Copper and gray hair

Melanocyte, the organelles that produce the skin and hair pigment melanin, require ATP generating mitochondria for their maturation. Mitofusin (Mfn) 2, the protein that allows mitochondria to fuse to the endoplasmic reticulum, is also found in the melanosome-mitochondrion contacts according to this 2014 electron microscope study. [1] The featured image of this post illustrates this fusion. These mitochondria contacts were found to be associated to the melanogenesis process. This study also demonstrated that pharmacological inhibition of mitochondrial ATP synthesis reduced not only the contact formation and impairs melanosome biogenesis. [1] The same year Wu and Hammer published a nice lay summary of this discovery. [2] The featured image is a truncated version of their Figure 1. [2]

Just as Wu and Hammer [2] published a short introduction to the Daniele 2014 TEM study [1] Philpott [3] gave a few interesting introductory insights into a new technique of watching hair turn gray [5].

Hair follicles are the “mini-organs” that produce hair shafts. The three stages are as follows:

1. Anagen, a period of active growth. This stage requires a lot of ATP and functioning mitochondria. It is during this phase that melanin production is turned on and off in a more plastic fashion than previously thought, [4,5]
2. Catagen, a period of regression
3. Telogen, a period of rest,

This image is a combination of a stock photo and the anatomy of a hair follicle from the Cruz review that we will com back to. [4] According to Philpott’s review of the literature, this cycle can last for as little as three months in eyebrow hair or as long as several years for scalp hair. [3]

Recent advances in hair follicle imaging and correlation of proteins therein have left us with the imagery that hair follicles are like tree rings with snap shots with what we might have been experiencing at the time.[4] Conventional wisdom states that stress can cause pigmented hair to turn white. White hairs can also regain their pigmentation. [4,3]

The proteomics of white and dark hair shafts

The Rosenberg study utilized two different protomics techniques in two different laboratories. Both techniques used 1 cm lengths of hair follicles. Both used the proteolytic enzyme trypsin to digest the hair proteins into peptides that were “sequenced” with two different mass spectrometry techniques. These sequences were used to search databases in order to identify the proteins within the hair samples.

Experiment 1: matched dark and white hairs collected at the same time from two closely age- and diet-matched individuals (one female and one male, both 35 years old, each dark and white HS measured twice, total n = 8)
Experiment 2 (validation): n = 17 hair segments from seven different individuals (four females and three males).

These figures are “Volcano Plots” that give us snap shots of significant changes in proteins. The higher the position of the dot, the more likely the protein is to be significantly more or less in white versus dark hairs. Note that we have a lot of mitochondria proteins (red dots) on the right hand “more in white hairs” side of the plots.

The next step is to look for proteins that are up and down regulated in both of these two rather diverse experiments.

1. CPT1A, Carnitine O-palmitoyltransferase catalyzes the transfer of the acyl group of long-chain fatty acid-CoA conjugates onto carnitine, an essential step for the mitochondrial uptake of long-chain fatty acids and their subsequent beta-oxidation in the mitochondrion
2. ACOT7 Cytosolic acyl coenzyme A thioester hydrolase catalyzes the hydrolysis of acyl-CoAs into free fatty acids and coenzyme A (CoASH), regulating their respective intracellular levels.
3. SOD1 Superoxide dismutase [Cu-Zn] Destroys (super oxide) radicals which are normally produced within the cells and which are toxic to biological systems.
4. CFL1 Cofilin binds to F-actin and exhibits pH-sensitive F-actin depolymerizing activity.
5. PGK1 phosphoglycerate kinase catalyzes one of the two ATP producing reactions in the glycolytic pathway via the reversible conversion of 1,3-diphosphoglycerate to 3-phosphoglycerate.
6. KRTAP3-1 Keratin associated protein 3-1…In the hair cortex, hair keratin intermediate filaments are embedded in an interfilamentous matrix, consisting of hair keratin-associated proteins (KRTAP), which are essential for the formation of a rigid and resistant hair shaft through their extensive disulfide bond cross-linking with abundant cysteine residues of hair keratins. The matrix proteins include the high-sulfur and high-glycine-tyrosine keratins.
7. KRTAP4-3 Keratin associated protein 4-3…In the hair cortex, hair keratin intermediate filaments are embedded in an interfilamentous matrix, consisting of hair keratin-associated proteins (KRTAP), which are essential for the formation of a rigid and resistant hair shaft through their extensive disulfide bond cross-linking with abundant cysteine residues of hair keratins. The matrix proteins include the high-sulfur and high-glycine-tyrosine keratins.

Wait, this makes no sense!

You may be asking yourself why increased levels of Cu/Zn SOD1, generally considered a good thing, be associated with hair going white, generally considered a bad thing. The answer may be found in the Wiriyasermkul 2020 review on ion transporters in melanosomes. [6]

These are some images from the Wiriyasermkul 2020 review.

UniProt as some additional things to say about these copper and zinc enzymes.

• Tyrosinase: “In addition to hydroxylating tyrosine to DOPA (3,4-dihydroxyphenylalanine), also catalyzes the oxidation of DOPA to DOPA-quinone, and possibly the oxidation of DHI (5,6-dihydroxyindole) to indole-5,6 quinone (PubMed:28661582).
• L-dopachrome tautomerase TYRP2.:..”Plays a role in melanin biosynthesis (PubMed:33100333). Catalyzes the conversion of L-dopachrome into 5,6-dihydroxyindole-2-carboxylic acid (DHICA)”

The following are screen shots from the UniProt.org website illustrating the requirement of Cu and Zn for TYR and TYRP2, respectively. Both proteins contain two Cu/Zn per subunit. The Zn vs. Cu requirement of TYP1 is a little more ambiguous. The interesting thing is that mutations in both the TYR and TYRP2 genes are associated with albinism.

Hypothesis: how Cu cures white hair

Melanin production enzymes require Cu and Zn. SOD1 also requires Cu and Zn to function. Perhaps, in hair follicles, under conditions of stress, more SOD1 is produced that competes with TYR and DCT for Cu and Zn, respectively. That Cu supplementation cures white hair might simply be a matter of relative availability of Cu versus Zn.

We don’t know why stress that is associated with white hair [4] might increase certain mitochondria proteins. The Cruz review on hair have very little to say about the keratin associated proteins. [5] The Cruz review does mention growth factors, cytokines, hormones, and neurotransmitters as factors controlling hair cycling. [5] Surely these factors have the potential to also control the expression of the proteins in the Rosenberg study. [4] More mitochondria proteins and Cu/Zn SOD1 could be argued to be a good thing during times of stress that produce white hair. Do we also argue that the aging process is itself a source of stress? During these high stress times, could supplying Cu and/or Zn to Cu/Zn SOD1 reduce the Cu and/or Zn getting to the enzymes responsible for melanin synthesis?

References

1. Daniele T, Hurbain I, Vago R, Casari G, Raposo G, Tacchetti C, Schiaffino MV. Mitochondria and melanosomes establish physical contacts modulated by Mfn2 and involved in organelle biogenesis. Curr Biol. 2014 Feb 17;24(4):393-403. free article
2. Wu X, Hammer JA. Organelle interactions: melanosomes and mitochondria get cozy. Curr Biol. 2014 Mar 17;24(6):R240-2. free article
3. Philpott MP. Watching hair turn grey. Elife. 2021 Jun 30;10:e70584. PMC free article
4. Rosenberg AM, Rausser S, Ren J, Mosharov EV, Sturm G, Ogden RT, Patel P, Kumar Soni R, Lacefield C, Tobin DJ, Paus R, Picard M. Quantitative mapping of human hair greying and reversal in relation to life stress. Elife. 2021 Jun 22;10:e67437. PMC free article
5. Cruz CF, Costa C, Gomes AC, Matamá T, Cavaco-Paulo A. Human Hair and the Impact of Cosmetic Procedures: A Review on Cleansing and Shape-Modulating Cosmetics. Cosmetics. 2016; 3(3):26. free article
6. Wiriyasermkul P, Moriyama S, Nagamori S. Membrane transport proteins in melanosomes: Regulation of ions for pigmentation. Biochim Biophys Acta Biomembr. 2020 Dec 1;1862(12):183318. PMC free article