The Porcine Albumin Quantitation Set (Bethyl Laboratories) was used for measuring Albumin secretion, according to the manufacturers instructions with minor modifications. Dil-AcLDL uptake, storage of lipids and glycogen and activity of cytochrome P450 enzymes CYP1A2 and CYP2C33 (CYP2C9 in humans). Moreover, we show that markers N-Carbamoyl-DL-aspartic acid of mature hepatocytes are highly expressed in 3TF-piHeps, while fibroblastic markers are reduced. We envision piHeps as useful cell sources for future studies on drug metabolism and toxicity as well as in vitro models for investigation of pig-to-human infectious diseases. and and different combinations of family of transcription factors, known to be the major hepatic pioneer TFs, due to their ability of binding to nucleosomal DNA and opening the chromatin for further genetic modifications during liver development22. The generation of human iHeps (hiHeps) was described more recently23,24, and hiHeps were shown to be positive for albumin and -fetoprotein (AFP), and displayed hepatic functions such as metabolism of drugs, urea production, glycogen and cholesterol storage23,24. Until date, the conversion of porcine somatic cells into pig iHeps (piHeps) has not yet N-Carbamoyl-DL-aspartic acid been reported. Here, we show for the first time the successful in vitro generation of piHep cells from primary adult fibroblasts via transduction of human transcription factors. To this end, we employed a three-phase screening of 12 different hepatic TFs for efficient generation of piHeps. We show that overexpression of a unique set of TFs, and in porcine kidney fibroblasts (PKFs) results in cells with a morphology very similar to porcine primary hepatocytes (PPH) and several hallmarks of hepatic functions, such as low density protein uptake, Oil Red O and Periodic acid-Schiff (PAS) stainings indicating lipid and glycogen storage, respectively, thereby recapitulating features of porcine hepatocytes. Moreover, piHeps can metabolize drugs such as -Naphthoflavone and Ibuprofen, thus demonstrating CYP450 enzyme activity, and express high levels of drug transporters, such as and Alpha-1-antitrypsinTransthyretinand Alpha-fetoproteinand from D12 to D15, but no further increase was observed on D18 (Supplementary Fig. S1b). Therefore, the time point D15 N-Carbamoyl-DL-aspartic acid was chosen for analysis of potentially directly reprogrammed hepatic-like cells. Taken together, a MOI of 5 per lentiviral vector and sample harvesting at D15 were chosen as most suitable experimental parameters for this?direct hepatic reprogramming method and were used in all subsequent experiments. Open in a separate window Figure 1 MOI determination for hepatic conversion of PKFs. (A) Schematic drawing?of lentivirus vector design and cell culture protocol for directed hepatic conversion. (B) Albumin secretion quantification and (C) hepatic markers N-Carbamoyl-DL-aspartic acid expression levels of cells directly reprogrammed with different MOIs per lentiviral vector of all 12?TFs, compared to Neg-Ctrl. All data were analyzed using two-way ANOVA, with Bonferronis post-test, except for gene, that was converted to mixed effects with Tukeys multiple comparison post-test due to be missing one value. Significance from n?=?3 independent values is displayed as *p? ?0.05; ****p??0.0001. Three-phase transcription factor screening While a set of 12 TFs was clearly able to push porcine fibroblasts towards cells which display typical hepatic features not present LUC7L2 antibody in mock treated cells, it was possible that some of those TFs were more detrimental to the process than others, or that some factors were even impeding hepatic conversion. Therefore, a systematic screening of all 12 candidate TFs was performed to identify the most functional set of TFs for converting PKFs into hepatocyte-like cells. Initially, for the first phase of TF screening, a similar approach as the one described for iPSCs27 and mouse iHeps generation20,21 was employed, omitting one TF at a time, and using only the remaining TFs (12-1). In cells treated with all factors except for or low levels of albumin secretion and expression as well as low expression were observed (Fig.?2). Notably, omission of and increased expression of hepatic markers, suggesting that they might be non-contributory to or possibly interfering with piHep generation. Surprisingly, omission of and did not change expression of hepatic markers. Moreover, the omission of did not reduce albumin secretion.