[nonbel]

>"Aggregates are age-related, but one needs explanations as to why that is the case."

I don't think there is much mystery here. As cells divide they accumulate (genetic, and other types of) errors. One thing that happens is proteins/peptides are more likely to end up in their most thermodynamically stable state, since it requires constant maintenance to avoid it.

http://www.nature.com/nrm/journal/v15/n6/full/nrm3810.html

[acjohnson55]

I don't think that necessarily explains how an offspring resets all of that. By that same logic, there should be a limit to how many generations of human there are.

[nonbel]

Apparently there are about 7 million oocytes created per generation[1], which could be done in 23 divisions: 2^23 = 8,388,608

So first, it doesn't require that many divisions per generation of human. Second, there are "errors" that get passed on to the offspring. Third, a lot of selection goes on so that only fertilized eggs without huge issues will eventually be born.

[1] https://en.wikipedia.org/wiki/Oogenesis

[acjohnson55]

Right, but it would seem like many such strategies could be applied to somatic cells. And we also know that there are complex organisms that don't meaningfully age.

[nonbel]

See my earlier reference here regarding somatic cells (they don't require so many divisions either): https://news.ycombinator.com/item?id=14397992

What organisms are you talking about that don't meaningfully age?

[ergothus]

You're dismissing the idea of (1) proving the "obvious" solution or disproving it via data, and you're ignoring the "how". "There are errors" doesn't say where they are errors, and how those errors translate into behavior. If the hypothesis in the source article is help up by more data, that is actually a huge deal, not just confirming something we already knew.

[nonbel]

The review I shared contains many ideas along these lines. Basically the AA sequences seem to be selected to disfavor aggregation, so most mutations should increase formation:

>"Many of the characteristics of proteins that enable the avoidance of aggregation, and amyloid formation in particular, are encoded by their amino acid sequences116. The elucidation of this code has enabled the identification of factors that determine the intrinsic aggregation propensity of these molecules117–119. Hence, it has been realized that globular proteins fold into structures that sequester aggregation-prone regions in their interior; in addition, typical features of the folding process, such as very high cooperativity, generate considerable kinetic barriers to the conversion of folded proteins into aggregation-prone species50,120. Furthermore, specific patterns of residues, such as alternating hydrophobic–hydrophilic stretches50,121, that tend to favour the amyloid state are commonly selected against during evolution119,121,122 or are otherwise neutralized by the insertion of highly aggregation-resistant residues, which are known as ‘gatekeepers’ (REFS 50,123)."

Really I doubt in the end there will be any disease not associated with amyloid/aggregate formation.

[subroutine]

So given that neurons almost never divide (1), and other cell types like skin cells divide every few hours (2), based on your formulation how do we explain that we never find A-beta plaques in skin cells?

----

1. It was thought that adult neurons didn't divided at all until like 1998; now we know some new neurons are produced from progenitor sources at very low rates.

2. 30,000 to 40,000 skin cells are produced every minute.

[nonbel]

What matters is how many divisions away from the fertilized egg. The "mainstream" idea has lead to many paradoxes: https://www.ncbi.nlm.nih.gov/pubmed/25459141