The evolving roles of Wnt signaling in stem cell proliferation and differentiation, the development of human diseases, and therapeutic opportunities

The evolutionarily conserved Wnt signaling pathway plays a central role in develop-ment and adult tissue homeostasis across species.Wnt proteins are secreted,lipid-modified signaling molecules that activate the canonical(β-catenin dependent)and non-canonical(β-catenin independent)Wnt signaling pathways.Cellular behaviors such as proliferation,differ-entiation,maturation,and proper body-axis specification are carried out by the canonical pathway,which is the best characterized of the known Wnt signaling paths.Wnt signaling has emerged as an important factor in stem cell biology and is known to affect the self-renewal of stem cells in various tissues.This includes but is not limited to embryonic,hematopoietic,mesenchymal,gut,neural,and epidermal stem cells.Wnt signaling has also been implicated in tumor cells that exhibit stem cell-like properties.Wnt signaling is crucial for bone formation and presents a potential target for the development of therapeutics for bone disorders.Not surprisingly,aberrant Wnt signaling is also associated with a wide variety of diseases,including cancer.Mutations of Wnt pathway members in cancer can lead to unchecked cell proliferation,epithelial-mesenchymal transition,and metastasis.Altogether,advances in the understand-ing of dysregulated Wnt signaling in disease have paved the way for the development of novel therapeutics that target components of the Wnt pathway.Beginning with a brief overview of the mechanisms of canonical and non-canonical Wnt,this review aims to summarize the cur-rent knowledge of Wnt signaling in stem cells,aberrations to the Wnt pathway associated with diseases,and novel therapeutics targeting the Wnt pathway in preclinical and clinical studies.

Canonical and noncanonical Wnt signaling: Multilayered mediators, signaling mechanisms and major signaling crosstalk

Wnt signaling plays a major role in regulating cell proliferation and differentiation.The Wnt ligands are a family of 19 secreted glycoproteins that mediate their signaling effects via binding to Frizzled receptors and LRP5/6 coreceptors and transducing the signal either throughβ-catenin in the canonical pathway or through a series of other proteins in the nonca-nonical pathway.Many of the individual components of both canonical and noncanonical Wnt signaling have additional functions throughout the body,establishing the complex interplay between Wnt signaling and other signaling pathways.This crosstalk between Wnt signaling and other pathways gives Wnt signaling a vital role in many cellular and organ processes.Dys-regulation of this system has been implicated in many diseases affecting a wide array of organ systems,including cancer and embryological defects,and can even cause embryonic lethality.The complexity of this system and its interacting proteins have made Wnt signaling a target for many therapeutic treatments.However,both stimulatory and inhibitory treatments come with potential risks that need to be addressed.This review synthesized much of the current knowl-edge on the Wnt signaling pathway,beginning with the history of Wnt signaling.It thoroughly described the different variants of Wnt signaling,including canonical,noncanonical Wnt/PCP,and the noncanonical Wnt/Ca2+pathway.Further description involved each of its components and their involvement in other cellular processes.Finally,this review explained the various other pathways and processes that crosstalk with Wnt signaling.

A simplified noncryogenic strategy to transport mesenchymal stem cells: Potential applications in cell therapy and regenerative medicine

With the rapid advances in stem cell research and po-tential cell-based therapies,there is an urgent need to develop safe and reliable cell transport strategies.Except for autologous stem cell-based therapies,allogeneic stem cell therapies and ex vivo genetically engineered cell therapies would require safe,efficient,and reliable cell preservation and transport methods.

Niclosamide(NA)overcomes cisplatin resistance in human ovarian cancer

Ovarian cancer(OC)is one of the most lethal malignancies of the female reproduc-tive system.OC patients are usually diagnosed at advanced stages due to the lack of early diag-nosis.The standard treatment for OC includes a combination of debulking surgery and platinum-taxane chemotherapy,while several targeted therapies have recently been approved for maintenance treatment.The vast majority of OC patients relapse with chemoresistant tu-mors after an initial response.Thus,there is an unmet clinical need to develop new therapeu-tic agents to overcome the chemoresistance of OC.The anti-parasite agent niclosamide(NA)has been repurposed as an anti-cancer agent and exerts potent anti-cancer activities in human cancers including OC.Here,we investigated whether NA could be repurposed as a therapeutic agent to overcome cisplatin-resistant(CR)in human OC cells.To this end,we first established two CR lines SKOV3CR and OVCAR8CR that exhibit the essential biological characteristics of cisplatin resistance in human cancer.We showed that NA inhibited cell proliferation,sup-pressed cell migration,and induced cell apoptosis in both CR lines at a low micromole range.Mechanistically,NA inhibited multiple cancer-related pathways including AP1,ELK/SRF,HIF1,and TCF/LEF,in SKOV3CR and OVCAR8CR cells.NA was further shown to effectively inhibit xenograft tumor growth of SKOV3CR cells.Collectively,our findings strongly suggest that NA may be repurposed as an efficacious agent to combat cisplatin resistance in chemoresistant hu-man OC,and further clinical trials are highly warranted.

Bone Morphogenic Protein 9(BMP9)/Growth Differentiation Factor 2(GDF2)modulates mouse adult hippocampal neurogenesis by regulating the survival of early neural progenitors

Adult neurogenesis occurs in two specialized regions of the mammalian brain,the subventricular zone(SVZ)and the subgranular zone(SGZ)of the dentate gyrus(DG).^(1)Adult hippocampal neural stem cells(NSCs),referred to as Type 1 cells represented by radial glia-like cells(RGLs),generate Type 2 cells that are divided into Type 2a and Type 2 b subpopulations,the latter of which give rise to Type 3 cells(neuroblasts).

SV40 large T antigen-induced immortalization reprograms mouse cardiomyocyte progenitors with mesenchymal stem cell characteristics and osteogenic potential

While progenitor cell-based cardiomyocyte regeneration holds great promise of repairing an injured heart,primary cardiomyogenic progenitors(CPs)have a limited life span in culture,hampering the use of CPs for in vitro and in vivo studies.We previously isolated primary CPs from mouse E15.5 fetal heart,and reversibly immortalized them with SV40 large T antigen(SV40 LTA),resulting in immortalized CPs(iCPs),which maintain long-term proliferation and ex-press cardiomyogenic markers and retain differentiation potential under appropriate differentiation conditions.

Bone Morphogenetic Protein (BMP) signaling in development and human diseases

Bone Morphogenetic Proteins(BMPs)are a group of signaling molecules that belongs to the Transforming Growth Factor-b(TGF-b)superfamily of proteins.Initially discovered for their ability to induce bone formation,BMPs are now known to play crucial roles in all organ systems.BMPs are important in embryogenesis and development,and also in maintenance of adult tissue homeostasis.Mouse knockout models of various components of the BMP signaling pathway result in embryonic lethality or marked defects,highlighting the essential functions of BMPs.In this review,we first outline the basic aspects of BMP signaling and then focus on genetically manipulated mouse knockout models that have helped elucidate the role of BMPs in development.A significant portion of this review is devoted to the prominent human pathologies associated with dysregulated BMP signaling.

Breast cancer development and progression:Risk factors,cancer stem cells,signaling pathways,genomics,and molecular pathogenesis

As the most commonly occurring cancer in women worldwide,breast cancer poses a formidable public health challenge on a global scale.Breast cancer consists of a group of biologically and molecularly heterogeneous diseases originated from the breast.While the risk factors associated with this cancer varies with respect to other cancers,genetic predisposition,most notably mutations in BRCA1 or BRCA2 gene,is an important causative factor for this malignancy.Breast cancers can begin in different areas of the breast,such as the ducts,the lobules,or the tissue in between.Within the large group of diverse breast carcinomas,there are various denoted types of breast cancer based on their invasiveness relative to the primary tumor sites.It is important to distinguish between the various subtypes because they have different prognoses and treatment implications.As there are remarkable parallels between normal development and breast cancer progression at the molecular level,it has been postulated that breast cancer may be derived from mammary cancer stem cells.Normal breast development and mammary stem cells are regulated by several signaling pathways,such as estrogen receptors(ERs),HER2,and Wnt/b-catenin signaling pathways,which control stem cell proliferation,cell death,cell differentiation,and cell motility.Furthermore,emerging evidence indicates that epigenetic regulations and noncoding RNAs may play important roles in breast cancer development and may contribute to the heterogeneity and metastatic aspects of breast cancer,especially for triple-negative breast cancer.This review provides a comprehensive survey of the molecular,cellular and genetic aspects of breast cancer.

Highly expressed BMP9/GDF2 in postnatal mouse liver and lungs may account for its pleiotropic effects on stem cell differentiation,angiogenesis,tumor growth and metabolism

Bone morphogenetic protein 9(BMP9)(or GDF2)was originally identified from fetal mouse liver cDNA libraries.Emerging evidence indicates BMP9 exerts diverse and pleiotropic functions during postnatal development and in maintaining tissue homeostasis.However,the expression landscape of BMP9 signaling during development and/or in adult tissues remains to be analyzed.Here,we conducted a comprehensive analysis of the expression landscape of BMP9 and its signaling mediators in postnatal mice.By analyzing mouse ENCODE transcriptome datasets we found Bmp9 was highly expressed in the liver and detectable in embryonic brain,adult lungs and adult placenta.We next conducted a comprehensive qPCR analysis of RNAs isolated from major mouse tissues/organs at various ages.We found that Bmp9 was highly expressed in the liver and lung tissues of young adult mice,but decreased in older mice.Interestingly,Bmp9 was only expressed at low to modest levels in developing bones.BMP9-associated TGFβ/BMPR type I receptor Alk1 was highly expressed in the adult lungs.Furthermore,the feedback inhibitor Smads Smad6 and Smad7 were widely expressed in mouse postnatal tissues.However,the BMP signaling antagonist noggin was highly expressed in fat and heart in the older age groups,as well as in kidney,liver and lungs in a biphasic fashion.Thus,our findings indicate that the circulating BMP9 produced in liver and lungs may account for its pleiotropic effects on postnatal tissues/organs although possible roles of BMP9 signaling in liver and lungs remain to be fully understood.

The versatile functions of Sox9 in development,stem cells,and human diseases

The transcription factor Sox9 was first discovered in patients with campomelic dysplasia,a haploinsufficiency disorder with skeletal deformities caused by dysregulation of Sox9 expression during chondrogenesis.Since then,its role as a cell fate determiner during embryonic development has been well characterized;Sox9 expression differentiates cells derived from all three germ layers into a large variety of specialized tissues and organs.However,recent data has shown that ectoderm-and endoderm-derived tissues continue to express Sox9 in mature organs and stem cell pools,suggesting its role in cell maintenance and specification during adult life.The versatility of Sox9 may be explained by a combination of posttranscriptional modifications,binding partners,and the tissue type in which it is expressed.Considering its importance during both development and adult life,it follows that dysregulation of Sox9 has been implicated in various congenital and acquired diseases,including fibrosis and cancer.This review provides a summary of the various roles of Sox9 in cell fate specification,stem cell biology,and related human diseases.Ultimately,understanding the mechanisms that regulate Sox9 will be crucial for developing effective therapies to treat disease caused by stem cell dysregulation or even reverse organ damage.

Ferroptosis as a novel form of regulated cell death:Implications in the pathogenesis,oncometabolism and treatment of human cancer

The treatment of cancer mainly involves surgical excision supplemented by radiotherapy and chemotherapy.Chemotherapy drugs act by interfering with tumor growth and inducing the death of cancer cells.Anti-tumor drugs were developed to induce apoptosis,but some patient’s show apoptosis escape and chemotherapy resistance.Therefore,other forms of cell death that can overcome the resistance of tumor cells are important in the context of cancer treatment.Ferroptosis is a newly discovered iron-dependent,non-apoptotic type of cell death that is highly negatively correlated with cancer development.Ferroptosis is mainly caused by the abnormal increase in iron-dependent lipid reactive oxygen species and the imbalance of redox homeostasis.This review summarizes the progression and regulatory mechanism of ferroptosis in cancer and discusses its possible clinical applications in cancer diagnosis and treatment.

Multifaceted signaling regulators of chondrogenesis:Implications in cartilage regeneration and tissue engineering

Defects of articular cartilage present a unique clinical challenge due to its poor self-healing capacity and avascular nature.Current surgical treatment options do not ensure consistent regeneration of hyaline cartilage in favor of fibrous tissue.Here,we review the current understanding of the most important biological regulators of chondrogenesis and their interactions,to provide insight into potential applications for cartilage tissue engineering.These include various signaling pathways,including fibroblast growth factors(FGFs),transforming growth factor b(TGF-b)/bone morphogenic proteins(BMPs),Wnt/b-catenin,Hedgehog,Notch,hypoxia,and angiogenic signaling pathways.Transcriptional and epigenetic regulation of chondrogenesis will also be discussed.Advances in our understanding of these signaling pathways have led to promising advances in cartilage regeneration and tissue engineering.

Characterization of the essential role of bone morphogenetic protein 9 (BMP9) in osteogenic differentiation of mesenchymal stem cells (MSCs) through RNA interference

Mesenchymal stem cells(MSCs)are multipotent stem cells and capable of differentiating into multiple cell types including osteoblastic,chondrogenic and adipogenic lineages.We previously identified BMP9 as one of the most potent BMPs that induce osteoblastic differentiation of MSCs although exact molecular mechanism through which BMP9 regulates osteogenic differentiation remains to be fully understood.Here,we seek to develop a recombinant adenovirus system to optimally silence mouse BMP9 and then characterize the important role of BMP9 in osteogenic differentiation of MSCs.Using two different siRNA bioinformatic prediction programs,we design five siRNAs targeting mouse BMP9(or simB9),which are expressed under the control of the converging H1 and U6 promoters in recombinant adenovirus vectors.We demonstrate that two of the five siRNAs,simB9-4 and simB9-7,exhibit the highest efficiency on silencing exogenous mouse BMP9 in MSCs.Furthermore,simB9-4 and simB9-7 act synergistically in inhibiting BMP9-induced expression of osteogenic markers,matrix mineralization and ectopic bone formation from MSCs.Thus,our findings demonstrate the important role of BMP9 in osteogenic differentiation of MSCs.The characterized simB9 siRNAs may be used as an important tool to investigate the molecular mechanism behind BMP9 osteogenic signaling.Our results also indicate that recombinant adenovirus-mediated expression of siRNAs is efficient and sustained,and thus may be used as an effective delivery vehicle of siRNA therapeutics.

Stem cell therapy for chronic skin wounds in the era of personalized medicine:From bench to bedside

With the significant financial burden of chronic cutaneous wounds on the healthcare system,not to the personal burden mention on those individuals afflicted,it has become increasingly essential to improve our clinical treatments.This requires the translation of the most recent benchtop approaches to clinical wound repair as our current treatment modalities have proven insufficient.The most promising potential treatment options rely on stem cellbased therapies.Stem cell proliferation and signaling play crucial roles in every phase of the wound healing process and chronic wounds are often associated with impaired stem cell function.Clinical approaches involving stem cells could thus be utilized in some cases to improve a body’s inhibited healing capacity.We aim to present the laboratory research behind the mechanisms and effects of this technology as well as current clinical trials which showcase their therapeutic potential.Given the current problems and complications presented by chronic wounds,we hope to show that developing the clinical applications of stem cell therapies is the rational next step in improving wound care.

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 TGFb1 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,a-SMA,Vimentin and Nestin,as well as fibrogenic factors CTGF and Col1a1.Collectively,our results strongly demonstrate that the newly engineered im-POD cells should be a valuable tool to study podocyte biology both under normal and under pathological conditions.

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 nonviral 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 adenovirusmediated 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.

Transition to resistance:An unexpected role of the EMT in cancer chemoresistance

Two recent studies provide intriguing evidence that challenges the role of the epithelialemesenchymal transition(EMT)as a critical mediator of cancer metastasis,while revealing an unexpected role in cancer drug resistance.1,2 While these findings may not settle the EMT’s role in metastasis,these studies suggest that targeting the EMT may inhibit both cancer metastasis and chemoresistance.

The development of a sensitive fluorescent protein-based transcript reporter for high throughput screening of negative modulators of lncRNAs

While the human genome is pervasively transcribed,<2%of the human genome is transcribed into protein-coding mRNAs,leaving most of the transcripts as noncoding RNAs,such as microRNAs and long-noncoding RNAs(lncRNAs),which are critical components of epigenetic regulation.lncRNAs are emerging as critical regulators of gene expression and genomic stability.However,it remains largely unknown about how lncRNAs are regulated.Here,we develop a highly sensitive and dynamic reporter that allows us to identify and/or monitor negative modulators of lncRNA transcript levels in a high throughput fashion.Specifically,we engineer a fluorescent fusion protein by fusing three copies of the PEST destruction domain of mouse ornithine decarboxylase(MODC)to the C-terminal end of the codon-optimized bilirubin-inducible fluorescent protein,designated as dBiFP,and show that the dBiFP protein is highly destabilized,compared with the commonly-used eGFP protein.We further demonstrate that the dBiFP signal is effectively down-regulated when the dBiFP and mouse lncRNA H19 chimeric transcript is silenced by mouse H19-specific siRNAs.Therefore,our results strongly suggest that the dBiFP fusion protein may serve as a sensitive and dynamic transcript reporter to monitor the inhibition of lncRNAs by microRNAs,synthetic regulatory RNA molecules,RNA binding proteins,and/or small molecule inhibitors so that novel and efficacious inhibitors targeting the epigenetic circuit can be discovered to treat human diseases such as cancer and other chronic disorders.

Melanoma:Molecular genetics,metastasis,targeted therapies,immunotherapies,and therapeutic resistance

Cutaneous melanoma is a common cancer and cases have steadily increased since the mid 70s.For some patients,early diagnosis and surgical removal of melanomas is lifesaving,while other patients typically turn to molecular targeted therapies and immunotherapies as treatment options.Easy sampling of melanomas allows the scientific community to identify the most prevalent mutations that initiate melanoma such as the BRAF,NRAS,and TERT genes,some of which can be therapeutically targeted.Though initially effective,many tumors acquire resistance to the targeted therapies demonstrating the need to investigate compensatory pathways.Immunotherapies represent an alternative to molecular targeted therapies.However,inter-tumoral immune cell populations dictate initial therapeutic response and even tumors that responded to treatment develop resistance in the long term.As the protocol for combination therapies develop,so will our scientific understanding of the many pathways at play in the progression of melanoma.The future direction of the field may be to find a molecule that connects all of the pathways.Meanwhile,noncoding RNAs have been shown to play important roles in melanoma development and progression.Studying noncoding RNAs may help us to understand how resistance e both primary and acquired e develops;ultimately allow us to harness the true potential of current therapies.This review will cover the basic structure of the skin,the mutations and pathways responsible for transforming melanocytes into melanomas,the process by which melanomas metastasize,targeted therapeutics,and the potential that noncoding RNAs have as a prognostic and treatment tool.

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 upregulated 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.