Stem cell factor/c-Kit signalling in normal and androgenetic alopecia hair follicles.

Androgens stimulate many hair follicles to alter hair colour and size via the hair growth cycle; in androgenetic alopecia tiny, pale hairs gradually replace large, pigmented ones. Since stem cell factor (SCF) is important in embryonic melanocyte migration and maintaining adult rodent pigmentation, we investigated SCF/c-Kit signalling in human hair follicles to determine whether this was altered in androgenetic alopecia. Quantitative immunohistochemistry detected three melanocyte-lineage markers and c-Kit in four focus areas: the epidermis, infundibulum, hair bulb (where pigment is formed) and mid-follicle outer root sheath (ORS).

Autocrine catecholamine biosynthesis and the beta-adrenoceptor signal promote pigmentation in human epidermal melanocytes.

Earlier it has been shown that human proliferating/undifferentiated basal keratinocytes hold the full capacity for autocrine catecholamine synthesis/degradation and express beta2-adrenoceptors (beta2-AR). In this report, we show that human melanocytes also express all of the mRNA and enzymes for autocrine synthesis of norepinephrine but fail to produce epinephrine. So far, it was established that human melanocytes express alpha1-AR which are induced by norepinephrine yielding the inosine triphosphate diacylglycerol signal.

Tyrosine hydroxylase isoenzyme I is present in human melanosomes: a possible novel function in pigmentation.

Both human epidermal melanocytes and keratinocytes have the full capacity for de novo synthesis of 6(R) L-erythro 5,6,7,8, tetrahydrobiopterin, the essential cofactor for the rate limiting step in catecholamine synthesis, via tyrosine hydroxylase. Catecholamine synthesis has been demonstrated in proliferating keratinocytes of the epidermis in human skin. This study presented herein identified for the first time the expression of tyrosine hydroxylase isozyme I mRNA within the melanocyte.