A novel mechanoeffector role of fibroblast S100A4 in myofibroblast transdifferentiation and fibrosis

Fibroblast to myofibroblast transdifferentiation mediates numerous fibrotic disorders, such as idiopathic pulmonary fibrosis (IPF). We have previously demonstrated that non-muscle myosin II (NMII) is activated in response to fibrotic lung extracellular matrix, thereby mediating myofibroblast transdifferentiation. NMII-A is known to interact with the calcium-binding protein S100A4, but the mechanism by which S100A4 regulates fibrotic disorders is unclear. In this study, we show that fibroblast S100A4 is a calcium-dependent, mechanoeffector protein that is uniquely sensitive to pathophysiologic-range lung stiffness (8-25 kPa) and thereby mediates myofibroblast transdifferentiation. Re-expression of endogenous fibroblast S100A4 rescues the myofibroblastic phenotype in S100A4 KO fibroblasts. Analysis of NMII-A/actin dynamics reveals that S100A4 mediates the unraveling and redistribution of peripheral actomyosin to a central location, resulting in a contractile myofibroblast. Furthermore, S100A4 loss protects against murine in vivo pulmonary fibrosis, and S100A4 expression is dysregulated in IPF. Our data reveal a novel mechanosensor/effector role for endogenous fibroblast S100A4 in inducing cytoskeletal redistribution in fibrotic disorders such as IPF.

Expert consensus on the management of systemic sclerosis-associated interstitial lung disease

BACKGROUND

Systemic sclerosis (SSc) is a rare, complex, connective tissue disorder. Interstitial lung disease (ILD) is common in SSc, occurring in 35-52% of patients and accounting for 20-40% of mortality. Evolution of therapeutic options has resulted in a lack of consensus on how to manage this condition. This Delphi study was initiated to develop consensus recommendations based on expert physician insights regarding screening, progression, treatment criteria, monitoring of response, and the role of recent therapeutic advances with antifibrotics and immunosuppressants in patients with SSc-ILD.

METHODS

A modified Delphi process was completed by pulmonologists (n = 13) and rheumatologists (n = 12) with expertise in the management of patients with SSc-ILD. Panelists rated their agreement with each statement on a Likert scale from - 5 (complete disagreement) to + 5 (complete agreement). Consensus was predefined as a mean Likert scale score of ≤  - 2.5 or ≥  + 2.5 with a standard deviation not crossing zero.

RESULTS

Panelists recommended that all patients with SSc be screened for ILD by chest auscultation, spirometry with diffusing capacity of the lungs for carbon monoxide, high-resolution computed tomography (HRCT), and/or autoantibody testing. Treatment decisions were influenced by baseline and changes in pulmonary function tests, extent of ILD on HRCT, duration and degree of dyspnea, presence of pulmonary hypertension, and potential contribution of reflux. Treatment success was defined as stabilization or improvement of signs or symptoms of ILD and functional status. Mycophenolate mofetil was identified as the initial treatment of choice. Experts considered nintedanib a therapeutic option in patients with progressive fibrotic ILD despite immunosuppressive therapy or patients contraindicated/unable to tolerate immunotherapy. Concomitant use of nintedanib with MMF/cyclophosphamide can be considered in patients with advanced disease at initial presentation, aggressive ILD, or significant disease progression. Although limited consensus was achieved on the use of tocilizumab, the experts considered it a therapeutic option for patients with early SSc and ILD with elevated acute-phase reactants.

CONCLUSIONS

This modified Delphi study generated consensus recommendations for management of patients with SSc-ILD in a real-world setting. Findings from this study provide a management algorithm that will be helpful for treating patients with SSc-ILD and addresses a significant unmet need.

Prospective cohort of cryobiopsy in interstitial lung diseases: a single center experience

Rationale

Transbronchial cryobiopsy has been increasingly used to diagnose interstitial lung diseases. However, there is uncertainty regarding its accuracy and risks, mainly due to a paucity of prospective or randomized trials comparing cryobiopsy to surgical biopsy.

Objectives

To evaluate the diagnostic yield and complications of cryobiopsy in patients selected by multidisciplinary discussion.

Methods

This was a prospective cohort from 2017 to 2019. We included consecutive patients with suspected interstitial lung diseases being considered for lung biopsy presented at our multidisciplinary meeting.

Measurements and main results

Of 112 patients, we recommended no biopsy in 31, transbronchial forceps biopsy in 16, cryobiopsy in 54 and surgical biopsy in 11. By the end of the study, 34 patients had had cryobiopsy and 24 patients, surgical biopsy. Overall pathologic and multidisciplinary diagnostic yield of cryobiopsy was 47.1% and 61.8%, respectively. The yield increased over time for both pathologic (year 1: 28.6%, year 2: 54.5%, year 3: 66.7%, p = 0.161) and multidisciplinary (year 1: 50%, year 2: 63.6%, year 3: 77.8%, p = 0.412) diagnosis. Overall rate of grade 4 bleeding after cryobiopsy was 11.8%. Cryobiopsy required less chest tube placement (11.8% vs 100%, p < 0.001) and less hospitalizations compared to surgical biopsy (26.5% vs 95.7%, p < 0.001), but hospitalized patients had a longer median hospital stay (2 days vs 1 day, p = 0.004).

Conclusions

Diagnostic yield of cryobiopsy increased over time but the overall grade 4 bleeding rate was 11.8%.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-022-01990-4.

Stretching the Function of Innate Immune Cells

The importance of innate immune cells to sense and respond to their physical environment is becoming increasingly recognized. Innate immune cells (e.g. macrophages and neutrophils) are able to receive mechanical signals through several mechanisms. In this review, we discuss the role of mechanosensitive ion channels, such as Piezo1 and transient receptor potential vanilloid 4 (TRPV4), and cell adhesion molecules, such as integrins, selectins, and cadherins in biology and human disease. Furthermore, we explain that these mechanical stimuli activate intracellular signaling pathways, such as MAPK (p38, JNK), YAP/TAZ, EDN1, NF-kB, and HIF-1α, to induce protein conformation changes and modulate gene expression to drive cellular function. Understanding the mechanisms by which immune cells interpret mechanosensitive information presents potential targets to treat human disease. Important areas of future study in this area include autoimmune, allergic, infectious, and malignant conditions.

Delphi Consensus Recommendations on Management of Dosing, Adverse Events, and Comorbidities in the Treatment of Idiopathic Pulmonary Fibrosis with Nintedanib

Purpose:

Nintedanib is an approved treatment for idiopathic pulmonary fibrosis (IPF), which slows disease progression. Management of patients with IPF receiving nintedanib can be complicated by tolerability issues, comorbidities, and concomitant medications. We developed consensus recommendations on the management of dosing, adverse events and comorbidities in patients with IPF treated with nintedanib.

Methods:

A modified Delphi process using 3 questionnaires was used to survey 14 pulmonologists experienced in using nintedanib. Panelists rated their agreement with statements on a Likert scale from −5 (strongly disagree) to +5 (strongly agree). Consensus was predefined as a mean score of ⩽−2.5 or ⩾+2.5 with a standard deviation not crossing zero.

Results:

The panelists’ recommendations were largely aligned with clinical trial data, real-world evidence, and the prescribing information, and provided additional guidance regarding minimizing gastrointestinal effects, periodic monitoring for liver dysfunction, caution with respect to concomitant administration of cytochrome P450 3A4 and P-glycoprotein 1 inhibitors and inducers and anticoagulants, and management of comorbidities. The panelists unanimously agreed that adverse event management should be individualized, based on careful consideration of the risks and benefits of each possible intervention and discussion with the patient.

Conclusions:

These consensus recommendations provide additional guidance on the appropriate management of IPF with nintedanib, for use alongside evidence-based literature and the prescribing information.

Activated intestinal muscle cells promote preadipocyte migration: a novel mechanism for creeping fat formation in Crohn's disease

OBJECTIVE

Creeping fat, the wrapping of mesenteric fat around the bowel wall, is a typical feature of Crohn's disease, and is associated with stricture formation and bowel obstruction. How creeping fat forms is unknown, and we interrogated potential mechanisms using novel intestinal tissue and cell interaction systems.

DESIGN

Tissues from normal, UC, non-strictured and strictured Crohn's disease intestinal specimens were obtained. The muscularis propria matrisome was determined via proteomics. Mesenteric fat explants, primary human preadipocytes and adipocytes were used in multiple ex vivo and in vitro cell migration systems on muscularis propria muscle cell derived or native extracellular matrix. Functional experiments included integrin characterisation via flow cytometry and their inhibition with specific blocking antibodies and chemicals.

RESULTS

Crohn's disease muscularis propria cells produced an extracellular matrix scaffold which is in direct spatial and functional contact with the immediately overlaid creeping fat. The scaffold contained multiple proteins, but only fibronectin production was singularly upregulated by transforming growth factor-β1. The muscle cell-derived matrix triggered migration of preadipocytes out of mesenteric fat, fibronectin being the dominant factor responsible for their migration. Blockade of α5β1 on the preadipocyte surface inhibited their migration out of mesenteric fat and on 3D decellularised intestinal tissue extracellular matrix.

CONCLUSION

Crohn's disease creeping fat appears to result from the migration of preadipocytes out of mesenteric fat and differentiation into adipocytes in response to an increased production of fibronectin by activated muscularis propria cells. These new mechanistic insights may lead to novel approaches for prevention of creeping fat-associated stricture formation.

The Role of TRPV4 in Regulating Innate Immune Cell Function in Lung Inflammation

Ion channels/pumps are essential regulators of innate immune cell function. Macrophages have been increasingly recognized to have phenotypic plasticity and location-specific functions in the lung. Transient receptor potential vanilloid 4 (TRPV4) function in lung injury has been shown to be stimulus- and cell-type specific. In the current review, we discuss the importance of TRPV4 in macrophages and its role in phagocytosis and cytokine secretion in acute lung injury/acute respiratory distress syndrome (ARDS). Furthermore, TRPV4 controls a MAPK molecular switch from predominately c-Jun N-terminal kinase, JNK activation, to that of p38 activation, that mediates phagocytosis and cytokine secretion in a matrix stiffness-dependent manner. Expanding knowledge regarding the downstream mechanisms by which TRPV4 acts to tailor macrophage function in pulmonary inflammatory diseases will allow for formulation of novel therapeutics.

Patients with interstitial lung disease and pulmonary sarcoidosis are at high risk for severe illness related to COVID-19

Analyses of COVID-19 patients with preexisting interstitial lung disease (ILD) or pulmonary sarcoidosis is lacking but registries are ongoing. Treatment of COVID-19 in patients with underlying ILD or sarcoidosis may include hospital admission, possible drug treatment, caution with steroids, and avoidance of mechanical ventilation in acute exacerbation of ILD. Patients with COVID-19 respiratory illness are at risk for developing ILD.

Transient Receptor Potential Vanilloid 4 (TRPV4) Protects the Lung from Bacterial Pneumonia via MAPK Molecular Switching

Mechanical cell-matrix interactions can drive the innate immune responses to infection, however the molecular underpinnings of these responses remain elusive. We have discovered that the biophysical properties of the matrix in the range of injured fibrotic lung (≥ 25 kPa) conditions the macrophage response to LPS and infection respectively through the mechanosensitive cation channel, TRPV4 in vitro and in vivo. Studies suggest that LPS-induced macrophage activation is controlled in part by the MAPK pathway (i.e. p38, ERK, JNK). Thus, we investigated if TRPV4 plays a role in the macrophage activation response after LPS through alteration of the MAPK pathway. TRPV4 KO mice exhibited reduced lung bacterial clearance by macrophages (6-fold, p=0.012) after intratracheal P. aeruginosa administration and increased lung injury as measured by inflammatory cell infiltration (≥80±3%, p&lt;0.05), vascular permeability (BAL total protein ≥63±6%, p&lt;0.05), and pro-inflammatory cytokine secretion in BALF (IL-6, CCL2, CXCL1 ≥71±4%, p&lt;0.05). LPS-induced p38 activation was decreased (69%, p&lt;0.05) while JNK activation was increased (2-fold, p&lt;0.05) in a stiffness-dependent manner with no change in ERK activation in TRPV4 KO BMDMs. Inhibition of p38 (SB203580, BIRB796) decreased phagocytosis whereas inhibition of JNK (SP600125) decreased cytokine secretion (IL-6, CCL2, and CXCL1) after LPS (2 fold, p&lt;0.05). DUSP1/MKP1 (MAPK phosphatase) protein was reduced by 3-fold in TRPV4 KO and inhibition of DUSP1 decreased phagocytosis and selectively increased activation of JNK. These data are the first to demonstrate new roles for macrophage TRPV4 in regulating innate immunity in a mechanosensitive manner, through MAPK activation switching.

Performance of diagnostic criteria in patients clinically judged to have cardiac sarcoidosis: Is it time to regroup?

BACKGROUND

The diagnosis of cardiac sarcoidosis (CS) is challenging. Because of the current limitations of endomyocardial biopsy as a reference standard, physicians rely on advanced cardiac imaging, multidisciplinary evaluation, and diagnostic criteria to diagnose CS.

AIMS

To compare the 3 main available diagnostic criteria in patients clinically judged to have CS.

METHODS

We prospectively included patients clinically judged to have CS by a multidisciplinary sarcoidosis team from November 2016 to October 2017. We included only incident cases (diagnosis of CS within 1 year of inclusion). We applied retrospectively the following diagnostic criteria: the World Association of Sarcoidosis and Other Granulomatous Diseases (WASOG), the Heart Rhythm Society (HRS), and the Japanese Circulation Society (JCS) 2016 criteria.

RESULTS

We identified 69 patients. Diagnostic criteria classified patients as follows: WASOG as highly probable (1.4%), probable (52.2%), possible (0%), some criteria (40.6%), and no criteria (5.8%); HRS as histological diagnosis (1.4%), probable (52.2%), some criteria (40.6%), and no criteria (5.8%); JCS as histological diagnosis (1.4%), clinical diagnosis (58%), some criteria (39.1%), and no criteria (1.4%). Concordance was high between WASOG and HRS (κ = 1) but low between JCS and the others (κ = 0.326).

CONCLUSIONS

A high proportion of patients clinically judged to have CS are unable to be classified according to the 3 main diagnostic criteria. There is low concordance between JCS criteria and the other 2 criteria (WASOG and HRS).

TRPV4 Protects the Lung from Bacterial Pneumonia via MAPK Molecular Pathway Switching

Mechanical cell-matrix interactions can drive the innate immune responses to infection; however, the molecular underpinnings of these responses remain elusive. This study was undertaken to understand the molecular mechanism by which the mechanosensitive cation channel, transient receptor potential vanilloid 4 (TRPV4), alters the in vivo response to lung infection. For the first time, to our knowledge, we show that TRPV4 protects the lung from injury upon intratracheal Pseudomonas aeruginosa in mice. TRPV4 functions to enhance macrophage bacterial clearance and downregulate proinflammatory cytokine secretion. TRPV4 mediates these effects through a novel mechanism of molecular switching of LPS signaling from predominant activation of the MAPK, JNK, to that of p38. This is accomplished through the activation of the master regulator of inflammation, dual-specificity phosphatase 1. Further, TRPV4's modulation of the LPS signal is mechanosensitive in that both upstream activation of p38 and its downstream biological consequences depend on pathophysiological range extracellular matrix stiffness. We further show the importance of TRPV4 on LPS-induced activation of macrophages from healthy human controls. These data are the first, to our knowledge, to demonstrate new roles for macrophage TRPV4 in regulating innate immunity in a mechanosensitive manner through the modulation of dual-specificity phosphatase 1 expression to mediate MAPK activation switching.

Translocation of TRPV4-PI3Kγ complexes to the plasma membrane drives myofibroblast transdifferentiation

Myofibroblasts are key contributors to pathological fibrotic conditions of several major organs. The transdifferentiation of fibroblasts into myofibroblasts requires both a mechanical signal and transforming growth factor-β (TGF-β) signaling. The cation channel transient receptor potential vanilloid 4 (TRPV4) is a critical mediator of myofibroblast transdifferentiation and in vivo fibrosis through its mechanosensitivity to extracellular matrix stiffness. Here, we showed that TRPV4 promoted the transdifferentiation of human and mouse lung fibroblasts through its interaction with phosphoinositide 3-kinase γ (PI3Kγ), forming nanomolar-affinity, intracellular TRPV4-PI3Kγ complexes. TGF-β induced the recruitment of TRPV4-PI3Kγ complexes to the plasma membrane and increased the activities of both TRPV4 and PI3Kγ. Using gain- and loss-of-function approaches, we showed that both TRPV4 and PI3Kγ were required for myofibroblast transdifferentiation as assessed by the increased production of α-smooth muscle actin and its incorporation into stress fibers, cytoskeletal changes, collagen-1 production, and contractile force. Expression of various mutant forms of the PI3Kγ catalytic subunit (p110γ) in cells lacking PI3Kγ revealed that only the noncatalytic, amino-terminal domain of p110γ was necessary and sufficient for TGF-β-induced TRPV4 plasma membrane recruitment and myofibroblast transdifferentiation. These data suggest that TGF-β stimulates a noncanonical scaffolding action of PI3Kγ, which recruits TRPV4-PI3Kγ complexes to the plasma membrane, thereby increasing myofibroblast transdifferentiation. Given that both TRPV4 and PI3Kγ have pleiotropic actions, targeting the interaction between them could provide a specific therapeutic approach for inhibiting myofibroblast transdifferentiation.

TRPV4 Mediates the Macrophage Phagocytic and Cytokine Response to Leptin

Obesity is characterized by chronic activation of the innate immune system. Leptin is an adipokine upregulated in obesity that has been shown to stimulate macrophage function through an unidentified signal. Our lab recently showed that the mechanosensitive calcium channel, transient receptor potential vanilloid 4 (TRPV4) mediates macrophage phagocytosis in response to infection. This study seeks to determine if TRPV4 also mediates the macrophage response to leptin. Bone marrow derived macrophages were isolated from 7–10 week old WT and TRPV4 KO mice and incubated in the presence of pathophysiological range leptin concentrations (0.1–1μg/mL; 24 hr) ± LPS (E coli 0111:B4 as a positive control) ± TRPV4 inhibitor. Macrophage phagocytosis was measured as uptake of fluorescently-labeled E coli particles. Intracellular calcium was measured using the FLIPR Calcium 5 Assay in the presence of a selective TRPV4 agonist (GSK). MIP-2 and IL-8 secretion was measured by ELISA. Leptin increases phagocytosis of E coli particles by 17% (59% of the LPS response) and TRPV4 activity by 24% (51% of the LPS response). The phagocytic response and calcium influx are abrogated by either pharmacologic inhibition or deletion of TRPV4. Secretion of MIP-2 and IL-8 in response to leptin increases by 8-fold after pharmacologic inhibition of TRPV4. Our data show that TRPV4 mediates macrophage phagocytosis of E coli particles, and suppresses proinflammatory cytokine release, in response to leptin. In addition, we show that TRPV4 function is increased by leptin. In vitro results predict that TRPV4 enhances host defense and suppresses inflammation in the setting of obesity-induced hyperleptinemia, thus potentially modulating pneumonia severity in obese patients.

Transient Receptor Potential Vanilloid 4 (TRPV4) Regulates the Host Defense Response to Bacterial Pneumonia Through a MAPK Molecular Switch

We have shown that macrophage activation in response to lipopolysaccharide (LPS) is sensitive to the biophysical properties of the matrix through the mechanosensitive channel, transient receptor potential vanilloid 4 (TRPV4). However, the signals that drive macrophage activation are not fully known. Studies suggest that LPS-induced macrophage activation is controlled in part by the MAPK pathway (i.e. p38, ERK, JNK). Thus, we investigated if TRPV4 mediates the macrophage response to LPS through MAPKs. In TRPV4 deleted BMDMs, p38 activation was decreased (69%) while JNK activation was increased (2-fold), and ERK was unchanged after LPS, in a matrix stiffness-dependent manner. Further studies reveal that activation of p38 enhances LPS-induced macrophage phagocytosis (2-fold), but blocks IL-1β secretion (2-fold); while JNK enhances secretion of IL-6, IL-8, and MIP-2 (2 fold). Hence, the TRPV4 and LPS signals synergizes to activate p38 which increases phagocytosis and limits IL-1β secretion while downregulating JNK activation to limit other pro-inflammatory cytokines. In order to evaluate the role of TRPV4 in chronic pneumonia/lung injury, WT and TRPV4 KO mice were intratracheally administered agarose-embedded P. aeruginosa. Loss of TRPV4 led to decreased phagocytosis/bacterial clearance (6-fold), increased lung inflammation as measured by inflammatory cell infiltration (80±3%), vascular permeability (63±6%), and pro-inflammatory cytokine secretion (IL-1β &gt; by 71±4%). Thus, in the setting of lung infection TRPV4 functions to induce a molecular switch towards p38 which mediates bacterial clearance and downregulates pro-inflammatory cytokine secretion, to reduce infection-associated lung inflammation.

Idiopathic pulmonary fibrosis: What primary care physicians need to know

Idiopathic pulmonary fibrosis (IPF) is a specific type of fibrosing interstitial pneumonia of unknown cause. It is usually chronic and progressive, tends to affect mainly adults over age 60, has a predilection for men, and is often fatal. The condition is still underappreciated by pulmonologists and primary care physicians. This article attempts to close that information gap by reviewing the natural course of IPF and presenting an algorithmic approach to diagnosis and treatment based on evidence-based international guidelines. New treatment options are briefly discussed, to raise awareness of new medications that target pulmonary fibrosis.

The Mechanosensitive Ion Channel, Transient Receptor Potential Vanilloid 4 (TRPV4) in Macrophages Regulates the Host Defense Response to Bacterial Pneumonia

Macrophage phagocytosis and cytokine production are sensitive to the surrounding matrix and thereby mediate host defense and lung tissue injury. The consequences and mechanism of this matrix sensitivity are unknown. We have determined that the mechanosensitive channel, TRPV4, responds to extracellular matrix biophysical properties and thereby modulates the macrophage response to pathogens. We undertook this study to determine the in vivo consequences and the intracellular signaling pathway by which TRPV4 modulates macrophage responses. In order to evaluate the role of TRPV4 in chronic pneumonia/lung injury, WT and TRPV4 KO mice were administered agarose bead embedded-Pseudomonas aeruginosa. Loss of TRPV4 led to decreased phagocytosis by macrophages (6-fold), and increased lung injury as measured by inflammatory cell infiltration (≥ 80 ± 3%), vascular permeability (total protein ≥ 63 ± 6%), and cytokine secretion (IL-1β ≥ 71 ± 4%). In vivo, lung alveolar macrophages predominantly expressed TRPV4 and were the key phagocytic cell, as assessed by FACS and immunofluorescence. Known LPS signaling pathways were investigated in vitro. Loss of TRPV4 abrogates LPS-induced p38 activation and phagocytosis of E. coli particles. Additionally, loss of TRPV4 increased basal pro-/active IL-1β expression (2-fold), thereby enhancing IL-1β secretion independent of caspase 1 cleavage and blockade. These findings demonstrate that TRPV4 is important for bacterial clearance, lung injury and cytokine production in macrophages. TRPV4 mediates these effects through p38 and through upregulation of IL-1β protein expression in an inflammasome-independent manner. The results implicate macrophage TRPV4 as a key component of the host defense.

The Role of Transient Receptor Potential Vanilloid 4 in Pulmonary Inflammatory Diseases

Ion channels/pumps are essential regulators of organ homeostasis and disease. In the present review, we discuss the role of the mechanosensitive cation channel, transient receptor potential vanilloid 4 (TRPV4), in cytokine secretion and pulmonary inflammatory diseases such as asthma, cystic fibrosis (CF), and acute lung injury/acute respiratory distress syndrome (ARDS). TRPV4 has been shown to play a role in lung diseases associated with lung parenchymal stretch or stiffness. TRPV4 indirectly mediates hypotonicity-induced smooth muscle contraction and airway remodeling in asthma. Further, the literature suggests that in CF TRPV4 may improve ciliary beat frequency enhancing mucociliary clearance, while at the same time increasing pro-inflammatory cytokine secretion/lung tissue injury. Currently it is understood that the role of TRPV4 in immune cell function and associated lung tissue injury/ARDS may depend on the injury stimulus. Uncovering the downstream mechanisms of TRPV4 action in pulmonary inflammatory diseases is likely important to understanding disease pathogenesis and may lead to novel therapeutics.

Managing interstitial lung disease detected on CT during lung cancer screening

As long-term smokers undergo computed tomography (CT) to screen for lung cancer, cases of interstitial lung disease are being discovered incidentally. This article explains how to distinguish among the most common forms of interstitial lung disease in this situation and the role of primary care physicians in managing them.

Matrix-driven Myosin II Mediates the Pro-fibrotic Fibroblast Phenotype

Pro-fibrotic mesenchymal cells are known to be the key effector cells of fibroproliferative disease, but the specific matrix signals and the induced cellular responses that drive the fibrogenic phenotype remain to be elucidated. The key mediators of the fibroblast fibrogenic phenotype were characterized using a novel assay system that measures fibroblast behavior in response to actual normal and fibrotic lung tissue. Using this system, we demonstrate that normal lung promotes fibroblast motility and polarization, while fibrotic lung immobilizes the fibroblast and promotes myofibroblast differentiation. These context-specific phenotypes are surprisingly both mediated by myosin II. The role of myosin II is supported by the observation of an increase in myosin phosphorylation and a change in intracellular distribution in fibroblasts on fibrotic lung, as compared with normal lung. Moreover, loss of myosin II activity has opposing effects on protrusive activity in fibroblasts on normal and fibrotic lung. Loss of myosin II also selectively inhibits myofibroblast differentiation in fibroblasts on fibrotic lung. Importantly, these findings are recapitulated by varying the matrix stiffness of polyacrylamide gels in the range of normal and fibrotic lung tissue. Comparison of the effects of myosin inhibition on lung tissue with that of polyacrylamide gels suggests that matrix fiber organization drives the fibroblast phenotype under conditions of normal/soft lung, while matrix stiffness drives the phenotype under conditions of fibrotic/stiff lung. This work defines novel roles for myosin II as a key regulatory effector molecule of the pro-fibrotic phenotype, in response to biophysical properties of the matrix.

TRPV4 Mechanosensitive Ion Channel Regulates Lipopolysaccharide-Stimulated Macrophage Phagocytosis

Macrophage phagocytosis of particles and pathogens is an essential aspect of innate host defense. Phagocytic function requires cytoskeletal rearrangements that depend on the interaction between macrophage surface receptors, particulates/pathogens, and the extracellular matrix. In the present study we determine the role of a mechanosensitive ion channel, transient receptor potential vanilloid 4 (TRPV4), in integrating the LPS and matrix stiffness signals to control macrophage phenotypic change for host defense and resolution from lung injury. We demonstrate that active TRPV4 mediates LPS-stimulated murine macrophage phagocytosis of nonopsonized particles (Escherichia coli) in vitro and opsonized particles (IgG-coated latex beads) in vitro and in vivo in intact mice. Intriguingly, matrix stiffness in the range seen in inflamed or fibrotic lung is required to sensitize the TRPV4 channel to mediate the LPS-induced increment in macrophage phagocytosis. Furthermore, TRPV4 is required for the LPS induction of anti-inflammatory/proresolution cytokines. These findings suggest that signaling through TRPV4, triggered by changes in extracellular matrix stiffness, cooperates with LPS-induced signals to mediate macrophage phagocytic function and lung injury resolution. These mechanisms are likely to be important in regulating macrophage function in the context of pulmonary infection and fibrosis.

TRPV4 mediates myofibroblast differentiation and pulmonary fibrosis in mice

Idiopathic pulmonary fibrosis (IPF) is a fatal fibrotic lung disorder with no effective medical treatments available. The generation of myofibroblasts, which are critical for fibrogenesis, requires both a mechanical signal and activated TGF-β; however, it is not clear how fibroblasts sense and transmit the mechanical signal(s) that promote differentiation into myofibroblasts. As transient receptor potential vanilloid 4 (TRPV4) channels are activated in response to changes in plasma membrane stretch/matrix stiffness, we investigated whether TRPV4 contributes to generation of myofibroblasts and/or experimental lung fibrosis. We determined that TRPV4 activity is upregulated in lung fibroblasts derived from patients with IPF. Moreover, TRPV4-deficient mice were protected from fibrosis. Furthermore, genetic ablation or pharmacological inhibition of TRPV4 function abrogated myofibroblast differentiation, which was restored by TRPV4 reintroduction. TRPV4 channel activity was elevated when cells were plated on matrices of increasing stiffness or on fibrotic lung tissue, and matrix stiffness-dependent myofibroblast differentiation was reduced in response to TRVP4 inhibition. TRPV4 activity modulated TGF-β1-dependent actions in a SMAD-independent manner, enhanced actomyosin remodeling, and increased nuclear translocation of the α-SMA transcription coactivator (MRTF-A). Together, these data indicate that TRPV4 activity mediates pulmonary fibrogenesis and suggest that manipulation of TRPV4 channel activity has potential as a therapeutic approach for fibrotic diseases.

Urokinase-type plasminogen activator receptor (uPAR) ligation induces a raft-localized integrin signaling switch that mediates the hypermotile phenotype of fibrotic fibroblasts

The urokinase-type plasminogen activator receptor (uPAR) is a glycosylphosphatidylinositol-linked membrane protein with no cytosolic domain that localizes to lipid raft microdomains. Our laboratory and others have documented that lung fibroblasts from patients with idiopathic pulmonary fibrosis (IPF) exhibit a hypermotile phenotype. This study was undertaken to elucidate the molecular mechanism whereby uPAR ligation with its cognate ligand, urokinase, induces a motile phenotype in human lung fibroblasts. We found that uPAR ligation with the urokinase receptor binding domain (amino-terminal fragment) leads to enhanced migration of fibroblasts on fibronectin in a protease-independent, lipid raft-dependent manner. Ligation of uPAR with the amino-terminal fragment recruited α5β1 integrin and the acylated form of the Src family kinase, Fyn, to lipid rafts. The biological consequences of this translocation were an increase in fibroblast motility and a switch of the integrin-initiated signal pathway for migration away from the lipid raft-independent focal adhesion kinase pathway and toward a lipid raft-dependent caveolin-Fyn-Shc pathway. Furthermore, an integrin homologous peptide as well as an antibody that competes with β1 for uPAR binding have the ability to block this effect. In addition, its relative insensitivity to cholesterol depletion suggests that the interactions of α5β1 integrin and uPAR drive the translocation of α5β1 integrin-acylated Fyn signaling complexes into lipid rafts upon uPAR ligation through protein-protein interactions. This signal switch is a novel pathway leading to the hypermotile phenotype of IPF patient-derived fibroblasts, seen with uPAR ligation. This uPAR dependent, fibrotic matrix-selective, and profibrotic fibroblast phenotype may be amenable to targeted therapeutics designed to ameliorate IPF.

Anatomic asymmetries of the posterior superior temporal lobes: a postmortem study

OBJECTIVE

To examine for structural asymmetries in the posterior superior temporal lobe at the microscopic level in an effort to explain the gross anatomical and functional asymmetries of this brain region.

BACKGROUND

The posterior superior temporal lobe is typically larger on the left and damage to this area frequently results in an aphasia. This has led to the hypothesis that the structural asymmetry determines the functional asymmetry, but no definite confirmation of this hypothesis exists.

METHODS

Sixteen men were studied at postmortem. Posterior superior temporal lobe dimensions, gray matter volume, white matter volume, SMI-32 immunopositive neuronal density, and glia cell volume were measured for both the left and right hemispheres. In a subset of eight subjects, myelin sheath and axon diameters were measured with electron microscopy.

RESULTS

Posterior superior temporal lobe white matter volume was greater on the left (p = 0.003, t test for dependent samples). This asymmetry did not appear to be the result of an isolated proliferation of glia (p = 0.46, t test for dependent samples), nor the density of cortical to cortical projections neurons in the overlying cortex (p = 0.71, t test for dependent samples). In a subset of eight subjects studied with electron microscopy, axons of the left posterior superior temporal lobe were more thickly myelinated (57 nm [SD = 27] left, 46 nm [SD = 24], p < 0.001, ANOVA).

CONCLUSIONS

As axons with thicker myelin sheaths conduct faster and require a greater volume, these results suggest asymmetry of myelination as an explanation for both a left hemisphere dominance for rapid sensory signal processing, leading to a functional asymmetry for language, and a larger left planum temporale.