Induced pluripotent stem cells from homozygous Runx2-deficient mice show poor response to vitamin D during osteoblastic differentiation.

Cleidocranial dysplasia (CCD) is a hereditary disorder associated with skeletal dysplasia and dental abnormalities. CCD arises from heterozygous loss of function mutations in the Runt-related transcription factor 2 (RUNX2) gene. Osteoporosis is often observed in CCD patients and conventional vitamin D supplementation is recommended. However, sufficient evidences have not been presented yet. This study investigated the role of RUNX2 in osteoblastic differentiation and sought to identify potential target genes for the treatment of osteoporosis associated with CCD, using induced pluripotent stem cell (iPSC) technology. We successfully established Runx2-/-, Runx2+/- and wild-type miPSCs from litter-matched mice and found poor Vdr expression in Runx2-/-cells. Significant down-regulation of osteoblastic differentiation in Runx2-/- miPSCs was observed. Gene expression array revealed unexpected results such as remarkable increase of Rankl expression and decrease of Vdr in Runx2-/- cells. Insufficient response to vitamin D in Runx2-/- cells was also observed. Our results suggest that RUNX2 functions as a regulator of Rankl and Vdr and thereby controls bone density. These findings also suggest that conventional vitamin D supplementation may not be as effective as previously expected, in the treatment of osteoporosis associated with CCD, and that inhibiting RANKL function might be worth considering as an alternative treatment strategy.

Efficient Reprogramming of Canine Peripheral Blood Mononuclear Cells into Induced Pluripotent Stem Cells.

Forced coexpression of the transcription factors Oct3/4, Klf4, Sox2, and c-Myc reprograms somatic cells into pluripotent stem cells (PSCs). Such induced PSCs (iPSCs) can generate any cell type of the adult body or indefinitely proliferate without losing their potential. Accordingly, iPSCs can serve as an unlimited cell source for the development of various disease models and regenerative therapies for animals and humans. Although canine peripheral blood mononuclear cells (PBMCs) can be easily obtained, they have a very low iPSC reprogramming efficiency. In this study, we determined the reprogramming efficiency of canine PBMCs under several conditions involving three types of media supplemented with small-molecule compounds. We found that canine iPSCs (ciPSCs) could be efficiently generated from PBMCs using N2B27 medium supplemented with leukemia inhibitory factor (LIF), basic fibroblast growth factor (bFGF), and a small-molecule cocktail (Y-27632, PD0325901, CHIR99021, A-83-01, Forskolin, and l-ascorbic acid). We generated five ciPSC lines that could be maintained in StemFit® medium supplemented with LIF. The SeVdp(KOSM)302L vectors were appropriately silenced in four ciPSC lines. Of the two lines characterized, both were positive for alkaline phosphatase activity and expressed pluripotency markers, including the Oct3/4, Sox2, and Nanog transcripts, as well as the octamer-binding transcription factor (OCT) 3/4 and NANOG proteins, and the SSEA-1 carbohydrate antigen. The ciPSCs could form embryoid bodies and differentiate into the three germ layers, as indicated by marker gene and protein expression. Furthermore, one ciPSC line formed teratomas comprising several tissues from every germ layer. Our ciPSC lines maintained a normal karyotype even after multiple passages. Moreover, our new reprogramming method was able to generate ciPSCs from multiple donor PBMCs. In conclusion, we developed an easy and efficient strategy for the generation of footprint-free ciPSCs from PBMCs. We believe that this strategy can be useful for disease modeling and regenerative medicine in the veterinary field.

Template Activating Factor-I α Regulates Retroviral Silencing during Reprogramming.

Reprogramming somatic cells to induced pluripotent stem cells (iPSCs) is accompanied by dramatic changes in epigenetic programs, including silencing of endogenous and exogenous retroviruses. Here, we utilized replication-defective and persistent Sendai virus (SeVdp)-based vectors to monitor retroviral silencing during reprogramming. We observed that retroviral silencing occurred at an early reprogramming stage without a requirement for KLF4 or the YY1-binding site in the retroviral genome. Insertional chromatin immunoprecipitation (iChIP) enabled us to isolate factors assembled on the silenced provirus, including components of inhibitor of histone acetyltransferase (INHAT), which includes the SET/TAF-I oncoprotein. Knockdown of SET/TAF-I in mouse embryonic fibroblasts (MEFs) diminished retroviral silencing during reprogramming, and overexpression of template activating factor-I α (TAF-Iα), a SET/TAF-I isoform predominant in embryonic stem cells (ESCs), reinforced retroviral silencing by an SeVdp-based vector that is otherwise defective in retroviral silencing. Our results indicate an important role for TAF-Iα in retroviral silencing during reprogramming.