induced rapid hair growth on the dorsal skin of healthy mice (Figure 1). In this study, the increased number of anagen hairs was retained over the entire treatment period but decreased to control levels within 14 days of treatment cessation. Figure 1 Source: Philp et al 2004 a) Control vehicle-treated rat skin after 7 days. b) Control vehicle-treated mouse skin after 28 days. c) Gross appearance of control vehicle-treated mouse skin after 28 days. d) Rat skin after 7 days of thymosin β4 treatment. e) Mouse skin after 28 days of thymosin β4 treatment. f) Gross appearance of mice after 28 days of thymosin β4treatment. Similarly, rat whiskers grown in vitro showed rapid growth when treated with Tβ4 (Philp et al, 2007). Upon examination, high levels of Tβ4 expression were observed in the developing hair follicles. Additionally, Tβ4 expression was also found to be high in the developing hair follicles of mice in vitro for 7–10 days (Cha H-J et al, 2010). This confirmed that Tβ4 promotes hair growth. Meier et al (2012) conducted a study on human hair follicles in organ culture and demonstrated that thymic peptides are produced by the human hair follicle epithelium and function as direct modulators of hair growth. They also suggested that thymic peptides may be therapeutically exploited for stimulating or inhibiting hair growth. It has long been claimed that Tβ4 stimulates human hair growth (Renner et al., 1986; Sawaya and Shapiro, 2000), but studies showing how it modulates human hair growth are limited. Therefore, although the above studies establish the basis for the further exploration of Tβ4 function and its molecular mechanisms in hair growth, clinical studies need to be performed to assess its possible role in the treatment and prevention of hair loss.
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