In recent posts we've explored the basis of pattern hair loss and touched on treatment methods used to blunt the onset and progression of the disorder.   In our most recent post we also discussed the importance of hair cycle biodynamics -- and why this offers a potentially intriguing target for the development of advanced hair growth stimulants.

Recall that human scalp hair growth differs from most other mammals in that almost all other hair bearing animals shed in waves, but each hair on a person's head grows and sheds according to its own time clock.  This mosaic pattern of hair growth means that we are constantly growing and shedding hair, typically in a ratio of 80% anagen (growth) & 20% catagen/telogen (shed/rest).  

As we observed, in persons affected by AGA (androgenetic alopecia) the hair cycle becomes disturbed with more frequent resting cycles and shorter growing cycles.  Therefore, the source of biochemical and genetic signals which regulate hair cycling constitutes a particularly interesting therapeutic target.  

In AGA-susceptible persons, the circulating hormone 5 alpha-DHT constitutes the most well-studied trigger; taking vibrant, growing hair and precipitating a transition into gradually weaker, finer "thinner" hair.  Additionally, in our lab and elsewhere, work has been underway to explore the role inflammation plays in shifting previously healthy hair follicles into a negative growth cycle.  

One of the more intriguing clues has comes from organogenesis, i.e. the differential cell lineages that arise as a human embryo evolves.  Recently, it has been shown that the areas of the scalp most susceptible to AGA arise from a tissue substrate known as neural-ectoderm.  And the occipital fringe, i.e. scalp hair that generally remains unaffected by AGA, appears to come from the mesoderm during gastrulation.

Of further import, each cell lineage responds to a unique set of genetic markers.  And each displays a genetic architecture responsible for establishing the species-based topographic arrangement of the individual tissues. The gene transcription signals overlying this plan rely upon complex interactions including BMP, FGF, interleukin, and Wnt signaling pathways.  As we unravel the stream of signals from each of these pathways, we start to see how each influences hair follicle biodynamics, both during normative homeostasis, and also during the transition to a negative growth cycle.  Thus, future therapeutic targets will undoubtedly be directed toward at least some of these heretofore novel factors.