LGR4 and LGR5 are R-spondin receptors mediating Wnt/β-catenin and Wnt/PCP signalling

Extracellular matrix stiffness and Wnt/β-catenin signaling in physiology and disease

The Wnt/β-catenin signaling pathway plays fundamental roles during development, stem cell differentiation, and homeostasis, and its abnormal activation can lead to diseases. In recent years, it has become clear that this pathway integrates signals not only from Wnt ligands but also from other proteins and signaling routes. For instance, Wnt/β-catenin signaling involves YAP and TAZ, which are transcription factors with crucial roles in mechanotransduction. On the other hand, Wnt/β-catenin signaling is also modulated by integrins. Therefore, mechanical signals might similarly modulate the Wnt/β-catenin pathway. However, and despite the relevance that mechanosensitive Wnt/β-catenin signaling might have during physiology and diseases such as cancer, the role of mechanical cues on Wnt/β-catenin signaling has received less attention. This review aims to summarize recent evidence regarding the modulation of the Wnt/β-catenin signaling by a specific type of mechanical signal, the stiffness of the extracellular matrix. The review shows that mechanical stiffness can indeed modulate this pathway in several cell types, through differential expression of Wnt ligands, receptors and inhibitors, as well as by modulating β-catenin levels. However, the specific mechanisms are yet to be fully elucidated.

The kinase PERK represses translation of the G-protein-coupled receptor LGR5 and receptor tyrosine kinase ERBB3 during ER stress in cancer cells

As a branch of the unfolded protein response, protein kinase R-like endoplasmic reticulum kinase (PERK) represses global translation in response to endoplasmic reticulum (ER) stress. This pathophysiological condition is associated with the tumor microenvironment in cancer. Previous findings in our lab have suggested that PERK selectively represses translation of some mRNAs, but this possibility awaits additional investigation. In this study, we show that a stem-cell marker protein, leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5), is rapidly depleted in colon cancer cells during ER stress, an effect that depended on the PERK-mediated translational repression. Indeed, the PERK inhibition led to the accumulation of premature, underglycosylated forms of LGR5, which were produced only at low levels during proper PERK activation. Unlike the mature LGR5 form, which is constitutively degraded regardless of PERK activation, the underglycosylated LGR5 exhibited a prolonged half-life and accumulated inside the cells without being expressed on the cell surface. We also found that Erb-B2 receptor tyrosine kinase 3 (ERBB3) is subjected to a similarly-regulated depletion by PERK, whereas the epidermal growth factor receptor (EGFR), stress-inducible heat-shock protein family A (Hsp70) member 5 (HSPA5), and anterior gradient 2 protein-disulfide isomerase family member (AGR2) were relatively. insensitive to the PERK-mediated repression of translation. These results indicate that LGR5 and ERBB3 are targets for PERK-mediated translational repression during ER stress.

Stem Cell Signaling Pathways in the Small Intestine

The ability of stem cells to divide and differentiate is necessary for tissue repair and homeostasis. Appropriate spatial and temporal mechanisms are needed. Local intercellular signaling increases expression of specific genes that mediate and maintain differentiation. Diffusible signaling molecules provide concentration-dependent induction of specific patterns of cell types or regions. Differentiation of adjacent cells, on the other hand, requires cell–cell contact and subsequent signaling. These two types of signals work together to allow stem cells to provide what organisms require. The ability to grow organoids has increased our understanding of the cellular and molecular features of small “niches” that modulate stem cell function in various organs, including the small intestine.

Wnt5a Signaling in Gastric Cancer

Gastric cancer remains an important health challenge, accounting for a significant number of cancer-related deaths worldwide. Therefore, a deeper understanding of the molecular mechanisms involved in gastric cancer establishment and progression is highly desirable. The Wnt pathway plays a fundamental role in development, homeostasis, and disease, and abnormal Wnt signaling is commonly observed in several cancer types. Wnt5a, a ligand that activates the non-canonical branch of the Wnt pathway, can play a role as a tumor suppressor or by promoting cancer cell invasion and migration, although the molecular mechanisms explaining these roles have not been fully elucidated. Wnt5a is increased in gastric cancer samples; however, most gastric cancer cell lines seem to exhibit little expression of this ligand, thus raising the question about the source of this ligand in vivo. This review summarizes available research about Wnt5a expression and signaling in gastric cancer. In gastric cancer, Wnt5a promotes invasion and migration by modulating integrin adhesion turnover. Disheveled, a scaffolding protein with crucial roles in Wnt signaling, mediates the adhesion-related effects of Wnt5a in gastric cancer cells, and several studies provide growing support for a model whereby Disheveled-interacting proteins mediates Wnt5a signaling to modulate cytoskeleton dynamics. However, Wnt5a might induce other effects in gastric cancer cells, such as cell survival and induction of gene expression. On the other hand, the available evidence suggests that Wnt5a might be expressed by cells residing in the tumor microenvironment, where feedback mechanisms sustaining Wnt5a secretion and signaling might be established. This review analyzes the possible functions of Wnt5a in this pathological context and discusses potential links to mechanosensing and YAP/TAZ signaling.

The Emerging Role of Rab5 in Membrane Receptor Trafficking and Signaling Pathways

Ras analog in brain (Rab) proteins are small guanosine triphosphatases (GTPases) that belong to the Ras-like GTPase superfamily, and they can regulate vesicle trafficking. Rab proteins alternate between an activated (GTP-bound) state and an inactivated (GDP-bound) state. Early endosome marker Rab5 GTPase, a key member of the Rab family, plays a crucial role in endocytosis and membrane transport. The activated-state Rab5 recruits its effectors and regulates the internalization and trafficking of membrane receptors by regulating vesicle fusion and receptor sorting in the early endosomes. In this review, we summarize the role of small Rab GTPases Rab5 in membrane receptor trafficking and the activation of signaling pathways, such as Ras/MAPK and PI3K/Akt, which ultimately affect cell growth, apoptosis, tumorigenesis, and tumor development. This review may provide some insights for our future research and novel therapeutic targets for diseases.

The Role Played by Wnt/β-Catenin Signaling Pathway in Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is an aggressive hematologic neoplastic disorder that arises from the clonal expansion of transformed T-cell or B-cell precursors. Thanks to progress in chemotherapy protocols, ALL outcome has significantly improved. However, drug-resistance remains an unresolved issue in the treatment of ALL and toxic effects limit dose escalation of current chemotherapeutics. Therefore, the identification of novel targeted therapies to support conventional chemotherapy is required. The Wnt/β-catenin pathway is a conserved signaling axis involved in several physiological processes such as development, differentiation, and adult tissue homeostasis. As a result, deregulation of this cascade is closely related to initiation and progression of various types of cancers, including hematological malignancies. In particular, deregulation of this signaling network is involved in the transformation of healthy HSCs in leukemic stem cells (LSCs), as well as cancer cell multi-drug-resistance. This review highlights the recent findings on the role of Wnt/β-catenin in hematopoietic malignancies and provides information on the current status of Wnt/β-catenin inhibitors with respect to their therapeutic potential in the treatment of ALL.

NEDD4 and NEDD4L regulate Wnt signalling and intestinal stem cell priming by degrading LGR5 receptor

The intestinal stem cell (ISC) marker LGR5 is a receptor for R-spondin (RSPO) that functions to potentiate Wnt signalling in the proliferating crypt. It has been recently shown that Wnt plays a priming role for ISC self-renewal by inducing RSPO receptor LGR5 expression. Despite its pivotal role in homeostasis, regeneration and cancer, little is known about the post-translational regulation of LGR5. Here, we show that the HECT-domain E3 ligases NEDD4 and NEDD4L are expressed in the crypt stem cell regions and regulate ISC priming by degrading LGR receptors. Loss of Nedd4 and Nedd4l enhances ISC proliferation, increases sensitivity to RSPO stimulation and accelerates tumour development in Apcmin mice with increased numbers of high-grade adenomas. Mechanistically, we find that both NEDD4 and NEDD4L negatively regulate Wnt/β-catenin signalling by targeting LGR5 receptor and DVL2 for proteasomal and lysosomal degradation. Our findings unveil the previously unreported post-translational control of LGR receptors via NEDD4/NEDD4L to regulate ISC priming. Inactivation of NEDD4 and NEDD4L increases Wnt activation and ISC numbers, which subsequently enhances tumour predisposition and progression.

Roles of nAChR and Wnt signaling in intestinal stem cell function and inflammation

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that signal using endogenous acetylcholine (ACh) and the agonist, nicotine. The nAChR signaling pathway is a central regulator of physiological homeostasis in the central and peripheral nervous systems. The receptors are expressed not only in the nervous system, but also play a pivotal role in regulation of epithelial cell growth, migration, differentiation, and inflammation processes in various mammalian non-neuronal cells. In the intestine, the Wnt signaling pathway plays a central role in the epithelium and is a principal regulator of intestinal stem cell (ISC) identity and proliferation. Since Wnt signaling was first described more than 40 years ago in ISCs, large amounts of scientific evidence have demonstrated remarkable long-term self-renewal capacity of ISCs. Intestinal organoids are commonly used for studying ISC biology and intestinal pathophysiology. The contribution of non-neuronal nAChR signaling to Wnt signaling in the intestine has received less attention. Experiments using cultured intestinal organoids that lack nerve and immune cells were performed. Endogenous ACh is synthesized in the intestinal epithelium and drives organoid growth and differentiation through activation of nAChR signaling. Furthermore, nAChR signaling is coordinated with Wnt signaling for regulation of ISC function. Elucidating the mechanism of the coordinated activities of nAChR and Wnt signaling in the intestine provides new insight into epithelial homeostasis, and may be of particular relevance in inflammatory bowel diseases such as ulcerative colitis and Crohn's disease.

TMEM98 is a negative regulator of FRAT mediated Wnt/ß-catenin signalling

Wnt/ß-catenin signalling is crucial for maintaining the balance between cell proliferation and differentiation, both during tissue morphogenesis and in tissue maintenance throughout postnatal life. Whereas the signalling activities of the core Wnt/ß-catenin pathway components are understood in great detail, far less is known about the precise role and regulation of the many different modulators of Wnt/ß-catenin signalling that have been identified to date. Here we describe TMEM98, a putative transmembrane protein of unknown function, as an interaction partner and regulator of the GSK3-binding protein FRAT2. We show that TMEM98 reduces FRAT2 protein levels and, accordingly, inhibits the FRAT2-mediated induction of ß-catenin/TCF signalling. We also characterize the intracellular trafficking of TMEM98 in more detail and show that it is recycled between the plasma membrane and the Golgi. Together, our findings not only reveal a new layer of regulation for Wnt/ß-catenin signalling, but also a new biological activity for TMEM98.

Production, purification and characterization of recombinant human R-spondin1 (RSPO1) protein stably expressed in human HEK293 cells

Background

The R-Spondin proteins comprise a family of secreted proteins, known for their important roles in cell proliferation, differentiation and death, by inducing the Wnt pathway. Several studies have demonstrated the importance of RSPOs in regulation of a number of tissue-specific processes, namely: bone formation, skeletal muscle tissue development, proliferation of pancreatic β-cells and intestinal stem cells and even cancer. RSPO1 stands out among RSPOs molecules with respect to its potential therapeutic use, especially in the Regenerative Medicine field, due to its mitogenic activity in stem cells. Here, we generated a recombinant human RSPO1 (rhRSPO1) using the HEK293 cell line, obtaining a purified, characterized and biologically active protein product to be used in Cell Therapy. The hRSPO1 coding sequence was synthesized and subcloned into a mammalian cell expression vector. HEK293 cells were stably co-transfected with the recombinant expression vector containing the hRSPO1 coding sequence and a hygromycin resistance plasmid, selected for hygro^r and subjected to cell clones isolation.

Results

rhRSPO1 was obtained, in the absence of serum, from culture supernatants of transfected HEK293 cells and purified using a novel purification strategy, involving two sequential chromatographic steps, namely: heparin affinity chromatography, followed by a molecular exclusion chromatography, designed to yield a high purity product. The purified protein was characterized by Western blotting, mass spectrometry and in vitro (C2C12 cells) and in vivo (BALB/c mice) biological activity assays, confirming the structural integrity and biological efficacy of this human cell expression system. Furthermore, rhRSPO1 glycosylation analysis allowed us to describe, for the first time, the glycan composition of this oligosaccharide chain, confirming the presence of an N-glycosylation in residue Asn137 of the polypeptide chain, as previously described. In addition, this analysis revealing the presence of glycan structures such as terminal sialic acid, N-acetylglucosamine and/or galactose.

Conclusion

Therefore, a stable platform for the production and purification of recombinant hRSPO1 from HEK293 cells was generated, leading to the production of a purified, fully characterized and biologically active protein product to be applied in Tissue Engineering.

The tumor suppressor PTPRK promotes ZNRF3 internalization and is required for Wnt inhibition in the Spemann organizer

A hallmark of Spemann organizer function is its expression of Wnt antagonists that regulate axial embryonic patterning. Here we identify the tumor suppressor Protein tyrosine phosphatase receptor-type kappa (PTPRK), as a Wnt inhibitor in human cancer cells and in the Spemann organizer of Xenopus embryos. We show that PTPRK acts via the transmembrane E3 ubiquitin ligase ZNRF3, a negative regulator of Wnt signaling promoting Wnt receptor degradation, which is also expressed in the organizer. Deficiency of Xenopus Ptprk increases Wnt signaling, leading to reduced expression of Spemann organizer effector genes and inducing head and axial defects. We identify a '4Y' endocytic signal in ZNRF3, which PTPRK maintains unphosphorylated to promote Wnt receptor depletion. Our discovery of PTPRK as a negative regulator of Wnt receptor turnover provides a rationale for its tumor suppressive function and reveals that in PTPRK-RSPO3 recurrent cancer fusions both fusion partners, in fact, encode ZNRF3 regulators.

How human and other animals form distinct head- and tail-ends as embryos is a fundamental question in biology. The fertilized eggs of the African clawed frog (also known as Xenopus) become embryos and grow into tadpoles within two days. This rapid growth makes Xenopus particularly suitable as a model to study how animals with backbones form their body plans.

In Xenopus embryos, a small group of cells known as the Spemann organizer plays a pivotal role in forming the body plan. It produces several enzymes known as Wnt inhibitors that repress a signal pathway known as Wnt signaling to determine the head- and tail-ends of the embryo.

Chang, Kim et al. searched for new Wnt inhibitors in the Spemann organizer of Xenopus embryos. The experiments revealed that the Spemann organizer produced an enzyme known as PTPRK that was essential to permit the head-to-tail patterning of the brain. PTPRK inhibited Wnt signaling by activating another enzyme known as ZNRF3.

Previous studies have shown that defects in Wnt signaling and in the activities of PTPRK and ZNRF3 are involved in colon cancer in mammals. Thus, these findings may help to develop new approaches for treating cancer in the future.

Surrogate R-spondins for tissue-specific potentiation of Wnt Signaling

Secreted R-spondin1-4 proteins (RSPO1-4) orchestrate stem cell renewal and tissue homeostasis by potentiating Wnt/β-catenin signaling. RSPOs induce the turnover of negative Wnt regulators RNF43 and ZNRF3 through a process that requires RSPO interactions with Leucine-rich repeat-containing G-protein coupled receptors (LGRs), or through an LGR-independent mechanism that is enhanced by RSPO binding to heparin sulfate proteoglycans (HSPGs). Here, we describe the engineering of 'surrogate RSPOs' that function independently of LGRs to potentiate Wnt signaling on cell types expressing a target surface marker. These bispecific proteins were generated by fusing an RNF43- or ZNRF3-specific single chain antibody variable fragment (scFv) to the immune cytokine IL-2. Surrogate RSPOs mimic the function of natural RSPOs by crosslinking the extracellular domain (ECD) of RNF43 or ZNRF3 to the ECD of the IL-2 receptor CD25, which sequesters the complex and results in highly selective amplification of Wnt signaling on CD25+ cells. Furthermore, surrogate RSPOs were able substitute for wild type RSPO in a colon organoid growth assay when intestinal stem cells were transduced to express CD25. Our results provide proof-of-concept for a technology that may be adapted for use on a broad range of cell- or tissue-types and will open new avenues for the development of Wnt-based therapeutics for regenerative medicine.

Fractionated head and neck irradiation impacts taste progenitors, differentiated taste cells, and Wnt/β-catenin signaling in adult mice

Head and neck cancer patients receiving conventional repeated, low dose radiotherapy (fractionated IR) suffer from taste dysfunction that can persist for months and often years after treatment. To understand the mechanisms underlying functional taste loss, we established a fractionated IR mouse model to characterize how taste buds are affected. Following fractionated IR, we found as in our previous study using single dose IR, taste progenitor proliferation was reduced and progenitor cell number declined, leading to interruption in the supply of new taste receptor cells to taste buds. However, in contrast to a single dose of IR, we did not encounter increased progenitor cell death in response to fractionated IR. Instead, fractionated IR induced death of cells within taste buds. Overall, taste buds were smaller and fewer following fractionated IR, and contained fewer differentiated cells. In response to fractionated IR, expression of Wnt pathway genes, Ctnnb1, Tcf7, Lef1 and Lgr5 were reduced concomitantly with reduced progenitor proliferation. However, recovery of Wnt signaling post-IR lagged behind proliferative recovery. Overall, our data suggest carefully timed, local activation of Wnt/β-catenin signaling may mitigate radiation injury and/or speed recovery of taste cell renewal following fractionated IR.

Uterine Glands: Developmental Biology and Functional Roles in Pregnancy

All mammalian uteri contain glands in the endometrium that develop only or primarily after birth. Gland development or adenogenesis in the postnatal uterus is intrinsically regulated by proliferation, cell-cell interactions, growth factors and their inhibitors, as well as transcription factors, including forkhead box A2 (FOXA2) and estrogen receptor α (ESR1). Extrinsic factors regulating adenogenesis originate from other organs, including the ovary, pituitary, and mammary gland. The infertility and recurrent pregnancy loss observed in uterine gland knockout sheep and mouse models support a primary role for secretions and products of the glands in pregnancy success. Recent studies in mice revealed that uterine glandular epithelia govern postimplantation pregnancy establishment through effects on stromal cell decidualization and placental development. In humans, uterine glands and, by inference, their secretions and products are hypothesized to be critical for blastocyst survival and implantation as well as embryo and placental development during the first trimester before the onset of fetal-maternal circulation. A variety of hormones and other factors from the ovary, placenta, and stromal cells impact secretory function of the uterine glands during pregnancy. This review summarizes new information related to the developmental biology of uterine glands and discusses novel perspectives on their functional roles in pregnancy establishment and success.

The Hippo and Wnt signalling pathways: crosstalk during neoplastic progression in gastrointestinal tissue

The Hippo and Wnt signalling pathways play crucial roles in maintaining tissue homeostasis and organ size by orchestrating cell proliferation, differentiation and apoptosis. These pathways have been frequently found to be dysregulated in human cancers. While the canonical signal transduction of Hippo and Wnt has been well studied, emerging evidence shows that these two signalling pathways contribute to and exhibit overlapping functions in gastrointestinal (GI) tumorigenesis. In fact, the core effectors YAP/TAZ in Hippo signalling pathway cooperate with β-catenin in Wnt signalling pathway to promote GI neoplasia. Here, we provide a brief review to summarize the molecular mechanisms underlying the crosstalk between these two pathways and elucidate their involvement in GI tumorigenesis, particularly focusing on the intestine, stomach and liver.

Cell-Intrinsic Wnt4 Influences Conventional Dendritic Cell Fate Determination to Suppress Type 2 Immunity

Whether conventional dendritic cells (cDC) acquire subset identity under direction of Wnt family glycoproteins is unknown. We demonstrate that Wnt4, a β-catenin-independent Wnt ligand, is produced by both hematopoietic and nonhematopoietic cells and is both necessary and sufficient for preconventional DC1/cDC1 maintenance. Whereas bone marrow cDC precursors undergo phosphoJNK/c-Jun activation upon Wnt4 treatment, loss of cDC Wnt4 in CD11c^CreWnt4^flox/flox mice impaired differentiation of CD24⁺, Clec9A⁺, CD103⁺ cDC1 compared with CD11c^Cre controls. Conversely, single-cell RNA sequencing analysis of bone marrow revealed a 2-fold increase in cDC2 gene signature genes, and flow cytometry demonstrated increased numbers of SIRP-α⁺ cDC2 amid lack of Wnt4. Increased cDC2 numbers due to CD11c-restricted Wnt4 deficiency increased IL-5 production, group 2 innate lymphoid cell expansion, and host resistance to the hookworm parasite Nippostrongylus brasiliensis Collectively, these data uncover a novel and unexpected role for Wnt4 in cDC subset differentiation and type 2 immunity.

Serum R-Spondin 1 Is a New Surrogate Marker for Obesity and Insulin Resistance

BACKGROUND

Recent in vivo studies indicated that R-spondin 1 (RSPO1) regulates food intake and increases insulin secretion, but its role in humans remains unknown. This study investigated the association between serum levels of RSPO1 and diverse metabolic parameters in humans.

METHODS

The study population consisted of 43 subjects with newly diagnosed diabetes mellitus, and 79 non-diabetic participants. Serum levels of RSPO1 were measured using the enzyme-linked immunosorbent assay. The relationships between circulating RSPO1 and diverse metabolic parameters were analyzed.

RESULTS

Circulating RSPO1 levels increased to a greater extent in the obese group than in the lean group. Moreover, serum levels of RSPO1 were higher in the insulin-resistant group than in the insulin-sensitive group. Serum levels of RSPO1 were significantly correlated with a range of metabolic parameters including body mass index, fasting C-peptide, homeostasis model assessment of insulin resistance index, and lipid profile. Moreover, levels were significantly associated with insulin resistance and obesity in non-diabetic subjects.

CONCLUSION

This study demonstrated the association between serum levels of RSPO1 and a range of metabolic parameters in humans. Serum levels of RSPO1 are significantly related to obesity and insulin resistance, although the precise mechanisms remain unknown.

R-spondin signaling as a pivotal regulator of tissue development and homeostasis

R-spondins (Rspos) are cysteine-rich secreted glycoproteins which control a variety of cellular functions and are essential for embryonic development and tissue homeostasis. R-spondins (Rspo1 to 4) have high structural similarity and share 60% sequence homology. It has been shown that their cysteine-rich furin-like (FU) domain and the thrombospondin (TSP) type I repeat domain are essential for initiating downstream signaling cascades and therefore for their biological functions. Although numerous studies have unveiled their pivotal role as critical developmental regulators, the most important finding is that Rspos synergize Wnt signaling. Recent studies have identified novel receptors for Rspos, the Lgr receptors, closely related orphans of the leucin-rich repeat containing G protein-coupled receptors, and proposed that Rspos potentiate canonical Wnt signaling via these receptors. Given that Wnt signaling is one of the most important developmental signaling pathways that controls cell fate decisions and tissue development, growth and homeostasis, Rspos may function as key players for these processes as well as potential therapeutic targets. Here, I recapitulate the Wnt signaling and then outline the biological role of Rspos in tissue development and homeostasis and explore the possibility that Rspos may be used as therapeutic targets.

RSPO3 is a prognostic biomarker and mediator of invasiveness in prostate cancer

Background

While prostate cancer can often manifest as an indolent disease, the development of locally-advanced or metastatic disease can cause significant morbidity or mortality. Elucidation of molecular mechanisms contributing to disease progression is crucial for more accurate prognostication and effective treatments. R-Spondin 3 (RSPO3) is a protein previously implicated in the progression of colorectal and lung cancers. However, a role for RSPO3 in prostate cancer prognosis and behaviour has not been explored.

Methods

We compare the relative levels of RSPO3 expression between normal prostate tissue and prostate cancer in two independent patient cohorts (Taylor and GSE70768—Cambridge). We also examine the association of biochemical relapse with RSPO3 levels in these cohorts. For elucidation of the biological effect of RSPO3, we use siRNA technology to reduce the levels of RSPO3 in established prostate cancer cell lines, and perform in vitro proliferation, invasion, western blotting for EMT markers and clonogenic survival assays for radiation resistance. Furthermore, we show consequences of RSPO3 knockdown in an established chick chorioallantoic membrane (CAM) assay model of metastasis.

Results

RSPO3 levels are lower in prostate cancer than normal prostate, with a tendency for further loss in metastatic disease. Patients with lower RSPO3 expression have lower rates of biochemical relapse-free survival. SiRNA-mediated loss of RSPO3 results in no change to clonogenic survival and a lower proliferative rate, but increased invasiveness in vitro with induction of epithelial–mesenchymal transition (EMT) markers. Consistent with these results, lower RSPO3 expression translates to greater metastatic capacity in the CAM assay. Together, our preclinical findings identify a role of RSPO3 downregulation in prostate cancer invasiveness, and provide a potential explanation for how RSPO3 functions as a positive prognostic marker in prostate cancer.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1878-3) contains supplementary material, which is available to authorized users.

Molecular determinants of WNT9b responsiveness in nephron progenitor cells

Primed nephron progenitor cells (NPCs) appear in metanephric mesenchyme by E11.5 and differentiate in response to the inductive WNT9b signal from the ureteric bud. However, the NPC WNT-receptor complex is unknown. We obtained M15 cells from E10.5 mesonephric mesenchyme and systematically analyzed components required for canonical WNT9b-responsiveness. When M15 cells were transfected with a β-catenin luciferase reporter plasmid, exposure to recombinant WNT9b resulted in minimal luciferase activity. We then analyzed mRNA-expression of WNT-pathway components and identified Fzd1-6 and Lrp6 transcripts but not Rspo1. When M15 cells were treated with recombinant RSPO1 the response to transfected WNT9b was augmented 4.8-fold. Co-transfection of M15 cells with Fzd5 (but no other Fzd family member) further increased the WNT9b signal to 16.8-fold and siRNA knockdown of Fzd5 reduced the signal by 52%. Knockdown of Lrp6 resulted in 60% WNT9b signal reduction. We confirmed Fzd5, Lrp6 and Rspo1 mRNA expression in CITED1(+) NPCs from E15.5 embryonic mouse kidney. Thus, while many WNT signaling-pathway components are present by E10.5, optimum responsiveness of E11.5 cap mesenchyme requires that NPCs acquire RSPO1, FZD5 and LRP6.

C‑mannosylation of R‑spondin2 activates Wnt/β‑catenin signaling and migration activity in human tumor cells

R‑spondin2 (Rspo2), one of the four members of the R‑spondin family of proteins, has agonistic activity in the Wnt/β‑catenin signaling pathway, and it is associated with normal development, as well as disease, such as cancer. The present study focused on the C‑mannosylation of Rspo2, which is a novel and unique type of glycosylation that occurs via a C‑C linkage between the tryptophan residue and an α‑mannose. Although Rspo2 has two putative C‑mannosylation sites at residues Trp150 and Trp153, it had not been reported to date whether these sites are C‑mannosylated. Firstly, results from mass spectrometry demonstrated that Rspo2 was C‑mannosylated at the Trp150 and Trp153 residues. Notably, while this C‑mannosylation of Rspo2 resulted in increased extracellular secretion in human fibrosarcoma HT1080 cells, in other human tumor cell lines it inhibited secretion. However, C‑mannosylation had consistent effects on the activation of Wnt/β‑catenin signaling in PANC1 and MDA‑MB‑231 cells, as well as HT1080 cells. Furthermore, overexpression of wild‑type Rspo2 significantly increased the migratory ability of A549 and HT1080 cells, whereas overexpression of a C‑mannosylation‑defective mutant enhanced migration to a lesser degree. These results suggested that C‑mannosylation of Rspo2 may promote cancer progression and that the inhibition of C‑mannosylation may serve as a potential novel therapeutic approach for cancer therapy.

Targeting the crosstalks of Wnt pathway with Hedgehog and Notch for cancer therapy

Wnt pathway is an evolutionarily conserved signaling pathway determining patterning of animal embryos, cell fate, cell polarity, and a substantial role in the origin and maintenance of stem cells. It has been found to crosstalk with two other major developmental pathways, Hedgehog and Notch, in many embryological development cascades and in maintaining stemness of stem cells Research has shown that all the three pathways are potent in inducing tumorigenesis, driving tumor progression and aiding epithelial to mesenchymal transition in malignant cells, apart from maintaining cancer stem cells population inside the tumor tissue. Cancer stem cells are thought to aid in the process of tumor relapse, as they survive therapy by displaying drug resistance and then repopulating tumor tissues. Hence the role of these crosstalks in cancer is under intensive research. Inhibition of all the three pathways individually have resulted in tumor regression, but not optimally, as treatment failure and cancer relapse have been found to occur. Hence, instead of targeting a single pathway, targeting the crosstalk network could be a better alternative to conventional cancer treatment. Also, elimination of both tumor cells as well as cancer stem cells implies a reduced chance of relapse. Drugs developed to target these crosstalking networks, when used in combinatorial therapy, can potentially increase the efficacy of the therapy to a very large extent.

LGR4 is essential for R-spondin1-mediated suppression of food intake via pro-opiomelanocortin

Leucine-rich repeat-containing G-protein coupled receptor 4 (LGR4) suppresses food intake after its activation by binding of its ligands, R-spondins. We investigated the mechanism of food intake suppression by R-spondin1 in a region-specific Lgr4 gene knockout (LGR4 cKO) mouse model, generated by deletion of the Lgr4 gene in arcuate nucleus (ARC) using Lgr4^fx/fx mice combined with infection of an AAV-Cre vector. After R-spondin1 administration, LGR4 cKO mice didn't exhibit a suppressed appetite, compared to that in control mice, which received a vehicle. In ARC of LGR4 cKO mice, Pomc mRNA expression was reduced, leading to suppressed food intake. On the other hand, neurons-specific LGR4 KO mice exhibited no differences in Pomc expression, and no structural differences were observed in the ARC of mutant mice. These results suggest that LGR4 is an essential part of the mechanism, inducing Pomc gene expression with R-spondin1 in ARC neurons in mice, thereby regulating feeding behavior. Abbreviations: LGR4: Leucine-rich repeat-containing G-protein coupled receptor 4; RSPOs: roof plate-specific spondins; ARC: arcuate nucleus; AAV: adeno associated virus; POMC: pro-opiomelanocortin; CART: cocaine and amphetamine-regulated transcript; NPY: neuropeptide Y; AgRP: agouti-related peptide; Axin2: axis inhibition protein 2; Lef1: lymphoid enhancer binding factor 1; ccnd1: cyclin D1.

Contribution of Zinc and Zinc Transporters in the Pathogenesis of Inflammatory Bowel Diseases

Intestinal epithelial cells cover the surface of the intestinal tract. The cells are important for preserving the integrity of the mucosal barriers to protect the host from luminal antigens and pathogens. The mucosal barriers are maintained by the continuous and rapid self-renewal of intestinal epithelial cells. Defects in the self-renewal of these cells are associated with gastrointestinal diseases, including inflammatory bowel diseases and diarrhea. Zinc is an essential trace element for living organisms, and zinc deficiency is closely linked to the impaired mucosal integrity. Recent evidence has shown that zinc transporters contribute to the barrier function of intestinal epithelial cells. In this review, we describe the recent advances in understanding the role of zinc and zinc transporters in the barrier function and homeostasis of intestinal epithelial cells.

Znhit1 controls intestinal stem cell maintenance by regulating H2A.Z incorporation

Lgr5+ stem cells are crucial to gut epithelium homeostasis; however, how these cells are maintained is not fully understood. Zinc finger HIT-type containing 1 (Znhit1) is an evolutionarily conserved subunit of the SRCAP chromosome remodeling complex. Currently, the function of Znhit1 in vivo and its working mechanism in the SRCAP complex are unknown. Here we show that deletion of Znhit1 in intestinal epithelium depletes Lgr5+ stem cells thus disrupts intestinal homeostasis postnatal establishment and maintenance. Mechanistically, Znhit1 incorporates histone variant H2A.Z into TSS region of genes involved in Lgr5+ stem cell fate determination, including Lgr5, Tgfb1 and Tgfbr2, for subsequent transcriptional regulation. Importantly, Znhit1 promotes the interaction between H2A.Z and YL1 (H2A.Z chaperone) by controlling YL1 phosphorylation. These results demonstrate that Znhit1/H2A.Z is essential for Lgr5+ stem cell maintenance and intestinal homeostasis. Our findings identified a dominant role of Znhit1/H2A.Z in controlling mammalian organ development and tissue homeostasis in vivo.

Immunoexpression of LGR4 and Β-Catenin in Gastric Cancer and Normal Gastric Mucosa

Background:

We evaluated the immunoexpression of LGR4 and β-catenin in primary gastric carcinomas, lymph node metastases and histologically normal gastric mucosa in the surgical margins of gastric primary tumours.

Methods:

We performed a cross-sectional, observational study, based on 75 gastric carcinoma specimens from gastrectomies conducted at the hospital of the Federal University of Ceará, Brazil. The samples were analysed by tissue microarray and immunohistochemistry. Chi-square, Fisher’s exact test and Pearson’s linear regression were used in this study.

Results:

LGR4 expression was greater in the histologically normal gastric mucosa (basal third of the epithelial thickness) of the tumour surgical resection margin than in the cases of primary carcinomas (P<0.001, mainly diffuse-histotype cancer margins), and also in the number of cells stained in the normal mucosa (P<0.0001). Primary intestinal-type carcinomas showed greater positivity for LGR4 than diffuse tumours (59% vs 13%, P<0.0001) and in these the positivity was higher in the metastases (P=0.0242). The membranous immunoexpression of β-catenin was ubiquitous in the normal mucosa and present in 2/3 of the positive carcinomas. In only one case, nuclear β-catenin expression was observed. Most LGR4-positive cases were stained for membranous β-catenin but not the opposite (P<0.01).

Conclusion:

LGR4 is a likely biomarker of stem cells in the normal gastric mucosa and carcinomas of the stomach, not specific to cancer cells and positively associated with cell proliferation. LGR4 immunoexpression is more frequent and found in a larger number of cells in normal tissues than in tumour samples. Expression of β-catenin in the junctional membrane-complex occurred predominantly, in positive cases of gastric carcinomas and very rarely in the nucleus. LGR4 apparently influenced the membranous expression of β-catenin. These findings suggest a controversial role for LGR4, related to proliferative status and inversely related to tumour progression, in contrast to most previous reports.

Altered R-spondin 1/CART neurocircuit in the hypothalamus contributes to hyperphagia in diabetes

Hyperphagia is common in diabetes and may worsen hyperglycemia and diabetic complications. The responsible mechanisms are not well understood. The hypothalamus is a key center for the control of appetite and energy homeostasis. The ventromedial nucleus (VMH) and arcuate nucleus (ARC) are two critical nuclei involved in these processes. We have reported that R-spondin 1 (Rspo1) and its receptor leucin-rich repeat and G protein-coupled receptor 4 (LGR4) in the VMH and ARC suppressed appetite, but the downstream neuronal pathways are unclear. Here we show that neurons containing cocaine and amphetamine-regulated transcript (CART) in ARC express both LGR4 and insulin receptor; intracerebroventricular injection of Rspo1 induced c-Fos expression in CART neurons of ARC; and silencing CART in ARC attenuated the anorexigenic actions of Rspo1. In diabetic and obese fa/fa rats, Rspo1 mRNA in VMH and CART mRNA in ARC were reduced; this was accompanied by increased food consumption. Insulin treatment restored Rspo1 and CART gene expressions and normalized eating behavior. Chronic intracerebroventricular injection of Rspo1 inhibited food intake and normalized diabetic hyperphagia; intracerebroventricular injection of Rspo1 or insulin increased CART mRNA in ARC. In the CART neuron cell line, Rspo1 and insulin potentiated each other on pERK and β-catenin, and in rats, they acted synergistically to inhibit food intake. Silencing Rspo1 in VMH reduced CART expression in ARC and attenuated the inhibitory effect of insulin on food intake. In conclusion, our data indicated that CART works downstream of Rspo1 and Rspo1 mediated the action of insulin centrally. The altered Rspo1/CART neurocircuit in the hypothalamus contributes to hyperphagia in diabetes. NEW & NOTEWORTHY This study reports that cocaine and amphetamine-regulated transcript (CART) neurons in the arcuate nucleus (ARC) of hypothalamus acted downstream of R-spondin 1 (Rspo1) to inhibit food intake. The Rspo1 mRNA level in ventromedial nucleus (VMH) and CART mRNA level in ARC were reduced in type 1 diabetic rat and obese fa/fa rat. Rspo1 and insulin acted synergistically on phospho-ERK and β-catenin signal pathways and in suppressing food intake. The current results proposed that altered Rspo1/CART neurocircuit in the hypothalamus contributes to hyperphagia in diabetes.

Tales from the crypt: new insights into intestinal stem cells

The intestinal epithelium withstands continuous mechanical, chemical and biological insults despite its single-layered, simple epithelial structure. The crypt-villus tissue architecture in combination with rapid cell turnover enables the intestine to act both as a barrier and as the primary site of nutrient uptake. Constant tissue replenishment is fuelled by continuously dividing stem cells that reside at the bottom of crypts. These cells are nurtured and protected by specialized epithelial and mesenchymal cells, and together constitute the intestinal stem cell niche. Intestinal stem cells and early progenitor cells compete for limited niche space and, therefore, the ability to retain or regain stemness. Those cells unable to do so differentiate to one of six different mature cell types and move upwards towards the villus, where they are shed into the intestinal lumen after 3-5 days. In this Review, we discuss the signals, cell types and mechanisms that control homeostasis and regeneration in the intestinal epithelium. We investigate how the niche protects and instructs intestinal stem cells, which processes drive differentiation of mature cells and how imbalance in key signalling pathways can cause human disease.

Overexpression of cancer stem cell marker Lgr5 in colorectal cancer patients and association with clinicopathological findings

BACKGROUND

To determine the expression of cancer stem cell marker Leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5) in colorectal carcinoma samples compared to normal adjacent tissue and any possible association with clinicopathological findings.

METHODS

This study was performed on forty samples of cancerous colorectal tissues (case group) and their adjacent normal mucosa (control group) in Imam Khomeini Hospital (Sari, Mazandaran, Iran). Expression of Lgr5 in tissue sections was done by immunohistochemistry. Statistical analysis was carried out using SPSS software.

RESULTS

Forty colorectal cancer patients including 21 males (57.8±11.6 years) and 19 females (58.4±12.77 years) were enrolled. Lgr5 was overexpressed in tumoral samples than normal adjacent tissues (77.5% vs 27.5%, p<0.001). Also, no association was found between primary tumor, regional lymph nodes, invasion, histological type, grade, distant metastasis and IHC results. Patients with low Lgr5 expression had a better survival rate than patients with high expression but this was not statistically significant (p=0.121).

CONCLUSION

The higher immunoreactivity of Lgr5 in colorectal cancer tissues may indicate its role as a cancer stem cell marker in tumor carcinogenesis and patient's survival however; Lgr5 is not associated with pathological prognostic variables.

Molecular regulation of mammalian hepatic architecture

The essential liver exocrine and endocrine functions require a precise spatial arrangement of the hepatic lobule consisting of the central vein, portal vein, hepatic artery, intrahepatic bile duct system, and hepatocyte zonation. This allows blood to be carried through the liver parenchyma sampled by all hepatocytes and bile produced by the hepatocytes to be carried out of the liver through the intrahepatic bile duct system composed of cholangiocytes. The molecular orchestration of multiple signaling pathways and epigenetic factors is required to set up lineage restriction of the bipotential hepatoblast progenitor into the hepatocyte and cholangiocyte cell lineages, and to further refine cell fate heterogeneity within each cell lineage reflected in the functional heterogeneity of hepatocytes and cholangiocytes. In addition to the complex molecular regulation, there is a complicated morphogenetic choreography observed in building the refined hepatic epithelial architecture. Given the multifaceted molecular and cellular regulation, it is not surprising that impairment of any of these processes can result in acute and chronic hepatobiliary diseases. To enlighten the development of potential molecular and cellular targets for therapeutic options, an understanding of how the intricate hepatic molecular and cellular interactions are regulated is imperative. Here, we review the signaling pathways and epigenetic factors regulating hepatic cell lineages, fates, and epithelial architecture.

Usp16 modulates Wnt signaling in primary tissues through Cdkn2a regulation

Regulation of the Wnt pathway in stem cells and primary tissues is still poorly understood. Here we report that Usp16, a negative regulator of Bmi1/PRC1 function, modulates the Wnt pathway in mammary epithelia, primary human fibroblasts and MEFs, affecting their expansion and self-renewal potential. In mammary glands, reduced levels of Usp16 increase tissue responsiveness to Wnt, resulting in upregulation of the downstream Wnt target Axin2, expansion of the basal compartment and increased in vitro and in vivo epithelial regeneration. Usp16 regulation of the Wnt pathway in mouse and human tissues is at least in part mediated by activation of Cdkn2a, a regulator of senescence. At the molecular level, Usp16 affects Rspo-mediated phosphorylation of LRP6. In Down’s Syndrome (DS), triplication of Usp16 dampens the activation of the Wnt pathway. Usp16 copy number normalization restores normal Wnt activation in Ts65Dn mice models. Genetic upregulation of the Wnt pathway in Ts65Dn mice rescues the proliferation defect observed in mammary epithelial cells. All together, these findings link important stem cell regulators like Bmi1/Usp16 and Cdkn2a to Wnt signaling, and have implications for designing therapies for conditions, like DS, aging or degenerative diseases, where the Wnt pathway is hampered.

Wnt signaling dynamics in head and neck squamous cell cancer tumor-stroma interactions

Wnt pathway activation maintains the cancer stem cell (CSC) phenotype and promotes tumor progression, making it an attractive target for anti-cancer therapy. Wnt signaling at the tumor and tumor microenvironment (TME) front have not been investigated in depth in head and neck squamous cell carcinoma (HNSCC). In a cohort of 48 HNSCCs, increased Wnt signaling, including Wnt genes (AXIN2, LGR6, WISP1) and stem cell factors (RET, SOX5, KIT), were associated with a more advanced clinical stage. Key Wnt pathway proteins were most abundant at the cancer epithelial-stromal boundary. To investigate these observations, we generated three pairs of cancer-cancer associated fibroblast (CAF) cell lines derived from the same HNSCC patients. 3D co-culture of cancer spheres and CAFs mimicked these in vivo interactions, and using these we observed increased expression of Wnt genes (eg, WNT3A, WNT7A, WNT16) in both compartments. Of these Wnt ligands, we found Wnt3a, and less consistently Wnt16, activated Wnt signaling in both cancer cells and CAFs. Wnt activation increased CSC characteristics like sphere formation and invasiveness, which was further regulated by the presence of CAFs. Time lapse microscopy also revealed preferential Wnt activation of cancer cells. Wnt inhibitors, OMP-18R5 and OMP-54F28, significantly reduced growth of HNSCC patient-derived xenografts and suppressed Wnt activation at the tumor epithelial-stromal boundary. Taken together, our findings suggest that Wnt signaling is initiated in cancer cells which then activate CAFs, and in turn perpetuate a paracrine signaling loop. This suggests that targeting Wnt signaling in the TME is essential.

Wnt/β-Catenin Signaling Pathway Governs a Full Program for Dopaminergic Neuron Survival, Neurorescue and Regeneration in the MPTP Mouse Model of Parkinson's Disease

Wingless-type mouse mammary tumor virus (MMTV) integration site (Wnt) signaling is one of the most critical pathways in developing and adult tissues. In the brain, Wnt signaling contributes to different neurodevelopmental aspects ranging from differentiation to axonal extension, synapse formation, neurogenesis, and neuroprotection. Canonical Wnt signaling is mediated mainly by the multifunctional β-catenin protein which is a potent co-activator of transcription factors such as lymphoid enhancer factor (LEF) and T-cell factor (TCF). Accumulating evidence points to dysregulation of Wnt/β-catenin signaling in major neurodegenerative disorders. This review highlights a Wnt/β-catenin/glial connection in Parkinson's disease (PD), the most common movement disorder characterized by the selective death of midbrain dopaminergic (mDAergic) neuronal cell bodies in the subtantia nigra pars compacta (SNpc) and gliosis. Major findings of the last decade document that Wnt/β-catenin signaling in partnership with glial cells is critically involved in each step and at every level in the regulation of nigrostriatal DAergic neuronal health, protection, and regeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD, focusing on Wnt/β-catenin signaling to boost a full neurorestorative program in PD.

Exploring major signaling cascades in melanomagenesis: a rationale route for targetted skin cancer therapy

Although most melanoma cases may be treated by surgical intervention upon early diagnosis, a significant portion of patients can still be refractory, presenting low survival rates within 5 years after the discovery of the illness. As a hallmark, melanomas are highly prone to evolve into metastatic sites. Moreover, melanoma tumors are highly resistant to most available drug therapies and their incidence have increased over the years, therefore leading to public health concerns about the development of novel therapies. Therefore, researches are getting deeper in unveiling the mechanisms by which melanoma initiation can be triggered and sustained. In this context, important progress has been achieved regarding the roles and the impact of cellular signaling pathways in melanoma. This knowledge has provided tools for the development of therapies based on the intervention of signal(s) promoted by these cascades. In this review, we summarize the importance of major signaling pathways (mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K)-Akt, Wnt, nuclear factor κ-light-chain-enhancer of activated B cell (NF-κB), Janus kinase (JAK)-signal transducer and activator of transcription (STAT), transforming growth factor β (TGF-β) and Notch) in skin homeostasis and melanoma progression. Available and developing melanoma therapies interfering with these signaling cascades are further discussed.

Cellular Interactions in the Intestinal Stem Cell Niche

Epithelial cells are one of the most actively cycling cells in a mammalian organism and therefore are prone to malignant transformation. Already during organogenesis, the connective tissue (mesenchyme) provides instructive signals for the epithelium. In an adult organism, the mesenchyme is believed to provide crucial regulatory signals for the maintenance and regeneration of epithelial cells. Here, we discuss the role of intestinal myofibroblasts, α-smooth muscle actin-positive stromal (mesenchymal) cells, as an important regulatory part of the intestinal stem cell niche. Better understanding of the cross-talk between myofibroblasts and the epithelium in the intestine has implications for advances in regenerative medicine, and improved therapeutic strategies for inflammatory bowel disease, intestinal fibrosis and colorectal cancer.

Wnt signaling in human and mouse breast cancer: Focusing on Wnt ligands, receptors and antagonists

Wnt proteins, a group of secreted glycoproteins, mainly combine with receptors Frizzled (FZD) and/or low-density-lipoprotein receptor-related proteins 5/6 (LRP5/6), initiating β-catenin-dependent and -independent signaling pathways. These pathways, which can be regulated by some secreted antagonists such as secreted Frizzled-related proteins (SFRP) and dickkopf-related protein (DKK), play a critical role in embryo development and adult homeostasis. Overactivation of Wnt signaling has been implicated in some human diseases including cancer. Wnt transgenic mice provide convincing evidence that Wnt signaling is involved in breast cancer initiation and progression, which is further strengthened by observations on human clinical breast cancer patients and studies on in vitro cultured human breast cancer cells. This review focuses on the roles of Wnt ligands, receptors and antagonists in breast cancer development instead of molecules or signaling transactivating β-catenin independent on Wnt upstream components.

Tales from the crypt: intestinal niche signals in tissue renewal, plasticity and cancer

Rapidly renewing tissues such as the intestinal epithelium critically depend on the activity of small-sized stem cell populations that continuously generate new progeny to replace lost and damaged cells. The complex and tightly regulated process of intestinal homeostasis is governed by a variety of signalling pathways that balance cell proliferation and differentiation. Accumulating evidence suggests that stem cell control and daughter cell fate determination is largely dictated by the microenvironment. Here, we review recent developments in the understanding of intestinal stem cell dynamics, focusing on the roles, mechanisms and interconnectivity of prime signalling pathways that regulate stem cell behaviour in intestinal homeostasis. Furthermore, we discuss how mutational activation of these signalling pathways endows colorectal cancer cells with niche-independent growth advantages during carcinogenesis.

The Intestinal Stem Cell Niche: Homeostasis and Adaptations

The intestinal epithelium is a rapidly renewing cellular compartment. This constant regeneration is a hallmark of intestinal homeostasis and requires a tightly regulated balance between intestinal stem cell (ISC) proliferation and differentiation. Since intestinal epithelial cells directly contact pathogenic environmental factors that continuously challenge their integrity, ISCs must also actively divide to facilitate regeneration and repair. Understanding niche adaptations that maintain ISC activity during homeostatic renewal and injury-induced intestinal regeneration is therefore a major and ongoing focus for stem cell biology. Here, we review recent concepts and propose an active interconversion of the ISC niche between homeostasis and injury-adaptive states that is superimposed upon an equally dynamic equilibrium between active and reserve ISC populations.

The Matricellular Protein R-Spondin 2 Promotes Midbrain Dopaminergic Neurogenesis and Differentiation

The development of midbrain dopaminergic (mDA) neurons is controlled by multiple morphogens and transcription factors. However, little is known about the role of extracellular matrix proteins in this process. Here we examined the function of roof plate-specific spondins (RSPO1-4) and the floor plate-specific, spondin 1 (SPON1). Only RSPO2 and SPON1 were expressed at high levels during mDA neurogenesis, and the receptor LGR5 was expressed by midbrain floor plate progenitors. Surprisingly, RSPO2, but not SPON1, specifically promoted the differentiation of mDA neuroblasts into mDA neurons in mouse primary cultures and embryonic stem cells (ESCs). In addition, RSPO2 was found to promote not only mDA differentiation, but also mDA neurogenesis in human ESCs. Our results thus uncover an unexpected function of the matricellular protein RSPO2 and suggest an application to improve mDA neurogenesis and differentiation in human stem cell preparations destined to cell replacement therapy or drug discovery for Parkinson disease.

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Rspo2 is dynamically expressed during midbrain dopaminergic neuron development

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RSPO2 promotes the dopaminergic differentiation of mouse neurons in culture

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RSPO2 increases dopaminergic neurogenesis and differentiation of human ESCs

Organoids for Drug Discovery and Personalized Medicine

A wide variety of organs are in a dynamic state, continuously undergoing renewal as a result of constant growth and differentiation. Stem cells are required during these dynamic events for continuous tissue maintenance within the organs. In a steady state of production and loss of cells within these tissues, new cells are constantly formed by differentiation from stem cells. Today, organoids derived from either adult stem cells or pluripotent stem cells can be grown to resemble various organs. As they are similar to their original organs, organoids hold great promise for use in medical research and the development of new treatments. Furthermore, they have already been utilized in the clinic, enabling personalized medicine for inflammatory bowel disease. In this review, I provide an update on current organoid technology and summarize the application of organoids in basic research, disease modeling, drug development, personalized treatment, and regenerative medicine.

Expression Profile of LGR5 and Its Prognostic Significance in Colorectal Cancer Progression

We investigated the expression profile of leucine-rich, repeat-containing, G-protein-coupled receptor 5 (LGR5) during colorectal cancer (CRC) progression and determined the prognostic impact of LGR5 in a large cohort of CRC samples. LGR5 expression was higher in CRCs than in normal mucosa, and was not associated with other cancer stem cell markers. LGR5 positivity was observed in 68% of 788 CRCs and was positively correlated with older age, moderately to well-differentiated cells, and nuclear β-catenin expression. Enhanced LGR5 expression remained persistent during the adenoma-carcinoma transition, but markedly declined in the budding cancer cells at the invasive fronts, which was not due to altered wingless-type mouse mammary tumor virus integration site family (Wnt) or epithelial-mesenchymal transition signaling. LGR5 showed negative correlations with microsatellite instability and CpG island methylator phenotype, and was not associated with KRAS or BRAF mutation. Notably, LGR5 positivity was an independent prognostic marker for better clinical outcomes in CRC patients. LGR5 overexpression attenuated tumor growth by decreasing ERK phosphorylation along with decreased colony formation and migration abilities in DLD1 cells. Likewise, knockdown of LGR5 expression resulted in a decline in the colony-forming and migration capacities in LoVo cells. Taken together, our data suggest a suppressive role of LGR5 in CRC progression.

Leucine-rich G Protein-coupled Receptor-5 Is Significantly Increased in the Aqueous Humor of Human Eye with Proliferative Diabetic Retinopathy

Leucine-rich G protein-coupled receptor-5 (LGR5) is known to be a stem cell marker in many organs. LGR5 may have important roles in proliferative diabetic retinopathy (PDR) because LGR5 potentiate the Wnt/β-catenin pathway, which plays crucial roles in pathologic neovascularization in the retina. The association between LGR5 and retinal pathologic neovascularization has not yet been reported. In the present study, LGR5 was compared in human aqueous humor (AH) between normal control and patients with PDR to confirm the relationship between LGR5 and PDR. AH was collected from 7 naïve PDR patients and 3 control subjects before intravitreal injection and cataract surgery, respectively. LGR5 and key members of Wnt/β-catenin were assessed by western blotting. In the present study, it was confirmed for the first time that LGR5 is detected in AH and it increases in PDR patients. Key members of Wnt/β-catenin pathway were also increased in AH of PDR patients compared to control. These findings might support the hypothesis that LGR5 has important roles in PDR especially considering the roles of the Wnt/β-catenin pathway, which is activated by LGR5, contributing to retinal pathologic neovascularization.

Wnt/β-Catenin Signaling and Obesity

Obesity has become epidemic worldwide, which triggers several obesity-associated complications. Obesity is characterized by excess fat storage mainly in the visceral white adipose tissue (vWAT), subcutaneous WAT (sWAT), and other tissues. Myriad studies have demonstrated the crucial role of canonical Wnt/β-catenin cascade in the development of organs and physiological homeostasis, whereas recent studies show that genetic variations/mutations in the Wnt/β-catenin pathway are associated with human metabolic diseases. In this review, we highlight the regulation of updated Wnt/β-catenin signaling in obesity, especially the distinctly depot-specific roles between subcutaneous and visceral adipose tissue under high-fed diet stimulation and WAT browning process.

Cynoglossus semilaevis Rspo3 Regulates Embryo Development by Inhibiting the Wnt/β-Catenin Signaling Pathway

Cynoglossus semilaevis is an important economic fish species and has long been cultivated in China. Since the completion of its genome and transcriptome sequencing, genes relating to C. semilaevis development have been extensively studied. R-spondin 3 (Rspo3) is a member of the R-spondin family. It plays an important role in biological processes such as vascular development and oncogenesis. In this study, we cloned and characterized the expression patterns and functions of C. semilaevisRspo3. Initial structural and phylogenetic analyses revealed a unique FU3 domain that exists only in ray-finned fish RSPO3. Subsequent embryonic expression profile analysis showed elevating expression of Rspo3 from gastrulation to the formation of the eye lens, while, in tail bud embryos, Rspo3 expression was significantly high in the diencephalon and mesencephalon. The overexpression of C. semilaevis Rspo3 in Danio rerio embryos resulted in a shortened rostral–caudal axis, edema of the pericardial cavity, stubby yolk extension, and ecchymosis. Vascular anomalies were also observed, which is consistent with Rspo3 role in vascular development. Drug treatment and a dual-luciferase reporter assay confirmed the inhibitory role of C. semilaevis Rspo3 in D. rerio Wnt/β-catenin signaling pathway. We further concluded that the FU2, FU3, and TSP1 domains regulate the maternal Wnt/β-catenin signaling pathway, while the FU1 domain regulates the zygotic Wnt/β-catenin signaling pathway. This study enriches Rspo3 research in non-model animals and serves as the basis for further research into the interactions between Rspo and the Wnt/β-catenin signaling pathway.

Wnt signalling: conquering complexity

The history of the Wnt pathway is an adventure that takes us from mice and flies to frogs, zebrafish and beyond, sketching the outlines of a molecular signalling cascade along the way. Here, we specifically highlight the instrumental role that developmental biology has played throughout. We take the reader on a journey, starting with developmental genetics studies that identified some of the main molecular players, through developmental model organisms that helped unravel their biochemical function and cell biological activities. Culminating in complex analyses of stem cell fate and dynamic tissue growth, these efforts beautifully illustrate how different disciplines provided missing pieces of a puzzle. Together, they have shaped our mechanistic understanding of the Wnt pathway as a conserved signalling process in development and disease. Today, researchers are still uncovering additional roles for Wnts and other members of this multifaceted signal transduction pathway, opening up promising new avenues for clinical applications.