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ObjectiveCreeping 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.DesignTissues 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.ResultsCrohn’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.ConclusionCrohn’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.

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.

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.

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.

Idiopathic pulmonary fibrosis (IPF) is a fatal fibrotic lung disorder with marginally effective medical treatment. Myofibroblasts are critical to the fibrogenic lung repair process; however, the mechanism whereby the mechanical signal that leads to myofibroblast generation is sensed and transmitted remains to be determined. As transient receptor potential vanilloid 4 (TRPV4) ion channels are activated by plasma membrane stretch/matrix stiffness, we investigated whether TRPV4 plays a role in myofibroblast differentiation and/or in vivo lung fibrosis. TRPV4 inhibition by small-molecule inhibitors almost completely abrogated both the calcium influx response to TPRV4 agonist in a dose-dependent manner and the myofibroblast differentiation response to transforming growth factor-β. Similar findings were noted on TRPV4 deletion with small interfering RNA or in TRPV4 KO murine lung fibroblasts. Further, TRPV4 exhibited its mechanosensing and myofibroblast-differentiating effect under conditions of matrix stiffness in the pathophysiological range (1–25 kPa). Mechanistically, TRPV4 activity modulates transforming growth factor β actions in a Smad-independent manner, in part through enhanced actomyosin remodeling with resultant nuclear translocation of the α–smooth muscle actin transcription coactivator (myocardin-related transcription factor-A). The myofibroblast differentiation response to actual fibrotic lung tissue was also completely inhibited on TRPV4 blockade. Furthermore, TRPV4 deficiency protects mice from fibrosis-inducing effects of bleomycin (1 or 4 U/kg dose) at the biochemical (75% less hydroxyproline; P < 0.05), histologic, and physiologic levels (57% less impairment of compliance; P < 0.05). These data identify TRPV4 as a long-elusive mechanosensor/transducer that mediates myofibroblast differentiation and in vivo pulmonary fibrogenesis. Successful manipulation of TRPV4 channel activity may be a novel therapeutic approach for fibrotic diseases of the lung and other organs.

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic lung disease whose underlying molecular mechanisms are largely unknown. Herein, we show that focal adhesion kinase–related nonkinase (FRNK) plays a key role in limiting the development of lung fibrosis. Loss of FRNK function in vivo leads to increased lung fibrosis in an experimental mouse model. The increase in lung fibrosis is confirmed at the histological, biochemical, and physiological levels. Concordantly, loss of FRNK function results in increased fibroblast migration and myofibroblast differentiation and activation of signaling proteins that drive these phenotypes. FRNK-deficient murine lung fibroblasts also have an increased capacity to produce and contract matrix proteins. Restoration of FRNK expression in vivo and in vitro reverses these profibrotic phenotypes. These data demonstrate the multiple antifibrotic actions of FRNK. More important, FRNK expression is down-regulated in human IPF, and down-regulation of FRNK in normal human lung fibroblasts recapitulates the profibrotic phenotype seen in FRNK-deficient cells. The effect of loss and gain of FRNK in the experimental model, when taken together with its down-regulation in human IPF, suggests that FRNK acts as an endogenous negative regulator of lung fibrosis by repressing multiple profibrotic responses.