This work, I think, is not significant for the hair growth, but for the fact that the researchers involved have found a simple way to enhance the activity of a stem cell population. It suggests that the research community might expect to find analogous (but probably quite different) simple ways to selectively achieve the same outcome in other stem cell populations that support other tissue types. Losing hair is somewhere in the vicinity of inconvenient and annoying. There are any number of other tissues in which the age-related decline of stem cell activity is ultimately fatal, and those seem to me to be the more important challenges to focus upon.
Hair follicle stem cells are long-lived cells in the hair follicle; they are present in the skin and produce hair throughout a person's lifetime. They are quiescent, meaning they are normally inactive, but they quickly activate during a new hair cycle, which is when new hair growth occurs. The quiescence of hair follicle stem cells is regulated by many factors. In certain cases they fail to activate, which is what causes hair loss.
Researchers found that hair follicle stem cell metabolism is different from other cells of the skin. Cellular metabolism involves the breakdown of the nutrients needed for cells to divide, make energy and respond to their environment. The process of metabolism uses enzymes that alter these nutrients to produce metabolites. As hair follicle stem cells consume the nutrient glucose - a form of sugar - from the bloodstream, they process the glucose to eventually produce a metabolite called pyruvate. The cells then can either send pyruvate to their mitochondria - the part of the cell that creates energy - or can convert pyruvate into another metabolite called lactate. "Our observations about hair follicle stem cell metabolism prompted us to examine whether genetically diminishing the entry of pyruvate into the mitochondria would force hair follicle stem cells to make more lactate, and if that would activate the cells and grow hair more quickly."
The research team first blocked the production of lactate genetically in mice and showed that this prevented hair follicle stem cell activation. Conversely, they increased lactate production genetically in the mice and this accelerated hair follicle stem cell activation, increasing the hair cycle. "Before this, no one knew that increasing or decreasing the lactate would have an effect on hair follicle stem cells. Once we saw how altering lactate production in the mice influenced hair growth, it led us to look for potential drugs that could be applied to the skin and have the same effect."
The team identified two drugs that, when applied to the skin of mice, influenced hair follicle stem cells in distinct ways to promote lactate production. The first drug, called RCGD423, activates a cellular signaling pathway called JAK-Stat, which transmits information from outside the cell to the nucleus of the cell. The research showed that JAK-Stat activation leads to the increased production of lactate and this in turn drives hair follicle stem cell activation and quicker hair growth. The other drug, called UK5099, blocks pyruvate from entering the mitochondria, which forces the production of lactate in the hair follicle stem cells and accelerates hair growth in mice.