The expression of CD90 correlated with fibrogenesis. However, the association between urinary soluble CD90 and renal disease severity, and whether it predicts outcomes in patients with DKD are still unclear.

Methods

Urinary sCD90 was measured in 285 patients with DKD in a longitudinal cohort. The composite endpoint was defined as end-stage renal disease (ESRD) or 40% reduction of estimated glomerular filtration rate (eGFR). The associations between urinary sCD90/Cr and clinical parameters, as well as renal outcomes were evaluated. Moreover, we detected the intrarenal CD90 expression, and demonstrated the correlation of intrarenal CD90 with clinico-pathological parameters.

Results

The urinary sCD90 level of DKD patients is significantly higher than diabetes patients without kidney injuries and healthy controls. We further showed urinary sCD90/Cr had significantly correlations with eGFR (r=−0.373, P<0.001), uACR (r=0.303, P<0.001), serum creatinine (r=0.344, P<0.001), and the eGFR slope (r=−0.27, P<0.001). Elevated urinary sCD90/Cr was an independent risk factor for the composite endpoint, adjustment for potential confounders in DKD patients (HR 1.20, 95% CI: 1.04–1.38, P=0.015). However, the CD90 expression in the renal tubulointerstitial compartment in DKD patients was significantly lower than healthy controls, and showed significant negative correlations with the interstitial fibrosis and tubular atrophy score (IFTA) (r=−0.3, P=0.047), and urinary sCD90/Cr (r=−0.399, P=0.029).

Conclusions

This study provided evidence that urinary sCD90 could reflect the disease severity and serve as a valuable factor for renal outcome prediction in patients with DKD.

Therapeutic targeting of argininosuccinate synthase 1 (ASS1)-deficient pulmonary fibrosis

Argininosuccinate synthase 1 (ASS1) serves as a critical enzyme in arginine biosynthesis; however, its role in interstitial lung diseases, particularly idiopathic pulmonary fibrosis (IPF), remains largely unknown. This study aims at characterization and targeting of ASS1 deficiency in pulmonary fibrosis. We find that ASS1 was significantly decreased and inversely correlated with fibrotic status. Transcriptional downregulation of ASS1 was noted in fibroblastic foci of primary lung fibroblasts isolated from IPF patients. Genetic manipulations of ASS1 studies confirm that ASS1 expression inhibited fibroblast cell proliferation, migration, and invasion. We further show that the hepatocyte growth factor receptor (Met) receptor was activated and acted upstream of the Src-STAT3 axis signaling in ASS1-knockdown fibroblasts. Interestingly, both arginine-free conditions and arginine deiminase treatment were demonstrated to kill fibrotic fibroblasts, attenuated bleomycin-induced pulmonary fibrosis in mice, as well as synergistically increased nintedanib efficacy. Our data suggest ASS1 deficiency as a druggable target and also provide a unique therapeutic strategy against pulmonary fibrosis.

Research Advances on DNA Methylation in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic complex lung disease with no specific treatment and poor prognosis, characterized by the pulmonary progressive fibrosis and dysfunctions that lead to respiratory failure. Several factors may impact the progress of IPF, including age, cigarette smoking, and dusts, of which genetic and epigenetic factors mainly contribute to lung tissue fibrosis. DNA methylation is one of epigenetic processes that occur in many diseases and regulate chromosomal and extrachromosomal DNA functions in response to environmental exposures. The methylation plays pivotal roles in regulation of gene expression to facilitate the formation of fibroblastic foci and lung fibrosis. This chapter will describe alterations and effects of the DNA methylation on gene expression, the potential application of DNA methylation as a biomarker, and significance as therapeutic targets. Those understanding will provide us new insight into the treatment and prognosis of IPF.

Idiopathic Pulmonary Fibrosis and Lung Cancer. A Systematic Review and Meta-analysis

Rationale: The association between idiopathic pulmonary fibrosis (IPF) and lung cancer has been previously reported. However, there is the potential for significant confounding by age and smoking, and an accurate summary risk estimate has not been previously ascertained.Objectives: To determine the risk and burden of lung cancer in patients with IPF, accounting for known confounders.Methods: We conducted a comprehensive literature search of MEDLINE, EMBASE, and SCOPUS databases and used the Newcastle Ottawa criteria to assess study quality. We then assessed the quality of ascertainment of IPF cases based on modern consensus criteria. Data that relied on administrative claims or autopsies were excluded. We calculated summary risk estimates using a random effects model.Results: Twenty-five cohort studies were included in the final analysis. The estimated adjusted incidence rate ratio from two studies was 6.42 (95% confidence interval [CI], 3.21-9.62) and accounted for age, sex, and smoking. The summary incidence rate from 11 studies was 2.07 per 100 person-years (95% CI, 1.46-2.67), and the summary mortality rate was 1.06 per 100 person-years (95% CI, 0.62-1.51) obtained from three studies. The summary prevalence from 11 studies was 13.74% (95% CI, 10.17-17.30), and the proportion of deaths attributable to lung cancer was 10.20 (95% CI, 8.52-11.87) and was obtained from nine studies.Conclusions: IPF is an increased independent risk factor for lung cancer, even after accounting for smoking. Further well-designed studies using modern consensus criteria are needed to explore mechanisms of this association.

DNA Methylation in Pulmonary Fibrosis

DNA methylations, including global methylation pattern and specific gene methylation, are associated with pathogenesis and progress of pulmonary fibrosis. This chapter illustrates alteration of DNA methylation in pulmonary fibrosis as a predictive or prognostic factor. Treatment with the DNA methylation inhibitors will be an emerging anti-fibrosis therapy, although we are still in the pre-clinical stage of using epigenetic markers as potential targets for biomarkers and therapeutic interventions.

The elephant in the lung: Integrating lineage-tracing, molecular markers, and single cell sequencing data to identify distinct fibroblast populations during lung development and regeneration

During lung development, the mesenchyme and epithelium are dependent on each other for instructive morphogenic cues that direct proliferation, cellular differentiation and organogenesis. Specification of epithelial and mesenchymal cell lineages occurs in parallel, forming cellular subtypes that guide the formation of both transitional developmental structures and the permanent architecture of the adult lung. While epithelial cell types and lineages have been relatively well-defined in recent years, the definition of mesenchymal cell types and lineage relationships has been more challenging. Transgenic mouse lines with permanent and inducible lineage tracers have been instrumental in identifying lineage relationships among epithelial progenitor cells and their differentiation into distinct airway and alveolar epithelial cells. Lineage tracing experiments with reporter mice used to identify fibroblast progenitors and their lineage trajectories have been limited by the number of cell specific genes and the developmental timepoint when the lineage trace was activated. In this review, we discuss major developmental mesenchymal lineages, focusing on time of origin, major cell type, and other lineage derivatives, as well as the transgenic tools used to find and define them. We describe lung fibroblasts using function, location, and molecular markers in order to compare and contrast cells with similar functions. The temporal and cell-type specific expression of fourteen "fibroblast lineage" genes were identified in single-cell RNA-sequencing data from LungMAP in the LGEA database. Using these lineage signature genes as guides, we clustered murine lung fibroblast populations from embryonic day 16.5 to postnatal day 28 (E16.5-PN28) and generated heatmaps to illustrate expression of transcription factors, signaling receptors and ligands in a temporal and population specific manner.

Allogeneic Decellularized Muscle Scaffold Is Less Fibrogenic and Inflammatory than Acellular Dermal Matrices in a Rat Model of Skeletal Muscle Regeneration

BACKGROUND

Skeletal muscle trauma can produce grave functional deficits, but therapeutic options remain limited. The authors studied whether a decellularized skeletal muscle scaffold would provide benefits in inducing skeletal muscle regeneration over acellular dermal matrices.

METHODS

Eighty-two rat muscle defects were surgically created and assigned to no intervention or implantation of AlloDerm, Strattice, decellularized rat muscle, or decellularized rat dermis to 30 or 60 days. Decellularized rat muscle and dermis were prepared using a negative pressure-assisted protocol. Assessment for cellularity, neovascularization, myogenesis, inflammation and fibrosis were done histologically and by polymerase chain reaction.

RESULTS

Histology showed relative hypercellularity of AlloDerm (p < 0.003); Strattice appeared encapsulated. Immunofluorescence for CD31 and myosin heavy chain in decellularized rat muscle revealed dense microvasculature and peripheral islands of myogenesis. MyoD expression in muscle scaffolds was 23-fold higher than in controls (p < 0.01). Decellularized rat muscle showed no up-regulation of COX-2 (p < 0.05), with less expression than decellularized rat dermis and Strattice (p < 0.002). Decellularized rat muscle scaffolds expressed tumor necrosis factor-α less than Strattice, AlloDerm, and decellularized rat dermis (p < 0.01); collagen-1a less than decellularized rat dermis and Strattice (p < 0.04); α-smooth muscle actin 7-fold less than AlloDerm (p = 0.04); and connective tissue growth factor less than Strattice, AlloDerm, and decellularized rat dermis (p < 0.02).

CONCLUSION

Decellularized muscle matrix appears to reduce inflammation and fibrosis in an animal muscle defect as compared with dermal matrices and promotes greater expression of myocyte differentiation-inducing genes.

Brd4-p300 inhibition downregulates Nox4 and accelerates lung fibrosis resolution in aged mice

Tissue regeneration capacity declines with aging in association with heightened oxidative stress. Expression of the oxidant-generating enzyme, NADPH oxidase 4 (Nox4), is elevated in aged mice with diminished capacity for fibrosis resolution. Bromodomain-containing protein 4 (Brd4) is a member of the bromodomain and extraterminal (BET) family of proteins that function as epigenetic "readers" of acetylated lysine groups on histones. In this study, we explored the role of Brd4 and its interaction with the p300 acetyltransferase in the regulation of Nox4 and the in vivo efficacy of a BET inhibitor to reverse established age-associated lung fibrosis. BET inhibition interferes with the association of Brd4, p300, and acetylated histone H4K16 with the Nox4 promoter in lung fibroblasts stimulated with the profibrotic cytokine, TGF-β1. A number of BET inhibitors, including I-BET-762, JQ1, and OTX015, downregulate Nox4 gene expression and activity. Aged mice with established and persistent lung fibrosis recover capacity for fibrosis resolution with OTX015 treatment. This study implicates epigenetic regulation of Nox4 by Brd4 and p300 and supports BET/Brd4 inhibition as an effective strategy for the treatment of age-related fibrotic lung disease.

The multiple roles of Thy-1 in cell differentiation and regeneration

Thy-1 is a 25-37 kDa glycophosphatidylinositol (GPI)-anchored cell surface protein that was discovered more than 50 years ago. Recent findings have suggested that Thy-1 is expressed on thymocytes, mesenchymal stem cells (MSCs), cancer stem cells, hematopoietic stem cells, fibroblasts, myofibroblasts, endothelial cells, neuronal smooth muscle cells, and pan T cells. Thy-1 plays vital roles in cell migration, adhesion, differentiation, transdifferentiation, apoptosis, mechanotransduction, and cell division, which in turn are involved in tumor development, pulmonary fibrosis, neurite outgrowth, and T cell activation. Studies have increasingly indicated a significant role of Thy-1 in cell differentiation and regeneration. However, despite recent research, many questions remain regarding the roles of Thy-1 in cell differentiation and regeneration. This review aimed to summarize the roles of Thy-1 in cell differentiation and regeneration. Furthermore, since Thy-1 is an outer leaflet membrane protein anchored by GPI, we attempted to address how Thy-1 regulates intracellular pathways through cis and trans signals. Due to the complexity and mystery surrounding the issue, we also summarized the Thy-1-related pathways in different biological processes, and this might provide novel insights in the field of cell differentiation and regeneration.

MeCP2 epigenetically regulates alpha-smooth muscle actin in human lung fibroblasts

BACKGROUND

A critical feature for fibroblasts differentiation into myofibroblasts is the expression of alpha-smooth muscle actin (α-SMA) during the tissue injury and repair process. The epigenetic mechanism, DNA methylation, is involved in regulating α-SMA expression. It is not clear how methyl-CpG-binding protein 2 (MeCP2) interacts with CpG-rich region in α-SMA, and if the CpG methylation status would affect MeCP2 binding and regulation of α-SMA expression.

METHODS

The association of MeCP2 with α-SMA CpG rich region were examined by chromatin immunoprecipitation (ChIP) assays in primary fibroblasts from idiopathic pulmonary fibrosis (IPF) and non-IPF control individuals, and in the lung fibroblasts treated with profibrotic cytokine transforming growth factor β1 (TGF-β1). The regulation of α-SMA by MeCP2 was examined by knocking down MeCP2 with small interfering RNA (siRNA). To explore the effects of the DNA methylation status of the CpG rich region on α-SMA expression, the cells were treated with DNA methyltransferase inhibitor, 5'-azacytidine (5'-aza). The expression of α-SMA was examined by Western blot and quantitative polymerase chain reaction, the association with MeCP2 was assessed by ChIP assays, and the methylation status was checked by bisulfate sequencing.

RESULTS

The human lung fibroblasts with increased α-SMA showed an enriched association of MeCP2, while knockdown MeCP2 by siRNA reduced α-SMA upregulation by TGF-β1. The 5'-Aza-treated cells have decreased α-SMA expression with reduced MeCP2 association. However, bisulfite sequencing revealed that most CpG sites are unmethylated despite the different expression levels of α-SMA after being treated by TGF-β1 or 5'-aza.

CONCLUSION

Our data indicate that the methyl-binding protein MeCP2 is critical for α-SMA expression in human lung myofibroblast, and the DNA methylation status at the CpG rich region of α-SMA is not a determinative factor for its inducible expression.

Lack of Thy1 defines a pathogenic fraction of cardiac fibroblasts in heart failure

In response to heart injury, inflammation, or mechanical overload, quiescent cardiac fibroblasts (CFs) can become activated myofibroblasts leading to pathological matrix remodeling and decline in cardiac function. Specific targeting of fibroblasts may thus enable new therapeutic strategies to delay or reverse the progression of heart failure and cardiac fibrosis. However, it remains unknown if all CFs are equally responsive to specific pathological insults and if there exist sub-populations of resident fibroblasts in the heart that have distinctive pathogenic phenotypes. Here, we show that in response to transverse aortic constriction (TAC)-induced heart failure, previously uncharacterized Thy1^neg (Thy1-/MEFSK4+/CD45-/CD31-) fraction of mouse ventricular fibroblasts became more abundant and attained a more activated, pro-fibrotic myofibroblast phenotype compared to Thy1^Pos fraction. In a tissue-engineered 3D co-culture model of healthy cardiomyocytes and freshly isolated CFs, Thy1^neg CFs from TAC hearts significantly decreased cardiomyocyte contractile function and calcium transient amplitude, and increased extracellular collagen deposition yielding a profibrotic heart tissue phenotype. In vivo, mice with global knockout of Thy1 developed more severe cardiac dysfunction and fibrosis in response to TAC-induced heart failure than wild-type mice. Taken together, our studies identify cardiac myofibroblasts lacking Thy1 as a pathogenic CF fraction in cardiac fibrosis and suggest important roles of Thy1 in pathophysiology of heart failure.

CD248 and integrin alpha-8 are candidate markers for differentiating lung fibroblast subtypes

Background

Lung fibrosis is a serious life-threatening condition whose manifestation varies according to the localization and characteristics of fibroblasts, which are considered heterogeneous. Therefore, to better understand the pathology and improve diagnosis and treatment of this disease, it is necessary to elucidate the nature of this heterogeneity and identify markers for the accurate classification of human lung fibroblast subtypes.

Methods

We characterized distinct mouse lung fibroblast subpopulations isolated by fluorescence-activated cell sorting (FACS) and performed microarray analysis to identify molecular markers that could be useful for human lung fibroblast classification. Based on the expression of these markers, we evaluated the fibroblast-like cell subtype localization in normal human lung samples and lung samples from patients with idiopathic pulmonary fibrosis (IPF).

Results

Mouse lung fibroblasts were classified into Sca-1^high fibroblasts and Sca-1^low fibroblasts by in vitro biological analyses. Through microarray analysis, we demonstrated CD248 and integrin alpha-8 (ITGA8) as cell surface markers for Sca-1^high fibroblasts and Sca-1^low fibroblasts, respectively. In mouse lungs, Sca-1^high fibroblasts and Sca-1^low fibroblasts were localized in the collagen fiber-rich connective tissue and elastic fiber-rich connective tissue, respectively. In normal human lungs and IPF lungs, two corresponding major fibroblast-like cell subtypes were identified: CD248^highITGA8^low fibroblast-like cells and CD248^lowITGA8^high fibroblast-like cells, localized in the collagen fiber-rich connective tissue and in the elastic fiber-rich connective tissue, respectively.

Conclusion

CD248^highITGA8^low fibroblast-like cells and CD248^lowITGA8^high fibroblast-like cells were localized in an almost exclusive manner in human lung specimens. This human lung fibroblast classification using two cell surface markers may be helpful for further detailed investigations of the functions of lung fibroblast subtypes, which can provide new insights into lung development and the pathological processes underlying fibrotic lung diseases.

Glutaminolysis Epigenetically Regulates Antiapoptotic Gene Expression in Idiopathic Pulmonary Fibrosis Fibroblasts

Fibrotic responses involve multiple cellular processes, including epigenetic changes. Epigenetic changes are sensitive to alterations in the tissue microenvironment such as the flux of tricarboxylic acid (TCA) cycle metabolites. TCA metabolites directly regulate epigenetic states, in part by regulating histone modification-related enzymes. Glutaminolysis is a critical metabolic process by which glutamine is converted to glutamate by glutaminase and then to α-ketoglutarate (α-KG), a TCA cycle metabolite. Idiopathic pulmonary fibrosis (IPF) is a disease characterized by aberrant metabolism, including enhanced glutaminolysis. IPF fibroblasts are apoptosis resistant. In this study, we explored the relationship between glutaminolysis and the resistance to apoptosis of IPF fibroblasts. Inhibition of glutaminolysis decreased expression of XIAP and survivin, members of the inhibitor of apoptosis protein (IAP) family. α-KG is a cofactor for JMJD3 histone demethylase, which targets H3K27me3. In the absence of glutamine, JMJD3 activity in fibroblasts is significantly decreased, whereas H3K27me3 levels are increased. Chromatin immunoprecipitation assays confirmed that JMJD3 directly interacts with XIAP and survivin promoter regions in a glutamine-dependent manner. Exogenous α-KG partially restores JMJD3 function and its interaction with the XIAP and survivin promoter regions under glutamine-deficient conditions. Interestingly, α-KG upregulates XIAP, but not survivin, suggesting differential α-KG-dependent and -independent mechanisms by which glutamine regulates these IAPs. Our data demonstrate a novel mechanism of metabolic regulation in which glutaminolysis promotes apoptosis resistance of IPF fibroblasts through epigenetic regulation of XIAP and survivin.

Soluble Thy-1 reverses lung fibrosis via its integrin-binding motif

Loss of Thy-1 expression in fibroblasts correlates with lung fibrogenesis; however, the clinical relevance of therapeutic targeting of myofibroblasts via Thy-1-associated pathways remains to be explored. Using single (self-resolving) or repetitive (nonresolving) intratracheal administration of bleomycin in type 1 collagen-GFP reporter mice, we report that Thy-1 surface expression, but not mRNA, is reversibly diminished in activated fibroblasts and myofibroblasts in self-resolving fibrosis. However, Thy-1 mRNA expression is silenced in lung with nonresolving fibrosis following repetitive bleomycin administration, associated with persistent activation of αv integrin. Thy1-null mice showed progressive αv integrin activation and myofibroblast accumulation after a single dose of bleomycin. In vitro, targeting of αv integrin by soluble Thy-1-Fc (sThy-1), but not RLE-mutated Thy-1 or IgG, reversed TGF-β1-induced myofibroblast differentiation in a dose-dependent manner, suggesting that Thy-1's integrin-binding RGD motif is required for the reversibility of myofibroblast differentiation. In vivo, treatment of established fibrosis induced either by single-dose bleomycin in WT mice or by induction of active TGF-β1 by doxycycline in Cc10-rtTA-tTS-Tgfb1 mice with sThy-1 (1000 ng/kg, i.v.) promoted resolution of fibrosis. Collectively, these findings demonstrate that sThy-1 therapeutically inhibits the αv integrin-driven feedback loop that amplifies and sustains fibrosis.

Tackling MARCKS-PIP3 circuit attenuates fibroblast activation and fibrosis progression

Targeting activated fibroblasts, including myofibroblast differentiation, has emerged as a key therapeutic strategy in patients with idiopathic pulmonary fibrosis (IPF). However, there is no available therapy capable of selectively eradicating myofibroblasts or limiting their genesis. Through an integrative analysis of the regulator genes that are responsible for the activation of IPF fibroblasts, we noticed the phosphatidylinositol 4,5-bisphosphate (PIP2)-binding protein, myristoylated alanine-rich C-kinase substrate (MARCKS), as a potential target molecule for IPF. Herein, we have employed a 25-mer novel peptide, MARCKS phosphorylation site domain sequence (MPS), to determine if MARCKS inhibition reduces pulmonary fibrosis through the inactivation of PI3K/protein kinase B (AKT) signaling in fibroblast cells. We first observed that higher levels of MARCKS phosphorylation and the myofibroblast marker α-smooth muscle actin (α-SMA) were notably overexpressed in all tested IPF lung tissues and fibroblast cells. Treatment with the MPS peptide suppressed levels of MARCKS phosphorylation in primary IPF fibroblasts. A kinetic assay confirmed that this peptide binds to phospholipids, particularly PIP2, with a dissociation constant of 17.64 nM. As expected, a decrease of phosphatidylinositol (3,4,5)-trisphosphate pools and AKT activity occurred in MPS-treated IPF fibroblast cells. MPS peptide was demonstrated to impair cell proliferation, invasion, and migration in multiple IPF fibroblast cells in vitro as well as to reduce pulmonary fibrosis in bleomycin-treated mice in vivo. Surprisingly, we found that MPS peptide decreases α-SMA expression and synergistically interacts with nintedanib treatment in IPF fibroblasts. Our data suggest MARCKS as a druggable target in pulmonary fibrosis and also provide a promising antifibrotic agent that may lead to effective IPF treatments.-Yang, D. C., Li, J.-M., Xu, J., Oldham, J., Phan, S. H., Last, J. A., Wu, R., Chen, C.-H. Tackling MARCKS-PIP3 circuit attenuates fibroblast activation and fibrosis progression.

Thy-1 (CD90) promotes bone formation and protects against obesity

Osteoporosis and obesity result from disturbed osteogenic and adipogenic differentiation and present emerging challenges for our aging society. Because of the regulatory role of Thy-1 in mesenchyme-derived fibroblasts, we investigated the impact of Thy-1 expression on mesenchymal stem cell (MSC) fate between osteogenic and adipogenic differentiation and consequences for bone formation and adipose tissue development in vivo. MSCs from Thy-1-deficient mice have decreased osteoblast differentiation and increased adipogenic differentiation compared to MSCs from wild-type mice. Consistently, Thy-1-deficient mice exhibited decreased bone volume and bone formation rate with elevated cortical porosity, resulting in lower bone strength. In parallel, body weight, subcutaneous/epigonadal fat mass, and bone fat volume were increased. Thy-1 deficiency was accompanied by reduced expression of specific Wnt ligands with simultaneous increase of the Wnt inhibitors sclerostin and dickkopf-1 and an altered responsiveness to Wnt. We demonstrated that disturbed bone remodeling in osteoporosis and dysregulated adipose tissue accumulation in patients with obesity were mirrored by reduced serum Thy-1 concentrations. Our findings provide new insights into the mutual regulation of bone formation and obesity and open new perspectives to monitor and to interfere with the dysregulated balance of adipogenesis and osteogenesis in obesity and osteoporosis.

Interplay between EZH2 and G9a Regulates CXCL10 Gene Repression in Idiopathic Pulmonary Fibrosis

Selective repression of the antifibrotic gene CXCL10 contributes to tissue remodeling in idiopathic pulmonary fibrosis (IPF). We have previously reported that histone deacetylation and histone H3 lysine 9 (H3K9) methylation are involved in CXCL10 repression. In this study, we explored the role of H3K27 methylation and the interplay between the two histone lysine methyltransferases enhancer of zest homolog 2 (EZH2) and G9a in CXCL10 repression in IPF. By applying chromatin immunoprecipitation, Re-ChIP, and proximity ligation assays, we demonstrated that, like G9a-mediated H3K9 methylation, EZH2-mediated histone H3 lysine 27 trimethylation (H3K27me3) was significantly enriched at the CXCL10 promoter in fibroblasts from IPF lungs (F-IPF) compared with fibroblasts from nonfibrotic lungs, and we also found that EZH2 and G9a physically interacted with each other. EZH2 knockdown reduced not only EZH2 and H3K27me3 but also G9a and H3K9me3, and G9a knockdown reduced not only G9 and H3K9me3 but also EZH2 and H3K27me3. Depletion and inhibition of EZH2 and G9a also reversed histone deacetylation and restored CXCL10 expression in F-IPF. Furthermore, treatment of fibroblasts from nonfibrotic lungs with the profibrotic cytokine transforming growth factor-β1 increased EZH2, G9a, H3K27me3, H3K9me3, and histone deacetylation at the CXCL10 promoter, similar to that observed in F-IPF, which was correlated with CXCL10 repression and was prevented by EZH2 and G9a knockdown. These findings suggest that a novel and functionally interdependent interplay between EZH2 and G9a regulates histone methylation-mediated epigenetic repression of the antifibrotic CXCL10 gene in IPF. This interdependent interplay may prove to be a target for epigenetic intervention to restore the expression of CXCL10 and other antifibrotic genes in IPF.

Molecular Mechanisms of Pulmonary Fibrogenesis and Its Progression to Lung Cancer: A Review

Idiopathic pulmonary fibrosis (IPF) is defined as a specific form of chronic, progressive fibrosing interstitial pneumonia of unknown cause, occurring primarily in older adults, and limited to the lungs. Despite the increasing research interest in the pathogenesis of IPF, unfavorable survival rates remain associated with this condition. Recently, novel therapeutic agents have been shown to control the progression of IPF. However, these drugs do not improve lung function and have not been tested prospectively in patients with IPF and coexisting lung cancer, which is a common comorbidity of IPF. Optimal management of patients with IPF and lung cancer requires understanding of pathogenic mechanisms and molecular pathways that are common to both diseases. This review article reflects the current state of knowledge regarding the pathogenesis of pulmonary fibrosis and summarizes the pathways that are common to IPF and lung cancer by focusing on the molecular mechanisms.

Thy-1 in Integrin Mediated Mechanotransduction

The glycosylphosphatidylinositol (GPI) anchored glycoprotein Thy-1 has been prevalently expressed on the surface of various cell types. The biological function of Thy-1 ranges from T cell activation, cell adhesion, neurite growth, differentiation, metastasis and fibrogenesis and has been extensively reviewed elsewhere. However, current discoveries implicate Thy-1 also functions as a key mechanotransduction mediator. In this review, we will be focusing on the role of Thy-1 in translating extracellular mechanic cues into intracellular biological cascades. The mechanotransduction capability of Thy-1 relies on trans and cis interaction between Thy-1 and RGD-binding integrins; and will be discussed in depth in the review.

A Profibrotic Phenotype in Naïve and in Fibrotic Lung Myofibroblasts Is Governed by Modulations in Thy-1 Expression and Activation

Lung fibrosis is characterized by abnormal accumulation of Thy-deficient fibroblasts in the interstitium of the alveolar space. We have previously shown in bleomycin-treated chimeric Thy1-deficient mice with wild-type lymphocytes that Thy1-deficient fibroblasts accumulate and promote fibrosis and an “inflammation-free” environment. Here, we aimed to identify the critical effects of Thy1, or the absence of Thy1, in lung myofibroblast profibrotic functions, particularly proliferation and collagen deposition. Using specific Thy1 siRNA in Thy1-positive cells, Thy1 knockout cells, Thy1 cDNA expression vector in Thy1-deficient cells, and Thy1 cross-linking, we evaluated cell proliferation (assessed by cell mass and BrdU uptake), differentiation (using immunofluorescence), and collagen deposition (using Sircol assay). We found that myofibroblast Thy1 cross-linking and genetic manipulation modulate cell proliferation and expression of Fgf (fibroblast growth factor) and Angtl (angiotensin) receptors (using qPCR) that are involved in myofibroblast proliferation, differentiation, and collagen deposition. In conclusion, lung myofibroblast downregulation of Thy1 expression is critical to increase proliferation, differentiation, and collagen deposition.

Histological and Immunohistochemical Characterization of the Similarity and Difference Between Ovarian Endometriomas and Deep Infiltrating Endometriosis

Ovarian endometrioma (OMA) and deep infiltrating endometriosis (DIE) have long been recognized to have different histology and, as such, postulated to be 2 separate disease entities. Few studies, however, have attempted to elucidate the causes for their differences. Making use of ectopic endometrial tissue samples from 25 and 20 women with OMA and DIE, respectively, and control endometrial tissue samples from 25 women without endometriosis, we conducted an immunohistochemical analysis to evaluate the expression of a group of carefully chosen markers for epithelial-mesenchymal transition (EMT), fibroblast-to-myofibroblast transdifferentiation (FMT), smooth muscle metaplasia (SMM), fibrosis, vascularity, hormonal receptors, and proteins involved in epigenetic modifications. We found that both OMA and DIE lesions exhibited the same cellular changes consistent with EMT, FMT, SMM, and fibrosis as already shown in animal models. Compared to OMA, DIE lesions underwent more thorough and extensive EMT, FMT, and SMM and, consequently, displayed significantly higher fibrotic content but less vascularity. The 2 conditions also showed different expression levels of hormonal receptors. Both OMA and DIE lesions, especially the latter, showed significantly higher staining of enhancer of zeste homolog 2, H3K9me3, and H3K27me3 than that of control endometrium, suggesting progressive epigenetic changes concomitant with cellular ones. Finally, proteins that are known to be involved in fibrogenesis, such as thymocyte differentiation antigen 1 and peroxisome proliferator-activated receptor γ , were also aberrantly expressed under both conditions. The many similarities shared by both OMA and DIE indicate that the 2 conditions may actually share the same pathogenesis/pathophysiology. Their differences, however, suggest that the source of these differences may result from the different lesional microenvironments.

Lung cancer in patients with idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic fibrotic lung disease of unknown etiology. With a gradually increasing worldwide prevalence and a mortality rate exceeding that of many cancers, IPF diagnosis and management are critically important and require a comprehensive multidisciplinary approach. This approach also involves assessment of comorbid conditions, such as lung cancer, that exerts a dramatic impact on disease survival. Emerging evidence suggests that progressive lung scarring in the context of IPF represents a risk factor for lung carcinogenesis. Both disease entities present with major similarities in terms of pathogenetic pathways, as well as potential causative factors, such as smoking and viral infections. Besides disease pathogenesis, anti-cancer agents, including nintedanib, have been successfully applied in the treatment of patients with IPF while an oncologic approach with a cocktail of several pleiotropic anti-fibrotic agents is currently in the therapeutic pipeline of IPF. Nevertheless, epidemiologic association between IPF and lung cancer does not prove causality. Currently there is significant lack of knowledge supporting a direct association between lung fibrosis and cancer reflecting to disappointing therapeutic algorithms. An optimal therapeutic strategy for patients with both IPF and lung cancer represents an amenable need. This review article synthesizes the current state of knowledge regarding pathogenetic commonalities between IPF and lung cancer and focuses on clinical and therapeutic data that involve both disease entities.

Mesothelin/mucin 16 signaling in activated portal fibroblasts regulates cholestatic liver fibrosis

Cholestatic liver fibrosis is caused by obstruction of the biliary tract and is associated with early activation of portal fibroblasts (PFs) that express Thy-1, fibulin 2, and the recently identified marker mesothelin (MSLN). Here, we have demonstrated that activated PFs (aPFs) and myofibroblasts play a critical role in the pathogenesis of liver fibrosis induced by bile duct ligation (BDL). Conditional ablation of MSLN+ aPFs in BDL-injured mice attenuated liver fibrosis by approximately 50%. Similar results were observed in MSLN-deficient mice (Msln-/- mice) or mice deficient in the MSLN ligand mucin 16 (Muc16-/- mice). In vitro analysis revealed that MSLN regulates TGF-β1-inducible activation of WT PFs by disrupting the formation of an inhibitory Thy-1-TGFβRI complex. MSLN also facilitated the FGF-mediated proliferation of WT aPFs. Therapeutic administration of anti-MSLN-blocking Abs attenuated BDL-induced fibrosis in WT mice. Liver specimens from patients with cholestatic liver fibrosis had increased numbers of MSLN+ aPFs/myofibroblasts, suggesting that MSLN may be a potential target for antifibrotic therapy.

Thy-1 interaction with Fas in lipid rafts regulates fibroblast apoptosis and lung injury resolution

Thy-1-negative lung fibroblasts are resistant to apoptosis. The mechanisms governing this process and its relevance to fibrotic remodeling remain poorly understood. By using either sorted or transfected lung fibroblasts, we found that Thy-1 expression is associated with downregulation of anti-apoptotic molecules Bcl-2 and Bcl-xL, as well as increased levels of cleaved caspase-9. Addition of rhFasL and staurosporine, well-known apoptosis inducers, caused significantly increased cleaved caspase-3, -8, and PARP in Thy-1-transfected cells. Furthermore, rhFasL induced Fas translocation into lipid rafts and its colocalization with Thy-1. These in vitro results indicate that Thy-1, in a manner dependent upon its glycophosphatidylinositol anchor and lipid raft localization, regulates apoptosis in lung fibroblasts via Fas-, Bcl-, and caspase-dependent pathways. In vivo, Thy-1 deficient (Thy1^-/-) mice displayed persistence of myofibroblasts in the resolution phase of bleomycin-induced fibrosis, associated with accumulation of collagen and failure of lung fibrosis resolution. Apoptosis of myofibroblasts is decreased in Thy1^-/- mice in the resolution phase. Collectively, these findings provide new evidence regarding the role and mechanisms of Thy-1 in initiating myofibroblast apoptosis that heralds the termination of the reparative response to bleomycin-induced lung injury. Understanding the mechanisms regulating fibroblast survival/apoptosis should lead to novel therapeutic interventions for lung fibrosis.

Lipopolysaccharide promotes pulmonary fibrosis in acute respiratory distress syndrome (ARDS) via lincRNA-p21 induced inhibition of Thy-1 expression

Acute respiratory distress syndrome (ARDS) is a common clinical disorder characterized by pulmonary edema leading to acute lung damage and arterial hypoxemia. Pulmonary fibrosis is a progressive, fibrotic lung disorder, whose pathogenesis in ARDS remains speculative. LincRNA-p21 was a novel regulator of cell proliferation, apoptosis and DNA damage response. This study aims to investigate the effects and mechanism of lincRNA-p21 on pulmonary fibrosis in ARDS. Purified 10 mg/kg LPS was dropped into airways of C57BL/6 mice. Expression levels of lincRNA-p21 and Thy-1 were measured by real-time PCR or western blotting. Proliferation of lung fibroblasts was analyzed by BrdU incorporation assay. Lung and BAL collagen contents were estimated using colorimetric Sircol assay. LincRNA-p21 expression was time-dependently increased and Thy-1 expression was time-dependently reduced in a mouse model of ARDS and in LPS-treated lung fibroblasts. Meanwhile, lung fibroblast proliferation was also time-dependently elevated in LPS-treated lung fibroblasts. In addition, lung fibroblast proliferation could be promoted by lincRNA-p21 overexpression and LPS treatment, however, the elevated lung fibroblast proliferation was further abrogated by Thy-1 overexpression or lincRNA-p21 interference. And Thy-1 interference could elevate cell viability of lung fibroblasts and rescue the reduction of lung fibroblast proliferation induced by lincRNA-p21 interference. Moreover, lincRNA-p21 overexpression dramatically inhibited acetylation of H3 and H4 at the Thy-1 promoter and Thy-1 expression levels in HLF1 cells. Finally, lincRNA-p21 interference rescued LPS-induced increase of lung and BAL collagen contents. LincRNA-p21 could lead to pulmonary fibrosis in ARDS by inhibition of the expression of Thy-1.