Aging Causes Alzheimer's Disease

It is not particularly controversial to say that aging causes Alzheimer's disease, at least in the most common version of the condition in which there is no gene variant known to accelerate pathology. How exactly aging causes Alzheimer's disease is very much debated, however. This is not unusual; most age-related conditions have the same issue and the same debate.

The end stage pathology of age-related conditions is fairly well mapped, and we have a good idea as to what the root causes of aging are, the forms of damage and disarray that accumulate as a result of the operation of a normal metabolism. In between what is known of the cause and what is known of the end result, the map is poor at best, however. Drawing clear lines of cause and effect between those two areas of study remains very challenging. The operation of metabolism is ferociously complex, and deciphering cause and effect in a network of interacting processes is not as easy as one might think.

It is likely the case that even when the first body of rejuvenation therapies based on periodic repair of root cause damage exists and is widely used, there will still be debate and investigation over how exactly the processes of aging combine to cause the more complicated age-related conditions.

When aging switches on Alzheimer's

Aging increases the risk for developing Alzheimer's disease (AD). Pathological hallmarks of AD include abnormal deposits of extracellular beta amyloid (Aβ) plaques and intracellular neurofibrillary tangles, which are proposed to impair synaptic function to foster progressive cognitive impairment. Although aging and AD undeniably share a number of common features, such as oxidative stress, mitochondrial impairment, bioenergetic, and metabolic shifts, AD is not the inevitable co-morbidity of aging. This escape from AD arouses hope that anti-aging interventions could decelerate aging switches for AD dementia.

Our environment, lifestyle, stress, physical activity, and habits all modulate epigenetic control of gene expression for continuous environmental tracking. Age-related redox stress, often measured as oxidative stress in aging and AD, launches a global switch in the epigenetic landscape, widely affecting methylation, histone modification, and noncoding RNA regulation, to further drive downstream metabolic and energetic shifts.

According to a modified amyloid cascade hypothesis, amyloid-mediated oxidative stress triggers a cascade of downstream effects including mitochondrial dysfunction, excitotoxicity, synaptic loss, and neuroinflammation. However, the failure of anti-amyloid and anti-inflammatory therapy in clinical trials allows us to entertain other causal possibilities including an age-related oxidative redox shift as an upstream switch that changes amyloid processing, deposition, or clearance. Intriguingly, some resilient older individuals present with similar loads of Aβ and tangles compared to AD cases without experiencing dementia.

Further studies in resilient brains point out distinct upregulation of anti-inflammatory cytokines in entorhinal cortex, increased expression of neurotrophic factors and reduced expression of chemokines linked to microglial recruitment, which all suggest activated neuroglial inflammation in non-resilient AD. Since inflammation is switched on by an oxidative redox state, normal microglia that selectively remove excitotoxic synapses could be over-activated toward inflammatory neurodegeneration in AD. Suitable redox markers could enable measured redox therapies to decelerate inflammation and the neurodegenerative cascade.

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https://academic.oup.com/brain/advance-article/doi/10.1093/brain/awab129/6297373

Innate immunity stimulation via CpG oligodeoxynucleotides ameliorates Alzheimer's disease pathology in aged squirrel monkeys

Alzheimer's disease is the most common cause of dementia and the only illness among the top 10 causes of death for which there is no disease-modifying therapy. The failure rate of clinical trials is very high, in part due to the premature translation of successful results in transgenic mouse models to patients. Extensive evidence suggests that dysregulation of innate immunity and microglia/macrophages plays a key role in Alzheimer's disease pathogenesis. Activated resident microglia and peripheral macrophages can display protective or detrimental phenotypes depending on the stimulus and environment. Toll-like receptors (TLRs) are a family of innate immune regulators known to play an important role in governing the phenotypic status of microglia. We have shown in multiple transgenic Alzheimer's disease mouse models that harnessing innate immunity via TLR9 agonist CpG oligodeoxynucleotides (ODNs) modulates age-related defects associated with immune cells and safely reduces amyloid plaques, oligomeric amyloid-β, tau pathology, and cerebral amyloid angiopathy (CAA) while promoting cognitive benefits. In the current study we have used a non-human primate model of sporadic Alzheimer's disease pathology that develops extensive CAA-elderly squirrel monkeys. The major complications in current immunotherapeutic trials for Alzheimer's disease are amyloid-related imaging abnormalities, which are linked to the presence and extent of CAA; hence, the prominence of CAA in elderly squirrel monkeys makes them a valuable model for studying the safety of the CpG ODN-based concept of immunomodulation. We demonstrate that long-term use of Class B CpG ODN 2006 induces a favourable degree of innate immunity stimulation without producing excessive or sustained inflammation, resulting in efficient amelioration of both CAA and tau Alzheimer's disease-related pathologies in association with behavioural improvements and in the absence of microhaemorrhages in aged elderly squirrel monkeys. CpG ODN 2006 has been well established in numerous human trials for a variety of diseases. The present evidence together with our earlier, extensive preclinical research, validates the beneficial therapeutic outcomes and safety of this innovative immunomodulatory approach, increasing the likelihood of CpG ODN therapeutic efficacy in future clinical trials.

Posted by: Jones at June 15th, 2021 2:53 PM

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