Aβ Phagocytosis Research Articles

The Beneficial Effects of Combining Anti-Aβ Antibody NP106 and Curcumin Analog TML-6 on the Treatment of Alzheimer's Disease in APP/PS1 Mice.

Alzheimer’s disease (AD) is a progressive neurodegenerative disease with a multifactorial etiology. A multitarget treatment that modulates multifaceted biological functions might be more effective than a single-target approach. Here, the therapeutic efficacy of combination treatment using anti-Aβ antibody NP106 and curcumin analog TML-6 versus monotherapy was investigated in an APP/PS1 mouse model of AD. Our data demonstrate that both combination treatment and monotherapy attenuated brain Aβ and improved the nesting behavioral deficit to varying degrees. Importantly, the combination treatment group had the lowest Aβ levels, and insoluble forms of Aβ were reduced most effectively. The nesting performance of APP/PS1 mice receiving combination treatment was better than that of other APP/PS1 groups. Further findings indicate that enhanced microglial Aβ phagocytosis and lower levels of proinflammatory cytokines were concurrent with the aforementioned effects of NP106 in combination with TML-6. Intriguingly, combination treatment also normalized the gut microbiota of APP/PS1 mice to levels resembling the wild-type control. Taken together, combination treatment outperformed NP106 or TML-6 monotherapy in ameliorating Aβ pathology and the nesting behavioral deficit in APP/PS1 mice. The superior effect might result from a more potent modulation of microglial function, cerebral inflammation, and the gut microbiota. This innovative treatment paradigm confers a new avenue to develop more efficacious AD treatments.

Glycative Stress and the progression of Alzheimer-type Dementia: From the Perspective of Amyloid-beta Clearance

Glycative stress is a conception of a state that causes an excess of carbohydrate-derived or fatty acid-derived short-chain aldehydes in the body. Short-chain aldehydes, which are highly reactive, undergo a carbonylation process with lysine and arginine residues in proteins and form advanced glycation endproducts (AGEs). When postprandial hyperglycemia occurs, open-ring glucose with exposed aldehyde groups (-CHO) increases and various carbohydrate-derived aldehydes are formed simultaneously (this phenomenon is named “aldehyde sparks”). Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is an enzyme abundant intracellularly as the keystone of defense against glycative stress and plays a role in metabolizing highly toxic glyceraldehyde, however, under diabetic conditions, the enzyme activity is markedly reduced by forming S-(2-succinyl) cysteine-GAPDH. We also found that a high-fat diet reduced GAPDH activity and increased glyceraldehyde and methylglyoxal. High animal fat diets in particular require caution because they increase preference dependence on animal fat. In the lipid-rich brain, they promotes the formation of lipid-derived AGEs formed by methylglyoxal and acrolein providing evidence of their close association with amyloid cascade, ultimately leading to the onset of Alzheimer-type dementia. Through the process of amylod beta (Aβ) glycation modification and cross-linking, Aβ polymerization is promoted and deposited in the brain. Thus, neurotoxicity is aggravated. Furthermore, Aβ progresses toward being persistent and Aβ clearance is reduced. Tau proteins similarly undergo glycation modification and trigger polymerization. methylglyoxal or acrolein-derived glycated Aβ clearance by primary microglia cultured cells reduced significantly compared to the unglycated Aβ provides evidence of the reduced clearance upon glycation. It was also shown that melatonin, which promotes glycolytic cross-linking degradation, may promote microglial Aβ phagocytosis. We next plan to examine the potential of plant extracts that promote glycation cross-linking degradation to improve Aβ phagocytosis. Advanced Alzheimer-type dementia with a disoriented neural network hardly recovers with treatment. In this review article, we discussed possible future therapeutic strategies for Alzheimer-type dementia by increasing Aβ clearance from the early stage such as the prevention of Aβ-glycation and the promotion of glycated-Aβ degradation, which may be a paradigm shift.

Anti-inflammatory effects of 9-cis-retinoic acid on β-amyloid treated human microglial cells

Objective: Alzheimer’s disease (AD) is a neurodegenerative disease that abolishes cognitive and analytical abilities to perform basic day-to-day tasks. Microglia are involved in AD-associated neuroinflammation in response to amyloid β‐peptide (Aβ). This study focused on observing the immunomodulatory effects of 9-cis-retinoic acid (9-Cis-RA) the active metabolite of vitamin A, on Aβ-treated human microglial HMO6 cells. Methods: HMO6 cells were treated with Aβ42 in the absence or presence of 9-cis-RA, and the expression of M1-and M2-associated molecules, Toll like receptors (TLRs), and triggering receptor expressed on myeloid cells 2 (TREM2) were examined. Results: The levels of M1-markers [cluster of differentiation (CD86) and inducible nitric oxide synthase (iNOS)] and -cytokines [tumor necrosis factor (TNF-α), interleukin (IL)-6, and IL-1β], inflammatory receptors (TLR2 and TLR4), and reactive oxygen species increased significantly in Aβ-treated HMO6 cells. In contrast, the levels of M2-markers (CD206 and arginase-1) and -cytokines (IL-10, IL-4, and C-C motif chemokine ligand 17) the anti-inflammatory receptor TLR10 was significantly suppressed. However, 9-cis-RA treatment reversed the Aβ-induced upregulation of expression of M1-associated molecules and upregulated the expression of M2-associated molecules. Moreover, 9-cis-RA treatment augmented Aβ uptake by HMO6 cells, possibly by increasing the cell surface protein levels of TREM2, which is a receptor of Aβ that promotes Aβ phagocytosis by microglia. Conclusion: Our results suggest that 9-cis-RA is a potential therapeutic agent for AD.

Targeting MicroRNA-485-3p Blocks Alzheimer's Disease Progression.

Alzheimer’s disease (AD) is a form of dementia characterized by progressive memory decline and cognitive dysfunction. With only one FDA-approved therapy, effective treatment strategies for AD are urgently needed. In this study, we found that microRNA-485-3p (miR-485-3p) was overexpressed in the brain tissues, cerebrospinal fluid, and plasma of patients with AD, and its antisense oligonucleotide (ASO) reduced Aβ plaque accumulation, tau pathology development, neuroinflammation, and cognitive decline in a transgenic mouse model of AD. Mechanistically, miR-485-3p ASO enhanced Aβ clearance via CD36-mediated phagocytosis of Aβ in vitro and in vivo. Furthermore, miR-485-3p ASO administration reduced apoptosis, thereby effectively decreasing truncated tau levels. Moreover, miR-485-3p ASO treatment reduced secretion of proinflammatory cytokines, including IL-1β and TNF-α, and eventually relieved cognitive impairment. Collectively, our findings suggest that miR-485-3p is a useful biomarker of the inflammatory pathophysiology of AD and that miR-485-3p ASO represents a potential therapeutic candidate for managing AD pathology and cognitive decline.

Targeting microRNA‐485‐3p blocks Alzheimer's disease progression

AbstractBackgroundAlzheimer’s disease (AD) is a form of dementia characterized by progressive memory decline and cognitive dysfunction, which affects more than 44 million people worldwide. Currently, there is no effective therapy for AD despite its increasing global incidence; thus, effective treatment strategies for AD are urgently needed. While several drugs that decrease amyloid beta (Aβ) production or increase Aβ clearance in the brain have been identified, treatment with these drugs is poorly correlated with improvements in AD severity and cognitive dysfunction.MethodExpression of miR‐485‐3p was analysed by real‐time PCR in the human frontal cortex (8 healthy controls (HC), 7 AD patients), precentral gyrus (6 HC, 8 AD), cerebrospinal fluid (CSF) (6 HC, 7 AD), plasma exosomes (10 HC, 17 mild cognitive impairment (MCI), 12 AD). Aβ 1–42 plaque immunofluorescence and tau pathology were imaged in primary cultured mouse neurons after lentivirus‐derived miR485‐3p transduction. MiR‐485‐3p antisense oligonucleotide (ASO, 1.5 μg) or control oligonucleotide formulated with the in vivo jetPEI reagent was injected into 8‐month‐old 5XFAD mice by ICV injection once weekly for two weeks. Behavioral tests were performed at 8 months and their brain pathology was examined after 8‐week‐washout at 10 months.ResultWe found that the miR‐485‐3p is overexpressed in brain tissues and CSF of AD patients, and its ASO reduces Aβ plaques, tau pathology, neuroinflammation, and cognitive decline in a transgenic mouse model of AD. Mechanistically, miR‐485‐3p ASO enhanced Aβ clearance via CD36‐mediated phagocytosis of Aβ in vitro and in vivo. We found that miR‐485‐3p ASO reduces apoptosis, which effectively decreases truncated tau levels. Further, miR‐485‐3p ASO reduced secretion of pro‐inflammatory cytokines, including IL‐1β and TNF‐α, and eventually relieved cognitive impairment.ConclusionCollectively, our findings suggest that miR‐485‐3p is a useful biomarker as well as a causative factor of the inflammatory pathophysiology of AD; furthermore, miR‐485‐3p ASO represents a candidate therapy for AD pathology and cognitive decline, establishing a new paradigm in the AD field.

The role of microglia niacin receptor (HCAR2) in Alzheimer's disease.

Dietary intake of niacin reduces the risk of Alzheimer´s disease (AD) and protects against age-related cognitive decline. Niacin is a ligand for the niacin receptor (HCAR2), which, in the brain, is selectively expressed by microglia. HCAR2 is significantly increased in the AD brain, and activation of this receptor has been shown to be neuroprotective in stroke and demyelination models. Thus, we hypothesized that microglial HCAR2 plays a protective role in AD. To understand the role of HCAR2 in AD, we compared disease progression of the AD mouse model 5xFAD lacking the Hcar2 gene (5xFAD;Hcar2 -/- ) with 5xFAD;Hcar2 +/+ . Plaque burden, neuronal loss, microglial function, cognition and gene expression were analyzed in both genotypes at 4 and 6 months of age. Furthermore, 5 month-old 5xFAD mice were treated with a FDA-approved formulation of niacin (Niaspan®) daily, by oral gavage for 30 days with 100 mg niacin/kg to assess the effects of pharmacological activation of HCAR2 on disease progression in these mice. Our results show a dramatic increase of microglial HCAR2 expression in the AD brain. In 5xFAD mice, the induction of Hcar2 is selective for microglia associated with amyloid plaques. 5xFAD;Hcar2 -/- exhibit a more severe amyloid pathology compared to controls, increased plaque load and neuronal loss, decreased Aβ phagocytosis by microglia and accelerated onset of cognitive deficits. On the other hand, activation of HCAR2 in 5xFAD with niacin treatment reduces neuronal loss and plaque burden, increases Aβ phagocytosis and rescues working memory deficits. Our data suggest the microglia receptor HCAR2 plays a protective role in AD, and is part of an endogenous response from microglia to tackle the disease. HCAR2 is a potential therapeutic target to modulate microglia phenotype towards beneficial outcomes in AD. Our results indicate that the activation of HCAR2 with the FDA-approved formulation of niacin, Niaspan®, leads to neuroprotective effects in AD, even after the onset of severe amyloid pathology, highlighting the translational potential of this strategy into clinical practice, supporting further study of this therapeutic approach.

A new blood‐based biomarker of Aβ clearance: The monocyte Aβ mid‐domain assay

AbstractBackgroundDeficiency in cerebral Amyloid beta (Aβ) clearance is implicated in the pathogenesis of Alzheimer’s disease (AD), and Aβ clearance systems are potential therapeutic targets in AD. Clearance of Aβ is a complex process were phagocytosis and degradation of Aβ are two important components. Innate immune‐linked genetic risk factors contribute to AD, and innate immune cells; microglia in the brain and monocytes/macrophages in the peripheral blood (PB), phagocytose Aβ and contribute to clearance. Our objective was to develop an assay measuring Aβ mid‐domain peptides in relevant biological specimens. The intracellular concentration of peptides containing mid‐domain fragments may reflect phagocytic activity or Aβ degradation efficiency.MethodAn immunoassay on the Quanterix Single Molecule Array (Simoa) platform was developed against an Ab 20‐34 peptide using a proprietary anti‐mid‐domain sheep monoclonal antibody as capture antibody (2A9). The detector reagent consists of an anticomplex antibody using Bio‐Rad HuCAL technology (H3) ensuring the optimal Aβ mid‐domain peptide specificity and assay sensitivity. Monocytes were isolated from 8 ml blood samples using a combination of BD CPT blood sampling tubes and RosetteSep antibodies from StemCell.ResultThe 2A9/H3 immunoassay run on the Simoa platform detected Aβ mid‐domain containing peptides with a lower limit of quantification (LLOQ) of approximately 0,7 pg/ml resulting in measurable levels of the peptides in both CSF and monocyte lysates (figure 1 a).ConclusionAs shown in figure 1 b, the 2A9/H3 combination has a high specificity for mid‐domain restricted peptides. Here we show that as used in a sensitive Simoa‐assay, this assay detects Aβ mid‐domain containing peptides both in CSF and monocyte lysates, and may serve as a tool for PB measurement of Aβ catabolism in both disease progression studies and intervention studies. The PreADx ™ assay is an accurate and highly sensitive immunoassay for quantification of mid domain Aβ peptides in relevant biological fluids and cells. The assay demonstrates high precision with monocyte lysates and linearity in spiking and dilution experiments (not shown).

Combinational therapy, concomitantly targeting post‐translational modified Aβ peptides and CD33, leads to an add‐on effect in passive immunotherapy

AbstractBackgroundPassive immunotherapy is a very promising approach for the treatment of Alzheimer’s disease (AD). We recently demonstrated that the antibody‐mediated targeting of isoD7‐modified Aβ peptides leads to the attenuation of AD‐like amyloid pathology in 5xFAD mice (Gnoth et al., 2020). Targeting post‐translationally modified Aβ peptides is a promising approach for reduction of effective therapeutic antibody amount and thereby decreasing treatment‐related side effects. Nevertheless, high dosing of monoclonal antibodies and appearance of side effects such as amyloid‐related imaging abnormalities (ARIAs) provide room for approaches such as combination therapies.MethodWe investigated the role of CD33 for Aβ phagocytosis in transgenic mice treated with an isoD7‐Aβ antibody. CD33 or sialic‐acid‐binding immunoglobulin‐like lectin 3 (Siglec‐3) is an inhibitory receptor molecule on the surface of brain microglia. We generated a new mouse line by crossing 5xFAD mice (Oakley et al., 2006) with CD33 knock out mice (Brinkman‐Van der Linden et al., 2003). This mouse line was then used for treatment studies with our anti‐isoD7‐Aβ antibody K11_IgG2a. Therefore, 3month‐old female 5xFAD and 5xFAD/CD33 mice were treated with 4 mg/kg K11_IgG2a and IgG2a isotype control. After 38 weeks treatment an Elevated Plus Maze (EPM) test have been performed, followed by the preparation of mouse brain and the read out by ELISA and Immunohistochemistry.ResultWe could demonstrate that CD33 knock out leads to the reduction of Aβ plaque load as well as the rescue of behavioral deficits in 5xFAD mice. Above that, we detected elevated amounts of plaque surrounding microglia in 5xFAD/CD33KO mice receiving antibody treatment, followed by an even more decrease of Aβ plaque load.ConclusionIn summary, a combinational therapy, concomitantly targeting post‐translational modified Aβ peptides and CD33, leads to an add‐on effect in passive immunotherapy.

Nogo receptor impairs the clearance of fibril amyloid-β by microglia and accelerates Alzheimer's-like disease progression.

Alzheimer's disease (AD) is characterized by the progressive accumulation of β‐amyloid (Aβ)‐containing amyloid plaques, and microglia play a critical role in mediating Aβ clearance. Mounting evidence has confirmed that the ability of microglia in clearing Aβ decreased with aging and AD progress, but the underlying mechanisms are unclear. Previously, we have demonstrated that Nogo receptor (NgR), a receptor for three axon growth inhibitors associated with myelin, can decrease adhesion and migration of microglia to fibrils Aβ with aging. However, whether NgR expressed on microglia affect microglia phagocytosis of fibrils Aβ with aging remains unclear. Here, we found that aged but not young microglia showed increased NgR expression and decreased Aβ phagocytosis in APP/PS1 transgenic mice. NgR knockdown APP/PS1 mice showed simultaneous reduced amyloid burden and improved spatial learning and memory, which were associated with increased Aβ clearance. Importantly, Nogo‐P4, an agonist of NgR, enhanced the protein level of p‐Smad2/3, leading to a significant transcriptional inhibition of CD36 gene expression, which in turn decreased the microglial phagocytosis of Aβ. Moreover, ROCK accounted for Nogo‐P4‐induced activation of Smad2/3 signaling. Finally, the decreasing effect of NgR on microglial Aβ uptake was confirmed in a mouse model of intra‐hippocampal fAβ injection. Our findings suggest that NgR may play an important role in the regulation of Aβ homeostasis, and has potential as a therapeutic target for AD.

Recent advances in molecular pathways and therapeutic implications targeting neuroinflammation for Alzheimer's disease.

Alzheimer’s disease (AD) is a major contributor of dementia leading to the degeneration of neurons in the brain with major symptoms like loss of memory and learning. Many evidences suggest the involvement of neuroinflammation in the pathology of AD. Cytokines including TNF-α and IL-6 are also found increasing the BACE1 activity and expression of NFκB resulting in generation of Aβ in AD brain. Following the interaction of Aβ with microglia and astrocytes, other inflammatory molecules also get translocated to the site of inflammation by chemotaxis and exaggerate neuroinflammation. Various pathways like NFκB, p38 MAPK, Akt/mTOR, caspase, nitric oxide and COX trigger microglia to release inflammatory cytokines. PPARγ agonists like pioglitazone increases the phagocytosis of Aβ and reduces inflammatory cytokine IL-1β. Celecoxib and roficoxib like selective COX-2 inhibitors also ameliorate neuroinflammation. Non-selective COX inhibitor indomethacin is also potent inhibitor of inflammatory mediators released from microglia. Mitophagy process is considered quite helpful in reducing inflammation due to microglia as it promotes the phagocytosis of over activated microglial cells and other inflammatory cells. Mitophagy induction is also beneficial in the removal of damaged mitochondria and reduction of infiltration of inflammatory molecules at the site of accumulation of the damaged mitochondria. Targeting these pathways and eventually ameliorating the activation of microglia can mitigate neuroinflammation and come out as a better therapeutic option for the treatment of Alzheimer’s disease.

BAD-mediated neuronal apoptosis and neuroinflammation contribute to Alzheimer's disease pathology

SummaryAlzheimer’s disease (AD) is the most common progressive neurodegenerative disease. However, the underlying molecular mechanism is incompletely understood. Here we report that the pro-apoptotic protein BAD as a key regulator for neuronal apoptosis, neuroinflammation and Aβ clearance in AD. BAD pro-apoptotic activity is significantly increased in neurons of AD patients and 5XFAD mice. Conversely, genetic disruption of Bad alleles restores spatial learning and memory deficits in 5XFAD mice. Mechanistically, phosphorylation and inactivation of BAD by neurotropic factor-activated Akt is abrogated in neurons under AD condition. Through reactive oxygen species (ROS)-oxidized mitochondrial DNA (mtDNA) axis, BAD also promotes microglial NLRP3 inflammasome activation, thereby skewing microglia toward neuroinflammatory microglia to inhibit microglial phagocytosis of Aβ in AD mice. Our results support a model in which BAD contributes to AD pathologies by driving neuronal apoptosis and neuroinflammation but suppressing microglial phagocytosis of Aβ, suggesting that BAD is a potential therapeutic target for AD.

Role of Neuron and Glia in Alzheimer’s Disease and Associated Vascular Dysfunction

Amyloidogenicity and vascular dysfunction are the key players in the pathogenesis of Alzheimer’s disease (AD), involving dysregulated cellular interactions. An intricate balance between neurons, astrocytes, microglia, oligodendrocytes and vascular cells sustains the normal neuronal circuits. Conversely, cerebrovascular diseases overlap neuropathologically with AD, and glial dyshomeostasis promotes AD-associated neurodegenerative cascade. While pathological hallmarks of AD primarily include amyloid-β (Aβ) plaques and neurofibrillary tangles, microvascular disorders, altered cerebral blood flow (CBF), and blood-brain barrier (BBB) permeability induce neuronal loss and synaptic atrophy. Accordingly, microglia-mediated inflammation and astrogliosis disrupt the homeostasis of the neuro-vascular unit and stimulate infiltration of circulating leukocytes into the brain. Large-scale genetic and epidemiological studies demonstrate a critical role of cellular crosstalk for altered immune response, metabolism, and vasculature in AD. The glia associated genetic risk factors include APOE, TREM2, CD33, PGRN, CR1, and NLRP3, which correlate with the deposition and altered phagocytosis of Aβ. Moreover, aging-dependent downregulation of astrocyte and microglial Aβ-degrading enzymes limits the neurotrophic and neurogenic role of glial cells and inhibits lysosomal degradation and clearance of Aβ. Microglial cells secrete IGF-1, and neurons show a reduced responsiveness to the neurotrophic IGF-1R/IRS-2/PI3K signaling pathway, generating amyloidogenic and vascular dyshomeostasis in AD. Glial signals connect to neural stem cells, and a shift in glial phenotype over the AD trajectory even affects adult neurogenesis and the neurovascular niche. Overall, the current review informs about the interaction of neuronal and glial cell types in AD pathogenesis and its critical association with cerebrovascular dysfunction.

Biomimetic Dendrimer-Peptide Conjugates for Early Multi-Target Therapy of Alzheimer's Disease by Inflammatory Microenvironment Modulation.

Current therapeutic strategies for Alzheimer's disease (AD) treatments mainly focus on β-amyloid (Aβ) targeting. However, such therapeutic strategies have limited clinical outcomes due to the chronic and irreversible impairment of the nervous system in the late stage of AD. Recently, inflammatory responses, manifested in oxidative stress and glial cell activation, have been reported as hallmarks in the early stages of AD. Based on the crosstalk between inflammatory response and brain cells, a reactive oxygen species (ROS)-responsive dendrimer-peptide conjugate (APBP) is devised to target the AD microenvironment and inhibit inflammatory responses at an early stage. With the modification of the targeting peptide, this nanoconjugate can efficiently deliver peptides to the infected regions and restore the antioxidant ability of neurons by activating the nuclear factor (erythroid-derived 2)-like 2 signaling pathway. Moreover, this multi-target strategy exhibits a synergistic function of ROS scavenging, promoting Aβ phagocytosis, and normalizing the glial cell phenotype. As a result, the nanoconjugate can reduce ROS level, decrease Aβ burden, alleviate glial cell activation, and eventually enhance cognitive functions in APPswe/PSEN1dE9 model mice. These results indicate that APBP can be a promising candidate for the multi-target treatment of AD.

Inhibition of Smad3 in macrophages promotes Aβ efflux from the brain and thereby ameliorates Alzheimer's pathology

Impaired amyloid-β (Aβ) clearance is believed to be a primary cause of Alzheimer's disease (AD), and peripheral abnormalities in Aβ clearance have recently been linked to AD pathogenesis and progression. Data from recent genome-wide association studies have linked genetic risk factors associated with altered functions of more immune cells to AD pathology. Here, we first identified correlations of Smad3 signaling activation in peripheral macrophages with AD progression and phagocytosis of Aβ. Then, manipulating the Smad3 signaling regulated macrophage phagocytosis of Aβ and induced switch of macrophage inflammatory phenotypes in our cell cultures. In our mouse models, flag-tagged or fluorescent-dye conjugated Aβ was injected into the lateral ventricles or tail veins, and traced. Interestingly, blocking Smad3 signaling efficiently increased Aβ clearance by macrophages, reduced Aβ in the periphery and thereby enhanced Aβ efflux from the brain. Moreover, in our APP/PS1 transgenic AD model mice, Smad3 inhibition significantly attenuated Aβ deposition and neuroinflammation, and ameliorated cognitive deficits, probably by enhancing the peripheral clearance of Aβ. In conclusion, enhancing Aβ clearance by peripheral macrophages through Smad3 inhibition attenuated AD-related pathology and cognitive deficits, which may provide a new perspective for understanding AD and finding novel therapeutic approaches.

Genetic knockdown of Klk8 has sex-specific multi-targeted therapeutic effects on Alzheimer's pathology in mice.

Previous work in our lab has identified the protease kallikrein-8 (KLK8) as a potential upstream mover in the pathogenesis of Alzheimer's disease (AD). We showed pathologically elevated levels of KLK8 in the cerebrospinal fluid and blood of patients with mild cognitive impairment or dementia due to AD, and in brains of patients and transgenic CRND8 (TgCRND8) mice in incipient stages of the disease. Furthermore, short-term antibody-mediated KLK8 inhibition in moderate stage disease alleviated AD pathology in female mice. However, it remains to be shown whether long-term reversal of KLK8 overexpression can also counteract AD. Therefore, the effects of genetic Klk8-knockdown were determined in TgCRND8 mice. The effects of heterozygous ablation of murine Klk8 (mKlk8) gene on AD pathology of both sexes were examined by crossbreeding TgCRND8 [hAPP+/-] with mKlk8-knockdown [mKlk8+/-] mice resulting in animals with or without AD pathology which revealed pathologically elevated or normal KLK8 levels. mKlk8-knockdown had negligible effects on wildtype animals but led to significant decline of amyloid beta (Aβ) and tau pathology as well as an improvement of structural neuroplasticity in a sex-specific manner in transgenics. These changes were mediated by a shift to non-amyloidogenic cleavage of the human amyloid precursor protein (APP), recovery of the neurovascular unit and maintaining microglial metabolic fitness. Mechanistically, Klk8-knockdown improved Aβ phagocytosis in primary glia and Aβ resistance in primary neurons. Most importantly, transgenic mice revealed less anxiety and a better memory performance. These results reinforce the potential of KLK8 as a therapeutic target in AD.

Bacille Calmette-Guérin attenuates vascular amyloid pathology and maximizes synaptic preservation in APP/PS1 mice following active amyloid-β immunotherapy

Despite effective clearance of parenchymal amyloid-β (Aβ) in patients with Alzheimer’s disease, Aβ immunotherapy exacerbates the vascular Aβ (VAβ)-associated pathology in the brain. We have previously shown that BCG immunization facilitates protective monocyte recruitment to the brain of APP/PS1 mice. Here, we confirmed that the 4Aβ1-15 vaccine exacerbates VAβ deposits in this model, which coincides with a decrease in the number of cerebrovascular endothelial cells and pericytes, infiltration of neutrophils into the brain, and induction of cerebral microhemorrhage. Moreover, combined 4Aβ1-15/BCG treatment abrogates the development of the VAβ-associated pathology. In addition, BCG treatment is required for the upregulation of interleukin-10 in the brain. Notably, BCG treatment selectively enhances Aβ phagocytosis by recruited macrophages. Furthermore, combined 4Aβ1-15/BCG treatment is more effective than 4Aβ1-15 monotherapy in synaptic preservation and the enhancement of the learning efficiency. Overall, our study suggests that the combination of Aβ-targeted therapy with an immunomodulatory strategy may improve the efficacy of Aβ vaccine in Alzheimer’s disease.

Conditional genetic deletion of CSF1 receptor in microglia ameliorates the physiopathology of Alzheimer\u2019s disease

BackgroundAlzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia in the world. Microglia are the innate immune cells of CNS; their proliferation, activation, and survival in pathologic and healthy brain have previously been shown to be highly dependent on CSF1R.MethodsHere, we investigate the impact of such receptor on AD etiology and microglia. We deleted CSF1R using Cre/Lox system; the knockout (KO) is restricted to microglia in the APP/PS1 mouse model. We induced the knockout at 3 months old, before plaque formation, and evaluated both 6- and 8-month-old groups of mice.ResultsOur findings demonstrated that CSF1R KO did not impair microglial survival and proliferation at 6 and 8 months of age in APP cKO compared to their littermate-control groups APPSwe/PS1. We have also shown that cognitive decline is delayed in CSF1R-deleted mice. Ameliorations of AD etiology are associated with a decrease in plaque volume in the cortex and hippocampus area. A compensating system seems to take place following the knockout, since TREM2/β-Catenin and IL-34 expression are significantly increased. Such a compensatory mechanism may promote microglial survival and phagocytosis of Aβ in the brain.ConclusionsOur results provide new insights on the role of CSF1R in microglia and how it interacts with the TREM2/β-Catenin and IL-34 system to clear Aβ and ameliorates the physiopathology of AD.

Antiallergic drug desloratadine as a selective antagonist of 5HT2A receptor ameliorates pathology of Alzheimer's disease model mice by improving microglial dysfunction.

Alzheimer's disease (AD) is a progressively neurodegenerative disease characterized by cognitive deficits and alteration of personality and behavior. As yet, there is no efficient treatment for AD. 5HT2A receptor (5HT2AR) is a subtype of 5HT2 receptor belonging to the serotonin receptor family, and its antagonists have been clinically used as antipsychotics to relieve psychopathy. Here, we discovered that clinically first‐line antiallergic drug desloratadine (DLT) functioned as a selective antagonist of 5HT2AR and efficiently ameliorated pathology of APP/PS1 mice. The underlying mechanism has been intensively investigated by assay against APP/PS1 mice with selective 5HT2AR knockdown in the brain treated by adeno‐associated virus (AAV)‐ePHP‐si‐5HT2AR. DLT reduced amyloid plaque deposition by promoting microglial Aβ phagocytosis and degradation, and ameliorated innate immune response by polarizing microglia to an anti‐inflammatory phenotype. It stimulated autophagy process and repressed neuroinflammation through 5HT2AR/cAMP/PKA/CREB/Sirt1 pathway, and activated glucocorticoid receptor (GR) nuclear translocation to upregulate the transcriptions of phagocytic receptors TLR2 and TLR4 in response to microglial phagocytosis stimulation. Together, our work has highly supported that 5HT2AR antagonism might be a promising therapeutic strategy for AD and highlighted the potential of DLT in the treatment of this disease.

NLRP3 inflammasome activation regulates microglial migration

AbstractBackgroundThis laboratory has demonstrated an important role for the NLRP3 inflammasome in the progression of Alzheimer’s disease (AD) with activation found in post‐mortem tissue from individuals with AD (Heneka et al., 2013) and in transgenic mouse models of AD expressing amyloid precursor protein (APP) and presenilin 1 (PS1; APP/PS1 mice). However, APP/PS1 mice deficient for NLRP3 were protected from AD‐pathology, with a significant reduction in cleaved‐caspase‐1 and IL‐1β. We wanted to examine the wider implications of NLRP3 inflammasome deficiency beyond IL‐1β, and uncover other pathways and signaling mechanisms employed by microglia to protect the brain from the build up of Aβ.MethodRNA sequencing was performed on CD11b+ cells from the brains of 4, 6 and 12 month old wildtype, APP/PS1, NLRP3‐/‐ and APP/PS1.NLRP3‐/‐ mice. Microglia were prepared from the brains of 1‐day old wildtype and NLRP3‐/‐ mice for live cell imaging, migratory assays and flow cytometric analysis. In a separate series of experiments CD11b+ cells were isolated from the brains of wildtype, APP/PS1, NLRP3‐/‐ and APP/PS1.NLRP3‐/‐ mice and myeloid cells were also prepared from the blood of humans with and without AD to replicate all findings in these models.ResultThe RNA sequencing analysis found a significant increase in pathways related to chemokine signaling in NLRP3‐/‐ and APP/PS1. NLRP3‐/‐ mice. Wildtype microglia significantly migrated to Aβ, however NLRP3‐/‐ microglia or cells treated with NLRP3 inhibitors had increased migration to Aβ and greater Aβ phagocytosis, which was associated with CCL2 release and mediated via the receptors CCR2 and CCR4. Importantly, we were able to replicate these findings using monocyte‐derived microglia‐like cells from humans and in NLRP3‐/‐ and APP/PS1/NLRP3‐/‐ mice ex vivo.ConclusionWe have identified a new mechanism where microglia release CCL2 to migrate to Aβ and phagocytose this peptide. Critically, this activity is increased in NLRP3‐/‐ cells or those treated with NLRP3‐specific inhibitors, together demonstrating a previously unknown role for the NLRP3 inflammasome in regulating cellular migratory and phagocytic behavior. These findings provide insights into the pathogenesis of AD and importantly highlight the NLRP3 inflammasome as a serious target for prevention and early treatment of AD.

AXL activation leads to reduced amyloid plaque deposition in APP/PS‐1 mice

AbstractBackgroundMicroglia, the immune cells of the brain, play seemingly antagonistic roles in the Alzheimer’s disease (AD) brain. On one hand, microglia contribute to clearance of amyloid beta (Aβ) plaques via phagocytosis. On the other hand, activated microglia produce inflammatory cytokines that contribute to a hostile neuronal environment, exacerbating AD pathogenesis. Axl, a member of the TAM receptor family, is increased on microglia that surround Aβ plaques. Gas6, the primary ligand for Axl, promotes phagocytosis and suppresses inflammation in peripheral immune cells.MethodTo test the hypothesis that manipulation of the Axl‐Gas6 pathway contributes to Aβ clearance, we carried out intrahippocampal injections of an AAV‐Gas6 vector in male and female APP/PS‐1 mice at 4 or 7 months of age.ResultHippocampal overexpression of Gas6 for one or six months led to decreased Aβ plaque load when compared to the opposite hippocampus injected with a control AAV‐Gas6(delta) vector that lacks the Gla and EGF domains required for Axl phosphorylation. We are currently quantifying microglial responses in these brains as well as carrying out in vitro studies with microglia from Axl knockout mice to better determine the roles of the Gas6‐Axl signaling pathway in mediating Aβ phagocytosis and microglial inflammatory responses.ConclusionAxl activation in vivo leads to reduced Aβ plaque load. Results from this work will provide insight regarding potential mechanisms that may be harnessed to reduce AD‐related pathology.