Aditi Mathur

Semaphorin 7a+ Regulatory T Cells Are Associated with Progressive Idiopathic Pulmonary Fibrosis and Are Implicated in Transforming Growth Factor-β1–induced Pulmonary Fibrosis

RATIONALE Lymphocytes are increasingly associated with idiopathic pulmonary fibrosis (IPF). Semaphorin 7a (Sema 7a) participates in lymphocyte activation. OBJECTIVES To define the relationship between Sema 7a and lymphocytes in IPF. METHODS We characterized the significance of Sema 7a+ lymphocytes in humans with IPF and in a mouse model of lung fibrosis caused by lung-targeted, transgenic overexpression of TGF-β1. We determined the site of Sema 7a expression in human and murine lungs and circulation and used adoptive transfer approaches to define the relevance of lymphocytes coexpressing Sema7a and the markers CD19, CD4, or CD4+CD25+FoxP3+ in TGF-β1-induced murine lung fibrosis. MEASUREMENTS AND MAIN RESULTS Subjects with IPF show expression of Sema 7a on lung CD4+ cells and circulating CD4+ or CD19+ cells. Sema 7a expression is increased on CD4+ cells and CD4+CD25+FoxP3+ regulatory T cells, but not CD19+ cells, in subjects with progressive IPF. Sema 7a is expressed on lymphocytes expressing CD4 but not CD19 in the lungs and spleen of TGF-β1-transgenic mice. Sema 7a expressing bone marrow-derived cells induce lung fibrosis and alter the production of T-cell mediators, including IFN-γ, IL-4, IL-17A, and IL-10. These effects require CD4 but not CD19. In comparison to Sema 7a-CD4+CD25+FoxP3+ cells, Sema7a+CD4+CD25+FoxP3+ cells exhibit reduced expression of regulatory genes such as IL-10, and adoptive transfer of these cells induces fibrosis and remodeling in the TGF-β1-exposed murine lung. CONCLUSIONS Sema 7a+CD4+CD25+FoxP3+ regulatory T cells are associated with disease progression in subjects with IPF and induce fibrosis in the TGF-β1-exposed murine lung.

Review: Interstitial lung disease associated with systemic sclerosis and idiopathic pulmonary fibrosis: How similar and distinct?

Fibrosis of the lung, a common complication of systemic sclerosis (SSc) and the hallmark of idiopathic pulmonary fibrosis (IPF), is associated with substantial mortality and has no approved therapy. Despite some degree of overlap in their clinical features and pathogenesis, SSc-associated interstitial lung disease (ILD) and IPF have differences, with significant implications for diagnosis, evaluation, and management. To shed light on these issues, this review compares and contrasts salient features of these 2 entities, focusing on clinical manifestations, lung imaging, and pathology, along with current concepts of pathogenesis, including animal models, translational studies, genetic factors, and predictive biomarkers. We conclude by posing questions that might unveil new areas of investigation and inform novel and targeted approaches to therapy.

Chitinase 3–Like 1 Suppresses Injury and Promotes Fibroproliferative Responses in Mammalian Lung Fibrosis

Chitinase 3–like 1 protects against lung injury but has a profibrotic role during the repair phase. Two-Face Chitinase Idiopathic pulmonary fibrosis is a devastating—currently incurable—disease where scars develop deep in the lung, making it hard to breathe. Now, Zhou et al. report a breath of fresh air for IPF. They found that the protein chitinase 3–like 1 (CHI3L1) is elevated in IPF patients, and that high levels of CHI3L1 are associated with disease progression. However, things were not as simple as they seemed. CHI3L1 actually played a protective, anti-apoptotic role against lung injury, but contributed to fibrosis during the repair phase, in part through inducing myofibroblast transformation. This insight into the two sides of CHI3L1 provides mechanistic understanding of the pathogenesis of IPF, which is necessary to the development of successful therapeutics. Epithelial injury, alternative macrophage accumulation, and fibroproliferation coexist in the lungs of patients with idiopathic pulmonary fibrosis (IPF). Chitinase 3–like 1 (CHI3L1) is a prototypic chitinase-like protein that has been retained over species and evolutionary time. However, the regulation of CHI3L1 in IPF and its ability to regulate injury and/or fibroproliferative repair have not been fully defined. We demonstrated that CHI3L1 levels were elevated in patients with IPF. High levels of CHI3L1 are associated with progression—as defined by lung transplantation or death—and with scavenger receptor–expressing circulating monocytes in an ambulatory IPF population. In preterminal acute exacerbations of IPF, CHI3L1 levels were reduced and associated with increased levels of apoptosis. We also demonstrated that in bleomycin-treated mice, CHI3L1 expression was acutely and transiently decreased during the injury phase and returned toward and eventually exceeded baseline levels during the fibrotic phase. In this model, CHI3L1 played a protective role in injury by ameliorating inflammation and cell death, and a profibrotic role in the repair phase by augmenting alternative macrophage activation, fibroblast proliferation, and matrix deposition. Using three-dimensional culture system of a human fibroblast cell line, we found that CHI3L1 is sufficient to induce low grade myofibroblast transformation. In combination, these studies demonstrate that CHI3L1 is stimulated in IPF, where it represents an attempt to diminish injury and induce repair. They also demonstrate that high levels of CHI3L1 are associated with disease progression in ambulatory patients and that a failure of the CHI3L1 antiapoptotic response might contribute to preterminal disease exacerbations.

Fibroblast engraftment in the decellularized mouse lung occurs via a β1-integrin-dependent, FAK-dependent pathway that is mediated by ERK and opposed by AKT

Creation of bioartificial organs has been enhanced by the development of strategies involving decellularized mammalian lung. Because fibroblasts critically support lung function through a number of mechanisms, study of these cells in the context of the decellularized lung has the potential to improve the structure and function of tissue-engineered lungs. We characterized the engraftment and survival of a mouse fibroblast cell line in decellularized rat lung slices and found a time-dependent increase in cell numbers assessed by hematoxylin and eosin staining, cell proliferation assessed by Ki67 staining, and minimal cell death assessed by TUNEL staining. We developed a repopulation index to allow quantification of cell survival that accounts for variation in cell density throughout the seeded scaffold. We then applied this method to the study of mouse lung scaffolds and found that decellularization of presliced mouse lungs produced matrices with preserved alveolar architecture and proteinaceous components including fibronectin, collagens I and IV, laminin, and elastin. Treatment with a β1-integrin-neutralizing antibody significantly reduced the repopulation index after 24 h of culture. Treatment with focal adhesion kinase (FAK) inhibitor and extracellular signal-regulated kinase (ERK) inhibitor further reduced initial repopulation scores while treatment with AKT inhibitor increased initial scores. Rho-associated kinase inhibitor had no discernible effect. These data indicate that initial adhesion and survival of mouse fibroblasts in the decellularized mouse lung occur in a β1-integrin-dependent, FAK/ERK-dependent manner that is opposed by AKT.

Plexin C1 deficiency permits synaptotagmin 7-mediated macrophage migration and enhances mammalian lung fibrosis.

Pulmonary fibrosis is a progressive and often fatal condition that is believed to be partially orchestrated by macrophages. Mechanisms that control migration of these cells into and within the lung remain undefined. We evaluated thecontributions of the semaphorinreceptor, plexinC1 (PLXNC1), andtheexocytic calcium sensor, synaptotagmin 7 (Syt7), in these processes. Weevaluated the role of PLXNC1 in macrophagemigration by using Boyden chambers and scratch tests, characterized its contribution to experimentally induced lung fibrosis inmice, and defined themechanism for our observations. Our findings reveal that relative to controlparticipants, patients with idiopathic pulmonary fibrosis demonstrate excessive monocyte migration and underexpression of PLXNC1 in the lungs and circulation, a finding that is recapitulated in the setting of scleroderma‐related interstitial lung disease. Relative to wild type, PLXNC1‐/‐ mouse macrophages are excessively migratory, and PLXNC1‐/‐ mice show exacerbated collagen accumulation in response to either inhaled bleomycin or inducible lung targeted TGF‐β1 overexpression. These findings are ameliorated by replacement of PLXNC1 on bone marrow–derived cells or by genetic deletion of Syt7. These data demonstrate the previously unrecognized observation that PLXNC1 deficiency permits Syt7‐mediated macrophage migration and enhances mammalian lung fibrosis.—Peng, X., Moore, M., Mathur, A., Zhou, Y., Sun, H., Gan, Y., Herazo‐Maya, J. D., Kaminski, N., Hu, X., Pan, H., Ryu, C., Osafo‐Addo, A., Homer, R. J., Feghali‐Bostwick, C., Fares, W.H., Gulati, M.,Hu, B., Lee, C.‐G., Elias, J. A.,Herzog, E. L. Plexin C1 deficiency permits synaptotagmin 7–mediated macrophage migration and enhances mammalian lung fibrosis. FASEB J. 30, 4056–4070 (2016). www.fasebj.org

Pulmonary Embolism in Older Patients

Pulmonary embolism is a common geriatric medical condition that accounts for significant morbidity and mortality. It is responsible for greater than 200,000 deaths annually and 10% of hospital deaths [1–3]. The incidence of venous thromboembolic disease (VTE), encompassing deep vein thrombosis (DVT) and pulmonary embolism (PE), rises sharply after the age of 60 and reaches 1% per year in the very old. However, while most major studies looking at diagnosis and treatment concentrate on middle-aged subjects [4], almost 70% of all VTE are diagnosed in patients over the age of 60 [1]. This chapter focuses on the pathophysiology of thromboembolic disease in the elderly and explores risk factors, presentation, diagnosis, prevention, and treatment as it pertains to the geriatric population. Complications of treatment are also considered.

Editorial: Sticking it to fibrocytes with serum amyloid P

Fibrocytes are a bone marrow-derived mesenchymal population whose existence was first proposed over 150 years ago following the detailed microscopic observations of James Paget [1]. Whereas bloodborne connective tissue cell precursors are also described in the writings of Cohnheim, Metchnikov, Fischer, and Maximow [1], it was not until 1994 that the term “fibrocyte” was coined to describe this unique population of cells possessing the tissue-remodeling properties of fibroblasts and the proinflammatory properties of monocytes [2, 3]. Accumulating data gleaned from animal modeling and human studies suggest that circulating and/or local fibrocytes contribute to a broad range of chronic inflammatory conditions, including those affecting the lung, liver, autoimmune disease, skin, and even normal aging [3]. Fibrocyte differentiation is suppressed by serum amyloid P (SAP) [4], a short pentraxin protein that is produced by the liver as an acute-phase reactant. Interestingly, whereas the in vivo activitiy of SAP on human fibrocyte biology appears to involve certain Fc gamma receptors (Fc Rs) and aggregated IgG [5], the precise mechanism of the inhibitory effects of SAP on the monocyte-to-fibrocyte transition remains unclear. Fc Rs are cell surface molecules that bind or “stick” to the Fc portion of IgG to activate downstream signaling pathways that engender or impede critical events, such as phagocytosis, cell activation, release of soluble mediators, and microbe killing [6]. Human Fc Rs include Fc RI (CD64), Fc RIIa (CD32a), Fc RIIb (CD32b), Fc RIIIa (CD16a), and Fc RIIIb (CD16b). Murine studies have identified four classes of Fc Rs bearing similarity to those found in humans: Fc RI, Fc RII, Fc RIII (which seems most closely related to Fc IIa in humans), and Fc IV (which corresponds most closely to human Fc RIII) [7]. Despite differences in overall Fc fragment affinity and downstream signaling, murine studies of Fc Rs are considered helpful in terms of understanding human biology [8], and complementary mouse and human studies, such as those performed in the Crawford paper [9], can be particularly useful. Fc Rs differ in their binding affinity for the Fc portion of IgG. In mice and humans, Fc RI displays high affinity Fc fragment binding, whereas the affinity of the other Fc Rs is much lower. Fc RI, along with most other Fc Rs, contains an and -chains and functions as an activating receptor via ITAMs. In contrast, Fc RIIB contains only a single -chain containing a cytoplasmic ITIM [6]. Whereas it has long been known that Fc Rs, at least partially, mediate SAP’s inhibition of fibrocyte differentiation [5], a clear understanding of how the activating and inhibitory components synergize in this process is lacking—lacking, that is, until now. In this month’s issue of JLB, Crawford and colleagues [9] define, for the first time, the concerted roles of Fc Rs in mediating the inhibitory effects of SAP on fibrocyte development. The most salient features of this paper are as follows. With the use of a sophisticated translational approach combining sitedirected mutagenesis and murine modeling with studies of primary human cells, the authors demonstrate that in mice, the activity of SAP appears to be dependent on the common -chain of activating Fc Rs and specifically, on Fc RI (Table 1). Deletion of other activating receptors, such as Fc RIII, had no effect. As expected, deletion of Fc RIIb (the inhibitory Fc R) increased sensitivity to SAP; however, this effect was absent in the setting of triple deletion of Fc RIIb, III, and IV. Similar findings were seen in small interfering RNA-treated primary human cells, where knockdown of Fc common chain or Fc RI reduced sensitivity to SAP, but knockdown of other activating receptors, such as Fc RIIa (the human homologue of mouse Fc RIII) and Fc RIII (the human homolog of mouse Fc RIV), had no effect. Similar to the effects in mice, knockdown of Fc IIb increased SAP sensitivity. Interestingly, in the mouse and human studies, common chain and Fc RI deletion attenuated but did not completely abolish SAP sensitivity, suggesting that some of the effects of SAP require neither Fc RI nor an intact common -chain. These findings demonstrate that the inhibitory ef-