The effects of microRNAs on human neural stem cell differentiation in two- and three-dimensional cultures

INTRODUCTION: Stem cells have the ability to self-renew or to differentiate into numerous cell types; however, our understanding of how to control and exploit this potential is currently limited. An emerging hypothesis is that microRNAs (miRNAs) play a central role in controlling stem cell-fate determination. Herein, we have characterized the effects of miRNAs in differentiated human neural stem cells (hNSCs) by using a cell line currently being tested in clinical trials for stroke disability (NCT01151124, Clinicaltrials.gov). METHODS: HNSCs were differentiated on 2- (2D) and 3-dimensional (3D) cultures for 1 and 3 weeks. Quantification of hNSC differentiation was measured with real-time PCR and axon outgrowth. The miRNA PCR arrays were implemented to investigate differential expression profiles in differentiated hNSCs. Evaluation of miRNA effects on hNSCs was performed by using transfection of miRNA mimics, real-time PCR, Western blot, and immunocytochemistry. RESULTS: The 3D substrate promoted enhanced hNSC differentiation coupled with a loss of cell proliferation. Differentiated hNSCs exhibited a similar miRNA profiling. However, in 3D samples, the degree and timing of regulation were significantly different in miRNA members of cluster mi-R17 and miR-96-182, and hsa-miR-302a. Overall, hNSC 3D cultures demonstrated differential regulation of miRNAs involved in hNSC stemness, cell proliferation, and differentiation. The miRNA mimic analysis of hsa-miR-146b-5p and hsa-miR-99a confirmed induction of lineage-committed progenitors. Downregulated miRNAs were more abundant; those most significantly downregulated were selected, and their putative target mRNAs analyzed with the aim of unraveling their functionality. In differentiated hNSCs, downregulated hsa-miR-96 correlated with SOX5 upregulation of gene and protein expression; similar results were obtained for hsa-miR-302a, hsa-miR-182, hsa-miR-7, hsa-miR-20a/b, and hsa-miR-17 and their target NR4A3. Moreover, SOX5 was identified as a direct target gene of hsa-miR-96, and NR43A, a direct target of hsa-miR-7 and hsa-mir-17 by luciferase reporter assays. Therefore, the regulatory role of these miRNAs may occur through targeting NR4A3 and SOX5, both reported as modulators of cell-cycle progression and axon length. CONCLUSIONS: The results provide new insight into the identification of specific miRNAs implicated in hNSC differentiation. These strategies may be exploited to optimize in vitro hNSC differentiation potential for use in preclinical studies and future clinical applications

The Development of Stem Cell-derived Exosomes as a Cell-free Regenerative Medicine

A successful strategy in regenerative medicine over the last decade has been the translation of stem cell therapy to repair diseased or damaged tissue in a wide range of indications, despite limited evidence attributing any therapeutic benefit to cell survival or differentiation. Recent findings, however, have demonstrated that the conditioned media from stem cell cultures can produce similar efficacious effects compared to those observed for cells. This has led to the stem cell paracrine hypothesis, proposing that secreted factors released from the stem cells contribute significantly to their beneficial effects. It has been well documented that stem cells have the ability to release a range of growth factors, cytokines and chemokines relevant to their function; however, these factors are released at levels too low to account for the reported therapeutic effects. Further purification of the conditioned media has since identified that not only are small molecules released by the stem cells, but so too are a large quantity of membrane-bound vesicles, including exosomes, in a functionally relevant manner. In this review, we present our current understanding and explore the evidence supporting the development of stem cell-derived exosomes as a cell-free regenerative medicine

Investigation of Content, Stoichiometry and Transfer of miRNA from Human Neural Stem Cell Line Derived Exosomes

Exosomes are small (30-100 nm) membrane vesicles secreted by a variety of cell types and only recently have emerged as a new avenue for cell-to-cell communication. They are natural shuttles of RNA and protein cargo, making them attractive as potential therapeutic delivery vehicles. MicroRNAs (miRNAs) are short non-coding RNAs which regulate biological processes and can be found in exosomes. Here we characterized the miRNA contents of exosomes derived from human neural stem cells (hNSCs). Our investigated hNSC line is a clonal, conditionally immortalized cell line, compliant with good manufacturing practice (GMP), and in clinical trials for stroke and critical limb ischemia in the UK (clinicaltrials.gov: NCT01151124, NCT02117635, and NCT01916369). By using next generation sequencing (NGS) technology we identified the presence of a variety of miRNAs in both exosomal and cellular preparations. Many of these miRNAs were enriched in exosomes indicating that cells specifically sort them for extracellular release. Although exosomes have been proven to contain miRNAs, the copy number quantification per exosome of a given miRNA remains unclear. Herein we quantified by real-time PCR a highly shuttled exosomal miRNA subtype (hsa-miR-1246) in order to assess its stoichiometry per exosome. Furthermore, we utilized an in vitro system to confirm its functional transfer by measuring the reduction in luciferase expression using a 3' untranslated region dual luciferase reporter assay. In summary, NGS analysis allowed the identification of a unique set of hNSC derived exosomal miRNAs. Stoichiometry and functional transfer analysis of one of the most abundant identified miRNA, hsa-miR-1246, were measured to support biological relevance of exosomal miRNA delivery

The characterization of exosomes derived from hNSCs.

<p>Size distribution of exosomes analyzed with the NTA (A) and qNano (B), representative traces. In agreement with exosome sizes, isolated exosomes had a mode of approximately 100 nm. (C) Molecular characterization of exosomes and producer hNSCs by Western blotting. Protein extracts from hNSCs and exosomes were assessed using antibodies against exosomal protein markers (CD81 and CD61), and hNSC protein marker (MYC).</p

Absolute quantification of selected miRNA.

<p>(A) Example of standard curve obtained for miRNA quantification. MiRNA mimic was diluted to a concentration range of 3.01×10¹²–3.01×10⁷ copies per well. Each point plotted is an average of triplicate fluorescence values for each standard concentration measured. (B) Diagram showing the quantification of hsa-miR-1246 copy number per hNSC and per exosome (EXO). Exosome particle quantification was performed using two independent methods, NTA and qNano; cell number quantification was performed by hemocytometer analysis. The error bars represent ± SEM.</p

MiRNA next generation sequencing.

<p>Cellular (A) and exosomal (B) total RNAs were processed by an Agilent 2100 Bioanalyzer. The corresponding virtual gel images generated by the software are depicted as electropherograms. (C) Representative diagram of differential miRNA distribution in exosomes compared to hNSC producers. MiRNA types preferentially released in exosomes are presented in red or retained within the hNSCs in blue, data expressed as log₂ ratio of exosomal/cellular miRNAs normalized read counts. Pie chart representation of the distribution of small RNA categories in hNSC (D) and exosome (E) samples.</p