Genomic Reprogramming and Skin-Like Maturation of Engineered Human Skin Substitutes

Abstract

Background: Cultured skin substitutes (CSS) have been evaluated in clinical trials as an adjunctive treatment for large full-thickness burn wounds. Prepared with autologous fibroblasts, keratinocytes, and biopolymers, CSS can provide permanent wound closure upon engraftment to excised burns.

The problem: CSS containing only two cell types are limited in anatomy and physiology compared with normal uninjured skin. Identifying deficiencies in CSS can instruct further tissue engineering advances.

Basic/clinical science advances: Expression profiling of CSS during in vitro maturation and after transplantation in vivo with Affymetrix GeneChip^® Arrays was used to characterize pathways that are abnormal or deficient in CSS compared with normal human skin. Examination of the large data set generated from microarray expression analysis revealed similarities between healed CSS and normal skin, particularly in expression of genes involved in epidermal differentiation and barrier function. However, deficiencies in several pathways were also noted, such as the genetic pathways regulating development of adnexal structures, including hair follicles.

Clinical care relevance: A deeper understanding of the cellular and molecular events guiding morphogenesis of engineered skin can lead to improvements that will increase clinical efficacy.

Conclusion: The results of GeneChip analysis highlighted the processes that act to regulate tissue development in vitro and adaptation to the wound environment and healing in vivo. This knowledge can be used to inform modifications to the model that will facilitate incorporation of additional cell types for increased homology with native human skin and improved functional outcome for burn patients treated with engineered skin grafts.

Dorothy M. Supp

Figure 1.

Heat map depicting expression levels of 10,349 probe sets expressed in cultured skin substitutes in vitro or in vivo. Expression levels are depicted by color: red for high expression (>1), blue for low expression (<1), and black for mean expression (day 3 in vitro = 1). Each vertical column represents the mean for all samples in each group (n = 3), as indicated at the bottom of the figure. Each row represents a separate probe set, as indicated in the gene tree at the left side of the figure. Eleven clusters of genes were identified using hierarchical clustering; these clusters are color-coded and aligned with the right side of the heat map. As an example, cluster 1, the largest cluster, is identified by the yellow color block and contains genes that have the following expression pattern: expressed at low to moderate levels in vitro, increasing in vitro and after grafting, peaking at day 28 in vivo and then decreasing, and expressed at relatively low levels in NHS. Adapted from target article. d., day; C1–C11, 11 clusters; NHS, normal human skin.