Differential expression of matrix metalloproteinase-1 in vitro corresponds to tissue morphogenesis and quality assurance of cultured skin substitutes

Engineered Skin Substitute Regenerates the Skin with Hair Follicle Formation

Currently, engineered skin substitutes (ESS) are unable to regenerate cutaneous appendages. Recent studies have shown that skin-derived precursors (SKPs), which are extensively available, have the potential to induce hair follicle neogenesis. Here, we demonstrate that ESS consisting of culture-expanded SKPs and epidermal stem cells (Epi-SCs) reconstitute the skin with hair follicle regeneration after grafting into nude mice. SKPs seeded in a C-GAG matrix proliferated and expressed higher levels of hair induction signature genes—such as Akp2, Sox2, CD133 and Bmp6—compared to dermal fibroblasts. Moreover, when ESS prepared by seeding a mixture of culture-expanded murine SKPs and human adult Epi-SCs into a C-GAG matrix was grafted into full-thickness skin wounds in nude mice, black hairs were generated within 3 weeks. Immunofluorescence analysis showed that the SKPs were localized to the dermal papillae of the newly-formed hair follicle. Our results indicate that SKPs can serve as the hair-inductive cells in ESS to furnish it with hair genesis potential

Matrix-metalloproteinases as targets for controlled delivery in cancer: An analysis of upregulation and expression

While commonly known for degradation of the extracellular matrix, matrix metalloproteinases (MMPs) exhibit broad potential for use in targeting of bioactive and imaging agents in cancer treatment. MMPs are upregulated at all stages of expression in cancers. A comprehensive analysis of published literature on expression of all MMP subtypes at the genetic, protein, and activity levels in normal and diseased tissues indicate targeting applicability in a variety of cancers. This expression significantly increases at advanced cancer stages, providing an improved opportunity for controlled release in higher-stage patients. Since MMPs are integral at every stage of metastasis, MMP roles in cancer are discussed with a focus on MMP distribution and mobility within cells and tumors for cancer targeting applications. Several strategies for MMP utilization in targeting - such as matrix degradation, MMP cleavage, MMP binding, and MMP-induced environmental changes - are addressed.

Building a microphysiological skin model from induced pluripotent stem cells

The discovery of induced pluripotent stem cells (iPSCs) in 2006 was a major breakthrough for regenerative medicine. The establishment of patient-specific iPSCs has created the opportunity to model diseases in culture systems, with the potential to rapidly advance the drug discovery field. Current methods of drug discovery are inefficient, with a high proportion of drug candidates failing during clinical trials due to low efficacy and/or high toxicity. Many drugs fail toxicity testing during clinical trials, since the cells on which they have been tested do not adequately model three-dimensional tissues or their interaction with other organs in the body. There is a need to develop microphysiological systems that reliably represent both an intact tissue and also the interaction of a particular tissue with other systems throughout the body. As the port of entry for many drugs is via topical delivery, the skin is the first line of exposure, and also one of the first organs to demonstrate a reaction after systemic drug delivery. In this review, we discuss our strategy to develop a microphysiological system using iPSCs that recapitulates human skin for analyzing the interactions of drugs with the skin.

Integration of blood outgrowth endothelial cells in dermal fibroblast sheets promotes full thickness wound healing

Vascularization is the cornerstone of wound healing. We introduced human blood outgrowth endothelial cells (hBOEC) in a self-assembled human dermal fibroblast sheet (hDFS), intended as a tissue-engineered dermal substitute with inherent vascular potential. hBOEC were functionally and molecularly different from early endothelial progenitor cells and human umbilical vein endothelial cells (HUVEC). hBOEC alone, unlike HUVEC, efficiently revascularized and re-oxygenated the wound bed, both by active incorporation into new vessels and by trophic stimulation of host angiogenesis in a dose-dependent manner. Furthermore, hBOEC alone, but not HUVEC, accelerated epithelial coverage and matrix organization of the wound bed. In addition, integration of hBOEC in hDFS not only further improved vascularization, epithelial coverage and matrix organization but also prevented excessive wound contraction. In vitro analyses with hBOEC, fibroblasts and keratinocytes revealed that these effects were both due to growth factor crosstalk and to short cutting hypoxia. Among multiple growth factors secreted by hBOEC, placental growth factor mediated at least in part the beneficial effects on keratinocyte migration and proliferation. Overall, this combined tissue engineering approach paves the way for clinical development of a fully autologous vascularized dermal substitute for patients with large skin defects that do not heal properly.

Wound closure with EDC cross-linked cultured skin substitutes grafted to athymic mice

Collagen-glycosaminoglycan (C-GAG) sponges are commonly utilized as a substitute for the extracellular matrix of dermal tissue. Cultured skin substitutes (CSS) were assessed, after fabrication using sponges cross-linked with 1-ethyl-3-3-dimethylaminopropylcarbodiimide hydrochloride (EDC) at 0, 1, 5, or 50 mm, for development of viable, stratified skin tissue anatomy in vitro, and for wound contraction and cell viability in vivo. Cross-linking the C-GAG sponges with EDC reduced in vitro contraction of the CSS from a 39% reduction in area in the 0 mm CSS to 0% in the 50 mm group. Conversely, the wounds closed with 0, 1 and 5 mm EDC groups exhibited significantly less wound contraction than the 50 mm group. Engraftment of human cells occurred in 86%, 83%, and 83% of the wounds treated with CSS fabricated using 0, 1, and 5 mm EDC cross-linked sponges, respectively, which were significantly higher engraftment rates than the 50 mm group (17%). These data suggest that low concentrations of EDC can be used to improve the biochemical stability of the C-GAG component of CSS in vitro, and promote stable wound closure.

EDC cross-linking improves skin substitute strength and stability

Collagen-based scaffolds are extensively utilized as an analog for the extracellular matrix in cultured skin substitutes (CSS). To improve the mechanical properties and degradation rates of collagen scaffolds, chemical cross-linking is commonly employed. In this study, freeze-dried collagen-GAG sponges were crosslinked with increasing concentrations of 1-ethyl-3-3-dimethylaminopropylcarbodiimide hydrochloride (EDC; 0, 1, 5, 10, 50mm). Cross-linking with EDC at concentrations >1mm was shown to greatly decrease degradation by collagenase up to 21 days. Ultimate tensile strength (UTS) of acellular collagen sponges scaled positively with EDC concentration up to 10mm. At 50mm EDC, the UTS decreased dramatically likely due to the brittle nature of the highly crosslinked material. Co-culture of human fibroblasts (HF) and keratinocytes (HK) on these substrates reveals an apparent cytotoxicty of the EDC at high concentrations with reduced cell viability and poor cellular organization in CSS fabricated with scaffolds crosslinked with 10 or 50mm EDC. From the data gathered in this study, intermediate concentrations of EDC, specifically 5mm, increase collagen sponge stability and strength while providing an environment in which HF and HK can attach, proliferate and organize in a manner conducive to dermal and epidermal regeneration.