Microglial VPS35 deficiency impairs Aβ phagocytosis and Aβ-induced disease-associated microglia, and enhances Aβ associated pathology

VPS35-Retromer: Multifunctional Roles in Various Biological Processes - A Focus on Neurodegenerative Diseases and Cancer

The Vacuolar Protein Sorting 35 (VPS35)-Retromer complex plays a pivotal role in intracellular protein trafficking and recycling. As an integral component of the Retromer complex, VPS35 selectively recognizes and retrogradely transports membrane protein receptors to the trans-Golgi network, thereby preventing the degradation of transmembrane proteins by lysosomes after they have fulfilled their physiological functions, and facilitating their continued activity. VPS35 regulates autophagy, mitophagy, mitochondrial homeostasis, and various other biological processes, including epidermal regeneration, neuronal iron homeostasis, and synaptic function. Studies have shown that mutations or dysfunctions in VPS35 disrupt the normal operation of Retromer, impair neuronal health and survival, and contribute to the onset of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases. Additionally, VPS35 modulates tumor growth and metastasis in cancers such as liver and breast cancer through the regulation of multiple signaling pathways. Targeting VPS35 might be a potential therapy in clinic treatment of neurodegenerative diseases and cancers.

Asrij/OCIAD1 depletion reduces inflammatory microglial activation and ameliorates Aβ pathology in an Alzheimer's disease mouse model

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-beta (Aβ) plaques and neurofibrillary tangles, neuroinflammation, and glial activation. Asrij/OCIAD1 (Ovarian Carcinoma Immunoreactive Antigen Domain containing protein 1) is an AD-associated factor. Increased Asrij levels in the brains of AD patients and mouse models are linked to the severity of neurodegeneration. However, the contribution of Asrij to AD progression and whether reducing Asrij levels is sufficient to mitigate Aβ pathology in vivo is unclear.

METHODS

To explore the impact of Asrij on AD pathology, we deleted asrij in the APP/PS1 mouse model of AD and analyzed the effects on AD hallmarks. We used the Morris water maze and open field test to assess behavioral performance. Using immunohistochemistry and biochemical analyses, we evaluated Aβ plaque load, neuronal and synaptic damage, and gliosis. Further, we utilized confocal microscopy imaging, flow cytometry, and RNA sequencing analysis to comprehensively investigate changes in microglial responses to Aβ pathology upon Asrij depletion.

RESULTS

Asrij depletion ameliorates cognitive impairments, Aβ deposition, neuronal and synaptic damage, and reactive astrogliosis in the AD mouse. Notably, Asrij-deficient microglia exhibit reduced plaque-associated proliferation and decreased phagocytic activation. Transcriptomic analyses of AD microglia reveal upregulation of energy metabolism pathways and downregulation of innate immunity and inflammatory pathways upon Asrij depletion. Mechanistically, loss of Asrij increases mitochondrial activity and impedes the acquisition of a pro-inflammatory disease-associated microglia (DAM) state. Reduced levels of proinflammatory cytokines and decreased STAT3 and NF-κB activation indicate protective changes in AD microglia. Taken together, our results suggest that increased Asrij levels reported in AD, may suppress microglial metabolic activity and promote inflammatory microglial activation, thereby exacerbating AD pathology.

CONCLUSIONS

In summary, we show that Asrij depletion ameliorates Aβ pathology, neuronal and synaptic damage, gliosis, and improves behavioral performance in APP/PS1 mice. This supports that Asrij exacerbates the AD pathology. Mechanistically, Asrij is critical for the development of DAM and promotes neuroinflammatory signaling activation in microglia, thus restricting neuroprotective microglial responses. Hence, reducing Asrij in this context may help retard AD. Our work positions Asrij as a critical molecular regulator that links microglial dysfunction to AD pathogenesis.

Galectin-1 Regulates Inflammatory Responses and Promotes Microglial M2 Polarization in Chronic Migraine

Chronic migraine (CM) is a severe and debilitating neurological disorder with an unclear pathophysiology. Galectin-1, a β-galactoside-binding protein, is known for its anti-inflammatory and immune-regulatory effects in various inflammation-related diseases. However, its role in CM has not been fully elucidated. In this study, we analysed data from CM patients and employed a nitroglycerin-induced CM mouse model to explore the potential role of galectin-1. Serum galectin-1 levels were significantly lower in CM patients compared with healthy controls. Additionally, galectin-1 levels were negatively correlated with Visual Analogue Scale (VAS) and Headache Impact Test (HIT-6) scores. CM patients also exhibited elevated levels of IL-6 and TNF-α and reduced levels of IL-10. Notably, galectin-1 levels were inversely correlated with IL-6 and TNF-α and positively correlated with IL-10. In the CM mouse model, galectin-1 expression was significantly reduced in the spinal trigeminal nucleus caudalis (Sp5C) region. Supplementation with galectin-1 significantly increased paw and periorbital mechanical thresholds and reduced light aversion and anxiety-like behaviours. Moreover, galectin-1 enhanced microglial morphology, promoted M2 polarization, reduced the expression of pro-inflammatory factors IL-6 and TNF-α and increased levels of the anti-inflammatory cytokine IL-10. Mechanistically, the effects of galectin-1 on microglia may involve the activation of the PI3K/AKT signalling pathway, as evidenced by increased phosphorylation of PI3K and AKT. In summary, our study demonstrates that galectin-1 plays a crucial role in the pathogenesis of chronic migraine. Exogenous supplementation of galectin-1 effectively alleviates migraine symptoms and promotes microglial M2 polarization, suggesting that galectin-1 may represent a novel therapeutic target for CM.

Endosomal traffic disorders: a driving force behind neurodegenerative diseases

Endosomes are crucial sites for intracellular material sorting and transportation. Endosomal transport is a critical process involved in the selective uptake, processing, and intracellular transport of substances. The equilibrium between endocytosis and circulation mediated by the endosome-centered transport pathway plays a significant role in cell homeostasis, signal transduction, and immune response. In recent years, there have been hints linking endosomal transport abnormalities to neurodegenerative diseases, including Alzheimer's disease. Nonetheless, the related mechanisms remain unclear. Here, we provide an overview of endosomal-centered transport pathways and highlight potential physiological processes regulated by these pathways, with a particular focus on the correlation of endosomal trafficking disorders with common pathological features of neurodegenerative diseases. Additionally, we summarize potential therapeutic agents targeting endosomal trafficking for the treatment of neurodegenerative diseases.

The crucial role of VPS35 and SHH in Parkinson's disease: Understanding the mechanisms behind the neurodegenerative disorder

Parkinson's disease (PD) is indeed a complex neurodegenerative disorder recognized by the progressive depletion of dopaminergic neurons in the brain, particularly in the substantia nigra region, leading to motor impairments and other symptoms. But at the molecular level, the study about PD still lacks. As the number of cases worldwide continues to increase, it is critical to focus on the cellular and molecular mechanisms of the disease's presentation and neurodegeneration to develop novel therapeutic approaches. At the molecular level, the complexity is more due to the involvement of vacuolar protein sorting 35 (VPS35) and sonic hedgehog (SHH) signaling in PD (directly or indirectly), leading to one of the most prominent hallmarks of the disease, which is an accumulation of α-synuclein. This elevated pathogenesis may result from impaired autophagy due to mutation in the case of VPS35 and impairment in SHH signaling at the molecular level. The traditional understanding of PD is marked by the disruption of dopaminergic neurons and dopaminergic signaling, which exacerbates symptoms of motor function deficits. However, the changes at the molecular level that are being disregarded also impact the overall health of the dopaminergic system. Gaining insight into these two unique mechanisms is essential to determine whether they give neuroprotection or have no effect on the health of neurons. Hence, here we tried to simplify the understanding of the role of VPS35 and SHH signaling to comprehend it in one direction.

Berberine modulates microglial polarization by activating TYROBP in Alzheimer's disease

BACKGROUND

Characterized by β-amyloid (Aβ) plaques, neurofibrillary tangles, and aberrant neuroinflammation in the brain, Alzheimer's disease (AD) is the most common neurodegenerative disease. Microglial polarization is a subtle mechanism which maintains immunological homeostasis and has emerged as a putative therapeutic to combat AD. Berberine (BBR) is a natural alkaloid compound with multiple pharmacological effects, and has shown considerable therapeutic potential against inflammatory disorders. However, BBR functions and underlying mechanisms in neuroinflammation remain unclear.

PURPOSE

To examine BBR pharmacological effects and mechanisms in neuroinflammation with a view to treating AD.

METHODS

BBR effects on cognitive performance in 5 × FAD mice were assessed using open field, Y-maze, and Morris Water Maze (MWM) tests. Neuroinflammation-related markers and Aβ pathology were examined in brain sections from mice. Transcriptomic analyses of hippocampus tissues were also conducted. Microglial BV2 cells were also used to verify potential BBR mechanisms in neuroinflammation and microglial polarization.

RESULTS

BBR improved cognitive performance, reduced amyloid pathology, and alleviated aberrant neuroinflammation in an AD mouse model. BBR induced microglial polarization to an M2-like phenotype, which was manifested by lowered and elevated proinflammatory and anti-inflammatory cytokine production, respectively, improved microglial uptake and Aβ clearance. Mechanistically, BBR directly interacted with TYROBP and promoted its activation by stabilizing TYROBP oligomerization. TYROBP knockdown aggravated M1-like polarization and pro-inflammatory gene expression in microglial cells in the presence of lipopolysaccharide (LPS)+Aβ, while blocked microglial M2-like polarization benefited from BBR administration.

CONCLUSIONS

BBR modulated neuroinflammation by regulating microglial polarization via TYROBP activation. Our study provided new insight into BBR pharmacological actions in regulating microglial homeostasis and combating AD.

Haploinsufficiency and Alzheimer's Disease: The Possible Pathogenic and Protective Genetic Factors

Alzheimer's disease (AD) is a complex neurodegenerative disorder influenced by various genetic factors. In addition to the well-established amyloid precursor protein (APP), Presenilin-1 (PSEN1), Presenilin-2 (PSEN2), and apolipoprotein E (APOE), several other genes such as Sortilin-related receptor 1 (SORL1), Phospholipid-transporting ATPase ABCA7 (ABCA7), Triggering Receptor Expressed on Myeloid Cells 2 (TREM2), Phosphatidylinositol-binding clathrin assembly protein (PICALM), and clusterin (CLU) were implicated. These genes contribute to neurodegeneration through both gain-of-function and loss-of-function mechanisms. While it was traditionally thought that heterozygosity in autosomal recessive mutations does not lead to disease, haploinsufficiency was linked to several conditions, including cancer, autism, and intellectual disabilities, indicating that a single functional gene copy may be insufficient for normal cellular functions. In AD, the haploinsufficiency of genes such as ABCA7 and SORL1 may play significant yet under-explored roles. Paradoxically, heterozygous knockouts of PSEN1 or PSEN2 can impair synaptic plasticity and alter the expression of genes involved in oxidative phosphorylation and cell adhesion. Animal studies examining haploinsufficient AD risk genes, such as vacuolar protein sorting-associated protein 35 (VPS35), sirtuin-3 (SIRT3), and PICALM, have shown that their knockout can exacerbate neurodegenerative processes by promoting amyloid production, accumulation, and inflammation. Conversely, haploinsufficiency in APOE, beta-secretase 1 (BACE1), and transmembrane protein 59 (TMEM59) was reported to confer neuroprotection by potentially slowing amyloid deposition and reducing microglial activation. Given its implications for other neurodegenerative diseases, the role of haploinsufficiency in AD requires further exploration. Modeling the mechanisms of gene knockout and monitoring their expression patterns is a promising approach to uncover AD-related pathways. However, challenges such as identifying susceptible genes, gene-environment interactions, phenotypic variability, and biomarker analysis must be addressed. Enhancing model systems through humanized animal or cell models, utilizing advanced research technologies, and integrating multi-omics data will be crucial for understanding disease pathways and developing new therapeutic strategies.

Functional Relationships between L1CAM, LC3, ATG12, and Aβ

Abnormal protein accumulations in the brain are linked to aging and the pathogenesis of dementia of various types, including Alzheimer's disease. These accumulations can be reduced by cell indigenous mechanisms. Among these is autophagy, whereby proteins are transferred to lysosomes for degradation. Autophagic dysfunction hampers the elimination of pathogenic protein aggregations that contribute to cell death. We had observed that the adhesion molecule L1 interacts with microtubule-associated protein 1 light-chain 3 (LC3), which is needed for autophagy substrate selection. L1 increases cell survival in an LC3-dependent manner via its extracellular LC3 interacting region (LIR). L1 also interacts with Aβ and reduces the Aβ plaque load in an AD model mouse. Based on these results, we investigated whether L1 could contribute to autophagy of aggregated Aβ and its clearance. We here show that L1 interacts with autophagy-related protein 12 (ATG12) via its LIR domain, whereas interaction with ubiquitin-binding protein p62/SQSTM1 does not depend on LIR. Aβ, bound to L1, is carried to the autophagosome leading to Aβ elimination. Showing that the mitophagy-related L1-70 fragment is ubiquitinated, we expect that the p62/SQSTM1 pathway also contributes to Aβ elimination. We propose that enhancing L1 functions may contribute to therapy in humans.

Microglial senescence in neurodegeneration: Insights, implications, and therapeutic opportunities

The existing literature on neurodegenerative diseases (NDDs) reveals a common pathological feature: the accumulation of misfolded proteins. However, the heterogeneity in disease onset mechanisms and the specific brain regions affected complicates the understanding of the diverse clinical manifestations of individual NDDs. Dementia, a hallmark symptom across various NDDs, serves as a multifaceted denominator, contributing to the clinical manifestations of these disorders. There is a compelling hypothesis that therapeutic strategies capable of mitigating misfolded protein accumulation and disrupting ongoing pathogenic processes may slow or even halt disease progression. Recent research has linked disease-associated microglia to their transition into a senescent state-characterized by irreversible cell cycle arrest-in aging populations and NDDs. Although senescent microglia are consistently observed in NDDs, few studies have utilized animal models to explore their role in disease pathology. Emerging evidence from experimental rat models suggests that disease-associated microglia exhibit characteristics of senescence, indicating that deeper exploration of microglial senescence could enhance our understanding of NDD pathogenesis and reveal novel therapeutic targets. This review underscores the importance of investigating microglial senescence and its potential contributions to the pathophysiology of NDDs, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Additionally, it highlights the potential of targeting microglial senescence through iron chelation and senolytic therapies as innovative approaches for treating age-related NDDs.

Exploring the triad: VPS35, neurogenesis, and neurodegenerative diseases

Vacuolar protein sorting 35 (VPS35), a critical component of the retromer complex, plays a pivotal role in the pathogenesis of neurodegenerative diseases (NDs). It is involved in protein transmembrane sorting, facilitating the transport from endosomes to the trans-Golgi network (TGN) and plasma membrane. Recent investigations have compellingly associated mutations in the VPS35 gene with neurodegenerative disorders such as Parkinson's and Alzheimer's disease. These genetic alterations are implicated in protein misfolding, disrupted autophagic processes, mitochondrial dysregulation, and synaptic impairment. Furthermore, VPS35 exerts a notable impact on neurogenesis by influencing neuronal functionality, protein conveyance, and synaptic performance. Dysregulation or mutation of VPS35 may escalate the progression of neurodegenerative conditions, underscoring its pivotal role in safeguarding neuronal integrity. This review comprehensively discusses the role of VPS35 and its functional impairments in NDs. Furthermore, we provide an overview of the impact of VPS35 on neurogenesis and further explore the intricate relationship between neurogenesis and NDs. These research advancements offer novel perspectives and valuable insights for identifying potential therapeutic targets in the treatment of NDs.

VPS35 or retromer as a potential target for neurodegenerative disorders: barriers to progress

INTRODUCTION

Vacuolar Protein Sorting 35 (VPS35) is pivotal in the retromer complex, governing transmembrane protein trafficking within cells, and its dysfunction is implicated in neurodegenerative diseases. A missense mutation, Asp620Asn (D620N), specifically ties to familial late-onset Parkinson's, while reduced VPS35 levels are observed in Alzheimer's, amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and tauopathies. VPS35's absence in certain neurons during development can initiate neurodegeneration, highlighting its necessity for neural health. Present therapeutic research mainly targets the clearance of harmful protein aggregates and symptom management. Innovative treatments focusing on VPS35 are under investigation, although fully understanding the mechanisms and optimal targeting strategies remain a challenge.

AREAS COVERED

This review offers a detailed account of VPS35's discovery, its role in neurodegenerative mechanisms - especially in Parkinson's and Alzheimer's - and its link to other disorders. It shines alight on recent insights into VPS35's function in development, disease, and as a therapeutic target.

EXPERT OPINION

VPS35 is integral to cellular function and disease association, making it a significant candidate for developing therapies. Progress in modulating VPS35's activity may lead to breakthrough treatments that not only slow disease progression but may also act as biomarkers for neurodegeneration risk, marking a step forward in managing these complex conditions.

Intermittent hypoxia training enhances Aβ endocytosis by plaque associated microglia via VPS35-dependent TREM2 recycling in murine Alzheimer's disease

BACKGROUND

Beta-amyloid (Aβ) deposition in the brain parenchyma is a crucial initiating step in the amyloid cascade hypothesis of Alzheimer's disease (AD) pathology. Furthermore, dysfunction of plaque-associated microglia, also known as disease-associated microglia (DAM) has been reported to accelerate Aβ deposition and cognitive impairment. Our previous research demonstrated that intermittent hypoxia training (IHT) improved AD pathology by upregulating autophagy in DAM, thereby enhancing oligomeric Aβ (oAβ) clearance. Considering that oAβ internalization is the initial stage of oAβ clearance, this study focused on the IHT mechanism involved in upregulating Aβ uptake by DAM.

METHODS

IHT was administered to 8-month-old APP/PS1 mice or 6-month-old microglial vacuolar protein sorting 35 (VPS35) knockout mice in APP/PS1 background (MG VPS35 KO: APP/PS1) for 28 days. After the IHT, the spatial learning-memory capacity of the mice was assessed. Additionally, AD pathology was determined by estimating the nerve fiber and synapse density, Aβ plaque deposition, and Aβ load in the brain. A model of Aβ-exposed microglia was constructed and treated with IHT to explore the related mechanism. Finally, triggering receptor expressed on myeloid cells 2 (TREM2) intracellular recycling and Aβ internalization were measured using a fluorescence tracing technique.

RESULTS

Our results showed that IHT ameliorated cognitive function and Aβ pathology. In particular, IHT enhanced Aβ endocytosis by augmenting the intracellular transport function of microglial TREM2, thereby contributing to Aβ clearance. Furthermore, IHT specifically upregulated VPS35 in DAM, the primary cause for the enhanced intracellular recycling of TREM2. IHT lost ameliorative effect on Aβ pathology in MG VPS35 KO: APP/PS1 mice brain. Lastly, the IHT mechanism of VPS35 upregulation in DAM was mediated by the transcriptional regulation of VPS35 by transcription factor EB (TFEB).

CONCLUSION

IHT enhances Aβ endocytosis in DAM by upregulating VPS35-dependent TREM2 recycling, thereby facilitating oAβ clearance and mitigation of Aβ pathology. Moreover, the transcriptional regulation of VPS35 by TFEB demonstrates a close link between endocytosis and autophagy in microglia. Our study further elucidates the IHT mechanism in improving AD pathology and provides evidence supporting the potential application of IHT as a complementary therapy for AD.

Rbm8a regulates neurogenesis and reduces Alzheimer's disease-associated pathology in the dentate gyrus of 5×FAD mice

Alzheimer's disease is a prevalent and debilitating neurodegenerative condition that profoundly affects a patient's daily functioning with progressive cognitive decline, which can be partly attributed to impaired hippocampal neurogenesis. Neurogenesis in the hippocampal dentate gyrus is likely to persist throughout life but declines with aging, especially in Alzheimer's disease. Recent evidence indicated that RNA-binding protein 8A (Rbm8a) promotes the proliferation of neural progenitor cells, with lower expression levels observed in Alzheimer's disease patients compared with healthy people. This study investigated the hypothesis that Rbm8a overexpression may enhance neurogenesis by promoting the proliferation of neural progenitor cells to improve memory impairment in Alzheimer's disease. Therefore, Rbm8a overexpression was induced in the dentate gyrus of 5×FAD mice to validate this hypothesis. Elevated Rbm8a levels in the dentate gyrus triggered neurogenesis and abated pathological phenotypes (such as plaque formation, gliosis reaction, and dystrophic neurites), leading to ameliorated memory performance in 5×FAD mice. RNA sequencing data further substantiated these findings, showing the enrichment of differentially expressed genes involved in biological processes including neurogenesis, cell proliferation, and amyloid protein formation. In conclusion, overexpressing Rbm8a in the dentate gyrus of 5×FAD mouse brains improved cognitive function by ameliorating amyloid-beta-associated pathological phenotypes and enhancing neurogenesis.

Endocytosis and Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and is the most common cause of dementia. The pathogenesis of AD still remains unclear, including two main hypotheses: amyloid cascade and tau hyperphosphorylation. The hallmark neuropathological changes of AD are extracellular deposits of amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFTs). Endocytosis plays an important role in a number of cellular processes including communication with the extracellular environment, nutrient uptake, and signaling by the cell surface receptors. Based on the results of genetic and biochemical studies, there is a link between neuronal endosomal function and AD pathology. Taking this into account, we can state that in the results of previous research, endolysosomal abnormality is an important cause of neuronal lesions in the brain. Endocytosis is a central pathway involved in the regulation of the degradation of amyloidogenic components. The results of the studies suggest that a correlation between alteration in the endocytosis process and associated protein expression progresses AD. In this article, we discuss the current knowledge about endosomal abnormalities in AD.

Gene Co-Expression Analysis of Multiple Brain Tissues Reveals Correlation of FAM222A Expression with Multiple Alzheimer's Disease-Related Genes

Background

Alzheimer's disease (AD) is the most common form of dementia in the elderly marked by central nervous system (CNS) neuronal loss and amyloid plaques. FAM222A, encoding an amyloid plaque core protein, is an AD brain atrophy susceptibility gene that mediates amyloid-β aggregation. However, the expression interplay between FAM222A and other AD-related pathway genes is unclear.

Objective

Our goal was to study FAM222A's whole-genome co-expression profile in multiple tissues and investigate its interplay with other AD-related genes.

Methods

We analyzed gene expression correlations in Genotype-Tissue Expression (GTEx) tissues to identify FAM222A co-expressed genes and performed functional enrichment analysis on identified genes in CNS system.

Results

Genome-wide gene expression profiling identified 673 genes significantly correlated with FAM222A (p < 2.5×10-6) in 48 human tissues, including 298 from 13 CNS tissues. Functional enrichment analysis revealed that FAM222A co-expressed CNS genes were enriched in multiple AD-related pathways. Gene co-expression network analysis for identified genes in each brain region predicted other disease associated genes with similar biological function. Furthermore, co-expression of 25 out of 31 AD-related pathways genes with FAM222A was replicated in brain samples from 107 aged subjects from the Aging, Dementia and TBI Study.

Conclusion

This gene co-expression study identified multiple AD-related genes that are associated with FAM222A, indicating that FAM222A and AD-associated genes can be active simultaneously in similar biological processes, providing evidence that supports the association of FAM222A with AD.

Inhibition of LRRK2 kinase activity rescues deficits in striatal dopamine physiology in VPS35 p.D620N knock-in mice

Dysregulation of dopamine neurotransmission profoundly affects motor, motivation and learning behaviors, and can be observed during the prodromal phase of Parkinson's disease (PD). However, the mechanism underlying these pathophysiological changes remains to be elucidated. Mutations in vacuolar protein sorting 35 (VPS35) and leucine-rich repeat kinase 2 (LRRK2) both lead to autosomal dominant PD, and VPS35 and LRRK2 may physically interact to govern the trafficking of synaptic cargos within the endo-lysosomal network in a kinase-dependent manner. To better understand the functional role of VPS35 and LRRK2 on dopamine physiology, we examined Vps35 haploinsufficient (Haplo) and Vps35 p.D620N knock-in (VKI) mice and how their behavior, dopamine kinetics and biochemistry are influenced by LRRK2 kinase inhibitors. We found Vps35 p.D620N significantly elevates LRRK2-mediated phosphorylation of Rab10, Rab12 and Rab29. In contrast, Vps35 haploinsufficiency reduces phosphorylation of Rab12. While striatal dopamine transporter (DAT) expression and function is similarly impaired in both VKI and Haplo mice, that physiology is normalized in VKI by treatment with the LRRK2 kinase inhibitor, MLi-2. As a corollary, VKI animals show a significant increase in amphetamine induced hyperlocomotion, compared to Haplo mice, that is also abolished by MLi-2. Taken together, these data show Vps35 p.D620N confers a gain-of-function with respect to LRRK2 kinase activity, and that VPS35 and LRRK2 functionally interact to regulate DAT function and striatal dopamine transmission.

Relevance of tissue-resident memory CD8 T cells in the onset of Parkinson's disease and examination of its possible etiologies: infectious or autoimmune?

Tissue-resident memory CD8 T cells are responsible for local immune surveillance in different tissues, including the brain. They constitute the first line of defense against pathogens and cancer cells and play a role in autoimmunity. A recently published study demonstrated that CD8 T cells with markers of residency containing distinct granzymes and interferon-γ infiltrate the parenchyma of the substantia nigra and contact dopaminergic neurons in an early premotor stage of Parkinson's disease. This infiltration precedes α-synuclein aggregation and neuronal loss in the substantia nigra, suggesting a relevant role for CD8 T cells in the onset of the disease. To date, the nature of the antigen that initiates the adaptive immune response remains unknown. This review will discuss the role of tissue-resident memory CD8 T cells in brain immune homeostasis and in the onset of Parkinson's disease and other neurological diseases. We also discuss how aging and genetic factors can affect the CD8 T cell immune response and how animal models can be misleading when studying human-related immune response. Finally, we speculate about a possible infectious or autoimmune origin of Parkinson's disease.

Attenuation of Alzheimer's brain pathology in 5XFAD mice by PTH1-34, a peptide of parathyroid hormone

BACKGROUND

Alzheimer's disease (AD) and osteoporosis are two distinct diseases but often occur in the same patient. Their relationship remains poorly understood. Studies using Tg2576 AD animal model demonstrate bone deficits, which precede the brain phenotypes by several months, arguing for the independence of bone deficits on brain degeneration and raising a question if the bone deficits contribute to the AD development. To address this question, we investigated the effects of PTH_1-34, a peptide of parathyroid hormone analog and a well-recognized effective anabolic therapy drug for patients with osteoporosis, on 5XFAD animal model.

METHODS

5XFAD mice, an early onset β-amyloid (Aβ)-based AD mouse model, were treated with PTH_1-34 intermittently [once daily injection of hPTH_1-34 (50 μg/Kg), 5 days/week, starting at 2-month old (MO) for 2-3 month]. Wild type mice (C57BL/6) were used as control. The bone phenotypes were examined by microCT and evaluated by measuring serum bone formation and resorption markers. The AD relevant brain pathology (e.g., Aβ and glial activation) and behaviors were assessed by a combination of immunohistochemical staining analysis, western blots, and behavior tests. Additionally, systemic and brain inflammation were evaluated by serum cytokine array, real-time PCR (qPCR), and RNAscope.

RESULTS

A reduced trabecular, but not cortical, bone mass, accompanied with a decrease in bone formation and an increase in bone resorption, was detected in 5XFAD mice at age of 5/6-month old (MO). Upon PTH_1-34 treatments, not only these bone deficits but also Aβ-associated brain pathologies, including Aβ and Aβ deposition levels, dystrophic neurites, glial cell activation, and brain inflammatory cytokines, were all diminished; and the cognitive function was improved. Further studies suggest that PTH_1-34 acts on not only osteoblasts in the bone but also astrocytes in the brain, suppressing astrocyte senescence and expression of inflammatory cytokines in 5XFAD mice.

CONCLUSIONS

These results suggest that PTH_1-34 may act as a senolytic-like drug, reducing systemic and brain inflammation and improving cognitive function, and implicate PTH_1-34's therapeutic potential for patients with not only osteoporosis but also AD.

Promoting Endogenous Neurogenesis as a Treatment for Alzheimer's Disease

Alzheimer's disease (AD) is the most universal neurodegenerative disorder characterized by memory loss and cognitive impairment. AD is biologically defined by production and aggregation of misfolded protein including extracellular amyloid β (Aβ) peptide and intracellular microtubule-associated protein tau tangles in neurons, leading to irreversible neuronal loss. At present, regulation of endogenous neurogenesis to supplement lost neurons has been proposed as a promising strategy for treatment of AD. However, the exact underlying mechanisms of impaired neurogenesis in AD have not been fully explained and effective treatments targeting neurogenesis for AD are limited. In this review, we mainly focus on the latest research of impaired neurogenesis in AD. Then we discuss the factors affecting stages of neurogenesis and the interplay between neural stem cells (NSCs) and neurogenic niche under AD pathological conditions. This review aims to explore potential therapeutic strategies that promote endogenous neurogenesis for AD treatments.

LRRK2 Kinase Inhibition Attenuates Astrocytic Activation in Response to Amyloid β1-42 Fibrils

Intracerebral accumulation of amyloid-β in the extracellular plaques of Alzheimer's disease (AD) brains represents the main cause of reactive astrogliosis and neuroinflammatory response. Of relevance, leucine-rich repeat kinase 2 (LRRK2), a kinase linked to genetic and sporadic Parkinson's disease (PD), has been identified as a positive mediator of neuroinflammation upon different inflammatory stimuli, however its pathogenicity in AD remains mainly unexplored. In this study, by using pharmacological inhibition of LRRK2 and murine primary astrocytes, we explored whether LRRK2 regulates astrocytic activation in response to amyloid-β_1-42 (Aβ_1-42). Our results showed that murine primary astrocytes become reactive and recruit serine 935 phosphorylated LRRK2 upon Aβ_1-42 fibril exposure. Moreover, we found that pharmacological inhibition of LRRK2, with two different kinase inhibitors, can attenuate Aβ_1-42-mediated inflammation and favor the clearance of Aβ_1-42 fibrils in astrocytes. Overall, our findings report that LRRK2 kinase activity modulates astrocytic reactivity and functions in the presence of Aβ_1-42 deposits and indicate that PD-linked LRRK2 might contribute to AD-related neuroinflammation and pathogenesis.

Photo-Oxygenation as a New Therapeutic Strategy for Neurodegenerative Proteinopathies by Enhancing the Clearance of Amyloid Proteins

Alzheimer disease (AD) is associated with the aggregation of two amyloid proteins: tau and amyloid-β (Aβ). The results of immunotherapies have shown that enhancing the clearance and suppressing the aggregation of these two proteins are effective therapeutic strategies for AD. We have developed photocatalysts that attach oxygen atoms to Aβ and tau aggregates via light irradiation. Photo-oxygenation of these amyloid aggregates reduced their neurotoxicity by suppressing their aggregation both in vitro and in vivo. Furthermore, photo-oxygenation enhanced the clearance of Aβ in the brain and microglial cells. Here, we describe the effects of photo-oxygenation on tau and Aβ aggregation, and the potential of photo-oxygenation as a therapeutic strategy for AD, acting via microglial clearance.

Beware of Misdelivery: Multifaceted Role of Retromer Transport in Neurodegenerative Diseases

Retromer is a highly integrated multimeric protein complex that mediates retrograde cargo sorting from endosomal compartments. In concert with its accessory proteins, the retromer drives packaged cargoes to tubular and vesicular structures, thereby transferring them to the trans-Golgi network or to the plasma membrane. In addition to the endosomal trafficking, the retromer machinery participates in mitochondrial dynamics and autophagic processes and thus contributes to cellular homeostasis. The retromer components and their associated molecules are expressed in different types of cells including neurons and glial cells, and accumulating evidence from genetic and biochemical studies suggests that retromer dysfunction is profoundly involved in the pathogenesis of neurodegenerative diseases including Alzheimer’s Disease and Parkinson’s disease. Moreover, targeting retromer components could alleviate the neurodegenerative process, suggesting that the retromer complex may serve as a promising therapeutic target. In this review, we will provide the latest insight into the regulatory mechanisms of retromer and discuss how its dysfunction influences the pathological process leading to neurodegeneration.