PPARalpha downregulates airway inflammation induced by lipopolysaccharide in the mouse

BACKGROUND: Inflammation is a hallmark of acute lung injury and chronic airway diseases. In chronic airway diseases, it is associated with profound tissue remodeling. Peroxisome proliferator-activated receptor-alpha (PPARalpha) is a ligand-activated transcription factor, that belongs to the nuclear receptor family. Agonists for PPARalpha have been recently shown to reduce lipopolysaccharide (LPS)- and cytokine-induced secretion of matrix metalloproteinase-9 (MMP-9) in human monocytes and rat mesangial cells, suggesting that PPARalpha may play a beneficial role in inflammation and tissue remodeling. METHODS: We have investigated the role of PPARalpha in a mouse model of LPS-induced airway inflammation characterized by neutrophil and macrophage infiltration, by production of the chemoattractants, tumor necrosis factor-alpha (TNF-alpha), keratinocyte derived-chemokine (KC), macrophage inflammatory protein-2 (MIP-2) and monocyte chemoattractant protein-1 (MCP-1), and by increased MMP-2 and MMP-9 activity in bronchoalveolar lavage fluid (BALF). The role of PPARalpha in this model was studied using both PPARalpha-deficient mice and mice treated with the PPARalpha activator, fenofibrate. RESULTS: Upon intranasal exposure to LPS, PPARalpha-/- mice exhibited greater neutrophil and macrophage number in BALF, as well as increased levels of TNF-alpha, KC, MIP-2 and MCP-1, when compared to PPARalpha+/+ mice. PPARalpha-/- mice also displayed enhanced MMP-9 activity. Conversely, fenofibrate (0.15 to 15 mg/day) dose-dependently reduced the increase in neutrophil and macrophage number induced by LPS in wild-type mice. In animals treated with 15 mg/day fenofibrate, this effect was associated with a reduction in TNF-alpha, KC, MIP-2 and MCP-1 levels, as well as in MMP-2 and MMP-9 activity. PPARalpha-/- mice treated with 15 mg/day fenofibrate failed to exhibit decreased airway inflammatory cell infiltrate, demonstrating that PPARalpha mediates the anti-inflammatory effect of fenofibrate. CONCLUSION: Using both genetic and pharmacological approaches, our data clearly show that PPARalpha downregulates cell infiltration, chemoattractant production and enhanced MMP activity triggered by LPS in mouse lung. This suggests that PPARalpha activation may have a beneficial effect in acute or chronic inflammatory airway disorders involving neutrophils and macrophages.

The organization, promoter analysis, and expression of the human PPARgamma gene

Johan Auwerx, Kristina Schoonjans

PPARgamma is a member of the PPAR subfamily of nuclear receptors. In this work, the structure of the human PPARgamma cDNA and gene was determined, and its promoters and tissue-specific expression were functionally characterized. Similar to the mouse, two PPAR isoforms, PPARgamma1 and PPARgamma2, were detected in man. The relative expression of human PPARgamma was studied by a newly developed and sensitive reverse transcriptase-competitive polymerase chain reaction method, which allowed us to distinguish between PPARgamma1 and gamma2 mRNA. In all tissues analyzed, PPARgamma2 was much less abundant than PPARgamma1. Adipose tissue and large intestine have the highest levels of PPARgamma mRNA; kidney, liver, and small intestine have intermediate levels; whereas PPARgamma is barely detectable in muscle. This high level expression of PPARgamma in colon warrants further study in view of the well established role of fatty acid and arachidonic acid derivatives in colonic disease. Similarly as mouse PPARgammas, the human PPARgammas are activated by thiazolidinediones and prostaglandin J and bind with high affinity to a PPRE. The human PPARgamma gene has nine exons and extends over more than 100 kilobases of genomic DNA. Alternate transcription start sites and alternate splicing generate the PPARgamma1 and PPARgamma2 mRNAs, which differ at their 5'-ends. PPARgamma1 is encoded by eight exons, and PPARgamma2 is encoded by seven exons. The 5'-untranslated sequence of PPARgamma1 is comprised of exons A1 and A2, whereas that of PPARgamma2 plus the additional PPARgamma2-specific N-terminal amino acids are encoded by exon B, located between exons A2 and A1. The remaining six exons, termed 1 to 6, are common to the PPARgamma1 and gamma2. Knowledge of the gene structure will allow screening for PPARgamma mutations in humans with metabolic disorders, whereas knowledge of its expression pattern and factors regulating its expression could be of major importance in understanding its biology.

1997

SIRT2 Deficiency Modulates Macrophage Polarization and Susceptibility to Experimental Colitis

Johan Auwerx, Giuseppe Lo Sasso, Keir Joe Menzies, Adrienne Joëlle Laurence Mottis, Alessia Perino, Alessandra Piersigilli, Kristina Schoonjans, Hiroyasu Yamamoto

Background: SIRT2 belongs to a highly conserved family of NAD(+)-dependent deacylases, consisting of seven members (SIRT1-SIRT7), which vary in subcellular localizations and have substrates ranging from histones to transcription factors and enzymes. Recently SIRT2 was revealed to play an important role in inflammation, directly binding, deacetylating, and inhibiting the p65 subunit of NF-kB. Methods: A Sirt2 deficient mouse line (Sirt2(-/-)) was generated by deleting exons 5-7, encoding part of the SIRT2 deacetylase domain, by homologous recombination. Age-and sex-matched Sirt2(-/-) and Sirt2(+/+) littermate mice were subjected to dextran sulfate sodium (DSS)-induced colitis and analyzed for colitis susceptibility. Results: Sirt2(-/-) mice displayed more severe clinical and histological manifestations after DSS colitis compared to wild type littermates. Notably, under basal condition, Sirt2 deficiency does not affect the basal phenotype and intestinal morphology Sirt2 deficiency, however, affects macrophage polarization, creating a pro-inflammatory milieu in the immune cells compartment. Conclusion: These data confirm a protective role for SIRT2 against the development of inflammatory processes, pointing out a potential role for this sirtuin as a suppressor of colitis. In fact, SIRT2 deletion promotes inflammatory responses by increasing NF-kappa B acetylation and by reducing the M2-associated anti-inflammatory pathway. Finally, we speculate that the activation of SIRT2 may be a potential approach for the treatment of inflammatory bowel disease.

Public Library of Science2014

The Transcription Factor Nfix Requires RhoA-ROCK1 Dependent Phagocytosis to Mediate Macrophage Skewing during Skeletal Muscle Regeneration

Giuliana Rossi

Macrophages (MPs) are immune cells which are crucial for tissue repair. In skeletal muscle regeneration, pro-inflammatory cells first infiltrate to promote myogenic cell proliferation, then they switch into an anti-inflammatory phenotype to sustain myogenic cells differentiation and myofiber formation. This phenotypical switch is induced by dead cell phagocytosis. We previously demonstrated that the transcription factor Nfix, a member of the nuclear factor I (Nfi) family, plays a pivotal role during muscle development, regeneration and in the progression of muscular dystrophies. Here, we show that Nfix is mainly expressed by anti-inflammatory macrophages. Upon acute injury, mice deleted for Nfix in myeloid line displayed a significant defect in the process of muscle regeneration. Indeed, Nfix is involved in the macrophage phenotypical switch and macrophages lacking Nfix failed to adopt an anti-inflammatory phenotype and interact with myogenic cells. Moreover, we demonstrated that phagocytosis induced by the inhibition of the RhoA-ROCK1 pathway leads to Nfix expression and, consequently, to acquisition of the anti-inflammatory phenotype. Our study identified Nfix as a link between RhoA-ROCK1-dependent phagocytosis and the MP phenotypical switch, thus establishing a new role for Nfix in macrophage biology for the resolution of inflammation and tissue repair.

2020

The organization, promoter analysis, and expression of the human PPARgamma gene

Johan Auwerx, Kristina Schoonjans

1997