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Genome editing is poised to revolutionize treatment of genetic diseases, but poor understanding and control of DNA repair outcomes hinders its therapeutic potential. DNA repair is especially understudied in nondividing cells like neurons, which must withstand decades of DNA damage without replicating. This lack of knowledge limits the efficiency and precision of genome editing in clinically relevant cells. To address this, we used induced pluripotent stem cells (iPSCs) and iPSC-derived neurons to examine how postmitotic human neurons repair Cas9-induced DNA damage. We discovered that neurons can take weeks to fully resolve this damage, compared to just days in isogenic iPSCs. Furthermore, Cas9-treated neurons upregulated unexpected DNA repair genes, including factors canonically associated with replication. Manipulating this response with chemical or genetic perturbations allowed us to direct neuronal repair toward desired editing outcomes. By studying DNA repair in postmitotic human cells, we uncovered unforeseen challenges and opportunities for precise therapeutic editing.

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Human-induced pluripotent stem cell-derived endothelial cells (iECs) provide opportunities to study vascular development and regeneration, develop cardiovascular therapeutics, and engineer model systems for drug screening. The differentiation and characterization of iECs are well established; however, the mechanisms governing their angiogenic phenotype remain unknown. Here, we aimed to determine the angiogenic phenotype of iECs and the regulatory mechanism controlling their regenerative capacity. In a comparative study with HUVECs, we show that iECs increased expression of vascular endothelial growth factor receptor 2 (VEGFR2) mediates their highly angiogenic phenotype via regulation of glycolysis enzymes, filopodia formation, VEGF mediated migration, and robust sprouting. We find that the elevated expression of VEGFR2 is epigenetically regulated via intrinsic acetylation of histone 3 at lysine 27 by histone acetyltransferase P300. Utilizing a zebrafish xenograft model, we demonstrate that the ability of iECs to promote the regeneration of the amputated fin can be modulated by P300 activity. These findings demonstrate how the innate epigenetic status of iECs regulates their phenotype with implications for their therapeutic potential.

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Ischemic retinopathies are major causes of blindness worldwide. Local hypoxia created by loss of vascular supply leads to tissue injury and aberrant neovascularization in the retina. There is a great need for therapies that enhance revascularization of hypoxic neuroretinal tissue. To test the therapeutic feasibility of human-induced pluripotent stem cell-derived endothelial cells (hiPSC-ECs) for the treatment of ischemic retinopathies, we compared the angiogenic potential of hiPSC-ECs with mature human retinal endothelial cells (HRECs) in response to hypoxia. hiPSC-ECs formed more robust and complex vascular networks in collagen gels, whereas HRECs displayed minimal sprouting. The cells were further tested in the mouse oxygen-induced retinopathy (OIR) model. Retinas with hiPSC-EC injection showed colocalization with host vessels, whereas HRECs lacked such responses. hiPSC-ECs markedly reduced vaso-obliteration and pathological neovascularization. This beneficial effect of hiPSC-ECs was explained by the stromal cell-derived factor-1a (SDF1a)/CXCR4 axis; hiPSC-ECs exhibited much higher cell-surface expression of CXCR4 than HRECs and greater chemotaxis toward SDF1a-embedded 3D collagen hydrogel. Furthermore, treatment with neutralizing antibody to CXCR4 abolished recruitment of hiPSCs in the OIR model. These findings suggest superior angiogenic potential of hiPSC-ECs under hypoxia and underscore the importance of SDF1a/CXCR4 in the reparative function of hiPSC-ECs in ischemic diseases.

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Pericytes wrap blood microvessels and are believed to play important roles in vascular morphogenesis, maturation, and stability. In addition, pericytes have emerged as candidates for targeting cancer growth and for wound healing. In order to model these processes and test new therapies, it is desirable to have a reliable, scalable source of pericytes. Human pluripotent stem cells (hPSCs), which possess the ability to differentiate into any cell type in the body, have been used to generate pericytes in vitro quickly, consistently, and with high yields. In this chapter, we consider the differentiation of pericytes from hPSCs. We compare the approaches taken by multiple groups and discuss characterization of hPSC-pericytes. Studying pericyte differentiation in vitro provides the opportunity to identify factors influencing pericyte development and to establish the ontogenic relationships between pericytes and similar cells. The development of highly specific, defined pericyte populations from hPSCs will enable downstream applications requiring large quantities of cells, including tissue engineered models and cell therapies.

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The role of primary cilia in mechanosensation is essential in endothelial cell (EC) shear responsiveness. Here, we find that venous, capillary, and progenitor ECs respond to shear stress in vitro in a cilia-dependent manner. We then demonstrate that primary cilia assembly in human induced pluripotent stem cell (hiPSC)-derived ECs varies between different cell lines with marginal influence of differentiation protocol. hiPSC-derived ECs lacking cilia do not align to shear stress, lack stress fiber assembly, have uncoordinated migration during wound closure in vitro, and have aberrant calcium influx upon shear exposure. Transcriptional analysis reveals variation in regulatory genes involved in ciliogenesis among different hiPSC-derived ECs. Moreover, inhibition of histone deacetylase 6 (HDAC6) activity in hiPSC-ECs lacking cilia rescues cilia formation and restores mechanical sensing. Taken together, these results show the importance of primary cilia in hiPSC-EC mechano-responsiveness and its modulation through HDAC6 activity varies among hiPSC-ECs.

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Development of pluripotent stem cells (PSCs) is a remarkable scientific advancement that allows scientists to harness the power of regenerative medicine for potential treatment of disease using unaffected cells. PSCs provide a unique opportunity to study and combat cardiovascular diseases, which continue to claim the lives of thousands each day. Here, we discuss the differentiation of PSCs into vascular cells, investigation of the functional capabilities of the derived cells, and their utilization to engineer microvascular beds or vascular grafts for clinical application. Graphical Abstract Human iPSCs generated from patients are differentiated toward ECs and perivascular cells for use in disease modeling, microvascular bed development, or vascular graft fabrication.

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As the lifeline of almost all living tissues, blood vessels are a major focus of tissue-regenerative therapies. Rebuilding blood vessels has vast implications for the study of vascular growth and treatment of diseases in which vascular function is compromised. Toward this end, human pluripotent stem cells have been widely studied for their differentiation capacity toward vascular lineages. We demonstrate methods to derive a bicellular population of early specialized vascular cells from human pluripotent stem cells, to differentiate these toward mature endothelial cells and pericytes, and to utilize a collagen scaffold to facilitate organization into vascular networks.

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