Cells in culture undergo replicative senescence. In this study, we analyzed functional, genetic and epigenetic sequels of long-term culture in human mesenchymal stem cells (MSC). Already within early passages the fibroblastoid colonyforming unit (CFU-f) frequency and the differentiation potential of MSC declined significantly. Relevant chromosomal aberrations were not detected by karyotyping and SNP-microarrays. Subsequently, we have compared DNA-methylation profiles with the Infinium HumanMethylation27 Bead Array and the profiles differed markedly in MSC derived from adipose tissue and bone marrow. Notably, all MSC revealed highly consistent senescence-associated modifications at specific CpG sites. These DNA-methylation changes correlated with histone marks of previously published data sets, such as trimethylation of H3K9, H3K27 and EZH2 targets. Taken together, culture expansion of MSC has profound functional implications - these are hardly reflected by genomic instability but they are associated with highly reproducible DNA-methylation changes which correlate with repressive histone marks. Therefore replicative senescence seems to be epigenetically controlled.

Supplemental Digital Content is Available in the Text. Human sodium channel Na V 1.7 in induced pluripotent stem cell–derived sensory neurons sets the action potential threshold but does not support subthreshold depolarizations.

Human induced pluripotent stem (iPS) cells can differentiate into cells of all three germ layers, including hematopoietic stem cells and their progeny. Interferon regulatory factor 8 (IRF8) is a transcription factor, which acts in hematopoiesis as lineage determining factor for myeloid cells, including dendritic cells (DC). Autosomal recessive or dominant IRF8 mutations occurring in patients cause severe monocytic and DC immunodeficiency. To study IRF8 in human hematopoiesis we generated human IRF82/2 iPS cells and IRF82/2 embryonic stem (ES) cells using RNA guided CRISPR/Cas9n genome editing. Upon induction of hematopoietic differentiation, we demonstrate that IRF8 is dispensable for iPS cell and ES cell differentiation into hemogenic endothelium and for endothelial-to-hematopoietic transition, and thus development of hematopoietic progenitors. We differentiated iPS cell and ES cell derived progenitors into CD1411 cross-presenting cDC1 and CD1c1 classical cDC2 and CD3031 plasmacytoid DC (pDC). We found that IRF8 deficiency compromised cDC1 and pDC development, while cDC2 development was largely unaffected. Additionally, in an unrestricted differentiation regimen, IRF82/2 iPS cells and ES cells exhibited a clear bias toward granulocytes at the expense of monocytes. IRF82/2 DC showed reduced MHC class II expression and were impaired in cytokine responses, migration, and antigen presentation. Taken together, we engineered a human IRF8 knockout model that allows studying molecular mechanisms of human immunodeficiencies in vitro, including the pathophysiology of IRF8 deficient DC. STEM CELLS 2017;35:898-908 SIGNIFICANCE STATEMENTPluripotent stem cells and CRISPR/Cas9n technology are particularly well suited for engineering cells to study the impact of specific factors on cell development, including antigen presenting dendritic cells (DC). So far, DC research was limited to primary cell samples obtained for example, from mice or men. In the mouse system, genetically modified DC are readily obtained by using transgenic, knockout, and knockin mice. In the human system studies with mutated DC relied on patients harboring specific mutations and there was a paucity of techniques for genetic engineering directly in human cells. Induced pluripotent stem (iPS) cell and CRISPR/ Cas9n technology now allow to overcome these limitations. Here, we generated interferon regulatory factor 8 (IRF8) knockout human iPS cells and ES cells, and IRF82/2 DC derived thereof. We show that IRF82/2 cells recapitulate the phenotype of individuals with an IRF8 loss of function mutation. Our IRF82/2 iPS cells and ES cells provide a platform to study IRF8 deficient DC subset specification and DC function independent of donor variation or availability. In summary, our IRF82/2 iPS cells and ES cells represent a valid and powerful model to elucidate mechanisms of human DC development and functional diversity.

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