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Introductory Chapter: Keratins - What to Do with Too Much? What to Do with Too Little?

Written By

Miroslav Blumenberg and Sidra Younis

Submitted: 22 May 2018 Published: 05 November 2018

DOI: 10.5772/intechopen.79998

From the Edited Volume

Keratin

Edited by Miroslav Blumenberg

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1. Introduction

Keratin, from the Greek word for horn, κέρατο, denotes the proteinaceous covering layers and structures produced by chordates, including mammals, birds, fish, reptiles, and amphibians. The dead outermost layer of the epidermis, hair and wool, horns, claws, hooves, feathers, and scales is composed of keratin. Keratin is completely insoluble in water and is resistant to proteases that degrade other proteins—1000-year-old Egyptian and other ancient mummies often have full head of hair, virtually undamaged keratin. Keratin proteins can be either alpha-helical in structure, in the skin, hair, and wool of mammals, or parallel sheets of beta-pleated polypeptide chains found in the feathers of birds and scales of reptiles. Rich in amino acid cysteine, keratins become covalently crosslinked via disulfide bonds, which confers a great chemical and biochemical stability to keratin. Thus, keratin serves as important resilient structural and protective functions for the organism.

Importantly, keratin is also the resilient structural intracellular protein that protects living epithelial cells from mechanical damage or stress. In cytoplasm, keratin constitutes a filamentous cytoskeletal protein network, extending from the nucleus to the cell periphery, the intermediate filaments, thicker than the actin filaments but thinner than microtubules [1]. Two large families of keratin genes encode multiple proteins with both common and cell-type-specific functions [2].

The indispensable fundamental intracellular keratin functions are revealed in congenital human skin diseases caused by mutations in keratin genes, for example, Epidermolysis bullosa simplex and Epidermolytic hyperkeratosis or in Meesmann’s Corneal Dystrophy, the disease caused by a mutation in the gene specifically encoding a corneal keratin [3]. Most keratin gene mutations have a dominant-negative effect, disrupting the filamentous structure formation even from the natural allele and leaving the cell with a deficient cytoskeleton.

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2. What to do with too little?

Several chapters in this volume address the diseases associated with keratin deficiencies (see manuscripts by Komine et al., Zhang et al.). Corrective gene therapy approaches attempt to specifically target the mutant keratin gene allele, thus allowing the normal keratin protein to decrease cell fragility [4]. Short inhibitory RNA (siRNA) technology was effectively used to downregulate mutant K6a and K14 allele expressions in cultured PC and EBS cells, respectively [57]. This mutation-specific siRNA therapy has been used in a human clinical trial, resulting in effective siRNA treatment of a skin disorder [8]. The functional redundancy of keratins in tissues affected by keratin mutation allows for a possibility to use gene-specific silencing, rather than allele-specific siRNA. Spliceosome-mediated RNA trans-splicing uses the endogenous spliceosome machinery to excise mutant exons and was used to replace the first seven exons of the KRT14 gene in an EBS cell line [9].

Induced pluripotent stem cells and even patient-specific-induced pluripotent stem cells have been generated for use in treatment of inherited keratinopathies [1012]. Such cell-based therapies have been proposed in conjunction with CRISPR/Cas9- and TALEN-based gene-editing techniques for targeting mutations in the keratin genes [1315].

A naturally occurring phenomenon, whereby a subpopulation of mutant cells spontaneously reverts to the wild-type phenotype, “revertant mosaicism,” has been observed in several patients with EB [1620]. Revertant mosaicism keratinopathies have two major advantages: (1) the revertant skin is visible and easily accessible and (2) the revertant keratinocytes often have a growth advantage over their mutant progenitors, and so may outgrow and correct the patient’s ichthyotic phenotype [21]. Harvesting, expanding, and autologous re-grafting the revertant tissue therefore may be feasible in a clinical setting.

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3. What to do with too much?

The increased importance of ecological dangers and ways to alleviate them focused attention on the very large volume of keratin industrial waste. Several chapters in this volume address the incipient remediation efforts (see manuscripts by Ningthoujam et al., Sharma et al., and Nugroho et al.). The mechanical and chemical methodology, cumbersome and inadequate, seems to be giving in to the new biological technology. We can expect deeper understanding of the microbiome and its efficient biodegradation capabilities to play ever more important role. Especially promising are the studies of complex microbiomes, and we can expect in the not-so-distant future that combinations, communities of specific microbes, will be able to convert the obnoxious keratin waste into delightful new materials [22, 23].

References

  1. 1. Loschke F, Seltmann K, Bouameur JE, Magin TM. Regulation of keratin network organization. Current Opinion in Cell Biology. 2015;32:56-64. DOI: 10.1016/j.ceb.2014.12.006. PubMed PMID: 25594948
  2. 2. Jacob JT, Coulombe PA, Kwan R, Omary MB. Types I and II keratin intermediate filaments. Cold Spring Harbor Perspectives in Biology. 2018;10(4):pii: a018275. DOI: 10.1101/cshperspect.a018275. PubMed PMID: 29610398
  3. 3. Chamcheu JC, Siddiqui IA, Syed DN, Adhami VM, Liovic M, Mukhtar H. Keratin gene mutations in disorders of human skin and its appendages. Archives of Biochemistry and Biophysics. 2011;508(2):123-137. DOI: 10.1016/j.abb.2010.12.019. PubMed PMID: 21176769
  4. 4. Cao T, Longley MA, Wang XJ, Roop DR. An inducible mouse model for epidermolysis bullosa simplex: Implications for gene therapy. Journal of Cell Biology. 2001;152(3):651-656. PubMed PMID: 11157990
  5. 5. Dykxhoorn DM, Lieberman J. Knocking down disease with siRNAs. Cell. 2006;126(2):231-235. PubMed PMID: 16873051
  6. 6. Leachman SA, Hickerson RP, Hull PR, Smith FJ, Milstone LM, Lane EB, Bale SJ, Roop DR, McLean WH, Kaspar RL. Therapeutic siRNAs for dominant genetic skin disorders including pachyonychia congenita. Journal of Dermatological Science. 2008;51(3):151-157. DOI: 10.1016/j.jdermsci.2008.04.003. PubMed PMID: 18495438
  7. 7. Werner NS, Windoffer R, Strnad P, Grund C, Leube RE, Magin TM. Epidermolysis bullosa simplex-type mutations alter the dynamics of the keratin cytoskeleton and reveal a contribution of actin to the transport of keratin subunits. Molecular Biology of the Cell. 2004;15(3):990-1002. PubMed PMID: 14668478
  8. 8. Leachman SA, Hickerson RP, Schwartz ME, Bullough EE, Hutcherson SL, Boucher KM, et al. First-in-human mutation-targeted siRNA phase Ib trial of an inherited skin disorder. Molecular Therapy. 2010;18(2):442-446. DOI: 10.1038/mt.2009.273. PubMed PMID: 19935778
  9. 9. Wally V, Brunner M, Lettner T, Wagner M, Koller U, Trost A, Murauer EM, et al. K14 mRNA reprogramming for dominant epidermolysis bullosa simplex. Human Molecular Genetics. 2010;19(23):4715-4725. DOI: 10.1093/hmg/ddq405. PubMed PMID: 20861136
  10. 10. Uitto J, Christiano AM, McLean WH, McGrath JA. Novel molecular therapies for heritable skin disorders. The Journal of Investigative Dermatology. 2012;132(3 Pt 2):820-828. DOI: 10.1038/jid.2011.389. PubMed PMID: 22158553
  11. 11. Itoh M, Kiuru M, Cairo MS, Christiano AM. Generation of keratinocytes from normal and recessive dystrophic epidermolysis bullosa-induced pluripotent stem cells. Proceedings of the National Academy of Sciences of the United States of America. 2011;108(21):8797-8802. DOI: 10.1073/pnas.1100332108. PubMed PMID: 21555586
  12. 12. Umegaki-Arao N, Pasmooij AM, Itoh M, Cerise JE, Guo Z, Levy B, et al. Induced pluripotent stem cells from human revertant keratinocytes for the treatment of epidermolysis bullosa. Science Translational Medicine. 2014;6(264):264ra164. DOI: 10.1126/scitranslmed.3009342. PMID: 25429057
  13. 13. Kocher T, Peking P, Klausegger A, Murauer EM, Hofbauer JP, Wally V, et al. Cut and paste: Efficient homology-directed repair of a dominant negative KRT14 mutation via CRISPR/Cas9 nickases. Molecular Therapy. 2017;25(11):2585-2598. DOI: 10.1016/j.ymthe.2017.08.015. PMID: 28888469
  14. 14. Courtney DG, Moore JE, Atkinson SD, Maurizi E, Allen EH, Pedrioli DM, et al. CRISPR/Cas9 DNA cleavage at SNP-derived PAM enables both in vitro and in vivo KRT12 mutation-specific targeting. Gene Therapy. 2016;23(1):108-112. DOI: 10.1038/gt.2015.82. PMID: 26289666
  15. 15. Aushev M, Koller U, Mussolino C, Cathomen T, Reichelt J. Traceless targeting and isolation of gene-edited immortalized keratinocytes from epidermolysis bullosa simplex patients. Molecular Therapy—Methods and Clinical Development. 2017;6:112-123. DOI: 10.1016/j.omtm.2017.06.008. PMID: 28765827
  16. 16. Kiritsi D, Nanda A, Kohlhase J, Bernhard C, Bruckner-Tuderman L, Happle R, Has C. Extensive postzygotic mosaicism for a novel keratin 10 mutation in epidermolytic ichthyosis. Acta Dermato-Venereologica. 2014;94(3):346-348. DOI: 10.2340/00015555-1695. PubMed PMID: 24096702
  17. 17. Smith FJ, Morley SM, McLean WH. Novel mechanism of revertant mosaicism in Dowling-Meara epidermolysis bullosa simplex. The Journal of Investigative Dermatology. 2004;122(1):73-77. PubMed PMID: 14962092
  18. 18. Schuilenga-Hut PH, Scheffer H, Pas HH, Nijenhuis M, Buys CH, Jonkman MF. Partial revertant mosaicism of keratin 14 in a patient with recessive epidermolysis bullosa simplex. The Journal of Investigative Dermatology. 2002;118(4):626-630. PubMed PMID: 11918708
  19. 19. Lim YH, Fisher JM, Choate KA. Revertant mosaicism in genodermatoses. Cellular and Molecular Life Sciences. 2017;74(12):2229-2238. DOI: 10.1007/s00018-017-2468-2. PMID: 28168442
  20. 20. Lai-Cheong JE, McGrath JA, Uitto J. Revertant mosaicism in skin: Natural gene therapy. Trends in Molecular Medicine. 2011;17(3):140-148. DOI: 10.1016/j.molmed.2010.11.003. PMID: 21195026
  21. 21. van den Akker PC, Pasmooij AMG, Joenje H, Hofstra RMW, TeMeerman GJ, Jonkman MF. A late-but-fitter revertant cell explains the high frequency of revertant mosaicism in epidermolysis bullosa. PLoS One. 2018;13(2):e0192994. DOI: 10.1371/journal.pone.0192994. PMID: 29470523
  22. 22. Toju H, Peay KG, Yamamichi M, Narisawa K, Hiruma K, Naito K, Fukuda S, Ushio M, Nakaoka S, Onoda Y, Yoshida K, Schlaeppi K, Bai Y, Sugiura R, Ichihashi Y, Minamisawa K, Kiers ET. Core microbiomes for sustainable agroecosystems. Nature Plants. 2018;4(5):247-257. DOI: 10.1038/s41477-018-0139-4. PubMed PMID: 29725101
  23. 23. Zengler K, Zaramela LS. The social network of microorganisms—How auxotrophies shape complex communities. Nature Reviews. Microbiology. 2018;16(6):383-390. DOI: 10.1038/s41579-018-0004-5. PubMed PMID: 29599459

Written By

Miroslav Blumenberg and Sidra Younis

Submitted: 22 May 2018 Published: 05 November 2018