Generation of equine induced pluripotent stem cells from keratinocytes
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Induced pluripotent stem cells (iPSCs) are generated by reprogramming somatic cells to an embryonic state. Therefore iPSCs represent an extremely valuable tool for modelling disease and organ toxicity, with enormous potential in veterinary medicine. Several equine diseases are currently untreatable and can result in euthanasia on medical grounds. In contrast to humans, in vitro models for cellular research in equine do not exist. Therefore it has been necessary to explore the use of stem cells in constructing cell based equine models. Pluripotent stem cell populations are of great interest in this field given their ability to form the three germ layers found in the developing embryo. While a promising notion, the isolation of equine embryonic stem cells has thus far proved elusive and therefore it has been necessary to explore other pluripotent stem cell populations. A very limited number of induced PSC lines have so far been generated from equine fibroblasts but studies in humans showed that other cell types such as keratinocytes were more amenable to reprogramming and generated iPSCs with much higher efficiency; whether this may be also the case in other species has not been investigated. Moreover, iPSC lines reported so far from domestic species, including the horse, depended on complex culture conditions for growth, including feeder layers and media supplementation with several growth factors. Although a promising alternative to fibroblast for generation of induced pluripotent stem cells there is dearth in literature on equine keratinocyte culture techniques. In this work I am reporting a novel approach to generate equine iPSCs lines from keratinocytes. Skin biopsies were used to derive keratinocyte cultures. The three dimensional culture systems were developed for robust culture of equine keratinocytes. These cells were then transduced with retroviral constructs coding for murine Oct-4, Sox-2, c-Myc and Klf-4 sequences, following the original Yamanaka protocol. Following transduction, tight cell colonies with sharp boundaries staining positive for alkaline phosphatase resembling previously reported human iPSCs were generated. The reprogrammed cells were successfully maintained in feeder free and serum free conditions with LIF supplementation. Immunochemistry and qPCR analyses revealed the equine iPSCs lines expressed pluripotency markers expressed in equine embryonic stages including, OCT4, SOX2, SSEA1, LIN 28, NANOG, REX1 and DNMT3B. Equine iPSCs were able to form embryoid bodies and differentiate into derivatives of the three germ layers in vitro. Equine iPSCs were pluripotent in vivo as demonstrated by the formation of teratoma consisting of tissue derivatives of all three lineages such as bone, cartilage, pulmonary epithelium and mature neurons in SCID mice. Importantly, equine iPSCs should not only have the ability to differentiate in a non-directed manner. Therefore, the ability for efficient and directed cellular differentiation was analysed. Equine iPSCs were successfully induced to differentiate into neurospheres forming extensive neuronal projections and synapses. Equine iPSCs were differentiated to neurons using a novel and robust approach. The neurons expressed FOXG1, TUBB3 at induction before ISL1 up regulation, a potent and specific inducer of motor neurons, during terminal differentiation. The neurons tested could fire multiple action potentials and also induce TTX –sensitive action potentials. The iPSC line that showed in vivo differentiation in bone and cartilage was tested for directed differentiation into bone and results were compared to equine mesenchymal stem cells. This study provides the first demonstration of the potential of iPSCs in equine biomedicine. The ability to derive iPSC cells capable of direct differentiation in vitro opens the way for new and exciting applications in equine regenerative medicine.