Molecular Mechanism of Regulation of MTA1 Expression by Granulocyte Colony-stimulating Factor

Abstract

Parkinson disease (PD) is a neurodegenerative disorder with loss of dopaminergic neurons of the brain, which results in insufficient synthesis and action of dopamine. Metastasis-associated protein 1 (MTA1) is an upstream modulator of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis, and hence MTA1 plays a significant role in PD pathogenesis. To impart functional and clinical significance to MTA1, we analyzed MTA1 and TH levels in the substantia nigra region of a large cohort of human brain tissue samples by Western blotting, quantitative PCR, and immunohistochemistry. Our results showed that MTA1 and TH levels were significantly down-regulated in PD samples as compared with normal brain tissue. Correspondingly, immunohistochemistry analysis for MTA1 in substantia nigra sections revealed that 74.1% of the samples had a staining intensity of <6 in the PD samples as compared with controls, 25.9%, with an odds ratio of 8.54. Because of the clinical importance of MTA1 established in PD, we looked at agents to modulate MTA1 expression in neuronal cells, and granulocyte colony-stimulating factor (G-CSF) was chosen, due to its clinically proven neurogenic effects. Treatment of the human neuronal cell line KELLY and acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model with G-CSF showed significant induction of MTA1 and TH with rescue of phenotype in the mouse model. Interestingly, the observed induction of TH was compromised on silencing of MTA1. The underlying molecular mechanism of MTA1 induction by G-CSF was proved to be through induction of c-Fos and its recruitment to the MTA1 promoter. Parkinson disease (PD)4 is an idiopathic degenerative disorder of the central nervous system characterized by slow and decreased movement, pill-rolling tremor, and postural instability, and it is primarily caused by dopamine deficiency (1, 2). The rate-limiting enzyme for dopamine synthesis is tyrosine hydroxylase (TH) (3). Currently, there is no cure for PD, and patients are usually given drugs that provide symptomatic relief (4). Recently, it was shown that G-CSF enhances recovery in the mouse model of PD, and hence the G-CSF receptor might be a novel target for modifying the disease process in PD (5, 6). It is well documented that a consistent abnormality in PD is degeneration of dopaminergic neurons in SN leading to a reduction of striatal dopamine levels (7). TH catalyzes the formation of L-hydroxyphenylalanine, the rate-limiting step in the biosynthesis of dopamine. Thus, efficient treatment strategy for PD could be based on correcting or bypassing the TH enzyme deficiency or its downstream enzymes essential for catecholamine synthesis (8). For this, elucidation of the molecular mechanism of human TH gene regulation is very essential. Also, epigenetic profiling of the human TH promoter suggests that chromatin remodeling could have a significant impact in conferring tissue-specific gene expression of the human TH gene (9); however, its specific role in TH transcription remains poorly understood...

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