Novel Recombinant Tropoelastin Implants Restore Skin Extracellular Matrix

December 2020 | Volume 19 | Issue 12 | Original Article | 1166 | Copyright © December 2020


Published online November 28, 2020

Michal Graff Mitzmacher MSca*, Suzanne M. Mithieux PhDb,c, Anthony S. Weiss PhDb,c,d, Christopher K. Hee PhDe, Robert Daniels PhDa*

aElastagen Pty Ltd, Sydney, NSW, Australia
bCharles Perkins Centre, University of Sydney, Australia
cSchool of Life and Environmental Sciences, University of Sydney, Australia
dBosch Institute, University of Sydney, Australia
eAllergan Aesthetics, an AbbVie Company, Tissue Material Sciences, Irvine, CA

*Affiliation at the time the studies were conducted.

Abstract
Background: Elastin is an essential component of the dermis, providing skin with elasticity and integrity. Elastin and other dermal components are gradually lost through aging, sun damage, and following injury, highlighting a need to replace these components to repair the skin. Tropoelastin (TE) in monomeric form was previously shown to be utilized as a substrate by dermal fibroblasts during the production of elastin fibers in vitro.
Objective: To analyze coaccumulation of elastin and collagen and gene expression of biomarkers associated with elastin production, examine the ex vivo effects of recombinant human TE (rhTE) and hyaluronic acid (HA) on epidermal and dermal structures, and evaluate the in vivo response following intradermal injections of rhTE and HA.
Methods: Human dermal fibroblasts and 3-D skin patch models were cultured for in vitro analysis. Ex vivo analysis was performed using skin explants. In vivo studies were done in 6-week-old male CD Hairless rats. Different formulations of rhTE, soluble or crosslinked using derivatized HA (dHA), were tested and analyzed.
Results: rhTE in monomeric form was utilized as a substrate by dermal fibroblasts during the production of branched elastin and fibrous collagen networks in vitro. Formulations of rhTE crosslinked with dHA demonstrated increased expression of hyaluronic acid synthase 1 and ex vivo results revealed increased moisture content and glycosaminoglycan (GAG) deposition versus dermal filler control. Intradermal rhTE‒dHA injection produced colocalized human‒rat elastin fibers in vivo.
Conclusions: These results suggest that the novel rhTE‒dHA matrix is an attractive material to support skin tissue repair.

J Drugs Dermatol. 2020;19(12):1166-1172. doi:10.36849/JDD.2020.5375

INTRODUCTION

Skin is an integumentary system organ that interfaces with the environment to protect the body from physical and biological damage. In order to fulfill this role, the skin needs elasticity to respond to and recover from stretch and impact. Human skin sufficiently resembles that of other mammals, including rodents, to make these viable models for tissue repair.1-4 Skin comprises 2 major layers: the outer epidermis and the inner, thicker dermis, which is covered by the epidermis. Within the dermis, elastin dominates skin elasticity in the form of elastic fiber networks. Elastin is made by dermal fibroblasts during development and in tissue repair. Distributed elastin deposition is proposed to contribute to scarless healing.3,5 During development, elastin is mainly incorporated into the dermis before birth and in the first few years of life.6 Whereas some elastin is deposited subsequently, its deposition in response to wounding is typically abnormal.7-11 As such, this tapered production of elastin, coupled with occasional proteolytic loss over time, results in elastin gradually being lost during aging. This has a substantial impact on skin tissue, where the combination of decreased elastin and the loss of other macromolecular components like collagen and hyaluronic acid (HA) leads to the reduced structural integrity, hydration, and elasticity of skin.12-15 To counteract this effect, there is a strong demand for mechanisms that can increase the content of these macromolecules in the dermis, such as through de novo synthesis of elastin fibers that harmonize with endogenous collagen, HA, and skin fibroblast cells. Tropoelastin (TE) is the main (>90%) component of elastin, wherein crosslinked assembled coacervates of TE are exposed to lysyl oxidases and interact with microfibrils to expand elastin fibers.16,17 We have previously shown that monomeric TE is utilized as a substrate by dermal fibroblasts in the formation of elastin fibroblasts in vitro, where an exogenous supply of TE can feed into the process of elastogenesis.18 These studies benefit from the availability of purified recombinant human TE (rhTE) that is amenable for delivery to elastogenic cells in order