The molecular pathology of Alzheimer's disease.

In Alzheimer's disease (AD), abnormal accumulations of beta-amyloid are present in the brain and degenerating neurons exhibit cytoskeletal aberrations (neurofibrillary tangles). Roles for beta-amyloid in the neuronal degeneration of AD have been suggested based on recent data obtained in rodent studies demonstrating neurotoxic actions of beta- amyloid. However, the cellular mechanism of action of beta-amyloid is unknown, and there is no direct information concerning the biological activity of beta-amyloid in human neurons. We now report on experiments in human cerebral cortical cell cultures that tested the hypothesis that beta-amyloid can destabilize neuronal calcium regulation and render neurons more vulnerable to environmental stimuli that elevate intracellular calcium levels. Synthetic beta-amyloid peptides (beta APs) corresponding to amino acids 1–38 or 25–35 of the beta-amyloid protein enhanced glutamate neurotoxicity in cortical cultures, while a peptide with a scrambled sequence was without effect. beta APs alone had no effect on neuronal survival during a 4 d exposure period. beta APs enhanced both kainate and NMDA neurotoxicity, indicating that the effect was not specific for a particular subtype of glutamate receptor. The effects of beta APs on excitatory amino acid (EAA)-induced neuronal degeneration were concentration dependent and required prolonged (days) exposures. The beta APs also rendered neurons more vulnerable to calcium ionophore neurotoxicity, indicating that beta APs compromised the ability of the neurons to reduce intracellular calcium levels to normal limits. Direct measurements of intracellular calcium levels demonstrated that beta APs elevated rest levels of calcium and enhanced calcium responses to EAAs and calcium ionophore. The neurotoxicity caused by EAAs and potentiated by beta APs was dependent upon calcium influx since it did not occur in calcium-deficient culture medium. Finally, the beta APs made neurons more vulnerable to neurofibrillary tangle-like antigenic changes induced by EAAs or calcium ionophore (i.e., increased staining with tau and ubiquitin antibodies). Taken together, these data suggest that beta-amyloid destabilizes neuronal calcium homeostasis and thereby renders neurons more vulnerable to environmental insults.

https://www.jneurosci.org/content/jneuro/12/2/376.full.pdf

beta-Amyloid peptides destabilize calcium homeostasis and render human cortical neurons vulnerable to excitotoxicity

Cyclin-dependent kinase 5 (Cdk5) is required for proper development of the mammalian central nervous system. To be activated, Cdk5 has to associate with its regulatory subunit, p35. We have found that p25, a truncated form of p35, accumulates in neurons in the brains of patients with Alzheimer's disease. This accumulation correlates with an increase in Cdk5 kinase activity. Unlike p35, p25 is not readily degraded, and binding of p25 to Cdk5 constitutively activates Cdk5, changes its cellular location and alters its substrate specificity. In vivo the p25/Cdk5 complex hyperphosphorylates tau, which reduces tau's ability to associate with microtubules. Moreover, expression of the p25/Cdk5 complex in cultured primary neurons induces cytoskeletal disruption, morphological degeneration and apoptosis. These findings indicate that cleavage of p35, followed by accumulation of p25, may be involved in the pathogenesis of cytoskeletal abnormalities and neuronal death in neurodegenerative diseases.

Conversion of p35 to p25 deregulates Cdk5 activity and promotes neurodegeneration

Mutations in the amyloid precursor protein (APP) gene cause early-onset familial Alzheimer disease (AD) by affecting the formation of the amyloid β (Aβ) peptide, the major constituent of AD plaques. We expressed human APP751 containing these mutations in the brains of transgenic mice. Two transgenic mouse lines develop pathological features reminiscent of AD. The degree of pathology depends on expression levels and specific mutations. A 2-fold overexpression of human APP with the Swedish double mutation at positions 670/671 combined with the V717I mutation causes Aβ deposition in neocortex and hippocampus of 18-month-old transgenic mice. The deposits are mostly of the diffuse type; however, some congophilic plaques can be detected. In mice with 7-fold overexpression of human APP harboring the Swedish mutation alone, typical plaques appear at 6 months, which increase with age and are Congo Red-positive at first detection. These congophilic plaques are accompanied by neuritic changes and dystrophic cholinergic fibers. Furthermore, inflammatory processes indicated by a massive glial reaction are apparent. Most notably, plaques are immunoreactive for hyperphosphorylated tau, reminiscent of early tau pathology. The immunoreactivity is exclusively found in congophilic senile plaques of both lines. In the higher expressing line, elevated tau phosphorylation can be demonstrated biochemically in 6-month-old animals and increases with age. These mice resemble major features of AD pathology and suggest a central role of Aβ in the pathogenesis of the disease.

https://www.pnas.org/content/pnas/94/24/13287.full.pdf

Two amyloid precursor protein transgenic mouse models with Alzheimer disease-like pathology

Putative Alzheimer disease (AD)-specific proteins (A68) were purified to homogeneity and shown to be major subunits of one form of paired helical filaments (PHFs). The amino acid sequence and immunological data indicate that the backbone of A68 is indistinguishable from that of the protein tau (tau), but A68 could be distinguished from normal human tau by the degree to which A68 was phosphorylated and by the specific residues in A68 that served as phosphate acceptors. The larger apparent relative molecular mass (Mr) of A68, compared to normal human tau, was attributed to abnormal phosphorylation of A68 because enzymatic dephosphorylation of A68 reduced its Mr to close to that of normal tau. Moreover, the LysSerProVal motif in normal human tau appeared to be an abnormal phosphorylation site in A68 because the Ser in this motif was a phosphate acceptor site in A68, but not in normal human tau. Thus, the major subunits of a class of PHFs are A68 proteins and the excessive or inappropriate phosphorylation of normal tau may change its apparent Mr, thus transforming tau into A68.

https://science.sciencemag.org/content/sci/251/4994/675.full.pdf

A68: a major subunit of paired helical filaments and derivatized forms of normal Tau

A monoclonal antibody was prepared against pooled homogenates of brain tissue from patients with Alzheimer's disease. This antibody recognizes an antigen present in much higher concentration in certain brain regions of Alzheimer patients than in normal brain. The antigen appears to be a protein present in neurons involved in the formation of neuritic plaques and neurofibrillary tangles, and in some morphologically normal neurons in sections from Alzheimer brains. Partial purification and Western blot analysis revealed the antigen from Alzheimer brain to be a single protein with a molecular weight of 68,000. Application of the same purification procedure to normal brain tissue results in the detection of small amounts of a protein of lower molecular weight.

https://science.sciencemag.org/content/sci/232/4750/648.full.pdf

A neuronal antigen in the brains of Alzheimer patients.

A neuronal antigen in the brains of Alzheimer patients

Abstract Evidence of many interacting causes of aging has renewed interest in food and nutrient combinations that may blunt the main causes[PMC9184560, PMC8889622] and postpone aging, mild cognitive impairment and Alzheimer’s (“A-MCI-Alz”) in contrast to prior failures[PMC9232186]. We present an updated list of anti-aging/pro-longevity strategies to address limitations of previous food/nutrient combinations. Our list has two unusual features: (i) all interventions should be administered concurrently so no fundamental causes of A-MCI-Alz are without remediation and can inflame and leave smoldering important causal factors, (ii) all interventions should be provided daily or weekly to help avoid re-ignition of key factors driving A-MCI-Alz. These two features can help explain past longevity-trial failures[PMC9310407]: no previous study to our knowledge has included most or all of the following interventions, so untreated causes of A-MCI-Alz likely remained active[PMC9114803]. Our recommended interventions include intermittent-or-continuous calorie restriction or fasting[PMID: 33138875, PMC9351392, PMC7956384], protein- and/or methionine-restriction[PMC9197402, PMC4023024, PMC9197406], consumption of moderately-strong metal chelators (e.g. polyphenols in blueberries[PMC1413581], other berries[PMC8271923], grapes[PMC7096489, PMC6386230], cherries[PMC8745076], fruits with hesperidin/hesperitin [PMC9310407] like oranges, soybeans with genistein [PMC4286753], ginger [PMC5852742], ginseng [PMC9358063, PMC3830124, PMC6874434], green/rooibos/oolong teas[PMC6567241, PMIDs: 33285593, 19996359], coffee[PMC4926853, PMC9145055], chocolate[PMC9287426]), antioxidant-rich foods[PMC7530501], B vitamins including vitamin B5 (pantothenic acid[PMC9232186, PMC8725342, https://doi.org/10.3181%2F00379727-99-24442]) to help metabolize partly-toxic aldehydes[PMC6802361] and improve/lower lactate/pyruvate and NAD+/NADH ratios[PMC7346061], ingesting adequate-to-high amounts of longevity-correlated tyrosine[PMC6681387], cysteine[PMID: 20191258], glutathione[PMC8912885, PMC5005830], niacin, nicotine acid and/or NADH[PMC7346061, PMC6982340], spermidine[PMC8436989], anti-inflammatory NSAIDS[PMC4270464], autophagy inducers[PMC6191153] fiber[PMC8705837] and fluids[PMID: 21585170] to help remove excess metals, toxic metabolites and damaged organelles, while limiting methionine-rich, other pro-aging foods[PMC4023024].

Alex Pruchnicki

Papers

A neuronal antigen in the brains of Alzheimer patients.

A neuronal antigen in the brains of Alzheimer patients

Food and supplement combinations to prevent or postpone aging, mci, and alzheimer’s disease