Search

Hepatocyte-like cells differentiated from human iPS cells (human iPS-HLCs) are expected to be utilized in drug development and research. However, recent hepatic characterization of human iPS-HLCs showed that these cells resemble fetal hepatocytes rather than adult hepatocytes. Therefore, in this study, we aimed to develop a method to enhance the hepatic function of human iPS-HLCs. Because the gene expression levels of the hepatic transcription factors (activating transcription factor 5 (ATF5), CCAAT/enhancer-binding protein alpha (c/EBPα), and prospero homeobox protein 1 (PROX1)) in adult liver were significantly higher than those in human iPS-HLCs and fetal liver, we expected that the hepatic functions of human iPS-HLCs could be enhanced by adenovirus (Ad) vector-mediated ATF5, c/EBPα, and PROX1 transduction. The gene expression levels of cytochrome P450 (CYP) 2C9, 2E1, alpha-1 antitrypsin, transthyretin, Na+/taurocholate cotransporting polypeptide, and uridine diphosphate glucuronosyl transferase 1A1 and protein expression levels of CYP2C9 and CYP2E1 were upregulated by ATF5, c/EBPα, and PROX1 transduction. These results suggest that the hepatic functions of the human iPS-HLCs could be enhanced by ATF5, c/EBPα, and PROX1 transduction. Our findings would be useful for the hepatic maturation of human iPS-HLCs.

Recently, it has been reported that human hepatocyte-like cells can be generated from fibroblasts by direct reprogramming technology. However, the conversion efficiency of human induced hepatocyte-like cells (hiHeps) is not high enough. In addition, comparative analysis with the existing models of hepatocytes, such as human iPS cell-derived hepatocyte-like cells and primary human hepatocytes, has not been sufficiently carried out. In this study, we screened hepatic transcription factors for efficient direct hepatic reprogramming and compared hepatic functions between hiHeps and other existing hepatocyte models. We found that human fibroblasts were efficiently converted into hiHeps by using a combination of ATF5, PROX1, FOXA2, FOXA3, and HNF4A (albumin+/alpha-1 antitrypsin+ cells = 27%, asialoglycoprotein receptor 1+ cells = 22%). The CYP expression levels and CYP activities in hiHeps were higher than those in human iPS cell-derived hepatocyte-like cells, but lower than those in short-term (4 hr) cultured primary human hepatocytes and primary human hepatocytes collected immediately after thawing. These results suggested that functional hiHeps could be efficiently generated by ATF5, PROX1, FOXA2, FOXA3, and HNF4A transduction. We believe that hiHeps generated by our method will be useful for the drug-discovery activities such as hepatotoxicity screening and drug metabolism tests.

In this paper, stability of a two-wheeled inverted pendulum vehicle was evaluated using rider–vehicle modeling, electromyography of leg’s muscle of rider, and subjective evaluation. A rider and the vehicle are synthetically modeled as a series type double inverted pendulum. Utilizing auto-regressive exogenous (ARX) model methods, correlative relations were found between control gains and stability of the vehicle that achieves better ride comfort. The experimental results show that the higher the control gains, the smaller the activities of leg’s muscles. However, according to subjective evaluation of ride comfort, higher gains did not always achieve better ride comfort. Moreover, the rider-vehicle model has no unstable poles, even when the vehicle model has an unstable pole. The poles of the rider-vehicle model had tendency to have bigger negative real numbers, which suggests stability of the vehicle can be evaluated by the positions of the poles of the rider-vehicle model. Through identification of the rider-vehicle model, the control gains of the rider’s posture were calculated. It was found that the control gain against the rider’s posture is dominant, and the higher the control gains of vehicle, the smaller the gain against the rider’s posture. The results show stability of the vehicle can be evaluated by the control gains against the rider’s posture.Copyright © 2012 by ASME