A chemical chaperone, sodium 4-phenylbutyric acid, attenuates the pathogenic potency in human α-synuclein A30P + A53T transgenic mice
Introduction
Parkinson's disease (PD) is one of the most common neurodegenerative disorders. The occurrence of PD is largely sporadic, although several families with Mendelian segregation of PD were reported. Thirteen chromosome loci have been linked to familial PD [1]. α-Synuclein (α-Syn) is the major component of Lewy bodies (LBs) and Lewy neuritis which are the hallmark lesions found in the brains with PD and other synucleinopathies [2]. Point mutations of the α-synuclein gene have definite pathological potency. Mutations (A30P, A53T and E46K) promote the oligomer formation and fibrillization of α-Syn [3]. These mutant α-synuclein gene products tend to aggregate resulting in the formation of LBs which has been thought to have neurotoxic effects. However, there are some reports that inclusion bodies like LBs are cytoprotective against neuronal cells [4], [5]. Although the physiological functions of α-Syn still remain unclear, misfolding and aggregation of α-Syn have definite causative effects for enhancing PD onset.
Molecular chaperones such as heat shock proteins (Hsps) are known to protect other proteins from misfoldings, resulting in a reduction in protein–protein aggregate formations and hence, providing cellular protections. Hsp70 can reduce the amount of misfolded and aggregated α-Syn species in vivo and in vitro, and protect neuronal cells from α-Syn-dependent neurotoxicity [6]. Hsp104 reduced the phosphorylation of α-Syn inclusions and prevented the nigrostriatal dopaminergic neurodegeneration induced by mutant α-Syn (A30P) [7].
Chemical chaperones are small molecules with common features that mimic the functions of molecular chaperones. Sodium 4-phenylbutyric acid (PBA), one of the chemical chaperones, is an orally bioavailable short-chain fatty acid used for the treatment of various diseases such as urea metabolism disorders [8], homozygous β-thalassemia [9], spinal muscular atrophy [10] and tumor [11]. It has been shown that PBA could exert significant neuroprotective effects in some mouse models of human diseases [12], [13], [14]. Furthermore, several studies have been reported that PBA is able to reverse the mislocalization and/or aggregation of proteins associated with human diseases and as well as to suppress endoplasmic reticulum (ER) stress [15], [16], [17], [18], [19], [20], [21].
In this study, we observed the clinico-pathological effects of PBA in transgenic mice expressing human α-synuclein with both A30P and A53T mutations (TgαSYN #8713: Tg) [22].
Section snippets
Preparation of sodium 4-phenylbutyric acid
4-Phenylbutyric acid (Sigma–Aldrich, St. Louis, MO) was converted into the water-soluble sodium salt for the purposes of this study. Briefly, sodium ethoxide was obtained by reaction of sodium metal (Nacalai Tesque, Inc., Osaka, Japan) and absolute ethanol. Then, an equal molarity of 4-phenylbutyric acid was added. After the reaction, residual ethanol was removed by a vacuum pump. The lyophilized PBA was stored in a desiccator until use. The purity of synthesized PBA was determined by 1H NMR
Permeability of PBA against the BBB was estimated using an in vitro model of BBB
BBB permeability coefficient of PBA was assessed using an in vitro model of the BBB. The permeability coefficients (cm/min) were estimated as 162.91 ± 21.02 × 10−3 for sodium PBA (n = 4 inserts), and 2.18 ± 0.43 × 10−3 for Na-F (n = 8 inserts) (data not shown).
Oral PBA administration improved bradykinesia and motor coordination
In both the pole test and the rotarod treadmill task, significant differences were observed at the start of the PBA treatment (3 months old) between non-Tg (15 mice) and Tg (30 mice) mice groups. However there was no significant difference between
Discussion
At present, there is no disease modifying therapy for PD. Here we investigated the possibility of PBA treatment as a disease modifying therapy for PD. At first, the permeability of PBA through the BBB was assessed using an in vitro model. The result showed PBA had more than 70 times the permeability of the control (Na-F) [26]. It has been shown that PBA could exert significant neuroprotective effects in mouse models of neurodegenerative diseases sach as Huntington's disease [13] and amyotrophic
Acknowledgements
The authors are grateful to Dr. Kenji Yamagata and Dr. Fumi Okabe for their technical assistance in the preparation of PBA. We are also grateful to Dr. Shinya Dohgu for technical assistance in measuring the BBB permeability of PBA.
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