Use of γ-glutamyl transpeptidase activity as a marker of hair cycle and anagen induction in mouse hair follicles

Abstract γ-glutamyl transpeptidase activity was monitored in cycling mice by histologic localization and biochemical assay. Our objective for this study is to establish the relationship between γ-glutamyl transpeptidase activity and hair growth and to determine whether its activity can be correlated to induced hair growth. In cycling mouse skin, γ-glutamyl transpeptidase activity is pronounced during anagen and greatly diminished during telogen. In the skin, the enzyme is present exclusively in the outer and inner root sheaths of hair follicles. γ-glutamyl transpeptidase is limited to the follicle below the level of the sebaceous gland and is completely absent in the follicle above the sebaceous gland level. During anagen, the outer root sheath in the hypodermis is intensely positive for γ-glutamyl transpeptidase activity whereas the hair matrix cells and dermal papilla are negative. The inner root sheath above the bulb shows distinctive membrane staining for γ-glutamyl transpeptidase. γ-glutamyl transpeptidase activity can be seen to vary only in cycling follicles. Inducing anagen by plucking hair shafts results in an increase in γ-glutamyl transpeptidase activity directly correlated to hair regrowth. In a similar manner, mice were plucked and treated with a daily dose of 2% minoxidil. A slight difference in cycle lengths was seen in animals treated with minoxidil when compared to vehicle control. Minoxidil treatment may cause an early initiation of anagen, but both the minoxidil-treated skin and the vehicle-treated skin entered telogen at the same time. Together, these studies indicate that γ-glutamyl transpeptidase is a specific marker of anagen in growing hair.