Introduction Induced pluripotent stem cells

Introduction Induced pluripotent stem SW033291 (iPSC) have been used in an increasing number of applications since Takahashi and Yamanaka (Takahashi and Yamanaka, 2006) first demonstrated the reprogramming of adult somatic cells to produce iPSC. In combination with gene editing technology iPSC have been widely used to model human genetic diseases (Avior et al., 2016), providing a useful alternative to animal models. iPSC-derived cells are also valuable tools in drug discovery since these cells, which can carry phenotypes of a particular disease, can be used in high-throughput screening to find pharmacological compounds that may correct the phenotypes (Avior et al., 2016). Finally, iPSC have emerged as an attractive source of cells for regenerative medicine: the first clinical trial to treat macular degeneration using iPSC-derived retinal epithelium is ongoing (Kimbrel and Lanza, 2015; Reardon and Cyranoski, 2014). Improving cell reprogramming efficiency is therefore a very important focus of research. A number of studies have been centred on the identification of new reprogramming enhancers that can be used to improve reprogramming efficiency if added to the Yamanaka factors: Oct3/4, Sox2, Klf4, and Myc (OSKM). Several studies have identified factors that can improve cell reprogramming. These include several different types of molecules such as transcription factors, for example TBX3 (Han et al., 2010) and UTF1 (Zhao et al., 2008), oncogenes (e.g. Ras (Kwon et al., 2015)) and micro RNAs (for example miR-294, 295 and 291-3p (Judson et al., 2009)). However, most of these factors are not easily targetable using small molecule/pharmacological compounds, thus identification of novel reprogramming enhancers that are pharmacologically targetable would be very useful. Properties of the starting adult somatic cells are critical for the success of cell reprogramming. Several aspects are known to contribute to the reprogramming efficiency including cell type, age of cell donor and the differentiation stage of the starting cells. In addition, the proliferation rate is also essential. Actively proliferating cells are more easily reprogrammed than cells in senescence (Utikal et al., 2009). In this study we target a component of the Hippo pathway, the mammalian ste-20 like kinase 1 (Mst1), to improve cell reprogramming efficiency. The highly conserved Hippo pathway is an intrinsic regulator of organ size during development and is a major regulator of cell proliferation and survival (Yu and Guan, 2013). The core components of this pathway consist of kinases (Mst1/2 and Large tumour suppressor homologue (Lats1/2)) as well as adaptor molecules Salvador homologue (Sav1) and Mps one binder kinase activator-like 1 (MOB1) (Yu and Guan, 2013). In its active state the Hippo pathway will trigger phosphorylation of its effector Yes-associated protein (YAP) leading to cytoplasmic retention and inactivation. Thus, inhibition of core components of the Hippo pathway increases YAP activity, and hence enhances cell proliferation and reduces cell death/apoptosis (Yu and Guan, 2013). Here we use adult somatic cells (skin fibroblasts) isolated from mice with genetic ablation of the Mst1 gene (Mst1−/− mouse) to examine if inhibition of Mst1 will improve reprogramming efficiency and increase survival of the resulting iPSC.
Materials and methods
Results
Discussion The key findings of this study are: i) genetic deletion of Mst1 increases the efficiency of skin fibroblasts reprogramming to iPSC and ii) iPSC lacking Mst1 exhibits higher proliferation rates and increased survival when treated with chemical hypoxic agents. Mst1 is a core member of the Hippo signalling pathway, which is known as a major regulator of cell proliferation, apoptosis and survival (Yu and Guan, 2013). Here we demonstrated that ablation of Mst1 in iPSC resulted in the activation and nuclear translocation of YAP, the main Hippo effector, leading to an induction in proliferation and reduction of apoptosis.