Human adipose-derived mesenchymal stem cells: serial passaging, doubling time and cell senescence

Stem cell senescence. Effects of REAC technology on telomerase-independent and telomerase-dependent pathways

Decline in the gene expression of senescence repressor Bmi1, and telomerase, together with telomere shortening, underlay senescence of stem cells cultured for multiple passages. Here, we investigated whether the impairment of senescence preventing mechanisms can be efficiently counteracted by exposure of human adipose-derived stem cells to radio electric asymmetrically conveyed fields by an innovative technology, named Radio Electric Asymmetric Conveyer (REAC). Due to REAC exposure, the number of stem cells positively stained for senescence associated β-galactosidase was significantly reduced along multiple culturing passages. After a 90-day culture, REAC-treated cells exhibited significantly higher transcription of Bmi1 and enhanced expression of other stem cell pluripotency genes and related proteins, compared to unexposed cells. Transcription of the catalytic telomerase subunit (TERT) was also increased in REAC-treated cells at all passages. Moreover, while telomere shortening occurred at early passages in both REAC-treated and untreated cells, a significant rescue of telomere length could be observed at late passages only in REAC-exposed cells. Thus, REAC-asymmetrically conveyed radio electric fields acted on a gene and protein expression program of both telomerase-independent and telomerase-dependent patterning to optimize stem cell ability to cope with senescence progression.

A p38 MAPK-mediated alteration of COX-2/PGE2 regulates immunomodulatory properties in human mesenchymal stem cell aging

Because human mesenchymal stem cells (hMSC) have profound immunomodulatory effects, many attempts have been made to use hMSCs in preclinical and clinical trials. For hMSCs to be used in therapy, a large population of hMSCs must be generated by in vitro expansion. However, the immunomodulatory changes following the in vitro expansion of hMSCs have not been elucidated. In this study, we evaluated the effect of replicative senescence on the immunomodulatory ability of hMSCs in vitro and in vivo. Late-passage hMSCs showed impaired suppressive effect on mitogen-induced mononuclear cell proliferation. Strikingly, late-passage hMSCs had a significantly compromised protective effect against mouse experimental colitis, which was confirmed by gross and histologic examination. Among the anti-inflammatory cytokines, the production of prostaglandin E₂ (PGE₂) and the expression of its primary enzyme, cyclooxygenase-2 (COX-2), were profoundly increased by pre-stimulation with interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α), and this response was significantly decreased with consecutive passages. We demonstrated that the impaired phosphorylation activity of p38 MAP kinase (p38 MAPK) in late-passage hMSCs led to a compromised immunomodulatory ability through the regulation of COX-2. In conclusion, our data indicate that the immunomodulatory ability of hMSCs gradually declines with consecutive passages via a p38-mediated alteration of COX-2 and PGE₂ levels.

Immortalization of human adipose-derived stromal cells: production of cell lines with high growth rate, mesenchymal marker expression and capability to secrete high levels of angiogenic factors

INTRODUCTION

Human adipose-derived stromal cells (hASCs), due to their relative feasibility of isolation and ability to secrete large amounts of angiogenic factors, are being evaluated for regenerative medicine. However, their limited culture life span may represent an obstacle for both preclinical investigation and therapeutic use. To overcome this problem, hASCs immortalization was performed in order to obtain cells with in vitro prolonged life span but still maintain their mesenchymal marker expression and ability to secrete angiogenic factors.

METHODS

hASCs were transduced with the human telomerase reverse transcriptase (hTERT) gene alone or in combination with either SV-40 or HPV E6/E7 genes. Mesenchymal marker expression on immortalized hASCs lines was confirmed by flow cytometry (FC), differentiation potential was evaluated by immunocytochemistry and ELISA kits were used for evaluation of angiogenic factors. Green fluorescent protein (GFP) gene transduction was used to obtain fluorescent cells.

RESULTS

We found that hTERT alone failed to immortalize hASCs (hASCs-T), while hTERT/SV40 (hASCs-TS) or hTERT/HPV E6/E7 (hASCs-TE) co-transductions successfully immortalized cells. Both hASCs-TS and hASCs-TE were cultured for up to one year with a population doubling level (PDL) up to 100. Comparative studies between parental not transduced (hASCs-M) and immortalized cell lines showed that both hASCs-TS and hASCs-TE maintained a mesenchymal phenotypic profile, whereas differentiation properties were reduced particularly in hASCs-TS. Interestingly, hASCs-TS and hASCs-TE showed a capability to secrete significant amount of HGF and VEGF. Furthermore, hASCs-TS and hASCs-TE did not show tumorigenic properties in vitro although some chromosomal aberrations were detected. Finally, hASCs-TS and hASCs-TE lines were stably fluorescent upon transduction with the GFP gene.

CONCLUSIONS

Here we demonstrated, for the first time, that hASCs, upon immortalization, maintain a strong capacity to secrete potent angiogenic molecules. By combining hASCs immortalization and their paracrine characteristics, we have developed a "hybridoma-like model" of hASCs that could have potential applications for discovering and producing molecules to use in regenerative medicine (process scale-up).

Insights from a chimpanzee adipose stromal cell population: opportunities for adult stem cells to expand primate functional genomics

Comparisons between humans and chimpanzees are essential for understanding traits unique to each species. However, linking important phenotypic differences to underlying molecular changes is often challenging. The ability to generate, differentiate, and profile adult stem cells provides a powerful but underutilized opportunity to investigate the molecular basis for trait differences between species within specific cell types and in a controlled environment. Here, we characterize adipose stromal cells (ASCs) from Clint, the chimpanzee whose genome was first sequenced. Using imaging and RNA-Seq, we compare the chimpanzee ASCs with three comparable human cell lines. Consistent with previous studies on ASCs in humans, the chimpanzee cells have fibroblast-like morphology and express genes encoding components of the extracellular matrix at high levels. Differentially expressed genes are enriched for distinct functional classes between species: immunity and protein processing are higher in chimpanzees, whereas cell cycle and DNA processing are higher in humans. Although hesitant to draw definitive conclusions from these data given the limited sample size, we wish to stress the opportunities that adult stem cells offer for studying primate evolution. In particular, adult stem cells provide a powerful means to investigate the profound disease susceptibilities unique to humans and a promising tool for conservation efforts with nonhuman primates. By allowing for experimental perturbations in relevant cell types, adult stem cells promise to complement classic comparative primate genomics based on in vivo sampling.

Valproic acid promotes differentiation of hepatocyte-like cells from whole human umbilical cord-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are mesoderm-derived cells that are considered a good source of somatic cells for treatment of many degenerative diseases. Previous studies have reported the differentiation of mesodermal MSCs into endodermal and ectodermal cell types beyond their embryonic lineages, including hepatocytes and neurons. However, the molecular pathways responsible for the direct or indirect cell type conversion and the functional ability of the differentiated cells remain unclear and need further research. In the present study, we demonstrated that valproic acid (VPA), which is a histone deacetylase inhibitor, induced an increase in the expression of endodermal genes including CXCR4, SOX17, FOXA1, FOXA2, GSC, c-MET, EOMES, and HNF-1β in human umbilical cord derived MSCs (hUCMSCs). In addition, we found that VPA is able to increase these endodermal genes in hUCMSCs by activating signal transduction of AKT and ERK. VPA pretreatment increased hepatic differentiation at the expense of adipogenic differentiation. The effects of VPA on modulating hUCMSCs fate were diminished by blocking AKT and ERK activation using specific signaling inhibitors. Together, our results suggest that VPA contributes to the lineage conversion of hUCMSCs to hepatic cell fate by upregulating the expression of endodermal genes through AKT and ERK activation.

Patterned carbon nanotubes as a new three-dimensional scaffold for mesenchymal stem cells

We investigated the cellular adhesive features of mesenchymal stem cells (MSC) on non-coated and collagen coated patterned and vertically aligned carbon nanotube (CNT) structures mimicking the natural extra cellular matrix (ECM). Patterning was achieved using the elasto-capillary induced by water treatment on the CNT arrays. After confirmation with specific markers both at transcript and protein levels, MSCs from different passages were seeded on either collagen coated or non-coated patterned CNTs. Adhesion and growth of MSCs on the patterned CNT arrays were examined using scanning electron microscopy image analysis and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-tetrazolium bromide (MTT) assays. The highest MSC count was observed on the non-coated patterned CNTs at passage zero, while decreasing numbers of MSCs were found at the later passages. Similarly, MTT assay results also revealed a decrease in the viability of the MSCs for the later passages. Overall, the cell count and viability experiments indicated that MSCs were able to better attach to non-coated patterned CNTs compared to those coated with collagen. Therefore, the patterned CNT surfaces can be potentially used as a scaffold mimicking the ECM environment for MSC growth which presents an alternative approach to MSC-based transplantation therapy applications.

Potential for neural differentiation of mesenchymal stem cells

Adult human stem cells have gained progressive interest as a promising source of autologous cells to be used as therapeutic vehicles. Particularly, mesenchymal stem cells (MSCs) represent a great tool in regenerative medicine because of their ability to differentiate into a variety of specialized cells. Among adult tissues in which MSCs are resident, adipose tissue has shown clear advantages over other sources of MSCs (ease of surgical access, availability, and isolation), making adipose tissue the ideal large-scale source for research on clinical applications. Stem cells derived from the adipose tissue (adipose-derived stem cells = ADSCs) possess a great and unique regenerative potential: they are self-renewing and can differentiate along several mesenchymal tissue lineages (adipocytes, osteoblasts, myocytes, chondrocytes, endothelial cells, and cardiomyocytes), among which neuronal-like cells gained particular interest. In view of the promising clinical applications in tissue regeneration, research has been conducted towards the creation of a successful protocol for achieving cells with a well-defined neural phenotype from adipose tissue. The promising results obtained open new scenarios for innovative approaches for a cell-based treatment of neurological degenerative disorders.