Several of you have asked why I don’t update this blog more often. My priority is to take effective interventions for age-related diseases to FDA phase 1 human trials, rather than blogging about the process. Each week, Outlook reminds me to update the blog, but there are many tasks that need doing if we are […]
Genes and Aging
Several of you have asked why I don’t update this blog more often. My priority is to take effective interventions for age-related diseases to FDA phase 1 human trials, rather than blogging about the process. Each week, Outlook reminds me to update the blog, but there are many tasks that need doing if we are going to get to human trials, which remains our primary target.
In working on age-related disease, however, I am reminded that we can do very little unless we understand aging. Most of us assume we already understand what we mean by aging, but our assumptions prevent us from a more fundamental and valid understanding of the aging process. In short, our unexamined assumptions get in the way of effective solutions. To give an analogy, if we start with the assumption that the Earth is the center of the solar system, then no matter how carefully we calculate the orbits of the planets, we will fail. If we start with the assumption that the plague results from evil spirits rather than Yersinia pestis, then no matter how many exorcisms we invoke, we will fail. We don’t fail because of any lack of effort, we fail because of misdirected effort.
Our assumptions define the limits of our abilities.
When we look at aging, too often we take only a narrow view. Humans age, as do all the mammals and birds (livestock and pets come to mind) that have played common roles in human culture and human history. When most people think of aging, they seldom consider trees, hydra, yeast, bacteria, or individual cells (whatever the species). Worse, even when we do look at these, we never question our quotidian assumptions. We carry our complacent assumptions along with us, a ponderous baggage, dragging us down, restricting our ability to move ahead toward a more sophisticated (and accurate) understanding. If we looked carefully, we would see that not all cells age and not all organisms age. Moreover, of those that age, not all organisms age at the same rate and, within an organism, not all cells age at the same rate. In short, neither the rate of aging, nor aging itself is universal. As examples, dogs age faster than humans and, among humans, progeric children age faster than normal humans. The same is true when we consider cells: somatic cells age faster than stem cells, while germ cells (sperm and ova) don’t age at all. So much for aging being universal.
The key question isn’t “why do all things age?”, but rather “why does aging occur in some cases and not in others, and at widely different rates when it occurs at all?” The answer certainly isn’t hormones, heartbeats, entropy, mitochondria, or free radicals, for none of these can explain the enormous disparity in what ages and what doesn’t, nor why cells age at different rates. Nor is aging genetic in any simplistic sense. While genes play a prominent role in how we age, there are no “aging genes”. Aging is not a “genetic disease”, but rather a matter of epigenetics – it’s not which genes you have, but how those genes are expressed and how their expression changes over time, particularly over the life of the organism or over multiple cell divisions in the life of a cell. In a sense, you age not because of entropy, but because your cells downregulate the ability to maintain themselves in the face of that entropy. Cell senescence effects a broad change in gene expression that results in a gradual failure to deal with DNA repair, mitochondrial repair, free radical damage, and molecular turnover in general. Aging isn’t a matter of damage, it’s a matter of no longer repairing the damage.
All of this wouldn’t matter – it’s mere words and theory – were it not for our ability to intervene in age-related disease. Once we understand how aging works, once we look carefully at our assumptions and reconsider them, our more accurate and fundamental understanding allows suggests how we might cure age-related disease, to finally treat the diseases we have so long thought beyond our ability. It is our ability to see with fresh eyes, to look at all organisms and all cells without preconceptions, that permits us to finally do something about Alzheimer’s and other age-related disease.
Only an open mind will allow us to save lives.
I realize you are a busy man, but do you have a take on this very recent news on Alzheimer’s?
ApoE4 markedly exacerbates tau-mediated neurodegeneration in a mouse model of tauopathy, Nature (2017) doi:10.1038/nature24016
Again, as Michael explains in this post, this would be a case of a misdirected effort. Alzheimer is not a genetic disease but an age-related disease. Quoting from his latest book:
“When we consider genes that correlate with the diseases of aging, such as APO-E4 with Alzheimer’s disease or the genes related to cholesterol metabolism with atherosclerosis, there is never 100 percent penetrance (i.e., some people have the gene but not the disease, while others have the disease but not the gene). Yet the simplistic assumption is that if we could only locate the full panel of the genes that “cause” the disease , then we could predict the disease with certainty. The reality is that it is not the genes that cause the disease, but their expression, and gene expression is controlled by myriad factors including both our behaviors and our telomeres. Genes cause disease depending on how they are expressed and in what circumstances.”