Is tau a suitable therapeutical target in tauopathies?

The novel GLP-1/GIP analogue DA5-CH reduces tau phosphorylation and normalizes theta rhythm in the icv. STZ rat model of AD

INTRODUCTION

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease for which there is no cure. Recent studies have shown a close link between type 2 diabetes and AD, which suggested that drugs for type 2 diabetes may be effective for AD. GLP-1 and GIP are incretin hormones that can ameliorate diabetes.

METHODS

In the present study, we tested the novel dual GLP-1/GIP receptor agonist DA5-CH in the icv. streptozotocin (STZ)-induced insulin desensitization model of AD in rats to explore the protective effects of DA5-CH.

RESULTS

The results show that DA5-CH could reverse the STZ-induced working memory impairments in a Y-maze tests, and spatial memory impairments in the water maze task, and decrease the levels of phosphorylated tauS396 protein in the hippocampus. In EEG recordings, STZ treatment diminished the power of the theta band frequency. DA5-CH was able to increase the energy of theta band activity in the hippocampal CA1 region. The drug also increased the expression of synapse-related proteins in the hippocampus. After DA5-CH treatment, mitochondrial stress was alleviated as shown by the improved ratio of Bax/Bcl-2 in the hippocampus. Growth factor signaling was also normalized as shown by the increased level of the transcription factor P-CREBS133 . In addition, we were able to show that DA5-CH can cross the blood-brain barrier at an increased rate compared with other dual GLP-1/GIP or single GLP-1 receptor agonists.

CONCLUSION

Therefore, our results demonstrate that DA5-CH has neuroprotective effects in the STZ-induced animal model and that DA5-CH has potential to treat neurodegenerative disorders such as AD.

An experimental rat model of sporadic Alzheimer's disease and rescue of cognitive impairment with a neurotrophic peptide

Alzheimer's disease (AD) is multifactorial and, to date, no single cause of the sporadic form of this disease, which accounts for over 99% of the cases, has been established. In AD brain, protein phosphatase-2A (PP2A) activity is known to be compromised due to the cleavage and translocation of its potent endogenous inhibitor, I2PP2A, from the neuronal nucleus to the cytoplasm. Here, we show that adeno-associated virus vector-induced expression of the N-terminal I2NTF and C-terminal I2CTF halves of I2PP2A , also called SET, in brain reproduced key features of AD in Wistar rats. The I2NTF-CTF rats showed a decrease in brain PP2A activity, abnormal hyperphosphorylation and aggregation of tau, a loss of neuronal plasticity and impairment in spatial reference and working memories. To test whether early pharmacologic intervention with a neurotrophic molecule could rescue neurodegeneration and behavioral deficits, 2.5-month-old I2NTF-CTF rats and control littermates were treated for 40 days with Peptide 6, an 11-mer peptide corresponding to an active region of the ciliary neurotrophic factor. Peripheral administration of Peptide 6 rescued neurodegeneration and cognitive deficit in I2NTF-CTF animals by increasing dentate gyrus neurogenesis and mRNA level of brain derived neurotrophic factor. Moreover, Peptide 6-treated I2NTF-CTF rats showed a significant increase in dendritic and synaptic density as reflected by increased expression of synapsin I, synaptophysin and MAP2, especially in the pyramidal neurons of CA1 and CA3 of the hippocampus.

(Val⁸) glucagon-like peptide-1 prevents tau hyperphosphorylation, impairment of spatial learning and ultra-structural cellular damage induced by streptozotocin in rat brains

It has being shown that glucagon-like peptide-1 (GLP-1), a new anti-diabetes agent, significantly attenuated beta-amyloid (Aβ) levels in rats. In the present study, (Val(8))GLP-1 was used to prevent impairments in memory formation, tau hyperphosphorylation and ultra-structural changes induced by streptozotocin intracerebroventricular (i.c.v.) injection. A spatial water maze task was used to test the rats' learning and memory formation, Western blot was used to measure tau hyperphosphorylation/total tau, and transmission electron microscope was used to find ultra-structural changes. The results shown that streptozotocin induced a series of Alzheimer disease -like changes in behaviour, a significant decline in learning and memory formation, an increased expression of total tau and an increased ratio of phosphorylated tau, and damage to nucleus and nucleolus as seen in electron micrographs. After treatment with (Val(8))GLP-1 (50 μM in 10 μl i.c.v.), there is a significant improvement in learning and memory, a reduction in total tau expression and hyperphosphorylated tau levels, and a recovery of damaged cell nuclei and nucleolus. Our results indicated that (Val(8))GLP-1 might prevent age-related neurodegenerative changes by preventing decline of learning and memory formation, reduction of phosphorylated tau levels and protection of subcellular structures and morphology of neurons. Therefore, (Val(8))GLP-1 is potentially a novel treatment for Alzheimer's disease.