Porcine Kidney Organoids Derived from Naïve-like Embryonic Stem Cells.

The scarcity of donor kidneys greatly impacts the survival of patients with end-stage renal failure. Pigs are increasingly becoming potential organ donors but are limited by immunological rejection. Based on the human kidney organoid already established with the CHIR99021 and FGF9 induction strategy, we generated porcine kidney organoids from porcine naïve-like ESCs (nESCs). The derived porcine organoids had a tubule-like constructure and matrix components. The porcine organoids expressed renal markers including AQP1 (proximal tubule), WT1 and PODO (podocyte), and CD31 (vascular endothelial cells). These results imply that the organoids had developed the majority of the renal cell types and structures, including glomeruli and proximal tubules. The porcine organoids were also identified to have a dextran absorptive function. Importantly, porcine organoids have a certain abundance of vascular endothelial cells, which are the basis for investigating immune rejection. The derived porcine organoids might serve as materials for immunosuppressor screening for xenotransplantation.

Species origin of exogenous transcription factors affects the activation of endogenous pluripotency markers and signaling pathways of porcine induced pluripotent stem cells.

The incomplete silencing of exogenous transcription factors (TFs) and the lack of endogenous counterpart activation hampers the application of porcine induced pluripotent stem cells (piPSCs). We used porcine, bovine and murine TFs to reprogram porcine fetal fibroblasts. Porcine TFs-derived piPSCs (ppiPSCs) showed the highest levels of endogenous pluripotency markers activation, were able to differentiate into three germ layers and primordial germ cell-like cells (PGCLCs) and integrated into neural ectoderm of E7.5 mouse embryos in vitro. The bovine TFs derived piPSCs (bpiPSCs) expressed endogenous pluripotency markers higher than murine TFs derived piPSCs (mpiPSCs), but both had limited differentiation ability in vitro and depended on continuous expression of exogenous TFs for the maintenance. RNA sequencing confirmed ppiPSCs had distinct global transcriptional profiling, upregulated Hippo, PI3K-Akt, MAPK and relevant pluripotency signaling pathways as porcine blastocyst inner cell mass and expressed PGC early related genes. In addition, a positive and a negative correlation between exogenous and endogenous TFs' expression level were observed in ppiPSCs and bpiPSCs lines, respectively. The TFs' protein structures in pig were more similar to cattle than to mouse. In conclusion, the species affinity of the exogenous TFs is a key element, and the own species origin of TFs is optimal for iPSCs generation and application.

Development of a Lung Vacancy Mouse Model through CRISPR/Cas9-Mediated Deletion of Thyroid Transcription Factor 1 Exon 2.

A developmental niche vacancy in host embryos is necessary for stem cell complementation-based organ regeneration (SCOG). Thyroid transcription factor 1 (TTF-1) is a tissue-specific transcription factor that regulates the embryonic development and differentiation of the thyroid and, more importantly, lungs; thus, it has been considered as a master gene to knockout in order to develop a lung vacancy host. TTF-1 knockout mice were originally produced by inserting a stop codon in Exon 3 of the gene (E3stop) through embryonic stem cell-based homologous recombination. The main problems of utilizing E3stop host embryos for lung SCOG are that these animals all have a tracheoesophageal fistula (TEF), which cannot be corrected by donor stem cells, and most of them have monolateral sac-like lungs. To improve the mouse model towards achieving SCOG-based lung generation, in this project, we used the CRISPR/Cas9 tool to remove Exon 2 of the gene by zygote microinjection and successfully produced TTF-1 knockout (E2del) mice. Similar to E3stop, E2del mice are birth-lethal due to retarded lung development with sac-like lungs and only a rudimentary bronchial tree, increased basal cells but without alveolar type II cells and blood vessels, and abnormal thyroid development. Unlike E3stop, 57% of the E2del embryos presented type I tracheal agenesis (TA, a kind of human congenital malformation) with a shortened trachea and clear separations of the trachea and esophagus, while the remaining 43% had TEF. Furthermore, all the E2del mice had bilateral sac-like lungs. Both TA and bilateral sac-like lungs are preferred in SCOG. Our work presents a new strategy for producing SCOG host embryos that may be useful for lung regeneration.