α-Synuclein mRNA and soluble α-synuclein protein levels in post-mortem brain from patients with Parkinson's disease, dementia with Lewy bodies, and Alzheimer's disease.

α-Synuclein is a neuronal protein implicated in the etiology of Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Whilst increased α-synuclein expression due to gene duplication or triplication can cause familial PD, previous studies of α-synuclein levels in idiopathic disease have produced conflicting data. We quantified α-synuclein mRNA and soluble protein in five human post-mortem brain regions from four groups of individuals with PD, DLB, Alzheimer's disease (AD) and matched controls. α-Synuclein mRNA levels, measured using quantitative real-time PCR, did not differ significantly between groups in any brain regions examined. In contrast, levels of soluble α-synuclein protein, measured by ELISA, were significantly lower in 4 of the 5 regions for patients with DLB, and in 2 of the 5 regions for patients with PD, compared to controls. Soluble α-synuclein protein levels were not significantly different in the AD patients, compared to controls, in 4 of the 5 regions. This study indicates that although levels of soluble α-synuclein protein are lower in DLB and PD, there is no evidence for a corresponding decrease in α-synuclein mRNA levels. This might result from altered translation, or removal of α-synuclein protein from a soluble detectable state, either by turnover or conversion to an insoluble form.

Zinc transporter mRNA levels in Alzheimer's disease postmortem brain.

Zinc (Zn2+) is concentrated into pre-synaptic vesicles and co-released with neurotransmitter at some synapses. Zn2+ can accelerate assembly of the amyloid-ß peptides (Aß) and tau protein central to the neuropathological changes found in Alzheimer's disease (AD). Altered protein levels of the membrane Zn2+ transporters ZnT1, ZnT4, and ZnT6 have been reported in AD postmortem brain tissue. The present study analyzed mRNA levels of five established (LIV1, ZIP1, ZnT1, ZnT4, and ZnT6) and one potential (PRNP) Zn2+ transporter in human postmortem brain tissue from Braak-staged individuals with AD and controls using quantitative real-time PCR. Four cortical regions (middle temporal gyrus, superior occipital gyrus, superior parietal gyrus, and superior frontal gyrus) and cerebellum were examined. PRNP mRNA levels were decreased by ∼30% in all four cortical regions examined in AD patients, but unchanged in the cerebellum. In contrast, some increases in mRNA levels of the other more established Zn2+ transporters (LIV1, ZIP1, ZnT1, ZnT6) were found in AD cortex. The ratios of the mRNA levels of LIV1, ZIP1, ZnT1, ZnT4, and ZnT6/mRNA level of neuron specific enolase increased significantly as the disease progressed and Braak stage increased. Significant correlations were also identified between mRNA levels of several of the Zn2+ transporters investigated. These expression changes could either reflect or cause the altered cortical Zn2+ distribution in AD, potentially increasing the likelihood of interactions between Zn2+ and Aß or tau protein.

BACE1 mRNA expression in Alzheimer's disease postmortem brain tissue.

ß-site AßPP cleaving enzyme 1 (BACE1) catalyses the rate-limiting step for production of amyloid-ß (Aß) peptides, involved in the pathological cascade underlying Alzheimer's disease (AD). Elevated BACE1 protein levels and activity have been reported in AD postmortem brains. Our study explored whether this was due to elevated BACE1 mRNA expression. RNA was prepared from five brain regions in three study groups: controls, individuals with AD, and another neurodegenerative disease group affected by either Parkinson's disease (PD) or dementia with Lewy bodies (DLB). BACE1 mRNA levels were measured using quantitative realtime PCR (qPCR) and analyzed by qbasePLUS using validated stably-expressed reference genes. Expression of glial and neuronal markers (glial fibrillary acidic protein (GFAP) and neuron-specific enolase (NSE), respectively) were also analyzed to quantify the changing activities of these cell populations in the tissue. BACE1 mRNA levels were significantly elevated in medial temporal and superior parietal gyri, compared to the PD/DLB and/or control groups. Superior frontal gryus BACE1 mRNA levels were significantly increased in the PD/DLB group, compared to AD and control groups. For the AD group, BACE1 mRNA changes were analyzed in the context of the reduced NSE mRNA, and strongly increased GFAP mRNA levels apparent as AD progressed (indicated by Braak stage). This analysis suggested that increased BACE1 mRNA expression in remaining neuronal cells may contribute to the increased BACE1 protein levels and activity found in brain regions affected by AD.

ZnT3 mRNA levels are reduced in Alzheimer's disease post-mortem brain.

BACKGROUND: ZnT3 is a membrane Zn(2+ )transporter that is responsible for concentrating Zn(2+ )into neuronal presynaptic vesicles. Zn(2+ )homeostasis in the brain is relevant to Alzheimer's disease (AD) because Zn(2+ )released during neurotransmission may bind to Abeta peptides, accelerating the assembly of Abeta into oligomers which have been shown to impair synaptic function. RESULTS: We quantified ZnT3 mRNA levels in Braak-staged human post mortem (pm) brain tissue from medial temporal gyrus, superior occipital gyrus, superior parietal gyrus, superior frontal gyrus and cerebellum from individuals with AD (n = 28), and matched controls (n = 5) using quantitative real-time PCR. ZnT3 mRNA levels were significantly decreased in all four cortical regions examined in the AD patients, to 45-60% of control levels. This reduction was already apparent at Braak stage 4 in most cortical regions examined. Quantification of neuronal and glial-specific markers in the same samples (neuron-specific enolase, NSE; and glial fibrillary acidic protein, GFAP) indicated that loss of cortical ZnT3 expression was more pronounced, and occurred prior to, significant loss of NSE expression in the tissue. Significant increases in cortical GFAP expression were apparent as the disease progressed. No gene expression changes were observed in the cerebellum, which is relatively spared of AD neuropathology. CONCLUSIONS: This first study to quantify ZnT3 mRNA levels in human pm brain tissue from individuals with AD and controls has revealed a significant loss of ZnT3 expression in cortical regions, suggesting that neuronal cells in particular show reduced expression of ZnT3 mRNA in the disease. This suggests that altered neuronal Zn(2+ )handling may be an early event in AD pathogenesis.