Lineage reprogramming of fibroblasts into induced cardiac progenitor cells by CRISPR/Cas9-based transcriptional activators

Overexpression of exogenous lineage-determining factors succeeds in directly reprogramming fibroblasts to various cell types. Several studies have reported reprogramming of fibroblasts into induced cardiac progenitor cells (iCPCs). CRISPR/Cas9-mediated gene activation is a potential approach for cellular reprogramming due to its high precision and multiplexing capacity. Here we show lineage reprogramming to iCPCs through a dead Cas9 (dCas9)-based transcription activation system. Targeted and robust activation of endogenous cardiac factors, including GATA4, HAND2, MEF2C and TBX5 (G, H, M and T; GHMT), can reprogram human fibroblasts toward iCPCs. The iCPCs show potentials to differentiate into cardiomyocytes, smooth muscle cells and endothelial cells in vitro. Addition of MEIS1 to GHMT induces cell cycle arrest in G2/M and facilitates cardiac reprogramming. Lineage reprogramming of human fibroblasts into iCPCs provides a promising cellular resource for disease modeling, drug discovery and individualized cardiac cell therapy.

Reprogramming human retinal pigmented epithelial cells to neurons using recombinant proteins

Somatic cells can be reprogrammed to an altered lineage by overexpressing specific transcription factors. To avoid introducing exogenous genetic material into the genome of host cells, cell-penetrating peptides can be used to deliver transcription factors into cells for reprogramming. Position-dependent C-end rule (CendR) cell- and tissue-penetrating peptides provide an alternative to the conventional cell-penetrating peptides, such as polyarginine. In this study, we used a prototypic, already active CendR peptide, RPARPAR, to deliver the transcription factor SOX2 to retinal pigmented epithelial (RPE) cells. We demonstrated that RPE cells can be directly reprogrammed to a neuronal fate by introduction of SOX2. Resulting neuronal cells expressed neuronal marker mRNAs and proteins and downregulated expression of RPE markers. Cells produced extensive neurites and developed synaptic machinery capable of dye uptake after depolarization with potassium. The RPARPAR-mediated delivery of SOX2 alone was sufficient to allow cell lineage reprogramming of both fetal and stem cell-derived RPE cells to become functional neurons.

Somatic MIWI2 Hinders Direct Lineage Reprogramming From Fibroblast to Hepatocyte

Remodeling of the gene regulatory network in cells is believed to be a prerequisite for their lineage reprogramming. However, its key regulatory factors are not yet elucidated. In this article, we investigate the role of PIWI proteins and provide evidence that one of them, MIWI2, is elicited during transdifferentiation of fibroblasts into hepatocyte‐like cells. In coincidence with the peak expression of MIWI2, we identified the appearance of a unique intermediate epigenetic state characterized by a specific Piwi‐interacting RNA (piRNA) profile consisting of 219 novel sequences. Knockout of MIWI2 greatly improved the formation of the induced hepatocytes, whereas overexpression of exogenous MIWI2 completely abolished the stimulated effect. A bioinformatics analysis of piRNA interaction network, followed by experimental validation, revealed the Notch signaling pathway as one of the immediate effectors of MIWI2. Altogether, our results show for the first time that temporal expression of MIWI2 contributes negatively to cell plasticity not only in germline, but also in developed cells, such as mouse fibroblasts. stem cells2019;37:803–812

An Efficient Direct Conversion Strategy to Generate Functional Astrocytes from Human Adult Fibroblasts

Direct reprogramming approaches offer an attractive alternative to stem-cell-derived models, allowing the retention of epigenetic information and age-associated cellular phenotypes, and providing an expedited method to generate target cell types. Several groups have previously generated multiple neuronal subtypes, neural progenitor cells, oligodendrocytes, and other cell types directly from fibroblasts. However, while some groups have had success at the efficient conversion of embryonic fibroblasts to astrocytes, they have not yet achieved similar conversion efficiency for adult human fibroblasts. To generate astrocytes for the study of adult-stage disorders, we developed an improved direct conversion strategy employing a combination of small molecules to activate specific pathways that induce trans-differentiation of human adult fibroblasts to astrocytes. We demonstrate that this method produces mature GFAP+/S100β+ cells at high efficiency (40-45%), comparable to previous studies utilizing embryonic fibroblasts. Further, Fibroblast-derived induced Astrocytes (FdiAs) are enriched for markers of astrocyte functionality, including ion-channel buffering, gap-junction communication, and glutamate uptake; and exhibit astrocyte-like calcium signaling and neuroinflammatory phenotypes. RNA-Seq analysis indicates a close correlation to human brain astrocytes and iPSC-derived astrocyte models. Fibroblast-derived induced astrocytes provide a useful tool in studying the adult brain and complement existing in vitro models of induced neurons (iNs), providing an additional platform to study adult-stage brain disorders.

Single-cell transcriptomics reveals liver developmental trajectory during lineage reprogramming of human induced hepatocyte-like cells

Hepatocytes are crucial for drug screening, disease modeling, and clinical transplantation, yet generating functional hepatocytes in vitro is challenging due to the difficulty of establishing their authentic gene regulatory networks (GRNs). We have previously developed a two-step lineage reprogramming strategy to generate functionally competent human induced hepatocytes (hiHeps), providing an effective model for studying the establishment of hepatocyte-specific GRNs. In this study, we utilized high-throughput single-cell RNA sequencing (scRNA-seq) to explore the cell-fate transition and the establishment of hepatocyte-specific GRNs involved in the two-step reprogramming process. Our findings revealed that the late stage of the reprogramming process mimics the natural trajectory of liver development, exhibiting similar transcriptional waves of developmental genes. CD24 and DLK1 were identified as surface markers enriching two distinct hepatic progenitor populations respectively. Lipid metabolism emerged as a key enhancer of hiHeps maturation. Furthermore, transcription factors HNF4A and HHEX were identified as pivotal gatekeepers directing cell fate decisions between hepatocytes and intestinal cells. Collectively, this study provides valuable insights into the establishment of hepatocyte-specific GRNs during hiHeps induction at single-cell resolution, facilitating more efficient production of functional hepatocytes for therapeutic applications.

Transplantation of human induced cerebellar granular-like cells improves motor functions in a novel mouse model of cerebellar ataxia

Stem cell-based reparative approaches have been applied to cerebellum-related disorders during the last two decades. Direct lineage reprogramming of human fibroblasts into functional granular neurons holds great promise for biomedical applications such as cerebellum regeneration and cellbased disease modeling. In the present study, we showed that a combination of Ascl1, Sox2 and OCT4, in a culture subsequently treated with secreted factors (BMP4, Wnt3a and FGF8b), was capable of converting human fibroblasts from the scalp tissue of patients with traumatic brain injury (TBI) into functional human induced cerebellar granular-like cells (hiCGCs). Morphological analysis, immunocytochemistry, gene expression and electrophysiological analysis were performed to identify the similarity of induced neuronal cells to human cerebellum granular cells. Our strategy improved the efficiency for hiCGCs induction, which gave the highest conversion efficiency 12.30±0.88%, and Ath1(+)/Tuj1(+) double positive cells to 5.56±0.80%. We transplanted hiCGCs into the cerebellum of Nmyc(TRE/TRE): tTS mice, a novel mouse model of cerebellar ataxia, and demonstrated that the hiCGCs were able to survive, migrate, proliferate and promote mild functional recovery after been grafted into cerebellum.

Development of de novo epithelialization method for treatment of cutaneous ulcers

Cutaneous ulcers are a common cause of morbidity. We have developed a de novo epithelialization method for treating cutaneous ulcers by means of reprogramming wound-resident mesenchymal cells in vivo into cells able to form a stratified epithelium: induced stratified epithelial progenitors (iSEPs). Administration of 4 transcription factors (DNP63A, GRHL2, TFAP2A, and cMYC) expressed via adeno-associated viral vectors enabled generation of epithelial cells and tissues, thereby acheiving de novo epithelialization from the surfaces of cutaneous ulcers in a mouse model. Generated epithelia, having barrier functions equivalent to the original epidermis, were maintained for more than 6 months. Our findings constitute a proof of concept for future development towards innovative therapies for cutaneous ulcers via de novo epithelialization.

Lineage reprogramming of human adipose mesenchymal stem cells to immune modulatory i-Heps

Pluripotent stem cell derived-hepatocytes depict fetal -hepatocyte characteristics/maturity and are immunogenic limiting their applications. Attempts have been made to derive hepatocytes from mesenchymal stem cells using developmental cocktails, epigenetic modulators and small molecules. However, achieving a stable terminally differentiated functional state had been a challenge. Inefficient hepatic differentiation could be due to lineage restrictions set during development. Hence a novel lineage reprogramming approach has been utilized to confer competence to adipose-mesenchymal stem cells (ADMSCs) to efficiently respond to hepatogenic cues and achieve a stable functional hepatic state. Lineage reprogramming involved co-transduction of ADMSCs with hepatic endoderm pioneer Transcription factor (TF)-FOXA2, HHEX-a homeobox gene and HNF4α-master TF indispensable for hepatic state maintenance. Lineage priming was evidenced by endogenous HFN4α promoter demethylation and robust responsiveness to minimal hepatic maturation cues. Induced hepatocytes (i-Heps) exhibited mesenchymal-to-epithelial transition and terminal hepatic signatures. Functional characterisation of i-Heps for hepatic drug detoxification systems, xenobiotic uptake/clearance, metabolic status and hepatotropic virus entry validated acquisition of stable hepatic state and junctional maturity Exhaustive analysis of MSC memory in i-Heps indicated loss of MSC-immunophenotype and terminal differentiation to osteogenic/adipogenic lineages. Importantly, i-Heps suppressed phytohemagglutinin-induced T-cell blasts, inhibited allogenic mixed-lymphocyte reactions (MLRs) and secreted immunomodulatory- indoleamine 2,3-dioxygenase in T-cell blast co-cultures akin to native ADMSCs. In a nutshell, the present study identifies a novel cocktail of TFs that reprogram ADMSCs to stable hepatic state. i-Heps exhibit adult hepatocyte functional maturity with robust immune-modulatory abilities rendering suitability for rigorous drug testing, hepatocyte-pathogen interaction studies and transplantation in allogenic settings.