Promoting tissue repair with natural cell-signalling peptides

Abstract

As the human lifespan has increased over the last few decades, so has our understanding of the ageing process at a molecular level. The skin, being our first barrier against environmental stressors, and being exposed to ultraviolet radiation, is an ideal model in which to study both intrinsic and extrinsic ageing. The composition of the dermal extracellular matrix (ECM) is similar to that of the vasculature, the lungs, and other ECM-rich tissues. The dermal ECM is known to be degraded during the ageing process, with a loss in structural and functional proteins such as collagen and elastin, and their associated proteins, as well as many glycosaminoglycans. Loss of these components results in functional changes in the skin, including a loss of the lipid barrier, thinning of the epidermis, and loss of elasticity and tensile strength of the skin. This degradation can produce matrix-derived peptides (matrikines), some of which have been proven to induce repair of damaged tissues, including the ECM of the photoaged dermis, and fibrotic tissue of the vasculature. Previous investigations into the action of topically applied peptides used to stimulate dermal repair were limited by study design and outcomes measured. Here, the optimisation and application of an in silico to in vivo pipeline is shown for the prediction and characterisation of novel matrix-derived peptides for use in anti-ageing topical formulations to stimulate dermal repair and homeostasis. Previously, an in silico protein cleavage algorithm has been used to predict cleavage products of key dermal ECM proteins. This thesis describes the optimisation of testing conditions for in-depth transcriptomic and proteomic screening of the peptide activity in vitro, and the utilisation of these ‘omics techniques to characterise their action on human dermal fibroblasts in vitro, and on human skin in vivo. Despite significant inter-individual variation and body site specificity of in vitro cultured cells, these two peptides, Pal-GPKG and Pal-LSVD, were capable of enhancing transcription of genes involved in ECM organisation, lipid and steroid metabolism and cell proliferation. Moreover, processes involved in skin barrier formation, and cell proliferation, as well as promoting epithelial and dermal remodelling were upregulated in vivo. Epidermal thickness was found to increase following treatment with the peptides. Together, this data suggests that these peptides could repair the lipid skin barrier that is lost during the ageing process, as well as reverse epidermal thinning. Finally, to bridge the gap between conventional two-dimensional monoculture study, and the three-dimensional (3D) environment provided to cells in vivo, initial steps were taken to optimise a dermal 3D model cell culture system for testing skin bioactives. While the peptide-based hydrogel system, PeptiGels, proved to be unsuitable for this use, a floating collagen hydrogel system showed promise in cell viability and proliferation, although further work is needed in optimising this system. To conclude, this work has provided a pipeline for discovery and characterisation of novel peptides, and could provide the foundation of study needed to better understand the mechanisms of matrikine action. This could have beneficial results not only in the fields of skin and ageing, but also in the cardiovascular system, the lungs, and other ECM-rich tissues.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Sherratt (Supervisor), Andrew Gilmore (Supervisor) & Matiss Ozols (Supervisor)