How are stem cells affected by their surrounding?
This simple question is what Dr. Xin Chen, associate professor of biology at Johns Hopkins University’s Krieger School of Arts and Sciences has, alongside six co-authors from her lab, sought to answer in a new manuscript published this week in Cell Reports.
By studying the aminopeptidase Slamdance (Sda) acts in the Drosophila testicular niche, the authors discovered that sda acts to both maintain germline stem cells (GSCs) and regulate progenitor germ cell dedifferentiation.
Earlier, the authors had reported that the role of sda is significant in the niche: loss-of-function in sda leads to abnormalities in the testis niche, including deterioration of the niche architecture and loss of stem cells.
This makes it critical, as a niche-specific factor, for both germline and cyst stem cell maintenance.
However, questions arise about how the niche itself is regulated and, moreover, how this knowledge can be used to direct stem cell fate.
Ultimately, the authors do concede that further work is necessary to elucidate such mechanisms which might provide some clinical efficacy.
The full paper can be accessed here.
While conversion of human fibroblasts into neuronal is not new, traditional methods involve genetic modifications to induce transcription factors that effect the conversion.
Now, in a new paper published in Cell Stem Cell, a group of researchers from the Chinese Academy of Sciences reports of a much more straightforward method of converting fibroblasts into neuronal cells with the use of small molecules only.
The procedure involves seven different small molecules which were applied to the cells for one week, followed by a three-week incubation period with three of the reprogramming molecules.
Two of these molecules are forskolin (a cyclic AMP promoter) and CHIR99021 (a glycogen synthase kinase 3 beta inhibitor). The exact mechanism is not known, though the authors reported that the small molecules acted on genes that were known to direct neuronal fate by erasing fibroblast-specific gene expression of the initial cells.
Starting from human aortal fibroblasts, the resultant cells resemble hPSC-derived neurons with respect to morphology, gene expression profiles, and electrophysiological properties.
Apart from demonstrating neuronal conversion of normal (control) cells, the authors also demonstrated the same effect from Alzheimer patients to create neurons which exhibited features of the disease including elevated Ab42 levels and higher total and phosphorylated Tau levels.
Meet Akron at Stem Cell Meeting on the Mesa
Next week, Akron Biotechnology will be attending the Stem Cell Meeting on the Mesa, organized by the Alliance for Regenerative Medicine, CIRM and the Sanford Consortium of Regenerative Medicine. The meeting runs from October 7-9 in La Jolla, CA. To meet us and talk to us, please get in touch.
While the use of stem cells in organ regeneration has resulted in a number of treatments that have shown significant clinical promise, improving cardiac function using stem cells has not yet resulted in significant clinical leaps due to low levels of engrafment following injection of stem cells into damaged heart tissue.
With the purpose of improving stem cell retention in the myocardium following transplantation, a new study by Roselle Abraham’s lab at John Hopkins School of Medicine describes the development of a new hydrogel-based bio-adhesive and biodegradable scaffold to achieve such retention.
The manuscript, titled Hyaluronic Acid-Human Blood Hydrogels for Stem Cell Transplantation and published in Biomaterials, describes the synthesis of a hydrogel scaffold from lysed blood and HA, whose carboxyl groups are functionalized with N-hydroxysuccinimide (NHS) to yield HA succinimidyl succinate (HA-NHS). These carboxyl groups in turn react with primary amines from blood and tissue to form amide bonds, resulting in hydrogels that covalently bind to transplanted tissue while entrapping stem cells and retaining them in the transplanted site.
Beside physical characterization of hydrogels, the authors also performed in vivo studies with female rats induced with myocardial infarction. Animals treated with intra-myocardially-implanted HA-blood hydrogels could survive for a few hours after transplantation, and cell encapsulation in these hydrogels greatly increased acute myocardial retention for 1 hr post-transplantation.
Once transplanted, it is believed that growth factors present in the blood, as well as extracellular matrix proteins fibronectin and vitronectin, promote cell proliferation.
Unlike intra-myocardial injections, which typically result in cell loss from the injection site, epicardial cell delivery via scaffolds allows for the transplantation of large numbers of cells which are retained in the heart. While these studies were carried out with a single cell line on one organism, the authors believe that the scaffolds could provide a same robust substrate for various cell types including mesenchymal stem cells and endothelial progenitor cells. Furthermore, high mortality rates observed are still an issue that needs investigation.
To add to this body of work, contact us to discuss custom scaffold manufacturing, growth factors and extracellular matrix proteins that can support your 3D cell culture efforts.
Despite being extensively studied as vehicles controlling cell-to-cell communication, exosomes -small vesicles secreted by all cell types and range in diameter from 30-50 nm – have not yet been reported as being involves in stem cell differentiation.
Last week, a new paper from the lab of Dr. Qiaobing Xu, assistant professor of biomedical engineering at Tufts School of Engineering, described a new paradigm for the role of exosomes in regenerative medicine by describing the utility of exosomes as inducers of differentiation of human stem cells.
In the paper, titled Neuronal Differentiation of Human Mesenchymal Stem Cells Using Exosomes Derived from Differentiating Neuronal Cells, and published in PLoS One, the authors used exosomes from PC12 cells (neuron-like progenitor cells derived from rats) and showed that they could, at various stages of their own differentiation could, in turn, cause bone marrow-derived hMSCs to become neuron-like cells.
The authors used hMSCs at passage 4, which they treated with PC12 exosomes for 1 week, which were growing in DMEM medium with the addition of bFGF.
After 7 days of culture, extracted mRNA expression of neuronal markers was analyzed by qPCR. The results demonstrated that expression of neuronal markers such as miR-221 and 222 was upregulated in the hMSC that successfully differentiated into neuronal lineages.
The table below shows miRNAs enriched in PC12 exosomes and upregulated after NGF treatment as reported in the paper. The hypothesis is that the exosomes acted be delivering miRNA into the stem cells.
While early, the study is the first example describing exosomes as a new paradigm for differentiation of stem cells, thereby setting the stage for further studies into the development of exosomal RNA that might direct differentiation.
At Akron, such differentiation of hMSCs is promoted by our integrated development of growth factors and media – from research to GMP grade – that supports the cells differentiation pathways.
While the generation of pluripotent stem cells from non-pluripotent counterparts is possible, control of differentiation is still largely poorly understood. A recent paper is hoping to change that.
Research from Dr. Timo Otonkoski’s lab at the Meilahti medical campus of the University of Helsinki uncovered a new method of modifying a gene’s behavior without making any modifications to the genome. These modifications include directing the differentiation of stem cells with small chemicals.
The work is described in the paper titled “Conditionally Stabilized dCas9 Activator for Controlling Gene Expression in Human Cell Reprogramming and Differentiation”, and published this week in Stem Cell Reports.
The method is based on CRISPR-Cas9 technology, which we described on this blog in the past. This particular approach employs transcription activator domain VP16 which, in addition to RNA regulators targeting the OCT4 promoter, induces the cell to become receptive to external factors that regulate the cells’ differentiation.
In this case, the factors are antibiotics. The authors used the antibiotics doxycycline and trimethoprim to control differentiation of human pluripotent stem cells into endodermal lineages.
Apart from stem cells, the authors demonstrated non-genetic regulation of a variety of other cells with this method. In all cases, transcriptional activation was similar, and the cells demonstrated reproducible responsiveness to chemical regulators.
While the potential therapeutic benefits of such an approach are multi-fold, the work is still preliminary and further extrapolations about clinical efficacy are still premature.
The paper can be accessed here.
The long-standing assumption that stem cell fate is not predetermined has been brought into question with a new paper published last week in Stem Cell Reports.
Titled “Computational Image Analysis Reveals Intrinsic Multigenerational Differences between Anterior and Posterior Cerebral Cortex Neural Progenitor Cells”, the manuscript describes the use of open-source software to write algorithms to analyze large numbers of images collected by time-lapse microscopy of development fates of mouse cerebral cortex neural progenitor cells. The data presented in the paper is a combination of computational analysis and real-life experimental data.
Led by professor Andrew Cohen at Drexel University in collaboration with Dr. Sally Temple, Scientific Director at the Neural Stem Cell Institute, the authors found that neural progenitor cells derived from the anterior cortex were shown to divide more slowly and ended up producing smaller clones, while progenitor cells derived from the posterior cortex divided quicker and produced larger clones.
In essence, this meant that stem cells derived from different sources followed correspondingly different developmental paths. In the context of neural stem cell development, this result demonstrated that neural cells do not develop into random structures, as both types of cells were given the same cell culture environments during analysis. Rather, there is some predetermined fate that these cells appeared to follow that was related to their source.
The programs used in this work to track and analyze cell division were developed in Dr. Cohen’s lab at the College of Engineering at Drexel University, and provided an unprecendented view into stem cell fate.
The manuscript can be accessed here.
A group of researchers from the University of California at San Francisco has developed a new method for differentiation of stem cells that relies on beams of light.
Until now, many different molecular cues that signal stem cells to differentiate into their mature form have been discovered. However, directing stem cells to differentiate on demand on a population level has been difficult. Now, a completely new method that relies on light signals to direct populations of stem cells to differentiate has been described.
The work originates from Dr. Matt Thompson’s lab at the Department of Cellular and Molecular and colleagues at the Center for Systems and Synthetic Biology at UCSF. Dr. Thompson and colleagues engineered cultured mouse embryonic stem cells which responded to a pulse of blue light to switch on the Brn2 gene, a potent neural differentiation cue. By exposing cells to pulses of Brn2, they discovered that differentiation was “Switched on” when both a certain magnitude and duration of light threshold were met. The signal was completely ignored when it was not long or not intense enough.
By fluorescently labeling transcription factor Nanog with a GFP reporter, they discovered that Nanog is in fact the key to directing differentiation by responding to Brn2 triggers.
The paper, titled “Transcription Factor Competition Allows Embryonic Stem Cells to Distinguish Authentic Signals from Noise,” was published this week in the journal Cell Systems.
While these are merely preliminary results and more work on both the in vitro and, in particular, the in vivo efficacy yet have to take place, there is the hope that such mechanisms may be applicable to other cell types and tissues.