Amyloid beta and its naturally occurring N-terminal variants are potent activators of human and mouse formyl peptide receptor 1

Innate immune activation in neurodegenerative diseases

Activation of the innate immune system following pattern recognition receptor binding has emerged as one of the major pathogenic mechanisms in neurodegenerative disease. Experimental, epidemiological, pathological, and genetic evidence underscores the meaning of innate immune activation during the prodromal as well as clinical phases of several neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and frontotemporal dementia. Importantly, innate immune activation and the subsequent release of inflammatory mediators contribute mechanistically to other hallmarks of neurodegenerative diseases such as aberrant proteostatis, pathological protein aggregation, cytoskeleton abnormalities, altered energy homeostasis, RNA and DNA defects, and synaptic and network disbalance and ultimately to the induction of neuronal cell death. In this review, we discuss common mechanisms of innate immune activation in neurodegeneration, with particular emphasis on the pattern recognition receptors (PRRs) and other receptors involved in the detection of damage-associated molecular patterns (DAMPs).

Amyloid-β and caspase-1 are indicators of sepsis and organ injury

Background

Sepsis is a life-threatening condition that results from a dysregulated host response to infection, leading to organ dysfunction. Despite the prevalence and associated socioeconomic costs, treatment of sepsis remains limited to antibiotics and supportive care, and a majority of intensive care unit (ICU) survivors develop long-term cognitive complications post-discharge. The present study identifies a novel regulatory relationship between amyloid-β (Aβ) and the inflammasome-caspase-1 axis as key innate immune mediators that define sepsis outcomes.

Methods

Medical ICU patients and healthy individuals were consented for blood and clinical data collection. Plasma cytokine, caspase-1 and Aβ levels were measured. Data were compared against indices of multiorgan injury and other clinical parameters. Additionally, recombinant proteins were tested in vitro to examine the effect of caspase-1 on a functional hallmark of Aβ, namely aggregation.

Results

Plasma caspase-1 levels displayed the best predictive value in discriminating ICU patients with sepsis from non-infected ICU patients (area under the receiver operating characteristic curve=0.7080). Plasma caspase-1 and the Aβ isoform Aβx-40 showed a significant positive correlation and Aβx-40 associated with organ injury. Additionally, Aβ plasma levels continued to rise from time of ICU admission to 7 days post-admission. In silico, Aβ harbours a predicted caspase-1 cleavage site, and in vitro studies demonstrated that caspase-1 cleaved Aβ to inhibit its auto-aggregation, suggesting a novel regulatory relationship.

Conclusions

Aβx-40 and caspase-1 are potentially useful early indicators of sepsis and its attendant organ injury. Additionally, Aβx-40 has emerged as a potential culprit in the ensuing development of post-ICU syndrome.

The Hidden Role of Non-Canonical Amyloid β Isoforms in Alzheimer's Disease

Recent advances have placed the pro-inflammatory activity of amyloid β (Aβ) on microglia cells as the focus of research on Alzheimer's Disease (AD). Researchers are confronted with an astonishing spectrum of over 100 different Aβ variants with variable length and chemical modifications. With the exception of Aβ1-42 and Aβ1-40, the biological significance of most peptides for AD is as yet insufficiently understood. We therefore aim to provide a comprehensive overview of the contributions of these neglected Aβ variants to microglia activation. First, the impact of Aβ receptors, signaling cascades, scavenger mechanisms, and genetic variations on the physiological responses towards various Aβ species is described. Furthermore, we discuss the importance of different types of amyloid precursor protein processing for the generation of these Aβ variants in microglia, astrocytes, oligodendrocytes, and neurons, and highlight how alterations in secondary structures and oligomerization affect Aβ neurotoxicity. In sum, the data indicate that gene polymorphisms in Aβ-driven signaling pathways in combination with the production and activity of different Aβ variants might be crucial factors for the initiation and progression of different forms of AD. A deeper assessment of their interplay with glial cells may pave the way towards novel therapeutic strategies for individualized medicine.