Inhibition of rab27a and rab27b has opposite effects on the regulation of hair cycle and hair growth

Rab27a/b are known to play an important role in the transport of melanosomes, with their knockout causing silvery gray hair. However, the relationship between Rab27a/b and hair growth is not well known. To evaluate the role of Rab27a/b in hair cycle, we investigated the expression of Rab27a/b during hair cycling and human outer root sheath (hORS) cells. The expression of Rab27a in ORS cells was mainly detected at the anagen, whereas expression of Rab27b in ORS, and epidermal cells was strongly expressed at the telogen. Additionally, Rab27a/b were expressed in the Golgi of hORS cells. To evaluate the role of Rab27a/b in hair growth, telogen-to-anagen transition animal and vibrissae hair follicles (HFs) organ culture models were assayed using Rab27a/b siRNAs. The knockdown of Rab27a or Rab27b suppressed or promoted hair growth, respectively. These results were also confirmed in human dermal papilla cells (hDPCs) and hORS cells, showing the opposite mitogenic effects. Moreover, Rab27b knockdown increased the expression levels of various growth factors in the hDPCs and hORS cells. Overall, the opposite temporal expression patterns during hair cycling and roles for hair growth of Rab27a/b suggested that Rab27a/b might regulate the hair cycle. Therefore, our study may provide a novel solution for the development of hair loss treatment by regulating Rab27a/b levels.