The physiological and pharmacological roles of prostaglandins in hair growth

Abstract

Hair loss is a common status found among people of all ages. Since the role of hair is much more related to culture and individual identity, hair loss can have a great influence on well-being and quality of life. It is a disorder that is observed in only scalp patients with androgenetic alopecia (AGA) or alopecia areata caused by stress or immune response abnormalities. Food and Drug Administration (FDA)-approved therapeutic medicines such as finasteride, and minoxidil improve hair loss temporarily, but when they stop, they have a limitation in that hair loss occurs again. As an alternative strategy for improving hair growth, many studies reported that there is a relationship between the expression levels of prostaglandins (PGs) and hair growth. Four major PGs such as prostaglandin D2 (PGD₂), prostaglandin I2 (PGI₂), prostaglandin E2 (PGE_2α), and prostaglandin F2 alpha (PGF_2α) are spatiotemporally expressed in hair follicles and are implicated in hair loss. This review investigated the physiological roles and pharmacological interventions of the PGs in the pathogenesis of hair loss and provided these novel insights for clinical therapeutics for patients suffering from alopecia.

Keywords: Alopecia areata; Androgenetic alopecia; Cyclooxygenase; Hair follicle; Prostaglandin.

Fig. 1. Diagram of prostanoids and their biological effects on hair follicles through stimulating different type of G protein-coupled receptors.

Prostanoids are classified into five types, namely thromboxane A2 (TXA₂), prostaglandin D2 (PGD₂), prostaglandin E2 (PGE₂), prostaglandin F2α (PGF_2α), and prostaglandin I2 (PGI₂). PGD₂ binds to prostaglandin D2 receptors (DP1, DP2), whereas PGE₂ binds to prostaglandin E2 receptors (EP1, EP2, EP3, EP4). PGF_2α binds to the prostaglandin F2α receptor (FP). PGI₂ binds to the prostaglandin I2 receptor (IP). TXA₂ binds to the thromboxane A2 receptor (TP). Human hair follicles remarkably expressed microsomal PGES (mPGES)-1, mPGES-2, and cytosolic PGES (cPGES), which converts PGH₂ to PGE₂. These human hair follicles also significantly expressed AKR1C3/PGFS, which catalyzes PGH₂ to PGF_2α. In addition, cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), prostaglandin G2 (PGG₂), prostaglandin H2 (PGH₂), PGD2 synthase (PGDS), PGE₂ synthase (PGES), PGF_2α synthase (PGFS), PGI₂ synthase (PGIS) are marked.