PTEN inhibition improves wound healing in lung epithelia through changes in cellular mechanics that enhance migration

Spatiotemporal distribution of PTEN before directed cell migration in monolayers

The intracellular distribution of phosphatase and tensin homolog (PTEN) is closely related to directed cell migration. In single cells, PTEN accumulates at the rear of the cell before and during directed migration; however, the spatiotemporal distribution of PTEN in confluent cell monolayers, particularly before directed migration, remains unclear. In this study, we wounded a cell in confluent fetal rat skin keratinocytes (FRSKs) and examined the dynamics of PTEN in the cells adjacent to the wounded cell. In contrast to single-cell migration, we found that PTEN translocated to the nucleus before the beginning of directed migration. This nuclear translocation of PTEN did not occur in disconnected cells, and it was also suppressed by importin-β inhibitor and actin inhibitor. When the nuclear localization of PTEN was inhibited by an importin-β inhibitor, cell elongation in the direction of migration was also significantly inhibited. Our results indicate that PTEN translocation is induced by the disruption of cell-cell adhesion and requires the involvement of importin-β and actin cytoskeleton signaling. In addition, phosphatidylinositol 3,4,5-triphosphate (PIP3) may regulate PTEN distribution through its localized accumulation at the cell edge. Our findings suggest that the translocation of PTEN is crucial for directed cell migration and for responding to mechanical environmental changes in confluent cell monolayers.

Post-translational modifications of beta-amyloid modulate its effect on cell mechanical properties and influence cytoskeletal signaling cascades

Post-translational modifications of beta-amyloid (Aβ) play an important role in the pathogenesis of Alzheimer's disease (AD). Aβ modifications such as Ser8 phosphorylation (pS8-Aβ42) and Asp7 isomerization (iso-Aβ42) can significantly alter the properties of Aβ and have been detected in vivo. One of the reasons for the different pathogenicity of Aβ isoforms may be the activation of different signaling cascades leading to changes in the mechanical properties of cells. In this paper, we used correlative scanning ion-conductance microscopy (SICM) and Pt-nanoelectrodes to compare the effects of Aβ isoforms on the Young's modulus of SH-SY5Y cells and the level of ROS. It was found that unmodified Aβ42 resulted in the largest increase in cell Young's modulus of all isoforms after 4 h of incubation, while pS8-Aβ42 induced the greatest increase in stiffness and ROS levels after 24 h of incubation. Analysis of signaling proteins involved in the regulation of the actin cytoskeleton showed that Aβ42, pS8-Aβ42 and iso-Aβ42 have different effects on cofilin, GSK3β, LIMK, ERK and p38. This indicates that post-translational modifications of Aβ modulate its effect on neuronal cells through the activation of various signaling cascades, which affects the mechanical properties of cells.

The Role of Ubiquitination and the E3 Ligase Nedd4 in Regulating Corneal Epithelial Wound Healing

Purpose

Ubiquitination serves as a fundamental post-translational modification in numerous cellular events. Yet, its role in regulating corneal epithelial wound healing (CEWH) remains elusive. This study endeavored to determine the function and mechanism of ubiquitination in CEWH.

Methods

Western blot and immunoprecipitation were used to discern ubiquitination alterations during CEWH in mice. Interventions, including neuronally expressed developmentally downregulated 4 (Nedd4) siRNA and proteasome/lysosome inhibitor, assessed their impact on CEWH. In vitro analyses, such as the scratch wound assay, MTS assay, and EdU staining, were conducted to gauge cell migration and proliferation in human corneal epithelial cells (HCECs). Moreover, transfection of miR-30/200 coupled with a luciferase activity assay ascertained their regulatory mechanism on Nedd4.

Results

Global ubiquitination levels were markedly increased during the mouse CEWH. Importantly, the application of either proteasomal or lysosomal inhibitors notably impeded the healing process both in vivo and in vitro. Furthermore, Nedd4 was identified as an essential E3 ligase for CEWH. Nedd4 expression was significantly upregulated during CEWH. In vivo studies revealed that downregulation of Nedd4 substantially delayed CEWH, whereas further investigations underscored its role in regulating cell proliferation and migration, through the Stat3 pathway by targeting phosphatase and tensin homolog (PTEN). Notably, our findings pinpointed miR-30/200 family members as direct regulators of Nedd4.

Conclusions

Ubiquitination holds pivotal significance in orchestrating CEWH. The critical E3 ligase Nedd4, under the regulatory purview of miR-30 and miR-200, facilitates CEWH through PTEN-mediated Stat3 signaling. This revelation sheds light on a prospective therapeutic target within the realm of CEWH.

Computational modeling and simulation of epithelial wound closure

Wounds in the epithelium may lead to serious injurious events or chronic inflammatory diseases, however, multicellular organisms have the ability to self-repair wounds through the movement of epithelial cell toward the wound area. Despite intensive studies exploring the mechanism of wound closure, the role of mechanics in epithelial wound closure is still not well explained. In order to investigate the role of mechanical properties on wound closure process, a three-dimensional continuum physics-based computational model is presented in this study. The model takes into account the material property of the epithelial cell, intercellular interactions between neighboring cells at cell-cell junctions, and cell-substrate adhesion between epithelial cells and ECM. Through finite element simulation, it is found that the closure efficiency is related to the initial gap size and the intensity of lamellipodial protrusion. It is also shown that cells at the wound edge undergo higher stress compared with other cells in the epithelial monolayer, and the cellular normal stress dominates over the cellular shear stress. The model presented in this study can be employed as a numerical tool to unravel the mechanical principles behind the complex wound closure process. These results might have the potential to improve effective wound management and optimize the treatment.

Astragalus Polysaccharides Promote Wound Healing in Diabetic Rats by Upregulating PETN and Inhibiting the mTOR Pathway

Objective. Presently, astragalus polysaccharide (APS) is being investigated for its therapeutic potential in various diseases; however, its underlying mechanism has not yet been clarified. This study was aimed at observing the effects of APS on wound healing in diabetic rats and at exploring its underlying mechanism. Methods. Streptozotocin was injected into the tail vein of SD rats to induce diabetic animal models, in which an incision on the back was made. Rats were treated with different dosages of APS to observe their wound healing. Additionally, RT-qPCR and Western blot assay were conducted to observe the expression levels of PTEN and mTOR pathway-associated factors. Results. Diabetic rats had a prolonged wound healing process, fewer blood vessels, and increased inflammatory response, in which decreased PTEN and elevated mTOR phosphorylation were also identified. APS effectively improved wound healing in a dose-dependent manner by inhibiting the release of inflammatory mediators and attenuating endothelial injuries. Suppression of PTEN could effectively increase the phosphorylation of mTOR and diminish the therapeutic functions of APS on wound healing in diabetic rats. Conclusion. This study highlighted that APS could promote wound healing in diabetic rats by upregulating PTEN and suppressing the mTOR pathway activation.

PTEN: An Emerging Potential Target for Therapeutic Intervention in Respiratory Diseases

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a potent tumor suppressor that regulates several key cellular processes, including proliferation, survival, genomic integrity, migration, and invasion, via PI3K-dependent and independent mechanisms. A subtle decrease in PTEN levels or catalytic activity is implicated not only in cancer but also in a wide spectrum of other diseases, including various respiratory diseases. A systemic overview of the advances in the molecular and cellular mechanisms of PTEN involved in the initiation and progression of respiratory diseases may offer novel targets for the development of effective therapeutics for the treatment of respiratory diseases. In the present review, we highlight the novel findings emerging from current research on the role of PTEN expression and regulation in airway pathological conditions such as asthma/allergic airway inflammation, pulmonary hypertension (PAH), chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and other acute lung injuries (ALI). Moreover, we discuss the clinical implications of PTEN alteration and recently suggested therapeutic possibilities for restoration of PTEN expression and function in respiratory diseases.

Cytokeratin profile and keratinocyte gene expression in keratinized lid margins of patients with chronic Stevens-Johnson syndrome

PURPOSE

To study the cytokeratin profile and keratinization-related gene expression in keratinized lid margins of chronic Stevens-Johnson syndrome (SJS) patients.

METHODS

Posterior eyelid margins from 24 chronic SJS patients undergoing mucous membrane grafting and six healthy margins (orbital exenteration, fresh body donors) were studied using immunofluorescence staining (CK10, CK1, filaggrin, transglutaminase 1 (TGM1), (CK19, MUC5AC)) and quantitative PCR (keratinization-related genes-HBEGF, KGF, EGF, TGFα, TGFβ, and TNFα). The staining and gene expression were studied separately in the lid margin epidermis (LME) and lid margin conjunctiva (LMC).

RESULTS

The expression of CK 1/10, filaggrin, and TGM1 in the LMC was similar to the LME in SJS patients. CK19 was expressed only in the basal epithelial layer of the LMC with loss of MUC5AC expression. Increased expression of KGF (p ≤ 0.056), TNFα (p ≤ 0.02), and TGFα (p ≤ 0.01) was observed in the LME of SJS patients compared to normal LME. LMC of SJS patients showed an increased expression of HBEGF (p ≤ 0.002), EGF (p ≤ 0.0002), KGF (p ≤ 0.02), TNFα (p ≤ 0.04), TGFα (p ≤ 0.003), and TGFβ (p ≤ 0.001) compared to normal LMC. Significant differences were observed in the expression of these genes between LME and LMC of SJS patients. These genes were validated using String analysis, which revealed the positive regulation of keratinization.

CONCLUSION

In lid margins of SJS, there is an increased expression of keratinization-related genes compared to the normal lid margin. Keratinized LMC shares similar cytokeratin profile and keratinization gene expression as seen in cutaneous epithelium of SJS patients, indicating the possibility of the cutaneous epithelium as a source for keratinized LMC.

Epithelial plasticity in COPD results in cellular unjamming due to an increase in polymerized actin

The airway epithelium is subjected to insults such as cigarette smoke (CS), a primary cause of chronic obstructive pulmonary disease (COPD) and serves as an excellent model to study cell plasticity. Here, we show that both CS-exposed and COPD-patient derived epithelia (CHBE) display quantitative evidence of cellular plasticity, with loss of specialized apical features and a transcriptional profile suggestive of partial epithelial-to-mesenchymal transition (pEMT), albeit with distinct cell motion indicative of cellular unjamming. These injured/diseased cells have an increased fraction of polymerized actin, due to loss of the actin-severing protein cofilin-1. We observed that decreasing polymerized actin restores the jammed state in both CHBE and CS-exposed epithelia, indicating that the fraction of polymerized actin is critical in unjamming the epithelia. Our kinetic energy spectral analysis suggests that loss of cofilin-1 results in unjamming, similar to that seen with both CS exposure and in CHBE cells. The findings suggest that in response to chronic injury, although epithelial cells display evidence of pEMT, their movement is more consistent with cellular unjamming. Inhibitors of actin polymerization rectify the unjamming features of the monolayer. This article has an associated First Person interview with the first author of the paper.

Using systems biology approaches to identify signalling pathways activated during chronic wound initiation

Chronic wounds are a significant health problem worldwide. However, nothing is known about how chronic wounds initiate and develop. Here we use a chronic wound model in diabetic mice and a Systems Biology Approach using nanoString nCounter technology and weighted gene correlation network analysis (WGCNA), with tissues collected at 6, 12, 24 and 48 h post-wounding, to identify metabolic signalling pathways involved in initiation of chronicity. Normalized counts obtained from the nanoString nCounter Mouse Metabolic Panel were used for the WGCNA, which groups genes into co-expression modules to visualize the correlation network. Genes with significant module membership and gene trait significance (p < 0.05) were used to identify signalling pathways that are important for the development of chronicity. The pathway analysis using the Reactome database showed stabilization of PTEN, which down-regulates PI3K/AKT1, which in turn down-regulates Nrf2, as shown by ELISA, thus disabling antioxidant production, resulting in high oxidative stress levels. We find that pathways involved in inflammation, including those that generate pro-inflammatory lipids derived from arachidonic acid metabolism, IFNγ and catecholamines, occur. Moreover, HIF3α is over-expressed, potentially blocking Hif1α and preventing activation of growth factors and cytokines that promote granulation tissue formation. We also find that FGF1 is under-expressed, while thrombospondin-1 is over-expressed, resulting in decreased angiogenesis, a process that is critical for healing. Finally, enzymes involved in glycolysis are down-regulated, resulting in decreased production of pyruvate, a molecule critical for ATP production, leading to extensive cell death and wound paralysis. These findings offer new avenues of study that may lead to the development of novel treatments of CW to be administered right after debridement.

Co-inhibition of CD73 and ADORA2B Improves Long-Term Cigarette Smoke Induced Lung Injury

Adenosine (ADO) involvement in lung injury depends on the activation of its receptors. The ADO A_2A receptor (ADORA2A) and A_2B receptor (ADORA2B) are best described to have both tissue-protective and tissue-destructive processes. However, no approach has been effective in delineating the mechanism(s) involved with ADO shifting from its tissue-protective to tissue-destructive properties in chronic airway injury. Using cigarette smoke (CS) as our model of injury, we chronically exposed Nuli-1 cells to 5% CS extract (CSE) for 3 years establishing a long-term CSE exposure model (LTC). We found significant morphological changes, decreased proliferation, and migration resulting in impaired airway wound closure in LTC. Further investigations showed that long-term CSE exposure upregulates CD73 and ADORA2B expression, increases ADO production, inhibits PKC alpha activity and p-ERK signaling pathway. Knocking down ADORA2B and/or CD73 in LTC activates PKC alpha and increases p-ERK signaling. Knocking down both showed better improvement in wound repair than either alone. In vivo experiments also showed that double knockout CD73 and ADORA2B remarkably improved CS-induced lung injury by activating PKC alpha, reducing the inflammatory cell number in bronchoalveolar lavage fluid and the production of inflammatory mediator IL-6, inhibiting the fibrosis-like lesions and decreasing collagen deposition surrounding bronchioles. Collectively, long-term CSE exposure upregulates CD73 expression and increases ADO production, which promotes low affinity ADORA2B activation and subsequent diminution of PKC alpha activity and ERK signaling pathway, and inhibition of airway wound repair. Moreover, the data suggesting ADORA2B and CD73 as potential therapeutic targets may be more efficacious in improving chronic CS lung diseases and impaired wound repair.

PTEN inhibitor improves vascular remodeling and cardiac function after myocardial infarction through PI3k/Akt/VEGF signaling pathway

Background

Myocardial infarction (MI) is the leading cause of death from cardiovascular disease (CVD). Currently, the efficacy for MI treatment remains unsatisfactory. Therefore, it is urgent to develop a novel therapeutic strategy.

Methods

Left anterior descending arteries (LAD) of mice were ligated to induce MI. Another set of mice were intravenously injected with PTEN inhibitor BPV (1 mg/kg) 1 h after LAD ligation and continued to receive BPV injection daily for the following 6 days. Mice were performed echocardiography 14 days after surgery.

Results

Mice in MI group displayed an increased expression of PTEN with impaired cardiac function, enhanced cardiomyocyte apoptosis and decreased angiogenesis. BPV treatment significantly improved cardiac function, with reduced cardiomyocyte apoptosis, promoted angiogenesis, and activated PI3K/Akt/vascular endothelial growth factor (VEGF) signaling pathway.

Conclusion

PTEN inhibitor BPV could effectively prevent myocardial infarction in mice, highlighting its potential as a candidate therapeutic drug.

Pharmacological PTEN inhibition: potential clinical applications and effects in tissue regeneration

Although the human body can heal, it takes time, and slow healing and chronic wounds often occur. Thus, identifying novel therapies to aid regeneration is needed. Here, we conducted a systematic review following the Preferred Reporting Items for Systematic Reviews guidelines and assessed preclinical studies on phosphatase and tensin homolog (PTEN) inhibitors and their effects on tissue repair and regeneration. In conditions associated with neurodegeneration, tissue injury and ischemia, the PTEN-regulated PI3K/AKT signaling pathway is activated. The use of PTEN inhibitors resulted in better tissue response by reducing the healing time and lesion sizes or inducing neuronal regeneration. Notably, all studies included in this systematic review indicated that pharmacological inhibition of PTEN enhanced the repair process of the eye, lung, muscle and nervous system.

PTEN Inhibition Facilitates Diabetic Corneal Epithelial Regeneration by Reactivating Akt Signaling Pathway

Purpose

To investigate the contribution of phosphatase and tensin homologue (PTEN) on the delayed epithelial regeneration and impaired Akt activation in diabetic mice.

Methods

The expression of PTEN on cornea was compared between normal and diabetic mice. The corneal epithelial and nerve regeneration rate was evaluated in diabetic mice after the treatment with PTEN small interfering RNA (siRNA), PTEN inhibitors, or Akt inhibitor. The reactivation of epithelial regeneration-related signaling, including phosphorylated (p)-Akt, p-Stat3, Sirt1, and Parkin, were assessed with Western blot and immunofluorescence staining. The effects of PTEN inhibition on cellular proliferation and migration were further evaluated in cultured mouse corneal epithelial cells.

Results

PTEN messenger RNA and protein levels exhibited up-regulation in diabetic cornea. Upon central epithelial debridement, the epithelial regeneration rate was significantly promoted in diabetic mice with the treatment of PTEN inhibition than that of vehicle control (P < 0.05), which accompanied with the recovered levels of p-Akt, p-Stat3, Sirt1, and Parkin. However, the promotion of diabetic corneal epithelial regeneration rate and Akt reactivation was completed reversed by Akt inhibitor. In vitro, PTEN inhibition promoted their migration, but not the proliferation capacity. In addition, PTEN inhibitor treatment also improved the recovery of corneal nerve fiber density and sensitivity that was impaired in diabetic mice.

Conclusions

Elevated PTEN expression contributes to the impaired corneal epithelial regeneration and Akt activation in diabetic mice, which can be improved with PTEN inhibition.

Translational Relevance

Our study suggests that PTEN inhibition may serve as a new strategy for restoring the impaired corneal epithelial regeneration ability in patients with diabetes.

miR-20a-5p regulates pulmonary surfactant gene expression in alveolar type II cells

MicroRNA (miRNA) critically controls gene expression in many biological processes, including lung growth and pulmonary surfactant biosynthesis. The present study was conducted to investigate whether miR‐20a‐5p had such regulatory functions on alveolar type II (AT‐II) cells. To accomplish this, miR‐20a‐5p–overexpressed and miR‐20a‐5p–inhibited adenoviral vectors were constructed and transfected into cultured AT‐II cells that were isolated from rat foetal lungs of 19 days' gestation. Transfection efficiency was confirmed by observing the fluorescence of green fluorescent protein (GFP) carried by the viral vector, whereas miR‐20a‐5p levels were verified by real‐time PCR. The CCK‐8 assay was used to compare the proliferation ability of AT‐II cells that had over‐ or underexpressed miR‐20a‐5p. The expression of surfactant‐associated proteins (SPs) and phosphatase and tensin homolog (PTEN) was measured by real‐time PCR and Western blotting. In AT‐II cells, transfection resulted in over‐ or under‐regulation of miR‐20a‐5p. While overexpression of miR‐20a‐5p promoted pulmonary surfactant gene expression, its underexpression inhibited it. Consistent with its role in negatively regulating the pulmonary surfactant gene, an opposite pattern was observed for miR‐20a‐5p regulation of PTEN. As a result, when miR‐20a‐5p was rendered overexpressed, PTEN was down‐regulated. By contrast, when miR‐20a‐5p was underexpressed, PTEN was up‐regulated. Neither overexpression nor underexpression of miR‐20a‐5p altered the cell proliferation. miR‐20a‐5p plays no role in proliferation of foetal AT‐II cells but is a critical regulator of surfactant gene expression. The latter appears to be achieved through a regulatory process that implicates expression of PTEN.

Effects of Periploca forrestii Schltr on wound healing by Src meditated Mek/Erk and PI3K/Akt signals

ETHNOPHARMACOLOGICAL RELEVANCE

Periploca forrestii Schltr. (PF) is a traditional folk medicine in China that has been used widely for treating rheumatoid arthritis and traumatic injuries for a long history. Previously, we have roughly demonstrated that the ethanol extract of PF possessed in vitro wound healing potential, and more in depth research deserves to be conducted.

AIM OF THE STUDY

The present study is aiming to fully evaluate the wound healing activity of PF in vitro and in vivo, clarify the mechanism of actions and the primary constituents responsible for wound healing.

MATERIALS AND METHODS

The total extract of Periploca forrestii Schltr. (EPF) and its fraction (65% ethanol fraction, EPFE65) were obtained and evaluated on in vitro wound healing properties using mouse dermal fibroblasts (L929). Cell proliferation was tested by MTT and EdU assay, confirmed by cell cycle analysis, cell migration was evaluated by scratch and transwell assay and collagen production was also determined. Then EPFE65 was tested on in vivo wound healing activity using the excision rat models. The wounded skin of rats was topically applied with 0.1% EPFE65 once daily for 6 days with hydrogel as the carrier and the recombinant bovine basic fibroblast growth factor hydrogel (rbFGF) as positive control. Histopathology of the wounded skin on day 6 and day 12 was studied via hematoxylin and eosin (HE) staining. The expression of phosphorylation of Src, Akt and Erk1/2 was determined after the treatment with EPFE65 by western blot. In order to figure out whether the activation of Src, Akt and Erk1/2 was directly in conjunction with wound healing process promoted by EPFE65, cell proliferation and migration were tested in the presence of three inhibitors of Src, Akt and Erk1/2. Finally, the chemical composition of the effective fraction EPFE65 was analyzed by HPLC-Q-TOF-MS/MS.

RESULTS

In vitro experiments suggested that EPFE65 was comparable to EPF that had potent effect on promoting L929 fibroblasts proliferation, migration and increasing collagen production. 0.1% EPFE65 hydrogel also exhibited significant effect on promoting wound healing in rats. The wound closure was significantly faster in EPFE65 and positive rbFGF group than that in negative control group since the third day post wounding (p < 0.05). Specifically, on day10-12, the wounds in EPFE65 and rbFGF group were almost healed as the wound areas diminished into 13.3-5.3% and 7.7-4.0%, while the wound in control group was still apparent with 36.8-22.1% wound area. HE staining demonstrated that EPFE65 and rbFGF group could advance re-epithelialization in the early days and promote the transition of granulation tissue into complete dermis tissue with more skin appendages resembling those of normal skin in the last days. Western blot results suggested that the active fraction EPFE65 could increase the phosphorylation of Src, Akt and Erk1/2 in both dose-dependent and time-dependent manner, whereas Akt and Erk1/2 phosphorylation caused by EPFE65 could be abolished by Src inhibition. Inhibition experiments confirmed that the activation of Src, Akt and Erk1/2 were involved in cell proliferation and migration. All of these demonstrated that EPFE65 promoted wound healing at least in part via Src mediated Mek/Erk and PI3K/Akt signaling pathways. Analysis of chemical composition of EPFE65 revealed that cardiac glycosides were major components in EPFE65, among which periplocin showed effectiveness on promoting fibroblasts proliferation indicating that cardiac glycosides in EPFE65 maybe the active compounds responsible for wound healing.

CONCLUSION

The present study confirmed that EPFE65, ethanol extract of Periploca forrestii Schltr. could accelerate wound healing in vitro and in vivo through Src meditated Mek/Erk and PI3K/Akt signaling pathways.

Identification and functional analysis of inflammation-related miRNAs in skin wound repair

Inflammation at a wound site is essential for preventing infection. However, misregulated inflammation leads to pathologies of the healing process, including chronic non-healing wounds and scarring. MicroRNAs (miRNAs) are key regulators of the inflammatory response and tissue repair, acting by translational processing of target mRNAs. In the final step of miRNA processing, Argonaute 2 (Ago2)-bound mature miRNA complexes bind to target mRNAs and inhibit their translation. A variety of wound healing-related miRNAs have been identified and their misregulation likely contributes to wound pathologies, including scarring and chronic healing. Recently, we have developed an Ago2-bound mature miRNA purification system that uses Ago2 antibody to analyze the expression of miRNAs from wound tissues by microarray and next generation sequencing. We have identified several wound inflammation-related miRNAs via Ago2-target immunoprecipitation assays and next generation sequencing of wound tissues from wild-type and PU.1 knockout mice, which exhibit no inflammatory response because of a lack of immune cell lineages. We demonstrated that miR-142, an identified inflammation-related miRNA, is essential role for neutrophilic chemotaxis via inhibition of small GTPase translation; its misregulation leads to susceptibility to infection against Staphylococcus aureus at skin wound sites. In this review, we summarize recent advances of miRNA studies in skin wound healing, introduce our miRNA purification system using an immunoprecipitation assay method, and discuss the function of miR-142 in skin wound healing.

PTEN Inhibition in Human Disease Therapy

The tumor suppressor PTEN is a major homeostatic regulator, by virtue of its lipid phosphatase activity against phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3], which downregulates the PI3K/AKT/mTOR prosurvival signaling, as well as by its protein phosphatase activity towards specific protein targets. PTEN catalytic activity is crucial to control cell growth under physiologic and pathologic situations, and it impacts not only in preventing tumor cell survival and proliferation, but also in restraining several cellular regeneration processes, such as those associated with nerve injury recovery, cardiac ischemia, or wound healing. In these conditions, inhibition of PTEN catalysis is being explored as a potentially beneficial therapeutic intervention. Here, an overview of human diseases and conditions in which PTEN inhibition could be beneficial is presented, together with an update on the current status of specific small molecule inhibitors of PTEN enzymatic activity, their use in experimental models, and their limitations as research or therapeutic drugs.

The Mechanics of Single Cell and Collective Migration of Tumor Cells

Metastasis is a dynamic process in which cancer cells navigate the tumor microenvironment, largely guided by external chemical and mechanical cues. Our current understanding of metastatic cell migration has relied primarily on studies of single cell migration, most of which have been performed using two-dimensional (2D) cell culture techniques and, more recently, using three-dimensional (3D) scaffolds. However, the current paradigm focused on single cell movements is shifting toward the idea that collective migration is likely one of the primary modes of migration during metastasis of many solid tumors. Not surprisingly, the mechanics of collective migration differ significantly from single cell movements. As such, techniques must be developed that enable in-depth analysis of collective migration, and those for examining single cell migration should be adopted and modified to study collective migration to allow for accurate comparison of the two. In this review, we will describe engineering approaches for studying metastatic migration, both single cell and collective, and how these approaches have yielded significant insight into the mechanics governing each process.

Correlative STED and Atomic Force Microscopy on Live Astrocytes Reveals Plasticity of Cytoskeletal Structure and Membrane Physical Properties during Polarized Migration

The plasticity of the cytoskeleton architecture and membrane properties is important for the establishment of cell polarity, adhesion and migration. Here, we present a method which combines stimulated emission depletion (STED) super-resolution imaging and atomic force microscopy (AFM) to correlate cytoskeletal structural information with membrane physical properties in live astrocytes. Using STED compatible dyes for live cell imaging of the cytoskeleton, and simultaneously mapping the cell surface topology with AFM, we obtain unprecedented detail of highly organized networks of actin and microtubules in astrocytes. Combining mechanical data from AFM with optical imaging of actin and tubulin further reveals links between cytoskeleton organization and membrane properties. Using this methodology we illustrate that scratch-induced migration induces cytoskeleton remodeling. The latter is caused by a polarization of actin and microtubule elements within astroglial cell processes, which correlates strongly with changes in cell stiffness. The method opens new avenues for the dynamic probing of the membrane structural and functional plasticity of living brain cells. It is a powerful tool for providing new insights into mechanisms of cell structural remodeling during physiological or pathological processes, such as brain development or tumorigenesis.

Region-specific role for Pten in maintenance of epithelial phenotype and integrity

Previous studies have demonstrated resistance to naphthalene-induced injury in proximal airways of mice with lung epithelial-specific deletion of the tumor-suppressor gene Pten, attributed to increased proliferation of airway progenitors. We tested effects of Pten loss following bleomycin injury, a model typically used to study distal lung epithelial injury, in conditional Pten^SFTPC-cre knockout mice. Pten-deficient airway epithelium exhibited marked hyperplasia, particularly in small bronchioles and at bronchoalveolar duct junctions, with reduced E-cadherin and β-catenin expression between cells toward the luminal aspect of the hyperplastic epithelium. Bronchiolar epithelial and alveolar epithelial type II (AT2) cells in Pten^SFTPC-cre mice showed decreased expression of epithelial markers and increased expression of mesenchymal markers, suggesting at least partial epithelial-mesenchymal transition at baseline. Surprisingly, and in contrast to previous studies, mutant mice were exquisitely sensitive to bleomycin, manifesting rapid weight loss, respiratory distress, increased early mortality (by day 5), and reduced dynamic lung compliance. This was accompanied by sloughing of the hyperplastic airway epithelium with occlusion of small bronchioles by cellular debris, without evidence of increased parenchymal lung injury. Increased airway epithelial cell apoptosis due to loss of antioxidant defenses, reflected by decreased expression of superoxide dismutase 3, in combination with deficient intercellular adhesion, likely predisposed to airway sloughing in knockout mice. These findings demonstrate an important role for Pten in maintenance of airway epithelial phenotype integrity and indicate that responses to Pten deletion in respiratory epithelium following acute lung injury are highly context-dependent and region-specific.

Kymographic Imaging of the Elastic Modulus of Epithelial Cells during the Onset of Migration

Epithelial cell migration during wound repair involves a complex interplay of intracellular processes that enable motility while preserving contact among the cells. Recent evidence suggests that fluctuations of the intracellular biophysical state of cells generate traction forces at the basal side of the cells that are necessary for the cells to migrate. However, less is known about the biophysical and structural changes throughout the cells that accompany these fluctuations. Here, we utilized, to our knowledge, a novel kymographic nanoindentation method to obtain spatiotemporal measurements of the elastic moduli of living cells during migration after wounding. At the onset of migration, the elastic modulus increased near the migration front. In addition, the intensity of fluctuations in the elastic modulus changed at the migration front, and these changes were dependent upon f-actin, one of the major components of the cytoskeleton. These results demonstrate the unique biophysical changes that occur at the onset of migration as cells transition from a stationary to a migratory state.

Simvastatin Treatment Modulates Mechanically-Induced Injury and Inflammation in Respiratory Epithelial Cells

Mechanical forces in the respiratory system, including surface tension forces during airway reopening and high transmural pressures, can result in epithelial cell injury, barrier disruption and inflammation. In this study, we investigated if a clinically relevant pharmaceutical agent, Simvastatin, could mitigate mechanically induced injury and inflammation in respiratory epithelia. Pulmonary alveolar epithelial cells (A549) were exposed to either cyclic airway reopening forces or oscillatory transmural pressure in vitro and treated with a wide range of Simvastatin concentrations. Simvastatin induced reversible depolymerization of the actin cytoskeleton and a statistically significant reduction the cell's elastic modulus. However, Simvastatin treatment did not result in an appreciable change in the cell's viscoelastic properties. Simvastatin treated cells did exhibit a reduced height-to-width aspect ratio and these changes in cell morphology resulted in a significant decrease in epithelial cell injury during airway reopening. Interestingly, although very high concentrations (25-50 µM) of Simvastatin resulted in dramatically less IL-6 and IL-8 pro-inflammatory cytokine secretion, 2.5 µM Simvastatin did not reduce the total amount of pro-inflammatory cytokines secreted during mechanical stimulation. These results indicate that although Simvastatin treatment may be useful in reducing cell injury during airway reopening, elevated local concentrations of Simvastatin might be needed to reduce mechanically-induced injury and inflammation in respiratory epithelia.

Substrate stiffness modulates lung cancer cell migration but not epithelial to mesenchymal transition

Biomechanical properties of the tumor microenvironment, including matrix/substrate stiffness, play a significant role in tumor evolution and metastasis. Epithelial to Mesenchymal Transition (EMT) is a fundamental biological process that is associated with increased cancer cell migration and invasion. The goal of this study was to investigate (1) how substrate stiffness modulates the migration behaviors of lung adenocarcinoma cells (A549) and (2) if stiffness-induced changes in cell migration correlate with biochemical markers of EMT. Collagen-coated polydimethylsiloxane (PDMS) substrates and an Ibidi migration assay were used to investigate how substrate stiffness alters the migration patterns of A549 cells. RT-PCR, western blotting and immunofluorescence were used to investigate how substrate stiffness alters biochemical markers of EMT, that is, E-cadherin and N-cadherin, and the phosphorylation of focal adhesion proteins. Increases in substrate stiffness led to slower, more directional migration but did not alter the biochemical markers of EMT. Interestingly, growth factor (i.e., Transforming Growth Factor-β) stimulation resulted in similar levels of EMT regardless of substrate stiffness. We also observed decreased levels of phosphorylated focal adhesion kinase (FAK) and paxillin on stiffer substrates which correlated with slower cell migration. These results indicate that substrate stiffness modulates lung cancer cell migration via focal adhesion signaling as opposed to EMT signaling.

Assessing the impact of engineered nanoparticles on wound healing using a novel in vitro bioassay

AIM

As engineered nanoparticles (ENPs) increasingly enter consumer products, humans become increasingly exposed. The first line of defense against ENPs is the epithelium, the integrity of which can be compromised by wounds induced by trauma, infection, or surgery, but the implications of ENPs on wound healing are poorly understood.

MATERIALS & METHODS

Herein, we developed an in vitro assay to assess the impact of ENPs on the wound healing of cells from human cornea.

RESULTS & DISCUSSION

We show that industrially relevant ENPs impeded wound healing and cellular migration in a manner dependent on the composition, dose and size of the ENPs as well as cell type. CuO and ZnO ENPs impeded both viability and wound healing for both fibroblasts and epithelial cells. Carboxylated polystyrene ENPs retarded wound healing of corneal fibroblasts without affecting viability.

CONCLUSION

Our results highlight the impact of ENPs on cellular wound healing and provide useful tools for studying the physiological impact of ENPs.

Spinal cord regeneration

Three theories of regeneration dominate neuroscience today, all purporting to explain why the adult central nervous system (CNS) cannot regenerate. One theory proposes that Nogo, a molecule expressed by myelin, prevents axonal growth. The second theory emphasizes the role of glial scars. The third theory proposes that chondroitin sulfate proteoglycans (CSPGs) prevent axon growth. Blockade of Nogo, CSPG, and their receptors indeed can stop axon growth in vitro and improve functional recovery in animal spinal cord injury (SCI) models. These therapies also increase sprouting of surviving axons and plasticity. However, many investigators have reported regenerating spinal tracts without eliminating Nogo, glial scar, or CSPG. For example, many motor and sensory axons grow spontaneously in contused spinal cords, crossing gliotic tissue and white matter surrounding the injury site. Sensory axons grow long distances in injured dorsal columns after peripheral nerve lesions. Cell transplants and treatments that increase cAMP and neurotrophins stimulate motor and sensory axons to cross glial scars and to grow long distances in white matter. Genetic studies deleting all members of the Nogo family and even the Nogo receptor do not always improve regeneration in mice. A recent study reported that suppressing the phosphatase and tensin homolog (PTEN) gene promotes prolific corticospinal tract regeneration. These findings cannot be explained by the current theories proposing that Nogo and glial scars prevent regeneration. Spinal axons clearly can and will grow through glial scars and Nogo-expressing tissue under some circumstances. The observation that deleting PTEN allows corticospinal tract regeneration indicates that the PTEN/AKT/mTOR pathway regulates axonal growth. Finally, many other factors stimulate spinal axonal growth, including conditioning lesions, cAMP, glycogen synthetase kinase inhibition, and neurotrophins. To explain these disparate regenerative phenomena, I propose that the spinal cord has evolved regenerative mechanisms that are normally suppressed by multiple extrinsic and intrinsic factors but can be activated by injury, mediated by the PTEN/AKT/mTOR, cAMP, and GSK3b pathways, to stimulate neural growth and proliferation.

microRNA-548l is involved in the migration and invasion of non-small cell lung cancer by targeting the AKT1 signaling pathway

PURPOSE

microRNAs (miRNAs) have been documented playing a critical role in cancer development and progression. In this study, we investigated the role of miR-548l in non-small cell lung cancer (NSCLC) migration and invasion.

METHODS

microRNAs microarray analysis was used to detect the differentially expressed miRNAs between various metastatic levels of NSCLC cells and further confirmed by real-time PCR analysis. To facilitate the delineation of the role of selected miR-548l in NSCLC pathology, we detected its expression in 22 NSCLC tissues. Proliferation, apoptosis, invasion and metastasis effects of the miRNA were evaluated using MTT, flow cytometry, wound healing and invasion assay following transfection with mimics and inhibitors. Luciferase assay and Western blot analysis were performed to assess miR-548l binding to AKT1 gene. AKT1 expression in the clinical tissues was evaluated using immunohistochemical staining.

RESULTS

The results showed a negative relationship between miR-548l expression and lymph node metastasis of NSCLC. Functional assays showed that over-expression of miR-548l suppressed NSCLC cell migration and invasion. Luciferase assays confirmed that miR-548l could directly bind to the 3' untranslated region of AKT1. Further data showed that the over-expression of AKT1 could rescue the effects of miR-548l in NSCLC cells, and the miR-548l expression was inversely correlated with AKT1 expression in NSCLC tissues. These results indicated that AKT1 was involved in miR-548l-induced suppression of NSCLC cell migration and invasion.

CONCLUSION

These results suggested that miR-548l may play a causal role through AKT1 in NSCLC invasion and metastasis.

Chemical intervention tools to probe phosphoinositide-dependent signalling

Chemical intervention tools have been beneficial to many investigations elucidating signalling networks and interactions. The present review summarizes the current status of chemical tools to probe phosphoinositide metabolism and signalling. In particular, phosphoinositide-targeting tools are compared with protein-targeting tools with respect to their unique advantages and possible applications.

Influence of airway wall compliance on epithelial cell injury and adhesion during interfacial flows

Interfacial flows during cyclic airway reopening are an important source of ventilator-induced lung injury. However, it is not known how changes in airway wall compliance influence cell injury during airway reopening. We used an in vitro model of airway reopening in a compliant microchannel to investigate how airway wall stiffness influences epithelial cell injury. Epithelial cells were grown on gel substrates with different rigidities, and cellular responses to substrate stiffness were evaluated in terms of metabolic activity, mechanics, morphology, and adhesion. Repeated microbubble propagations were used to simulate cyclic airway reopening, and cell injury and detachment were quantified via live/dead staining. Although cells cultured on softer gels exhibited a reduced elastic modulus, these cells experienced less plasma membrane rupture/necrosis. Cells on rigid gels exhibited a minor, but statistically significant, increase in the power law exponent and also exhibited a significantly larger height-to-length aspect ratio. Previous studies indicate that this change in morphology amplifies interfacial stresses and, therefore, correlates with the increased necrosis observed during airway reopening. Although cells cultured on stiff substrates exhibited more plasma membrane rupture, these cells experienced significantly less detachment and monolayer disruption during airway reopening. Western blotting and immunofluorescence indicate that this protection from detachment and monolayer disruption correlates with increased focal adhesion kinase and phosphorylated paxillin expression. Therefore, changes in cell morphology and focal adhesion structure may govern injury responses during compliant airway reopening. In addition, these results indicate that changes in airway compliance, as occurs during fibrosis or emphysema, may significantly influence cell injury during mechanical ventilation.

Loss of myoferlin redirects breast cancer cell motility towards collective migration

Cell migration plays a central role in the invasion and metastasis of tumors. As cells leave the primary tumor, they undergo an epithelial to mesenchymal transition (EMT) and migrate as single cells. Epithelial tumor cells may also migrate in a highly directional manner as a collective group in some settings. We previously discovered that myoferlin (MYOF) is overexpressed in breast cancer cells and depletion of MYOF results in a mesenchymal to epithelial transition (MET) and reduced invasion through extracellular matrix (ECM). However, the biomechanical mechanisms governing cell motility during MYOF depletion are poorly understood. We first demonstrated that lentivirus-driven shRNA-induced MYOF loss in MDA-MB-231 breast cancer cells (MDA-231(MYOF-KD)) leads to an epithelial morphology compared to the mesenchymal morphology observed in control (MDA-231(LTVC)) and wild-type cells. Knockdown of MYOF led to significant reductions in cell migration velocity and MDA-231(MYOF-KD) cells migrated directionally and collectively, while MDA-231(LTVC) cells exhibited single cell migration. Decreased migration velocity and collective migration were accompanied by significant changes in cell mechanics. MDA-231(MYOF-KD) cells exhibited a 2-fold decrease in cell stiffness, a 2-fold increase in cell-substrate adhesion and a 1.5-fold decrease in traction force generation. In vivo studies demonstrated that when immunocompromised mice were implanted with MDA-231(MYOF-KD) cells, tumors were smaller and demonstrated lower tumor burden. Moreover, MDA-231(MYOF-KD) tumors were highly circularized and did not invade locally into the adventia in contrast to MDA-231(LTVC)-injected animals. Thus MYOF loss is associated with a change in tumor formation in xenografts and leads to smaller, less invasive tumors. These data indicate that MYOF, a previously unrecognized protein in cancer, is involved in MDA-MB-231 cell migration and contributes to biomechanical alterations. Our results indicate that changes in biomechanical properties following loss of this protein may be an effective way to alter the invasive capacity of cancer cells.

Finite element analysis of traction force microscopy: influence of cell mechanics, adhesion, and morphology

The interactions between adherent cells and their extracellular matrix (ECM) have been shown to play an important role in many biological processes, such as wound healing, morphogenesis, differentiation, and cell migration. Cells attach to the ECM at focal adhesion sites and transmit contractile forces to the substrate via cytoskeletal actin stress fibers. This contraction results in traction stresses within the substrate/ECM. Traction force microscopy (TFM) is an experimental technique used to quantify the contractile forces generated by adherent cells. In TFM, cells are seeded on a flexible substrate and displacements of the substrate caused by cell contraction are tracked and converted to a traction stress field. The magnitude of these traction stresses are normally used as a surrogate measure of internal cell contractile force or contractility. We hypothesize that in addition to contractile force, other biomechanical properties including cell stiffness, adhesion energy density, and cell morphology may affect the traction stresses measured by TFM. In this study, we developed finite element models of the 2D and 3D TFM techniques to investigate how changes in several biomechanical properties alter the traction stresses measured by TFM. We independently varied cell stiffness, cell-ECM adhesion energy density, cell aspect ratio, and contractility and performed a sensitivity analysis to determine which parameters significantly contribute to the measured maximum traction stress and net contractile moment. Results suggest that changes in cell stiffness and adhesion energy density can significantly alter measured tractions, independent of contractility. Based on a sensitivity analysis, we developed a correction factor to account for changes in cell stiffness and adhesion and successfully applied this correction factor algorithm to experimental TFM measurements in invasive and noninvasive cancer cells. Therefore, application of these types of corrections to TFM measurements can yield more accurate estimates of cell contractility.

Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction

In this review we summarize recent major advances in our understanding on the molecular mechanisms, mediators, and biomarkers of acute lung injury (ALI) and alveolar-capillary barrier dysfunction, highlighting the role of immune cells, inflammatory and noninflammatory signaling events, mechanical noxae, and the affected cellular and molecular entities and functions. Furthermore, we address novel aspects of resolution and repair of ALI, as well as putative candidates for treatment of ALI, including pharmacological and cellular therapeutic means.

Loss of phosphatase and tensin homolog (PTEN) induces leptin-mediated leptin gene expression: feed-forward loop operating in the lung

Elevated levels of systemic and pulmonary leptin are associated with diseases related to lung injury and lung cancer. However, the role of leptin in lung biology and pathology, including the mechanism of leptin gene expression in the pathogenesis of lung diseases, including lung cancer, remains elusive. Here, using conditional deletion of tumor suppressor gene Pten in the lung epithelium in vivo in transgenic mice and human PTEN-null lung epithelial cells, we identify the leptin-driven feed-forward signaling loop in the lung epithelial cells. Leptin-mediated leptin/leptin-receptor gene expression likely amplifies leptin signaling that may contribute to the pathogenesis and severity of lung diseases, resulting in poor clinical outcomes. Loss of Pten in the lung epithelial cells in vivo activated adipokine signaling and induced leptin synthesis as ascertained by genome-wide mRNA profiling and pathway analysis. Leptin gene transcription was mediated by binding of transcription factors NRF-1 and CCAAT/enhancer-binding protein δ (C/EBP) to the proximal promoter regions and STAT3 to the distal promoter regions as revealed by leptin promoter-mutation, chromatin immunoprecipitation, and gain- and loss-of-function studies in lung epithelial cells. Leptin treatment induced expression of the leptin/leptin receptor in the lung epithelial cells via activation of MEK/ERK, PI3K/AKT/mammalian target of rapamycin (mTOR), and JAK2/STAT3 signaling pathways. Expression of constitutively active MEK-1, AKT, and STAT3 proteins increased expression, and treatment with MEK, PI3K, AKT, and mTOR inhibitors decreased LEP expression, indicating that leptin via MAPK/ERK1/2, PI3K/AKT/mTOR, and JAK2/STAT3 pathways, in turn, further induces its own gene expression. Thus, targeted inhibition of the leptin-mediated feed-forward loop provides a novel rationale for pharmacotherapy of disease associated with lung injury and remodeling, including lung cancer.

MicroRNA-99 family targets AKT/mTOR signaling pathway in dermal wound healing

Recent studies suggest that microRNAs play important roles in dermal wound healing and microRNA deregulation has been linked with impaired wound repair. Here, using a mouse experimental wound healing model, we identified a panel of 63 differentially expressed microRNAs during dermal wound healing, including members of miR-99 family (miR-99a, miR-99b, miR-100). We further demonstrated that miR-99 family members regulate cell proliferation, cell migration, and AKT/mTOR signaling. Combined experimental and bioinformatics analyses revealed that miR-99 family members regulate AKT/mTOR signaling by targeting multiple genes, including known target genes (e.g., IGF1R, mTOR) and a new target (AKT1). The effects of miR-99 family members on the expression of IGF1R, mTOR and AKT1 were validated at both the mRNA and protein levels. Two adjacent miR-99 family targeting sites were identified in the 3′-UTR of the AKT1 mRNA. The direct interaction of miR-100 with these targeting sites was confirmed using luciferase reporter assays. The microRNA-100-directed recruitment of AKT1 mRNA to the RNAi-induced silencing complex (RISC) was confirmed by a ribonucleoprotein-IP assay. In summary, we identified a panel of differentially expressed microRNAs which may play important roles in wound healing. We provide evidence that miR-99 family members contribute to wound healing by regulating the AKT/mTOR signaling.

Phospho-tyrosine phosphatase inhibitor Bpv(Hopic) enhances C2C12 myoblast migration in vitro. Requirement of PI3K/AKT and MAPK/ERK pathways

Muscle progenitor cell migration is an important step in skeletal muscle myogenesis and regeneration. Migration is required for muscle precursors to reach the site of damage and for the alignment of myoblasts prior to their fusion, which ultimately contributes to muscle regeneration. Limited spreading and migration of donor myoblasts are reported problems of myoblast transfer therapy, a proposed therapeutic strategy for Duchenne Muscular Dystrophy, warranting further investigation into different approaches for improving the motility and homing of these cells. In this article, the effect of protein phospho-tyrosine phosphatase and PTEN inhibitor BpV(Hopic) on C2C12 myoblast migration and differentiation was investigated. Applying a wound healing migration model, it is reported that 1 μM BpV(Hopic) is capable of enhancing the migration of C2C12 myoblasts by approximately 40 % in the presence of myotube conditioned media, without significantly affecting their capacity to differentiate and fuse into multinucleated myotubes. Improved migration of myoblasts treated with 1 μM BpV(Hopic) was associated with activation of PI3K/AKT and MAPK/ERK pathways, while their inhibition with either LY294002 or UO126, respectively, resulted in a reduction of C2C12 migration back to control levels. These results propose that bisperoxovanadium compounds may be considered as potential tools for enhancing the migration of myoblasts, while not reducing their differentiation capacity and underpin the importance of PI3K/AKT and MAPK/ERK signalling for the process of myogenic progenitor migration.

Calcitonin gene-related peptide promotes the wound healing of human bronchial epithelial cells via PKC and MAPK pathways

Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide derived from the calcitonin gene. CGRP is widely distributed in the central and peripheral neuronal systems. In the lung, CGRP could modulate dendritic cell function, stimulate proliferation of alveolar epithelial cells and mediate lung injury in mice. In this study, we investigated the effect of CGRP on the wound healing of human bronchial epithelial cells (HBECs) in vitro. The results showed that CGRP accelerated the recovery of wound area of monolayer HBECs in a dose-dependent manner. CGRP inhibited the lipopolysaccharide-induced apoptosis in HBECs. The percentage of S phase and G2/M phase was increased in HBECs after CGRP treatment. CGRP upregulated the expression of Ki67 in a dose-dependent manner. Some pathway inhibitors were used to investigate the signal pathway in which CGRP was involved. We found out that PKC pathway inhibitor (H-7) and MAPK pathway inhibitor (PD98059) could partially attenuate the effect of CGRP, which indicated that CGRP might promote the wound healing of HBECs via PKC and/or MAPK dependent pathway by accelerating migration and proliferation, and inhibiting apoptosis.

Epithelial Pten controls acute lung injury and fibrosis by regulating alveolar epithelial cell integrity

RATIONALE

Injury to alveolar epithelial cells (AECs) and to their repair process is integral to the pathogenesis of acute lung injury (ALI) and idiopathic pulmonary fibrosis (IPF). The mechanisms regulating the integrity of AECs and their intrinsic regulators remain unclear. Pten is a tumor suppressor, and its function in epithelial cells during organ fibrosis is unknown.

OBJECTIVES

To determine the role of epithelial Pten in ALI and lung fibrosis.

METHODS

Bronchioalveolar epithelium-specific Pten-deleted SP-C-rtTA/(tetO)(7)-Cre/Pten(Δ/Δ) (SOPten(Δ/Δ)) mice were studied by structural, biochemical, and physiologic analyses and compared with wild-type mice. Further mechanistic studies were performed in vivo, in vitro, and on samples from patients with IPF.

MEASUREMENTS AND MAIN RESULTS

SOPten(Δ/Δ) mice demonstrated exacerbated alveolar flooding and subsequent augmented lung scarring with enhanced disassembly of tight junctions (TJs) of AECs and degradation of basement membranes. The induction of dominant negative PTEN gene in lung epithelial cells led to augmented transforming growth factor-1-induced disruptions of TJs. Epithelial-derived myofibroblasts were increased in the epithelium-specific Pten-deficient mice. The lungs of bleomycin-treated SOPten(Δ/Δ) mice showed increased pAkt, pS6K, Snail, and matrix metalloproteinase expressions and decreased claudin-4, E-cadherin, and laminin-β1 expressions. Akt inactivation definitively saved SOPten(Δ/Δ) mice through amelioration of ALI and retention of AEC integrity. We detected a reduction of PTEN expression and AKT hyperactivation in the AECs of human IPF lungs.

CONCLUSIONS

Our results highlight epithelial Pten as a crucial gatekeeper controlling ALI and lung fibrosis by modulating AEC integrity, and the Pten/PI3K/Akt pathway as a potential therapeutic target in these intractable diseases.