Ever had the experience that something, or someone, you thought you understood turned out quite differently? Well, it happens all the time in science and medicine too.
Last week, a drug abandoned for Alzheimer disease was reported by Harvard researchers as a promising treatment for the hard of hearing. Inside the inner ear the tiny hair cells responsible for sending signals to the brain are easily damaged by loud noises from machinery, gunshots, and heavy rock music. After suddenly noticing that I could no longer hear bats calling and getting a touch of tinnitus, I guessed I had lost some of those cells. It’s very common. The only connection I could recall at the time was a heavy head cold, stuffing up my ears. My doctor assured me a virus couldn’t be the cause, although I generally listen to medical opinion with only one ear.
Anyway, the researchers showed the Alzheimer drug can restore at least limited hearing to mice that had been rendered completely deaf by noise. Apparently, it was triggering neighboring cells to transform into sensory hair cells, which we always thought were irreplaceable. This could be the start of a breakthrough for sufferers of hearing loss: perhaps cell therapy will supersede hearing aids and cochlear implants one day.
The story struck a chord while I’m preparing a chapter from a N.I.H. conference in October at which we discussed why eggs are lost from the ovaries. According to the text-book story, women are born with all the eggs they will ever have, a total store of about a million, and they run out with time. The ovary is like an hourglass with sand grains trickling down, but most eggs are lost by a mysterious degenerative process and very few are reserved for ovulation. It’s virtually an empty organ at the menopause.
Now there are two research groups, one in Shanghai and another in Boston, claiming the old story is wrong, that a few stem cells in the ovary continue to make new eggs. Presumably their theory supposes these cells eventually tire of replenishing the store, giving up altogether in middle age.
The story caused a stir in the media because, if true, it might in theory be possible to kick-start the stem cells into resuming egg production for the rest of life, like Prince Charming waking the sleeping princess with a kiss. Not only would the menopause be banished but, weirder still, factories for human egg manufacture might spring up. Eggs grown from stem cells in incubators could find all sorts of purposes, including cloning to make spare part tissues and organs for regenerative medicine. What angels they would be!
I still don’t buy it, and am sometimes characterized as the bête noire of those theorists. But there is no doubt that organs in some creatures are masters of regeneration. Both fish and birds can replace hair cells in their ‘ears’ (represented by the lateral line in fish), and replenish eggs in their ovaries too. Working with a fishery biologist some years ago, we found the Pacific rockfish can produce eggs throughout its life.
This is the Methuselah of the depths, living up to 150 years old with ovaries still chock-full of eggs budding from stem cells. Evidently it never has a pisceopause! Why these animals have tool-kits for cell replacement that are probably absent in ourselves is a wonder, and something I am grappling with for a new edition of my book on aging.
I don’t – and can’t – dismiss the existence of stem cells in ovaries altogether, I just find it hard to believe claims in the face of so much evidence to the contrary. Perhaps they are not angels at all, but devils. Perhaps they were responsible for taking away my mother with ovarian cancer.
Next post: Close encounters of the bear kind