Scientific Resources

The ability to create 3D tissues from induced pluripotent stem cells (iPSCs) is poised to revolutionize stem cell research and regenerative medicine,including individualized,patient-specific stem cell-based treatments. There are,however,few examples of tissue engineering using iPSCs. Their culture and differentiation is predominantly planar for monolayer cell support or induction of self-organizing embryoids (EBs) and organoids. Bioprinting iPSCs with advanced biomaterials promises to augment efforts to develop 3D tissues,ideally comprising direct-write printing of cells for encapsulation,proliferation,and differentiation. Here,such a method,employing a clinically amenable polysaccharide-based bioink,is described as the first example of bioprinting human iPSCs for in situ expansion and sequential differentiation. Specifically,There are extrusion printed the bioink including iPSCs,alginate (Al; 5% weight/volume [w/v]),carboxymethyl-chitosan (5% w/v),and agarose (Ag; 1.5% w/v),crosslinked the bioink in calcium chloride for a stable and porous construct,proliferated the iPSCs within the construct and differentiated the same iPSCs into either EBs comprising cells of three germ lineages-endoderm,ectoderm,and mesoderm,or more homogeneous neural tissues containing functional migrating neurons and neuroglia. This defined,scalable,and versatile platform is envisaged being useful in iPSC research and translation for pharmaceuticals development and regenerative medicine. View Publication

Human pluripotent stem cells (HPSCs) cultured in conditions that maintain pluripotency via FGF and TGFβ signaling have been described as being in a primed state. These cells have been shown to exhibit characteristics more closely related to mouse epiblast-derived stem cells than to so called naïve mouse PSCs said to possess a more ground state pluripotency that mimics the early mouse embryo inner cell mass. Initial attempts to create culture conditions favorable for generation of naïve HPSCs from primed HPSCs has required the use of mouse embryonic fibroblasts as a feeder layer to support this transition. A protocol for the routine derivation and maintenance of naïve HPSCs in completely defined conditions is highly desirable for stem cell researchers to enhance the study and clinical translation of naïve HPSCs. Here we describe a standard protocol for transitioning primed HPSCs to a naïve state using commercial RSet media and xeno-free recombinant vitronectin. View Publication

Recent reports have documented the differentiation of human pluripotent stem cells toward the skeletal myogenic lineage using transgene- and cell purification-free approaches. Although these protocols generate myocytes,they have not demonstrated scalability,safety,and in vivo engraftment,which are key aspects for their future clinical application. Here we recapitulate one prominent protocol,and show that it gives rise to a heterogeneous cell population containing myocytes and other cell types. Upon transplantation,the majority of human donor cells could not contribute to myofiber formation. As a proof-of-principle,we incorporated the inducible PAX7 lentiviral system into this protocol,which then enabled scalable expansion of a homogeneous population of skeletal myogenic progenitors capable of forming myofibers in vivo. Our findings demonstrate the methods for scalable expansion of PAX7(+) myogenic progenitors and their purification are critical for practical application to cell replacement treatment of muscle degenerative diseases. View Publication

Microglia,the immune cells of the brain,are crucial to proper development and maintenance of the CNS,and their involvement in numerous neurological disorders is increasingly being recognized. To improve our understanding of human microglial biology,we devised a chemically defined protocol to generate human microglia from pluripotent stem cells. Myeloid progenitors expressing CD14/CX3CR1 were generated within 30 days of differentiation from both embryonic and induced pluripotent stem cells (iPSCs). Further differentiation of the progenitors resulted in ramified microglia with highly motile processes,expressing typical microglial markers. Analyses of gene expression and cytokine release showed close similarities between iPSC-derived (iPSC-MG) and human primary microglia as well as clear distinctions from macrophages. iPSC-MG were able to phagocytose and responded to ADP by producing intracellular Ca(2+) transients,whereas macrophages lacked such response. The differentiation protocol was highly reproducible across several pluripotent stem cell lines. View Publication

Recent studies using defined transcription factors to convert skin fibroblasts into chondrocytes have raised the question of whether osteo-chondroprogenitors expressing SOX9 and RUNX2 could also be generated during the course of the reprogramming process. Here,we demonstrated that doxycycline-inducible expression of reprogramming factors (KLF4 [K] and c-MYC [M]) for 6 days were sufficient to convert murine fibroblasts into SOX9(+)/RUNX2(+) cellular aggregates and together with SOX9 (S) promoted the conversion efficiency when cultured in a defined stem cell medium,mTeSR. KMS-reprogrammed cells possess gene expression profiles akin to those of native osteo-chondroprogenitors with elevated osteogenic properties and can differentiate into osteoblasts and chondrocytes in vitro,but form bone tissue upon transplantation under the skin and in the fracture site of mouse tibia. Altogether,we provide a reprogramming strategy to enable efficient derivation of osteo-chondrogenic cells that may hold promise for cell replacement therapy not limited to cartilage but also for bone tissues. View Publication

Deubiquitinating enzymes may play a major regulatory role in pluripotent stem cells (PSCs) but few studies have investigated this topic. Within this family of enzymes,we found that the ubiquitin specific peptidase,USP44,is highly expressed in embryonic stem cells,induced PSCs and testes as compared to differentiated progenies and somatic organs. Analysis by qPCR and 5'RACE showed that alternate promoters are responsible for expression in PSCs and organs. We noticed 7 regions of transcription initiation,some of them with cell- or tissue-specific activity. Close analysis showed that one of the promoters involved in stem cell and testis-specific activity is differentially regulated in those tissues. At the epigenetic level,USP44 transcription was correlated with DNA methylation of a CpG island close to the main promoter region. These data imply a complex picture where regulating factors like OCT4 may interact with other epigenetic mechanisms to regulate USP44 expression in PSCs and testes. View Publication

A variety of tissue lineages can be differentiated from pluripotent stem cells by mimicking embryonic development through stepwise exposure to morphogens,or by conversion of one differentiated cell type into another by enforced expression of master transcription factors. Here,to yield functional human haematopoietic stem cells,we perform morphogen-directed differentiation of human pluripotent stem cells into haemogenic endothelium followed by screening of 26 candidate haematopoietic stem-cell-specifying transcription factors for their capacity to promote multi-lineage haematopoietic engraftment in mouse hosts. We recover seven transcription factors (ERG,HOXA5,HOXA9,HOXA10,LCOR,RUNX1 and SPI1) that are sufficient to convert haemogenic endothelium into haematopoietic stem and progenitor cells that engraft myeloid,B and T cells in primary and secondary mouse recipients. Our combined approach of morphogen-driven differentiation and transcription-factor-mediated cell fate conversion produces haematopoietic stem and progenitor cells from pluripotent stem cells and holds promise for modelling haematopoietic disease in humanized mice and for therapeutic strategies in genetic blood disorders. View Publication

Developmental pathways that orchestrate the fleeting transition of endothelial cells into haematopoietic stem cells remain undefined. Here we demonstrate a tractable approach for fully reprogramming adult mouse endothelial cells to haematopoietic stem cells (rEC-HSCs) through transient expression of the transcription-factor-encoding genes Fosb,Gfi1,Runx1,and Spi1 (collectively denoted hereafter as FGRS) and vascular-niche-derived angiocrine factors. The induction phase (days 0-8) of conversion is initiated by expression of FGRS in mature endothelial cells,which results in endogenous Runx1 expression. During the specification phase (days 8-20),RUNX1(+) FGRS-transduced endothelial cells commit to a haematopoietic fate,yielding rEC-HSCs that no longer require FGRS expression. The vascular niche drives a robust self-renewal and expansion phase of rEC-HSCs (days 20-28). rEC-HSCs have a transcriptome and long-term self-renewal capacity similar to those of adult haematopoietic stem cells,and can be used for clonal engraftment and serial primary and secondary multi-lineage reconstitution,including antigen-dependent adaptive immune function. Inhibition of TGFβ and CXCR7 or activation of BMP and CXCR4 signalling enhanced generation of rEC-HSCs. Pluripotency-independent conversion of endothelial cells into autologous authentic engraftable haematopoietic stem cells could aid treatment of haematological disorders. View Publication

Biologic TNFα inhibitors are a mainstay treatment option for patients with rheumatoid arthritis (RA) refractory to other treatment options. However,many patients either do not respond or relapse after initially responding to these agents. This study was carried out to identify biomarkers that can distinguish responder from non-responder patients before the initiation of treatment. The level of cytokines in plasma and those produced by ex vivo T cells,B cells and monocytes in 97 RA patients treated with biologic TNFα inhibitors was measured before treatment and after 1 and 3 months of treatment by multiplex analyses. The frequency of T cell subsets and intracellular cytokines were determined by flow cytometry. The results reveal that pre-treatment,T cells from patients who went on to respond to treatment with biologic anti-TNFα agents produced significantly more GM-CSF than non-responder patients. Furthermore,immune cells from responder patients produced higher levels of IL-1β,TNFα and IL-6. Cytokine profiling in the blood of patients confirmed the association between high levels of GM-CSF and responsiveness to biologic anti-TNFα agents. Thus,high blood levels of GM-CSF pre-treatment had a positive predictive value of 87.5% (61.6 to 98.5% at 95% CI) in treated RA patients. The study also shows that cells from most anti-TNFα responder patients in the current cohort produced higher levels of GM-CSF and TNFα pre-treatment than non-responder patients. Findings from the current study and our previous observations that non-responsiveness to anti-TNFα is associated with high IL-17 levels suggest that the disease in responder and non-responder RA patients is likely to be driven/sustained by different inflammatory pathways. The use of biomarker signatures of distinct pro-inflammatory pathways could lead to evidence-based prescription of the most appropriate biological therapies for different RA patients. View Publication

Activin A belongs to the superfamily of transforming growth factor beta (TGF$\beta$) and is a critical regulatory cytokine in breast cancer and inflammation. However,the role of activin A in migration of breast cancer cells and immune cells was not well characterized. Here,a microfluidic device was used to examine the effect of activin A on the migration of human breast cancer cell line MDA-MB-231 cells and human blood neutrophils as well as their migratory interaction. We found that activin A promoted the basal migration but impaired epidermal growth factor (EGF)-induced migration of breast cancer cells. By contrast,activin A reduced neutrophil chemotaxis and transendothelial migration to N-Formyl-Met-Leu-Phe (fMLP). Finally,activin A promoted neutrophil chemotaxis to the supernatant from breast cancer cell culture. Collectively,our study revealed the different roles of activin A in regulating the migration of breast cancer cells and neutrophils and their migratory interaction. These findings suggested the potential of activin A as a therapeutic target for inflammation and breast cancers. View Publication

Gerstmann-Sträussler-Scheinker (GSS) syndrome is a fatal autosomal dominant neurodegenerative prionopathy clinically characterized by ataxia,spastic paraparesis,extrapyramidal signs and dementia. In some GSS familiar cases carrying point mutations in the PRNP gene,patients also showed comorbid tauopathy leading to mixed pathologies. In this study we developed an induced pluripotent stem (iPS) cell model derived from fibroblasts of a GSS patient harboring the Y218N PRNP mutation,as well as an age-matched healthy control. This particular PRNP mutation is unique with very few described cases. One of the cases presented neurofibrillary degeneration with relevant Tau hyperphosphorylation. Y218N iPS-derived cultures showed relevant astrogliosis,increased phospho-Tau,altered microtubule-associated transport and cell death. However,they failed to generate proteinase K-resistant prion. In this study we set out to test,for the first time,whether iPS cell-derived neurons could be used to investigate the appearance of disease-related phenotypes (i.e,tauopathy) identified in the GSS patient. View Publication

The epicardium contributes both multi-lineage descendants and paracrine factors to the heart during cardiogenesis and cardiac repair,underscoring its potential for cardiac regenerative medicine. Yet little is known about the cellular and molecular mechanisms that regulate human epicardial development and regeneration. Here,we show that the temporal modulation of canonical Wnt signaling is sufficient for epicardial induction from 6 different human pluripotent stem cell (hPSC) lines,including a WT1-2A-eGFP knock-in reporter line,under chemically-defined,xeno-free conditions. We also show that treatment with transforming growth factor beta (TGF-β)-signalling inhibitors permitted long-term expansion of the hPSC-derived epicardial cells,resulting in a more than 25 population doublings of WT1+ cells in homogenous monolayers. The hPSC-derived epicardial cells were similar to primary epicardial cells both in vitro and in vivo,as determined by morphological and functional assays,including RNA-seq. Our findings have implications for the understanding of self-renewal mechanisms of the epicardium and for epicardial regeneration using cellular or small-molecule therapies. View Publication