Functional characteristics of reversibly immortalized hepatic progenitor cells derived from mouse embryonic liver

Modeling lung diseases using reversibly immortalized mouse pulmonary alveolar type 2 cells (imPAC2)

BACKGROUND

A healthy alveolar epithelium is critical to the gas exchange function of the lungs. As the major cell type of alveolar epithelium, alveolar type 2 (AT2) cells play a critical role in maintaining pulmonary homeostasis by serving as alveolar progenitors during lung injury, inflammation, and repair. Dysregulation of AT2 cells may lead to the development of acute and chronic lung diseases and cancer. The lack of clinically relevant AT2 cell models hampers our ability to understand pulmonary diseases. Here, we sought to establish reversibly immortalized mouse pulmonary alveolar type 2 cells (imPAC2) and investigate their potential in forming alveolar organoids to model pulmonary diseases.

METHODS

Primary mouse pulmonary alveolar cells (mPACs) were isolated and immortalized with a retroviral expression of SV40 Large T antigen (LTA). Cell proliferation and survival was assessed by crystal violet staining and WST-1 assays. Marker gene expression was assessed by qPCR, Western blotting, and/or immunostaining. Alveolar organoids were generated by using matrigel. Ad-TGF-β1 was used to transiently express TGF-β1. Stable silencing β-catenin or overexpression of mutant KRAS and TP53 was accomplished by using retroviral vectors. Subcutaneous cell implantations were carried out in athymic nude mice. The retrieved tissue masses were subjected to H & E histologic evaluation.

RESULTS

We immortalized primary mPACs with SV40 LTA to yield the imPACs that were non-tumorigenic and maintained long-term proliferative activity that was reversible by FLP-mediated removal of SV40 LTA. The EpCAM+ AT2-enriched subpopulation (i.e., imPAC2) was sorted out from the imPACs, and was shown to express AT2 markers and form alveolar organoids. Functionally, silencing β-catenin decreased the expression of AT2 markers in imPAC2 cells, while TGF-β1 induced fibrosis-like response by regulating the expression of epithelial-mesenchymal transition markers in the imPAC2 cells. Lastly, concurrent expression of oncogenic KRAS and mutant TP53 rendered the imPAC2 cells a tumor-like phenotype and activated lung cancer-associated pathways. Collectively, our results suggest that the imPAC2 cells may faithfully represent AT2 populations that can be further explored to model pulmonary diseases.

Bioartificial livers: a review of their design and manufacture

Acute liver failure (ALF) is a rapidly progressive disease with high morbidity and mortality rates. Liver transplantation and artificial liver support systems, such as artificial livers (ALs) and bioartificial livers (BALs), are the two major therapies for ALF. Compared to ALs, BALs are composed of functional hepatocytes that provide essential liver functions, including detoxification, metabolite synthesis, and biotransformation. Furthermore, BALs can potentially provide effective support as a form of bridging therapy to liver transplantation or spontaneous recovery for patients with ALF. In this review, we systematically discussed the currently available state-of-the-art designs and manufacturing processes for BAL support systems. Specifically, we classified the cell sources and bioreactors that are applied in BALs, highlighted the advanced technologies of hepatocyte culturing and bioreactor fabrication, and discussed the current challenges and future trends in developing next generation BALs for large scale clinical applications.

Reversibly immortalized keratinocytes (iKera) facilitate re-epithelization and skin wound healing: Potential applications in cell-based skin tissue engineering

Skin injury is repaired through a multi-phase wound healing process of tissue granulation and re-epithelialization. Any failure in the healing process may lead to chronic non-healing wounds or abnormal scar formation. Although significant progress has been made in developing novel scaffolds and/or cell-based therapeutic strategies to promote wound healing, effective management of large chronic skin wounds remains a clinical challenge. Keratinocytes are critical to re-epithelialization and wound healing. Here, we investigated whether exogenous keratinocytes, in combination with a citrate-based scaffold, enhanced skin wound healing. We first established reversibly immortalized mouse keratinocytes (iKera), and confirmed that the iKera cells expressed keratinocyte markers, and were responsive to UVB treatment, and were non-tumorigenic. In a proof-of-principle experiment, we demonstrated that iKera cells embedded in citrate-based scaffold PPCN provided more effective re-epithelialization and cutaneous wound healing than that of either PPCN or iKera cells alone, in a mouse skin wound model. Thus, these results demonstrate that iKera cells may serve as a valuable skin epithelial source when, combining with appropriate biocompatible scaffolds, to investigate cutaneous wound healing and skin regeneration.

Argonaute (AGO) proteins play an essential role in mediating BMP9-induced osteogenic signaling in mesenchymal stem cells (MSCs)

As multipotent progenitor cells, mesenchymal stem cells (MSCs) can renew themselves and give rise to multiple lineages including osteoblastic, chondrogenic and adipogenic lineages. It's previously shown that BMP9 is the most potent BMP and induces osteogenic and adipogenic differentiation of MSCs. However, the molecular mechanism through which BMP9 regulates MSC differentiation remains poorly understood. Emerging evidence indicates that noncoding RNAs, especially microRNAs, may play important roles in regulating MSC differentiation and bone formation. As highly conserved RNA binding proteins, Argonaute (AGO) proteins are essential components of the multi-protein RNA-induced silencing complexes (RISCs), which are critical for small RNA biogenesis. Here, we investigate possible roles of AGO proteins in BMP9-induced lineage-specific differentiation of MSCs. We first found that BMP9 up-regulated the expression of Ago1, Ago2 and Ago3 in MSCs. By engineering multiplex siRNA vectors that express multiple siRNAs targeting individual Ago genes or all four Ago genes, we found that silencing individual Ago expression led to a decrease in BMP9-induced early osteogenic marker alkaline phosphatase (ALP) activity in MSCs. Furthermore, we demonstrated that simultaneously silencing all four Ago genes significantly diminished BMP9-induced osteogenic and adipogenic differentiation of MSCs and matrix mineralization, and ectopic bone formation. Collectively, our findings strongly indicate that AGO proteins and associated small RNA biogenesis pathway play an essential role in mediating BMP9-induced osteogenic differentiation of MSCs.

Modeling colorectal tumorigenesis using the organoids derived from conditionally immortalized mouse intestinal crypt cells (ciMICs)

Intestinal cancers are developed from intestinal epithelial stem cells (ISCs) in intestinal crypts through a multi-step process involved in genetic mutations of oncogenes and tumor suppressor genes. ISCs play a key role in maintaining the homeostasis of gut epithelium. In 2009, Sato et al established a three-dimensional culture system, which mimicked the niche microenvironment by employing the niche factors, and successfully grew crypt ISCs into organoids or Mini-guts in vitro. Since then, the intestinal organoid technology has been used to delineate cellular signaling in ISC biology. However, the cultured organoids consist of heterogeneous cell populations, and it was technically challenging to introduce genomic changes into three-dimensional organoids. Thus, there was a technical necessity to develop a two-dimensional ISC culture system for effective genomic manipulations. In this study, we established a conditionally immortalized mouse intestinal crypt (ciMIC) cell line by using a piggyBac transposon-based SV40 T antigen expression system. We showed that the ciMICs maintained long-term proliferative activity under two-dimensional niche factor-containing culture condition, retained the biological characteristics of intestinal epithelial stem cells, and could form intestinal organoids in three-dimensional culture. While in vivo cell implantation tests indicated that the ciMICs were non-tumorigenic, the ciMICs overexpressing oncogenic β-catenin and/or KRAS exhibited high proliferative activity and developed intestinal adenoma-like pathological features in vivo. Collectively, these findings strongly suggested that the engineered ciMICs should be used as a valuable tool cell line to dissect the genetic and/or epigenetic underpinnings of intestinal tumorigenesis.

Antiparasitic mebendazole (MBZ) effectively overcomes cisplatin resistance in human ovarian cancer cells by inhibiting multiple cancer-associated signaling pathways

Ovarian cancer is the third most common cancer and the second most common cause of gynecologic cancer death in women. Its routine clinical management includes surgical resection and systemic therapy with chemotherapeutics. While the first-line systemic therapy requires the combined use of platinum-based agents and paclitaxel, many ovarian cancer patients have recurrence and eventually succumb to chemoresistance. Thus, it is imperative to develop new strategies to overcome recurrence and chemoresistance of ovarian cancer. Repurposing previously-approved drugs is a cost-effective strategy for cancer drug discovery. The antiparasitic drug mebendazole (MBZ) is one of the most promising drugs with repurposing potential. Here, we investigate whether MBZ can overcome cisplatin resistance and sensitize chemoresistant ovarian cancer cells to cisplatin. We first established and characterized two stable and robust cisplatin-resistant (CR) human ovarian cancer lines and demonstrated that MBZ markedly inhibited cell proliferation, suppressed cell wounding healing/migration, and induced apoptosis in both parental and CR cells at low micromole range. Mechanistically, MBZ was revealed to inhibit multiple cancer-related signal pathways including ELK/SRF, NFKB, MYC/MAX, and E2F/DP1 in cisplatin-resistant ovarian cancer cells. We further showed that MBZ synergized with cisplatin to suppress cell proliferation, induce cell apoptosis, and blunt tumor growth in xenograft tumor model of human cisplatin-resistant ovarian cancer cells. Collectively, our findings suggest that MBZ may be repurposed as a synergistic sensitizer of cisplatin in treating chemoresistant human ovarian cancer, which warrants further clinical studies.

Hypoxia Preconditioning Promotes the Proliferation and Migration of Human Urine-Derived Stem Cells in Chronically Injured Liver of Mice by Upregulating CXCR4

Our previous studies reported that urine-derived stem cells (USCs) possess a strong self-renewal ability and multidirectional differentiation potential and thus are an ideal candidate cell source for hepatocellular transplantation. USC transplantation may repair the pathological changes of chronic liver injury to a certain extent, and hypoxia pretreatment may improve the recovery efficiency of USCs. Therefore, the present study aimed to investigate the possible mechanism of the improved recovery efficiency of hypoxia-pretreated USCs. A chronic liver injury model was established by intraperitoneal injection of carbon tetrachloride into nude mice. USCs were transplanted via caudal vein injection. Hematoxylin and eosin staining and Masson's staining were performed to determine the pathology of the liver. Immunofluorescence and frozen section biopsy were performed to determine differentiation and cell fusion in vivo. Cell coculture was used to detect cell fusion in vitro. The proliferative ability of USCs was evaluated using cell viability and colony formation assays, and the migratory functions of USCs were evaluated using wound healing and transwell assays. The degeneration of hepatocytes and the level of fibrosis in the hypoxia transplantation group were improved compared with the normoxia transplantation group. It was found that exogenous USCs may be differentiated into functional hepatocytes or fused with hepatocytes in vivo. C-X-C motif chemokine (CXC) ligand 12 (CXCL12) expression levels in liver tissue of the chronic liver injury model were upregulated compared with those in the control group. The expression of CXC receptor 4 (CXCR4) in hypoxia-pretreated USCs was also significantly upregulated. The results suggested that USCs fused with different types of liver cells and that hypoxia treatment promoted the fusion rate in vitro by upregulating CXCR4 signaling. Furthermore, hypoxia pretreatment promoted cell proliferation, migration, and cell fusion by inducing CXCR4 signaling, leading to USC-elicited liver tissue recovery following injury in vivo.

Indocyanine Green Uptake and Periodic Acid-Schiff Staining Method for Function Detection of Liver Cells are Affected by Different Cell Confluence

Hepatic stem cell transplantation has been demonstrated as an effective alternative therapy for the end-stage liver failure patients. Therefore, the functional detection of hepatic stem cell is essentially required. The present study confirmed that adenovirus BMP9 (Ad-BMP9) could increase the ALB-Gluc activity of HP14-19 hepatic progenitor cells, the expression of specific hepatic markers ALB, TAT, UGT1A were up-regulated while the hepatic stem cell markers DLK, AFP were down-regulated, and the number of positive Periodic acid-Schiff (PAS) stained cells were significantly higher than those in control group. However, the indocyanine green (ICG) uptake failed to be detectable in induced hepatocytes, which was inconsistent. By using another cell line LC14d, we found out that positive ICG uptake cells were located in the area of low cell density, while positive PAS stained cells were mainly concentrated in the area where cells were overlapped, indicating that different cell confluence might affect the outcomes of ICG uptake and PAS staining. A manual wound healing of Ad-BMP9 induced HP14-19 cells was made, the crawling cells were stained positive for ICG but not for PAS. Therefore, our finding may provide evidence for better application of PAS staining and ICG uptake assay in functional detection of mature hepatocytes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-021-00453-8.

Bone morphogenetic protein 4 (BMP4) promotes hepatic glycogen accumulation and reduces glucose level in hepatocytes through mTORC2 signaling pathway

Liver is an important organ for regulating glucose and lipid metabolism. Recent studies have shown that bone morphogenetic proteins (BMPs) may play important roles in regulating glucose and lipid metabolism. In our previous studies, we demonstrated that BMP4 significantly inhibits hepatic steatosis and lowers serum triglycerides, playing a protective role against the progression of non-alcoholic fatty liver disease (NAFLD). However, the direct impact of BMP4 on hepatic glucose metabolism is poorly understood. Here, we investigated the regulatory roles of BMP4 in hepatic glucose metabolism. Through a comprehensive analysis of the 14 types of BMPs, we found that BMP4 was one of the most potent BMPs in promoting hepatic glycogen accumulation, reducing the level of glucose in hepatocytes and effecting the expression of genes related to glucose metabolism. Mechanistically, we demonstrated that BMP4 reduced the hepatic glucose levels through the activation of mTORC2 signaling pathway in vitro and in vivo. Collectively, our findings strongly suggest that BMP4 may play an essential role in regulating hepatic glucose metabolism. This knowledge should aid us to understand the molecular pathogenesis of NAFLD, and may lead to the development of novel therapeutics by exploiting the inhibitory effects of BMPs on hepatic glucose and lipid metabolism.

Dietary schizophyllan reduces mitochondrial damage by activating SIRT3 in mice

Schizophyllan (SPG), produced by Schizophyllum commune, is an exopolysaccharide with multiple academic and commercial uses, including in the food industry and for various medical functions. We previously demonstrated that SPG conjugated with c-Src peptide exerted a significant therapeutic effect on mouse models of the acute inflammatory diseases polymicrobial sepsis and ulcerative colitis. Here we extended these results by investigating whether SPG exerted a protective effect against mitochondrial damage in the liver via sirtuin 3 (SIRT3) induction, focusing on the deacetylation of succinate dehydrogenase A (SDHA) and superoxide dismutase 2 (SOD2). Liver damage models induced by alcohol or conjugated linoleic acid (CLA, which simulates lipodystrophy) in SIRT3^-/-, SOD2^-/-, and SDHA^-/- mice were used. Results showed that dietary supplementation with SPG induced SIRT3 activation; this was involved in mitochondrial metabolic resuscitation that countered the adverse effects of alcoholic liver disease and CLA-induced damage. The mitochondrial SIRT3 mediated the deacetylation and activation of SOD2 in the liver and SDHA in adipose tissues, suggesting that SPG supplementation reduced ethanol-induced liver damage and CLA-induced adverse dietary effects via SIRT3-SOD2 and SIRT3-SDHA signaling, respectively. Together, these results suggest that dietary SPG has a previously unrecognized role in SIRT3-mediated mitochondrial metabolic resuscitation during mitochondria-related diseases.

Long non-coding RNA (lncRNA) H19 induces hepatic steatosis through activating MLXIPL and mTORC1 networks in hepatocytes

Liver plays an essential role in regulating lipid metabolism, and chronically disturbed hepatic metabolism may cause obesity and metabolic syndrome, which may lead to non-alcoholic fatty liver disease (NAFLD). Increasing evidence indicates long non-coding RNAs (lncRNAs) play an important role in energy metabolism. Here, we investigated the role of lncRNA H19 in hepatic lipid metabolism and its potential association with NAFLD. We found that H19 was up-regulated in oleic acid-induced steatosis and during the development of high-fat diet (HFD)-induced NAFLD. Exogenous overexpression of H19 in hepatocytes induced lipid accumulation and up-regulated the expression of numerous genes involved in lipid synthesis, storage and breakdown, while silencing endogenous H19 led to a decreased lipid accumulation in hepatocytes. Mechanistically, H19 was shown to promote hepatic steatosis by up-regulating lipogenic transcription factor MLXIPL. Silencing Mlxipl diminished H19-induced lipid accumulation in hepatocytes. Furthermore, H19-induced lipid accumulation was effectively inhibited by PI3K/mTOR inhibitor PF-04691502. Accordingly, H19 overexpression in hepatocytes up-regulated most components of the mTORC1 signalling axis, which were inhibited by silencing endogenous H19. In vivo hepatocyte implantation studies further confirm that H19 promoted hepatic steatosis by up-regulating both mTORC1 signalling axis and MLXIPL transcriptional network. Collectively, these findings strongly suggest that H19 may play an important role in regulating hepatic lipid metabolism and may serve as a potential therapeutic target for NAFLD.

A simplified 3D liver microsphere tissue culture model for hepatic cell signaling and drug-induced hepatotoxicity studies

Although a number of experimental models have been developed for liver research, each has its own advantages and disadvantages. The present study attempted to develop a simple and effective 3‑dimensional mouse liver microsphere tissue culture (LMTC) model in vitro for the analysis of hepatic functions. Hepatic characteristics and potential applications of this model were compared with that of mouse model in vivo and mouse primary hepatocytes in vitro. Using freshly‑perfused mouse liver tissue passed through 80‑mesh sift strainer (sift80), it was demonstrated that under the optimal culture conditions, the sift80 microsphere tissue cultured in 2% bovine calf serum medium remained viable with marked proliferating cell nuclear antigen and anti‑Myc proto‑oncogene protein expression, exhibited normal hepatic functions including indocyanine green (ICG) uptake/release and periodic acid‑Schiff staining, and expressed hepatocyte‑specific genes for up to 2 weeks. The microsphere tissue was responsive to bone morphogenic protein 9 (BMP9) stimulation leading to upregulation of downstream targets of BMP9 signaling. Furthermore, 3 commonly‑used liver‑damaging drugs were indicated to effectively inhibit hepatic ICG uptake, and induce the expression of hepatotoxicity‑associated genes. Therefore, this simplified LMTC model may be a useful in vitro tissue culture model to investigate drug‑induced liver injury and metabolism, and hepatocyte‑based cell singling.

Comprehensive Analysis of Human microRNA-mRNA Interactome

MicroRNAs play a key role in the regulation of gene expression. A majority of microRNA–mRNA interactions remain unidentified. Despite extensive research, our ability to predict human microRNA-mRNA interactions using computational algorithms remains limited by a complexity of the models for non-canonical interactions, and an abundance of false-positive results. Here, we present the landscape of human microRNA–mRNA interactions derived from comprehensive analysis of HEK293 and Huh7.5 datasets, along with publicly available microRNA and mRNA expression data. We show that, while only 1–2% of human genes were the most regulated by microRNAs, few cell line–specific RNAs, including EEF1A1 and HSPA1B in HEK293 and AFP, APOB, and MALAT1 genes in Huh7.5, display substantial “sponge-like” properties. We revealed a group of microRNAs that are expressed at a very high level, while interacting with only a few mRNAs, which, indeed, serve as their specific expression regulators. In order to establish reliable microRNA-binding regions, we collected and systematically analyzed the data from 79 CLIP datasets of microRNA-binding sites. We report 46,805 experimentally confirmed mRNA–miRNA duplex regions. Resulting dataset is available at http://score.generesearch.ru/services/mirna/. Our study provides initial insight into the complexity of human microRNA–mRNA interactions.

ATRA induces the differentiation of hepatic progenitor cells by upregulating microRNA-200a

Hepatic progenitor cells (HPCs) are potential seed cells for hepatocyte transplantation treatment of liver diseases. ATRA can induce the differentiation and mature function of hepatic progenitor cells, but the mechanism is still poorly understood. Here, by using microRNA array to analyze the expression profiles of microRNA (miR), we found that miR-200 family molecules in HPCs were upregulated after ATRA treatment, especially miR-200a-3p, 200c-3p, and 141-3p. ATRA induction could downregulate the expression of hepatic stem markers Oct4 and AFP, and improve the expression of hepatic markers ALB, CK18, and TAT, and the activity of ALB-GLuc, as well as indocyanine green uptake and glycogen storage function of HPCs. These above effects of ATRA on HPC differentiation were almost inhibited by blocking of miR-200a-3p, but not miR-200c-3p and 141-3p using antagomir. Cell autophagy is associated with ATRA regulation in HPCs, compared with control group, the expression of LC3 and Beclin1 increased in ATRA-treated HPCs, and orange and red fluorescent spot, which represents autophagy flow, also enhanced after ATRA treatment. However, ATRA-induced cell autophagy level was inhibited in antagomir-200a-3p+ATRA-treated cells. Therefore, the present study indicates that antagomir-200a-3p is related to ATRA-induced hepatic differentiation of HPCs through regulating cell autophagy, supporting the possible use of ATRA as a key inducer in HPC-based therapy of liver diseases.

BMP9-induced osteoblastic differentiation requires functional Notch signaling in mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent progenitors that can differentiate into multiple lineages including osteoblastic lineage. Osteogenic differentiation of MSCs is a cascade that recapitulates most, if not all, of the molecular events occurring during embryonic skeletal development, which is regulated by numerous signaling pathways including bone morphogenetic proteins (BMPs). Through a comprehensive analysis of the osteogenic activity, we previously demonstrated that BMP9 is the most potent BMP for inducing bone formation from MSCs both in vitro and in vivo. However, as one of the least studied BMPs, the essential mediators of BMP9-induced osteogenic signaling remain elusive. Here we show that BMP9-induced osteogenic signaling in MSCs requires intact Notch signaling. While the expression of Notch receptors and ligands are readily detectable in MSCs, Notch inhibitor and dominant-negative Notch1 effectively inhibit BMP9-induced osteogenic differentiation in vitro and ectopic bone formation in vivo. Genetic disruption of Notch pathway severely impairs BMP9-induced osteogenic differentiation and ectopic bone formation from MSCs. Furthermore, while BMP9-induced expression of early-responsive genes is not affected by defective Notch signaling, BMP9 upregulates the expression of Notch receptors and ligands at the intermediate stage of osteogenic differentiation. Taken together, these results demonstrate that Notch signaling may play an essential role in coordinating BMP9-induced osteogenic differentiation of MSCs.

Monensin inhibits cell proliferation and tumor growth of chemo-resistant pancreatic cancer cells by targeting the EGFR signaling pathway

Pancreatic ductal adenocarcinoma (PDAC) is one of the most deadly malignancies with <5% five-year survival rate due to late diagnosis, limited treatment options and chemoresistance. There is thus an urgent unmet clinical need to develop effective anticancer drugs to treat pancreatic cancer. Here, we study the potential of repurposing monensin as an anticancer drug for chemo-resistant pancreatic cancer. Using the two commonly-used chemo-resistant pancreatic cancer cell lines PANC-1 and MiaPaCa-2, we show that monensin suppresses cell proliferation and migration, and cell cycle progression, while solicits apoptosis in pancreatic cancer lines at a low micromole range. Moreover, monensin functions synergistically with gemcitabine or EGFR inhibitor erlotinib in suppressing cell growth and inducing cell death of pancreatic cancer cells. Mechanistically, monensin suppresses numerous cancer-associated pathways, such as E2F/DP1, STAT1/2, NFkB, AP-1, Elk-1/SRF, and represses EGFR expression in pancreatic cancer lines. Furthermore, the in vivo study shows that monensin blunts PDAC xenograft tumor growth by suppressing cell proliferation via targeting EGFR pathway. Therefore, our findings demonstrate that monensin can be repurposed as an effective anti-pancreatic cancer drug even though more investigations are needed to validate its safety and anticancer efficacy in pre-clinical and clinical models.

Reversibly immortalized human umbilical cord-derived mesenchymal stem cells (UC-MSCs) are responsive to BMP9-induced osteogenic and adipogenic differentiation

Human mesenchymal stem cells (MSCs) are a heterogeneous subset of nonhematopoietic multipotent stromal stem cells and can differentiate into mesodermal lineage, such as adipocytes, osteocytes, and chondrocytes, as well as ectodermal and endodermal lineages. Human umbilical cord (UC) is one of the most promising sources of MSCs. However, the molecular and cellular characteristics of UC-derived MSCs (UC-MSCs) require extensive investigations, which are hampered by the limited lifespan and the diminished potency over passages. Here, we used the piggyBac transposon-based simian virus 40 T antigen (SV40T) immortalization system and effectively immortalized UC-MSCs, yielding the iUC-MSCs. A vast majority of the immortalized lines are positive for MSC markers but not for hematopoietic markers. The immortalization phenotype of the iUC-MSCs can be effectively reversed by flippase recombinase-induced the removal of SV40T antigen. While possessing long-term proliferation capability, the iUC-MSCs are not tumorigenic in vivo. Upon bone morphogenetic protein 9 (BMP9) stimulation, the iUC-MSC cells effectively differentiate into osteogenic, chondrogenic, and adipogenic lineages both in vitro and in vivo, which is indistinguishable from that of primary UC-MSCs, indicating that the immortalized UC-MSCs possess the characteristics similar to that of their primary counterparts and retain trilineage differentiation potential upon BMP9 stimulation. Therefore, the engineered iUC-MSCs should be a valuable alternative cell source for studying UC-MSC biology and their potential utilities in immunotherapies and regenerative medicine.

Reversibly immortalized hepatic progenitor cell line containing double suicide genes

A large number of functional hepatocytes is required for bioartificial liver therapy. Simian virus 40 T-antigen (SV40T) has been previously reported to improve the immortalized proliferation of primary hepatocytes to generate a sufficient number of cells; however, these long-term immortalized hepatocytes may induce further malignant transformation in vivo. In the present study, the SV40T immortalization gene and two suicide genes, herpes simplex virus thymidine kinase (HSV-tk) and cytosine deaminase (CD), were transducted into primary hepatocytes to construct a novel type of Cre/LoxP-mediated reversible immortalized hepatocyte line. Polymerase chain reaction analysis and western blotting confirmed that the SV40T, HSV-tk and CD genes were successfully inserted into hepatic progenitor cells and their expression was controlled by Cre/LoxP recombination. Total removal of SV40T could be achieved via the ganciclovir (GCV)/HSV-tk suicide system. Cells maintained their biosafety in vivo with CD gene expression and 5-fluoro-cytosine (5-FC) induced cell death. Following transplantation into the carbon tetrachloride (CCl₄) model group, the majority of cells had survived after 14 days post-implantation and a number of the cells had transported into the liver parenchyma. When compared with the CCl₄ model group, the transplanted cells repaired the liver biochemical index and pathological structure markedly. Thus, the present study reports a novel reversible immortalized hepatocyte with double suicide genes, which exhibited the cellular phenotype and recovery function of normal liver cells. This method maximally guaranteed the biological safety of immortalized hepatocytes for in vivo application, providing a reliable, safe and ideal cell material for the artificial liver technique.

A blockade of PI3Kγ signaling effectively mitigates angiotensin II-induced renal injury and fibrosis in a mouse model

Chronic kidney disease (CKD) poses a formidable challenge for public healthcare worldwide as vast majority of patients with CKD are also at risk of accelerated cardiovascular disease and death. Renal fibrosis is the common manifestation of CKD that usually leads to end-stage renal disease although the molecular events leading to chronic renal fibrosis and eventually chronic renal failure remain to be fully understood. Nonetheless, emerging evidence suggests that an aberrant activation of PI3Kγ signaling may play an important role in regulating profibrotic phenotypes. Here, we investigate whether a blockade of PI3Kγ signaling exerts any beneficial effect on alleviating kidney injury and renal fibrosis. Using a mouse model of angiotensin II (Ang II)-induced renal damage, we demonstrate that PI3Kγ inhibitor AS605240 effectively mitigates Ang II-induced increases in serum creatinine and blood urea nitrogen, renal interstitial collagen deposition, the accumulation of ECM proteins and the expression of α-Sma and fibrosis-related genes in vivo. Mechanistically, we reveal that AS605240 effectively inhibits Ang II-induced cell proliferation and phosphorylation of Akt in fibroblast cells. Furthermore, we demonstrate that Ang II-upregulated expression of IL-6, Tnf-α, IL-1β and Tgf-β1 is significantly attenuated in the mice treated with AS605240. Taken together, our results demonstrate that PI3Kγ may function as a critical mediator of Ang II-induced renal injury and fibrosis. It is thus conceivable that targeted inhibition of PI3Kγ signaling may constitute a novel therapeutic approach to the clinical management of renal fibrosis, renal hypertension and/or CKD.

Establishment and functional characterization of the reversibly immortalized mouse glomerular podocytes (imPODs)

Glomerular podocytes are highly specialized epithelial cells and play an essential role in establishing the selective permeability of the glomerular filtration barrier of kidney. Maintaining the viability and structural integrity of podocytes is critical to the clinical management of glomerular diseases, which requires a thorough understanding of podocyte cell biology. As mature podocytes lose proliferative capacity, a conditionally SV40 mutant tsA58-immortalized mouse podocyte line (designated as tsPC) was established from the Immortomouse over 20 years ago. However, the utility of the tsPC cells is hampered by the practical inconvenience of culturing these cells. In this study, we establish a user-friendly and reversibly-immortalized mouse podocyte line (designated as imPOD), on the basis of the tsPC cells by stably expressing the wildtype SV40 T-antigen, which is flanked with FRT sites. We show the imPOD cells exhibit long-term high proliferative activity, which can be effectively reversed by FLP recombinase. The imPOD cells express most podocyte-related markers, including WT-1, Nephrin, Tubulin and Vinculin, but not differentiation marker Synaptopodin. The imPOD cells do not form tumor-like masses in vivo. We further demonstrate that TGFβ1 induces a podocyte injury-like response in the FLP-reverted imPOD cells by suppressing the expression of slit diaphragm-associated proteins P-Cadherin and ZO-1 and upregulating the expression of mesenchymal markers, α-SMA, Vimentin and Nestin, as well as fibrogenic factors CTGF and Col1a1. Collectively, our results strongly demonstrate that the newly engineered imPOD cells should be a valuable tool to study podocyte biology both under normal and under pathological conditions.

Hepa1-6-FLuc cell line with the stable expression of firefly luciferase retains its primary properties with promising bioluminescence imaging ability

Reliable animal models are required for the in vivo study of the molecular mechanisms and effects of chemotherapeutic drugs in hepatocarcinoma. In vivo tracing techniques based on firefly luciferase (FLuc) may optimize the non-invasive monitoring of experimental animals. The present study established a murine Hepa1-6-FLuc cell line that stably expressed a retrovirus-delivered FLuc protein gene. The cell morphology, proliferation, migration and invasion ability of Hepa1-6-FLuc cells were the same as that of the Hepa1-6 cells, and thus is suitable to replace Hepa1-6 cells in the construction of hepatocarcinoma animal models. No differences in subcutaneous tumor mass and its pathomorphology from implanted Hepa1-6-FLuc cells were observed compared with Hepa1-6 control tumors. Bioluminescence imaging indicated that the Luc signal of the Hepa1-6-FLuc cells was consistently strengthened with increases in tumor mass; however, the Luc signal of Hepa1-6-AdFLuc became weaker and eventually disappeared during tumor development. Therefore, compared with the transient expression by adenovirus, stable expression of the FLuc gene in Hepa1-6 cells may better reflect cell proliferation and survival in vivo, and provide a reliable source for the establishment of hepatocarcinoma models.

Noncanonical Wnt signaling plays an important role in modulating canonical Wnt-regulated stemness, proliferation and terminal differentiation of hepatic progenitors

The liver provides vital metabolic, exocrine and endocrine functions in the body as such pathological conditions of the liver lead to high morbidity and mortality. The liver is highly regenerative and contains facultative stem cells that become activated during injury to replicate to fully recover mass and function. Canonical Wnt/β-catenin signaling plays an important role in regulating the proliferation and differentiation of liver progenitor cells during liver regeneration. However, possible roles of noncanonical Wnts in liver development and regeneration remain undefined. We previously established a reversibly-immortalized hepatic progenitor cell line (iHPx), which retains hepatic differentiation potential. Here, we analyze the expression pattern of the essential components of both canonical and noncanonical Wnt signaling pathways at different postnatal stages of mouse liver tissues and iHPx cells. We find that noncanonical Wnt4, Wnt5a, Wnt9b, Wnt10a and Wnt10b, are highly expressed concordantly with the high levels of canonical Wnts in late stages of liver tissues. Wnt5a, Wnt9b, Wnt10a and Wnt10b are able to antagonize Wnt3a-induced β-catenin/TCF activity, reduce the stemness of iHPx cells, and promote hepatic differentiation of liver progenitors. Stem cell implantation assay demonstrates that Wnt5a, Wnt9b, Wnt10a and Wnt10b can inhibit cell proliferation and promote hepatic differentiation of the iHPx progenitor cells. Our results strongly suggest that noncanonical Wnts may play an important role in fine-tuning Wnt/β-catenin functions during liver development and liver regeneration. Thus, understanding regulatory mechanisms governing proliferation and differentiation of liver progenitor cells may hold great promise to facilitate liver regeneration and/or progenitor cell-based therapies for liver diseases.

CRISPR/Cas9-mediated reversibly immortalized mouse bone marrow stromal stem cells (BMSCs) retain multipotent features of mesenchymal stem cells (MSCs)

Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells that can undergo self-renewal and differentiate into multi-lineages. Bone marrow stromal stem cells (BMSCs) represent one of the most commonly-used MSCs. In order to overcome the technical challenge of maintaining primary BMSCs in long-term culture, here we seek to establish reversibly immortalized mouse BMSCs (imBMSCs). By exploiting CRISPR/Cas9-based homology-directed-repair (HDR) mechanism, we target SV40T to mouse Rosa26 locus and efficiently immortalize mouse BMSCs (i.e., imBMSCs). We also immortalize BMSCs with retroviral vector SSR #41 and establish imBMSC41 as a control line. Both imBMSCs and imBMSC41 exhibit long-term proliferative capability although imBMSC41 cells have a higher proliferation rate. SV40T mRNA expression is 130% higher in imBMSC41 than that in imBMSCs. However, FLP expression leads to 86% reduction of SV40T expression in imBMSCs, compared with 63% in imBMSC41 cells. Quantitative genomic PCR analysis indicates that the average copy number of SV40T and hygromycin is 1.05 for imBMSCs and 2.07 for imBMSC41, respectively. Moreover, FLP expression removes 92% of SV40T in imBMSCs at the genome DNA level, compared with 58% of that in imBMSC41 cells, indicating CRISPR/Cas9 HDR-mediated immortalization of BMSCs can be more effectively reversed than that of retrovirus-mediated random integrations. Nonetheless, both imBMSCs and imBMSC41 lines express MSC markers and are highly responsive to BMP9-induced osteogenic, chondrogenic and adipogenic differentiation in vitro and in vivo. Thus, the engineered imBMSCs can be used as a promising alternative source of primary MSCs for basic and translational research in the fields of MSC biology and regenerative medicine.

Periodic acid‑Schiff staining method for function detection of liver cells is affected by 2% horse serum in induction medium

Developing a thorough understanding of experimental methods of hepatic differentiation in hepatic progenitor cells (HPCs) should expand the knowledge of hepatocyte induction in vitro and may help to develop cell transplantation therapies for the clinical usage of HPCs in liver diseases. A previous induction method effectively induced differentiation and metabolic abilities in HPCs. Periodic acid-Schiff (PAS) staining is used to identify glycogen synthesis and hepatocyte function; however, this method failed to detect induced hepatocytes. The present study aimed to investigate the possible factors affecting the previous confusing results of PAS staining. Removal of single induction factors, including dexamethasone, hepatic growth factor and fibroblast growth factor 4 from the induction media did not restore PAS staining, whereas replacement of 2% horse serum (HS) with 10% fetal bovine serum (FBS) significantly increased the number of PAS positive cells. Following 12 days of basal induction, replacing the induction medium with media containing 10% FBS for 12–72 h significantly improved PAS staining, but did not influence indocyanine green uptake. Furthermore, incubation in induction medium with 10% FBS following 12 days of normal induction did not affect the expression of hepatic markers and mature function of HPCs. Therefore, the present study suggested that 2% HS in the induction medium did not affect the hepatic function of induced cells, but did affect glycogen storage, whereas replacement of medium with 10% FBS in advance of PAS staining may restore the failure of PAS staining in low serum concentrations of induced hepatocytes.

lncRNA H19 mediates BMP9-induced osteogenic differentiation of mesenchymal stem cells (MSCs) through Notch signaling

Mesenchymal stem cells (MSCs) are multipotent progenitor cells that can undergo self-renewal and differentiate into multiple lineages. Osteogenic differentiation from MSCs is a well-orchestrated process and regulated by multiple signaling pathways. We previously demonstrated that BMP9 is one of the most potent osteogenic factors. However, molecular mechanism through which BMP9 governs osteoblastic differentiation remains to be fully understood. Increasing evidence indicates noncoding RNAs (ncRNAs) may play important regulatory roles in many physiological and/or pathologic processes. In this study, we investigate the role of lncRNA H19 in BMP9-regulated osteogenic differentiation of MSCs. We demonstrated that H19 was sharply upregulated at the early stage of BMP9 stimulation of MSCs, followed by a rapid decease and gradual return to basal level. This process was correlated with BMP9-induced expression of osteogenic markers. Interestingly, either constitutive H19 expression or silencing H19 expression in MSCs significantly impaired BMP9-induced osteogenic differentiation in vitro and in vivo, which was effectively rescued by the activation of Notch signaling. Either constitutive H19 expression or silencing H19 expression led to the increased expression of a group of miRNAs that are predicted to target Notch ligands and receptors. Thus, these results indicate that lncRNA H19 functions as an important mediator of BMP9 signaling by modulating Notch signaling-targeting miRNAs. Our findings suggest that the well-coordinated biphasic expression of lncRNA H19 may be essential in BMP9-induced osteogenic differentiation of MSCs, and that dysregulated H19 expression may impair normal osteogenesis, leading to pathogenic processes, such as bone tumor development.

BMP9 induces osteogenesis and adipogenesis in the immortalized human cranial suture progenitors from the patent sutures of craniosynostosis patients

The cranial suture complex is a heterogeneous tissue consisting of osteogenic progenitor cells and mesenchymal stem cells (MSCs) from bone marrow and suture mesenchyme. The fusion of cranial sutures is a highly coordinated and tightly regulated process during development. Craniosynostosis is a congenital malformation caused by premature fusion of cranial sutures. While the progenitor cells derived from the cranial suture complex should prove valuable for studying the molecular mechanisms underlying suture development and pathogenic premature suture fusion, primary human cranial suture progenitors (SuPs) have limited life span and gradually lose osteoblastic ability over passages. To overcome technical challenges in maintaining sufficient and long-term culture of SuPs for suture biology studies, we establish and characterize the reversibly immortalized human cranial suture progenitors (iSuPs). Using a reversible immortalization system expressing SV40 T flanked with FRT sites, we demonstrate that primary human suture progenitor cells derived from the patent sutures of craniosynostosis patients can be efficiently immortalized. The iSuPs maintain long-term proliferative activity, express most of the consensus MSC markers and can differentiate into osteogenic and adipogenic lineages upon BMP9 stimulation in vitro and in vivo. The removal of SV40 T antigen by FLP recombinase results in a decrease in cell proliferation and an increase in the endogenous osteogenic and adipogenic capability in the iSuPs. Therefore, the iSuPs should be a valuable resource to study suture development, intramembranous ossification and the pathogenesis of craniosynostosis, as well as to explore cranial bone tissue engineering.

Transcription factor Oct4 promotes osteosarcoma by regulating lncRNA AK055347

Osteosarcoma is the most common primary bone tumor in children and adolescents, typically presenting with a poor prognosis. Octamer-binding transcription factor 4 (Oct4) protein, encoded by the POU class 5 homeobox 1 gene, is important in maintaining self-renewal of pluripotent stem cells, and is closely associated with cancer. However, its role in osteosarcoma remains to be elucidated. The present study observed Oct4 was markedly increased in osteosarcoma cell lines and in human osteosarcoma tissue samples. Following Oct4 downregulation by small interfering RNA (siRNA) in osteosarcoma F5M2 cells, the cells exhibited significant decreases in proliferation and invasion ability, and an increase in cell apoptosis. Notably, downregulation of Oct4 decreased the expression of AK055347, a newly identified long noncoding RNA (lncRNA) in human tissues. The downregulation of AK055347 by siRNA resulted in a significant suppressive effect on proliferative and invasive ability, and promotion of cell apoptosis in osteosarcoma cells. Thus, the current study suggests Oct4 exerts a promoting effect in osteosarcoma, and identifies a novel lncRNA in osteosarcoma progression.

The Prodomain-Containing BMP9 Produced from a Stable Line Effectively Regulates the Differentiation of Mesenchymal Stem Cells

BACKGROUND

BMPs play important roles in regulating stem cell proliferation and differentiation. Using adenovirus-mediated expression of the 14 types of BMPs we demonstrated that BMP9 is one of the most potent BMPs in inducing osteogenic differentiation of mesenchymal stem cells (MSCs), which was undetected in the early studies using recombinant BMP9 proteins. Endogenous BMPs are expressed as a precursor protein that contains an N-terminal signal peptide, a prodomain and a C-terminal mature peptide. Most commercially available recombinant BMP9 proteins are purified from the cells expressing the mature peptide. It is unclear how effectively these recombinant BMP9 proteins functionally recapitulate endogenous BMP9.

METHODS

A stable cell line expressing the full coding region of mouse BMP9 was established in HEK-293 cells by using the piggyBac transposon system. The biological activities and stability of the conditioned medium generated from the stable line were analyzed.

RESULTS

The stable HEK-293 line expresses a high level of mouse BMP9. BMP9 conditioned medium (BMP9-cm) was shown to effectively induce osteogenic differentiation of MSCs, to activate BMP-R specific Smad signaling, and to up-regulate downstream target genes in MSCs. The biological activity of BMP9-cm is at least comparable with that induced by AdBMP9 in vitro. Furthermore, BMP9-cm exhibits an excellent stability profile as its biological activity is not affected by long-term storage at -80ºC, repeated thawing cycles, and extended storage at 4ºC.

CONCLUSIONS

We have established a producer line that stably expresses a high level of active BMP9 protein. Such producer line should be a valuable resource for generating biologically active BMP9 protein for studying BMP9 signaling mechanism and functions.

Increased efficiency of testicular tumor chemotherapy by ultrasound microbubble-mediated targeted transfection of siMDR1

The MDR1 gene encoding P-glycoprotein (P-gp) is an ATP-dependent drug efflux transporter and is related to drug resistance of yolk sac tumors. Drug resistence may be an important factor for the low efficiency of chemotherapy in the treatment of testicular tumors. P-gp, encoded by the MDR1 gene, is an ATP-binding cassette transporter. P-gp exhibits high expression in capillary endothelial cells of the testis and prevents the intracellular accumulation of chemotherapy agents in testicular tumor cells, resulting in drug resistance. In the present study, we aimed to use specific siRNA to silence the expression of the MDR1 gene and P-gp, leading to the reversal of multidrug resistance of testicular tumors and contributing a suitable condition for chemotherapy. Ultrasound microbubble-mediated delivery is a safe and effective tool for gene delivery. In the present study, we demonstrated that ultrasound microbubble-mediated delivery effectively improved the siMDR1 gene transfection in interstitial capillary endothelial cells of the testis, inhibited the expression of P-gp and increased daunorubicin accumulation. The testis tumor model was successfully constructed by injecting 1x10(7) yolk sac tumor cells in 3-week-old Sprague-Dawley rats. Ultrasound microbubble-mediated siMDR1 gene therapy improved the effect of chemotherapy on the testicular tumors. The testicular volume was reduced, the number of tumor cells within the testicular tissues decreased, and pathological changes were mostly recovered. Therefore, the present study indicated that ultrasound microbubble-mediated siMDR1 gene therapy in vivo reversed drug resistance by regulating P-gp expression, providing a promising method for the treatment of testicular tumors.

TqPCR: A Touchdown qPCR Assay with Significantly Improved Detection Sensitivity and Amplification Efficiency of SYBR Green qPCR

The advent of fluorescence-based quantitative real-time PCR (qPCR) has revolutionized the quantification of gene expression analysis in many fields, including life sciences, agriculture, forensic science, molecular diagnostics, and medicine. While SYBR Green-based qPCR is the most commonly-used platform due to its inexpensive nature and robust chemistry, quantifying the expression of genes with low abundance or RNA samples extracted from highly restricted or limited sources can be challenging because the detection sensitivity of SYBR Green-based qPCR is limited. Here, we develop a novel and effective touchdown qPCR (TqPCR) protocol by incorporating a 4-cycle touchdown stage prior to the quantification amplification stage. Using the same cDNA templates, we find that TqPCR can reduce the average Cq values for Gapdh, Rps13, and Hprt1 reference genes by 4.45, 5.47, and 4.94 cycles, respectively, when compared with conventional qPCR; the overall average Cq value reduction for the three reference genes together is 4.95. We further find that TqPCR can improve PCR amplification efficiency and thus increase detection sensitivity. When the quantification of Wnt3A-induced target gene expression in mesenchymal stem cells is analyzed, we find that, while both conventional qPCR and TqPCR can detect the up-regulation of the relatively abundant target Axin2, only TqPCR can detect the up-regulation of the lowly-expressed targets Oct4 and Gbx2. Finally, we demonstrate that the MRQ2 and MRQ3 primer pairs derived from mouse reference gene Tbp can be used to validate the RNA/cDNA integrity of qPCR samples. Taken together, our results strongly suggest that TqPCR may increase detection sensitivity and PCR amplification efficiency. Overall, TqPCR should be advantageous over conventional qPCR in expression quantification, especially when the transcripts of interest are lowly expressed, and/or the availability of total RNA is highly restricted or limited.

Three-dimensional co-culture of hepatic progenitor cells and mesenchymal stem cells in vitro and in vivo

INTRODUCTION

Here we co-cultured hepatic progenitor cells (HPCs) and mesenchymal stem cells (MSCs) to investigate whether the co-culture environments could increase hepatocytes form.

METHODS

Three-dimensional (3D) co-culture model of HPCs and MSCs was developed and morphological features of cells were continuously observed. Hepatocyte specific markers Pou5f1/Oct4, AFP, CK-18 and Alb were analyzed to confirm the differentiation of HPCs. The mRNA expression of CK-18 and Alb was analyzed by RT-PCR to investigate the influence of co-culture model to the terminal differentiation process of mature hepatocytes. The functional properties of hepatocyte-like cells were detected by continuously monitoring the albumin secretion using Gaussia luciferase assays. Scaffolds with HPCs and MSCs were implanted into nude mouse subcutaneously to set up the in vivo co-culture model.

RESULTS

Although two groups formed smooth spheroids and high expressed of CK-18 and Alb, hybrid spheroids had more regular structures and higher cell density. CK-18 and Alb mRNA were at a relatively higher expression level in co-culture system during the whole cultivation time (P < 0.05). Albumin secretion rates in the hybrid spheroids had been consistently higher than that in the mono-culture spheroids (P < 0.05). In vivo, the hepatocyte-like cells were consistent with the morphological features of mature hepatocytes and more well-differentiated hepatocyte-like cells were observed in the co-culture group.

CONCLUSIONS

HPCs and MSCs co-culture system is an efficient way to form well-differentiated hepatocyte-like cells, hence, may be helpful to the cell therapy of hepatic tissues and alleviate the problem of hepatocytes shortage.

Sustained high level transgene expression in mammalian cells mediated by the optimized piggyBac transposon system

Sustained, high level transgene expression in mammalian cells is desired in many cases for studying gene functions. Traditionally, stable transgene expression has been accomplished by using retroviral or lentiviral vectors. However, such viral vector-mediated transgene expression is often at low levels and can be reduced over time due to low copy numbers and/or chromatin remodeling repression. The piggyBac transposon has emerged as a promising non-viral vector system for efficient gene transfer into mammalian cells. Despite its inherent advantages over lentiviral and retroviral systems, piggyBac system has not been widely used, at least in part due to their limited manipulation flexibilities. Here, we seek to optimize piggyBac-mediated transgene expression and generate a more efficient, user-friendly piggyBac system. By engineering a panel of versatile piggyBac vectors and constructing recombinant adenoviruses expressing piggyBac transposase (PBase), we demonstrate that adenovirus-mediated PBase expression significantly enhances the integration efficiency and expression level of transgenes in mesenchymal stem cells and osteosarcoma cells, compared to that obtained from co-transfection of the CMV-PBase plasmid. We further determine the drug selection timeline to achieve optimal stable transgene expression. Moreover, we demonstrate that the transgene copy number of piggyBac-mediated integration is approximately 10 times higher than that mediated by retroviral vectors. Using the engineered tandem expression vector, we show that three transgenes can be simultaneously expressed in a single vector with high efficiency. Thus, these results strongly suggest that the optimized piggyBac system is a valuable tool for making stable cell lines with sustained, high transgene expression.