TWIST1 and TSG6 are coordinately regulated and function as potency biomarkers in human MSCs.

Mesenchymal stem/stromal cells (MSCs) have been evaluated in >1500 clinical trials, but outcomes remain suboptimal because of knowledge gaps in quality attributes that confer potency. We show that TWIST1 directly represses TSG6 expression that TWIST1 and TSG6 are inversely correlated across bone marrow-derived MSC (BM-MSC) donor cohorts and predict interdonor differences in their proangiogenic, anti-inflammatory, and immune suppressive activity in vitro and in sterile inflammation and autoimmune type 1 diabetes preclinical models. Transcript profiling of TWIST1HiTSG6Low versus TWISTLowTSG6Hi BM-MSCs revealed previously unidentified roles for TWIST1/TSG6 in regulating cellular oxidative stress and TGF-ß2 in modulating TSG6 expression and anti-inflammatory activity. TWIST1 and TSG6 levels also correlate to donor stature and predict differences in iPSC-derived MSC quality attributes. These results validate TWIST1 and TSG6 as biomarkers that predict interdonor differences in potency across laboratories and assay platforms, thereby providing a means to manufacture MSC products tailored to specific diseases.

Mesenchymal Stem Cells from COPD Patients Are Capable of Restoring Elastase-Induced Emphysema in a Murine Experimental Model.

COPD is a chronic lung disease that affects millions of people, declining their lung function and impairing their life quality. Despite years of research and drug approvals, we are still not capable of halting progression or restoring normal lung function. Mesenchymal stem cells (MSC) are cells with extraordinary repair capacity, and MSC-based therapy brings future hope for COPD treatment, although the best source and route of administration are unclear. MSC from adipose tissue (AD-MSC) represents an option for autologous treatment; however, they could be less effective than donor MSC. We compared in vitro behavior of AD-MSC from COPD and non-COPD individuals by migration/proliferation assay, and tested their therapeutic potential in an elastase mouse model. In addition, we tested intravenous versus intratracheal routes, inoculating umbilical cord (UC) MSC and analyzed molecular changes by protein array. Although COPD AD-MSC have impaired migratory response to VEGF and cigarette smoke, they were as efficient as non-COPD in reducing elastase-induced lung emphysema. UC-MSC reduced lung emphysema regardless of the administration route and modified the inflammatory profile in elastase-treated mice. Our data demonstrate equal therapeutic potential of AD-MSC from COPD and non-COPD subjects in the pre-clinical model, thus supporting their autologous use in disease.

Inhibition of antiapoptotic BCL-2 proteins with ABT-263 induces fibroblast apoptosis, reversing persistent pulmonary fibrosis.

Patients with progressive fibrosing interstitial lung diseases (PF-ILDs) carry a poor prognosis and have limited therapeutic options. A hallmark feature is fibroblast resistance to apoptosis, leading to their persistence, accumulation, and excessive deposition of extracellular matrix. A complex balance of the B cell lymphoma 2 (BCL-2) protein family controlling the intrinsic pathway of apoptosis and fibroblast reliance on antiapoptotic proteins has been hypothesized to contribute to this resistant phenotype. Examination of lung tissue from patients with PF-ILD (idiopathic pulmonary fibrosis and silicosis) and mice with PF-ILD (repetitive bleomycin and silicosis) showed increased expression of antiapoptotic BCL-2 family members in α-smooth muscle actin-positive fibroblasts, suggesting that fibroblasts from fibrotic lungs may exhibit increased susceptibility to inhibition of antiapoptotic BCL-2 family members BCL-2, BCL-XL, and BCL-W with the BH3 mimetic ABT-263. We used 2 murine models of PF-ILD to test the efficacy of ABT-263 in reversing established persistent pulmonary fibrosis. Treatment with ABT-263 induced fibroblast apoptosis, decreased fibroblast numbers, and reduced lung collagen levels, radiographic disease, and histologically evident fibrosis. Our studies provide insight into how fibroblasts gain resistance to apoptosis and become sensitive to the therapeutic inhibition of antiapoptotic proteins. By targeting profibrotic fibroblasts, ABT-263 offers a promising therapeutic option for PF-ILDs.

Role of metabolic reprogramming in pro-inflammatory cytokine secretion from LPS or silica-activated macrophages.

In the lungs, macrophages constitute the first line of defense against pathogens and foreign bodies and play a fundamental role in maintaining tissue homeostasis. Activated macrophages show altered immunometabolism and metabolic changes governing immune effector mechanisms, such as cytokine secretion characterizing their classic (M1) or alternative (M2) activation. Lipopolysaccharide (LPS)-stimulated macrophages demonstrate enhanced glycolysis, blocked succinate dehydrogenase (SDH), and increased secretion of interleukin-1 beta (IL-1ß) and tumor necrosis factor-alpha (TNF-α). Glycolysis suppression using 2 deoxyglucose in LPS-stimulated macrophages inhibits IL-1ß secretion, but not TNF-α, indicating metabolic pathway specificity that determines cytokine production. In contrast to LPS, the nature of the immunometabolic responses induced by non-organic particles, such as silica, in macrophages, its contribution to cytokine specification, and disease pathogenesis are not well understood. Silica-stimulated macrophages activate pattern recognition receptors (PRRs) and NLRP3 inflammasome and release IL-1ß, TNF-α, and interferons, which are the key mediators of silicosis pathogenesis. In contrast to bacteria, silica particles cannot be degraded, and the persistent macrophage activation results in an increased NADPH oxidase (Phox) activation and mitochondrial reactive oxygen species (ROS) production, ultimately leading to macrophage death and release of silica particles that perpetuate inflammation. In this manuscript, we reviewed the effects of silica on macrophage mitochondrial respiration and central carbon metabolism determining cytokine specification responsible for the sustained inflammatory responses in the lungs.

Silica Induced Lung Fibrosis Is Associated With Senescence, Fgr, and Recruitment of Bone Marrow Monocyte/Macrophages.

BACKGROUND/AIM: The role of senescence and bone marrow-derived cells in silica-induced pulmonary fibrosis is unknown. MATERIALS AND METHODS: C57BL/6HNsd, p16+/LUC, and tdTOMp16+ mice were intratracheally injected with 200 mg/kg crystalline silica or irradiated (20 Gy) to the thoracic cavity and followed for the development of lung fibrosis. RESULTS: The p16+/LUC mice demonstrated senescence by day 7 after silica exposure. C57BL/6 mice exposed to silica demonstrated upregulation of p16, p21, and tyrosine kinase Fgr by day 7, whereas thoracic irradiation induced p21 and Fgr by day 50 and p16 by day 110. Silica exposed GFP+ bone marrow chimeric C57BL/6 mice demonstrated senescent cells and gfp+/Fgr+ monocyte/macrophages in the lungs on day 21. The Fgr inhibitor TL02-59 abrogated monocyte/macrophages recruitment in in vitro transwell experiments. CONCLUSION: Both silica and radiation exposure induce senescence and upregulate tyrosine kinase Fgr for the recruitment of bone marrow-derived monocyte/macrophages and the development of pulmonary fibrosis.

Metabolic Adaptation of Macrophages as Mechanism of Defense against Crystalline Silica.

Silicosis is a lethal pneumoconiosis for which no therapy is available. Silicosis is a global threat, and more than 2.2 million people per year are exposed to silica in the United States. The initial response to silica is mediated by innate immunity. Phagocytosis of silica particles by macrophages is followed by recruitment of mitochondria to phagosomes, generation of mitochondrial reactive oxygen species, and cytokine (IL-1ß, TNF-α, IFN-ß) release. In contrast with LPS, the metabolic remodeling of silica-exposed macrophages is unclear. This study contrasts mitochondrial and metabolic alterations induced by LPS and silica on macrophages and correlates them with macrophage viability and cytokine production, which are central to the pathogenesis of silicosis. Using high-resolution respirometer and liquid chromatography-high-resolution mass spectrometry, we determined the effects of silica and LPS on mitochondrial respiration and determined changes in central carbon metabolism of murine macrophage cell lines RAW 264.7 and IC-21. We show that silica induces metabolic reprogramming of macrophages. Silica, as well as LPS, enhances glucose uptake and increases aerobic glycolysis in macrophages. In contrast with LPS, silica affects mitochondria respiration, reducing complex I and enhancing complex II activity, to sustain cell viability. These mitochondrial alterations are associated in silica, but not in LPS-exposed macrophages, with reductions of tricarboxylic acid cycle intermediates, including succinate, itaconate, glutamate, and glutamine. Furthermore, in contrast with LPS, these silica-induced metabolic adaptations do not correlate with IL-1ß or TNF-α production, but with the suppressed release of IFN-ß. Our data highlight the importance of complex II activity and tricarboxylic acid cycle remodeling to macrophage survival and cytokine-mediated inflammation in silicosis.

Critical considerations for the development of potency tests for therapeutic applications of mesenchymal stromal cell-derived small extracellular vesicles.

Mesenchymal stromal/stem cells (MSCs) have been widely tested against many diseases, with more than 1000 registered clinical trials worldwide. Despite many setbacks, MSCs have been approved for the treatment of graft-versus-host disease and Crohn disease. However, it is increasingly clear that MSCs exert their therapeutic functions in a paracrine manner through the secretion of small extracellular vesicles (sEVs) of 50-200 nm in diameter. Unlike living cells that can persist long-term, sEVs are non-living and non-replicative and have a transient presence in the body. Their small size also renders sEV preparations highly amenable to sterilization by filtration. Together, acellular MSC-sEV preparations are potentially safer and easier to translate into the clinic than cellular MSC products. Nevertheless, there are inherent challenges in the development of MSC-sEV drug products. MSC-sEVs are products of living cells, and living cells are sensitive to changes in the external microenvironment. Consequently, quality control metrics to measure key identity and potency features of MSC-sEV preparations have to be specified during development of MSC-sEV therapeutics. The authors have previously described quantifiable assays to define the identity of MSC-sEVs. Here the authors discuss requirements for prospective potency assays to predict the therapeutic effectiveness of the drug substance in accordance with International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines. Although potency assays should ideally reflect the mechanism of action (MoA), this is challenging because the MoA for the reported efficacy of MSC-sEV preparations against multiple diseases of diverse underlying pathology is likely to be complex and different for each disease and difficult to fully elucidate. Nevertheless, robust potency assays could be developed by identifying the EV attribute most relevant to the intended biological activity in EV-mediated therapy and quantifying the EV attribute. Specifically, the authors highlight challenges and mitigation measures to enhance the manufacture of consistent and reproducibly potent sEV preparations, to identify and select the appropriate EV attribute for potency assays despite a complex "work-in-progress" MoA and to develop assays likely to be compliant with regulatory guidance for assay validation.

International Society for Extracellular Vesicles and International Society for Cell and Gene Therapy statement on extracellular vesicles from mesenchymal stromal cells and other cells: considerations for potential therapeutic agents to suppress coronavirus disease-19.

STATEMENT: The International Society for Cellular and Gene Therapies (ISCT) and the International Society for Extracellular Vesicles (ISEV) recognize the potential of extracellular vesicles (EVs, including exosomes) from mesenchymal stromal cells (MSCs) and possibly other cell sources as treatments for COVID-19. Research and trials in this area are encouraged. However, ISEV and ISCT do not currently endorse the use of EVs or exosomes for any purpose in COVID-19, including but not limited to reducing cytokine storm, exerting regenerative effects or delivering drugs, pending the generation of appropriate manufacturing and quality control provisions, pre-clinical safety and efficacy data, rational clinical trial design and proper regulatory oversight.

IL-33-mediated IL-13 secretion by ST2+ Tregs controls inflammation after lung injury.

Acute respiratory distress syndrome is an often fatal disease that develops after acute lung injury and trauma. How released tissue damage signals, or alarmins, orchestrate early inflammatory events is poorly understood. Herein we reveal that IL-33, an alarmin sequestered in the lung epithelium, is required to limit inflammation after injury due to an unappreciated capacity to mediate Foxp3+ Treg control of local cytokines and myeloid populations. Specifically, Il33-/- mice are more susceptible to lung damage-associated morbidity and mortality that is typified by augmented levels of the proinflammatory cytokines and Ly6Chi monocytes in the bronchoalveolar lavage fluid. Local delivery of IL-33 at the time of injury is protective but requires the presence of Treg cells. IL-33 stimulates both mouse and human Tregs to secrete IL-13. Using Foxp3Cre × Il4/Il13fl/fl mice, we show that Treg expression of IL-13 is required to prevent mortality after acute lung injury by controlling local levels of G-CSF, IL-6, and MCP-1 and inhibiting accumulation of Ly6Chi monocytes. Our study identifies a regulatory mechanism involving IL-33 and Treg secretion of IL-13 in response to tissue damage that is instrumental in limiting local inflammatory responses and may shape the myeloid compartment after lung injury.

Treatment with allogeneic mesenchymal stromal cells for moderate to severe acute respiratory distress syndrome (START study): a randomised phase 2a safety trial.

BACKGROUND: Treatment with bone-marrow-derived mesenchymal stromal cells (MSCs) has shown benefits in preclinical models of acute respiratory distress syndrome (ARDS). Safety has not been established for administration of MSCs in critically ill patients with ARDS. We did a phase 2a trial to assess safety after administration of MSCs to patients with moderate to severe ARDS. METHODS: We did a prospective, double-blind, multicentre, randomised trial to assess treatment with one intravenous dose of MSCs compared with placebo. We recruited ventilated patients with moderate to severe ARDS (ratio of partial pressure of oxygen to fractional inspired oxygen <27 kPa and positive end-expiratory pressure [PEEP] ≥8 cm H2O) in five university medical centres in the USA. Patients were randomly assigned 2:1 to receive either 10 × 106/kg predicted bodyweight MSCs or placebo, according to a computer-generated schedule with a variable block design and stratified by site. We excluded patients younger than 18 years, those with trauma or moderate to severe liver disease, and those who had received cancer treatment in the previous 2 years. The primary endpoint was safety and all analyses were done by intention to treat. We also measured biomarkers in plasma. MSC viability was tested in a post-hoc analysis. This trial is registered with ClinicalTrials.gov, number NCT02097641. FINDINGS: From March 24, 2014, to Feb 9, 2017 we screened 1038 patients, of whom 60 were eligible for and received treatment. No patient experienced any of the predefined MSC-related haemodynamic or respiratory adverse events. One patient in the MSC group died within 24 h of MSC infusion, but death was judged to be probably unrelated. 28-day mortality did not differ between the groups (30% in the MSC group vs 15% in the placebo group, odds ratio 2·4, 95% CI 0·5-15·1). At baseline, the MSC group had numerically higher mean scores than the placebo group for Acute Physiology and Chronic Health Evaluation III (APACHE III; 104 [SD 31] vs 89 [33]), minute ventilation (11·1 [3·2] vs 9·6 [2·4] L/min), and PEEP (12·4 [3·7] vs 10·8 [2·6] cm H2O). After adjustment for APACHE III score, the hazard ratio for mortality at 28 days was 1·43 (95% CI 0·40-5·12, p=0·58). Viability of MSCs ranged from 36% to 85%. INTERPRETATION: One dose of intravenous MSCs was safe in patients with moderate to severe ARDS. Larger trials are needed to assess efficacy, and the viability of MSCs must be improved. FUNDING: National Heart, Lung, and Blood Institute.

Protein Tyrosine Phosphatase-N13 Promotes Myofibroblast Resistance to Apoptosis in Idiopathic Pulmonary Fibrosis.

RATIONALE: Idiopathic pulmonary fibrosis (IPF) is a progressive, fibrotic interstitial lung disease characterized by (myo)fibroblast accumulation and collagen deposition. Resistance to Fas-induced apoptosis is thought to facilitate (myo)fibroblast persistence in fibrotic lung tissues by poorly understood mechanisms. OBJECTIVES: To test the hypothesis that PTPN13 (protein tyrosine phosphatase-N13) is expressed by IPF lung (myo)fibroblasts, promotes their resistance to Fas-induced apoptosis, and contributes to the development of pulmonary fibrosis. METHODS: PTPN13 was localized in lung tissues from patients with IPF and control subjects by immunohistochemical staining. Inhibition of PTPN13 function in primary IPF and normal lung (myo)fibroblasts was accomplished by: 1) downregulation with TNF-α (tumor necrosis factor-α)/IFN-γ, 2) siRNA knockdown, or 3) a cell-permeable Fas/PTPN13 interaction inhibitory peptide. The role of PTPN13 in the development of pulmonary fibrosis was assessed in mice with genetic deficiency of PTP-BL, the murine ortholog of PTPN13. MEASUREMENTS AND MAIN RESULTS: PTPN13 was constitutively expressed by (myo)fibroblasts in the fibroblastic foci of patients with IPF. Human lung (myo)fibroblasts, which are resistant to Fas-induced apoptosis, basally expressed PTPN13 in vitro. TNF-α/IFN-γ or siRNA-mediated PTPN13 downregulation and peptide-mediated inhibition of the Fas/PTPN13 interaction in human lung (myo)fibroblasts promoted Fas-induced apoptosis. Bleomycin-challenged PTP-BL-/- mice, while developing inflammatory lung injury, exhibited reduced pulmonary fibrosis compared with wild-type mice. CONCLUSIONS: These findings suggest that PTPN13 mediates the resistance of human lung (myo)fibroblasts to Fas-induced apoptosis and promotes pulmonary fibrosis in mice. Our results suggest that strategies aimed at interfering with PTPN13 expression or function may represent a novel strategy to reduce fibrosis in IPF.

A Clinical Indications Prediction Scale Based on TWIST1 for Human Mesenchymal Stem Cells.

In addition to their stem/progenitor properties, mesenchymal stem cells (MSCs) also exhibit potent effector (angiogenic, antiinflammatory, immuno-modulatory) functions that are largely paracrine in nature. It is widely believed that effector functions underlie most of the therapeutic potential of MSCs and are independent of their stem/progenitor properties. Here we demonstrate that stem/progenitor and effector functions are coordinately regulated at the cellular level by the transcription factor Twist1 and specified within populations according to a hierarchical model. We further show that manipulation of Twist1 levels by genetic approaches or by exposure to widely used culture supplements including fibroblast growth factor 2 (Ffg2) and interferon gamma (IFN-gamma) alters MSC efficacy in cell-based and in vivo assays in a predictable manner. Thus, by mechanistically linking stem/progenitor and effector functions our studies provide a unifying framework in the form of an MSC hierarchy that models the functional complexity of populations. Using this framework, we developed a CLinical Indications Prediction (CLIP) scale that predicts how donor-to-donor heterogeneity and culture conditions impact the therapeutic efficacy of MSC populations for different disease indications.

Mesenchymal stem cells use extracellular vesicles to outsource mitophagy and shuttle microRNAs.

Mesenchymal stem cells (MSCs) and macrophages are fundamental components of the stem cell niche and function coordinately to regulate haematopoietic stem cell self-renewal and mobilization. Recent studies indicate that mitophagy and healthy mitochondrial function are critical to the survival of stem cells, but how these processes are regulated in MSCs is unknown. Here we show that MSCs manage intracellular oxidative stress by targeting depolarized mitochondria to the plasma membrane via arrestin domain-containing protein 1-mediated microvesicles. The vesicles are then engulfed and re-utilized via a process involving fusion by macrophages, resulting in enhanced bioenergetics. Furthermore, we show that MSCs simultaneously shed micro RNA-containing exosomes that inhibit macrophage activation by suppressing Toll-like receptor signalling, thereby de-sensitizing macrophages to the ingested mitochondria. Collectively, these studies mechanistically link mitophagy and MSC survival with macrophage function, thereby providing a physiologically relevant context for the innate immunomodulatory activity of MSCs.

TNFR1/phox interaction and TNFR1 mitochondrial translocation Thwart silica-induced pulmonary fibrosis.

Macrophages play a fundamental role in innate immunity and the pathogenesis of silicosis. Phagocytosis of silica particles is associated with the generation of reactive oxygen species (ROS), secretion of cytokines, such as TNF, and cell death that contribute to silica-induced lung disease. In macrophages, ROS production is executed primarily by activation of the NADPH oxidase (Phox) and by generation of mitochondrial ROS (mtROS); however, the relative contribution is unclear, and the effects on macrophage function and fate are unknown. In this study, we used primary human and mouse macrophages (C57BL/6, BALB/c, and p47(phox-/-)) and macrophage cell lines (RAW 264.7 and IC21) to investigate the contribution of Phox and mtROS to silica-induced lung injury. We demonstrate that reduced p47(phox) expression in IC21 macrophages is linked to enhanced mtROS generation, cardiolipin oxidation, and accumulation of cardiolipin hydrolysis products, culminating in cell death. mtROS production is also observed in p47(phox-/-) macrophages, and p47(phox-/-) mice exhibit increased inflammation and fibrosis in the lung following silica exposure. Silica induces interaction between TNFR1 and Phox in RAW 264.7 macrophages. Moreover, TNFR1 expression in mitochondria decreased mtROS production and increased RAW 264.7 macrophage survival to silica. These results identify TNFR1/Phox interaction as a key event in the pathogenesis of silicosis that prevents mtROS formation and reduces macrophage apoptosis.

Future directions in idiopathic pulmonary fibrosis research. An NHLBI workshop report.

The median survival of patients with idiopathic pulmonary fibrosis (IPF) continues to be approximately 3 years from the time of diagnosis, underscoring the lack of effective medical therapies for this disease. In the United States alone, approximately 40,000 patients die of this disease annually. In November 2012, the NHLBI held a workshop aimed at coordinating research efforts and accelerating the development of IPF therapies. Basic, translational, and clinical researchers gathered with representatives from the NHLBI, patient advocacy groups, pharmaceutical companies, and the U.S. Food and Drug Administration to review the current state of IPF research and identify priority areas, opportunities for collaborations, and directions for future research. The workshop was organized into groups that were tasked with assessing and making recommendations to promote progress in one of the following six critical areas of research: (1) biology of alveolar epithelial injury and aberrant repair; (2) role of extracellular matrix; (3) preclinical modeling; (4) role of inflammation and immunity; (5) genetic, epigenetic, and environmental determinants; (6) translation of discoveries into diagnostics and therapeutics. The workshop recommendations provide a basis for directing future research and strategic planning by scientific, professional, and patient communities and the NHLBI.

Tumor necrosis factor-α accelerates the resolution of established pulmonary fibrosis in mice by targeting profibrotic lung macrophages.

Idiopathic pulmonary fibrosis (IPF) is a relentless, fibrotic parenchymal lung disease in which alternatively programmed macrophages produce profibrotic molecules that promote myofibroblast survival and collagen synthesis. Effective therapies to treat patients with IPF are lacking, and conventional therapy may be harmful. We tested the hypothesis that therapeutic lung delivery of the proinflammatory cytokine tumor necrosis factor (TNF)-α into wild-type fibrotic mice would reduce the profibrotic milieu and accelerate the resolution of established pulmonary fibrosis. Fibrosis was assessed in bleomycin-instilled wild-type and TNF-α(-/-) mice by measuring hydroxyproline levels, static compliance, and Masson's trichrome staining. Macrophage infiltration and programming status was assessed by flow cytometry of enzymatically digested lung and in situ immunostaining. Pulmonary delivery of TNF-α to wild-type mice with established pulmonary fibrosis was found to reduce their fibrotic burden, to improve lung function and architecture, and to reduce the number and programming status of profibrotic alternatively programmed macrophages. In contrast, fibrosis and alternative macrophage programming were prolonged in bleomycin-instilled TNF-α(-/-) mice. To address the role of the reduced numbers of alternatively programmed macrophages in the TNF-α-induced resolution of established pulmonary fibrosis, we conditionally depleted macrophages in MAFIA (MAcrophage Fas-Induced Apoptosis) mice. Conditional macrophage depletion phenocopied the resolution of established pulmonary fibrosis observed after therapeutic TNF-α delivery. Taken together, our results show for the first time that TNF-α is involved in the resolution of established pulmonary fibrosis via a mechanism involving reduced numbers and programming status of profibrotic macrophages. We speculate that pulmonary delivery of TNF-α or augmenting its signaling pathway represent a novel therapeutic strategy to resolve established pulmonary fibrosis.

LPS-treated macrophage cytokines repress surfactant protein-B in lung epithelial cells.

In the mouse lung, Escherichia coli LPS can decrease surfactant protein-B (SFTPB) mRNA and protein concentrations. LPS also regulates the expression, synthesis, and concentrations of a variety of gene and metabolic products that inhibit SFTPB gene expression. The purpose of the present study was to determine whether LPS acts directly or indirectly on pulmonary epithelial cells to trigger signaling pathways that inhibit SFTPB expression, and whether the transcription factor CCAAT/enhancer binding protein (C/EBP)-ß (CEBPB) is a downstream inhibitory effector. To investigate the mechanism of SFTPB repression, the human pulmonary epithelial cell lines NCI-H441 (H441) and NCI-H820 (H820) and the mouse macrophage-like cell line RAW264.7 were treated with LPS. Whereas LPS did not decrease SFTPB transcripts in H441 or H820 cells, the conditioned medium of LPS-treated RAW264.7 cells decreased SFTPB transcripts in H441 and H820 cells, and inhibited SFTPB promoter activity in H441 cells. In the presence of neutralizing anti-tumor necrosis factor (TNF) antibodies, the conditioned medium of LPS-treated RAW264.7 cells did not inhibit SFTPB promoter activity. In H441 cells treated with recombinant TNF protein, SFTPB transcripts decreased, whereas CEBPB transcripts increased and the transient coexpression of CEBPB decreased SFTPB promoter activity. Further, CEBPB short, interfering RNA increased basal SFTPB transcripts and countered the decrease of SFTPB transcripts by TNF. Together, these findings suggest that macrophages participate in the repression of SFTPB expression by LPS, and that macrophage-released cytokines (including TNF) regulate the transcription factor CEBPB, which can function as a downstream transcriptional repressor of SFTPB gene expression in pulmonary epithelial cells.

Atmospheric oxygen inhibits growth and differentiation of marrow-derived mouse mesenchymal stem cells via a p53-dependent mechanism: implications for long-term culture expansion.

Large scale expansion of human mesenchymal stem cells (MSCs) is routinely performed for clinical therapy. In contrast, developing protocols for large scale expansion of primary mouse MSCs has been more difficult due to unique aspects of rodent biology. Currently, established methods to isolate mouse MSCs select for rapidly dividing subpopulations that emerge from bone marrow cultures following long-term (months) expansion in atmospheric oxygen. Herein, we demonstrate that exposure to atmospheric oxygen rapidly induced p53, TOP2A, and BCL2-associated X protein (BAX) expression and mitochondrial reactive oxygen species (ROS) generation in primary mouse MSCs resulting in oxidative stress, reduced cell viability, and inhibition of cell proliferation. Alternatively, procurement and culture in 5% oxygen supported more prolific expansion of the CD45(-ve) /CD44(+ve) cell fraction in marrow, produced increased MSC yields following immunodepletion, and supported sustained MSC growth resulting in a 2,300-fold increase in cumulative cell yield by fourth passage. MSCs cultured in 5% oxygen also exhibited enhanced trilineage differentiation. The oxygen-induced stress response was dependent upon p53 since siRNA-mediated knockdown of p53 in wild-type cells or exposure of p53(-/-) MSCs to atmospheric oxygen failed to induce ROS generation, reduce viability, or arrest cell growth. These data indicate that long-term culture expansion of mouse MSCs in atmospheric oxygen selects for clones with absent or impaired p53 function, which allows cells to escape oxygen-induced growth inhibition. In contrast, expansion in 5% oxygen generates large numbers of primary mouse MSCs that retain sensitivity to atmospheric oxygen, and therefore a functional p53 protein, even after long-term expansion in vitro.