Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder causing memory loss, language problems and behavioural disturbances. AD is associated with the accumulation of fibrillar amyloid‐β (Aβ) and the formation of neurofibrillary tau tangles. Fibrillar Aβ itself represents a danger‐associated molecular pattern, which is recognized by specific microglial receptors. One of the key players is formation of the NOD‐, LRR‐ and pyrin domain‐containing 3 (NLRP3) inflammasome, whose activation has been demonstrated in AD patient brains and transgenic animal models of AD. Here, we investigated whether Aβ oligomers or protofibrils that represent lower molecular aggregates prior to Aβ deposition are able to activate the NLRP3 inflammasome and subsequent interleukin‐1 beta (IL‐1β) release by microglia. In our study, we used Aβ preparations of different sizes: small oligomers and protofibrils of which the structure was confirmed by atomic force microscopy. Primary microglial cells from C57BL/6 mice were treated with the respective Aβ preparations and NLRP3 inflammasome activation, represented by caspase‐1 cleavage, IL‐1β production, and apoptosis‐associated speck‐like protein containing a CARD speck formation was analysed. Both protofibrils and low molecular weight Aβ aggregates induced a significant increase in IL‐1β release. Inflammasome activation was confirmed by apoptosis‐associated speck‐like protein containing a CARD speck formation and detection of active caspase‐1. The NLRP3 inflammasome inhibitor MCC950 completely inhibited the Aβ‐induced immune response. Our results show that the NLRP3 inflammasome is activated not only by fibrillar Aβ aggregates as reported before, but also by lower molecular weight Aβ oligomers and protofibrils, highlighting the possibility that microglial activation by these Aβ species may initiate innate immune responses in the central nervous system prior to the onset of Aβ deposition. image Cover Image for this issue: https://doi.org/10.1111/jnc.14773.

Cas9 and Cas12 nucleases of class 2 CRISPR-Cas systems provide immunity in prokaryotes through RNA-guided cleavage of foreign DNA. Here we characterize a set of compact CRISPR-Cas12m (subtype V-M) effector proteins and show that they provide protection against bacteriophages and plasmids through the targeted DNA binding rather than DNA cleavage. Biochemical assays suggest that Cas12m effectors can act as roadblocks inhibiting DNA transcription and/or replication, thereby triggering interference against invaders. Cryo-EM structure of Gordonia otitidis (Go) Cas12m ternary complex provided here reveals the structural mechanism of DNA binding ensuring interference. Harnessing GoCas12m innate ability to bind DNA target we fused it with adenine deaminase TadA-8e and showed an efficient A-to-G editing in Escherichia coli and human cells. Overall, this study expands our understanding of the functionally diverse Cas12 protein family, revealing DNA-binding dependent interference mechanism of Cas12m effectors that could be harnessed for engineering of compact base-editing tools.

The central molecule in the pathogenesis of Alzheimer’s disease (AD) is believed to be a small-sized polypeptide – beta amyloid (Aβ) which has an ability to assemble spontaneously into oligomers. Various studies concerning therapeutic and prophylactic approaches for AD are based on the immunotherapy using antibodies against Aβ. It has been suggested that either active immunization with Aβ or passive immunization with anti-Aβ antibodies might help to prevent or reduce the symptoms of the disease. However, knowledge on the mechanisms of Aβ-induced immune response is rather limited. Previous research on Aβ1-42 oligomers in rat brain cultures showed that the neurotoxicity of these oligomers considerably depends on their size. In the current study, we evaluated the dependence of immunogenicity of Aβ1-42 oligomers on the size of oligomeric particles and identified the immunodominant epitopes of the oligomers.

Beta amyloid (Aβ) oligomers are thought to contribute to the pathogenesis of Alzheimer's disease. However, clinical trials using Aβ immunization were unsuccessful due to strong brain inflammation, the mechanisms of which are poorly understood. In this study we tested whether monoclonal antibodies to oligomeric Aβ would prevent the neurotoxicity of Aβ oligomers in primary neuronal‐glial cultures. However, surprisingly, the antibodies dramatically increased the neurotoxicity of Aβ. Antibodies bound to monomeric Aβ fragments were non‐toxic to cultured neurons, while antibodies to other oligomeric proteins: hamster polyomavirus major capsid protein, human metapneumovirus nucleocapsid protein, and measles virus nucleocapsid protein, strongly potentiated the neurotoxicity of their antigens. The neurotoxicity of antibody‐oligomeric antigen complexes was abolished by removal of the Fc region from the antibodies or by removal of microglia from cultures, and was accompanied by inflammatory activation and proliferation of the microglia in culture. In conclusion, we find that immune complexes formed by Aβ oligomers or other oligomeric/multimeric antigens and their specific antibodies can cause death and loss of neurons in primary neuronal‐glial cultures via Fc‐dependent microglial activation. The results suggest that therapies resulting in antibodies to oligomeric Aβ or oligomeric brain virus proteins should be used with caution or with suppression of microglial activation. image Immunization against Aβ in Alzheimer's disease carries a significant risk of neuroinflammation, the mechanisms of which are poorly understood. In this study we show that oligomeric antigens such as Aβ and viral proteins complexed with their specific antibodies can exert neurotoxic effects by Fc‐dependent microglia activation. This suggests that therapies using antibodies against oligomeric proteins should be used with caution.

Activation of macrophages is one of the key processes in generating the immune response against pathogens or misfolded/aggregated otherwise unharmful host’s proteins. Antigens and their immune complexes (IC) may shape macrophage phenotype in various directions. Data on the impact of protein structure during inflammation are evident; however, some separate steps of this process involving changes in macrophage phenotype are not fully understood. Our aim was to investigate the phenotype of macrophages after activation with different oligomeric proteins and their IC. We have used amyloid beta (Aβ_1–42) that plays a role in neurodegenerative inflammation as a model of host-associated protein and three oligomeric viral antigens as pathogen-associated proteins. Murine cell lines J774, BV-2, and macrophage primary cell culture were treated with oligomeric proteins and their IC. After 48 h, expression of surface markers F4/80, CD68, CD86, and CD206 and secreted cytokines IL-10, IL-12, IL-23, and TNF-αwas analysed. Aβ_1–42oligomers stimulated expression of both inflammatory and anti-inflammatory molecules; however, fibrils induced less intense expression of markers investigated as compared to small and large oligomers. Two out of three viral oligomeric proteins induced the inflammatory response of macrophages. Data suggest that macrophage activation pattern depends on the origin, size, and structure of oligomeric proteins.