Dr. Hideo Uno is one of the leading researchers of hair loss using animal models in the world. He has been involved in many of the early tests of drugs which are the most effective, including Minoxidil, Proscar, and RU58841.

Hideo Uno, MD, PhD
Senior Scientist
Wisconsin Regional Primate Research Center
Adjunct Associate Professor
Department of Pathology and Lataratory Medicine
University of Wisconsin
Madison, Wisconsin

Contents

• Introduction
• Hair Loss and Hair Follicle Abnormality
• The Structure and Cyclic Growth of the Hair Follicle
• Fetal Folliculogenesis
• Cyclic Growth of the Hair Follicle
• Cyclic Dynamics of Hair Follicle Development
• Hair Growth in Normal Development
• Follicular Changes in Male Pattern Baldness (Androgenetic Alopecia)
• Androgenetic Alopecia in Men
• Androgenetic Alopecia in Women
• Androgenetic Alopecia in Stump-tailed Macaques
• Alopecia Areata
• Histological Changes of Hair Follicles
• Alopecia in Abnormal Conditions
• Conclusions
• References

Androgenetic Alopecia in Stump-tailed Macaques

Baldness is not solely an affliction of mankind. Several species of nonhuman primates - chim panzees, stump-tailed macaques, and South American nakari - exhibit progressive thinning of the scalp hair after adolescence. The hair loss is asymptomatic and slowly progressive in nature. It begins as a thinning in the diameter of the hair, and gradually all terminal hairs are replaced with small, fine, colorless vellus hairs. In advanced stages of baldness in old animals, the scalp skin is almost denuded. The most prominent and greatest incidence of baldness occurs in the stump-tailed macaque, a species of Old World monkeys inhabiting Southeast Asia and China. Since Montagna reported this unique baldness, extensive studies on the biological notuce of the baldness in stump-tailed macaques have been reported. Baldness is hardly ever observed among other species of Old World monkeys such as rhesus, Japanese, and cynomol gus macaquas. Thus, this frontal-scalp alopecia of the stump-tailed macaque is a unique species- specific phenomenon and is widely recognized in both captive and wild groups. Moreover nearly 100% of postadolescent animals in both sexes exhibit the development of baldness. The stump-tailed macaqua seems to possess a genetic factor similar to the human bald trait. Like the development of male pattern bald- ness in humans, androgens are an indispensable triggering factor in macaqua baldness. Thinning of the frontal scalp hairs begins to appear around the same age (4 years) when serum levels of testosterone become drastically elevated in male animals. Although the elevation of testosterone in females is approximately one tenth that of the male level, there is no difference in the incidence and the age of onset of baldness between male and female stump-tailed macaquas (Figure 22). In earlier studies, Takashima at al observed that testosterone enhanced development of baldness in prepubertally ovariactomizad female stump-tailed macaquas. Recently, we observed that topical application of an antiandrogen (inhibitor of the enzyme steroid 5a-reductase) prevented the development of baldness in periadolescent animals of both sexes. Microscopically, the baldness in maqaques is a result of miniaturization of the hair follicles. The transformation of the hair follicles in the frontal scalp from terminal to vellus follicles is an essential change of the balding process. Interestingly, hair follicles transplanted from the occipital scalp (where the baldness does not develop during the entire life span) to the frontal scalp maintained their terminal hair growth for over seven years.

Figure 22 Serum testosterone levels in periadolescent male and female stump-tailed macagues

 Male  
 Female

Monthly samples were collected from 2 years 10 months old to 6 years 3 months old. Age of adults ranged from 7 to 24 years.

This shows that the expression of androgenmediated change (miniaturization) is apparently a regional genetic characteristic. Baldness certainly extends over the frontoparietal scalp, but all animals have retained long terminal hairs in the temporal and occipital scalp. A similar regional pattern is also seen in human baldness.

Thus, macaque baldness appears to be a usefull model for the study of human male pattern baldness for a number of reasons: Baldness has a prevalence of nearly 100% in both sexes; it displays an age-dependent, postpubertal development; it is localized on the frontal scalp; it shows similar biological features to human male pattern baldness (androgen-dependent, slowly progressive, and irreversible) and similar microscopic changes of the hair follicles; it allows both genetic and environmental control; and it occurs in animals that mature more quickly than humans.

Development of Baldness and Hair Follicle Changes

The scalp hairs in stump-tailed macaques become fully matured and the whole scalp is covered with long, coarse, darkly pigmented hairs prepubertally ( between 3.5 and 4.0 years). However, soon after the hair in the frontal scalp reaches its highest developmental peak, thinning begins (Figures 24a,b). Around the age of 4 years, the frontal scalp hairs begin to show a sign of thinning in most stump-tails. Microscopically, hair follicles in the nonbald frontal scalp area are the large terminal type, and a majority of them are in the growing anagen phase. On the other hand, the follicles in the bald scalp are all small vellus follicles (Figures 25a,b). Other than a miniaturization of the hair follicle, the bald scalp shows no abnormal changes in the epidermis, sebaceous glands, and dermal tissues. An essential phenomenon of macaque baldness is a progressive transformation of terminal follicles to the vellus type similar to the follicular changes that occur in human male pattern baldness. Morphometric study of the proportion of hair follicles in the different cyclic phases and of their size clearly showed that hair follicles in the bald scalp are much smaller than those in the nonbald scalp, and a majority of the follicles in the bald scalp were in the resting phase, whereas the follicles in the nonbald scalp were primarily in the anagen phase (Figures 20 and 27a,b). The folliculogram of the bald scalp in all adult animals always showed the same pattern (Figure 27b). This may be because transformed vellus follicles in the bald scalp have long resting phases and short anagen phases. Thus, the bald scalp of macaques is furnished with short, fine hairs. Our earlier studies revealed no difference between the number of hair follicles per square millimeter in the bald adult and nonbald pre- adolescent scalp skin. We also observed the hair follicles in advanced baldness of several aged macaques over 25 years (longevity in captivity can reach 34 years) and found that the vellus follicles showed no dystrophic changes: there were still signs of active cyclic growth. Because baldness in stump-tailed macaques is a suitable model for the study of human male pattern baldness, it allows both fundamental research into baldness and an examination of therapeutic challenges of baldness by various drugs. Indeed, we have studied both therapeutic and prophylactic effects of various compounds and antiandrogens on baldness using this model. All the studies involving normal development, the balding process, and successful treatment for regrowth of hair in the bald scalp revealed that the hair follicle growth cycle plays a major role in either the progressive or retrogressive trans- formation of the hair follicles.

Figure 23 Transplanted terminal hairs

Long terminal hairs growing in the three transplants of the occipital scalp skin in the bald frontal scalp seven years after the graft.

Figure 24 Macaque scalp hair patterns

Fully grown terminal hairs in the frontal scalp of a 3.3-year-old female (a). Bald frontal scalp of a 7-year-old male (b).

Ftgure 25 Macaque hair follicles

Long terminal anagen follicles in nonbald scalp of a periadolescent (a). Small vellus anagen and telogen follicles in the bald scalp of an adult animal (hi: note that the epidermis, sebaceous gland, dermis, and follicular structure show no abnormal change.

To support this concept, we have used an auto- radiographic method to study deoxyribonucleic acid (DNA) synthesis in the hair follicles of the stump-tailed macaques during normal develop- mental stages and after topical treatment. The method involves the uptake of radioactive thymidine, a precursor of DNA, into the hair follicle cells following in vitro incubation of scalp skin slices. The cells synthesizing DNA are thus labeled with 3H-thymidine and visualized in microscopic sections. As seen in Figure 28, a telogen (resting) follicle contained no DNA- synthesizing cells (a). However, in the early anagen follicles, the follicular cells in the base of the anchoring telogen follicle and the germinal peg contain several labeled cells (b). In the mid- and late-anagen follicles, the proliferating follicular cells that differentiate and form the outer and inner root sheath and bulb of the new anagen follicles show continuous activity of DNA synthesis (c and d). This mitotic activity (DNA synthesis) of the follicular germinal cells is greatly enhanced in the early anagon follicles that respond to treatment (Figure 20).

Figure 26 Folliculogram - Percent of total follicles in each cyclic phase

* Telogen
* Early and mid-anagen
* Anages
* Catagen

(Adopted mith potminnion tram Uno H, cappon A, Schlogel c: Cyclic dynamics of hair follicles and the effect of minoxidil on the bald scalps of stamptailed macaques.

Figure 27 Folliculogram of nonbald and bald scalp

a. Nonbald scalp

* Telogen
* Early and mid-anagen
* Anagen
* Catagen

Folliculogram and diagrammatic representation of the size and proportional distribution of telogen, mid-anagen, anagen, and catagen follicles: nonbald scalp containing many anagen and some telogen follicles (a), bald scalp containing large numbere of small telogen and some anagen follicles (b)

These results clearly suggest that any com- pounds that stimulate hair growth act on the follicular cells that actively proliferate and produce new anagen follicles, particularly in early to mid-anagen stages of the cycle. The increased number of follicular germinal cells can make new anagen follicles larger than the anagen follicles in the previous cycle. Conversely, those compounds that suppress the mitotic activity of the follicular cells induce a reduction in size of new anagen follicles. Accordingly, androgens act in a bidirectional manner to stimulate mitosis in vellus hair follicles in the body regions showing secondary sexual and facial hair growth and to suppress mitosis in the terminal hair follicles in the scalp of bald-trait men and women and of stump-tailed macaques.

Figure 28
3N-thymidine autoradiography of hair follicles

Autoradiographic pictures of cyclic follicles: 3H-thymidine- labeled (DNA-synlhesizing( cells are absent in a telogen follicle (a). The labeled cells appear in the follicular and base of anchoring telogen follicle (b). Many labeled cells are seen in the outer and inner sheaths of mid- anagen (c) and bulb and perifollicular sheaths of anagen germ follicle (d). Labeled cells (arrows).

Figure 29 Autoradiograph of macaque early anagen follicles

Autoradiographic pictures of early anagen follicles of the frontal scalp of the macaques treated with vehicle (a) and a compound that stimulates terminal hair growth (b) for 3 months. After treatment there mass significant increase in DNA-synthesizing cells (arrows) in the follicular germ and dermal papilla of early anagen follicles compared with that in vehicle-treated animals. Dp = dermal papilla.

Alopecia Areata

This hair-loss disease usually occurs asympto matically, and the progression of hair loss is rather rapid. Initially, patchy loss of scalp hair appears as a round area surrounded by normal scalp hairs, This stage is usually called "alopecia areata" The patchy hair loss sometimes extends over the surrounding scalp as one patch whose diameter enlarges or as several initially isolated scalp lesions tbat coalesce into one large area. Generally, this type of lesion shows spontaneous remission and complete recovery occurs. If the disease persists and hair loss extends over the entire scalp, it is called "alopecia totalis" In some cases the process extends further to the loss of eyebrow, beard, axillary, pubic, and all other terminal hair; it is then called "alopecia uni vecsaIis" Both alopecia totalis and alopecia universalis are refractory diseases and sponta- neous recovery rarely occurs. These three types of hair-loss disease generally show similar pathological changes in the hair follicles and the surrounding dermal tissues.

The cause of alopecia areata has been a matter of dispute, and many theories of its pathogenesis have been discussed in the literature; hereditary, hormonal, psychological, and inflammatory disorders or an atopic condition are often con- sidered. Historically, some theories have predominated in certain periods because of new knowledge and advanced techniques in medical research. The sequence of progress or further addition to complexity in our understanding of the pathogenesis of alopecia aceata is described in the reviews of earlier papers and in a recent paper. After the detailed histological studies of Van Scott, inflammatory changes in the affected skin and dystrophic changes of the hair follicles were considered to be characteristic of the pathology of alopecia areata. Later, studies by Braun-Falco and Zaun and Thies showed the unique inflammatory changes of hair follicles in many cases of alopecia areata. Recently, advanced knowledge in immunology and improved techniques of immunological investigation have supported the inflammatory theories, particularly as a type of cell-mediated immune process suggesting an autoimmune disease. However, direct evidence to explain a specific triggering factor for the immune process remains unknown.

Histological Changes of Hair Follicles

Our recent study of 60 biopsies of scalp skins from 36 patients in various clinical stages of alopecia areata, alopecia totalis, and alopecia universalis showed essentially similar hair follicle and dermal pathology to that found in the lesions described in earlier reports. The hair follicles in the scalp remain in the anagen phase for many years, and so the acute stage of this inflammatory change appears to occur primarily in the anagen follicles. The disease usually persists for many years, and exacerbation and remission of pathological changes may continually occur in the same anagen follicle.

Most frequently observed are severe dystrophic changes of the suprabulbar region of anagen follicles with dense infiltration of lym phocytes around or in the perifollicular con nective tissue sheath of the lower follicular portion (Figure 30). The degree of the follicular changes varies greatly: some follicles retain their outer and inner root sheath and bulbar struc- tures but the hair matrix shows dystrophic change in the level of the keratinizing zone, (Figure 31a). The follicles showing severe degen erative changes undergo disintegration of all lower follicular structures with breakage of the hair shaft (Figure 31b).

Figure 30 Follicles of patient with alopecia areata

Four anagen follicles in the scalp skin of a patient with alopecia universalis, showing degeneration changes (arrows) in the suprabulbar portion and lymphocytic cell infiltration in the perifollicular sheath (arrowheads).

Severe degenerative changes of the lower follicular structure cause disruption of the bulb and follicular sheath and hair shaft (Figure 32). Occasionally, very small follicles showing some abortive anagen activity are surrounded with a dense infiltration of lymphocytic cells (Figure 33). The other type of follicular degeneration found in alopecia aceata is a rather circum scribed cystic change in the suprabulbar region above the dermal papilla (Figure 34). This cystic lesion may be caused by liquefied degeneration of the primary hair medulla cells and subsequent desquamation of the cortical kecatinocytos. This cystic degeneration of the bulb is often asso- ciated with severe dystrophic change of the hair matrix (Figure 35).

All changes described above were in acute (or florid) inflammatory disease stages. However our sequential study for three years revealed that in many cases of alopecia totalis and alopecia universalis, these degenerative inflammatory changes of hair follicles were observed in every biopsy of scalp skin taken once a year for three years.

The peculiar cystic degeneration with apoptotic keratinocytes of the bulb has been described by Thies and Messenger et al. In our study, one patient with alopecia univen salis had persistently shown this cystic follicular lesion for three years. In addition, our morpho motric analyses (folliculograms) revealed that about 90% of the cases had overwhelmingly high populations of anagen follicles. These data suggest that most degenerative anagen follicles remain in the anagen state for a long time rather than entering the catagen phase prematurely or aberrantly. In fact, in our study we only rarely found catagen or telogen follicles. We occasion ally found that the anagen follicles showed an aberrant formation of the outer and inner sheath with fairly well-formed bulb structure and that their lower follicular portions were surrounded with multilayered perifollicular connective tissue sheath (Figures 36a,b). Although no one can predict the fate of such follicular changes, many anagen follicles may remain in an aberrant or restrained state for an extended period. In some patients who showed local recovery of hair growth, skin biopsies from the area of regrowth often showed cessation of inflamma tory changes in the dermis and a peculiar type of regenerative growth of the follicles (Figure 37). The elongated follicular epithelial peg, ac- companied by condensed dermal papilla cells, appeared to grow into the fibrous sheath. These changes were not seen in normal cyclic growth but were usually found in the area of alopecia areata now showing hair growth. The follicles of alopecia areata showed diverse morphological expression and bizarre sequential changes that were not analogous to those of the dynamic cyclic process of normal hair follicles. Normal telogen and catagen follicles were encountered in very few of the 60 biopsies of skin specimens from 30 patients with alopecia areata, alopecia totalis, and alopecia universalis. Our finding contradicts data from earlier studies of alopecia areata (including totalis and univer salis) in which a higher proportion of telogen follicles were encountered.

Figure 31 Dystrophic anagen follicle in alopecia areata

a                                                              

Pystrophic anagen follicle showing degeneration of hair in     
the keratinizing zone and dense infiltration of lymphocytes    
around the lower follicular sheath (a). Pegeneralive anagen     

b

follicle showing disintegrated inner and outer follicular
sheath and bulb with breakage of hair. Dense infiltration of
lymphocytes around and in the follicle (b)

Figure 32 Follicular change in alopecia areata

Severe degeneration of the lower follicle and breakage of hair of an anagen follicle. Lamellar proliferation of fibrocytic cells with lymphocytic infiltration below the follicle.

Figure 33 Follicular change in alopecia areata

A small aberrant anagen follicle (microfollicle) surrounded by dense infiltration of lymphocytes.

Figure 34 Follicular change in alopecia areata

Focal cystic degeneration with despuamation of presumptive hair cortical cell in the suprabulbar region just above the dermal papilla. Abnormal deposition of hyalinoid substance and dense aggregation of blast-type cells in the darns) papilla (arrow).

Figure 35 Follicular change in alopecia areata

Focal cystic degeneration in the suprabulbar region and severe dystrophy of hair matrix (arrow). Scar-like collagenous change of the perifollicular sheath with mild degree of lymphocylic infiltration.

The diverse follicular changes found in alopecia areata patients, which include various degrees of folliculac degeneration, inflammatory cell infiltration, dystrophic hair matrices, and the concomitant presence of uninvolved (or at least apparently normal) cyclic follicles, are all likely due to the different clinical stages, previous treatment, and probably different pathogenetic background of each patient. These differences are also probably the reason immunological profiles of both circulating and tissue antigens show contradictory data in alopecia areata patients.

Figure 36 Follicular change in alopecia areata

Two elongated follicular pegs in the fibrous sheath accompanied bye peculiar appearance of dermal papilla (arrows) (a). One follicular peg (right side) with dermal papilla appears to grow in a long, stretched fibrous sheath (arrows) containing a few melanin-laden cells (arrow heads) (hi. An anagen follicle (left side) shows cystic degeneration in the suprabulbar region.

Figure 37 Dystrophic anagen follicle in alopecia areata

An anagen follicle showing normal bulbar structure wilh aberrant formation of outer and inner root aheath sur rounded by multilamellar scar-like perifollicular sheath (arrows).

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