Abstract
BackgroundThe kynurenine pathway (KP) is the main route of tryptophan degradation in the human body and generates several neuroactive and immunomodulatory metabolites. Altered levels of KP-metabolites have been observed in neuropsychiatric and neurodegenerative disorders as well as in patients with affective disorders. The purpose of the present study was to investigate if skin derived human fibroblasts are useful for studies of expression of enzymes in the KP.MethodsFibroblast cultures were established from cutaneous biopsies taken from the arm of consenting volunteers. Such cultures were subsequently treated with interferon (IFN)-γ 200 U/ml and/or tumor necrosis factor (TNF)-α, 100 U/ml for 48 hours in serum-free medium. Levels of transcripts encoding different enzymes were determined by real-time PCR and levels of kynurenic acid (KYNA) were determined by HPLC.ResultsAt base-line all cultures harbored detectable levels of transcripts encoding KP enzymes, albeit with considerable variation across individuals. Following cytokine treatment, considerable changes in many of the transcripts investigated were observed. For example, increases in the abundance of transcripts encoding indoleamine 2,3-dioxygenase, kynureninase or 3-hydroxyanthranilic acid oxygenase and decreases in the levels of transcripts encoding tryptophan 2,3-dioxygenase, kynurenine aminotransferases or quinolinic acid phosphoribosyltransferase were observed following IFN-γ and TNF-α treatment. Finally, the fibroblast cultures released detectable levels of KYNA in the cell culture medium at base-line conditions, which were increased after IFN-γ, but not TNF-α, treatments.ConclusionsAll of the investigated genes encoding KP enzymes were expressed in human fibroblasts. Expression of many of these appeared to be regulated in response to cytokine treatment as previously reported for other cell types. Fibroblast cultures, thus, appear to be useful for studies of disease-related abnormalities in the kynurenine pathway of tryptophan degradation.
Highlights
The kynurenine pathway (KP) is the main route of tryptophan degradation in the human body and generates several neuroactive and immunomodulatory metabolites [1,2]
While human fibroblasts have previously been employed for studying the role of IDO1 in controlling experimental infections [24,25,26], expression or functionality of genes encoding downstream enzymes in the KP have not been investigated in such cells
The levels of expression varied considerably across the different genes, with transcripts encoding IDO1 detected at the lowest level and those encoding KAT3 detected at the highest level
Summary
The kynurenine pathway (KP) is the main route of tryptophan degradation in the human body and generates several neuroactive and immunomodulatory metabolites [1,2]. The enzyme indoleamine 2,3dioxygenase (IDO1) is the first and rate-limiting step of this pathway and is highly induced by the pro-inflammatory cytokine interferon (IFN)-g [22,23]. It is not clear if pro-inflammatory cytokines affect expression of genes encoding other enzymes of the KP. While human fibroblasts have previously been employed for studying the role of IDO1 in controlling experimental infections [24,25,26], expression or functionality of genes encoding downstream enzymes in the KP have not been investigated in such cells.
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