Munenari Itoh

Generation of keratinocytes from normal and recessive dystrophic epidermolysis bullosa-induced pluripotent stem cells

Embryonic stem cells (ESCs) have an unlimited proliferative capacity and extensive differentiation capability. They are an alternative source for regenerative therapies with a potential role in the treatment of several human diseases. The clinical use of ESCs, however, has significant ethical and biological obstacles related to their derivation from embryos and potential for immunological rejection, respectively. These disadvantages can be circumvented by the alternative use of induced pluripotent stem cells (iPSCs), which are generated from an individuals (autologous) somatic cells by exogenous expression of defined transcription factors and have biological characteristics similar to ESCs. In recent years, patient-specific iPSCs have been generated to study disease mechanisms and develop iPSC-based therapies. The development of iPSC-based therapies for skin diseases requires successful differentiation of iPSCs into cellular components of the skin, including epidermal keratinocytes. Here, we succeeded in generating iPSCs not only from normal human fibroblasts but also from fibroblasts isolated from the skin of two patients with recessive dystrophic epidermolysis bullosa. Moreover, we differentiated both of these iPSCs into keratinocytes with high efficiency, and generated 3D skin equivalents using iPSC-derived keratinocytes, suggesting that they were fully functional. Our studies indicate that autologous iPSCs have the potential to provide a source of cells for regenerative therapies for specific skin diseases.

Generation of 3D Skin Equivalents Fully Reconstituted from Human Induced Pluripotent Stem Cells (iPSCs)

Recent generation of patient-specific induced pluripotent stem cells (PS-iPSCs) provides significant advantages for cell- and gene-based therapy. Establishment of iPSC-based therapy for skin diseases requires efficient methodology for differentiating iPSCs into both keratinocytes and fibroblasts, the major cellular components of the skin, as well as the reconstruction of skin structures using these iPSC-derived skin components. We previously reported generation of keratinocytes from human iPSCs for use in the treatment of recessive dystrophic epidermolysis bullosa (RDEB) caused by mutations in the COL7A1 gene. Here, we developed a protocol for differentiating iPSCs into dermal fibroblasts, which also produce type VII collagen and therefore also have the potential to treat RDEB. Moreover, we generated in vitro 3D skin equivalents composed exclusively human iPSC-derived keratinocytes and fibroblasts for disease models and regenerative therapies for skin diseases, first demonstrating that iPSCs can provide the basis for modeling a human organ derived entirely from two different types of iPSC-derived cells.

Induced pluripotent stem cells from human revertant keratinocytes for the treatment of epidermolysis bullosa

Epidermolysis bullosa patient–specific iPSCs were generated from spontaneously corrected revertant keratinocytes for skin reconstitution. “Natural Gene Therapy” for Rare, Genetic Skin Disease Epidermolysis bullosa (EB) is a rare, inherited skin disorder that causes such severe blistering that patients are often relegated to a delicate life in bandages. Like a patchwork quilt, the skin of a patient with EB can consist of both mutated skin cells (which cause the disease) and spontaneously genetically corrected “normal” cells; this patchwork phenomenon is known as revertant mosaicism. In a new study, Umegaki-Arao and colleagues demonstrated that these revertant cells could be used to generate healthy skin, representing a possible cell therapy for patients with EB who have no treatment options. The authors took revertant keratinocytes (skin cells) from a patient with junctional EB, who have mutations in the gene expressing type XVII collagen. These revertant keratinocytes were used to generate induced pluripotent stem cells, which, in turn, could be differentiated into a keratinocyte lineage that created normal-looking skin layers not only in vitro but also in vivo in mice. Because the cells already expressed type XVII collagen, there was no need for genetic correction, thus avoiding many of the pitfalls that gene and cell therapies face during translation to the clinic. Revertant mosaicism is a naturally occurring phenomenon involving spontaneous correction of a pathogenic gene mutation in a somatic cell. It has been observed in several genetic diseases, including epidermolysis bullosa (EB), a group of inherited skin disorders characterized by blistering and scarring. Induced pluripotent stem cells (iPSCs), generated from fibroblasts or keratinocytes, have been proposed as a treatment for EB. However, this requires genome editing to correct the mutations, and, in gene therapy, efficiency of targeted gene correction and deleterious genomic modifications are still limitations of translation. We demonstrate the generation of iPSCs from revertant keratinocytes of a junctional EB patient with compound heterozygous COL17A1 mutations. These revertant iPSCs were then differentiated into naturally genetically corrected keratinocytes that expressed type XVII collagen (Col17). Gene expression profiling showed a strong correlation between gene expression in revertant iPSC–derived keratinocytes and the original revertant keratinocytes, indicating the successful differentiation of iPSCs into the keratinocyte lineage. Revertant-iPSC keratinocytes were then used to create in vitro three-dimensional skin equivalents and reconstitute human skin in vivo in mice, both of which expressed Col17 in the basal layer. Therefore, revertant keratinocytes may be a viable source of spontaneously gene-corrected cells for developing iPSC-based therapeutic approaches in EB.

Melanin Transfer in Human 3D Skin Equivalents Generated Exclusively from Induced Pluripotent Stem Cells

The current utility of 3D skin equivalents is limited by the fact that existing models fail to recapitulate the cellular complexity of human skin. They often contain few cell types and no appendages, in part because many cells found in the skin are difficult to isolate from intact tissue and cannot be expanded in culture. Induced pluripotent stem cells (iPSCs) present an avenue by which we can overcome this issue due to their ability to be differentiated into multiple cell types in the body and their unlimited growth potential. We previously reported generation of the first human 3D skin equivalents from iPSC-derived fibroblasts and iPSC-derived keratinocytes, demonstrating that iPSCs can provide a foundation for modeling a complex human organ such as skin. Here, we have increased the complexity of this model by including additional iPSC-derived melanocytes. Epidermal melanocytes, which are largely responsible for skin pigmentation, represent the second most numerous cell type found in normal human epidermis and as such represent a logical next addition. We report efficient melanin production from iPSC-derived melanocytes and transfer within an entirely iPSC-derived epidermal-melanin unit and generation of the first functional human 3D skin equivalents made from iPSC-derived fibroblasts, keratinocytes and melanocytes.

Bone Marrow Stem Cell Therapy for Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe inherited blistering disease caused by mutations in the type VII collagen gene, resulting in defective anchoring fibrils at the epidermal-dermal junction. At present, no curative treatment for RDEB exists. Mounting evidence on reprogramming of bone marrow stem cells into skin has prompted the authors and others to develop novel strategies for treatment of RDEB. The rationale for bone marrow stem cell therapies for RDEB is based on the evidence that bone marrow-derived cells are guided into becoming skin cells, given the right microenvironment. Preclinical studies in mouse models have shown that wild-type bone marrow-derived cells can ameliorate the phenotype of RDEB and improve survival by restoring the expression of type VII collagen and the anchoring fibrils. At present, several clinical studies are ongoing around the world to study the therapeutic effects of bone marrow stem cell transplantation for RDEB. These studies provide a framework for future development of standardized, effective methods for stem cell transplantation to cure severe inherited skin diseases, including RDEB.

Reprogramming of Human Hair Follicle Dermal Papilla Cells into Induced Pluripotent Stem Cells

Abbreviations: DP, dermal papilla; ESC, embryonic stem cell; iPSC, induced pluripotent stem cell

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.