Increased Cholinergic Response in α-Synuclein Transgenic Mice (h-α-synL62)

LETC inhibits α-Syn aggregation and ameliorates motor deficiencies in the L62 mouse model of synucleinopathy

Alpha-Synuclein (α-Syn) aggregation is a pathological feature of synucleinopathies, neurodegenerative disorders that include Parkinson's disease (PD). Here, we explored the efficacy of N,N,N',N'-tetraethyl-10H-phenothiazine-3,7-diamine dihydrochloride (LETC), a protein aggregation inhibitor, on α-Syn aggregation. In both cellular models and transgenic mice, α-Syn aggregation was achieved by the overexpression of full-length human α-Syn fused with a signal sequence peptide. α-Syn accumulated in transfected DH60.21 neuroblastoma cells and α-Syn aggregation was inhibited by LETC with an EC50 of 0.066 ± 0.047 μM. Full-length human α-Syn overexpressing Line 62 (L62) mice accumulated neuronal α-Syn that was associated with a decreased motor performance in the open field and automated home cage. LETC, administered orally for 6 weeks at 10 mg/kg significantly decreased α-Syn-positive neurons in multiple brain regions and this resulted in a rescue of movement deficits in the open field in these mice. LETC however, did not improve activity deficits of L62 mice in the home cage environment. The results suggest that LETC may provide a potential disease modification therapy in synucleinopathies through the inhibition of α-Syn aggregation.

Solubility of α-synuclein species in the L62 mouse model of synucleinopathy

The accumulation of α-synuclein (α-Syn) into Lewy bodies is a hallmark of synucleinopathies, a group of neurological disorders that include Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Small oligomers as well as larger fibrils of α-Syn have been suggested to induce cell toxicity leading to a degenerative loss of neurones. A richer understanding of α-Syn aggregation in disease, however, requires the identification of the different α-Syn species and the characterisation of their biochemical properties. We here aimed at a more in-depth characterisation of the α-Syn transgenic mice, Line 62 (L62), and examined the deposition pattern and solubility of human and murine α-Syn in these mice using immunohistochemical and biochemical methods. Application of multiple antibodies confirmed mAb syn204 as the most discriminatory antibody for human α-Syn in L62. Syn204 revealed an intense and widespread immunohistochemical α-Syn labelling in parietal cortex and hippocampus, and to a lower level in basal forebrain and hindbrain regions. The labelled α-Syn represented somatic inclusions as well as processes and synaptic endings. Biochemical analysis revealed a Triton-resistant human α-Syn pool of large oligomers, a second pool of small oligomers that was not resistant to solubilization with urea/Triton. A third SDS-soluble pool of intermediate sized aggregates containing a mixture of both, human and mouse α-Syn was also present. These data suggest that several pools of α-Syn can exist in neurones, most likely in different cellular compartments. Information about these different pools is important for the development of novel disease modifying therapies aimed at α-Syn.

Peripheral hearing in Parkinson's disease: a systematic review

OBJECTIVE

To investigate the implications of Parkinson's disease (PD) in the peripheral auditory system, a systematic survey of the scientific literature was conducted.

DESIGN

Systematic review.

STUDY SAMPLE

An electronic search of the non-gray literature in the last decade was conducted using the digital databases MEDLINE® (PubMed interface), LILACS® (Virtual Health Library), Web of Science® (CAPES publications portal), and SciELO®. Studies addressing peripheral auditory function as part of the range of nonmotor PD symptoms were selected for analysis.

RESULTS

Pure tone audiometry data suggested that sensorineural hearing loss was more severe in the PD population than in the control groups. The effects of PD on cochlear function were evidenced by a decrease in the levels of otoacoustic emissions.

CONCLUSIONS

Sensorineural hearing loss and cochlear impairment are more severe in the PD population than in the control groups. Additional studies are recommended to further understand the characteristics of the peripheral auditory system in PD patients, which constitutes an emerging subject in the scientific literature.

Glutamatergic transmission and receptor expression in the synucleinopathy h-α-synL62 mouse model: Effects of hydromethylthionine

The accumulation of alpha-synuclein (α-Syn) into Lewy bodies in cortical and subcortical regions has been linked to the pathogenesis of synucleinopathies such as Parkinson's disease (PD) and dementia with Lewy bodies (DLB). While there is a strong link between synuclein aggregates and the reduction in dopamine function in the emergence of PD, less is known about the consequences of α-Syn accumulation in glutamatergic neurons and how this could be exploited as a therapeutic target. Transgenic h-α-synL62 (L62) mice, in which synuclein aggregation is achieved through the expression of full-length human α-Syn fused with a signal sequence peptide, were used to characterise glutamatergic transmission using a combination of behavioural, immunoblotting, and histopathological approaches. The protein aggregation inhibitor hydromethylthionine mesylate (HMTM) alone, or in combination with the glutamatergic compounds 3-((2-Methyl-4-thiazolyl)ethynyl)pyridine hydrochloride (MTEP) and memantine, was used to target α-Syn aggregation. We show that accumulation of α-Syn aggregates in glutamatergic synapses affected synaptic protein expression including metabotropic glutamate receptor 5 (mGLUR5) levels and ratio of N-methyl-d-aspartate (NMDA) receptor subunits GluN1/GluN2A. The ratio of NMDA receptor subunits and levels of mGLUR5 were both normalised by HMTM in L62 mice. These alterations, however, did not affect glutamate release in synaptosomes derived from L62 mice or behavioural endpoints following pharmacological manipulations of glutamate functions. Our results confirm that HMTM acts in the L62 mouse model of PD as an inhibitor of pathological aggregation of synuclein and show that HMTM treatment normalises both the ratio of NMDA receptor subunits and mGLUR5 levels. These findings support the potential utility of HMTM as a disease-modifying treatment for PD aiming to reduce synuclein aggregation pathology.

Restoration and targeting of aberrant neurotransmitters in Parkinson's disease therapeutics

Neurotransmitters are considered as a fundamental regulator in the process of neuronal growth, differentiation and survival. Parkinson's Disease (PD) occurs due to extensive damage of dopamine-producing neurons; this causes dopamine deficits in the midbrain, followed by the alternation of various other neurotransmitters (glutamate, GABA, serotonin, etc.). It has been observed that fluctuation of neurotransmission in the basal ganglia exhibits a great impact on the pathophysiology of PD. Dopamine replacement therapy, such as the use of L-DOPA, can increase the dopamine level, but it majorly ameliorates the motor symptoms and is also associated with long-term complications (for e.g., LID). While the non-dopaminergic system can efficiently target non-motor symptoms, for instance, the noradrenergic system regulates the synthesis of BDNF via the MAPK pathway, which is important in learning and memory. Herein, we briefly discuss the role of different neurotransmitters, implementation of neurotransmitter receptors in PD. We also illustrate the recent advances of neurotransmitter-based drugs, which are currently under in vivo and clinical studies. Reinstating normal neurotransmitter levels has been believed to be advantageous in the treatment of PD. Thus, there is an increasing demand for drugs that can specifically target the neurotransmission system and reinstate the normal levels of neurotransmitters, which might prevent or delay neurodegeneration in PD.

Cholinergic relevant functional reactivity is associated with dopamine responsiveness of tremor in Parkinson's disease

Tremor in Parkinson’s disease (PD) has distinct responsiveness to dopamine, which is supposed not be exclusively related to dopamine deficiency but has a close relationship with cholinergic system. This phenomenon indicates that cholinergic system may be an important regulatory for distinct dopamine responsiveness of parkinsonian tremor. Through investigating the alterations of cholinergic and dopaminergic network during levodopa administration, we aimed at exploring the mechanisms of differed dopamine responsiveness of parkinsonian tremor. Fifty-two PD patients with tremor were enrolled. MRI scanning, UPDRS III and its sub-symptom scores were collected in OFF and ON status (dopaminergic challenge test). Then, patients were divided into two groups (dopamine-resistant tremor and dopamine-responsive tremor) according to the tremor change rate median score. Dopaminergic and cholinergic network were obtained. LASSO regression was conducted to identify functional connectivity with distinct reactivity during levodopa administration between groups. Afterwards, detailed group comparisons, interaction and correlation analyses were performed. The reactivity of cholinergic connectivity showed the highest possibility to distinguish two groups, especially connectivity of right basal forebrain 123 to right parietal operculum cortex (R.BF123-R.PO). After levodopa administration, connectivity of R.BF123-R.PO was decreased for dopamine-responsive tremor while which remained unchanged for dopamine-resistant tremor. The reactivity of R.BF123-R.PO was negatively correlated with tremor change rate. Reduced cholinergic connectivity to parietal operculum may be an underlying mechanism for the responsive tremor in PD and the distinct cholinergic reactivity of parietal operculum to levodopa may be a core pathophysiology for the differed DA responsiveness of tremor in PD.

[18F]Nifene PET/CT Imaging in Mice: Improved Methods and Preliminary Studies of α4β2* Nicotinic Acetylcholinergic Receptors in Transgenic A53T Mouse Model of α-Synucleinopathy and Post-Mortem Human Parkinson's Disease

We report [¹⁸F]nifene binding to α4β2* nicotinic acetylcholinergic receptors (nAChRs) in Parkinson’s disease (PD). The study used transgenic Hualpha-Syn(A53T) PD mouse model of α-synucleinopathy for PET/CT studies in vivo and autoradiography in vitro. Additionally, postmortem human PD brain sections comprising of anterior cingulate were used in vitro to assess translation to human studies. Because the small size of mice brain poses challenges for PET imaging, improved methods for radiosynthesis of [¹⁸F]nifene and simplified PET/CT procedures in mice were developed by comparing intravenous (IV) and intraperitoneal (IP) administered [¹⁸F]nifene. An optimal PET/CT imaging time of 30–60 min post injection of [¹⁸F]nifene was established to provide thalamus to cerebellum ratio of 2.5 (with IV) and 2 (with IP). Transgenic Hualpha-Syn(A53T) mice brain slices exhibited 20–35% decrease while in vivo a 20–30% decrease of [¹⁸F]nifene was observed. Lewy bodies and α-synuclein aggregates were confirmed in human PD brain sections which lowered the [¹⁸F]nifene binding by more than 50% in anterior cingulate. Thus [¹⁸F]nifene offers a valuable tool for PET imaging studies of PD.

Mechanisms of Anticholinesterase Interference with Tau Aggregation Inhibitor Activity in a Tau-Transgenic Mouse Model

Background

Symptomatic treatments of Alzheimer’s Disease (AD) with cholinesterase inhibitors and/or memantine are relatively ineffective and there is a need for new treatments targeting the underlying pathology of AD. In most of the failed disease-modifying trials, patients have been allowed to continue taking symptomatic treatments at stable doses, under the assumption that they do not impair efficacy. In recently completed Phase 3 trials testing the tau aggregation inhibitor leuco-methylthioninium bis (hydromethane-sulfonate) (LMTM), we found significant differences in treatment response according to whether patients were taking LMTM either as monotherapy or as an add-on to symptomatic treatments.

Methods

We have examined the effect of either LMTM alone or chronic rivastigmine prior to LMTM treatment of tau transgenic mice expressing the short tau fragment that constitutes the tangle filaments of AD. We have measured acetylcholine levels, synaptosomal glutamate release, synaptic proteins, mitochondrial complex IV activity, tau pathology and Choline Acetyltransferase (ChAT) immunoreactivity.

Results

LMTM given alone increased hippocampal Acetylcholine (ACh) levels, glutamate release from synaptosomal preparations, synaptophysin levels in multiple brain regions and mitochondrial complex IV activity, reduced tau pathology, partially restored ChAT immunoreactivity in the basal forebrain and reversed deficits in spatial learning. Chronic pretreatment with rivastigmine was found to reduce or eliminate almost all these effects, apart from a reduction in tau aggregation pathology. LMTM effects on hippocampal ACh and synaptophysin levels were also reduced in wild-type mice.

Conclusion

The interference with the pharmacological activity of LMTM by a cholinesterase inhibitor can be reproduced in a tau transgenic mouse model and, to a lesser extent, in wild-type mice. Long-term pretreatment with a symptomatic drug alters a broad range of brain responses to LMTM across different transmitter systems and cellular compartments at multiple levels of brain function. There is, therefore, no single locus for the negative interaction. Rather, the chronic neuronal activation induced by reducing cholinesterase function produces compensatory homeostatic downregulation in multiple neuronal systems. This reduces a broad range of treatment responses to LMTM associated with a reduction in tau aggregation pathology. Since the interference is dictated by homeostatic responses to prior symptomatic treatment, it is likely that there would be similar interference with other drugs tested as add-on to the existing symptomatic treatment, regardless of the intended therapeutic target or mode of action. The present findings outline key results that now provide a working model to explain interference by symptomatic treatment.

Central cholinergic function and metabolic changes in streptozotocin-induced rat brain injury

As glucose hypometabolism in the brain is an early sign of Alzheimer´s dementia (AD), the diabetogenic drug streptozotocin (STZ) has been used to induce Alzheimer-like pathology in rat brain by intracereboventricular injection (icv-STZ). However, many details of the pathological mechanism of STZ in this AD model remain unclear. Here, we report metabolic and cholinergic effects of icv-STZ using microdialysis in freely moving animals. We found that icv-STZ at a dose of 3 mg/kg (2 × 1.5 mg/kg) causes overt toxicity reflected in body weight loss. Three weeks after STZ administration, histological examination revealed a high number of glial fibrillary acidic protein reactive cells in the hippocampus, accompanied by Fluoro-Jade C-positive cells in the CA1 region. Glucose and lactate levels in microdialysates were unchanged, but mitochondrial respiration measured ex vivo was reduced by 9%-15%. High-affinity choline uptake, choline acetyltransferase, and acetylcholine esterase (AChE) activities in the hippocampus were reduced by 16%, 28%, and 30%, respectively. Importantly, extracellular acetylcholine (ACh) levels in the hippocampus were unchanged and responded to behavioral and pharmacological challenges. In comparison, extracellular ACh levels and cholinergic parameters in the striatum were unchanged or slightly increased. We conclude that the icv-STZ model poorly reflects central cholinergic dysfunction, an important characteristic of dementia. The icv-STZ model may be more aptly described as an animal model of hippocampal gliosis.