Human endogenous retrovirus HERV-K(HML-2) RNA causes neurodegeneration through Toll-like receptors.

Although human endogenous retroviruses (HERVs) represent a substantial proportion of the human genome and some HERVs, such as HERV-K(HML-2), are reported to be involved in neurological disorders, little is known about their biological function. We report that RNA from an HERV-K(HML-2) envelope gene region binds to and activates human Toll-like receptor (TLR) 8, as well as murine Tlr7, expressed in neurons and microglia, thereby causing neurodegeneration. HERV-K(HML-2) RNA introduced into the cerebrospinal fluid (CSF) of either C57BL/6 wild-type mice or APPPS1 mice, a mouse model for Alzheimer's disease (AD), resulted in neurodegeneration and microglia accumulation. Tlr7-deficient mice were protected against neurodegenerative effects but were resensitized toward HERV-K(HML-2) RNA when neurons ectopically expressed murine Tlr7 or human TLR8. Transcriptome data sets of human AD brain samples revealed a distinct correlation of upregulated HERV-K(HML-2) and TLR8 RNA expression. HERV-K(HML-2) RNA was detectable more frequently in CSF from individuals with AD compared with controls. Our data establish HERV-K(HML-2) RNA as an endogenous ligand for species-specific TLRs 7/8 and imply a functional contribution of human endogenous retroviral transcripts to neurodegenerative processes, such as AD.

Interleukin-12/23 deficiency differentially affects pathology in male and female Alzheimer's disease-like mice.

Pathological aggregation of amyloid-ß (Aß) is a main hallmark of Alzheimer's disease (AD). Recent genetic association studies have linked innate immune system actions to AD development, and current evidence suggests profound gender differences in AD pathogenesis. Here, we characterise gender-specific pathologies in the APP23 AD-like mouse model and find that female mice show stronger amyloidosis and astrogliosis compared with male mice. We tested the gender-specific effect of lack of IL12p40, the shared subunit of interleukin (IL)-12 and IL-23, that we previously reported to ameliorate pathology in APPPS1 mice. IL12p40 deficiency gender specifically reduces Aß plaque burden in male APP23 mice, while in female mice, a significant reduction in soluble Aß1-40 without changes in Aß plaque burden is seen. Similarly, plasma and brain cytokine levels are altered differently in female versus male APP23 mice lacking IL12p40, while glial properties are unchanged. These data corroborate the therapeutic potential of targeting IL-12/IL-23 signalling in AD, but also highlight the importance of gender considerations when studying the role of the immune system and AD.

Deposition of C-terminally truncated Aß species Aß37 and Aß39 in Alzheimer's disease and transgenic mouse models.

In Alzheimer's disease (AD) a variety of amyloid ß-peptides (Aß) are deposited in the form of extracellular diffuse and neuritic plaques (NP), as well as within the vasculature. The generation of Aß from its precursor, the amyloid precursor protein (APP), is a highly complex procedure that involves subsequent proteolysis of APP by ß- and γ-secretases. Brain accumulation of Aß due to impaired Aß degradation and/or altered ratios between the different Aß species produced is believed to play a pivotal role in AD pathogenesis. While the presence of Aß40 and Aß42 in vascular and parenchymal amyloid have been subject of extensive studies, the deposition of carboxyterminal truncated Aß peptides in AD has not received comparable attention. In the current study, we for the first time demonstrate the immunohistochemical localization of Aß37 and Aß39 in human sporadic AD (SAD). Our study further included the analysis of familial AD (FAD) cases carrying the APP mutations KM670/671NL, E693G and I716F, as well as a case of the PSEN1 ΔExon9 mutation. Aß37 and Aß39 were found to be widely distributed within the vasculature in the brains of the majority of studied SAD and FAD cases, the latter also presenting considerable amounts of Aß37 containing NPs. In addition, both peptides were found to be present in extracellular plaques but only scarce within the vasculature in brains of a variety of transgenic AD mouse models. Taken together, our study indicates the importance of C-terminally truncated Aß in sporadic and familial AD and raises questions about how these species are generated and regulated.

Alzheimer therapy with an antibody against N-terminal Abeta 4-X and pyroglutamate Abeta 3-X.

Full-length Aß1-42 and Aß1-40, N-truncated pyroglutamate Aß3-42 and Aß4-42 are major variants in the Alzheimer brain. Aß4-42 has not been considered as a therapeutic target yet. We demonstrate that the antibody NT4X and its Fab fragment reacting with both the free N-terminus of Aß4-x and pyroglutamate Aß3-X mitigated neuron loss in Tg4-42 mice expressing Aß4-42 and completely rescued spatial reference memory deficits after passive immunization. NT4X and its Fab fragment also rescued working memory deficits in wild type mice induced by intraventricular injection of Aß4-42. NT4X reduced pyroglutamate Aß3-x, Aßx-40 and Thioflavin-S positive plaque load after passive immunization of 5XFAD mice. Aß1-x and Aßx-42 plaque deposits were unchanged. Importantly, for the first time, we demonstrate that passive immunization using the antibody NT4X is therapeutically beneficial in Alzheimer mouse models showing that N-truncated Aß starting with position four in addition to pyroglutamate Aß3-x is a relevant target to fight Alzheimer's disease.

Abundance of Aß5-x like immunoreactivity in transgenic 5XFAD, APP/PS1KI and 3xTG mice, sporadic and familial Alzheimer's disease.

BACKGROUND: According to the modified amyloid hypothesis the main event in the pathogenesis of Alzheimer's disease (AD) is the deposition of neurotoxic amyloid ß-peptide (Aß) within neurons. Additionally to full-length peptides, a great diversity of N-truncated Aß variants is derived from the larger amyloid precursor protein (APP). Vast evidence suggests that Aßx₋42 isoforms play an important role triggering neurodegeneration due to its high abundance, amyloidogenic propensity and toxicity. Although N-truncated and Aßx₋42 species have been pointed as crucial players in AD etiology, the Aß5-x isoforms have not received much attention. RESULTS: The present study is the first to show immunohistochemical evidence of Aß5-x in familial cases of AD (FAD) and its distribution in APP/PS1KI, 5XFAD and 3xTG transgenic mouse models. In order to probe Aß5-x peptides we generated the AB5-3 antibody. Positive plaques and congophilic amyloid angiopathy (CAA) were observed among all the FAD cases tested carrying either APP or presenilin 1 (PS1) mutations and most of the sporadic cases of AD (SAD). Different patterns of Aß5-x distribution were found in the mouse models carrying different combinations of autosomal mutations in the APP, PS1 and Tau genes. All of them showed extracellular Aß deposits but none CAA. Additionally, they were all affected by a severe amyloid pathology in the hippocampus among other areas. Interestingly, neither 5XFAD nor APP/PS1KI showed any evidence for intraneuronal Aß5-x. CONCLUSIONS: Different degrees of Aß5-x accumulations can be found in the transgenic AD mouse models and human cases expressing the sporadic or the familial form of the disease. Due to the lack of intracellular Aß5-x, these isoforms might not be contributing to early mechanisms in the cascade of events triggering AD pathology. Brain sections obtained from SAD cases showed higher Aß5-x-immunoreactivity in vascular deposits than in extracellular plaques, while both are equally important in the FAD cases. The difference may rely on alternative mechanisms involving Aß5-x peptides and operating in a divergent way in the late and early onset forms of the disease.

N-truncated Abeta starting with position four: early intraneuronal accumulation and rescue of toxicity using NT4X-167, a novel monoclonal antibody.

BACKGROUND: The amyloid hypothesis in Alzheimer disease (AD) considers amyloid ß peptide (Aß) deposition causative in triggering down-stream events like neurofibrillary tangles, cell loss, vascular damage and memory decline. In the past years N-truncated Aß peptides especially N-truncated pyroglutamate AßpE3-42 have been extensively studied. Together with full-length Aß1-42 and Aß1-40, N-truncated AßpE3-42 and Aß4-42 are major variants in AD brain. Although Aß4-42 has been known for a much longer time, there is a lack of studies addressing the question whether AßpE3-42 or Aß4-42 may precede the other in Alzheimer's disease pathology. RESULTS: Using different Aß antibodies specific for the different N-termini of N-truncated Aß, we discovered that Aß4-x preceded AßpE3-x intraneuronal accumulation in a transgenic mouse model for AD prior to plaque formation. The novel Aß4-x immunoreactive antibody NT4X-167 detected high molecular weight aggregates derived from N-truncated Aß species. While NT4X-167 significantly rescued Aß4-42 toxicity in vitro no beneficial effect was observed against Aß1-42 or AßpE3-42 toxicity. Phenylalanine at position four of Aß was imperative for antibody binding, because its replacement with alanine or proline completely prevented binding. Although amyloid plaques were observed using NT4X-167 in 5XFAD transgenic mice, it barely reacted with plaques in the brain of sporadic AD patients and familial cases with the Arctic, Swedish and the presenilin-1 PS1Δ9 mutation. A consistent staining was observed in blood vessels in all AD cases with cerebral amyloid angiopathy. There was no cross-reactivity with other aggregates typical for other common neurodegenerative diseases showing that NT4X-167 staining is specific for AD. CONCLUSIONS: Aß4-x precedes AßpE3-x in the well accepted 5XFAD AD mouse model underlining the significance of N-truncated species in AD pathology. NT4X-167 therefore is the first antibody reacting with Aß4-x and represents a novel tool in Alzheimer research.