Efficient homology-directed gene editing by CRISPR/Cas9 in human stem and primary cells using tube electroporation.

CRISPR/Cas9 efficiently generates gene knock-out via nonhomologous end joining (NHEJ), but the efficiency of precise homology-directed repair (HDR) is substantially lower, especially in the hard-to-transfect human stem cells and primary cells. Herein we report a tube electroporation method that can effectively transfect human stem cells and primary cells with minimal cytotoxicity. When applied to genome editing using CRISPR/Cas9 along with single stranded DNA oligonucleotide (ssODN) template in human induced pluripotent stem cells (iPSCs), up to 42.1% HDR rate was achieved, drastically higher than many reported before. We demonstrated that the high HDR efficiency can be utilized to increase the gene ablation rate in cells relevant to clinical applications, by knocking-out ß2-microglobulin (B2M) in primary human mesenchymal stem cells (MSCs, 37.3% to 80.2%), and programmed death-1 (PD-1) in primary human T cells (42.6% to 58.6%). Given the generality and efficiency, we expect that the method will have immediate impacts in cell research as well as immuno- and transplantation therapies.

Cell type-dependent Erk-Akt pathway crosstalk regulates the proliferation of fetal neural progenitor cells.

Neural progenitor (NP) cells are the multipotent cells that produce neurons and glia in the central nervous system. Compounds regulating their proliferation are key to both understanding brain development and unlocking their potential in regenerative repair. We discuss a chemical screen that unexpectedly identified inhibitors of Erk signaling potently promoting the self-renewing divisions of fetal NP cells. This occurred through crosstalk between Erk and Akt signaling cascades. The crosstalk mechanism is cell type-specific, and is not detected in adult NP cells as well as brain tumor cells. The mechanism was also shown to be independent from the GSK-3 signaling pathway, which has been reported to be a major regulator of NP cell homeostasis and inhibitors to which were also identified in the screen. In vitro Erk inhibition led to the prolonged rapid expansion of fetal NP cells while retaining their multipotency. In vivo inhibitor administration significantly inhibited the neuronal differentiation, and resulted in increased proliferative progenitor cells in the ventricular/subventricular zone (VZ/SVZ) of the embryonic cortex. Our results uncovered a novel regulating pathway for NP cell proliferation in the developing brain. The discovery provides a pharmacological basis for in vitro expansion and in vivo manipulation of NP cells.

A High-content screen identifies compounds promoting the neuronal differentiation and the midbrain dopamine neuron specification of human neural progenitor cells.

Small molecule compounds promoting the neuronal differentiation of stem/progenitor cells are of pivotal importance to regenerative medicine. We carried out a high-content screen to systematically characterize known bioactive compounds, on their effects on the neuronal differentiation and the midbrain dopamine (mDA) neuron specification of neural progenitor cells (NPCs) derived from the ventral mesencephalon of human fetal brain. Among the promoting compounds three major pharmacological classes were identified including the statins, TGF-ßRI inhibitors, and GSK-3 inhibitors. The function of each class was also shown to be distinct, either to promote both the neuronal differentiation and mDA neuron specification, or selectively the latter, or promote the former but suppress the latter. We then carried out initial investigation on the possible mechanisms underlying, and demonstrated their applications on NPCs derived from human pluripotent stem cells (PSCs). Our study revealed the potential of several small molecule compounds for use in the directed differentiation of human NPCs. The screening result also provided insight into the signaling network regulating the differentiation of human NPCs.

Effect of MDM2 and vascular endothelial growth factor inhibition on tumor angiogenesis and metastasis in neuroblastoma.

Neuroblastoma is the most common pediatric abdominal tumor and principally a p53 wild-type, highly vascular, aggressive tumor, with limited response to anti-VEGF therapies alone. MDM2 is a key inhibitor of p53 and a positive activator of hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) activity with an important role in neuroblastoma pathogenesis. We hypothesized that concurrent inhibition of both MDM2 and VEGF signaling would have cooperative anti-tumor effects, potentiating anti-angiogenic strategies for neuroblastoma and other p53 wild-type tumors. We orthotopically implanted SH-SY5Y neuroblastoma cells into nude mice (n = 40) and treated as follows: control, bevacizumab, Nutlin-3a, combination of bevacizumab plus Nutlin-3a. Expression of HIF-1α and VEGF were measured by qPCR, Western blot, and ELISA. Tumor apoptosis was measured by immunohistochemistry and caspase assay. Angiogenesis was evaluated by immunohistochemistry for vascular markers (CD-31, type-IV collagen, αSMA). Both angiogenesis and metastatic burden were digitally quantified. In vitro, Nutlin-3a suppresses HIF-1α expression with subsequent downregulation of VEGF. Bevacizumab plus Nutlin-3a leads to significant suppression of tumor growth compared to control (P < 0.01) or either agent alone. Combination treated xenograft tumors display a marked decrease in endothelial cells (P < 0.0001), perivascular basement membrane (P < 0.04), and vascular mural cells (P < 0.004). Nutlin-3a alone and in combination with bevacizumab leads to significant tumor apoptosis (P < 0.0001 for both) and significant decrease in incidence of metastasis (P < 0.05) and metastatic burden (P < 0.03). Bevacizumab plus Nutlin-3a cooperatively inhibits tumor growth and angiogenesis in neuroblastoma in vivo with dramatic effects on tumor vascularity. Concomitantly targeting VEGF and p53 pathways potently suppresses tumor growth, and these results support further clinical development of this approach.