Selective targeting of 3 repeat Tau with brain penetrating single chain antibodies for the treatment of neurodegenerative disorders

Recombinant Antibody Fragments for Neurological Disorders: An Update

Recombinant antibody fragments are promising alternatives to full-length immunoglobulins, creating big opportunities for the pharmaceutical industry. Nowadays, antibody fragments such as antigen-binding fragments (Fab), single-chain fragment variable (scFv), single-domain antibodies (sdAbs), and bispecific antibodies (bsAbs) are being evaluated as diagnostics or therapeutics in preclinical models and in clinical trials. Immunotherapy approaches, including passive transfer of protective antibodies, have shown therapeutic efficacy in several animal models of Alzheimer's disease (AD), Parkinson's disease (PD), frontotemporal dementia (FTD), Huntington's disease (HD), transmissible spongiform encephalopathies (TSEs) and multiple sclerosis (MS). There are various antibodies approved by the Food and Drug Administration (FDA) for treating multiple sclerosis and two amyloid beta-specific humanized antibodies, Aducanumab and Lecanemab, for AD. Our previous review summarized data on recombinant antibodies evaluated in pre-clinical models for immunotherapy of neurodegenerative diseases. Here, we explore recent studies in this fascinating research field, give an update on new preventive and therapeutic applications of recombinant antibody fragments for neurological disorders and discuss the potential of antibody fragments for developing novel approaches for crossing the blood-brain barrier (BBB) and targeting cells and molecules of interest in the brain.

Tau-targeting therapies for Alzheimer disease: current status and future directions

Alzheimer disease (AD) is the most common cause of dementia in older individuals. AD is characterized pathologically by amyloid-β (Aβ) plaques and tau neurofibrillary tangles in the brain, with associated loss of synapses and neurons, which eventually results in dementia. Many of the early attempts to develop treatments for AD focused on Aβ, but a lack of efficacy of these treatments in terms of slowing disease progression led to a change of strategy towards targeting of tau pathology. Given that tau shows a stronger correlation with symptom severity than does Aβ, targeting of tau is more likely to be efficacious once cognitive decline begins. Anti-tau therapies initially focused on post-translational modifications, inhibition of tau aggregation and stabilization of microtubules. However, trials of many potential drugs were discontinued because of toxicity and/or lack of efficacy. Currently, the majority of tau-targeting agents in clinical trials are immunotherapies. In this Review, we provide an update on the results from the initial immunotherapy trials and an overview of new therapeutic candidates that are in clinical development, as well as considering future directions for tau-targeting therapies.

Awareness and Perception Toward Alzheimer's Disease Among Residents Living in the Jazan Province, Saudi Arabia: A Cross-Sectional Study

BACKGROUND

Alzheimer's disease (AD) is a growing public health concern, yet misconceptions about the condition are common. This study assessed awareness and social perceptions of AD in Jazan.

METHODS

A cross-sectional survey of 925 adults was conducted. Knowledge was assessed using a 30-item Alzheimer's Disease Knowledge Scale (ADKS). Social perceptions were evaluated using a 10-item questionnaire.

RESULTS

Many had misconceptions about AD epidemiology, causes, management, and care. The mean ADKS score was 8.89 ± 5.17 out of 30. Knowledge was poorest for symptoms, risk factors, treatment, caregiving, and life impact. Knowledge was highest in those aged >45 years (p = 0.018), in those with income > 15K SR (p = 0.004), in retired individuals (p = 0.023), and in those who learned about AD from books (p = 0.001), healthcare professionals (p = 0.001), or had an affected relative (p = 0.001). However, knowledge was low across all domains, averaging only 29% correct answers. Most respondents held positive social perceptions, yet sizable minorities saw isolation, legal intervention, and institutionalization as appropriate. Additionally, a portion of respondents associated stigma with individuals affected by AD and expressed a sense of burden associated with the condition.

CONCLUSIONS

There are substantial knowledge gaps and some stigmatizing attitudes about AD in Jazan. Awareness regarding the causes, diagnosis, and management of AD was low. Misconceptions exist that AD only affects older people. Improved public education, especially for higher-risk groups, is needed to address misconceptions and promote social inclusion for those with dementia. Healthcare professionals can play a crucial role.

Immunogenicity of MultiTEP platform technology-based Tau vaccine in non-human primates

Pathological forms of Tau protein are directly associated with neurodegeneration and correlate with Alzheimer's Disease (AD) symptoms, progression, and severity. Previously, using various mouse models of Tauopathies and AD, we have demonstrated the immunogenicity and efficacy of the MultiTEP-based adjuvanted vaccine targeting the phosphatase activating domain (PAD) of Tau, AV-1980R/A. Here, we analyzed its immunogenicity in non-human primates (NHP), the closest phylogenic relatives to humans with a similar immune system, to initiate the transition of this vaccine into clinical trials. We have demonstrated that AV-1980R/A is highly immunogenic in these NHPs, activating a broad but unique to each monkey repertoire of MultiTEP-specific T helper (Th) cells that, in turn, activate B cells specific to PAD. The resulting anti-PAD IgG antibodies recognize pathological Tau tangles and Tau-positive neuritis in AD case brain sections with no staining in control non-AD cases. These published data and efficacy results support the AV-1980R/A vaccine progression to first-in-human clinical trials.

Inhibition of Tau seeding by targeting Tau nucleation core within neurons with a single domain antibody fragment

Tau proteins aggregate into filaments in brain cells in Alzheimer's disease and related disorders referred to as tauopathies. Here, we used fragments of camelid heavy-chain-only antibodies (VHHs or single domain antibody fragments) targeting Tau as immuno-modulators of its pathologic seeding. A VHH issued from the screen against Tau of a synthetic phage-display library of humanized VHHs was selected for its capacity to bind Tau microtubule-binding domain, composing the core of Tau fibrils. This parent VHH was optimized to improve its biochemical properties and to act in the intra-cellular compartment, resulting in VHH Z70. VHH Z70 precisely binds the PHF6 sequence, known for its nucleation capacity, as shown by the crystal structure of the complex. VHH Z70 was more efficient than the parent VHH to inhibit in vitro Tau aggregation in heparin-induced assays. Expression of VHH Z70 in a cellular model of Tau seeding also decreased the aggregation-reporting fluorescence signal. Finally, intra-cellular expression of VHH Z70 in the brain of an established tauopathy mouse seeding model demonstrated its capacity to mitigate accumulation of pathological Tau. VHH Z70, by targeting Tau inside brain neurons, where most of the pathological Tau resides, provides an immunological tool to target the intra-cellular compartment in tauopathies.

Novel Brain-Penetrating Single Chain Antibodies Directed Against 3RTau for the Treatment of Alzheimer's Disease and Related Dementias

Alzheimer's disease (AD), Pick's disease, fronto-temporal lobar degeneration, cortico-basal degeneration, and primary age related tauopathy are examples of neurodegenerative disorders with tau accumulation and jointly referred as "tauopathies." The mechanisms through which tau leads to neurodegeneration are not fully understood but include conversion into toxic oligomers and protofibrils, cell-to-cell propagation, post-transcriptional modifications and as a mediator of cell death signals among others. Potential therapeutics includes reducing tau synthesis (e.g., anti-sense); targeting selective tau species and aggregates or blocking cell-to-cell transmission (e.g., antibodies) or by promoting clearance of tau (e.g., autophagy activators). Among them, immunotherapy is currently one of the approaches most actively explored including active, passive, and cellular. A potential problem with immunotherapy has been the trafficking of the antibodies into the CNS. In this chapter, we describe a method for the production and testing of viral vector driven, brain-penetrating, single chain antibodies that specifically recognize 3RTau. These single chain antibodies are modified by the addition of a fragment of the apoB protein to facilitate trafficking into the brain, once in the CNS these antibody fragments recognize tau with potential value for the treatment of AD and related dementias.

Current Status of Clinical Trials on Tau Immunotherapies

Tau immunotherapies have advanced from proof-of-concept studies to over a dozen clinical trials for Alzheimer's disease (AD) and other tauopathies. Mechanistic studies in animal and culture models have provided valuable insight into how these therapies may work but multiple pathways are likely involved. Different groups have emphasized the importance of intracellular vs extracellular antibody-mediated clearance of the tau protein and there is no consensus on which pool of tau should ideally be targeted. Likewise, various normal and disease-selective epitopes are being targeted, and the antibody isotypes either favor phagocytosis of the tau-antibody complex or are neutral in that aspect. Most of the clinical trials are in early stages, thus their efficacy is not yet known, but all have been without any major adverse effects and some have reported target engagement. A few have been discontinued. One in phase I, presumably because of a poor pharmacokinetic profile, and three in phase II for a lack of efficacy although this trial stage is not well powered for efficacy measures. In these phase II studies, trials with two antibodies in patients with progressive supranuclear palsy or other primary tauopathies were halted but are continuing in patients with AD, and one antibody trial was stopped in early-stage AD but is continuing in moderate AD. These three antibodies have been reported to only work extracellularly and tau is not increased in the cerebrospinal fluid of primary tauopathies, which may explain the failures of two of them. In the discontinued AD trial, there are some concerns about how much of extracellular tau contains the N-terminal epitope that is being targeted. In addition, extracellular tau is only a small part of total tau, compared to intracellular tau. Targeting only the former may not be sufficient for functional benefits. Given these outcomes, decision makers within the pharmaceutical companies who green light these trials should attempt to target tau not only extracellularly but also intracellularly to increase their chances of success. Hopefully, some of the ongoing trials will provide some functional benefits to the large number of patients with tauopathies.

A Single-Chain Variable Fragment Antibody Inhibits Aggregation of Phosphorylated Tau and Ameliorates Tau Toxicity in vitro and in vivo

BACKGROUND

Alzheimer's disease (AD) is a common cause of dementia among elderly people. Hyperphosphorylation and aggregation of tau correlates with the clinical progression of AD; therefore, therapies targeting the aggregation of tau may have potential applications for anti-AD drug development. Several inhibitors of tau aggregation, including small molecules and antibodies, have been found to decrease the aggregation of tau and the corresponding pathology.

OBJECTIVE

To screen one kind of single-chain variable fragment (scFv) antibody which could inhibit the aggregation of tau and ameliorate its cytotoxicity.

METHODS/RESULTS

Using phosphorylated tau (pTau) as an antigen, we obtained a scFv antibody via the screening of a high-capacity phage antibody library. Biochemical analysis revealed that this scFv antibody (scFv T1) had a strong ability to inhibit pTau aggregation both in dilute solutions and under conditions of macromolecular crowding. ScFv T1 could also depolymerize preformed pTau aggregates in vitro. Furthermore, scFv T1 was found to be able to inhibit the cytotoxicity of extracellular pTau aggregates and ameliorate tau-mediated toxicity when coexpressed with a hTauR406W mutant in the eye of transgenic Drosophila flies.

CONCLUSION

This scFv T1 antibody may be a potential new therapeutic agent against AD. Our methods can be used to develop novel strategies against protein aggregation for the treatment of neurodegenerative diseases.

Mutant three-repeat tau expression initiates retinal ganglion cell death through Caspase-2

The microtubule-associated protein tau is implicated in multiple degenerative diseases including retinal diseases such as glaucoma; however, the way tau initiates retinopathy is unclear. Previous retinal assessments in mouse models of tauopathy suggest that mutations in four-repeat (4R) tau are associated with disease-induced retinal dysfunction, while shifting tau isoform ratio to favor three-repeat (3R) tau production enhanced photoreceptor function. To further understand how alterations in tau expression impact the retina, we analyzed the retinas of transgenic mice overexpressing mutant 3R tau (m3R tau-Tg), a model known to exhibit Pick's Disease pathology in the brain. Analysis of retinal cross-sections from young (3 month) and adult (9 month) mice detected asymmetric 3R tau immunoreactivity in m3R tau-Tg retina, concentrated in the retinal ganglion and amacrine cells of the dorsal retinal periphery. Accumulation of hyperphosphorylated tau was detected specifically in the detergent insoluble fraction of the adult m3R tau-Tg retina. RNA-seq analysis highlighted biological pathways associated with tauopathy that were uniquely altered in m3R tau-Tg retina. The upregulation of transcript encoding apoptotic protease caspase-2 coincided with increased immunostaining in predominantly 3R tau positive retinal regions. In adult m3R tau-Tg, the dorsal peripheral retina of the adult m3R tau-Tg exhibited decreased cell density in the ganglion cell layer (GCL) and reduced thickness of the inner plexiform layer (IPL) compared to the ventral peripheral retina. Together, these data indicate that mutant 3R tau may mediate toxicity in retinal ganglion cells (RGC) by promoting caspase-2 expression which results in RGC degeneration. The m3R tau-Tg line has the potential to be used to assess tau-mediated RGC degeneration and test novel therapeutics for degenerative diseases such as glaucoma.

Alternative splicing in aging and Alzheimer's disease: Highlighting the role of tau and estrogen receptor α isoforms in the hypothalamus

Human genes show the highest efficacy of alternative splicing (AS) in the brain as compared to other tissues. Within the brain, a remarkably rich diversity of AS events was identified in the hypothalamus. The AS frequency is increased in the aging brain. Such AS events, as intron retention and accumulation of circular RNAs, were acknowledged as some of the main hallmarks of the aging brain. In Alzheimer's disease (AD) pivotal (tau gene, in particular), risk, candidate and other genes show significant alterations in AS. Therefore AD has been suggested to be a disease of dysregulated AS. One of the reported risk factors for AD is estrogen deficiency that may interfere with the extension of neurobrillary tangles. Mounting evidence suggests that estrogens may decrease hyperphosphorylated tau deposition in the brain. Furthermore, AS of estrogen receptor α (ERα) mRNA is decreased in AD brain areas with the highest tau load. These potential interactions among tau, estrogens, and ERα AS may be important for the development of therapeutic and preventive strategies for AD. The intriguing point is that the amount of splice variants of ERα in the hypothalamus and the hippocampus is increased in aging and decreased in AD, while ERα is one of the regulators of AS and is subject to AS itself.

Recent progress on developing of plasmon biosensing of tumor biomarkers: Efficient method towards early stage recognition of cancer

Cancer is the second most extended disease with an improved death rate over the past several time. Due to the restrictions of cancer analysis methods, the patient's real survival rate is unknown. Therefore, early stage diagnosis of cancer is crucial for its strong detection. Bio-analysis based on biomarkers may help to overcome the problem Biosensors with high sensitivity and specificity, low-cost, high analysis speed and minimum limit of detection are practical alternatives for laboratory tests. Surface plasmon resonance (SPR) is reaching a maturity level sufficient for their application in detection and determination cancer biomarkers in clinical samples. This review discusses main concepts and performance characteristics of SPR biosensor. Mainly, it focuses on newly emerged enhanced SPR biosensors towards high-throughput and ultrasensitive screening of cancer biomarkers such as PSA, α-fetoprotein, CEA, CA125, CA 15-3, HER2, ctDNA, ALCAM, hCG, VEGF, TNF, Interleukin, IFN-γ, CD24, CD44, Ferritin, COLIV using labeling processes with focusing on the future application in biomedical research and clinical diagnosis. This article reviews current status of the field, showcasing a series of early successes in the application of SPR for clinical bioanalysis of cancer related biomolecules and detailing a series of considerations regarding sensing schemes, exposing issues with analysis in biofluids, while providing an outlook of the challenges currently associated with plasmonic materials, bioreceptor selection, microfluidics, and validation of a clinical bioassay for applying SPR biosensors to clinical samples. Research opportunities are proposed to further advance the field and transition SPR biosensors from research proof-of-concept stage to actual clinical usage.

Recent advances in tau-directed immunotherapy against Alzheimer's disease: an overview of pre-clinical and clinical development

Alzheimer's disease (AD) has been a worldwide concern for many years now. This is due to the fact that AD is an irreversible and progressive neurodegenerative disease that affects quality of life. Failure of some Phase II/III clinical trials in AD targeting accumulation of β-amyloid in the brain has led to an increase in interest in studying alternative treatments against tubulin-associated unit (Tau) pathology. These alternative treatments include active and passive immunisation. Based on numerous studies, Tau is reported as a potential immunotherapeutic target for tauopathy-related diseases including AD. Accumulation and aggregation of hyperphosphorylated Tau as neuropil threads and neurofibrillary tangles (NFT) are pathological hallmarks of AD. Both active and passive immunisation targeting Tau protein have shown the capabilities to decrease or prevent Tau pathology and improve either motor or cognitive impairment in various animal models. In this review, we summarise recent advances in active and passive immunisation targeting pathological Tau protein, and will discuss with data obtained from both animal and human trials. Together, we give a brief overview about problems being encountered in these immunotherapies.

Tau immunotherapies: Lessons learned, current status and future considerations

The majority of clinical trials targeting the tau protein in Alzheimer's disease and other tauopathies are tau immunotherapies. Because tau pathology correlates better with the degree of dementia than amyloid-β lesions, targeting tau is likely to be more effective in improving cognition than clearing amyloid-β in Alzheimer's disease. However, the development of tau therapies is in many ways more complex than for amyloid-β therapies as briefly outlined in this review. Most of the trials are on humanized antibodies, which may have very different properties than the original mouse antibodies. The impact of these differences are to a large extent unknown, can be difficult to decipher, and may not always be properly considered. Furthermore, the ideal antibody properties for efficacy are not well established and can depend on several factors. However, considering the varied approaches in clinical trials, there is a general optimism that at least some of these trials may provide functional benefits to patients suffering of various tauopathies. This article is part of the special issue entitled 'The Quest for Disease-Modifying Therapies for Neurodegenerative Disorders'.

Interference of dengue replication by blocking the access of 3' SL RNA to the viral RNA-dependent RNA polymerase

The four circulating serotypes of dengue virus (DENV) occasionally cause potentially fetal symptoms of severe dengue, which there is currently no specific treatment available. Extensive efforts have been made to inhibit viral replication processes by impeding the activity of an exclusive RNA-dependent RNA polymerase (RdRp) in the viral non-structural protein 5 (NS5). In our earlier work, we identified the characteristic, specific interaction between the C-terminal thumb subdomain of RdRp and an apical loop in the 3' stem-loop (SL) element in the DENV RNA genome, which is fundamental for viral replication. Here, we demonstrated a new approach for interfering viral replication via blocking of 3' SL RNA binding to RdRp by the single-chain variable fragments (scFvs). We isolated and cloned 3 different human scFvs that bound to RdRp from DENV serotype 2 and interfered with 3' SL-binding, utilizing a combination of phage-display panning and Alpha methods. When tagged with a cell penetrating peptide, a selected scFv clone, 2E3, entered cells and partially colocalized with NS5 in the cytoplasm of infected HuH-7 cells. 2E3 significantly inhibited DENV RNA replication with sub-nanomolar EC50 values and significantly reduced the production of infectious particles. The molecular docking models suggested that 2E3 recognized both palm and thumb subdomains of RdRp, and interacted with Lys⁸⁴¹, a key residue involved in RNA binding. Our results provide a new potential therapeutic molecule specific for flaviviral infection.

Intramuscular injection of vectorized-scFvMC1 reduces pathological tau in two different tau transgenic models

With evidence supporting the prion-like spreading of extracellular tau as a mechanism for the initiation and progression of Alzheimer's disease (AD), immunotherapy has emerged as a potential disease-modifying strategy to target tau. Many studies have proven effective to clear pathological tau species in animal models of AD, and several clinical trials using conventional immunotherapy with anti-tau native antibodies are currently active. We have previously generated a vectorized scFv derived from the conformation-dependent anti-tau antibody MC1, scFvMC1, and demonstrated that its intracranial injection was able to prevent tau pathology in adult tau mice. Here, we show that, in a prevention paradigm and in two different tau transgenic models (JNPL3 and P301S), a one-time intramuscular injection of AAV1-scFvMC1 generated a long-lasting peripheral source of anti-tau scFvMC1 and significantly reduced insoluble and soluble tau species in the brain. Moreover, our data showed that scFvMC1 was internalized by the microglia, in the absence of overt inflammation. This study demonstrates the efficacy of intramuscular delivery of vectorized scFv to target tau, and suggests a new potential application to treat AD and the other tauopathies.

Fibrillar form of α-synuclein-specific scFv antibody inhibits α-synuclein seeds induced aggregation and toxicity

Synucleinopathies including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA) are characterized by pathological accumulation of α-synuclein (α-syn). Amongst the various approaches attempting to tackle the pathological features of synucleinopathies, antibody-based immunotherapy holds much promise. However, the large size of antibodies and corresponding difficulty in crossing the blood-brain barrier has limited development in this area. To overcome this issue, we engineered single-chain variable fragments (scFvs) against fibrillar α-syn, a putative disease-relevant form of α-syn. The purified scFvs showed specific activity towards α-syn fibrils and oligomers in comparison to monomers and recognized intracellular inclusions in human post-mortem brain tissue of Lewy body disease cases, but not aged controls. In vitro studies indicated scFvs inhibit the seeding of α-syn aggregation in a time-dependent manner, decreased α-syn seed-induced toxicity in a cell model of PD, and reduced the production of insoluble α-syn phosphorylated at Ser-129 (pS129-α-syn). These results suggest that our α-syn fibril-specific scFvs recognize α-syn pathology and can inhibit the aggregation of α-syn in vitro and prevent seeding-dependent toxicity. Therefore, the scFvs described here have considerable potential to be utilized towards immunotherapy in synucleinopathies and may also have applications in ante-mortem imaging modalities.

Neuronally expressed anti-tau scFv prevents tauopathy-induced phenotypes in Drosophila models

We have derived single-chain variable fragments (scFv) from tau antibody hybridomas and previously shown their promise as imaging diagnostic agents. Here, we examined the therapeutic potential of anti-tau scFv in transgenic Drosophila models that express in neurons wild-type (WT) human tau (htau) or the human tauopathy mutation R406W. scFv expressing flies were crossed with the tauopathy flies and analyzed. Overall, the survival curves differed significantly (p < .0001). Control flies not expressing htau survived the longest, whereas R406W expressing flies had the shortest lifespan, which was greatly prolonged by co-expressing the anti-tau scFv (p < .0001). Likewise, htau WT expressing flies had a moderately short lifespan, which was prolonged by co-expressing the anti-tau scFv (p < .01). In addition, the htau expression impaired wing expansion after eclosion (p < .0001), and caused progressive abdomen expansion (p < .0001). These features were more severe in htau R406W flies than in htau WT flies. Importantly, both phenotypes were prevented by co-expression of the anti-tau scFv (p < .01-0.0001). Lastly, brain analyses revealed scFv-mediated tau clearance (p < .05-0.01), and its prevention of tau-mediated neurotoxicity (p < .05-0.001). In summary, these findings support the therapeutic potential of an anti-tau scFv, including as gene therapies, and the use of Drosophila models for such screening.

Single Domain Antibody Fragments as New Tools for the Detection of Neuronal Tau Protein in Cells and in Mice Studies

Tau is a neuronal protein linked to pathologies called tauopathies, including Alzheimer's disease. In Alzheimer's disease, tau aggregates into filaments, leading to the observation of intraneuronal fibrillary tangles. Molecular mechanisms resulting in tau aggregation and in tau pathology spreading through the brain regions are still not fully understood. New tools are thus needed to decipher tau pathways involved in the diseases. In this context, a family of novel single domain antibody fragments, or VHHs, directed against tau were generated and characterized. Among the selected VHHs obtained from screening of a synthetic library, a family of six VHHs shared the same CDR3 recognition loop and recognized the same epitope, located in the C-terminal domain of tau. Affinity parameters characterizing the tau/VHHs interaction were next evaluated using surface plasmon resonance spectroscopy. The equilibrium constants K_D were in the micromolar range, but despite conservation of the CDR3 loop sequence, a range of affinities was observed for this VHH family. One of these VHHs, named F8-2, was additionally shown to bind tau upon expression in a neuronal cell line model. Optimization of VHH F8-2 by yeast two-hybrid allowed the generation of an optimized VHH family characterized by lower K_D than that of the F8-2 wild-type counterpart, and recognizing the same epitope. The optimized VHHs can also be used as antibodies for detecting tau in transgenic mice brain tissues. These results validate the use of these VHHs for in vitro studies, but also their potential for in-cell expression and assays in mouse models, to explore the mechanisms underlying tau physiopathology.

Intersection of pathological tau and microglia at the synapse

Tauopathies are a heterogenous class of diseases characterized by cellular accumulation of aggregated tau and include diseases such as Alzheimer’s disease (AD), progressive supranuclear palsy and chronic traumatic encephalopathy. Tau pathology is strongly linked to neurodegeneration and clinical symptoms in tauopathy patients. Furthermore, synapse loss is an early pathological event in tauopathies and is the strongest correlate of cognitive decline. Tau pathology is additionally associated with chronic neuroinflammatory processes, such as reactive microglia, astrocytes, and increased levels of pro-inflammatory molecules (e.g. complement proteins, cytokines). Recent studies show that as the principal immune cells of the brain, microglia play a particularly important role in the initiation and progression of tau pathology and associated neurodegeneration. Furthermore, AD risk genes such as Triggering receptor expressed on myeloid cells 2 (TREM2) and Apolipoprotein E (APOE) are enriched in the innate immune system and modulate the neuroinflammatory response of microglia to tau pathology. Microglia can play an active role in synaptic dysfunction by abnormally phagocytosing synaptic compartments of neurons with tau pathology. Furthermore, microglia are involved in synaptic spreading of tau – a process which is thought to underlie the progressive nature of tau pathology propagation through the brain. Spreading of pathological tau is also the predominant target for tau-based immunotherapy. Active tau vaccines, therapeutic tau antibodies and other approaches targeting the immune system are actively explored as treatment options for AD and other tauopathies. This review describes the role of microglia in the pathobiology of tauopathies and the mechanism of action of potential therapeutics targeting the immune system in tauopathies.

Systemic peptide mediated delivery of an siRNA targeting α-syn in the CNS ameliorates the neurodegenerative process in a transgenic model of Lewy body disease

Neurodegenerative disorders of the aging population are characterized by progressive accumulation of neuronal proteins such as α-synuclein (α-syn) in Parkinson's Disease (PD) and Amyloid ß (Aß) and Tau in Alzheimer's disease (AD) for which no treatments are currently available. The ability to regulate the expression at the gene transcription level would be beneficial for reducing the accumulation of these proteins or regulating expression levels of other genes in the CNS. Short interfering RNA molecules can bind specifically to target RNAs and deliver them for degradation. This approach has shown promise therapeutically in vitro and in vivo in mouse models of PD and AD and other neurological disorders; however, delivery of the siRNA to the CNS in vivo has been achieved primarily through intra-cerebral or intra-thecal injections that may be less amenable for clinical translation; therefore, alternative approaches for delivery of siRNAs to the brain is needed. Recently, we described a small peptide from the envelope protein of the rabies virus (C2-9r) that was utilized to deliver an siRNA targeting α-syn across the blood brain barrier (BBB) following intravenous injection. This approach showed reduced expression of α-syn and neuroprotection in a toxic mouse model of PD. However, since receptor-mediated delivery is potentially saturable, each allowing the delivery of a limited number of molecules, we identified an alternative peptide for the transport of nucleotides across the BBB based on the apolipoprotein B (apoB) protein targeted to the family of low-density lipoprotein receptors (LDL-R). We used an 11-amino acid sequence from the apoB protein (ApoB11) that, when coupled with a 9-amino acid arginine linker, can transport siRNAs across the BBB to neuronal and glial cells. To examine the value of this peptide mediated oligonucleotide delivery system for PD, we delivered an siRNA targeting the α-syn (siα-syn) in a transgenic mouse model of PD. We found that ApoB11 was effective (comparable to C2-9r) at mediating the delivery of siα-syn into the CNS, co-localized to neurons and glial cells and reduced levels of α-syn protein translation and accumulation. Delivery of ApoB11/siα-syn was accompanied by protection from degeneration of selected neuronal populations in the neocortex, limbic system and striato-nigral system and reduced neuro-inflammation. Taken together, these results suggest that systemic delivery of oligonucleotides targeting α-syn using ApoB11 might be an interesting alternative strategy worth considering for the experimental treatment of synucleinopathies.