A simple material model to generate epidermal and dermal layers in vitro for skin regeneration

There is an urgent need for a rationally-designed, cellularized skin graft capable of reproducing the micro-environmental cues necessary to promote skin healing and regeneration. To address this need, we developed a composite scaffold, namely, CA/C-PEG, composing of a porous chitosan-alginate (CA) structure impregnated with a thermally reversible chitosan-poly(ethylene glycol) (C-PEG) gel to incorporate skin cells as a bi-layered skin equivalent. Fibroblasts were encapsulated in C-PEG to simulate the dermal layer while the keratinocytes were seeded on the top of CA/C-PEG composite scaffold to mimic the epidermal layer. The CA scaffold provided mechanical support for the C-PEG gel and the C-PEG gel physically segregated the keratinocytes from fibroblasts in the construct. Three different tissue culture micro-environments were tested: CA scaffolds without C-PEG cultured in cell culture medium without air-liquid interface (-gel-interface), CA scaffolds impregnated with C-PEG and cultured in cell culture medium without air-liquid interface (-gel-interface), and CA scaffolds impregnated with C-PEG cultured in cell culture medium with air-liquid interface (-gel- interface). We found that the presence of C-PEG increased the cellular proliferation rates of both keratinocytes and fibroblasts, and the air-liquid interface induced keratinocyte maturation. This CA/C-PEG composite scaffold design is able to recapitulate micro-environments relevant to skin tissue engineering, and may be a useful tool for future skin tissue engineering applications.

Xanthan gum inhibits cartilage degradation by down-regulating matrix metalloproteinase-1 and -3 expressions in experimental osteoarthritis

We previously reported that intra-articular injection of xanthan gum protected the joint cartilage and reduced osteoarthritis progression. In this study, the effects of xanthan gum on chondrocytes apoptosis were evaluated using the labeling assay, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay, to determine the protein expression of matrix metalloproteinase-1, 3, and tissue inhibitors of metalloproteinase-1 using immunohistochemistry and Western blot assay in cartilage of papain-induced rabbit osteoarthritis model. Compared to the negative control group, intra-articular injection of xanthan gum, once every 2 weeks for 5 weeks significantly inhibited chondrocytes apoptosis and matrix metalloproteinase-1 and -3 protein expression levels and also enhanced the tissue inhibitors of metalloproteinase-1 production in cartilage. No significant differences between the xanthan gum-treated group and the sodium hyaluronate-treated group (intra-articular injection of sodium hyaluronate only once a week for 5 weeks) were observed.

The effectiveness, cytotoxicity, and intracellular trafficking of nonviral vectors for gene delivery to bone mesenchymal stem cells

Nonviral gene delivery that enables exogenous gene expression in bone mesenchymal stem cells could accelerate clinical application of cell-based gene therapy. This study systematically investigated and compared the potential of polyethylenimine and Lipofectamine 2000 as gene carriers to modify bone mesenchymal stem cells including transfection efficiency, cytotoxicity, intracellular trafficking as well as cell membrane damage and apoptosis/necrosis. Polyethylenimine at its optimal N/P ratio of 10 demonstrated the same toxic effects but lower transfection efficiency (17.1% vs 39.5%) compared to Lipofectamine. Intracellular trafficking resulted in over 80% of bone mesenchymal stem cells that were able to take up polyethylenimine polyplexes, but only 20.69% showed nuclear uptake; however, for Lipofectamine, about half bone mesenchymal stem cells were found to uptake lipoplexes but about 30% displayed nuclear localization. Moreover, the percentages of nuclear localization of both vectors were in close relationship with their transfection efficiency. We concluded that for bone mesenchymal stem cell transfection, polyethylenimine displayed high cellular uptake but Lipofectamine was more effective in delivering genes into the nucleus, which was likely the underlying basis for a more efficient gene expression. Further structure modification of polyethylenimine such as improving its nuclear entry ability will eventually make it a better candidate for bone mesenchymal stem cells’ in vitro gene delivery.

Novel poly(glycidyl methacrylate-b-propylene oxide-b-glycidyl methacrylate) derivatives with low cytotoxicity and efficient gene delivery

Gene therapy has been developed for decades, but is still hampered for general clinical treatment by lack of gene delivery vectors with high transfection efficiency and low cytotoxicity. In this study, well-defined BAB triblock copolymer, poly(glycidyl methacrylate-b-propylene oxide-b-glycidyl methacrylate), P(GMA-b-PO-b-GMA), was prepared via atom transfer radical polymerization and modified by different ratios of ethylenediamine (EDA) and 1-(3-aminopropyl) imidazole (API) to obtain cationic amphiphilic polymers. The difference in the ratio of EDA and API had an influence on pDNA-binding capability, size, and zeta potential of P(GMA-b-PO-b-GMA) derivatives. All the cationic amphiphilic polymers exhibited low cytotoxicity and good transfection activity in comparison with 25 kDa polyethylenimine (PEI) due to their special architecture. The optimal polymer, with 89% API and 11% EDA, showed the highest transfection efficiency among these polymers. Its luciferase expression at N/P ratio of 30 was comparable to that of 25 kDa PEI in a serum-free medium and higher than that of 25 kDa PEI by roughly an order of magnitude in a medium with serum.

Modulation of collagen and keratin synthesis in co-cultures of fibroblasts and keratinocytes on hyaluronan-coated polysulfone membranes

Human epidermal keratinocytes and dermal fibroblasts were co-cultured on polysulfone (PSU) membranes, previously coated or not with hyaluronan (HA), and compared to monocultured keratinocytes and fibroblasts. The purpose was to define the interplay between both cell types and how it is influenced. The co-cultures reduced types I and III collagen levels, indicating that keratinocytes exerted an inhibition on matrix synthesis by fibroblasts. On the other hand, the amounts of keratins 17 and 10 were increased, suggesting that fibroblasts stimulate the production of keratins by keratinocytes. In contrast with naked PSU membranes, HA coatings increased types I and III collagens mRNA (messenger ribonucleic acid) levels, suggesting that HA counteracts the inhibition produced by keratinocytes. Changes were also observed in the expression of metalloproteinases (MMPs) on HA-coated PSU membranes. The presence of keratinocytes increased MMP1 and MMP3 synthesis by fibroblasts whereas HA exerted an inhibitory effect on MMP2 expression that depended on the culture conditions. The TGF-β3 mRNA levels were very high in co-cultures on PSU, whereas TGF-β1 mRNA was rather low; this was amplified on HA-coated membranes. These data provide a deeper insight into the intercellular interactions between dermal fibroblasts and keratinocytes, and their modulation by the culture support of these cells.

Bone Regeneration with BMP-2 Gene-modified Mesenchymal Stem Cells Seeded on Nano-hydroxyapatite/Collagen/ Poly(L-Lactic Acid) Scaffolds

In this study, the capacity of bone morphogenetic protein 2 (BMP-2) gene-transfected bone marrow-derived mesenchymal stem cells (MSCs) in combination with nano-hydroxyapatite/collagen/poly(L-lactic acid) (nHAC/ PLA) to improve the repair of bone defects in rabbit was explored. MSCs from New Zealand White rabbits were cultured and injected with pIRES2-EGFPhBMP-2 or pIRES2-EGFP by electroporation. After the transfer efficiency was determined through the expression of EGFP, the MSCs were seeded on scaffolds to generate an in vitro 3D cell/scaffold construct. The adhesion and proliferation of the MSCs cultured in the scaffold was assessed by SEM. The cellular constructs obtained were allografted into the 15 mm critical-sized segmental bone defects in the radius of New Zealand White rabbits for 12 weeks. The bone regeneration was assessed by radiographical and histological analyses. In vitro, nHAC/PLA facilitated MSC adhesion and proliferation on the scaffold, and gene transfer efficiency reached a maximum of 35.5 ± 3.8%. In vivo, the implantation of BMP-2 transfected MSCs/nHAC/PLA construct significantly enhanced the formation of new bone in the segmental defect, compared to the control groups. This novel 3D BMP-2 transfected MSCs/nHAC/PLA construct has the potential for bone repair by genetic tissue engineering approach.