Bioengineering Novel Ageing Skin Equivalents and their Application to Study the Importance of Dermal-Epidermal Interactions during Skin Ageing

Abstract

Recreating the structure of human tissues in the laboratory is valuable for fundamental research, testing interventions and reducing the use of animals. Critical to the use of such technology is the ability to develop tissue models that accurately recreate the microanatomy of the native tissue. In this thesis, we have bioengineered novel models of neonatal and ageing human skin, that recreate the structure of human skin in vitro. These skin equivalents have been applied to investigate the mechanisms of skin ageing, such as the influence of epidermal-dermal interactions.

We have successfully bioengineered a neonatal full thickness skin equivalent that accurately recreates aspects of the microanatomy of human skin. The skin equivalent was generated using a bottom-up tissue engineering approach, whereby the human fibroblasts secrete their own endogenous extracellular matrix proteins within the porous Alvetex® Scaffold. In-depth morphological analyses demonstrate close similarities with native human skin, such as an
organised, stratified and keratinised epidermis, the presence of a robust basement membrane and the deposition of extracellular matrix proteins within the dermal compartment.

Many dermal matrices used in skin tissue engineering are not suitable for ageing studies as they cannot be tailored to recapitulate the age-related decline in extracellular matrix in vitro. We have found that incorporating ageing dermal fibroblasts within the Alvetex® Scaffold, to form a dermal equivalent, enables age-related changes, such as decreased proliferation and reduced synthesis of extracellular matrix proteins, to be recreated in vitro. These ageing dermal equivalents have been applied to investigate the influence of epidermal-dermal interactions during ageing.

Dermal interactions are thought to influence the epidermal morphology during embryogenesis and in adult skin, however there is a paucity of information regarding the importance of epidermal-dermal interactions during ageing. Tissue engineering approaches described within this thesis suggest that an ageing dermis contributes to the age-related epidermal phenotype and influences
epidermal thickness, keratinocyte differentiation and the structure of basal keratinocytes.

In the current ageing demographic, there is a requirement for an ageing skin model for academic and industrial applications. We have bioengineered novel and advanced full thickness skin equivalents representative of female ageing skin, which recreate the structure of human skin in vitro, with regards to epidermal differentiation, the presence of a basement membrane and synthesis of extracellular matrix proteins. The ageing skin equivalents also successfully
recapitulate age-related changes in vitro such as epidermal atrophy, altered keratinocyte differentiation, and reduction of extracellular matrix proteins.