Aerobic exercise attenuates autophagy-lysosomal flux deficits by ADRB2/β2-adrenergic receptor-mediated V-ATPase assembly factor VMA21 signaling in APP-PSEN1/PS1 mice

Growing evidence suggests that macroautophagy/autophagy-lysosomal pathway deficits contribute to the accumulation of amyloid-β (Aβ) in Alzheimer disease (AD). Aerobic exercise (AE) has long been investigated as an approach to delay and treat AD, although the exact role and mechanism are not well known. Here, we revealed that AE could reverse autophagy-lysosomal deficits via activation of ADRB2/β2-adrenergic receptor, leading to significant attenuation of amyloid-β pathology in APP-PSEN1/PS1 mice. Molecular mechanism research found that AE could reverse autophagy deficits by upregulating the AMP-activated protein kinase (AMPK)-MTOR (mechanistic target of rapamycin kinase) signaling pathway. Moreover, AE could reverse V-ATPase function by upregulating VMA21 levels. Inhibition of ADRB2 by propranolol (antagonist, 30 μM) blocked AE-attenuated Aβ pathology and cognitive deficits by inhibiting autophagy-lysosomal flux. AE may mitigate AD via many pathways, while ADRB2-VMA21-V-ATPase could improve cognition by enhancing the clearance of Aβ through the autophagy-lysosomal pathway, which also revealed a novel theoretical basis for AE attenuating pathological progression and cognitive deficits in AD.

Danggui Buxue decoction ameliorates mitochondrial biogenesis and cognitive deficits through upregulating histone H4 lysine 12 acetylation in APP/PS1 mice

ETHNOPHARMACOLOGICAL RELEVANCE

Danggui Buxue decoction (DBD) is a classic herbal decoction consisting of Astragali Radix (AR) and Angelica Sinensis Radix (ASR) with a 5:1 wt ratio, which can supplement 'blood' and 'qi' (vital energy) for the treatment of clinical diseases. According to Traditional Chinese Medicine (TCM) theory, dementia is induced by Blood deficiency and Qi weakness, which causes a decline in cognition. However, the underlying mechanisms of DBD improving cognition deficits in neurodegenerative disease are no clear.

AIM OF THE STUDY

This study aims at revealing the underlying mechanisms of DBD plays a protective role in the cognitive deficits and pathology process of Alzheimer's disease (AD).

MATERIALS AND METHODS

The APP/PS1 (Mo/HuAPP695swe/PS1-dE9) double transgenic mice were adopted as an experimental model of AD. Qualitative and quantitative analysis of 3 compounds in DBT was analyzed by HPLC. Morris water maze test, Golgi staining and electrophysiology assays were used to evaluate the effects of DBD on cognitive function and synaptic plasticity in APP/PS1 mice. Western blot, immunofluorescence and Thioflavin S staining were used for the pathological evaluation of AD. Monitoring the level of ATP, mitochondrial membrane potential, SOD and MDA to evaluate the mitochondrial function, and with the usage of qPCR and CHIP for the changes of histone post-translational modification.

RESULTS

In the current study, we found that DBD could effectively attenuate memory impairments and enhance long-term potentiation (LTP) with concurrent increased expression of memory-associated proteins. DBD markedly decreased Aβ accumulation in APP/PS1 mice by decreasing the phosphorylation of APP at the Thr668 level but not APP, PS1 or BACE1. Further studies demonstrated that DBD restored mitochondrial biogenesis deficits and mitochondrial dysfunction. Finally, the restored mitochondrial biogenesis and cognitive deficits are under HADC2-mediated histone H4 lysine 12 (H4K12) acetylation at the peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α) and N-methyl-D-aspartate receptor type 2B (GluN2B) promoters.

CONCLUSIONS

These findings reveal that DBD could ameliorate mitochondrial biogenesis and cognitive deficits by improving H4K12 acetylation. DBD might be a promising complementary drug candidate for AD treatment.

Downregulating ANP32A rescues synapse and memory loss via chromatin remodeling in Alzheimer model

Background

The impairment of histone acetylation is causally linked to the cognitive decline in Alzheimer’s disease (AD). In addition to histone acetyltransferases (HATs) and histone deacetylases (HDACs), inhibitor of acetyltransferases (INHAT) can also regulate histone acetylation. As a key component of INHAT, level of ANP32A is selectively upregulated in the brain of AD patients. Here we investigated whether downregulating ANP32A can rescue AD-like synapse and memory deficits.

Methods

RFP-labeled lentiviral ANP32A-shRNA was infused stereotaxically into the hippocampal CA3 region of the human tau transgenic mice (termed htau). The spatial learning and memory were assessed by Morris water maze (MWM). The synaptic function was measured by electrophysiological recording and the spine density was detected by Golgi staining. RT-PCR and Western blotting were used to detect the mRNA and protein levels.

Results

Elevation of ANP32 in htau transgenic mice was correlated with learning deficits, while the hippocampal infusion of lenti-siANP32A to downregulate ANP32A in 12 m-old htau mice could rescue memory loss. Further studies demonstrated that downregulating ANP32A restored synapse morphology and the function. In the brain of htau mice, the acetylated histone decreased while knockdown ANP32A unmasked histone for a robust acetylation with reduced INHAT complex formation. Downregulating of ANP32A also attenuated AD-like tau hyperphosphorylation. Finally, several AD-associated risk factors, including tau accumulation, β-amyloid and H₂O₂ exposure, increased ANP32A by activating CCAAT/enhancer binding protein-β (C/EBPβ).

Conclusion

We conclude that downregulating ANP32A rescues synaptic plasticity and memory ability by reducing INHAT formation and unmasking histone for hyperacetylation. Our findings reveal novel mechanisms for AD memory loss and potential molecular markers for protection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-017-0178-8) contains supplementary material, which is available to authorized users.

Knockdown of pp32 Increases Histone Acetylation and Ameliorates Cognitive Deficits

Aging is a cause of cognitive decline in the elderly and the major risk factor for Alzheimer's disease, however, aging people are not all destined to develop into cognitive deficits, the molecular mechanisms underlying this difference in cognition of aging people are obscure. Epigenetic modifications, particularly histone acetylation in the nervous system, play a critical role in regulation of gene expression for learning and memory. An inhibitor of acetyltransferases (INHAT) is reported to suppress histone acetylation via a histone-masking mechanism, and pp32 is a key component of INHAT complex. In the present study, we divided ~18 m-old aged mice into the cognitive-normal and the cognitive-impaired group by Morris water maze, and found that pp32 level was significantly increased in the hippocampus of cognitive-impaired aged mice. The mRNA and protein levels of synaptic-associated proteins decreased with reduced dendrite complexity and histone acetylation. Knockdown of pp32 rescued cognitive decline in cognitive-impaired aged mice with restoration of synaptic-associated proteins, the increase of spine density and elevation of histone acetylation. Our study reveals a novel mechanism underlying the aging-associated cognitive disturbance, indicating that suppression of pp32 might represent a promising therapeutic approach for learning and memory impairments.

Activation of β2-adrenergic receptor promotes dendrite ramification and spine generation in APP/PS1 mice

Alzheimer's disease (AD) is the most common neurodegenerative disorder, and currently there is no effective cure for this devastating disease. Decreases in the levels of β₂-adrenoceptor (β₂-AR) and norepinephrine have been reported in several regions of AD brains. The activation of β₂AR can prevent the amyloid β (Aβ)-mediated inhibition of LTP (Long-term potentiation), but the mechanism is not fully understood. Here, we used APP/PS1 mice to study whether the activation of β₂AR could remodel synaptic and/or dendritic plasticity. We found that the activation of β₂AR by Clenbuterol (Clen) ameliorated memory deficits and promoted dendrite ramification and spine generation in hippocampal CA1 neurons, which was accompanied by the upregulation of postsynaptic density protein 95 (PSD95), synapsin 1 and synaptophysin. Conversely, the inhibition of β₂AR by a siRNA blocked the Clen-induced increase in dendrite ramification and dendritic spines in primary hippocampal neurons. Furthermore, the activation of β₂AR decreased cerebral amyloid plaques through the up-regulation of α-secretase activity and by decreasing the phosphorylation of APP at Thr668. Based on the roles of β₂AR in dendrite ramification and spine generation, memory deficits and AD pathogenesis, compounds designed to activate β₂AR might shed light on the cure of AD.

Spatial training promotes short-term survival and neuron-like differentiation of newborn cells in Aβ1-42-injected rats

Neurogenesis plays a role in hippocampus-dependent learning and impaired neurogenesis may correlate with cognitive deficits in Alzheimer's disease. Spatial training influences the production and fate of newborn cells in hippocampus of normal animals, whereas the effects on neurogenesis in Alzheimer-like animal are not reported until now. Here, for the first time, we investigated the effect of Morris water maze training on proliferation, survival, apoptosis, migration, and differentiation of newborn cells in β-amyloid-treated Alzheimer-like rats. We found that spatial training could preserve a short-term survival of newborn cells generated before training, during the early phase, and the late phase of training. However, the training had no effect on the long-term survival of mature newborn cells generated at previously mentioned 3 different phases. We also demonstrated that spatial training promoted newborn cell differentiation preferentially to the neuron direction. These findings suggest a time-independent neurogenesis induced by spatial training, which may be indicative for the cognitive stimulation in Alzheimer's disease therapy.

Beta 2-adrenergic receptor activation enhances neurogenesis in Alzheimer's disease mice

Impaired hippocampal neurogenesis is one of the early pathological features of Alzheimer's disease. Enhancing adult hippocampal neurogenesis has been pursued as a potential therapeutic strategy for Alzheimer's disease. Recent studies have demonstrated that environmental novelty activates β₂-adrenergic signaling and prevents the memory impairment induced by amyloid-β oligomers. Here, we hypothesized that β₂-adrenoceptor activation would enhance neurogenesis and ameliorate memory deficits in Alzheimer's disease. To test this hypothesis, we investigated the effects and mechanisms of action of β₂-adrenoceptor activation on neurogenesis and memory in amyloid precursor protein/presenilin 1 (APP/PS1) mice using the agonist clenbuterol (intraperitoneal injection, 2 mg/kg). We found that β₂-adrenoceptor activation enhanced hippocampal neurogenesis, ameliorated memory deficits, and increased dendritic branching and the density of dendritic spines. These effects were associated with the upregulation of postsynaptic density 95, synapsin 1 and synaptophysin in APP/PS1 mice. Furthermore, β₂-adrenoceptor activation decreased cerebral amyloid plaques by decreasing APP phosphorylation at Thr668. These findings suggest that β₂-adrenoceptor activation enhances neurogenesis and ameliorates memory deficits in APP/PS1 mice.

Spatial training preserves associative memory capacity with augmentation of dendrite ramification and spine generation in Tg2576 mice

Alzheimer's disease (AD) is the most common neurodegenerative disorder and there is currently no efficient cure for this devastating disease. Cognitive stimulation can delay memory loss during aging and in patients with mild cognitive impairment. In 3 × Tg-AD mice, training decreased the neuropathologies with transient amelioration of memory decline. However, the neurobiological mechanisms underlying the learning-improved memory capacity are poorly understood. Here, we found in Tg2576 mice spatial training in Morris water maze (MWM) remarkably improved the subsequent associative memory acquisition detected by contextual fear conditioning. We also found that spatial training enhanced long term potentiation, dendrite ramification and spine generation in hippocampal dentate gyrus (DG) and CA1 neurons at 24 h after the training. In the molecular level, the MWM training remarkably activated calcium/calmodulin-dependent protein kinase II (CaMKII) with elevation of glutamate AMPA receptor GluA1 subunit (GluA1), postsynaptic density protein 93 (PSD93) and postsynaptic density protein 95 (PSD95) in the hippocampus. Finally, the training also significantly ameliorated AD-like tau and amyloid pathologies. We conclude that spatial training in MWM preserves associative memory capacity in Tg2576 mice, and the mechanisms involve augmentation of dendrite ramification and spine generation in hippocampus.

CaMKII-dependent dendrite ramification and spine generation promote spatial training-induced memory improvement in a rat model of sporadic Alzheimer's disease

Participation in cognitively stimulating activities can preserve memory capacities in patients with Alzheimer's disease (AD), but the mechanism is not fully understood. Here, we used a rat model with hyperhomocysteinemia, an independent risk factor of AD, to study whether spatial training could remodel the synaptic and/or dendritic plasticity and the key molecular target(s) involved. We found that spatial training in water maze remarkably improved the subsequent short-term and long-term memory performance in contextual fear conditioning and Barnes maze. The trained rats showed an enhanced dendrite ramification, spine generation and plasticity in dentate gyrus (DG) neurons, and stimulation of long-term potentiation between perforant path and DG circuit. Spatial training also increased the levels of postsynaptic GluA1, GluN2A, GluN2B, and PSD93 with selective activation of calcium/calmodulin-dependent protein kinase II (CaMKII), although inhibition of CaMKII by stereotaxic injection of KN93 into hippocampal DG, abolished the training-induced cognitive improvement, dendrite ramification, and spine generation. We conclude that spatial training can preserve the cognitive function by CaMKII-dependent remodeling of dendritic plasticity in hyperhomocysteinemia-induced sporadic AD-like rats.

Phosphorylation of tau by death-associated protein kinase 1 antagonizes the kinase-induced cell apoptosis

The intracellular accumulation of hyperphosphorylated tau plays a crucial role in neurodegeneration of Alzheimer's disease (AD), but the mechanism is not fully understood. From the observation that tau hyperphosphorylation renders cells more resistant to chemically-induced cell apoptosis, we have proposed that tau-involved apoptotic abortion may be the trigger of neurodegeneration. Here, we further studied whether this phenomenon is also applicable for the cell death induced by constitutively expressed factors, such as death-associated protein kinase 1 (DAPK1). We found that DAPK1 was upregulated and accumulated in the brain of human tau transgenic mice. Overexpression of DAPK1 in HEK293 and N2a cells decreased cell viability with activation of caspase-3, whereas simultaneous expression of tau antagonized DAPK1-induced apoptotic cell death. Expression of DAPK1 induced tau hyperphosphorylation at Thr231, Ser262, and Ser396 with no effects on protein phosphatase 2A, glycogen synthase kinase-3β, protein kinase A, calcium/calmodulin dependent protein kinase II, cell division cycle 2, or cyclin dependent protein kinase 5. The phosphorylation level of microtubule affinity-regulating kinase 2 (MARK2) was increased by expression of DAPK1, but simultaneous downregulation of MARK2 did not affect the DAPK1-induced tau hyperphosphorylation. DAPK1 was co-immunoprecipitated with tau proteins both in vivo and in vitro, and expression of the kinase domain-truncated DAPK1 did not induce tau hyperphosphorylation. These data suggest that tau hyperphosphorylation at Thr231, Ser262, and Ser396 by DAPK1 renders the cells more resistant to the kinase-induced apoptotic cell death, providing new insights into the tau-involved apoptotic abortion in the course of chronic neurodegeneration.

Expression of Tau40 induces activation of cultured rat microglial cells

Accumulation of microtubule-associated protein tau has been observed in the brain of aging and tauopathies. Tau was observed in microglia, but its role is not illustrated. By immunofluorescence staining and the fractal dimension value assay in the present study, we observed that microglia were activated in the brains of rats and mice during aging, simultaneously, the immunoreactivities of total tau and the phosphorylated tau were significantly enhanced in the activated microglia. Furtherly by transient transfection of tau40 (human 2N/4R tau) into the cultured rat microglia, we demonstrated that expression of tau40 increased the level of Iba1, indicating activation of microglia. Moreover, expression of tau40 significantly enhanced the membranous localization of the phosphorylated tau at Ser396 in microglia possibly by a mechanism involving protein phosphatase 2A, extracellular signal-regulated kinase and glycogen synthase kinase-3β. It was also found that expression of tau40 promoted microglial migration and phagocytosis, but not proliferation. And we observed increased secretion of several cytokines, including interleukin (IL)-1β, IL-6, IL-10, tumor necrosis factor-α and nitric oxide after the expression of tau40. These data suggest a novel role of human 2N/4R tau in microglial activation.

Betaine attenuates Alzheimer-like pathological changes and memory deficits induced by homocysteine

Hyperhomocysteinemia (Hhcy) may induce memory deficits with β-amyloid (Aβ) accumulation and tau hyperphosphorylation. Simultaneous supplement of folate and vitamin B12 partially restored the plasma homocysteine level and attenuated tau hyperphosphorylation, Aβ accumulation and memory impairments induced by Hhcy. However, folate and vitamin B12 treatment have no effects on Hhcy which has the methylenetetrahydrofolate reductase genotype mutation. In this study, we investigated the effects of simultaneous supplement of betaine on Alzheimer-like pathological changes and memory deficits in hyperhomocysteinemic rats after a 2-week induction by vena caudalis injection of homocysteine (Hcy). We found that supplementation of betaine could ameliorate the Hcy-induced memory deficits, enhance long-term potentiation (LTP) and increase dendritic branches numbers and the density of the dendritic spines, with up-regulation of NR1, NR2A, synaptotagmin, synaptophysin, and phosphorylated synapsin I protein levels. Supplementation of betaine also attenuated the Hcy-induced tau hyperphosphorylation at multiple AD-related sites through activation protein phosphatase-2A (PP2A) with decreased inhibitory demethylated PP2A(C) at Leu309 and phosphorylated PP2A(C) at Tyr307. In addition, supplementation of betaine also decreased Aβ production with decreased presenilin-1 protein levels. Our data suggest that betaine could be a promising candidate for arresting Hcy-induced AD-like pathological changes and memory deficits.