Rodent Lung Research Articles

Clinical Diffuse Lung Injury and Remodeling

Lung structural abnormalities result primarily from two mechanisms: developmental abnormalities and lung injury with repair. The timing of distal airway and alveolar/vascular development in the human will be reviewed. Developmental disruptions such as renal dysplasia and congenital diaphragmatic hernia that result in pulmonary hypoplasia are relatively common causes of severe lung structural abnormalities. Preterm delivery can interfere with distal parenchymal development and alveolarization, which normally begins in the human at 32‐36 wks gestation. Clinical interventions such as mechanical ventilation and oxygen exposure of the preterm lung interfere with lung development and initiate injury/repair that results in a decreased alveolar septation and decreased microvascular development syndrome called bronchopulmonary dysplasia. Although alveolar septation has been thought to be complete by early childhood, new results suggest that new alveoli can form in the adult lung. As proof of principle, the adult rodent lung can develop emphysema with starvation, and the emphysema disappears with brief refeeding. Diffuse injuries to the mature lung caused by Acute Respiratory Distress Syndrome can resolve remarkably if fibrosis does not occur. The challenges are to learn how to promote alveolar/vascular regrowth and suppress fibrosis following lung injury.

A Rabbit Irradiation Platform for Outcome Assessment of Lung Stereotactic Radiosurgery

To evaluate a helical tomotherapy-based rodent radiosurgery platform that reproduces human image-guided radiosurgery treatment to study radiobiologic effects of stereotactic radiosurgery on lung tissues using functional magnetic resonance imaging (MRI). Hypofractionated radisourgery (20 Gy x 3) was delivered to the right lung of three New Zealand rabbits using Helical TomoTherapy with MVCT image guidance. Contrast-enhanced MR perfusion, hyperpolarized helium-3 MR ventilation, and CT were obtained before radiation and monthly for 4 months after radiation. All MRI was performed on a 1.5-T whole-body scanner with broad-band capabilities. Precise dose delivery to 1.6 cc of the lower right lung was achieved without additional immobilization. No deficits were detected at baseline with respect to perfusion and ventilation. Lung perfusion deficits in the irradiated lung regions began at 2 months after radiation and worsened with time. No ventilation deficits were observed after radiation. Decrease in lung CT density in irradiated regions was observed after radiation, but the changes were less significant than those in perfusion MRI. We demonstrated that highly conformal radiation can be reproducibly delivered to a small volume of rodent lung on a widely available clinical unit. The radiation-induced lung injury can be detected as early as 2 months after radiation with perfusion MRI. The primary pattern of injury agrees with previously reported endothelial damage to radiosurgical radiation doses. This experimental design provides a cost-effective methodology for producing radiosurgical injuries in rodents that reproduces current human treatments for studying radiation injury and agents that might affect it.

Drug uptake in a rodent sarcoma model after intravenous injection or isolated lung perfusion of free/liposomal doxorubicin

The distribution of free and liposomal doxorubicin (Liporubicin) administered by intravenous injection (IV) or isolated lung perfusion (ILP) was compared in normal and tumor tissues of sarcoma bearing rodent lungs. A single sarcomatous tumor was generated in the left lung of 35 Fischer rats, followed 10 days later by left-sided ILP (n=20) or IV drug administration (n=12), using 100 microg and 400 microg free or liposomal doxorubicin, respectively. The tumor and lung tissue drug concentration was measured by HPLC. Free doxorubicin administered by ILP resulted in a three-fold (100 microg) and 10-fold (400 microg) increase of the drug concentration in the tumor and normal lung tissue compared to IV administration. In contrast, ILP with Liporubicin resulted in a similar drug uptake in the tumor and lung tissue compared to IV injection. For both drug formulations and dosages, ILP resulted in a higher tumor to lung tissue drug ratio but also in a higher spatial heterogeneity of drug distribution within the lung compared to IV administration. ILP resulted in a higher tumor to lung tissue drug ratio and in a more heterogeneous drug distribution within the lung compared to IV drug administration.

Development of a bio-mathematical model in rats to describe clearance, retention and translocation of inhaled nano particles throughout the body

Studies of the translocation of inhaled nanoparticles from rodent lungs to different target organs provide data to model the inhalation and translocation of nanoparticles. A compartmental model was developed based on biological information about the major organs and how they interrelate. This model, which is quantified by a set of differential equations 'describing' the passage of nanoparticles through the body, gives estimates of the particle mass present in each organ. Optimal parameter estimates were found by minimising the model mean squared error. Data from two different studies in rats (one endotracheal instillation and one inhalation exposure) were used to calibrate the model. Most of the nanoparticle mass remained in the lungs. The overall fit of the model to the total measured particle mass in the body was very good for both studies (R2=0.98-0.99), although different parameter estimates were sometimes required to fit the study-specific data. The model fit to the measured particle mass by organ was very good for the lungs, brain, and spleen (R2=0.81-0.98) in both studies, but not as good for the liver and kidney (R2=0.32-0.53). While this model describes the retention and translocation of nanoparticles from the lungs reasonably well, further model evaluation and validation is needed using additional data.

Small interfering peptide (siP) for in vivo examination of the developing lung interactonome

To understand the role of reactive oxygen species in mechanosensory control of lung development a new approach to interfere with protein-protein interactions by means of a short interacting peptide was developed. This technology was used in the developing rodent lung to examine the role of NADPH oxidase (NOX), casein kinase 2 (CK2), and the cystic fibrosis transmembrane conductance regulator (CFTR) in stretch-induced differentiation. Interactions between these molecules was targeted in an in utero system with recombinant adeno-associated virus (rAAV) containing inserted DNA sequences that express a control peptide or small interfering peptides (siPs) specific for subunit interaction or phosphorylation predicted to be necessary for multimeric enzyme formation. In all cases only siPs with sequences necessary for a predicted normal function were found to interfere with assembly of the multimeric enzyme. A noninterfering control siP to nonessential regions or reporter genes alone had no effect. Physiologically, it was shown that siPs that interfered with the NOX-CFTR-CK2 complex that we call an "interactonome" affected markers of stretch-induced lung organogenesis including Wnt/beta-catenin signaling.

Phospholipid-Induced In Vivo Particle Migration to Enhance Pulmonary Deposition

Amount of drug actually reaching the target region in the lung following pulmonary inhalation is often estimated at less than 10% for older devices. Current particle and device engineering technologies have improved on this but still fail to recover the "wasted" fraction of the drug and deliver it deeper into the lungs, which is generally desirable. FDA has approved several exogenous surfactants for prophylaxis and rescue treatment of respiratory distress syndrome (RDS). Their approved mode of administration (intratracheal instillation) and site of action (alveolar spaces) suggest that the phospholipids in the exogenous surfactants can spread from the trachea to alveolar air spaces and exert advantageous effects. We investigated whether in vivo lung migration of particles based on this phenomenon was possible and could be quantified based on changes in total and regional deposition of fluorescently labeled latex beads, utilized as an insoluble drug model. Following intranasal administration of beads, migration to rodent lungs was monitored upon intranasal instillation of Survanta (exogenous surfactant) or saline (control). After intranasal instillation approximately 12% of beads were found to migrate to the lung, and total lung deposition increased by approximately 10% on administration of Survanta or saline (control). After intranasal administration approximately 1% of beads in the lung were found to migrate to peripheral regions of the lungs, and a four- to six-fold increase in peripheral lung deposition was observed after Survanta instillation, compared to the saline control, which was determined to be independent of dose and volume of Survanta instillate in the range we studied. The in vivo rodent studies provided support for the idea that intranasally administered particles deposited in non-target lung locations may be translocated to peripheral sites in the lung therapeutically after surfactant application.

Phasic Changes in Protein Tyrosine Nitration and Expression of Key Regulatory Proteins in the Rodent Lung Following a Radiation Exposure

Phasic Changes in Protein Tyrosine Nitration and Expression of Key Regulatory Proteins in the Rodent Lung Following a Radiation Exposure

Airborne nanoparticle exposures associated with the manual handling of nanoalumina and nanosilver in fume hoods

Manual handling of nanoparticles is a fundamental task of most nanomaterial research; such handling may expose workers to ultrafine or nanoparticles. Recent studies confirm that exposures to ultrafine or nanoparticles produce adverse inflammatory responses in rodent lungs and such particles may translocate to other areas of the body, including the brain. An important method for protecting workers handling nanoparticles from exposure to airborne nanoparticles is the laboratory fume hood. Such hoods rely on the proper face velocity for optimum performance. In addition, several other hood design and operating factors can affect worker exposure. Handling experiments were performed to measure airborne particle concentration while handling nanoparticles in three fume hoods located in different buildings under a range of operating conditions. Nanoalumina and nanosilver were selected to perform handling experiments in the fume hoods. Air samples were also collected on polycarbonate membrane filters and particles were characterized by scanning electron microscopy. Handling tasks included transferring particles from beaker to beaker by spatula and by pouring. Measurement locations were the room background, the researcher’s breathing zone and upstream and downstream from the handling location. Variable factors studied included hood design, transfer method, face velocity/sash location and material types. Airborne particle concentrations measured at breathing zone locations were analyzed to characterize exposure level. Statistics were used to test the correlation between data. The test results found that the handling of dry powders consisting of nano-sized particles inside laboratory fume hoods can result in a significant release of airborne nanoparticles from the fume hood into the laboratory environment and the researcher’s breathing zone. Many variables were found to affect the extent of particle release including hood design, hood operation (sash height, face velocity), work practices, type and quantity of the material being handled, room conditions, and the adequacy of the room exhaust.

A variable field strength system for hyperpolarized noble gas MR imaging of rodent lungs

AbstractHyperpolarized Noble Gas (HNG), 3He (helium) or 129Xe (xenon), MR imaging has become a promising approach for visualizing lung anatomy and function. It has been theoretically predicted that low field strengths (0.05–0.2 T) may provide optimal signal‐to‐noise ratio (SNR) and spatial resolution for clinical HNG MR imaging. These optimum field strengths correspond to frequencies between 1.62–6.5 MHz and 0.59–2.35 MHz for 3He and 129Xe respectively. The optimum field strength depends on the size and geometry of the sample and radiofrequency (RF) coil as well as the field dependence of the HNG MR properties in the lung (e.g., relaxation times, susceptibility effects). In particular, little is known about the field dependence of the apparent transverse relaxation time, T, which is expected to strongly influence HNG signal. In this paper, a broadband (0.1–100 MHz) variable field strength MR imaging system for rodents is described. A custom‐built resistive magnet was constructed and shimmed to provide the necessary homogeneity for imaging. RF coils and transmit/receive switches for different frequencies were also developed. Preliminary proton (1H) and hyperpolarized 129Xe images of test objects are presented, including a desiccated lung phantom. In vivo 129Xe signals from rat lungs were acquired at 73.5 mT and T was estimated to be approximately 80 ± 8 ms, in good agreement with previously reported values. The MR system developed should be useful for imaging rodent lungs at different field strengths to verify the expected SNR and spatial resolution possible using HNG imaging and to investigate long range diffusion and oxygen‐induced transverse relaxation. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 33B: 124–137, 2008

QS135. Pseudoglandular Lung Development Is Altered by Tracheal Occlusion

Background: Previous models of fetal development involving rodent lung explants have included tracheal occlusion (TO) during late gestation or focused on embryonic branching morphogenesis. TO in late gestation fetal explants and even in novel human observations demonstrate increased growth and accelerated maturation. The effect of retained lung fluid early in the development of airway branching has not yet been studied. Methods: Gestational day 15 (E15) and E16 fetal rat lung explants (term=22 d) underwent microscopic tracheal occlusion using 10-0 ligature, and were compared with sham controls and near-term fetal lungs.

Pulmonary perfusion imaging in the rodent lung using dynamic contrast-enhanced MRI

With the development of various models of pulmonary disease, there is tremendous interest in quantitative regional assessment of pulmonary function. While ventilation imaging has been addressed to a certain extent, perfusion imaging for small animals has not kept pace. In humans and large animals perfusion can be assessed using dynamic contrast-enhanced (DCE) MRI with a single bolus injection of a gadolinium (Gd)-based contrast agent. But the method developed for the clinic cannot be translated directly to image the rodent due to the combined requirements of higher spatial and temporal resolution. This work describes a novel image acquisition technique staggered over multiple, repeatable bolus injections of contrast agent using an automated microinjector, synchronized with image acquisition to achieve dynamic first-pass contrast enhancement in the rat lung. This allows dynamic first-pass imaging that can be used to quantify pulmonary perfusion. Further improvements are made in the spatial and temporal resolution by combining the multiple injection acquisition method with Interleaved Radial Imaging and "Sliding window-keyhole" reconstruction (IRIS). The results demonstrate a simultaneous increase in spatial resolution (<200 mum) and temporal resolution (<200 ms) over previous methods, with a limited loss in signal-to-noise-ratio.

Attenuation of rodent lung ischemia–reperfusion injury by sphingosine 1-phosphate

Objective. Lung ischemia–reperfusion (IR) injury, a sequela of transplantation characterized by alveolar damage, edema and inflammation in donor lungs, remains a significant cause of transplant failure despite improvements in lung preservation techniques. We investigated the effects of sphingosine 1-phosphate (S1P), a potent vascular barrier-protective agent, in a rat model of IR injury. Material and methods. S1P (26.5 mg/kg, i.v.) or vehicle was administered 15 min prior to ischemia via pulmonary artery ligation (1 h) and subsequent reperfusion (2 h). Lung vascular permeability and inflammation were assessed. Results. Animals pretreated with S1P exhibited reduced bronchoalveolar lavage (BAL) inflammatory cells (32% decrease; p<0.05), BAL neutrophils (63% decrease; p<0.04), and BAL albumin content (57% decrease; p<0.04) compared to controls. Lung myeloperoxidase activity, an index of parenchymal leukocyte infiltration, was also attenuated in S1P-treated animals (63% decrease; p<0.05). Finally, consistent ...

TGF‐β signaling is dynamically regulated during the alveolarization of rodent and human lungs

Although transforming growth factor-beta (TGF-beta) signaling negatively regulates branching morphogenesis in early lung development, few studies to date have addressed the role of this family of growth factors during late lung development. We describe here that the expression, tissue localization, and activity of components of the TGF-beta signaling machinery are dynamically regulated during late lung development in the mouse and human. Pronounced changes in the expression and localization of the TGF-beta receptors Acvrl1, Tgfbr1, Tgfbr2, Tgfbr3, and endoglin, and the intracellular messengers Smad2, Smad3, Smad4, Smad6, and Smad7 were noted as mouse and human lungs progressed through the canalicular, saccular, and alveolar stages of development. TGF-beta signaling, assessed by phosphorylation of Smad2, was detected in the vascular and airway smooth muscle, as well as the alveolar and airway epithelium throughout late lung development. These data suggest that active TGF-beta signaling is required for normal late lung development.

Intravenous Administration of Manganese Superoxide Dismutase-Plasmid Liposomes (MnSOD-PL) in a Mouse Model Protects Against Whole Body Irradiation.

Organ specific localized administration of manganese superoxide dismutase plasmid/liposome complexes (MnSOD-PL) confers protection of the rodent lung, esophagus, oral cavity, intestine and bladder from single fraction and fractionated ionizing irradiation by a mechanism dependent upon mitochondrial localized antioxidant effects. Intravenous injection of MnSOD-PL significantly increased survival of both male and female C57BL/6NHsd mice from the LD 50/30 whole body irradiation dose of 9.5 Gy (p = 0.0001 or 0.0059, respectively). To determine if systemic MnSOD-PL mediated improved survival at the expense of a deleterious delayed increase in development of cancer, life shortening, or neurodegenerative disease we followed all survivors. Fifty male and female C57BL/6NHsd mice per group were injected intravenously with MnSOD-PL (100 μg plasmid DNA in 0.1 ml) and irradiated with control mice to 0, 1 or 9.5 Gy whole body irradiation 24 hrs later. Moribund or dying mice were sacrificed, examined for tumors and bone marrow isolated stained with Wright Geimsa, and examined for abnormal hemogram. Small intestine was fixed in formalin, sectioned and examined for intestinal changes. Female mice pretreated with MnSOD-PL prior to 9.5 Gy (LD 50/30) had an increased survival over the first 30 days which is the time frame for death due to hematopoietic or intestinal damage with 90% survival compared to 58% for the control irradiated mice (p = 0.0059). Between 30 and 530 days there was no significant change in survival rate between MnSOD-PL treated and control irradiated 9.5 Gy or 1.0 Gy groups. Beginning at day 400, all groups have a similar death rate which can be attributed of the age of the mice. Male mice pretreated with MnSOD-PL and irradiated to 9.5 Gy had 75% survival after 30 days compared to 25% for the control mice (p < 0.0001). Between 30 and 375 days after irradiation, there was no significant change in survival rate between MnSOD-PL treated compared to control irradiated 9.5 or 1.0 Gy groups. There was no detectable difference in the incidence of deaths associated with tumor (thymoma), marrow, or intestinal damage. All mice are being followed until they become moribund as a result of irradiation or old age. The data indicate, at this time, that systemic MnSOD-PL treatment is not detectably harmful to surviving total body irradiated mice.

Novel Role for the Liver X Nuclear Receptor in the Suppression of Lung Inflammatory Responses

The liver X receptors (LXRalpha/beta) are part of the nuclear receptor family and are believed to regulate cholesterol and lipid homeostasis. It has also been suggested that LXR agonists possess anti-inflammatory properties. The aim of this work was to determine the effect of LXR agonists on the innate immune response in human primary lung macrophages and a pre-clinical rodent model of lung inflammation. Before profiling the impact of the agonist, we established that both the human macrophages and the rodent lungs expressed LXRalpha/beta. We then used two structurally distinct LXR agonists to demonstrate that activation of this transcription factor reduces cytokine production in THP-1 cells and lung macrophages. Then, using the expression profile of ATP binding cassettes A1 (ABCA-1; a gene directly linked to LXR activation) as a biomarker for lung exposure of the compound, we demonstrated an LXR-dependent reduction in lung neutrophilia rodents in vivo. This inhibition was not associated with a suppression of c-Fos/c-Jun mRNA expression or NF-kappaB/AP-1 DNA binding, suggesting that any anti-inflammatory activity of LXR agonists is not via inhibition of NF-kappaB/AP-1 transcriptional activity. These data do not completely rule out an impact of these agonists on these two prominent transcription factors. In summary, this study is the first to demonstrate anti-inflammatory actions of LXRs in the lung. Chronic innate inflammatory responses observed in some airway diseases is thought to be central to disease pathogenesis. Therefore, data suggest that LXR ligands have utility in the treatment of lung diseases that involves chronic inflammation mediated by macrophages and neutrophils.

MR microscopy of the lung in small rodents

Understanding how the mammalian respiratory system works and how it changes in disease states and under the influence of drugs is frequently pursued in model systems such as small rodents. These have many advantages, including being easily obtained in large numbers as purebred strains. Studies in small rodents are valuable for proof of concept studies and for increasing our knowledge about disease mechanisms. Since the recent developments in the generation of genetically designed animal models of disease, one needs the ability to assess morphology and function in in vivo systems. In this article, we first review previous reports regarding thoracic imaging. We then discuss approaches to take in making use of small rodents to increase MR microscopic sensitivity for these studies and to establish MR methods for clinically relevant lung imaging.

In a Mouse Model Intravenous Administration of Manganese Superoxide Dismutase-Plasmid Liposomes (MnSOD-PL) Protects Against Whole Body Irradiation

Organ specific localized administration of manganese superoxide dismutase plasmid/liposome complexes (MnSOD-PL) confers protection of the rodent lung, esophagus, oral cavity, intestine and bladder from single fraction and fractionated ionizing irradiation by a mechanism dependent upon mitochondrial localized antioxidant effects. Intravenous injection of MnSOD-PL significantly increased survival of both male and female C57BL/6NHsd mice from the LD 50/30 whole body irradiation dose of 9.5 Gy (p = 0.0001 or 0.0059, respectively).

Angiopoietin-1 Requires p190 RhoGAP to Protect against Vascular Leakage in Vivo

Angiopoietin-1 (Ang-1), a ligand of the endothelium-specific receptor Tie-2, inhibits permeability in the mature vasculature, but the mechanism remains unknown. Here we show that Ang-1 signals Rho family GTPases to organize the cytoskeleton into a junction-fortifying arrangement that enhances the permeability barrier function of the endothelium. Ang-1 phosphorylates Tie-2 and its downstream effector phosphatidylinositol 3-kinase. This induces activation of one endogenous GTPase, Rac1, and inhibition of another, RhoA. Loss of either part of this dual effect abrogates the cytoskeletal and anti-permeability actions of Ang-1, suggesting that coordinated GTPase regulation is necessary for the vessel-sealing effects of Ang-1. p190 RhoGAP, a GTPase regulatory protein, provides this coordinating function as it is phosphorylated by Ang-1 treatment, requires Rac1 activation, and is necessary for RhoA inhibition. Ang-1 prevents the cytoskeletal and pro-permeability effects of endotoxin but requires p190 RhoGAP to do so. Treatment with p190 RhoGAP small interfering RNA completely abolishes the ability of Ang-1 to rescue endotoxemia-induced pulmonary vascular leak and inflammation in mice. We conclude that Ang-1 prevents vascular permeability by regulating the endothelial cytoskeleton through coordinated and opposite effects on the Rho GTPases Rac1 and RhoA. By linking Rac1 activation and RhoA inhibition, p190 RhoGAP is critical to the protective effects of Ang-1 against endotoxin. These results provide mechanistic evidence that targeting the endothelium through Tie-2 may offer specific therapeutic strategies in life-threatening endotoxemic conditions such as sepsis and acute respiratory distress syndrome.

TGF-β, Smad3 and the process of progressive fibrosis

Transient adenovirus-mediated gene transfer of active TGF-beta1 (transforming growth factor-beta1) induces severe and progressive fibrosis in rodent lung without apparent inflammation. Alternatively, transfer of IL-1beta (interleukin 1beta) induces marked tissue injury and inflammation, which develops into progressive fibrosis, associated with an increase in TGF-beta1 concentrations in lung fluid and tissue. Both vector treatments induce a fibrotic response involving myofibroblasts and progressive matrix deposition starting at the peri-bronchial site of expression and extending over days to involve the entire lung and pleural surface. Administration of the TGF-beta1 vector to the pleural space induces progressive pleural fibrosis, which minimally extends into the lung parenchyma. The mechanisms involved in progressive fibrosis need to account for the limitation of fibrosis to specific organs (lung fibrosis and not liver fibrosis or vice versa) and the lack of effect of anti-inflammatory treatments in regulating progressive fibrosis. TGF-beta1 is a key cytokine in the process of fibrogenesis, using intracellular signalling pathways involving the ALK5 receptor and signalling molecules Smad2 and Smad3. Transient gene transfer of either TGF-beta1 or IL-1beta to Smad3-null mouse lung provides little evidence of progressive fibrosis and no fibrogenesis-associated genes are induced. These results suggest that mechanisms of progressive fibrosis involve factors presented within the context of the matrix that define the microenvironment for progressive matrix deposition.

The Angiotensin II Receptor 2 Is Expressed and Mediates Angiotensin II Signaling in Lung Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a severe interstitial lung disease unresponsive to currently available therapies. In IPF, initial alveolar epithelial cell damage leads to activation of fibroblast-(myo)fibroblasts, which deposit an increased amount of a collagen-rich extracellular matrix. Angiotensin II (ANGII) signaling, mediated via angiotensin II receptor type 1 (AGTR1) or type 2 (AGTR2), controls tissue remodeling in fibrosis, but the relevance of AGTR2 remains elusive. In the present study, we demonstrated increased expression of AGTR1 und AGTR2 in human and rodent lung tissues from patients with IPF and mice subjected to bleomycin-induced fibrosis, respectively. Both AGTR1 und AGTR2 localized to interstitial fibroblasts. Quantitative analysis of cell surface expression in primary mouse fibroblasts revealed a significant increase of AGTR2 surface expression in fibrotic fibroblasts, whereas AGTR1 surface expression levels remained similar. ANGII treatment of normal fibroblasts led to enhanced migration and proliferation, which was abrogated after pretreatment with losartan (LOS), an AGTR1 inhibitor. In contrast, in fibrotic fibroblasts, migration and proliferation was modified only by AGTR2, but not AGTR1 inhibition (using PD123319). ANGII-induced effects were mediated via phosphorylation of the mitogen-activated protein kinases p38 and p42/44, which was blocked via LOS and PD123319, respectively. Similar effects of AGTR1 and AGTR2 inhibition were observed using conditioned media of alveolar epithelial cells, a prominent source of ANGII in the lung in vivo. In summary, we conclude that ANGII signaling occurs primarily via AGTR1 in normal fibroblasts, while AGTR2-mediated effects are dominant on activated (myo)-fibroblasts, a receptor switch that may perturb epithelial-mesenchymal interaction, thereby further perpetuating fibrogenesis.