BackgroundAltered hypothalamo-pituitary-adrenal (HPA) axis activity may be accompanied by a modulation of pain sensitivity. In a model of neuropathic pain (chronic constriction injury, CCI) we investigated the onset and maintenance of mechanical allodynia/hyperalgesia and the expression of biochemical mediators potentially involved in spinal cell modulation in two rat strains displaying either hypo- (Lewis-LEW) or hyper- (Fischer 344-FIS) reactivity of the HPA axis.ResultsMechanical pain thresholds and plasmatic corticosterone levels were assessed before and during periods of 4 or 21 days following CCI surgery. At the end of the respective protocols, the mRNA expression of glial cell markers (GFAP and Iba1) and glutamate transporters (EAAT3 and EAAT2) were examined. We observed a correlation between the HPA axis reactivity and the pain behavior but not as commonly described in the literature; LEW rats seemed to be less sensitive than FIS from 4 to 14 days after the CCI surgery when looking at the mechanical allodynia/hyperalgesia. However, the biochemical spinal markers expression we observed is conflicting.ConclusionWe did not find a specific causal relation between the pain behavior and the glial cell activation or the expression of the glutamate transporters, suggesting that the interaction between the HPA axis and the spinal activation pattern is more complex in a context of neuropathic pain.

Abstract. Peroxisome proliferator-activated receptor Á (PPARÁ) is a member of the nuclear hormone receptor family. In colon, this transcription factor is involved in differentiation of absorptive cells. PPARÁ participates also in colon carcinogenesis and cancer progression. Two isoforms, namely PPARÁ1 and PPARÁ2, have been described. Recently, new PPARÁ1 transcripts whose translation raises PPARÁ1 protein have been characterised. They differ from each other by combination of untranslated exons localised in the 5' UTR of the PPARG gene. Here, we studied whether such a diversity of PPARÁ transcripts occurs in human colon cell models. Based on bioinformatic analysis, putative untranslated exons were identified in the human PPARG gene. By RT-PCR analysis, we have demonstrated that several of these untranslated exons are included in PPARÁ transcripts from colon-derived cell lines or in those derived from other tissue. Using HT-29 cells, changes in PPARÁ1 mRNA levels were observed after treatment with PPARÁ agonists such as pioglitazone and troglitazone. These modifications correlated with particular PPARÁ transcripts excluding the untranslated exon A2. HT-29 cells treatment with actinomycin D or cycloheximide showed that the presence of PPARÁ mRNA including exon A2 was dependent on de novo protein synthesis. We concluded that diverse PPARÁ1 mRNA exist in colorectal cells. Levels of PPARÁ1 transcript varied according to the phenotype of colon cell model used. We suggest that regulation of PPARÁ1 mRNA levels could be dependent in part on the composition of untranslated exon(s) in the 5' UTR of PPARÁ1 mRNA. IntroductionPeroxisome proliferator activated receptors (PPAR) belong to the nuclear hormone receptor superfamily (1). There are three isotypes named PPAR·, PPARß/‰ and PPARÁ (2). These nuclear receptors act as heterodimers with the 9-cis retinoic acid receptor and bind to a specific DNA sequence, the peroxisome proliferator response element, a direct repeat of the 5'-AGGTCA-3' sequence spaced by one base (3,4). After ligand activation, the heterodimer complex regulates the transcription of specific genes involved in several physiological functions (2). In colon, PPARÁ is implicated in differentiation of absorptive cells (5), in carcinogenesis or tumour progression even though contradictory results have been obtained in murine and human models (6).The PPARÁ gene is localised to chromosome 3, band 3p25 (7). The open reading frame consists of exons E1-E6 which encode the different domains of the protein. In human, two PPARÁ isoforms have been identified and referred to as PPARÁ1 and PPARÁ2 (7,8). PPARÁ2 differs from PPARÁ1 by an additional 28 amino acid NH2-terminal sequence (8). The 5' UTR region of PPARÁ transcripts, raising PPARÁ1 and -2 proteins, is highly variable and three exons termed A1, A2 and B have been described (9,10). Due to different promoter usage and alternative splicing, two other PPARÁ transcripts have been identified and they have been referred to as PPARÁ3 and -Á4 (10,11). PPARÁ1 mRNA consists of A...

Abstract. Peroxisome proliferator-activated receptor-γ (PPARγ) belongs to the nuclear hormone receptor family. This receptor is implicated in colon cell differentiation and in colon cancer. Receptor activation by specific agonists has been shown to protect against colon cancer progression. PPARγ protein content within cells is modulated by several mechanisms, including proteasome degradation, activation of Wnt signalling pathways and presence of fermentation products such as butyrate. Herein, we investigated the impact of L-glutamine on PPARγ expression during the differentiation of Caco-2 cells grown in medium containing dialyzed fetal calf serum supplemented or not with L-glutamine. Using RT-PCR and Western blotting, we demonstrated that PPARγ expression was decreased when L-glutamine was added to the medium. Using immunohistochemistry, we demonstrated that PPARγ immunostaining was mainly found in cytoplasm when cells were cultured with L-glutamine while it was found in nuclei and cytoplasm when cells were grown without the addition of L-glutamine. Supershift retardation assays demonstrated a decrease of PPARγ binding onto consensus peroxisome proliferator response element. We concluded that L-glutamine modulated PPARγ expression in Caco-2 cells.

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