Hair & Hair Growth Desmond J. Tobin
Hair & Hair Growth
Desmond J. Tobin PhD Dir: Centre for Skin Sciences, University of Bradford 1
Structure of presentation Part I • Biologic value of hair: in context of skin & its appendages • Hair follicle: a multi-cell type ‘mini-organ’ • Hair fibre: the hair follicle’s main secreted product • Hair follicle development & growth: a rare example of life-long activity cycling • Hair follicle as regeneration toolkit: stem cells & plasticity Part II • Hair as a sensor: hair follicle is hard-wired to core neuro-endo-immuno axes • Hair follicle pigmentation: an excellent aging model 2 • Hair growth: some common disorders
Biologic value of hair: in the context of the skin
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Biologic value of skin & hair
Skin: • Biologic barrier and the fluctuating environmental interaction • Recognizes, discriminates & integrates signals (via immune, pigmentary & neuroendocrine systems etc.) Hair follicle (HF): • Protection: trauma, radiation, insects, insulation, and cleansing skin surface • Sensory: environment perception, communication (visual, odorant etc.) • Maintenance: reservoir of many regenerative cells types • Immune: anti-microbial upper HF & sebaceous gland 4
I’ve hair, therefore I am…a mammal
• Simple HFs: humans, horses, cattle, pigs, sheep, rodents etc. Single hair fiber from single canal. Retained fibers (mouse) • Compound: dogs & cats. Several growing hairs in 1 canal Often 1o or guard fibers with smaller 2o undercoat fibers • Synchronous: wave-like e.g. Most rodents when young • Mosaic: asynchronous – humans, mice etc. with age • Telogenic: most mammals – continuous growth set by seasonality & then efficient retention of telogen hair fibers • Anagenic: rare (wounding response?) ~90% of human scalp HF hair to be cut. Some animals (e.g. poodle, angora etc.)
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Humans: so-called ‘naked’ ape
Why are humans a bit different? A case of ‘terminal decline’ – evolution transformed terminal HF to vellus
1) Mate selection? Lower infestations?
Mark Pagel (Uni of Reading) & Walter Bodmer (Oxford Uni)
2) Sweating advantage of having vellus not terminal hair – greater evaporation potential when hunting (Nina Jablonski)
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Some basic hair facts
1) ~5M (2% scalp). vs. black: blonde/brown ↑20%, red ↓20% 2) Types: Lanugo (>1 mm x <0.05 mm); Vellus (1 mm x <40 µm) Terminal (>1 mm x ↑ 0.12 mm) 3) ~500/cm2 on scalp. Africans/Asians < Caucasians Highest density on nose tip/cheek/forehead 4) Mongoloid - circular, Caucasian - oval, African - elliptical 5) Growth ~1cm/month (scalp) – cutting/shaving no effect 6) Scalp hair grows ↑ 10y (1.5 M) ~12wks (arm), 26wks (leg) 7) Normal scalp sheds ≈100 hairs/day 8) Scalp HF cycles about 10-20 times/average life
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The hair follicle: a multi-cell type ‘mini-organ’
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Hair follicle at organism level • A ‘mini-organ’ with multiple cell types and with own blood, nerves, immune & muscle systems • Source & target of numerous hormones • Cycles in cell division, differentiation & death Only adult tissue to do so!
HS HF Key: HS = hair shaft HF = hair follicle BV = blood vessel
BV 9
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Skin surface: barrier but also ‘open’ system ↑5 million Sweat Gland pores • Sterile electrolytes, metals etc. • Anti-microbials, proteases, growth factors, cytokines, Igs...) • Regulation - emotion/environment • 100 ml to 10 L /day of sweat
~5 million Hair follicles • Vellus, Sebaceous, Terminal HFs • ↑500/cm2 and Highly innervated • Neuroendocrine Axes • Terminal ~3 mm deep vs. Vellus 1 mm 10
Different hair follicle types in the adult human
Vellus HF Sebaceous HF
Terminal HF
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The hair fiber /shaft: HF’s main secreted product – variation in type & density across body
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Human hair shaft / fiber
HS IRS IRS Cu HCu Co
ORS d ICu Fiber surface by SEM HCu HS HCu Me ICu
Ref: Hair in toxicology: Key: HS = hair shaft; IRS = inner root sheath an important biomonitor; DJ Tobin, Royal Society of Chemistry 2005 ORS = Outer root sheath; HCu = HS cuticle 13ICu = IRS cuticle; Me = Medulla
Hair needs mechanical stability: breakdown of nuclear DNA appears crucial
Key: WT= wildtype KO = knockout Me = melanin
Ref: Fischer H, Tobin DJ et al. Essential role of the keratinocyte-specific endonuclease 14DNase1L2 in the removal of nuclear DNA from hair and nails; J Invest Dermatol 2011
One hair follicle – but many hair types
Same hair follicle produces hairs differing in: calibre, length, colour
Terminal
In utero – Lanugo 15 Vellus
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Variation in hair follicle density
300
250
200
150
100 Average HFs/cmAverage 50
0 Forehead Back Thorax Upper Forearm Thigh Calf arm
16Ref: Otberg N et al. Variations of hair follicle size & distribution in different body sites, J Invest Dermatol. 2004
Hair follicle development & growth: a rare example of life-long cyclic activity
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Hair follicle morphogenesis (1) Stage 1 Stage 2 Stage 3/4 Stage 4 Stage 5
KC DC SG FDP IRS BG FDP FDP IRS
KC MEL
FDP DC KC
DC
IRS
IRS
Refs: Hair in toxicology: an important biomonitor; MEL DJ Tobin, Roy, Soc Chem 2005; Paus R et al. FDP A comprehensive guide for the recognition & classification of distinct stages of hair follicle FDP morpho-genesis, J Invest Dermatol. 1999 FDP Key: KC = keratinocyte; DC = dermal condensation FDP = follicular dermal papilla; IRS = Inner root sheath 18SG = sebaceous gland; Mel = melanocyte; BG = bulge
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Hair follicle morphogenesis (2) Stage 6 Stage 8
HS
SG HS IRS BG SG
BG MEL IRS
HS
MEL IRS FDP FDP FDP
MEL
Ref: DJ Tobin Hair in toxicology: an important biomonitor Roy Soc Chem 2005 FDP Stage 8
Key: KC = keratinocyte; FDP = follicular dermal papilla IRS = Inner root sheath; HS = hair shaft; SG = sebaceous gland 19Mel = melanocyte; BG = bulge
The hair follicle growth cycle
Telogen/ Early Anagen early Anagen DP signals to Epithelium DP signals (e.g. KGF, HGF) to Stem Cells Epithelium signal (e.g. β-catenin) to DP (e.g. WNT) Anagen onset Epithelium Proliferation (e.g. STAT) (e.g. SHH, IGF-1, HGF)
Full Anagen Catagen Inducers (e.g. IGF-1, HGF, (e.g. FGF5, TGFβ1, 2, GDNF, NGF?) p75NTR, NT3, VDR, Hair Shaft IFNγ, IL-1, Prolactin Differentiation (+R), Hairless) (e.g. WNT, LEF1, BMP, Notch, FOXN1)
Refs: Alonso L, Fuchs E., The hair cycle, J Cell Sci. 2006; Enshell-Seijffers D et al. beta-catenin activity in the dermal Tobin DJ. The genetically-programmed hair growth papilla regulates morpho-genesis and regeneration of hair 20cycle & alopecia, Expert Rev Dermatol 2006 Dev Cell 2010
Hair cycle: test-tube of cell division, differentiation Early Catagen & death
Full DP Ref: Magerl M, Tobin DJ et al. Patterns of proliferation and apoptosis Anagen during murine hair follicle morphogenesis, J Invest Dermatol 2001
Mid next anagen
Telogen HS Late Catagen CH CH
Earliest next anagen BG
CH HS ES SG
DP TA DP DP DP 21 Mx
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Modulation of hair follicle vasculature & hair cycle
CD31 (PECAM-1) yellow Catagen Skin CD31 (Red) + TUNEL (Green) Anagen Skin Te lo ge n S ki n Anagen Skin Ki67 Red
Ref: Mecklenburg L, Tobin DJ et al. Active hair growth 22CD31Green is associated with angiogenesis, J Invest Dermatol 2000
Fibroblast dynamics during hair growth cycle CTS & DP 3 Mitosis 2 4
Anagen III/IV
Anagen II CTS & DP 1 Mitosis 6 Anagen VI CTS 5 Mitosis 7 Anagen I
CTS Apoptosis CTS Catagen III Telogen Apoptosis
Catagen VI Refs: Tobin DJ et al. Plasticity and Cytokinetic Dynamics of the hair follicle mesenchyme, J Invest Dermatol 2000. Chi W, Wu E, Morgan BA, Dermal papilla cell number specifies hair size, shape and cycling and its reduction causes follicular decline, 23Development 2013
Hair growth cycle directs hair pigmentation Variable states of melanocyte quiescence, melanogenic activity, senescence, & apoptosis
BULGE SG
APM IRS ORS AL MITOSIS Telogen
Early FP Late Anagen Catagen Mid Early Catagen Full Catagen Anagen
Refs: Tobin DJ et al. Do hair bulb melanocytes undergo apoptosis during hair follicle regression, J Invest Dermatol 1998; Slominski et al. Hair follicle pigmentation, J Invest Dermatol 2005; Commo S & Bernard BA., Melanocyte subpopulation turnover during 24FP the human hair cycle: an immunohistochemical study, Pigment Cell Res. 2000
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Hair cycle induction/regression mediators
Anagen • Trauma: e.g. plucking, depilation; releases inflammatory mediators? • Growth factors: many & varied • Drugs: minoxidil, cyclosporin, tretinoin etc. Catagen • Stress: e.g. psycho-social • Hormones: e.g. estrogen & glucocorticosteroids • Growth factors: many & varied
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The hair follicle - a regeneration toolkit: stem cells & plasticity
Intense evolutionary selective pressure to maintain coat; so unsurprising that HF jam-packed with regenerative capacity
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Stem cells & hair cycle
• HF stem cells are activated at the telogen-to-anagen transition, to initiate new round of hair growth • From reservoir of multi-potent epithelial stem cells in lowest permanent portion of HF, i.e. ‘bulge’ • Lower portion of HF regenerates to produce new hair • stem cells important for maintenance of sebaceous gland • Stem cells respond to epidermal wounding by generating short- lived 'transit amplifying' cells for acute wound repair
Refs: Ito M et al. Wnt-dependent de novo hair follicle regeneration in adult mouse skin after wounding, Nature 2007 Myung P, Ito M. Dissecting the bulge in hair regeneration, J Clin Invest 2012 Purba TS et al. Human epithelial hair follicle stem cells and their progeny: Current state of knowledge, the widening gap 27in translational research and future challenges, Bioessays 2014
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HF stem cells & wounding (mouse studies)
• HFs are not made postnatally (except in wound-healing?) • Bulge stem cells contribute to wound repair but not to epidermis homeostasis • Tissue regeneration & immune system (Fgf9 from γδ T cells) • De novo HF formation post-wounding is Wnt-dependent • Lgr6 stem cells generate all skin cell lineages and can permanently contribute to wound healing & hair neogenesis
Refs: Ito M et al. Stem cells in the hair follicle bulge contribute to wound repair but not to homeostasis of the epidermis, Nat Med. 2005; Langton AK et al. An extended epidermal response heals cutaneous wounds in the absence of a hair follicle stem cell contribution, J Invest Dermatol. 2008; Snippert HJ., Lgr6 marks stem cells in the hair follicle that generate all cell lineages 28of the skin, Science 2010; Gay D et al. Fgf9 from dermal γδ T cells induces hair follicle neogenesis after wounding, Nat Med. 2013
HF stem cell ’zoo’ Stem cells in resting Adult HF (from mouse data) Infundibulum m m m mm Gene/protein-expression m m Sebaceous gland m mm m m CD34 (bulge) m m LRC (bulge) Lgr6 (lower isthmus) Lgr5 (hair germ) Lrig1/MTS24 (isthmus) Blimp1 (sebaceous gland duct) Bulge/K15+ K15* (restricted to bulge)
LRC: Label retaining cell Hair germ IFE: Inter-follicular epidermis Papilla
29 Telogen pilo-sebaceous unit Ref: Jaks V et al. The hair follicle- a stem cell zoo, Exp Cell Res. 2010
Part II
Hair follicle as sensor: hair follicle is hard-wired to core neuro-endo-immuno axes
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Skin & hair follicle – a sensor organ (1)
31Ref: Slominski A…Tobin DJ et al. Key role of CRF in skin stress response system, Endocr Rev. 2013
Skin & hair follicle – a sensor organ (2)
CRF Cell pellets
CRF1 Ctrl 10-7 10-10 Control CRF [10-8 M] CRF [M] POMC
PC1 Tyrosinase Dopa-oxidase Activity DCT TRP-1 α-MSH ACTH PC2 -+ -+ -+ -+ MR-1R MR-2R 75 kD 62 kD 65 kD
67 kD Cortisol
Refs: Ito N et al. Human hair follicles display a functional equivalent of the hypothalamic-pituitary-adrenal axis and synthesize cortisol; FASEB J. 2005 Kauser S… Tobin DJ. Modulation of the human hair pigmentary unit 32 by corticotropin-releasing hormone and urocortin peptides; FASEB J 2006
Skin & hair follicle – a sensor organ (3)
α-MSH
Refs: Böhm M…Tobin DJ et al. Melanocortin receptor ligands: New horizons for skin biology and clinical dermatology 33J Invest Dermatol 2006; Tobin DJ & Kauser S., Hair melanocytes as neuro-endocrine sensors, Mol Cell Endocrinol 2005
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POMC peptides & hair pigmentation MC1-R variants predict red hair, α-MSH & ACTH regulate hair colour
α-MSH ACTH [10-8M] ctrl α-MSH ACTH
FP FP Cell pellets
HFM POMC
β-Endorphin μ-opiate R [10-8 M]
FP FP ctrl β-End
Red = β-End; Red = μ-Opiate R
Refs: Kauser K…Tobin DJ. A functional POMC/MC1R receptor system regulates the differentiation of human scalp hair follicle melanocytes, Endocrinol. 2005, Valverde et al. Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans, Nat Genet.1995 34Kauser S…Tobin DJ., β-endorphin as a regulator of hair follicle melanocyte biology, J Invest Dermatol 2004
Growing HF - an immune privileged site
• HF epithelium: very low MHC I & no MHC II • Langerhans cells: very few & lack MHC II • HF immunosuppression: (TGF-β1, α-MSH, IL-10) • HFs lack lymphatics • IP: Hides auto-/allo antigens from immune recognition Ref: Christoph T…Tobin DJ et al. The human hair follicle immune system: cellular composition & immune privilege, Br J Dermatol 2000; Westgate GE et al. Immune privilege in hair growth, J Invest Dermatol. 1991
Trans-gender induction of HFs: Transplantation of HF dermal sheath tissue between incompatible individuals of different sex can induce formation of new HFs 35Ref: Reynolds et al. Trans-gender induction of hair follicles, Nature 1999
Hair follicle pigmentation: an excellent aging model
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What is hair melanin for?
• Hair pigmentation not increased by UV-R (sunlight) • Evolution? long pigmented scalp hair rids toxins/metals from fish-diet; Excreted via very high cell turnover • Melanin - a sink for chemicals, toxins, heavy metals to prevent access to living tissue of vascularized scalp • Pigmented hair: Antioxidant/anti-microbial defense • Melanin - buffer for Ca++ a 2nd messenger for cell function • Pigmented hair - thermal insulation, camouflage, social & sexual communication • Our relative nakedness draws attention to face/scalp hair, - emphasized by color 37
Hair follicle pigmentary unit
MC
DP
Mc
Hair cone
ORS ? Mouse defined sub-pops. Mc DP
Human Hair Germ Stage HFM sub-types in human HF HFM re-populating 38 early anagen HF
HF & epidermis pigmentary units are distinct
Epidermis Kc Kc SC
Kc
SG Mc Dermis
HF ORS CTS Cu Mc IRS Me Co Co
FP Mx
39Refs: Tobin DJ., The cell biology of human hair follicle pigmentation, Pigment Cell Mel Res 2011
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Hair follicle pigmentary unit
SG
HS
HS
DP DP
Refs: Tobin DJ. The cell biology of human hair pigmentation, Pigment Cell Mel Res 2011; Tobin DJ & Bystryn J-C. Different 40populations of melanocytes are present in hair follicles and epidermis, Pigment Cell Res 1996
Hair follicle pigmentary unit – canities
Full Anagen
G Te lo ge n * *G Early Anagen
Early Catagen Mid Catagen Late Catagen
• Mc stem cells apoptose at entry to telogen • Genotoxic stress depletes MSC by differentiation
Refs: Tobin DJ., Human hair pigmentation--biological aspects, Int J Cosmet Sci. 2008; Nishimura EK, Granter SR, Fisher DE. Mechanisms of hair graying: incomplete melanocyte stem cell maintenance in the niche, Science 2005; Inomata K et al. Genotoxic 41stress abrogates renewal of melanocyte stem cells by triggering their differentiation, Cell 2009
Where do we go gray: HF bulb or bulge? Melanogenic bulb melanocytes can die intra-anagen VI to lead to pigment loss from growing hair fiber
DP DP DP DP
Should we focus on protecting the HF Pign Unit within anagen?
42Refs: Tobin DJ & Paus R. Gerontobiology of the hair follicle pigmentary unit, Exptl Gerontol 2001
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Hair graying is somewhat HF autonomous
• Is MC stem of similar ‘biologic’ age in adjacent HFs? • Can adjacent HFs have different initial MSc seeding densities? FP • Can adjacent HFs have different Me Me niches quality?
• Do adjacent HFM have similar MSc niches? Mc Mc Kc • What directs their cell fate? 43
Does canities alter keratinocyte behavior?
• Graying/white HFs grow faster than pigmented HFs • Altered KC differentiation: melanin transfer important? • Gray hair more easily damaged by UVR: stress-to-break, wet combing force, cuticle abrasion, swelling of fiber etc.
PC
Mu MU
PC Refs: Van Neste D & Tobin DJ. Hair cycle & hair pigmentation: dynamic interactions and changes with aging, Micron 2004; Arck PC et al. Mu Towards a "free radical theory of graying": melanocyte apoptosis in aging human hair follicle is indicator of oxidative stress induced tissue damage, FASEB J. 2006 FP FP 44
Melanocytes: redox-sensitive cells (1)
Young - low oxidative stress Old - high oxidative stress Efficient melanogenesis, Less efficient melanogenesis, DNA/protein repair, anti-oxidants DNA/protein repair, anti-oxidants, (Bcl2, SOD, Catalase) (Bcl2, SOD, Catalase etc.)
23y F66y (gray) 65y ORS
FP FP FP M M M Red = Catalase Green = gp100
Ref: Kauser S…Tobin DJ., Human hair follicle and epidermal melanocytes exhibit striking differences in their aging profile 45which involves catalase, J Invest Dermatol. 2011
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Melanocytes: redox-sensitive cells (2)
Exogenous H2O2 ↑catalase in young not aged donor HFM
Buthionine sulfoximine (BSO; glutathione depletor) at 10-5 M, 48h 67 Catalase 60 45 * * * *
H2O2 ↑ Catalase activity in HFM from Young donors NOT Aged donors 100 *** ** 75 75 moles/min/ml μ 50 n/s 50 ** % Survival 25 mean age: 28 yrs 25 mean age: 61 yrs 0 + 50 µM ***P<0.001 0
Catalase Activity Ctrl/ Ctrl/+ 50 µM + 50 µM (n = 5) @ 48h Ctrl/ Ctrl/+ 50 µM 46 Young Aged Young Aged
Common disorders of hair growth (e.g. Androgenetic alopecia & Alopecia areata)
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Alopecia areata
Patchy AA AA-totalis AA-universalis
(Clinical slides courtesy of Dr DA Fenton)
• Associations: Down Syndrome; Type I diabetes; Thyroid autoAbs • Systemic or Organ-specific? Anagen HF, nail (↑40%) eye (lens opacities ↑50%) epidermis & hair in nevi spared!
Ref: Tobin DJ, Fenton DA, Kendall MD., Ultrastructural study of exclamation-mark hair shafts in alopecia areata 48J Cutan Pathol. 1990
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Cell target in alopecia areata?
Slides courtesy of Dr DA Fenton
Before During Re-growth
• Preferential targeting Mc * Mx * FP** of pigmented hair * * Mc • Hair regrowth white Mx
• HF most ‘vulnerable’ Mc CTS at melanogenesis onset FP Mc • Some hair bulb Mc die
49Refs: Tobin DJ et al. Ultrastructural observations on the human bulb melanocytes in acute alopecia areata J Invest Dermatol 1990
Etiology & pathogenesis of alopecia areata
Immune-drive CD4 • HF with mononuclear infiltrates. Causality unclear • Adoptive transfer of AA to mice with activated T cells • Passive transfer by T cells by antibodies not shown • Immune response before hair loss CD8 • HLA haplotype and Genome-wide associations • Target antigen identified: some candidates…. • Autoimmunity after HF damage of other cause? Collapse of HF Immune Privilege
FP Refs: McElwee KJ, Tobin DJ et al. Alopecia areata: an autoimmune disease? Exp Dermatol. 1999; Gilhar A, Kalish RS. Alopecia areata: a tissue specific autoimmune disease of the hair follicle, Autoimmun Rev. 2006; McElwee KJ, Gilhar A, Tobin DJ et al. What causes alopecia areata? Exp Dermatol. 2013 50
Etiology & pathogenesis of alopecia areata Genetic-drive (1) Consensus: genetic - but appears to be poorly penetrant Family history: • ≈45% of early onset AA with ≥1 affected 10 family member • ≈55% monozygotic twins with same onset & type But variable extent, course & treatment responses HLA: In most autoimmunity; HLA present peptides to T cells associations may lead to >efficient autoantigen presentation • HLA class I – data inconsistent • HLA class II – regulate susceptibility & severity Good associations with some DR & DQ alleles esp. extensive AT or AU
Role in AA pathogenesis unclear – 51Case of just linkage disequilibrium with nearby disease genes?
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Etiology & pathogenesis of alopecia areata Genetic-drive (2)
Genome-wide association study: innate & adaptive immunity
• Associations: regions with genes controlling activation & proliferation of Treg cells, Tcyt-associated antigen 4, IL-2/IL-21, IL-2RA and Eos and the HLA region • Association with genes expressed in HF: PRDX5 & STX17; Peroxiredoxin & Syntaxin) and in ULBP cluster encoding activating ligands of natural killer cell receptor (NKG2D) • ULBP3: Expression unregulated in lesional AA HF (dermal sheath) during active disease • Innate & acquired immunity involved in pathogenesis
Ref: Petukhova L et al. Genome-wide association study in alopecia areata implicates both innate and adaptive immunity, 52Nature 2010
Etiology & pathogenesis of alopecia areata Antigen targets: HF-specific keratins
Trichohyalin region 205 → Epi 98 →
67 →
45 → Keratin Region HF Ctrl Sera AA Sera AA serum IgG react with multiple HF antigens
ORS
AA antibodies immuno- 46→ precipitate HF-specific 44→ keratins (44/46 kDa) AA Control
Ref: Tobin DJ et al. Antibodies to hair follicles in alopecia areata, J Invest Dermatol 1994 53Tobin DJ et al. Hair follicle structures targeted by antibodies in patients with alopecia areata, Arch Dermatol. 1997
Etiology & pathogenesis of alopecia areata Antigen targets - Trichohyalin
PCx He IRS Hux C
MX DP
THH
160
120
80 AA serum + 40 0 AA serum THH MoAb score MASCOT Average AA Normal Ref: Leung MC….Tobin DJ., Trichohyalin is a potential major autoantigen in 54human alopecia areata, J Proteome Res. 2010
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Alopecia areata - treatment
• No FDA-approved treatment • Steroids: topical, intra-lesional, systemic (e.g. triamcinolone acetonide, kenalog) • Topical immunotherapy: diphenylcyclopropenone/ diphencyprone, SADBE etc. • Topical minoxidil (5%) • Anthralin; Psoralen/UVA; Combination therapies • Recent trials: Biologics: anti-TNFα: adalimumab, etanercept, infliximab. CD2 (alefacept) or CD11a (efalizumab). Results poor so far 55
Hair follicles are androgen target tissues
• Androgen-driven ‘vellus-to-terminal’ HF transformation on beard and opposite ‘terminal-to-vellus’ on scalp. Paradox • Male pattern alopecia (androgenetic) FDA-treatments: topical minoxidil (5%) & finasteride (1mg/d) • Female pattern alopecia (may not be androgenetic) FDA-treatment: topical minoxidil (2%)
Refs: Tobin DJ., The genetically-programmed hair growth cycle & alopecia; Expert Rev Dermatol 2006 Miranda BH, Tobin DJ et al. Intermediate hair follicles: a new more clinically relevant model 56for hair growth investigations, Br J Dermatol. 2010
Cultivation of hair follicles & cells
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Hair follicle culture models
Hair fiber growth @ 8d in vitro
ORS KC used to regenerate epidermis, ‘skin equivalent’ models & engineered DS skin grafts since1980s
Refs: Tobin DJ. Ex vivo organ culture of human hair follicles: a model epithelial- ORS neuroectodermal-mesenchymal interaction system, Methods Mol Biol. 2011; Philpott MP, Green MR, Kealey T., Human hair growth in vitro., J Cell Sci. 1990; Westgate GE et al. Prolonged maintenance of human hair follicles in vitro in a serum-free medium, 58Br J Dermatol. 1993
Take home messages
• Mammal-specific trait: only example of self-renewing mini-organ • Hair growth cycle: selective pressure intense, with much redundancy. Master modulators e.g. WNT signalling • Stem cells: requirement for self-renewing tissue (epithelial, pigment & others). HF is source of promiscuous stem cells • Hair pigmentation: powerful ‘signal’, anti-microbial defence, camouflage etc. and powerful aging model • HF mesenchyme: drivers of hair cycle, significant plasticity • HF vascular supply: very rare example of physiological angiogenesis • Hormone responsive: target & source of numerous hormones • Hair disorders: examples – alopecia areata and androgenetic alopecia - very difficult to treat successfully 59• Hair follicle models: significant development of in vitro models
Acknowledgements
• I would like to thank the many colleagues with whom I have had the pleasure to collaborate over the years and whose work is included in this overview of hair & hair growth • Given the brief nature of this review, only a small representative selection of research data can be included
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