Ubiquitination and proteolysis in acute lung injury

The Emerging Roles of Tripartite Motif Proteins (TRIMs) in Acute Lung Injury

Acute lung injury (ALI) is an inflammatory disorder of the lung that causes high mortality and lacks any pharmacological intervention. Ubiquitination plays a critical role in the pathogenesis of ALI as it regulates the alveolocapillary barrier and the inflammatory response. Tripartite motif (TRIM) proteins are one of the subfamilies of the RING-type E3 ubiquitin ligases, which contains more than 80 distinct members in humans involved in a broad range of biological processes including antivirus innate immunity, development, and tumorigenesis. Recently, some studies have shown that several members of TRIM family proteins play important regulatory roles in inflammation and ALI. Herein, we integrate emerging evidence regarding the roles of TRIMs in ALI. Articles were selected from the searches of PubMed database that had the terms "acute lung injury," "ubiquitin ligases," "tripartite motif protein," "inflammation," and "ubiquitination" using both MeSH terms and keywords. Better understanding of these mechanisms may ultimately lead to novel therapeutic approaches by targeting TRIMs for ALI treatment.

TRIM proteins in lung cancer: Mechanisms, biomarkers and therapeutic targets

The tripartite motif (TRIM) family is defined by the presence of a Really Interesting New Gene (RING) domain, one or two B-box motifs and a coiled-coil region. TRIM proteins play key roles in many biological processes, including innate immunity, tumorigenesis, cell differentiation and ontogenetic development. Alterations in TRIM gene and protein levels frequently emerge in a wide range of tumors and affect tumor progression. As canonical E3 ubiquitin ligases, TRIM proteins participate in ubiquitin-dependent proteolysis of prominent components of the p53, NF-κB and PI3K/AKT signaling pathways. The occurrence of ubiquitylation events induced by TRIM proteins sustains internal balance between tumor suppressive and tumor promoting genes. In this review, we summarized the diverse mechanism of TRIM proteins responsible for the most common malignancy, lung cancer. Furthermore, we also discussed recent progress in both the diagnosis and therapeutics of tumors contributed by TRIM proteins.

The Role of Deubiquitinating Enzymes in Acute Lung Injury and Acute Respiratory Distress Syndrome

Acute lung injury and acute respiratory distress syndrome (ALI/ARDS) are characterized by an inflammatory response, alveolar edema, and hypoxemia. ARDS occurs most often in the settings of pneumonia, sepsis, aspiration of gastric contents, or severe trauma. The prevalence of ARDS is approximately 10% in patients of intensive care. There is no effective remedy with mortality high at 30-40%. Most functional proteins are dynamic and stringently governed by ubiquitin proteasomal degradation. Protein ubiquitination is reversible, the covalently attached monoubiquitin or polyubiquitin moieties within the targeted protein can be removed by a group of enzymes called deubiquitinating enzymes (DUBs). Deubiquitination plays an important role in the pathobiology of ALI/ARDS as it regulates proteins critical in engagement of the alveolo-capillary barrier and in the inflammatory response. In this review, we provide an overview of how DUBs emerge in pathogen-induced pulmonary inflammation and related aspects in ALI/ARDS. Better understanding of deubiquitination-relatedsignaling may lead to novel therapeutic approaches by targeting specific elements of the deubiquitination pathways.

Helicobacter pylori infection impairs chaperone-assisted maturation of Na-K-ATPase in gastric epithelium

Helicobacter pylori infection always induces gastritis, which may progress to ulcer disease or cancer. The mechanisms underlying mucosal injury by the bacteria are incompletely understood. Here, we identify a novel pathway for H. pylori-induced gastric injury, the impairment of maturation of the essential transport enzyme and cell adhesion molecule, Na-K-ATPase. Na-K-ATPase comprises α- and β-subunits that assemble in the endoplasmic reticulum (ER) before trafficking to the plasma membrane. Attachment of H. pylori to gastric epithelial cells increased Na-K-ATPase ubiquitylation, decreased its surface and total levels, and impaired ion balance. H. pylori did not alter degradation of plasmalemma-resident Na-K-ATPase subunits or their mRNA levels. Infection decreased association of α- and β-subunits with ER chaperone BiP and impaired assembly of α/β-heterodimers, as was revealed by quantitative mass spectrometry and immunoblotting of immunoprecipitated complexes. The total level of BiP was not altered, and the decrease in interaction with BiP was not observed for other BiP client proteins. The H. pylori-induced decrease in Na-K-ATPase was prevented by BiP overexpression, stopping protein synthesis, or inhibiting proteasomal, but not lysosomal, protein degradation. The results indicate that H. pylori impairs chaperone-assisted maturation of newly made Na-K-ATPase subunits in the ER independently of a generalized ER stress and induces their ubiquitylation and proteasomal degradation. The decrease in Na-K-ATPase levels is also seen in vivo in the stomachs of gerbils and chronically infected children. Further understanding of H. pylori-induced Na-K-ATPase degradation will provide insights for protection against advanced disease.NEW & NOTEWORTHY This work provides evidence that Helicobacter pylori decreases levels of Na-K-ATPase, a vital transport enzyme, in gastric epithelia, both in acutely infected cultured cells and in chronically infected patients and animals. The bacteria interfere with BiP-assisted folding of newly-made Na-K-ATPase subunits in the endoplasmic reticulum, accelerating their ubiquitylation and proteasomal degradation and decreasing efficiency of the assembly of native enzyme. Decreased Na-K-ATPase expression contributes to H. pylori-induced gastric injury.

Toll-like Receptor 8 Stability Is Regulated by Ring Finger 216 in Response to Circulating MicroRNAs

TLR8 (Toll-like receptor 8) is an intracellular pattern recognition receptor that senses RNA in endosomes to initiate innate immune signaling through NF-κB, and mechanisms regulating TLR8 protein abundance are not completely understood. Protein degradation is a cellular process controlling protein concentrations, accomplished largely through ubiquitin transfer directed by E3 ligase proteins to substrates. In the present study, we show that TLR8 has a short half-life in THP-1 monocytes (∼1 h) and that TLR8 is ubiquitinated and degraded in the proteasome. Treatment with the TLR8 agonist R848 causes rapid depletion of TLR8 concentrations at early time points, an effect blocked by proteasomal inhibition. We show a novel role for RNF216 (ring finger protein 216), an E3 ligase that targets TLR8 for ubiquitination and degradation. RNF216 overexpression reduces TLR8 concentrations, whereas RNF216 knockdown stabilizes TLR8. We describe a potential role for TLR8 activation by circulating RNA ligands in humans with acute respiratory distress syndrome (ARDS): Plasma and extracted RNA fractions from subjects with ARDS activated TLR8 in vitro. MicroRNA (miRNA) expression profiling revealed several circulating miRNAs from subjects with ARDS. miRNA mimics promoted TLR8 proteasomal degradation in THP-1 cells. These data show that TLR8 proteasomal disposal through RNF216 in response to RNA ligands regulates TLR8 cellular concentrations and may have implications for innate immune signaling. In addition, TLR8 activation by circulating RNA ligands may be a previously underrecognized stimulus contributing to excessive innate immune signaling characteristic of ARDS.

IL-13 Impairs Tight Junctions in Airway Epithelia

Interleukin-13 (IL-13) drives symptoms in asthma with high levels of T-helper type 2 cells (T_h2-cells). Since tight junctions (TJ) constitute the epithelial diffusion barrier, we investigated the effect of IL-13 on TJ in human tracheal epithelial cells. We observed that IL-13 increases paracellular permeability, changes claudin expression pattern and induces intracellular aggregation of the TJ proteins zonlua occludens protein 1, as well as claudins. Furthermore, IL-13 treatment increases expression of ubiquitin conjugating E2 enzyme UBE2Z. Co-localization and proximity ligation assays further showed that ubiquitin and the proteasomal marker PSMA5 co-localize with TJ proteins in IL-13 treated cells, showing that TJ proteins are ubiquitinated following IL-13 exposure. UBE2Z upregulation occurs within the first day after IL-13 exposure. Proteasomal aggregation of ubiquitinated TJ proteins starts three days after IL-13 exposure and transepithelial electrical resistance (TEER) decrease follows the time course of TJ-protein aggregation. Inhibition of JAK/STAT signaling abolishes IL-13 induced effects. Our data suggest that that IL-13 induces ubiquitination and proteasomal aggregation of TJ proteins via JAK/STAT dependent expression of UBE2Z, resulting in opening of TJs. This may contribute to barrier disturbances in pulmonary epithelia and lung damage of patients with inflammatory lung diseases.

Quantitative Analysis of Ubiquitinated Proteins in Human Pituitary and Pituitary Adenoma Tissues

Protein ubiquitination is an important post-translational modification that is associated with multiple diseases, including pituitary adenomas (PAs). Protein ubiquitination profiling in human pituitary and PAs remains unknown. Here, we performed the first ubiquitination analysis with an anti-ubiquitin antibody (specific to K-ε-GG)-based label-free quantitative proteomics method and bioinformatics to investigate protein ubiquitination profiling between PA and control tissues. A total of 158 ubiquitinated sites and 142 ubiquitinated peptides in 108 proteins were identified, and five ubiquitination motifs were found. KEGG pathway network analysis of 108 ubiquitinated proteins identified four statistically significant signaling pathways, including PI3K-AKT signaling pathway, hippo signaling pathway, ribosome, and nucleotide excision repair. R software Gene Ontology (GO) analysis of 108 ubiquitinated proteins revealed that protein ubiquitination was involved in multiple biological processes, cellular components, and molecule functions. The randomly selected ubiquitinated 14-3-3 zeta/delta protein was further analyzed with Western blot, and it was found that upregulated 14-3-3 zeta/delta protein in nonfunctional PAs might be derived from the significantly decreased level of its ubiquitination compared to control pituitaries, which indicated a contribution of 14-3-3 zeta/delta protein to pituitary tumorigenesis. These findings provided the first ubiquitinated proteomic profiling and ubiquitination-involved signaling pathway networks in human PAs. This study offers new scientific evidence and basic data to elucidate the biological functions of ubiquitination in PAs, insights into its novel molecular mechanisms of pituitary tumorigenesis, and discovery of novel biomarkers and therapeutic targets for effective treatment of PAs.

Ubiquitin-proteasome signaling in lung injury

Cell homeostasis requires precise coordination of cellular proteins function. Ubiquitination is a post-translational modification that modulates protein half-life and function and is tightly regulated by ubiquitin E3 ligases and deubiquitinating enzymes. Lung injury can progress to acute respiratory distress syndrome that is characterized by an inflammatory response and disruption of the alveolocapillary barrier resulting in alveolar edema accumulation and hypoxemia. Ubiquitination plays an important role in the pathobiology of acute lung injury as it regulates the proteins modulating the alveolocapillary barrier and the inflammatory response. Better understanding of the signaling pathways regulated by ubiquitination may lead to novel therapeutic approaches by targeting specific elements of the ubiquitination pathways.

Acute Respiratory Distress Syndrome: Bench-to-Bedside Approaches to Improve Drug Development

Despite 50 years of extensive research, no definite drug is currently available to treat acute respiratory distress syndrome (ARDS), and the supportive therapies remain the mainstay of treatment. To improve drug development for ARDS, researchers need to deeply analyze the “omics” approaches, reevaluate the suitable therapeutic targets, resolve the problems of inadequate animal modeling, develop the strategies to reduce the heterogeneity, and reconsider new therapeutic and analytical approaches for better designs of clinical trials.

Gas Exchange Disturbances Regulate Alveolar Fluid Clearance during Acute Lung Injury

Disruption of the alveolar-capillary barrier and accumulation of pulmonary edema, if not resolved, result in poor alveolar gas exchange leading to hypoxia and hypercapnia, which are hallmarks of acute lung injury and the acute respiratory distress syndrome (ARDS). Alveolar fluid clearance (AFC) is a major function of the alveolar epithelium and is mediated by the concerted action of apically-located Na⁺ channels [epithelial Na⁺ channel (ENaC)] and the basolateral Na,K-ATPase driving vectorial Na⁺ transport. Importantly, those patients with ARDS who cannot clear alveolar edema efficiently have worse outcomes. While hypoxia can be improved in most cases by O₂ supplementation and mechanical ventilation, the use of lung protective ventilation settings can lead to further CO₂ retention. Whether the increase in CO₂ concentrations has deleterious or beneficial effects have been a topic of significant controversy. Of note, both low O₂ and elevated CO₂ levels are sensed by the alveolar epithelium and by distinct and specific molecular mechanisms impair the function of the Na,K-ATPase and ENaC thereby inhibiting AFC and leading to persistence of alveolar edema. This review discusses recent discoveries on the sensing and signaling events initiated by hypoxia and hypercapnia and the relevance of these results in identification of potential novel therapeutic targets in the treatment of ARDS.

Role of Linear Ubiquitination in Health and Disease

The covalent attachment of ubiquitin to target proteins is one of the most prevalent post-translational modifications, regulating a myriad of cellular processes including cell growth, survival, and metabolism. Recently, a novel RING E3 ligase complex was described, called linear ubiquitin assembly complex (LUBAC), which is capable of connecting ubiquitin molecules in a novel head-to-tail fashion via the N-terminal methionine residue. LUBAC is a heteromeric complex composed of heme-oxidized iron-responsive element-binding protein 2 ubiquitin ligase-1L (HOIL-1L), HOIL-1L-interacting protein, and shank-associated RH domain-interacting protein (SHARPIN). The essential role of LUBAC-generated linear chains for activation of nuclear factor-κB (NF-κB) signaling was first described in the activation of tumor necrosis factor-α receptor signaling complex. A decade of research has identified additional pathways that use LUBAC for downstream signaling, including CD40 ligand and the IL-1β receptor, as well as cytosolic pattern recognition receptors including nucleotide-binding oligomerization domain containing 2 (NOD2), retinoic acid-inducible gene 1 (RIG-1), and the NOD-like receptor family, pyrin domain containing 3 inflammasome (NLRP3). Even though the three components of the complex are required for full activation of NF-κB, the individual components of LUBAC regulate specific cell type- and stimuli-dependent effects. In humans, autosomal defects in LUBAC are associated with both autoinflammation and immunodeficiency, with additional disorders described in mice. Moreover, in the lung epithelium, HOIL-1L ubiquitinates target proteins independently of the other LUBAC components, adding another layer of complexity to the function and regulation of LUBAC. Although many advances have been made, the diverse functions of linear ubiquitin chains and the regulation of LUBAC are not yet completely understood. In this review, we discuss the various roles of linear ubiquitin chains and point to areas of study that would benefit from further investigation into LUBAC-mediated signaling pathways in lung pathophysiology.

Nedd8 modification of Cullin-5 regulates lipopolysaccharide-induced acute lung injury

Lung infections are major causes of acute lung injury (ALI), with limited effective treatment available. Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an essential adaptor regulating Toll-like receptors (TLRs). We recently identified Cullin-5 (Cul-5) as a prominent component in the regulation of TRAF6 polyubiquitination, but its physiological significance in ALI has not been explored. In this study, we investigated the potential role of Cul-5 in regulating ALI using mice receiving intratracheal instillation of LPS. We observed that Cul-5-deficient mice displayed reduced lung injury compared with wild-type mice as evidenced by histological analysis, alveolar neutrophil infiltration, and lung liquid accumulation. In addition, inflammatory cytokine expression in bronchoalveolar lavage fluid and lung tissue was also markedly reduced in LPS-treated Cul-5-deficient mice. Interestingly, intratracheal adoptive transfer of Cul-5^+/- but not Cul-5^+/+ macrophages attenuated neutrophil recruitment, alveolar inflammation, and loss of barrier function in LPS-challenged wild-type mice. Finally, we demonstrated that Cul-5 neddylation following LPS exposure induced Cul-5 and TRAF6 interaction and, thereby, TFAR6 polyubiquitination, leading to NF-κB activation and generation of proinflammatory cytokines. Our data show that neural precursor cell expressed developmentally downregulated protein 8 (Nedd8) modification of Cul-5 is required for its interaction with TRAF6 and activation of the TLR4-TRAF6 signaling pathway in LPS-induced ALI, a feature that may be explored for therapeutic intervention.

Receptor for advanced glycation end products is targeted by FBXO10 for ubiquitination and degradation

The receptor for advanced glycation end products (RAGE) is a highly expressed cell membrane receptor serving to anchor lung epithelia to matrix components, and it also amplifies inflammatory signaling during acute lung injury. However, mechanisms that regulate its protein concentrations in cells remain largely unknown. Here we show that RAGE exhibits an extended life span in lung epithelia (t_½ 6 h), is monoubiquitinated at K374, and is degraded in lysosomes. The RAGE ligand ODN2006, a synthetic oligodeoxynucleotide resembling pathogenic hypomethylated CpG DNA, promotes rapid lysosomal RAGE degradation through activation of protein kinase Cζ (PKCζ), which phosphorylates RAGE. PKCζ overexpression enhances RAGE degradation, while PKCζ knockdown stabilizes RAGE protein levels and prevents ODN2006-mediated degradation. We identify that RAGE is targeted by the ubiquitin E3 ligase subunit F-box protein O10 (FBXO10), which associates with RAGE to mediate its ubiquitination and degradation. FBXO10 depletion in cells stabilizes RAGE and is required for ODN2006-mediated degradation. These data suggest that modulation of regulators involved in ubiquitin-mediated disposal of RAGE might serve as unique molecular inputs directing RAGE cellular concentrations and downstream responses, which are critical in an array of inflammatory disorders, including acute lung injury.-Evankovich, J., Lear, T., Mckelvey, A., Dunn, S., Londino, J., Liu, Y., Chen, B. B., Mallampalli, R. K. Receptor for advanced glycation end products is targeted by FBXO10 for ubiquitination and degradation.

Dysregulated Nox4 ubiquitination contributes to redox imbalance and age-related severity of acute lung injury

Acute respiratory distress syndrome (ARDS) is a devastating critical illness disproportionately affecting the elderly population, with both higher incidence and mortality. The integrity of the lung endothelial cell (EC) monolayer is critical for preservation of lung function. However, mechanisms mediating EC barrier regulation in the context of aging remain unclear. We assessed the severity of acute lung injury (ALI) in young (2 mo) and aged (18 mo) mice using a two-hit preclinical model. Compared with young cohorts, aged mice exhibited increased ALI severity, with greater vascular permeability characterized by elevated albumin influx and levels of bronchoalveolar lavage (BAL) cells (neutrophils) and protein. Aged/injured mice also demonstrated elevated levels of reactive oxygen species (ROS) in the BAL, which was associated with upregulation of the ROS-generating enzyme, Nox4. We evaluated the role of aging in human lung EC barrier regulation utilizing a cellular model of replicative senescence. Senescent EC populations were defined by increases in β-galactosidase activity and p16 levels. In response to lipopolysaccharide (LPS) challenge, senescent ECs demonstrate exacerbated permeability responses compared with control "young" ECs. LPS challenge led to a rapid induction of Nox4 expression in both control and senescent ECs, which was posttranslationally mediated via the proteasome/ubiquitin system. However, senescent ECs demonstrated deficient Nox4 ubiquitination, resulting in sustained expression of Nox4 and alterations in cellular redox homeostasis. Pharmacological inhibition of Nox4 in senescent ECs reduced LPS-induced alterations in permeability. These studies provide insight into the roles of Nox4/senescence in EC barrier responses and offer a mechanistic link to the increased incidence and mortality of ARDS associated with aging.

Differences in Host Innate Responses among Coccidioides Isolates in a Murine Model of Pulmonary Coccidioidomycosis

Coccidioides immitis and Coccidioides posadasii are soil-dwelling fungi and the causative agents of coccidioidomycosis, a mycosis endemic to certain semiarid regions in the Americas. The most common route of infection is by inhalation of airborne Coccidioides arthroconidia. Once a susceptible host inhales the conidia, a transition to mature endosporulated spherules can occur within the first 5 days of infection. For this study, we examined the host response in a murine model of coccidioidomycosis during a time period of infection that has not been well characterized. We collected lung tissue and bronchoalveolar lavage fluid (BALF) from BALB/c mice that were infected with a C. immitis pure strain, a C. immitis hybrid strain, or a C. posadasii strain as well as uninfected mice. We compared the host responses to the Coccidioides strains used in this study by assessing the level of transcription of selected cytokine genes in lung tissues and characterized host and fungal proteins present in BALF. Host response varied depending on the Coccidioides strain that was used and did not appear to be overly robust. This study provides a foundation to begin to dissect the host immune response early in infection, to detect abundant Coccidioides proteins, and to develop diagnostics that target these early time points of infection.

The acute respiratory distress syndrome: from mechanism to translation

The acute respiratory distress syndrome (ARDS) is a form of severe hypoxemic respiratory failure that is characterized by inflammatory injury to the alveolar capillary barrier, with extravasation of protein-rich edema fluid into the airspace. Although many modalities to treat ARDS have been investigated over the past several decades, supportive therapies remain the mainstay of treatment. In this article, we briefly review the definition, epidemiology, and pathophysiology of ARDS and present emerging aspects of ARDS pathophysiology that encompass modulators of the innate immune response, damage signals, and aberrant proteolysis that may serve as a foundation for future therapeutic targets.

The acute respiratory distress syndrome: from mechanism to translation

The acute respiratory distress syndrome (ARDS) is a form of severe hypoxemic respiratory failure that is characterized by inflammatory injury to the alveolar capillary barrier, with extravasation of protein-rich edema fluid into the airspace. Although many modalities to treat ARDS have been investigated over the past several decades, supportive therapies remain the mainstay of treatment. In this article, we briefly review the definition, epidemiology, and pathophysiology of ARDS and present emerging aspects of ARDS pathophysiology that encompass modulators of the innate immune response, damage signals, and aberrant proteolysis that may serve as a foundation for future therapeutic targets.

FTY720 (s)-phosphonate preserves sphingosine 1-phosphate receptor 1 expression and exhibits superior barrier protection to FTY720 in acute lung injury

OBJECTIVE

Effective therapies are needed to reverse the increased vascular permeability that characterizes acute inflammatory diseases such as acute lung injury. FTY720 is a pharmaceutical analog of the potent barrier-enhancing phospholipid, sphingosine 1-phosphate. Because both FTY720 and sphingosine 1-phosphate have properties that may limit their usefulness in patients with acute lung injury, alternative compounds are needed for therapeutic use. The objective of this study is to characterize the effects of FTY720 (S)-phosphonate, a novel analog of FTY720-phosphate, on variables of pulmonary vascular permeability in vitro and alveolar-capillary permeability in vivo.

SETTING

University-affiliated research institute.

SUBJECTS

Cultured human pulmonary endothelial cells; C57BL/6 mice.

INTERVENTIONS

Endothelial cells were stimulated with sphingosine 1-phosphate receptor 1 agonists to determine effects on sphingosine 1-phosphate receptor 1 expression. Acute lung injury was induced in C57BL/6 mice with bleomycin to assess effects of sphingosine 1-phosphate receptor 1 agonists.

MEASUREMENTS AND MAIN RESULTS

FTY720 (S)-phosphonate potently increases human pulmonary endothelial cell barrier function in vitro as measured by transendothelial electrical resistance. Reduction of sphingosine 1-phosphate receptor 1 with small interference RNA significantly attenuates this transendothelial electrical resistance elevation. FTY720 (S)-phosphonate maintains endothelial sphingosine 1-phosphate receptor 1 protein expression in contrast to greater than 50% reduction after incubation with sphingosine 1-phosphate, FTY720, or other sphingosine 1-phosphate receptor 1 agonists. FTY720 (S)-phosphonate does not induce β-arrestin recruitment, sphingosine 1-phosphate receptor 1 ubiquitination, and proteosomal degradation that occur after other agonists. Intraperitoneal administration of FTY720 (S)-phosphonate every other day for 1 week in normal or bleomycin-injured mice maintains significantly higher lung sphingosine 1-phosphate receptor 1 expression compared with FTY720. FTY720 fails to protect against bleomycin-induced acute lung injury in mice, while FTY720 (S)-phosphonate significantly decreases lung leak and inflammation.

CONCLUSION

FTY720 (S)-phosphonate is a promising barrier-promoting agent that effectively maintains sphingosine 1-phosphate receptor 1 levels and improves outcomes in the bleomycin model of acute lung injury.

Human adult bone marrow-derived stem cells decrease severity of lipopolysaccharide-induced acute respiratory distress syndrome in sheep

INTRODUCTION

Acute respiratory distress syndrome (ARDS) is the most common cause of respiratory failure among critically ill subjects, sepsis and severe bacterial pneumonia being its most common causes. The only interventions that have proven beneficial are protective ventilation strategies and fluid conservation approaches. New therapies are needed to address this common clinical problem. Others and we have previously shown the beneficial effect of infusion of exogenous adult stem cells in different pre-clinical models of ARDS.

METHODS

In the present study endotoxin was infused intravenously into 14 sheep from which 6 received different doses of adult stem cells by intrabronchial delivery to evaluate the effect of stem cell therapy.

RESULTS

After administration of endotoxin, there was a rapid decline in oxygenation to hypoxemic values, indicative of severe-to-moderate ARDS. None of the animals treated with saline solution recovered to normal baseline values during the 6 hours that the animals were followed. In contrast, sheep treated with a dose of 40 million adult stem cells returned their levels of oxygen in their blood to baseline two hours after the cells were infused. Similarly, improvements in carbon dioxide (CO2) clearance, pulmonary vascular pressures and inflammation were observed and confirmed by histology and by the decrease in lung edema.

CONCLUSIONS

We concluded that instillation of adult non-hematopoietic stem cells can diminish the impact of endotoxin and accelerate recovery of oxygenation, CO2 removal and inflammation in the ovine model, making the use of adult stem cells a real alternative for future therapies for ARDS.

The emerging role of the ubiquitin proteasome in pulmonary biology and disease

Derangements in normal cellular homeostasis at the protein level can cause or be the consequence of initiation and progression of pulmonary diseases related to genotype, infection, injury, smoking, toxin exposure, or neoplasm. We discuss one of the fundamental mechanisms of protein homeostasis, the ubiquitin proteasome system (UPS), as it relates to lung disease. The UPS effects selective degradation of ubiquitinated target proteins via ubiquitin ligase activity. Important pathobiological mechanisms relating to the UPS and lung disease have been the focus of research, with inappropriate cellular proteolysis now a validated therapeutic target. We review the contributions of this system in various lung diseases, and discuss the exciting area of UPS-targeting drug development for pulmonary disease.

Protein expression profile of rat type two alveolar epithelial cells during hyperoxic stress and recovery

In rodent model systems, the sequential changes in lung morphology resulting from hyperoxic injury are well characterized and are similar to changes in human acute respiratory distress syndrome. In the injured lung, alveolar type two (AT2) epithelial cells play a critical role in restoring the normal alveolar structure. Thus characterizing the changes in AT2 cells will provide insights into the mechanisms underpinning the recovery from lung injury. We applied an unbiased systems-level proteomics approach to elucidate molecular mechanisms contributing to lung repair in a rat hyperoxic lung injury model. AT2 cells were isolated from rat lungs at predetermined intervals during hyperoxic injury and recovery. Protein expression profiles were determined by using iTRAQ with tandem mass spectrometry. Of the 959 distinct proteins identified, 183 significantly changed in abundance during the injury-recovery cycle. Gene ontology enrichment analysis identified cell cycle, cell differentiation, cell metabolism, ion homeostasis, programmed cell death, ubiquitination, and cell migration to be significantly enriched by these proteins. Gene set enrichment analysis of data acquired during lung repair revealed differential expression of gene sets that control multicellular organismal development, systems development, organ development, and chemical homeostasis. More detailed analysis identified activity in two regulatory pathways, JNK and miR 374. A novel short time-series expression miner algorithm identified protein clusters with coherent changes during injury and repair. We concluded that coherent changes occur in the AT2 cell proteome in response to hyperoxic stress. These findings offer guidance regarding the specific molecular mechanisms governing repair of the injured lung.

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.

New insights on the function of SCF ubiquitin E3 ligases in the lung

Recent developments in pulmonary cell biology have shown that the maintenance of protein concentrations, proteostasis, is an integral process of all biologic systems. The balance of available protein is the sum total of three key elements of cell metabolism: production by transcription and translation, compartmentalization through processing and sorting, and proteolytic degradation of proteins at any stage of their life-span. Considerable advances are constantly made in each of these three essential fields, and our appreciation for the diversity of mechanisms of protein degradation has expanded greatly in the last decade. The ubiquitin proteasome system (UPS) has emerged as the predominant protein degradation pathway in eukaryotes, with the large cullin-RING family of E3 ligases responsible for ubiquitination of a broad array of proteins to be degraded. The Skip-Cullin-F-box (SCF) ubiquitin E3 ligase superfamily is the largest family of cullin-RING ligases, with interchangeable F-box proteins orchestrating the trafficking proteins for ubiquitination and degradation. We will discuss the best characterized and most recent developments in the role of this intriguing family of proteins in normal physiology and disorders of the lungs.

An omics strategy for discovering pulmonary biomarkers potentially relevant to the evaluation of tobacco products

Smoking is known to cause serious lung diseases including chronic bronchitis, chronic obstructive lung disease, obstruction of small airways, emphysema and cancer. Tobacco smoke is a complex chemical aerosol containing at least 8000 chemical constituents, either tobacco derived or added by tobacco product manufacturers. Identification of all of the toxic agents in tobacco smoke is challenging, and efforts to understand the mechanisms by which tobacco use causes disease will be informed by new biomarkers of exposure and harm. In 2009, President Obama signed into law the Family Smoking Prevention and Tobacco Control Act granting the US FDA the authority to regulate tobacco products to protect public health. This perspective article presents the background, rationale and strategy for using omics technologies to develop new biomarkers, which may be of interest to the FDA when implementing the Family Smoking Prevention and Tobacco Control Act.

Infusion of freshly isolated autologous bone marrow derived mononuclear cells prevents endotoxin-induced lung injury in an ex-vivo perfused swine model

INTRODUCTION

The acute respiratory distress syndrome (ARDS), affects up to 150,000 patients per year in the United States. We and other groups have demonstrated that bone marrow derived mesenchymal stromal stem cells prevent ARDS induced by systemic and local administration of endotoxin (lipopolysaccharide (LPS)) in mice.

METHODS

A study was undertaken to determine the effects of the diverse populations of bone marrow derived cells on the pathophysiology of ARDS, using a unique ex-vivo swine preparation, in which only the ventilated lung and the liver are perfused with autologous blood. Six experimental groups were designated as: 1) endotoxin alone, 2) endotoxin + total fresh whole bone marrow nuclear cells (BMC), 3) endotoxin + non-hematopoietic bone marrow cells (CD45 neg), 4) endotoxin + hematopoietic bone marrow cells (CD45 positive), 5) endotoxin + buffy coat and 6) endotoxin + in vitro expanded swine CD45 negative adherent allogeneic bone marrow cells (cultured CD45neg). We measured at different levels the biological consequences of the infusion of the different subsets of cells. The measured parameters were: pulmonary vascular resistance (PVR), gas exchange (PO2), lung edema (lung wet/dry weight), gene expression and serum concentrations of the pro-inflammatory cytokines IL-1β, TNF-α and IL-6.

RESULTS

Infusion of freshly purified autologous total BMCs, as well as non-hematopoietic CD45(-) bone marrow cells significantly reduced endotoxin-induced pulmonary hypertension and hypoxemia and reduced the lung edema. Also, in the groups that received BMCs and cultured CD45neg we observed a decrease in the levels of IL-1β and TNF-α in plasma. Infusion of hematopoietic CD45(+) bone marrow cells or peripheral blood buffy coat cells did not protect against LPS-induced lung injury.

CONCLUSIONS

We conclude that infusion of freshly isolated autologous whole bone marrow cells and the subset of non-hematopoietic cells can suppress the acute humoral and physiologic responses induced by endotoxemia by modulating the inflammatory response, mechanisms that do not involve engraftment or trans-differentiation of the cells. These observations may have important implications for the design of future cell therapies for ARDS.

Mesenchymal stem cells: a promising therapy for the acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a pulmonary syndrome with growing prevalence and high mortality and morbidity that increase with age. There is no current therapy able to restore pulmonary function in ARDS patients. Preclinical models of ARDS have demonstrated that intratracheal or systemic administration of mesenchymal stem cells (MSCs) protects the lung against injury. The mechanisms responsible for the protective effects are multiple, including the secretion of multiple paracrine factors capable of modulating the immune response and restoring epithelial and endothelial integrity. Recent studies have demonstrated that MSCs can also control oxidative stress, transfer functional mitochondria to the damaged cells, and control bacterial infection by secretion of antibacterial peptides. These characteristics make MSCs promising candidates for ARDS therapy.