Mammalian sirtuins are involved in the control of metabolism and life-span regulation. Here, we link the mitochondrial sirtuin SIRT4 with cellular senescence, skin aging, and mitochondrial dysfunction. SIRT4 expression significantly increased in human dermal fibroblasts undergoing replicative or stress-induced senescence triggered by UVB or gamma-irradiation. In-vivo, SIRT4 mRNA levels were upregulated in photoaged vs. non-photoaged human skin. Interestingly, in all models of cellular senescence and in photoaged skin, upregulation of SIRT4 expression was associated with decreased levels of miR-15b. The latter was causally linked to increased SIRT4 expression because miR-15b targets a functional binding site in the SIRT4 gene and transfection of oligonucleotides mimicking miR-15b function prevented SIRT4 upregulation in senescent cells. Importantly, increased SIRT4 negatively impacted on mitochondrial functions and contributed to the development of a senescent phenotype. Accordingly, we observed that inhibition of miR-15b, in a SIRT4-dependent manner, increased generation of mitochondrial reactive oxygen species, decreased mitochondrial membrane potential, and modulated mRNA levels of nuclear encoded mitochondrial genes and components of the senescence-associated secretory phenotype (SASP). Thus, miR-15b is a negative regulator of stress-induced SIRT4 expression thereby counteracting senescence associated mitochondrial dysfunction and regulating the SASP and possibly organ aging, such as photoaging of human skin.

Nonalcoholic fatty liver disease (NAFLD/steatosis) is a metabolic disease characterized by the incorporation of fat into hepatocytes. In this study, we developed an in vitro model for NAFLD based on hepatocyte-like cells (HLCs) differentiated from human pluripotent stem cells. We induced fat storage in these HLCs and detected major expression changes of metabolism-associated genes, as well as an overall reduction of liver-related microRNAs. We observed an upregulation of the lipid droplet coating protein Perilipin 2 (PLIN2), as well as of numerous genes of the peroxisome proliferator-activated receptor (PPAR) pathway, which constitutes a regulatory hub for metabolic processes. Interference with PLIN2 and PPARα resulted in major alterations in gene expression, especially affecting lipid, glucose, and purine metabolism. Our model recapitulates many metabolic changes that are characteristic for NAFLD. It permits the dissection of disease-promoting molecular pathways and allows us to investigate the influences of distinct genetic backgrounds on disease progression.

Human urine is a non-invasive source of renal stem cells with regeneration potential. Urine-derived renal progenitor cells were isolated from 10 individuals of both genders and distinct ages. These renal progenitors express pluripotency-associated proteins-TRA-1-60, TRA-1-81, SSEA4, C-KIT and CD133, as well as the renal stem cell markers-SIX2, CITED1, WT1, CD24 and CD106. The transcriptomes of all SIX2 + renal progenitors clustered together, and distinct from the human kidney biopsy-derived epithelial proximal cells (hRepcs). Stimulation of the urine-derived renal progenitor cells (UdRpcs) with the GSK3β-inhibitor (CHIR99021) induced differentiation. Transcriptome and KEGG pathway analysis revealed upregulation of Wnt-associated genes-AXIN2, JUN and NKD1. protein interaction network identified JUN-a downstream target of the WNT pathway in association with STAT3, ATF2 and MAPK1 as a putative negative regulator of self-renewal. furthermore, like pluripotent stem cells, self-renewal is maintained by FGF2-driven TGFβ-SMAD2/3 pathway. The urine-derived renal progenitor cells and the data presented should lay the foundation for studying nephrogenesis in human. According to the International Society of Nephrology, more than 850 million people worldwide are afflicted with kidney diseases 1 , which raises the quest for alternative therapies to overcome the limitations associated with current treatments including transplantation and dialysis. One of the most promising options is the utilization of renal stem cells for treating of kidney diseases, disease modelling, and drug development 2,3. Renal stem/ progenitor cells are self-renewing, multipotent cells with the ability to generate various cell types of the kidney to maintain renal function 4. These progenitors are in abundance during fetal kidney development in which the renal progenitor surface marker CD24 and stem cell self-renewal marker CD133 cells are required for primordial nephrogenesis 5,6. However, in adults, CD24, CD133 (Prominin-1) and vascular cell adhesion molecule 1 (CD106)-positive renal progenitors are present in renal tubules and capsules 7. Two progenitor cell populations can be distinguished based on the expression of CD106. For instance, CD24 + CD133 + CD106 − progenitors are present in proximal tubules whereas CD24 + CD133 + CD106 + cells are localized in the Bowman's capsule. The latter can differentiate into a variety of cell types of renal tissue such as podocytes and tubular epithelial cells 4-7. Several groups have identified urine as a non-invasive and repetitive source of renal progenitor cells 8,9. It has been estimated that each day approximately 2,000 to 7,000 cells composed of differentiated epithelial cells, bi-potential epithelial cells (transitional cells), multipotent mesenchymal stem cells, and glomerular parietal cells are flushed out from the renal tubular network and the upper urinary tract into urine 10-12. A subpopulation of these urine-derived cells are renal stem/progenitor cells which express master renal markers such as Sine...

The clonal distribution and stable expression of killer cell Ig-like receptor (KIR) genes is epigenetically regulated. To assess the epigenetic changes that occur during hemopoietic development we examined DNA methylation and chromatin structure of the KIR locus in early hemopoietic progenitor cells and major lymphocyte lineages. In hemopoietic progenitor cells, KIR genes exhibited the major hallmarks of epigenetic repression, which are dense DNA methylation, inaccessibility of chromatin to Micrococcus nuclease digest, and a repressive histone signature, characterized by strong H3K9 dimethylation and reduced H4K8 acetylation. In contrast, KIR genes of NK cells showed active histone signatures characterized by absence of H3K9 dimethylation and presence of H4K8 acetylation. Histone modifications correlated well with the competence of different lymphocyte lineages to express KIR; whereas H4K8 acetylation was high in NK and CD8+ T cells, it was almost absent in CD4+ T cells and B cells and, in the latter case, replaced by H3K9 dimethylation. In KIR-competent lineages, active histone signatures were also observed in silent KIR genes and in this case found in combination with dense DNA methylation of the promoter and nearby regions. The study suggests a two-step model of epigenetic regulation in which lineage-specific acquisition of euchromatic histone marks is a prerequisite for subsequent gene-specific DNA demethylation and expression of KIR genes.

BackgroundEstablished therapies for managing kidney dysfunction such as kidney dialysis and transplantation are limited due to the shortage of compatible donated organs and high costs. Stem cell-based therapies are currently under investigation as an alternative treatment option. As amniotic fluid is composed of fetal urine harboring mesenchymal stem cells (AF-MSCs), we hypothesized that third-trimester amniotic fluid could be a novel source of renal progenitor and differentiated cells.MethodsHuman third-trimester amniotic fluid cells (AFCs) were isolated and cultured in distinct media. These cells were characterized as renal progenitor cells with respect to cell morphology, cell surface marker expression, transcriptome and differentiation into chondrocytes, osteoblasts and adipocytes. To test for renal function, a comparative albumin endocytosis assay was performed using AF-MSCs and commercially available renal cells derived from kidney biopsies. Comparative transcriptome analyses of first, second and third trimester-derived AF-MSCs were conducted to monitor expression of renal-related genes.ResultsRegardless of the media used, AFCs showed expression of pluripotency-associated markers such as SSEA4, TRA-1-60, TRA-1-81 and C-Kit. They also express the mesenchymal marker Vimentin. Immunophenotyping confirmed that third-trimester AFCs are bona fide MSCs. AF-MSCs expressed the master renal progenitor markers SIX2 and CITED1, in addition to typical renal proteins such as PODXL, LHX1, BRN1 and PAX8. Albumin endocytosis assays demonstrated the functionality of AF-MSCs as renal cells. Additionally, upregulated expression of BMP7 and downregulation of WT1, CD133, SIX2 and C-Kit were observed upon activation of WNT signaling by treatment with the GSK-3 inhibitor CHIR99201. Transcriptome analysis and semiquantitative PCR revealed increasing expression levels of renal-specific genes (e.g., SALL1, HNF4B, SIX2) with gestational time. Moreover, AF-MSCs shared more genes with human kidney cells than with native MSCs and gene ontology terms revealed involvement of biological processes associated with kidney morphogenesis.ConclusionsThird-trimester amniotic fluid contains AF-MSCs of renal origin and this novel source of kidney progenitors may have enormous future potentials for disease modeling, renal repair and drug screening.Electronic supplementary materialThe online version of this article (10.1186/s13287-018-0864-7) contains supplementary material, which is available to authorized users.