Neuroprotective effects of aldehyde dehydrogenase 2 activation in rotenone-induced cellular and animal models of parkinsonism.

Many studies have shown that mitochondrial aldehyde dehydrogenase 2 (ALDH2) functions as a cellular protector against oxidative stress by detoxification of cytotoxic aldehydes. Within dopaminergic neurons, dopamine is metabolized by monoamine oxidase to yield 3,4-dihydroxyphenylacetaldehyde (DOPAL) then converts to a less toxic acid product by ALDH. The highly toxic and reactive DOPAL has been hypothesized to contribute to the selective neurodegeneration in Parkinson's disease (PD). In this study, we investigated the neuroprotective mechanism and therapeutic effect of ALDH2 in rotenone models for parkinsonism. Overexpression of wild-type ALDH2 gene, but not the enzymatically deficient mutant ALDH2*2 (E504K), reduced rotenone-induced cell death. Application of a potent activator of ALDH2, Alda-1, was effective in protecting against rotenone-induced apoptotic cell death in both SH-SY5Y cells and primary cultured substantia nigra (SN) dopaminergic neurons. In addition, intraperitoneal administration of Alda-1 significantly reduced rotenone- or MPTP-induced death of SN tyrosine hydroxylase (TH)-positive dopaminergic neurons. The attenuation of rotenone-induced apoptosis by Alda-1 resulted from decreasing ROS accumulation, reversal of mitochondrial membrane potential depolarization, and inhibition of activation of proteins related to mitochondrial apoptotic pathway. The present study demonstrates that ALDH2 plays a crucial role in maintaining normal mitochondrial function to protect against neurotoxicity and that Alda-1 is effective in ameliorating mitochondrial dysfunction and inhibiting mitochondria-mediated apoptotic pathway. These results indicate that ALDH2 activation could be a neuroprotective therapy for PD.

Polyglutamine-expanded ataxin-3 impairs long-term depression in Purkinje neurons of SCA3 transgenic mouse by inhibiting HAT and impairing histone acetylation.

Our previous study using a transgenic mouse model of spinocerebellar ataxia type 3 (SCA3) reported that disease-causing ataxin-3-Q79 caused cerebellar malfunction by inducing transcriptional downregulation. Long-term depression (LTD) of parallel fiber-Purkinje neuron glutamatergic transmission is believed to be a cellular mechanism for motor learning and motor coordination in the cerebellum. Downregulated mRNA expression of calcineurin B, IP3-R1, myosin Va and PLC ß4, which are required for the induction of cerebellar LTD, led to an impairment of LTD induction in Purkinje neurons of SCA3 transgenic mouse. Our study suggested that ataxin-3-Q79 caused hypoacetylation of cerebellar histone H3 or H4 by inhibiting the activity of histone acetyltransferase (HAT) without affecting the activity of histone deacetylase (HDAC). Consistent with the hypothesis that hypoacetylated H3 or H4 histone associated with promoter regions of downregulated genes is the molecular mechanism underlying ataxin-3-Q79-induced transcriptional repression, chromatin immunoprecipitation-quantitative real-time PCR analysis showed hypoacetylation of H3 or H4 histone associated with the proximal promoter of downregulated calcineurin B, IP3-R1, myosin Va or PLC ß4 gene in the cerebellum of SCA3 mouse. HDAC inhibitor sodium butyrate reversed ataxin-3-Q79-induced hypoacetylation of histone H3 or H4 associated with the proximal promoter of calcineurin B, IP3-R1, myosin Va or PLC ß4 gene. Sodium butyrate also prevented ataxin-3-Q79-induced impairment of LTD induction in Purkinje neurons of SCA3 mice. Our results suggest that polyglutamine-expanded ataxin-3-Q79 impairs HAT activity, leading to histone hypoacetylation, downregulated expression of cerebellar genes required for LTD induction and impaired induction of cerebellar LTD in the SCA3 transgenic mouse.

(G2019S) LRRK2 causes early-phase dysfunction of SNpc dopaminergic neurons and impairment of corticostriatal long-term depression in the PD transgenic mouse.

Twelve- to sixteen-month-old (G2019S) LRRK2 transgenic mice prepared by us displayed progressive neuronal death of substantia nigra pars compacta (SNpc) dopaminergic cells. In the present study, we hypothesized that prior to a late-phase death of SNpc dopaminergic neurons, (G2019S) LRRK2 also causes an early-phase neuronal dysfunction of SNpc dopaminergic cells in the (G2019S) LRRK2 mouse. Eight to nine-month-old (G2019S) LRRK2 transgenic mice exhibited the symptom of hypoactivity in the absence of the degeneration of SNpc dopaminergic neurons or nigrostriatal dopaminergic terminals. Whole-cell current-clamp recordings of SNpc dopaminergic cells in brain slices demonstrated a significant decrease in spontaneous firing frequency of SNpc dopaminergic neurons of 8-month-old (G2019S) LRRK2 mice. Carbon fiber electrode amperometry recording using striatal slices showed that (G2019S) LRRK2 transgenic mice at the age of 8 to 9months display an impaired evoked dopamine release in the dorsolateral striatum. Normal nigrostriatal dopaminergic transmission is required for the induction of long-term synaptic plasticity expressed at corticostriatal glutamatergic synapses of striatal medium spiny neurons. Whole-cell voltage-clamp recordings showed that in contrast to medium spiny neurons of 8 to 9-month-old wild-type mice, high-frequency stimulation of corticostriatal afferents failed to induce long-term depression (LTD) of corticostriatal EPSCs in medium spiny neurons of (G2019S) LRRK2 mice at the same age. Our study provides the evidence that mutant (G2019S) LRRK2 causes early-phase dysfunctions of SNpc dopaminergic neurons, including a decrease in spontaneous firing rate and a reduction in evoked dopamine release, and impairment of corticostriatal LTD in the (G2019S) LRRK2 transgenic mouse.