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.

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).

Structural and evolutionary characteristics of pyruvate phosphate dikinase in Giardia lamblia and other amitochondriate protozoa

Background Pyruvate phosphate dikinase （PPDK） reversibly catalyzes the interconversion of phosphoenolpyruvate （PEP） and pyruvic acid,leading to catabolism and adenosine triphosphate （ATP） synthesis or gluconeogenesis and ATP consumption.Molecular modeling of PPDKs from divergent organisms demonstrates that the orientation of the phosphorylatable histidine residue within the central domain of PPDK determines whether this enzyme promotes catabolism or gluconeogenesis.The goal of this study was to determine whether PDDK from Giardia underwent adaptive evolution in order to produce more energy under anaerobic conditions.Methods A total of 123 PPDK sequences from protozoans,proteobacteria,plants,and algae were selected,based upon sequence similarities to Giardia lamblia PPDK and Zea mays PPDK.Three-dimensional （3-D） models were generated for PPDKs from divergent organisms and were used to compare the orientation of the phosphorylatable histidine residue within the central domain of PPDKs.These PPDKs were compared using a maximum-likelihood tree.Results For PPDK from Giardia,as well as from other anaerobic protozoans,the central domain tilted toward the N-terminal nucleotide-binding domain,indicating that this enzyme catalyzed ATP synthesis.Furthermore,the orientation of this central domain was determined by interactions between the N-and C-terminal domains.Phylogenetic analysis of the N-and C-terminal sequences of PPDKs from different species suggested that PPDK has likely undergone adaptive evolution in response to differences in environmental and metabolic conditions.Conclusion These results suggested that PPDK in anaerobic organisms is functionally adapted to generate energy more efficiently in an anaerobic environment.

Corrigendum to ‘Modeling colorectal tumorigenesis using the organoids derived from conditionally immortalized mouse intestinal crypt cells (ciMICs)’ [Genes Dis 8 (2021) 814-826]

The authors regret that an image assembly(copy/paste)error in Figure 3D,in which the image for the organoid of"Primary MiCs"group was erroneously duplicated with an image of primary MICs that was previously published.The corrected figure is shown below.As shown in the corrected Figure 3D,this error does not adversely impact the conclusion of the original work.The authors would like to apologise forany inconvenience caused.

Syrosingopine,an anti-hypertensive drug and lactate transporter(MCT1/4)inhibitor,activates hepatic stellate cells and exacerbates liver fibrosis in a mouse model

Syrosingopine is an anti-hypertensive drug and can cause high intracellular lactate levels and end-product inhibition of lactate dehydrogenase by inhibiting the lactate transporters MCT1 and MCT4.Previous studies have shown that syrosingopine plays an essential role in the process of glycolytic blockade,ATP depletion,and cell death in cancer due to high intracellular levels of lactate.

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.

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 twodimensional 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 b-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.

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.

Long noncoding RNA(lncRNA)H19:An essential developmental regulator with expanding roles in cancer,stem cell differentiation,and metabolic diseases

Recent advances in deep sequencing technologies have revealed that,while less than 2%of the human genome is transcribed into mRNA for protein synthesis,over 80%of the genome is transcribed,leading to the production of large amounts of noncoding RNAs(ncRNAs).It has been shown that ncRNAs,especially long non-coding RNAs(lncRNAs),may play crucial regulatory roles in gene expression.As one of the first isolated and reported lncRNAs,H19 has gained much attention due to its essential roles in regulating many physiological and/or pathological processes including embryogenesis,development,tumorigenesis,osteogen-esis,and metabolism.Mechanistically,H19 mediates diverse regulatory functions by serving as competing endogenous RNAs(CeRNAs),Igf2/H19 imprinted tandem gene,modular scaffold,cooperating with H19 antisense,and acting directly with other mRNAs or lncRNAs.Here,we summarized the current understanding of H19 in embryogenesis and development,cancer development and progression,mesenchymal stem cell lineage-specific differentiation,and metabolic diseases.We discussed the potential regulatory mechanisms underlying H19’s func-tions in those processes although more in-depth studies are warranted to delineate the exact molecular,cellular,epigenetic,and genomic regulatory mechanisms underlying the physiolog-ical and pathological roles of H19.Ultimately,these lines of investigation may lead to the development of novel therapeutics for human diseases by exploiting H19 functions.

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.

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.

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.