Description

Bibliografia__________________________________________________________________________

Bragulla HH, Homberger DG. Structure and functions of keratin proteins in simple, stratified, keratinized and cornified epithelia. J Anat. 2009 Apr;214(4):516-59. doi: 10.1111/j.1469-7580.2009.01066.x. 

Abstract. Historically, the term 'keratin' stood for all of the proteins extracted from skin modifications, such as horns, claws and hooves. Subsequently, it was realized that this keratin is actually a mixture of keratins, keratin filament-associated proteins and other proteins, such as enzymes. Keratins were then defined as certain filament-forming proteins with specific physicochemical properties and extracted from the cornified layer of the epidermis, whereas those filament-forming proteins that were extracted from the living layers of the epidermis were grouped as 'prekeratins' or 'cytokeratins'. Currently, the term 'keratin' covers all intermediate filament-forming proteins with specific physicochemical properties and produced in any vertebrate epithelia. Similarly, the nomenclature of epithelia as cornified, keratinized or non-keratinized is based historically on the notion that only the epidermis of skin modifications such as horns, claws and hooves is cornified, that the non-modified epidermis is a keratinized stratified epithelium, and that all other stratified and non-stratified epithelia are non-keratinized epithelia. At this point in time, the concepts of keratins and of keratinized or cornified epithelia need clarification and revision concerning the structure and function of keratin and keratin filaments in various epithelia of different species, as well as of keratin genes and their modifications, in view of recent research, such as the sequencing of keratin proteins and their genes, cell culture, transfection of epithelial cells, immunohistochemistry and immunoblotting. Recently, new functions of keratins and keratin filaments in cell signaling and intracellular vesicle transport have been discovered. It is currently understood that all stratified epithelia are keratinized and that some of these keratinized stratified epithelia cornify by forming a Stratum corneum. The processes of keratinization and cornification in skin modifications are different especially with respect to the keratins that are produced. Future research in keratins will provide a better understanding of the processes of keratinization and cornification of stratified epithelia, including those of skin modifications, of the adaptability of epithelia in general, of skin diseases, and of the changes in structure and function of epithelia in the course of evolution. This review focuses on keratins and keratin filaments in mammalian tissue but keratins in the tissues of some other vertebrates are also considered.

Shavandi A, Silva TH, Bekhit AA, Bekhit AEA. Keratin: dissolution, extraction and biomedical application. Biomater Sci. 2017 Aug 22;5(9):1699-1735. doi: 10.1039/c7bm00411g. 

Abstract. Keratinous materials such as wool, feathers and hooves are tough unique biological co-products that usually have high sulfur and protein contents. A high cystine content (7-13%) differentiates keratins from other structural proteins, such as collagen and elastin. Dissolution and extraction of keratin is a difficult process compared to other natural polymers, such as chitosan, starch, collagen, and a large-scale use of keratin depends on employing a relatively fast, cost-effective and time efficient extraction method. Keratin has some inherent ability to facilitate cell adhesion, proliferation, and regeneration of the tissue, therefore keratin biomaterials can provide a biocompatible matrix for regrowth and regeneration of the defective tissue. Additionally, due to its amino acid constituents, keratin can be tailored and finely tuned to meet the exact requirement of degradation, drug release or incorporation of different hydrophobic or hydrophilic tails. This review discusses the various methods available for the dissolution and extraction of keratin with emphasis on their advantages and limitations. The impacts of various methods and chemicals used on the structure and the properties of keratin are discussed with the aim of highlighting options available toward commercial keratin production. This review also reports the properties of various keratin-based biomaterials and critically examines how these materials are influenced by the keratin extraction procedure, discussing the features that make them effective as biomedical applications, as well as some of the mechanisms of action and physiological roles of keratin. Particular attention is given to the practical application of keratin biomaterials, namely addressing the advantages and limitations on the use of keratin films, 3D composite scaffolds and keratin hydrogels for tissue engineering, wound healing, hemostatic and controlled drug release.

Smack DP, Korge BP, James WD. Keratin and keratinization. J Am Acad Dermatol. 1994 Jan;30(1):85-102. doi: 10.1016/s0190-9622(94)70012-5.

Abstract. A flood of new knowledge and discoveries in the basic science of keratins and keratinization has appeared in the past several years. This review summarizes this recent information with a focus on the epithelial keratin polypeptides, keratin intermediate filaments, keratohyaline granule proteins, cell envelope formation and cell envelope proteins, "soft" keratinization, true disorders of keratinization (i.e., epidermolysis bullosa simplex and epidermolytic hyperkeratosis), and disease and drug effects on keratinization.

Sun TT, Eichner R, Nelson WG, Tseng SC, Weiss RA, Jarvinen M, Woodcock-Mitchell J. Keratin classes: molecular markers for different types of epithelial differentiation. J Invest Dermatol. 1983 Jul;81(1 Suppl):109s-15s. doi: 10.1111/1523-1747.ep12540831.

Abstract. Keratins are a group of water-insoluble proteins (molecular weight range 40-70 K) that form 10-nm tonofilaments in a wide variety of epithelial cells. The subunit composition of the keratin filaments varies with cell type, period of embryonic development, stage of histologic differentiation, cellular growth environment, and disease state. To better understand the functional significance of individual keratin species, we have generated three monoclonal antikeratin antibodies to different subsets of keratins and used these antibodies to localize specific keratins in normal human epidermis by a combination of immunohistochemical and biochemical techniques. The results indicate that the 50 K and 58 K keratins are present in all cell layers including the relatively undifferentiated basal layer, whereas the 56.5 K and 65-67 K keratins are associated only with the more differentiated cells above the basal layer. In a separate series of experiments, we used the monoclonal antibodies to survey the keratins expressed by various nonepidermal epithelia. The data show that keratins can be divided into at least seven major classes according to their immunologic reactivity and size. Among the keratin classes, the 50 K and 58 K classes appear to be characteristic of all stratified squamous epithelia, whereas the 56.5 K and 65-67 K classes are unique to the keratinized epidermis. These findings suggest that specific keratin classes, as defined by monoclonal antibodies, may serve as useful markers for different types of epithelial differentiation (simple versus stratified, keratinized versus nonkeratinized).