Defects of immune regulation in the presenilin-1 mutant knockin mouse

Telomere shortening in neurological disorders: an abundance of unanswered questions

Telomeres, ribonucleoprotein complexes that cap eukaryotic chromosomes, typically shorten in leukocytes with aging. Aging is a primary risk factor for neurodegenerative disease (ND), and a common assumption has arisen that leukocyte telomere length (LTL) can serve as a predictor of neurological disease. However, the evidence for shorter LTL in Alzheimer's and Parkinson's patients is inconsistent. The diverse causes of telomere shortening may explain variability in LTL between studies and individuals. Additional research is needed to determine whether neuronal and glial telomeres shorten during aging and in neurodegenerative disorders, if and how LTL is related to brain cell telomere shortening, and whether telomere shortening plays a causal role in or exacerbates neurological disorders.

Implications of non-canonical G-protein signaling for the immune system

Heterotrimeric guanine nucleotide-binding proteins (G proteins), which consist of three subunits α, β, and γ, function as molecular switches to control downstream effector molecules activated by G protein-coupled receptors (GPCRs). The GTP/GDP binding status of Gα transmits information about the ligand binding state of the GPCR to intended signal transduction pathways. In immune cells heterotrimeric G proteins impact signal transduction pathways that directly, or indirectly, regulate cell migration, activation, survival, proliferation, and differentiation. The cells of the innate and adaptive immune system abundantly express chemoattractant receptors and lesser amounts of many other types of GPCRs. But heterotrimeric G-proteins not only function in classical GPCR signaling, but also in non-canonical signaling. In these pathways the guanine exchange factor (GEF) exerted by a GPCR in the canonical pathway is replaced or supplemented by another protein such as Ric-8A. In addition, other proteins such as AGS3-6 can compete with Gβγ for binding to GDP bound Gα. This competition can promote Gβγ signaling by freeing Gβγ from rapidly rebinding GDP bound Gα. The proteins that participate in these non-canonical signaling pathways will be briefly described and their role, or potential one, in cells of the immune system will be highlighted.

Exercise and early-onset Alzheimer's disease: theoretical considerations

BACKGROUND/AIMS

Although studies show a negative relationship between physical activity and the risk for cognitive impairment and late-onset Alzheimer's disease, studies concerning early-onset Alzheimer's disease (EOAD) are lacking. This review aims to justify the value of exercise interventions in EOAD by providing theoretical considerations that include neurobiological processes.

METHODS

A literature search on key words related to early-onset dementia, exercise, imaging, neurobiological mechanisms, and cognitive reserve was performed.

RESULTS/CONCLUSION

Brain regions and neurobiological processes contributing to the positive effects of exercise are affected in EOAD and, thus, provide theoretical support for exercise interventions in EOAD. Finally, we present the design of a randomized controlled trial currently being conducted in early-onset dementia patients.

Presenilin/gamma-Secretase and Inflammation

Presenilins (PS) are the catalytic components of γ-secretase, an aspartyl protease that regulates through proteolytic processing the function of multiple signaling proteins. Specially relevant is the γ-secretase-dependent cleavage of the β-amyloid precursor protein (APP) since generates the β-amyloid (Aβ) peptides that aggregate and accumulate in the brain of Alzheimer's disease (AD) patients. Abnormal processing and/or accumulation of Aβ disrupt synaptic and metabolic processes leading to neuron dysfunction and neurodegeneration. Studies in presenilin conditional knockout mice have revealed that presenilin-1 is essential for age-dependent Aβ accumulation and inflammation. By contrast, mutations in the presenilin genes responsible for early onset familial AD cause rapid disease progression and accentuate clinical and pathological features including inflammation. In addition, a number of loss of function mutations in presenilin-1 have been recently associated to non-Alzheimer's dementias including frontotemporal dementia and dementia with Lewy bodies. In agreement, total loss of presenilin function in the brain results in striking neurodegeneration and inflammation, which includes activation of glial cells and induction of proinflammatory genes, besides altered inflammatory responses in the periphery. Interestingly, some non-steroidal anti-inflammatory drugs that slow cognitive decline and reduce the risk of AD, decrease amyloidogenic Aβ42 levels by modulating allosterically PS/γ-secretase. In this review, I present current evidence supporting a role of presenilin/γ-secretase signaling on gliogenesis and gliosis in normal and pathological conditions. Understanding the cellular mechanisms regulated by presenilin/γ-secretase during chronic inflammatory processes may provide new approaches for the development of effective therapeutic strategies for AD.

Abnormal mitochondrial dynamics--a novel therapeutic target for Alzheimer's disease?

Mitochondria are dynamic organelles that undergo continuous fission and fusion, which could affect all aspects of mitochondrial function. Mitochondrial dysfunction has been well documented in Alzheimer's disease (AD). In the past few years, emerging evidence indicates that an imbalance of mitochondrial dynamics is involved in the pathogenesis of AD. In this review, we discuss in detail the abnormal mitochondrial dynamics in AD and how such abnormal dynamics may impact mitochondrial and neuronal function and contribute to the course of disease. Based on this discussion, we propose that mitochondrial dynamics could be a potential therapeutic target for AD.