Chromatographic separation of reaction products from the choline acetyltransferase and carnitine acetyltransferase assay: differential ChAT and CrAT activity in brain extracts from Alzheimer's disease versus controls

Understanding How Physical Exercise Improves Alzheimer’s Disease: Cholinergic and Monoaminergic Systems

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder, characterized by the accumulation of proteinaceous aggregates and neurofibrillary lesions composed of β-amyloid (Aβ) peptide and hyperphosphorylated microtubule-associated protein tau, respectively. It has long been known that dysregulation of cholinergic and monoaminergic (i.e., dopaminergic, serotoninergic, and noradrenergic) systems is involved in the pathogenesis of AD. Abnormalities in neuronal activity, neurotransmitter signaling input, and receptor function exaggerate Aβ deposition and tau hyperphosphorylation. Maintenance of normal neurotransmission is essential to halt AD progression. Most neurotransmitters and neurotransmitter-related drugs modulate the pathology of AD and improve cognitive function through G protein-coupled receptors (GPCRs). Exercise therapies provide an important alternative or adjunctive intervention for AD. Cumulative evidence indicates that exercise can prevent multiple pathological features found in AD and improve cognitive function through delaying the degeneration of cholinergic and monoaminergic neurons; increasing levels of acetylcholine, norepinephrine, serotonin, and dopamine; and modulating the activity of certain neurotransmitter-related GPCRs. Emerging insights into the mechanistic links among exercise, the neurotransmitter system, and AD highlight the potential of this intervention as a therapeutic approach for AD.

Oxidative Stress, Amyloid-β Peptide, and Altered Key Molecular Pathways in the Pathogenesis and Progression of Alzheimer's Disease

Oxidative stress is implicated in the pathogenesis and progression of Alzheimer's disease (AD) and its earlier stage, amnestic mild cognitive impairment (aMCI). One source of oxidative stress in AD and aMCI brains is that associated with amyloid-β peptide, Aβ1-42 oligomers. Our laboratory first showed in AD elevated oxidative stress occurred in brain regions rich in Aβ1-42, but not in Aβ1-42-poor regions, and was among the first to demonstrate Aβ peptides led to lipid peroxidation (indexed by HNE) in AD and aMCI brains. Oxidatively modified proteins have decreased function and contribute to damaged key biochemical and metabolic pathways in which these proteins normally play a role. Identification of oxidatively modified brain proteins by the methods of redox proteomics was pioneered in the Butterfield laboratory. Four recurring altered pathways secondary to oxidative damage in brain from persons with AD, aMCI, or Down syndrome with AD are interrelated and contribute to neuronal death. This "Quadrilateral of Neuronal Death" includes altered: glucose metabolism, mTOR activation, proteostasis network, and protein phosphorylation. Some of these pathways are altered even in brains of persons with preclinical AD. We opine that targeting these pathways pharmacologically and with lifestyle changes potentially may provide strategies to slow or perhaps one day, prevent, progression or development of this devastating dementing disorder. This invited review outlines both in vitro and in vivo studies from the Butterfield laboratory related to Aβ1-42 and AD and discusses the importance and implications of some of the major achievements of the Butterfield laboratory in AD research.

Microtopographical cues promote peripheral nerve regeneration via transient mTORC2 activation

Despite microsurgical repair, recovery of function following peripheral nerve injury is slow and often incomplete. Outcomes could be improved by an increased understanding of the molecular biology of regeneration and by translation of experimental bioengineering strategies. Topographical cues have been shown to be powerful regulators of the rate and directionality of neurite regeneration, and in this study we investigated the downstream molecular effects of linear micropatterned structures in an organotypic explant model. Linear topographical cues enhanced neurite outgrowth and our results demonstrated that the mTOR pathway is important in regulating these responses.

mTOR gene expression peaked between 48 and 72 h, coincident with the onset of rapid neurite outgrowth and glial migration, and correlated with neurite length at 48 h. mTOR protein was located to glia and in a punctate distribution along neurites. mTOR levels peaked at 72 h and were significantly increased by patterned topography (p < 0.05). Furthermore, the topographical cues could override pharmacological inhibition. Downstream phosphorylation assays and inhibition of mTORC1 using rapamycin highlighted mTORC2 as an important mediator, and more specific therapeutic target. Quantitative immunohistochemistry confirmed the presence of the mTORC2 component rictor at the regenerating front where it co-localised with F-actin and vinculin. Collectively, these results provide a deeper understanding of the mechanism of action of topography on neural regeneration, and support the incorporation of topographical patterning in combination with pharmacological mTORC2 potentiation within biomaterial constructs used to repair peripheral nerves.

Statement of Significance

Peripheral nerve injury is common and functionally devastating. Despite microsurgical repair, healing is slow and incomplete, with lasting functional deficit. There is a clear need to translate bioengineering approaches and increase our knowledge of the molecular processes controlling nerve regeneration to improve the rate and success of healing. Topographical cues are powerful determinants of neurite outgrowth and represent a highly translatable engineering strategy. Here we demonstrate, for the first time, that microtopography potentiates neurite outgrowth via the mTOR pathway, with the mTORC2 subtype being of particular importance. These results give further evidence for the incorporation of microtopographical cues into peripheral nerve regeneration conduits and indicate that mTORC2 may be a suitable therapeutic target to potentiate nerve regeneration.

Effects of Maternal Choline Supplementation on the Septohippocampal Cholinergic System in the Ts65Dn Mouse Model of Down Syndrome

Down syndrome (DS), caused by trisomy of chromosome 21, is marked by intellectual disability (ID) and early onset of Alzheimer's disease (AD) neuropathology including hippocampal cholinergic projection system degeneration. Here we determined the effects of age and maternal choline supplementation (MCS) on hippocampal cholinergic deficits in Ts65Dn mice compared to 2N mice sacrificed at 6-8 and 14-18 months of age. Ts65Dn mice and disomic (2N) littermates sacrificed at ages 6-8 and 14-18 mos were used for an aging study and Ts65Dn and 2N mice derived from Ts65Dn dams were maintained on either a choline-supplemented or a choline-controlled diet (conception to weaning) and examined at 14-18 mos for MCS studies. In the latter, mice were behaviorally tested on the radial arm Morris water maze (RAWM) and hippocampal tissue was examined for intensity of choline acetyltransferase (ChAT) immunoreactivity. Hippocampal ChAT activity was evaluated in a separate cohort. ChAT-positive fiber innervation was significantly higher in the hippocampus and dentate gyrus in Ts65Dn mice compared with 2N mice, independent of age or maternal diet. Similarly, hippocampal ChAT activity was significantly elevated in Ts65Dn mice compared to 2N mice, independent of maternal diet. A significant increase with age was seen in hippocampal cholinergic innervation of 2N mice, but not Ts65Dn mice. Degree of ChAT intensity correlated negatively with spatial memory ability in unsupplemented 2N and Ts65Dn mice, but positively in MCS 2N mice. The increased innervation produced by MCS appears to improve hippocampal function, making this a therapy that may be exploited for future translational approaches in human DS.

Low-dose total-body carbon-ion irradiations induce early transcriptional alteration without late Alzheimer's disease-like pathogenesis and memory impairment in mice

The cause and risk factors of Alzheimer's disease (AD) are largely unknown. Studies on possible radiation-induced AD-like pathogenesis and behavioral consequences are important because humans are exposed to ionizing radiation (IR) from various sources. It was reported that total-body irradiations (TBI) at 10 cGy of low linear energy transfer (LET) X-rays to mice triggered acute transcriptional alterations in genes associated with cognitive dysfunctions. However, it was unknown whether low doses of IR could induce AD-like changes late after exposure. We reported previously that 10 cGy X-rays induced early transcriptional response of several AD-related genes in hippocampi without late AD-like pathogenesis and memory impairment in mice. Here, further studies on two low doses (5 or 10 cGy) of high LET carbonion irradiations are reported. On expression of 84 AD-related genes in hippocampi, at 4 hr after TBI, 5 cGy induced a significant upregulation of three genes (Abca1, Casp3, and Chat) and 10 cGy led to a marked upregulation of one gene (Chat) and a downregulation of three genes (Apoe, Ctsd, and Il1α), and, at 1 year after TBI, one gene (Il1α) was significantly downregulated in 10 cGy-irradiated animals. Changes in spatial learning ability and memory and induction of AD-like pathogenesis were not detected by in vivo brain imaging for amyloid-β peptide accumulation and by immunohistochemical staining of amyloid precursor protein, amyloid-β protein, tau, and phosphorylated tau protein. These findings indicate that low doses of carbon-ion irradiations did not cause behavioral impairment or AD-like pathological change in mice.

Neural cell injury microenvironment induces neural differentiation of human umbilical cord mesenchymal stem cells

This study aimed to investigate the neural differentiation of human umbilical cord mesenchymal stem cells (hUCMSCs) under the induction of injured neural cells. After in vitro isolation and culture, passage 5 hUCMSCs were used for experimentation. hUCMSCs were co-cultured with normal or Aβ_1-40-injured PC12 cells, PC12 cell supernatant or PC12 cell lysate in a Transwell co-culture system. Western blot analysis and flow cytometry results showed that choline acetyltransferase and microtubule-associated protein 2, a specific marker for neural cells, were expressed in hUCMSCs under various culture conditions, and highest expression was observed in the hUCMSCs co-cultured with injured PC12 cells. Choline acetyltransferase and microtubule-associated protein 2 were not expressed in hUCMSCs cultured alone (no treatment). Cell Counting Kit-8 assay results showed that hUCMSCs under co-culture conditions promoted the proliferation of injured PC12 cells. These findings suggest that the microenvironment during neural tissue injury can effectively induce neural cell differentiation of hUCMSCs. These differentiated hUCMSCs likely accelerate the repair of injured neural cells.

Intracranial injection of PEG-PEI/ROCK II-siRNA improves cognitive impairment in a mouse model of Alzheimer's disease

PURPOSE

A plenty of studies have demonstrated that the Rho/ROCK pathway is involved in the neuronal loss and inhibition of axonal regeneration observed in Alzheimer's disease (AD). Therefore, we conducted this study to evaluate whether intracranial injection of PEG-PEI/ROCK II siRNA (PPRS) would improve the cognitive impairments in a senescence-accelerated mouse (SAM) model of AD.

MATERIALS AND METHODS

Five male senescence-resistant inbred strain (SAMR1) mice and 15 male senescence-accelerated mouse prone-8 (SAMP8) strain mice were divided into the following three groups:PPRS group, PEG-PEI/ ROCK II-Scramble (PPRScr) siRNA group, and normal group (SAMR1). Total volumes of 2.3 μl of nanoparticles or saline were intracranially injected under the guidance of a stereotaxic apparatus. The injections were performed every three days and lasted for two weeks. Four weeks after injection, the Morris water maze (MWM) was used to evaluate the spatial learning and memory functions of the mice. Choline acetyltransferase (ChAT) activity was detected by immunohistochemistry.

RESULTS

Mice in the PPRS-treated group exhibited decreases in escape latencies over the three successive days of navigating the test and crossing the target quadrant during the spatial probe test more frequently than did the mice in the PPRScr-treated group. Analyses of ChAT activity revealed that greater numbers of ChAT-positive cells were present in the hippocampal regions of the PPRS-treated mice than in the PPRScr group.

CONCLUSIONS

Intracranial injection of PPRS improved the cognitive impairments of SAM mice, and this improvement may have been mediated by enhancement of ChAT activity in the hippocampus.