Keratinocytes grown in KGM-Gold Media




The skin provides a vitally important protective separation between the internal and the external environments1. There are three structural layers to the skin: the epidermis, the dermis and subcutis. The epidermis is the outer layer, serving as the physical and chemical barrier between the interior body and the exterior environment. The dermis is a deeper layer providing the structural support of the skin.  Subcutis is made up of loose connective tissue and fat, which can be up to 3 cm thick on the abdomen. 


Epidermis is a stratified squamous epithelium consisting of several cell types. The most abundant cell type of epithelial layer of the skin is the keratinocytes which synthesize the protein keratin2. Protein bridges called desmosomes connect the keratinocytes, which are in a constant state of transition from the deeper layers to the superficial. The epidermis varies in thickness based on the tissue of origin. The four separate layers of the epidermis are stratum basale (basal or germinativum cell layer), stratum spinosum (spinous or prickle cell layer), stratum granulosum (granular cell layer) and stratum corneum (Fig. 1). These layers are formed by the differing stages of keratinocyte maturation.


Layers of Skin Epidermis 

The epidermis is a self-renewing tissue composed mainly of keratinocytes in various stages of terminal differentiation. Keratinocytes are produced in the stratum basale (basal layer), and undergo a programmed series of differentiation. Keratinocytes also receive melanin from melanocytes in the form of pre-packaged organelles termed melanosomes.


Image Courtesy of D'Orazio J, Jarrett S, Amaro-Ortiz A, Scott T - Int J Mol Sci (2013)

In addition to their structural and barrier function, keratinocytes also play a crucial role in influencing immune response by secreting inhibitory cytokines and activating Langerhans cells, in response to injury.


In vitro Applications of Epithelial Keratinocyte Cell Cultures in Research

Kerationocytes act as a protective barrier against the external and endogenous environment and also play an important role in maintaining tissue homeostasis. Primary keratinocytes, in vitro, provide a system to study control of dermal epithelial cell growth and differentiation, epidermal model, toxicity studies, skin cancer models, skin disease models, wound healing, dermal burns.


Cell Growth and Differentiation: The epidermis is a self-renewing, stratified, squamous epithelium . In the basal layer resides the basal stem cells that undergo a coordinated program of cell cycle arrest, outward migration, and terminal differentiation. Defects in keratinocyte differentiation and skin barrier are important features of inflammatory skin diseases like atopic dermatitis.    


Skin Models: Microfluidic systems hold promise for high throughput irritant and toxicity assays, but HEK growth kinetics have yet to be characterized within microscale culture chambers. Development of in vitro three-dimensional (3D) tissue models, known as human skin equivalents (HSEs), has furthered the understanding of epidermal cell biology and provided novel experimental systems.     


Cancer: Primary cultures of normal human keratinocytes are utilized to understand the effect of dysregulation of epidermal inhibitors in the development of cancer.    


Disease Models: The abnormal skin permeability barrier due to the genetic mutations in cornified envelope associated proteins, such as filaggrin, loricrin and keratin 10, has recently been suggested as one of primary etiological factors contributing to the development of various skin diseases. Psoriasis is one of the most common immune-mediated chronic inflammatory cutaneous disorders and is characterized by epidermal hyperplasia, dilated blood vessels, and increased leukocyte infiltration3



1) Richard LE and Ellen AR.  Molecular biology of keratinocyte differentiation. Environmental Health Perspectives (1989); 80: 109-116 2.

2) Skin Struct Bensouillah Ch01.pdf 

3) Frank ON, Daniel HK and Jonathan B. Psoriasis. The New England Journal of Medicine (2009); 361: 496–509