Desmond J. Tobin

Centre for Skin Sciences,

University of Bradford, Great Britain

The unique microenvironment of the aging human adult scalp

Anti-ageing Skin care Conference,

Royal College of Physicians

London 7-8 June 2016 1/31

Humans: so-called ‘Naked’ Ape

Why are we so different? ‘Terminal Decline’ - evolution appears to have transformed terminal to vellus HF for more & better sweat glands.

Sweating advantage of having vellus >> terminal hair - greater evaporation potential (Nina Jablonski)

Human dense scalp terminal hair – an anomaly in mammal hair growth?

Human communication focused on head & face – body sites with potential for dramatic and luxuriant hair growth variations.

2/31

Life Stories of the Human Hair Follicle

Phase change in: calibre, length, colour

Lanugo Vellus Terminal

‘Vellus

-like’

‘Turbo-terminal’ 3/31

4/14

Corneocyte layers: Genital skin (6 ± 2),

face (9 ± 2), neck (10 ± 2), scalp (12 ± 2),

trunk (13 ± 4), & extremities (15 ± 4),

Soles/ palms (> 50)

4/31

Is human scalp different across ethnicities?

HF density variable between ethnicities:

Highest in Caucasian blonds,

Lowest in Mongoloid Asians (& Red-haired Caucasians).

5/31

How is human scalp different from other skin?

Scalp barrier function: Scrotum (x43); Forehead (6x); Scalp

/Axilla (3.55x). (hydrocortisone volar arm = 1). HF important.

Scalp prone to dryness, redness, dandruff, itchiness, inflam etc.

Vasculature: Carries more blood - head wounds bleed profusely

Adnexa: Sebaceous & sweat-glands. Sebum protect hair & scalp.

Sweat - cools, acidifies, etc.

Oil: Can clog HFs; dandruff linked

to bacteria that metabolizes oil to

produce fatty acids that cause itching

/swelling. cell turnover to produce

flakes trapped in hair.

“Bacteria had a stronger relationship with the severity of dandruff than fungi.

…adjusting balance of the bacteria on the scalp, by enhancing Propionibacterium

and suppressing Staphylococcus, might be a potential solution to lessen dandruff”.

(Xu et al, 2016)

6/31

Children: Epidermis thin with low Ki67-positive cells.

Low proportional % thickness of involucrin-positive layer.

19-21ys: Highest cell turnover & maximal epidermis

thickness.

>21yrs: keratinocyte proliferative activity.

Involucrin-positive layer: Absolute thickness constant at

different ages, but proportion in total epidermal thickness .

(Nozdrin et al, 2011)

Scalp Intrerfollicular Epidermis change with Age

7/31

Chronologic age - a HF sculptor

(adapted from A Schwan-Jonczyk, 2009)

Young adult Child

Late teens/early adulthood. hair caliber, cross-sectional irregularity, variation (caliber/ellipticities) - results in ‘fuller’ hair.

60s 70-80s

Old-Age: diameter & medulla, symmetrical fibers - smoother hair.

40-50 year old

Mid-Age: hair medulla & asymmetrical fibers - stiffer, less elastic, duller.

M

8/31

Impact of Extending Life expectancy & Life Span

~2-3yr 60 yr >100yr

Maximum lifespan

in mammals Jeanne

Calment

122y

Male AGA: 50% by 50y; ~70% later

Female AGA: 6% <50y; ~40% >70y

9/31

Non-scaring hair loss: 3 types (Whiting). Pattern, Diffuse & ‘Senescent’

Prototypical Human HF ‘aging’ - Genetic hair loss

Miniaturization & asymmetric loss of thicker hairs? (Mirmirani et al, 2010)

Terminal Hair

Vellus-like Hair

kenogen density. Marked in PHL. Is empty HF & miniaturisation evidence of (similar) chronologic aging process? (Mohungoo & Messenger, 2010)

10/31

Does Senescent Alopecia Really Exist?

Diagnosis: Complicated by overlapping AGA or diffuse alopecia (Whiting)

Definition: Onset >60y. HF miniaturization with distinctive altered gene expression (Mirmirani et al, 2007)

SA: FGF5; DST, ACTN2, TNNI3, PARVB; JAK2, PRKD3, AK2, TRAP1, TRIO, ATP12A,

MLL4, STK22B. Oxidative stress and inflammatory response genes

AGA: Wnt, βcatenin, TGFα, TGFβ, Stat-3,

Stat-1; PPARd, IGF-1, Notch, Msx2, KRTs,

KAPs; Msx2, Activin, IGF-1. BDNF, BMP2,

BMP7, VDR, IL-1, ER; RAR

11/31

Primary histologic finding of HF downsizing; drop-out not

detected using elastic tissue stains Price et al 2001

Others: SA cumulative degeneration of selected HF?

Immune-controlled programmed organ deletion? (as seen in healthy murine skin, Eichmüller et al 1998).

Do HFs ‘drop-out’ in Senescent alopecia?

AR & Aromatase: >60yr levels were low. Comparable in

frontal & occipital scalp with or without thinning.

5a-reductase type 1/2 not significantly in men with thinning

hair vs men without. SA may not be fully androgen-dependent

12/31

IRF4 (Interferon-regulatory factor 4)

– 1st gene for gray hair

Baldness: Confirmed AR locus assoc.

but also SNPs in GRID1- role in hair biology?

Hair Aging Genes?

(Adhikari et al, 2016)

13/31

Acidification Theory of Aging

(Auto)-Immune Theory

Caloric Restriction Theory (worms only?)

Cross-Linking Theory (AGEs)

Death Hormone Theory (DECO)

DNA Damage Theories – accumulated DNA damage; replication errors,

ROS, eroded telomeres, chromosome breaks cellular senescence or

apoptosis (endo/exogenous sources)

Free Radical Theory

Hayflick Limit Theory

Mitochondrial Decline Theory

Neuro-endocrine Theory

Redundant DNA Theory

Thymic-Stimulating Theory

"Wear and Tear" Theory

Aging: Theories

14/31

18 mo (~62 yr) 24 mo (~70yr) 30 mo (~85 yr)

8 mo

12 mo

24 mo (H)

DDR - Transepidermal Elimination of HFSC

via COL17A1 Proteolysis leads to HF ‘aging’

24 mo (HL)

HF count after 12 mths (~58yr). HF miniaturization with dermis

Matsumura et al, 2016 15/31

Down-regulation of HFSC Signature

Precedes HF Miniaturization/Hair Loss During Aging

Matsumura et al, 2016

16/31

HF Aging by Trans-epidermal Elimination of Stem Cells

via COL17A1 Proteolysis

Matsumura et al, 2016

DDR-induced COL17A1deficiency drives HF

miniaturization - only very few HFs lost with aging? 32 mth (89y)

17/31

33yo F 68yo F Normal Mini

COL17A1/ K15/ DAPI

Human HF miniaturization

with loss of COL17A1 mimics Mouse HF Aging

Matsumura

et al, 2016

22y Epidermis 70y Epidermis

γH2AX/ K15/ DAPI

Bulge Bulge

γH2AX: DNA

ds breaks

18/31

■ KRT15hi HFSC preserved, but CD200hi

/ITGA6hi & CD34hi progenitors in bald scalp

Is it all about the stem cells? If so – which ones?

Garza et al, 2011; Ruzankina et al, 2007

■ Alopecia & canities in ATR ko mice:

tissue-specific stem/progenitor cells,

regenerative capacity

■ Restoration of HFSC pools before

irreversible tissue changes tissue

regeneration & anti-aging in skin/HF?

■ Deletion of DDR genes premature

age-related phenotypes?

19/31

Age vs Menopause: growth rate, density, % anagen, diameters greater in frontal vs occipital scalp (Mirmirani et al 2010)

Scalp hair density with age, but not markedly affected by menopause status

Frontal hair calibre in post-menopause - age independent.

Is HF Aging Different in Women?

hair calibre vs age (frontal)

hair growth rate vs age (frontal)

age

age

hair count vs age

age

20/24 20/31

Does Hair growth Duration (Anagen) or Hair Cycle

Frequency affect HF Aging?

Xie Qiuping, China

2004 growing hair

since 1973, 5.6 m.

■ Is prolonged TA division possible without HFSC?

Continuous melanin synthesis without McSC?

■ Why is canities onset age so variable (incl. on

same scalp) – really down to embryologic legacy?

■ Anagen duration/fiber caliber. Kenogen.

Maximal hair length with age. Hairs/ unit area.

■ Irregular course (stability/partial remission/marked

evolution) Courtois et al, 1995

■ Eyebrow HF: 6mth hair cycle.

x6-10 cycles than scalp HFs

but still appear ‘younger’?

21/31

Hair growth cycle - driver of hair pigmentation aging

(Tobin, 2008)

Telogen

Early Anagen

Full Anagen

Early Catagen Mid Catagen Late Catagen

*G

*G

22/31

Are Gray HF Intrinsically/Extrinsically Distinct?

■ White HFs grow faster than pigmented HFs

~10% faster (Van Neste & Tobin: Micron, 2004)

■ Gray HF: altered Kc differentiation – melanin role?

Melanin Ca2+ load & may hasten Kc differentiation

Gray hair initially coarser, diameter & medulla

Mu

MU

PC

FP

PC

FP

23/31

‘Free radical theory’ (Arck, Peters et al, 2006)

Apoptosing bulbar MC; 8-OHdG byproducts; loss of Bcl-2/Kit.

HFMc sensitive to MtDNA deletion ( in graying HFs)

Catalase (Kauser et al, 2008, 2010)

catalase activity in gray HF; Anti-oxidants catalase activity

H2O2-mediated oxidative stress (Wood et al, 2009)

mM H2O2 in gray/white hair fibers & tyrosinase inhibition

Low catalase with decreased Met-S=O repair in gray HF

HF Aging & Oxidative Stress

Old

- high oxidative stress

Less efficient melanogenesis,

DNA/protein repair, anti-oxidants,

(Bcl2, SOD, Catalase etc.)

Young

- low oxidative stress

Efficient melanogenesis, DNA/

protein repair, anti-oxidants

(Bcl2, SOD, Catalase) White Hair Shaft

Tyrosinase Protein

24/31

Catalase Expression in Aging Human HFs

Kauser et al,

2011

Endogenous H2O2 Catalase in Young not Aged Donor HFM

67

45

42 kDa Actin re-probe

Catalase

Buthionine sulfoximine (BSO; glutathione depletor) @10-5 M, 48h

* * * *

FP M

65y

F

P

M

23y

FP

M

55y

25/31

Antioxidants: Catalase Activity & Cell Survival of ROS-stressed Aged-donor HFMc

Ctrl BSO BSO

+

Vit E

BSO

+

Quer

BSO

+ Vit E

+ Quer

0

20

40

60

80

100

60.4

73.6 74.4

88.2

** ** **

**

% S

urv

ival

Survival

0

10

20

30

40

50

60

Ca

tala

se

Ac

tiv

ity

m

ole

s/m

in/m

l

Ctrl BSO BSO

+

Vit E

BSO

+

Quer

BSO

+ Vit E

+ Quer

n/s ** **

**

32.9 33.9

39.7 40.1

50.4 Catalase Activity

(n= 5) ** P<0.01

Vit E @10-5 M; Quer @10-6 M; BSO@10-5 M (48h)

26/31

Extrinsic Aging Influence - Smoking

C57BL/6 mice: Developed hair loss when exposed to cigarette smoke (D’Aggostini et al, 2007)

Apoptosis in hair bulbs at hair loss edge - prevented by oral N-acetylcysteine.

Mechanism: Constricted cutaneous micro-vasculature. Impaired circulation & wound healing in hair restoration surgery in smokers (Tur et al, 1992, Yin et al, 2000)

Smoking: Linked with premature AGA & Canities Twin studies (Treub 2003; Yeo et al, 2014; Su et al, 2007 etc.)

27/31

Clues from the Literature • (x-)irradiation therapy for cancer

• After etretinate therapy • Steroid treatment & erythrodermic eczema • Post-inflammatory; PUVA etc.

+IBMX

(Tobin, 2006)

Yrs before diagnosis At diagnosis

• Porphyria cutanea tarda

HFMc isolated from white HFs

Skin and HF Aging Reversal - possible ?

28/31

Reversal of Skin & HF Reversal - possible ?

■ Reversal of skin aging: apoptosis & Fas.

Ki-67

TUNEL

Pre-graft) Post-graft

Gilhar et al, 2004

HF aging reversal in young host?

Cao et al, 2016;

Also Chen et al, 2014

29/31

Who has the oldest hair follicles?

Nature

515,

346–347

(20 November 2014)

Nature

515,

346–347

(20 November 2014)

HF aging… it’s all a bit

metaphysical

102 yrs

17yrs

30/31

Thanks for your attention

31/31 www.skin.brad.ac.uk