I’m in the middle (er, maybe the first third) of a class on the neurobiology of aging. As such, we’ve covered a few different theories of aging, from the molecular (telomeres!) to the evolutionary (grandparents!). There are about as many overlapping theories of why we age as there are branches and specializations within biology. Aging affects all of us if we’re lucky, and all systems within our bodies, yet we don’t know precisely why it happens at all.
A new paper from scientists at the Salk Institute theorizes that cellular aging may be linked to “extremely long-lived proteins” (ELLPs). Keep in mind that cellular aging is slightly different from aging as a person; some cells throughout your body are constantly aging, dying, and being replaced, no matter what your age is. Other cells are mostly with you from birth until death — neurons are one such group of cells. With some slight, recently-discovered exceptions, there is very little neurogenesis (the birth of new cells in the brain) after childhood.
This new research into ELLPs focuses on the aging of brain cells, which is important, as they are not replaced when they are damaged or die off. Culturally, it’s also important because brain aging is a big deal in our population. I mentioned above that some cells (like skin cells or the lining of the stomach) are being replaced fairly regularly. Another mechanisms that cells use to repair damage is to replace or recycle the proteins that carry out cellular activities.
One important class of protein in brain cells is the transporter protein. The ELLPs in this study form channels that allow ions and other small molecules in and out of the cell past its membrane, which is how neurons signal to each other.
If this type of protein gets worn down or damaged, it is not able to be replaced or recycled, according to this paper. In that case, neurons will have a hard time signaling to each other, and the accumulated damage over many years could lead to problems throughout the brain.
This paper is new and interesting, although it doesn’t provide any easy answers, and definitely requires further study (For instance, the study was done on rats, which are a good model organism, but which also have much shorter lifespans than humans have). It does, however, illustrate one of my favorite differences between physicists, who have variously flavored quarks, and biologists, who have “extremely long-lived proteins.” I don’t know what that says about our respective fields, but it must mean something.