Growth factor mimetics for skin regeneration: In vitro profiling of primary human fibroblasts and keratinocytes

Small molecules have gained considerable interest in regenerative medicine, as they can effectively modulate cell fates in a spatiotemporal controllable fashion. A continuous challenge in the field represents genuine mimicry or activation of growth factor signaling with small molecules. Here, we selected and profiled three compounds for their capacity to directly or indirectly activate endogenous FGF-2, VEGF, or SHH signaling events in the context of skin regeneration. Phenotypic and functional analysis of primary skin fibroblasts and keratinocytes revealed unique, cell-specific activity profiles for the FGF-2 mimetic SUN11602 and the putative VEGF mimetic ONO-1301. Whereas SUN11602 exclusively stimulated keratinocyte differentiation, ONO-1301 mainly affected the proliferation and migration behavior of fibroblasts. In each skin cell type, both compounds selectively enhanced the expression of MMP1 and VEGFA. A combined small molecule FGF-2/VEGF mimicry may not only improve angiogenesis-related microcirculation but also reduce early fibrosis while facilitating wound remodeling at later stages. SUN11602 and ONO-1301 represent valuable tools for improving the management of difficult-to-heal wounds, particularly for the design and development of small molecule-functionalized, next-generation, engineered skin substitutes.

Sustained Postnatal Skin Regeneration Upon Prenatal Application of Functionalized Collagen Scaffolds

Primary closure of fetal skin in spina bifida protects the spinal cord and improves clinical outcome, but is also associated with postnatal growth malformations and spinal cord tethering. In this study, we evaluated the postnatal effects of prenatally closed full-thickness skin defects in sheep applying collagen scaffolds with and without heparin/vascular endothelial growth factor/fibroblast growth factor 2, focusing on skin regeneration and growth. At 6 months, collagen scaffold functionalized with heparin, VEGF, and FGF2 (COL-HEP/GF) resulted in a 6.9-fold increase of the surface area of the regenerated skin opposed to 1.7 × for collagen only. Epidermal thickness increased 5.7-fold at 1 month, in line with high gene expression of S100 proteins, and decreased to 2.1 at 6 months. Increased adipose tissue and reduced scaffold degradation and number of myofibroblasts were observed for COL-HEP/GF. Gene ontology terms related to extracellular matrix (ECM) organization were enriched for both scaffold treatments. In COL-HEP/GF, ECM gene expression resembled native skin. Expression of hair follicle-related genes in COL-HEP/GF was comparable to native skin, and de novo hair follicle generation was indicated. In conclusion, in utero closure of skin defects using functionalized collagen scaffolds resulted in long-term skin regeneration and growth. Functionalized collagen scaffolds that grow with the child may be useful for prenatal treatment of closure defects like spina bifida. Impact statement Prenatal closure of fetal skin in case of spina bifida prevents damage to the spinal cord. Closure of the defect is challenging and may result in postnatal growth malformations. In this study, the postnatal effects of a prenatally applied collagen scaffold functionalized with heparin and vascular endothelial growth factor (VEGF)/fibroblast growth factor (FGF) were investigated. An increase of the surface area of regenerated skin ("growing with the child") and generation of hair follicles was observed. Gene expression levels resembled those of native skin with respect to the extracellular matrix and hair follicles. Overall, in utero closure of skin defects using heparin/VEGF/FGF functionalized collagen scaffolds results in long-term skin regeneration.

Evaluation of cultured human dermal- and dermo-epidermal substitutes focusing on extracellular matrix components: Comparison of protein and RNA analysis

Treatment of full-thickness skin defects with split-thickness skin grafts is generally associated with contraction and scar formation and cellular skin substitutes have been developed to improve skin regeneration. The evaluation of cultured skin substitutes is generally based on qualitative parameters focusing on histology. In this study we focused on quantitative evaluation to provide a template for comparison of human bio-engineered skin substitutes between clinical and/or research centers, and to supplement histological data. We focused on extracellular matrix proteins since these components play an important role in skin regeneration. As a model we analyzed the human dermal substitute denovoDerm and the dermo-epidermal skin substitute denovoSkin. The quantification of the extracellular matrix proteins type III collagen and laminin 5 in tissue homogenates using western blotting analysis and ELISA was not successful. The same was true for assaying lysyl oxidase, an enzyme involved in crosslinking of matrix molecules. As an alternative, gene expression levels were measured using qPCR. Various RNA isolation procedures were probed. The gene expression profile for specific dermal and epidermal genes could be measured reliably and reproducibly. Differences caused by changes in the cell culture conditions could easily be detected. The number of cells in the skin substitutes was measured using the PicoGreen dsDNA assay, which was found highly quantitative and reproducible. The (dis) advantages of assays used for quantitative evaluation of skin substitutes are discussed.