In aged mice, the redox-regulated transcription factor nuclear factor-κB (NF-κB) becomes constitutively active in many tissues, as well as in cells of the hematopoietic system. This oxidative stress-induced activity promotes the production of a number of pro-inflammatory cytokines, which can contribute to the pathology of many disease states associated with aging. The administration to aged mice of agents capable of activating the α isoform of the peroxisome proliferator-activated receptor (PPARα) was found to restore the cellular redox balance, evidenced by a lowering of tissue lipid peroxidation, an elimination of constitutively active NF-κB, and a loss in spontaneous inflammatory cytokine production. Aged animals bearing a null mutation in PPARα failed to elicit these changes following treatment with PPARα activators, but remained responsive to vitamin E supplementation. Aged C57BL/6 mice were found to express reduced transcript levels of PPARα and the peroxisome-associated genes acyl-CoA oxidase and catalase. Supplementation of these aged mice with PPARα activators or with vitamin E caused elevations in these transcripts to levels seen in young animals. Our results suggest that PPARα and the genes under its control play a role in the evolution of oxidative stress excesses observed in aging.

Rationale: Tumor necrosis factor α (TNF-α) has been implicated as a key cytokine in many inflammatory lung diseases. These effects are currently unclear, because a transgenic mouse overexpressing TNF-α in the lung has been shown in separate studies to produce elements of both emphysema and pulmonary fibrosis. Objectives: We sought to elucidate the phenotypic effects of TNF-α overexpression in a mouse model. Measurements: We established the phenotype by measuring lung impedance and thoracic gas volume, and using micro–computed tomography and histology. Main Results: We found that airways resistance in this mouse was not different to control mice, but that lung tissue dampening, elastance, and hysteresivity were significantly elevated. Major heterogeneous abnormalities of the parenchyma were also apparent in histologic sections and in micro–computed tomography images of the lung. These changes included airspace enlargement, loss of small airspaces, increased collagen, and thickened pleural septa. We also found significant increases in lung and chest cavity volumes in the TNF-α–overexpressing mice. Conclusions: We conclude that TNF-α overexpression causes pathologic changes consistent with both emphysema and pulmonary fibrosis combined with a general lung inflammation, and consequently does not model any single human disease. Our study thus confirms the pleiotropic effects of TNF-α, which has been implicated in multiple inflammatory disorders, and underscores the necessity of using a wide range of investigative techniques to link gene expression and phenotype in animal models of disease.

IL-1β is a cytokine critical to several inflammatory diseases in which pathogenic Th17 responses are implicated. Activation of the NLRP3 inflammasome by microbial and environmental stimuli can enable the caspase-1–dependent processing and secretion of IL-1β. The acute-phase protein serum amyloid A (SAA) is highly induced during inflammatory responses, wherein it participates in systemic modulation of innate and adaptive immune responses. Elevated levels of IL-1β, SAA, and IL-17 are present in subjects with severe allergic asthma, yet the mechanistic relationship among these mediators has yet to be identified. In this study, we demonstrate that Saa3 is expressed in the lungs of mice exposed to several mixed Th2/Th17-polarizing allergic sensitization regimens. SAA instillation into the lungs elicits robust TLR2-, MyD88-, and IL-1–dependent pulmonary neutrophilic inflammation. Furthermore, SAA drives production of IL-1α, IL-1β, IL-6, IL-23, and PGE₂, causes dendritic cell (DC) maturation, and requires TLR2, MyD88, and the NLRP3 inflammasome for secretion of IL-1β by DCs and macrophages. CD4⁺ T cells polyclonally stimulated in the presence of conditioned media from SAA-exposed DCs produced IL-17, and the capacity of polyclonally stimulated splenocytes to secrete IL-17 is dependent upon IL-1, TLR2, and the NLRP3 inflammasome. Additionally, in a model of allergic airway inflammation, administration of SAA to the lungs functions as an adjuvant to sensitize mice to inhaled OVA, resulting in leukocyte influx after Ag challenge and a predominance of IL-17 production from restimulated splenocytes that is dependent upon IL-1R signaling.

Bone marrow‐derived mesenchymal stromal cells (BMSCs) mitigate inflammation in mouse models of acute lung injury. However, specific mechanisms of BMSC actions on CD4 T lymphocyte‐mediated inflammation in vivo remain poorly understood. Limited data suggests promotion of Th2 phenotype in models of Th1‐mediated diseases. However, whether this might alleviate or worsen Th2‐mediated diseases such as allergic asthma is unknown. To ascertain the effects of systemic administration of BMSCs in a mouse model of Th2‐mediated allergic airways inflammation, ovalbumin (OVA)‐induced allergic airways inflammation was induced in wild‐type C57BL/6 and BALB/c mice as well as in interferon‐γ (IFNγ) receptor null mice. Effects of systemic administration during antigen sensitization of either syngeneic or allogeneic BMSC on airways hyperreactivity, lung inflammation, antigen‐specific CD4 T lymphocytes, and serum immunoglobulins were assessed. Both syngeneic and allogeneic BMSCs inhibited airways hyperreactivity and lung inflammation through a mechanism partly dependent on IFNγ. However, contrary to existing data, BMSCs did not affect antigen‐specific CD4 T lymphocyte proliferation but rather promoted Th1 phenotype in vivo as assessed by both OVA‐specific CD4 T lymphocyte cytokine production and OVA‐specific circulating immunoglobulins. BMSCs treated to prevent release of soluble mediators and a control cell population of primary dermal skin fibroblasts only partly mimicked the BMSC effects and in some cases worsened inflammation. In conclusion, BMSCs inhibit Th2‐mediated allergic airways inflammation by influencing antigen‐specific CD4 T lymphocyte differentiation. Promotion of a Th1 phenotype in antigen‐specific CD4 T lymphocytes by BMSCs is sufficient to inhibit Th2‐mediated allergic airways inflammation through an IFNγ‐dependent process. STEM CELLS 2011;29:1137–1148