Morphological characteristics and factors in the plucked human hair follicle tissue of curved hair caused by acquired factors
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Presented by: Ippei Horibe
Introduction：The hair appearance varies depending on many things, such as hair shape, color and optical properties, and significantly affects the first impression given by a person. Examples of main factor include hair curving, in addition to congenitally hair curling, it is known that irregularly "curved hair" increases with age, and it leads to common hair problems. However, the physiological background of the "curved hair" due to acquired factor, such as aging, has not been clarified. In previous studies, we demonstrated that mRNA expression level of type IV collagen in hair follicle tissue of morphologically curved hair was about ten times less than that of straight hair, and that the structure of the plucked hair follicle tissue was asymmetrical rather than concentric shape.
Aim: The purpose of this study is to clarify the cause of "curved hair" thought to be due to acquired factors, and to find out methods for improving it.
Methods: Hair root tissues, obtained from the plucked hair of straight and curved hair in the same donor were embedded in paraffin. Thereafter, the continuous hair cross sections were prepared, and the morphological features of plucked hair follicle tissue were observed and immunohistochemical staining using antibodies to specific proteins involved in hair differentiation were performed.
Results: When we observed the plucked hair follicle tissue of "curved hair" obtained from six donors in their 30s to 50s, we found that the inner and outer root sheaths had distorted shapes. Furthermore, hair matrix cells based on different hair germs were fused in hair follicle to eventually form a single hair stem. Immunohistochemical staining was performed to confirm the characteristics of this morphological difference. The result show that KRT71, a type of keratin protein involved in the differentiation of inner hair root sheaths, were unevenly present in "curved hair". In addition, to obtain knowledge on the hair matrix fusion, we focused on the Wnt signaling pathway, which plays an important role in the developmental process, and examined the expression of related factors. As a result, no difference was found between Wnt5a or its receptor Frizzled6 expression level in straight hair and curved hair, while the expression of Dkk1, an inhibitor of Wnt, increased in curved hair.
Discussion and Conclusion: In the normal scalp, about one to three hairs with different hair cycles form a hair follicle unit and grow from single follicular pore. Usually, the hair papillae and secondary hair germs that form the basis of the new hair are independent at a certain distance, but if normal physiological functions are disturbed by some factor, their independence may be lost. In fact, a case called Pili multigemini in which multiple hairs are formed in single hair follicle has been reported. When we compared the difference "curved hair" and "straight hair" in the plucked hair follicle tissue of the same donor, it was observed that hair matrix cells based on different hair germs fuse with each other in a "curved hair" follicle, eventually forming a single hair stem. Namely, the investigation results indicated that acquired "curved hair" is caused by the multiple hair matrix fusion with different hair cycles, resulting in partial differences in speed and timing of differentiation, and the hair shape becomes asymmetric. Recently, it had been reported that inhibiting the planar cell polarity pathway (Wnt/PCP pathway), which regulates the cell polarity of the developmental process, causes abnormalities in the direction in which the scales extend in zebrafish (Iwasaki et al. 2018). Since it is well known that human hair is very similar in embryologically to fish scales, we thought that the Wnt/PCP pathway was involved in the hair matrix fusion observed in "curved hair". As a result, the expression of DKK1 related to that pathway increased. Thus, it was suggested that the hair matrix fusion may occur due to disorders of the Wnt/PCP pathway. Furthermore, we will report the relationship between the Wnt/PCP pathway and curved hair in genetic level, and study concerning the method of improving curved hair.
Aim: The purpose of this study is to clarify the cause of "curved hair" thought to be due to acquired factors, and to find out methods for improving it.
Methods: Hair root tissues, obtained from the plucked hair of straight and curved hair in the same donor were embedded in paraffin. Thereafter, the continuous hair cross sections were prepared, and the morphological features of plucked hair follicle tissue were observed and immunohistochemical staining using antibodies to specific proteins involved in hair differentiation were performed.
Results: When we observed the plucked hair follicle tissue of "curved hair" obtained from six donors in their 30s to 50s, we found that the inner and outer root sheaths had distorted shapes. Furthermore, hair matrix cells based on different hair germs were fused in hair follicle to eventually form a single hair stem. Immunohistochemical staining was performed to confirm the characteristics of this morphological difference. The result show that KRT71, a type of keratin protein involved in the differentiation of inner hair root sheaths, were unevenly present in "curved hair". In addition, to obtain knowledge on the hair matrix fusion, we focused on the Wnt signaling pathway, which plays an important role in the developmental process, and examined the expression of related factors. As a result, no difference was found between Wnt5a or its receptor Frizzled6 expression level in straight hair and curved hair, while the expression of Dkk1, an inhibitor of Wnt, increased in curved hair.
Discussion and Conclusion: In the normal scalp, about one to three hairs with different hair cycles form a hair follicle unit and grow from single follicular pore. Usually, the hair papillae and secondary hair germs that form the basis of the new hair are independent at a certain distance, but if normal physiological functions are disturbed by some factor, their independence may be lost. In fact, a case called Pili multigemini in which multiple hairs are formed in single hair follicle has been reported. When we compared the difference "curved hair" and "straight hair" in the plucked hair follicle tissue of the same donor, it was observed that hair matrix cells based on different hair germs fuse with each other in a "curved hair" follicle, eventually forming a single hair stem. Namely, the investigation results indicated that acquired "curved hair" is caused by the multiple hair matrix fusion with different hair cycles, resulting in partial differences in speed and timing of differentiation, and the hair shape becomes asymmetric. Recently, it had been reported that inhibiting the planar cell polarity pathway (Wnt/PCP pathway), which regulates the cell polarity of the developmental process, causes abnormalities in the direction in which the scales extend in zebrafish (Iwasaki et al. 2018). Since it is well known that human hair is very similar in embryologically to fish scales, we thought that the Wnt/PCP pathway was involved in the hair matrix fusion observed in "curved hair". As a result, the expression of DKK1 related to that pathway increased. Thus, it was suggested that the hair matrix fusion may occur due to disorders of the Wnt/PCP pathway. Furthermore, we will report the relationship between the Wnt/PCP pathway and curved hair in genetic level, and study concerning the method of improving curved hair.