Involvement of PPARs in the regulation of brain CYP2D by growth hormone

摘要

OBJECTIVE CYP2D is one of the most abundant subfamily of CYPs in the brain, especially in the cerebellum. Brain CYP2D is responsible for the metabolism of endogenous neurotransmitters such as tyramine and serotonin. Our previous studies have shown brain CYP2D can be regulated by exogenous and endogenous substances with tissue- specificity. The purpose of this study is to examine the effects of cerebral CYP2D on the mice behavior and the regulatory mechanism of brain CYP2D by growth hormone. METHODS Mice received the stereotaxic injection with CYP2D inhibitor quinine in deep cerebellar nuclei of cerebellum. The animals were tested with rotarod apparatus, balance beam, water maze, elevated plus maze and open field. The changes in CYP2D22, PPARαand PPARγ in brain regions and liver were assayed in male growth hormone receptor knockout mice, SH-SY5Y cells and HepG2 cells. RESULTS The inhibition of cerebellum CYP2D significantly affected the spatial learning and exploring ability of mice. Compared with WT mice, CYP2D expression was lower in brain regions from GHR(-/- ) male mice; however, hepatic CYP2D level was similar. Pulsatile GH decreased PPARα mRNA level, and increased mRNA levels of CYP2D6 and PPARα in SH- SY5Y cells. In HepG2 cells, pulsatile GH resulted in decreases in PPARα and PPARγ mRNA levels, but not CYP2D6. PPARα inhibitor induced CYP2D6 mRNA and protein by 1.32-fold and 1.43-fold in SH-SY5Y cells. PPARγ inhibitor decreased CYP2D6 mRNA and protein by 74.76% and 40.93%. PPARα agonist decreased the level of CYP2D22 mRNA in liver and cerebellum, while PPARγ agonist rosiglitazone resulted in diametrically increases. The luciferase assay showed that PPARγ actived the CYP2D6 gene promoter while PPARα inhibited its function. Pulsatile GH declined the binding of PPARα with CYP2D6 promoter by 40%, promoted the binding of PPARγ with CYP2D6 promoter by approximate 60%. The levels of brain and liver PPARα expression in male GHR(-/- ) mice is obviously higher than those in WT mice. The level of PPARγ in male GHR(-/- ) mice was decreased in the frontal cortex and hippocampus, while remained stable in the cerebellum and striatum; meanwhile, PPARγ was increased in the liver. CONCLUSION Brain CYP2D may be involved in learning and memory functions of central system. Masculine GH secretion altered the PPARs expression and the binding of PPARs to CYP2D promoter, leading to the elevated brain CYP2D in a tissue- specific manner. Growth hormone may specifically alter the metabolic and synthetic of important endogenous substances in the central nervous system (such as serotonin) through the specific regulation of brain CYP2D expression.