With so much research focusing on stem cells, I’ve been wondering lately whether researchers are overlooking other important, multipotent cell groups, specifically what are called “progenitor” cells. But then another part of me wonders whether these two groups are so very different from each other. Technically, the main difference between stem cells and progenitors is their lifespan, with progenitors’ being much shorter, but the line here seems blurry; most adult stem cells cannot be cultured for extensive amounts of time before they differentiate or senesce.
I was reminded of the issue of stem cells versus progenitors by a paper that came out earlier this month in The Journal of Clinical Investigation that showed, surprisingly, that patients with androgenic alopecia (AGA), or male pattern baldness, had a normal number of hair stem cells in their scalps, but a depleted number of different hair progenitor cells. The progenitors now look like a likely culprit for AGA. It’s been well-studied how stem cells in hair follicles give rise to new hairs over time, and it’s known that progenitors derived from these stem cells play key roles in this process, but it had not been studied with relation to AGA previously. It’s possible that the stem cells in bald AGA scalps are somehow dysfunctional or inactivated, and this could cause the loss of progenitor cells, but it still needs to be looked into (If you’d like to read more detailed coverage of this paper, I wrote a technical blog post about it on my blog All Things Stem Cell and a layman article on it for my column Biology Bytes.)
I wonder what would have happened to this recent study if when the researchers had found out that the number of hair stem cells was the same in haired and bald scalps, they then moved on to investigating other, maybe non-cellular suspects, without looking at the progenitors. Perhaps they would have then discovered a molecular abnormality in the stem cells, and then suspected the downstream progenitor groups. I just can’t help but wonder how many other diseases and biological phenomena have been investigated with a primary focus on the stem cells involved, when in some cases the progenitors may be a better initial indicator for what’s changed in the system. Or maybe using the terms “stem cells” and “progenitors” is really splitting hairs; stem cells vary significantly in potency and proliferation capacity from group to group, so maybe we should just expand the already expansive term “stem cells” to encompass a broader range of cells. While I like to think that a cell type’s name doesn’t affect whether a researcher studies it, I’d imagine it’s easier to get funding for “stem cell” research than “progenitor cell” research (or, with some funding agencies it may be the other way around), and this may definitely affect a researcher’s focus with funding as tight as it is.