Eosinophils have been implicated as playing a major role in allergic airway responses. However, the importance of these cells to the development of this disease has remained ambiguous despite many studies, partly because of lack of appropriate model systems. In this study, using transgenic murine models, we more clearly delineate a role for eosinophils in asthma. We report that, in contrast to results obtained on a BALB/c background, eosinophil-defi cient C57BL/6 ⌬ dblGATA mice (eosinophil-null mice via the ⌬ DblGATA1 mutation) have reduced airway hyperresponsiveness, and cytokine production of interleukin (IL)-4, -5, and -13 in ovalbumin-induced allergic airway infl ammation. This was caused by reduced T cell recruitment into the lung, as these mouse lungs had reduced expression of CCL7/MCP-3, CC11/eotaxin-1, and CCL24/eotaxin-2. Transferring eosinophils into these eosinophildefi cient mice and, more importantly, delivery of CCL11/eotaxin-1 into the lung during the development of this disease rescued lung T cell infi ltration and airway infl ammation when delivered together with allergen. These studies indicate that on the C57BL/6 background, eosinophils are integral to the development of airway allergic responses by modulating chemokine and/or cytokine production in the lung, leading to T cell recruitment.

Peroxisome proliferator-activated receptor (PPAR)beta/delta-null mice exhibit enhanced tumorigenesis in a two-stage chemical carcinogenesis model as compared with wild-type mice. Previous work showed that ligand activation of PPARbeta/delta induces terminal differentiation and inhibits proliferation of primary keratinocytes, and this effect does not occur in the absence of PPARbeta/delta expression. In the present studies, the effect of ligand activation of PPARbeta/delta on skin tumorigenesis was examined using both in vivo and ex vivo skin carcinogenesis models. Inhibition of chemically induced skin tumorigenesis was observed in wild-type mice administered GW0742, and this effect was likely the result of ligand-induced terminal differentiation and inhibition of replicative DNA synthesis. These effects were not found in similarly treated PPARbeta/delta-null mice. Ligand activation of PPARbeta/delta also inhibited cell proliferation and induced terminal differentiation in initiated/neoplastic keratinocyte cell lines representing different stages of skin carcinogenesis. These studies suggest that topical administration of PPARbeta/delta ligands may be useful as both a chemopreventive and/or a chemotherapeutic approach to inhibit skin cancer.

The effect of activation and over-expression of the nuclear receptor PPARβ/δ in human MDA-MB-231 (ER−) and MCF7 (ER+) breast cancer cell lines was examined. Target gene induction by ligand activation of PPARβ/δ was increased by over-expression of PPARβ/δ compared to controls. Over-expression of PPARβ/δ caused a decrease in cell proliferation in MCF7 and MDA-MB-231 cells compared to controls while ligand activation of PPARβ/δ further inhibited proliferation of MCF7 but not MDA-MB-231 cells. Over-expression and/or ligand activation of PPARβ/δ in MDA-MB-231 or MCF7 cells had no effect on experimental apoptosis. Decreased clonogenicity was observed in both MDA-MB-231 and MCF7 over-expressing PPARβ/δ in response to ligand activation of PPARβ/δ as compared to controls. Ectopic xenografts developed from MDA-MB-231 and MCF7 cells over-expressing PPARβ/δ were significantly smaller and ligand activation of PPARβ/δ caused an even greater reduction in tumor volume as compared to controls. Interestingly, the decrease in MDA-MB-231 tumor size after over-expressing PPARβ/δ and ligand activation of PPARβ/δ correlated with increased necrosis. These data show that ligand activation and/or over-expression of PPARβ/δ in two human breast cancer cell lines inhibits relative breast cancer tumorigenicity and provide further support for the development of ligands for PPARβ/δ to specifically inhibit breast carcinogenesis. These new cell-based models will be invaluable tools for delineating the role of PPARβ/δ in breast cancer and evaluating the effects of PPARβ/δ agonists.

Peroxisome proliferator-activated receptor (PPAR) beta/delta-null mice exhibit exacerbated hepatotoxicity in response to administration of carbon tetrachloride (CCl(4)). To determine whether ligand activation of the receptor protects against chemical toxicity in the liver, wild-type and PPARbeta/delta-null mice were administered CCl(4) with or without coadministration of the highly specific PPARbeta/delta ligand GW0742. Biomarkers of liver toxicity, including serum alanine aminotransferase (ALT) and hepatic tumor necrosis factor (TNF) alpha mRNA, were significantly higher in CCl(4)-treated PPARbeta/delta-null mice compared to wild-type mice. Hepatic expression of TNF-like weak inducer of apoptosis receptor (TWEAKr) and S100 calcium-binding protein A6 (S100A6/calcyclin), genes involved in nuclear factor kappa B signaling, was higher in the CCl(4)-treated PPARbeta/delta-null mice compared to wild-type mice. GW0742 treatment resulted in reduced serum ALT concentration and lower expression of CCl(4)-induced TNF-alpha, S100A6, monocyte chemoattractant protein-1 (MCP1), and TWEAKr in wild-type mice, and these effects were not observed in PPARbeta/delta-null mice. Expression of TNF-alpha was higher in PPARbeta/delta-null primary hepatocytes in response to interleukin-1beta treatment compared to wild-type hepatocytes, but GW0742 did not significantly modulate TNF-alpha expression in hepatocytes from either genotype. While PPARbeta/delta-null hepatic stellate exhibited higher rates of proliferation compared to wild-type cells, GW0742 did not affect alpha-smooth muscle actin expression in these cells. Combined, these findings demonstrate that ligand activation of PPARbeta/delta protects against chemically induced hepatotoxicity by downregulating expression of proinflammatory genes. Hepatocytes and hepatic stellate cells do not appear to directly mediate the inhibitory effects of ligand activation of PPARbeta/delta in liver, suggesting the involvement of paracrine and autocrine events mediated by hepatic cells.