Leucine-rich repeat-containing, G protein-coupled receptor 4 null mice exhibit intrauterine growth retardation associated with embryonic and perinatal lethality

Hepatic LGR4 aggravates cholestasis-induced liver injury in mice

Current therapy for hepatic injury induced by the accumulation of bile acids is limited. Leucine-rich repeat G protein-coupled receptor 4 (LGR4), also known as GPR48, is critical for cytoprotection and cell proliferation. Here, we reported a novel function for the LGR4 in cholestatic liver injury. In the bile duct ligation (BDL)-induced liver injury model, hepatic LGR4 expression was significantly downregulated. Deficiency of LGR4 in hepatocytes (Lgr4LKO) notably decreased BDL-induced liver injury measured by hepatic necrosis, fibrosis, and circulating liver enzymes and total bilirubin. Levels of total bile acids in plasma and liver were markedly reduced in these mice. However, deficiency of LGR4 in macrophages (Lyz2-Lgr4MKO) demonstrated no significant effect on liver injury induced by BDL. Deficiency of LGR4 in hepatocytes significantly attenuated S1PR2 and the phosphorylation of protein kinase B (AKT) induced by BDL. Recombinant Rspo1 and Rspo3 potentiated the taurocholic acid (TCA)-induced upregulation in S1PR2 and phosphorylation of AKT in hepatocytes. Inhibition of S1PR2-AKT signaling by specific AKT or S1PR2 inhibitors blocked the increase of bile acid secretion induced by Rspo1/3 in hepatocytes. Our studies indicate that the R-spondins (Rspos)-LGR4 signaling in hepatocytes aggravates the cholestatic liver injury by potentiating the production of bile acids in a S1PR2-AKT-dependent manner.NEW & NOTEWORTHY Deficiency of LGR4 in hepatocytes alleviates BDL-induced liver injury. LGR4 in macrophages demonstrates no effect on BDL-induced liver injury. Rspos-LGR4 increases bile acid synthesis and transport via potentiating S1PR2-AKT signaling in hepatocytes.

Rspo2-LGR4 exacerbates hepatocellular carcinoma progression via activation of Wnt/β-catenin signaling pathway

BACKGROUND

The leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4) plays an important role in stem cell differentiation, organ development and cancer. Whether LGR4 affects the progression of hepatocellular carcinoma (HCC) remains unknown. This study aimed to reveal the role of LGR4 in HCC.

METHODS

Clinical samples of HCC were collected to assess the expression of LGR4 and its correlation with patients' clinical characteristics. The expression level of LGR4 in HCC cells was altered by pharmacological and genetic methods, and the role of LGR4 in HCC progression was analyzed by in vivo and in vitro assays. HCC was induced by diethylnitrosamine (DEN) and carbon tetrachloride (CCl4) in wild-type and LGR4 deficient mice, the effect of LGR4 on HCC was examined by histopathological evaluation and biochemical assays.

RESULTS

LGR4 expression was up-regulated in HCC samples, and its expression level was positively correlated with tumor size, microvascular invasion (MVI), TNM stage and pathological differentiation grade of HCC patients. In the mouse HCC model induced by DEN+CCl4, knockdown of LGR4 effectively inhibited the progression of HCC. Silencing of LGR4 inhibited the proliferation, migration, invasion, stem cell-like properties and Warburg effect of HCC cells. These phenotypes were promoted by R-spondin2 (Rspo2), an endogenous ligand for LGR4. Rspo2 markedly increased the nuclear translocation of β-catenin, whereas IWR-1, an inhibitor of Wnt/β-catenin signaling, reversed its effect. Deficiency of LGR4 significantly reduced the nuclear translocation of β-catenin and the expression of its downstream target genes cyclinD1 and c-Myc.

CONCLUSIONS

LGR4 promotes HCC progression via Wnt/β-catenin signaling pathway.

Polymorphisms in transcription factor binding sites and enhancer regions and pancreatic ductal adenocarcinoma risk

Genome-wide association studies (GWAS) are a powerful tool for detecting variants associated with complex traits and can help risk stratification and prevention strategies against pancreatic ductal adenocarcinoma (PDAC). However, the strict significance threshold commonly used makes it likely that many true risk loci are missed. Functional annotation of GWAS polymorphisms is a proven strategy to identify additional risk loci. We aimed to investigate single-nucleotide polymorphisms (SNP) in regulatory regions [transcription factor binding sites (TFBSs) and enhancers] that could change the expression profile of multiple genes they act upon and thereby modify PDAC risk. We analyzed a total of 12,636 PDAC cases and 43,443 controls from PanScan/PanC4 and the East Asian GWAS (discovery populations), and the PANDoRA consortium (replication population). We identified four associations that reached study-wide statistical significance in the overall meta-analysis: rs2472632(A) (enhancer variant, OR 1.10, 95%CI 1.06,1.13, p = 5.5 × 10-8), rs17358295(G) (enhancer variant, OR 1.16, 95%CI 1.10,1.22, p = 6.1 × 10-7), rs2232079(T) (TFBS variant, OR 0.88, 95%CI 0.83,0.93, p = 6.4 × 10-6) and rs10025845(A) (TFBS variant, OR 1.88, 95%CI 1.50,1.12, p = 1.32 × 10-5). The SNP with the most significant association, rs2472632, is located in an enhancer predicted to target the coiled-coil domain containing 34 oncogene. Our results provide new insights into genetic risk factors for PDAC by a focused analysis of polymorphisms in regulatory regions and demonstrating the usefulness of functional prioritization to identify loci associated with PDAC risk.

Spatiotemporal expression patterns of R-spondins and their receptors, Lgrs, in the developing mouse telencephalon

Development of the mammalian telencephalon, which is the most complex region of the central nervous system, is precisely orchestrated by many signaling molecules. Wnt signaling derived from the cortical hem, a signaling center, is crucial for telencephalic development including cortical patterning and the induction of hippocampal development. Secreted protein R-spondin (Rspo) 1-4 and their receptors, leucine-rich repeat-containing G-protein-coupled receptor (Lgr) 4-6, act as activators of Wnt signaling. Although Rspo expression in the hem during the early stages of cortical development has been reported, comparative expression analysis of Rspos and Lgr4-6 has not been performed. In this study, we examined the detailed spatiotemporal expression patterns of Rspo1-4 and Lgr4-6 in the embryonic and postnatal telencephalon to elucidate their functions. In the embryonic day (E) 10.5-14.5 telencephalon, Rspo1-3 were prominently expressed in the cortical hem. Among their receptors, Lgr4 was observed in the ventral telencephalon, and Lgr6 was highly expressed throughout the telencephalon at the same stages. This suggests that Rspo1-3 and Lgr4 initially regulate telencephalic development in restricted regions, whereas Lgr6 functions broadly. From the late embryonic stage, the expression areas of Rspo1-3 and Lgr4-6 dramatically expanded; their expression was found in the neocortex and limbic system, such as the hippocampus, amygdala, and striatum. Increased Rspo and Lgr expression from the late embryonic stages suggests broad roles of Rspo signaling in telencephalic development. Furthermore, the Lgr+ regions were located far from the Rspo+ regions, especially in the E10.5-14.5 ventral telencephalon, suggesting that Lgrs act via a Rspo-independent pathway.

Large-scale analysis of de novo mutations identifies risk genes for female infertility characterized by oocyte and early embryo defects

BACKGROUND

Oocyte maturation arrest and early embryonic arrest are important reproductive phenotypes resulting in female infertility and cause the recurrent failure of assisted reproductive technology (ART). However, the genetic etiologies of these female infertility-related phenotypes are poorly understood. Previous studies have mainly focused on inherited mutations based on large pedigrees or consanguineous patients. However, the role of de novo mutations (DNMs) in these phenotypes remains to be elucidated.

RESULTS

To decipher the role of DNMs in ART failure and female infertility with oocyte and embryo defects, we explore the landscape of DNMs in 473 infertile parent-child trios and identify a set of 481 confident DNMs distributed in 474 genes. Gene ontology analysis reveals that the identified genes with DNMs are enriched in signaling pathways associated with female reproductive processes such as meiosis, embryonic development, and reproductive structure development. We perform functional assays on the effects of DNMs in a representative gene Tubulin Alpha 4a (TUBA4A), which shows the most significant enrichment of DNMs in the infertile parent-child trios. DNMs in TUBA4A disrupt the normal assembly of the microtubule network in HeLa cells, and microinjection of DNM TUBA4A cRNAs causes abnormalities in mouse oocyte maturation or embryo development, suggesting the pathogenic role of these DNMs in TUBA4A.

CONCLUSIONS

Our findings suggest novel genetic insights that DNMs contribute to female infertility with oocyte and embryo defects. This study also provides potential genetic markers and facilitates the genetic diagnosis of recurrent ART failure and female infertility.

Emerging Roles for LGR4 in Organ Development, Energy Metabolism and Carcinogenesis

The leucine-rich repeats containing G protein-coupled receptor 4 (LGR4) belonging to G protein-coupled receptors (GPCRs) family, had various regulatory roles at multiple cellular types and numerous targeting sites, and aberrant LGR4 signaling played crucial roles in diseases and carcinogenesis. On the basis of these facts, LGR4 may become an appealing therapeutic target for the treatment of diseases and tumors. However, a comprehensive investigation of its functions and applications was still lacking. Hence, this paper provided an overview of the molecular characteristics and signaling mechanisms of LGR4, its involvement in multiple organ development and participation in the modulation of immunology related diseases, metabolic diseases, and oxidative stress damage along with cancer progression. Given that GPCRs accounted for almost a third of current clinical drug targets, the in-depth understanding of the sophisticated connections of LGR4 and its ligands would not only enrich their regulatory networks, but also shed new light on designing novel molecular targeted drugs and small molecule blockers for revolutionizing the treatment of various diseases and tumors.

Wnt Pathway Extracellular Components and Their Essential Roles in Bone Homeostasis

The Wnt pathway is involved in several processes essential for bone development and homeostasis. For proper functioning, the Wnt pathway is tightly regulated by numerous extracellular elements that act by both activating and inhibiting the pathway at different moments. This review aims to describe, summarize and update the findings regarding the extracellular modulators of the Wnt pathway, including co-receptors, ligands and inhibitors, in relation to bone homeostasis, with an emphasis on the animal models generated, the diseases associated with each gene and the bone processes in which each member is involved. The precise knowledge of all these elements will help us to identify possible targets that can be used as a therapeutic target for the treatment of bone diseases such as osteoporosis.

LGR4, a G Protein-Coupled Receptor With a Systemic Role: From Development to Metabolic Regulation

Leucine-rich repeat-containing G protein-coupled receptor 4 (LGR4/GPR48), a member of the GPCR (G protein-coupled receptors) superfamily, subfamily B, is a common intestinal crypt stem cell marker. It binds R-spondins/Norrin as classical ligands and plays a crucial role in Wnt signaling potentiation. Interaction between LGR4 and R-spondins initiates many Wnt-driven developmental processes, e.g., kidney, eye, or reproductive tract formation, as well as intestinal crypt (Paneth) stem cell pool maintenance. Besides the well-described role of LGR4 in development, several novel functions of this receptor have recently been discovered. In this context, LGR4 was indicated to participate in TGFβ and NFκB signaling regulation in hematopoietic precursors and intestinal cells, respectively, and found to be a new, alternative receptor for RANKL (Receptor Activator of NF kappa B Ligand) in bone cells. LGR4 inhibits the process of osteoclast differentiation, by antagonizing the interaction between RANK (Receptor Activator of NF kappa B) and its ligand-RANKL. It is also known to trigger anti-inflammatory responses in different tissues (liver, intestine, cardiac cells, and skin), serve as a sensor of the circadian clock in the liver, regulate adipogenesis and energy expenditure in adipose tissue and skeletal muscles, respectively. The extracellular domain of LGR4 (LGR4-ECD) has emerged as a potential new therapeutic for osteoporosis and cancer. LGR4 integrates different signaling pathways and regulates various cellular processes vital for maintaining whole-body homeostasis. Yet, the role of LGR4 in many cell types (e.g. pancreatic beta cells) and diseases (e.g., diabetes) remains to be elucidated. Considering the broad spectrum of LGR4 actions, this review aims to discuss both canonical and novel roles of LGR4, with emphasis on emerging research directions focused on this receptor.

A Wnt-Independent LGR4-EGFR Signaling Axis in Cancer Metastasis

Leucine-rich repeat-containing G protein-coupled receptors 4, 5, and 6 (LGR4/5/6) play critical roles in development and cancer. The widely accepted mechanism is that these proteins, together with their R-spondin ligands, stabilize Wnt receptors, thus potentiating Wnt signaling. Here we show that LGR4 enhanced breast cancer cell metastasis even when Wnt signaling was deactivated pharmacologically or genetically. Furthermore, LGR4 mutants that cannot potentiate Wnt signaling nevertheless promoted breast cancer cell migration and invasion in vitro and breast cancer metastasis in vivo. Multiomic screening identified EGFR as a crucial mediator of LGR4 activity in cancer progression. Mechanistically, LGR4 interacted with EGFR and blocked EGFR ubiquitination and degradation, resulting in persistent EGFR activation. Together, these data uncover a Wnt-independent LGR4-EGFR signaling axis with broad implications for cancer progression and targeted therapy. SIGNIFICANCE: This work demonstrates a Wnt-independent mechanism by which LGR4 promotes cancer metastasis.See related commentary by Stevens and Williams, p. 4397.

The Role of LGR4 (GPR48) in Normal and Cancer Processes

Leucine-rich repeats containing G protein-coupled receptor 4 (LGR4) is a receptor that belongs to the superfamily of G protein-coupled receptors that can be activated by R-spondins (RSPOs), Norrin, circLGR4, and the ligand of the receptor activator of nuclear factor kappa-B (RANKL) ligands to regulate signaling pathways in normal and pathological processes. LGR4 is widely expressed in different tissues where it has multiple functions such as tissue development and maintenance. LGR4 mainly acts through the Wnt/β-catenin pathway to regulate proliferation, survival, and differentiation. In cancer, LGR4 participates in tumor progression, invasion, and metastasis. Furthermore, recent evidence reveals that LGR4 is essential for the regulation of the cancer stem cell population by controlling self-renewal and regulating stem cell properties. This review summarizes the function of LGR4 and its ligands in normal and malignant processes.

LGR5/R-Spo1/Wnt3a axis promotes stemness and aggressive phenotype in hepatoblast-like hepatocellular carcinoma cell lines

Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) is a newly defined stem cell marker in endoderm-derived organs such as the small intestine, colon and pancreas. Recently, LGR5 was demonstrated to be an important factor in liver regeneration and stem cell maintenance. Moreover, LGR5 expression is highly up-regulated in various cancers including hepatocellular carcinoma. Herein, we demonstrate that LGR5 expression is specifically observed in certain subset of HCC cell lines with "hepatoblast-like" appearance, characterized by the expression of liver fetal/progenitor markers. Notably, the activation of the canonical Wnt pathway significantly increases the expression of LGR5 in this subset of cell lines, whereas it does not cause any induction of LGR5 expression in mesenchymal like cell lines SNU-475 and SNU-449. Furthermore, we showed that treatment of the hepatoblast-like HCC cell lines HuH-7 and Hep3B with LGR5 ligand R-Spo1 significantly amplifies the induction of LGR5 expression, the phosphorylation of LRP6 and β-catenin resulting in enhanced TCF/LEF activity either alone or in combination with Wnt3a. Consistently, the silencing of the LGR5 gene attenuates the co-stimulatory effect of R-Spo1/Wnt3a on TCF/LEF activity while overexpression of LGR5 enhances it. On the contrary, overexpression of LGR5 does not change TCF/LEF activity induced by R-Spo1/Wnt3a in mesenchymal-like HCC line, SNU-449. Importantly, LGR5-overexpressing cells have increased expression of several Wnt target genes and stemness-related genes including EpCAM and CK19 upon R-Spo1/Wnt3a treatment. LGR5-overexpressing cells also have increased spheroid forming, migration and invasion abilities and stimulation with R-Spo1/Wnt3a augments these abilities of LGR5-overexpressing cells. In addition, ectopic overexpression of LGR5 significantly increases cell proliferation rate independent of R-Spo1/Wnt3a stimulation. Moreover, in vitro tubulogenesis assay demonstrates that treatment with R-Spo1/Wnt3a enhances the sprouting of capillary tubules in only LGR5-overexpressing cells. Finally, R-Spo1/Wnt3a significantly promotes dissemination of LGR5-overexpressing cells in vivo in a zebrafish xenograft model. Our study unravels a tumor-promoting role for LGR5 through activation of canonical Wnt/β-catenin signaling in the hepatoblast-like HCCs. In conclusion, our results suggest that LGR5/R-Spo1/Wnt3a generates an axis that mediates the acquisition of aggressive phenotype specifically in hepatoblast-like subset of HCCs and might represent a valuable target for treatment of HCC tumors with aberrant activation of Wnt/β-catenin pathway.

β-catenin in adrenal zonation and disease

The Wnt signaling pathway is a critical mediator of the development and maintenance of several tissues. The adrenal cortex is highly dependent upon Wnt/β-catenin signaling for proper zonation and endocrine function. Adrenocortical cells emerge in the peripheral capsule and subcapsular cortex of the gland as progenitor cells that centripetally differentiate into steroid hormone-producing cells of three functionally distinct concentric zones that respond robustly to various endocrine stimuli. Wnt/β-catenin signaling mediates adrenocortical progenitor cell fate and tissue renewal to maintain the gland throughout life. Aberrant Wnt/β-catenin signaling contributes to various adrenal disorders of steroid production and growth that range from hypofunction and hypoplasia to hyperfunction, hyperplasia, benign adrenocortical adenomas, and malignant adrenocortical carcinomas. Great strides have been made in defining the molecular underpinnings of adrenocortical homeostasis and disease, including the interplay between the capsule and cortex, critical components involved in maintaining the adrenocortical Wnt/β-catenin signaling gradient, and new targets in adrenal cancer. This review seeks to examine these and other recent advancements in understanding adrenocortical Wnt/β-catenin signaling and how this knowledge can inform therapeutic options for adrenal disease.

LGR4 silence aggravates ischemic injury by modulating mitochondrial function and oxidative stress via ERK signaling pathway in H9c2 cells

It is reported that LGR4 (leucine-rich repeat domain containing G protein-coupled receptor 4) plays a crucial role in the physiological function of many organs. However, few data are available on the function and mechanism of LGR4 in myocardial ischemia-reperfusion (I/R) injury. The aim of this study was to explore the function and mechanism of LGR4 in I/R injury. We incubated H9c2 cells in simulating ischemia buffer and then re-incubated them in normal culture medium to establish a model of I/R injury in vitro. The expression of LGR4 was evaluated by RT-PCR and western blot. Besides, the cell apoptosis was evaluated by flow cytometric analysis and the content of ROS, SOD, MDA, LDH, CK, ATP, cyt c were detected by special commercial kits. The expression of mitochondrial function-related proteins were detected by western blot. Then, the roles of ERK signaling pathway was determined with TBHQ (ERK activator) treatment. Our data have demonstrated that I/R boosted the expression of LGR4 in H9c2 cells. Knockdown of LGR4 increased the apoptosis rate of H9c2 cells and led to excessed oxidant stress and impaired mitochondrial function by increasing the levels of ROS, MDA, LDH, CK and cyt c and inhibiting SOD activity, ATP production. In addition, LGR4 silence inhibited the activation of ERK pathway. And TBHQ partially reversed the effects of LGR4 knockdown on H9c2 cells. To conclude, our study indicated that LGR4 regulated mitochondrial dysfunction and oxidative stress by ERK signaling pathways, which provides a potential cardiac protective target against I/R.

LGR4 overexpression is associated with clinical parameters and poor prognosis of serous ovarian cancer

OBJECTIVE

LGR4 expression in serous ovarian cancer paraffin-embedded tissues and fresh tissues were investigated, and its expression associated with clinicopathological parameters and prognosis in serous ovarian cancer was explored.

METHODS

From Dec, 2009 to Jan, 2020, 122 paraffin-embedded serous ovarian cancer patients and 41 paired paratumor tissues who were both diagnosed and operated at the memorial hospital of Sun Yat-sen University and Integrated Hospital of Traditional Chinese Medicine, Southern Medical University were selected in this research, respectively, and all of these tissues were performed by immunohistochemistry (IHC) with a polyclonal antibody for LGR4. Meanwhile, from Aug, 2013 to Mar, 2019, 15 cases of serous ovarian cancer fresh tissues and 15 cases of paratumor fresh tissues who were operated at Integrated Hospital of Traditional Chinese Medicine, Southern Medical University were performed with Quantitative Real-time PCR to detect the mRNA expression of LGR4, respectively.

RESULTS

LGR4 expression was much higher both in paraffin-embedded and fresh cancer tissues than that in paratumor tissues, respectively, and its expression was associated with recurrence free survival and overall survival in serous ovarian cancer patients. Moreover, in a multivariate model LGR4 was an indeed independent predictor of poor survival in serous ovarian cancer patients.

CONCLUSION

LGR4 is upregulated in serous ovarian cancer, and LGR4 is an indeed useful independent prognostic predictor in serous ovarian cancer, and it may provide important clinical value of serous ovarian cancer.

Ablation of LGR4 signaling enhances radiation sensitivity of prostate cancer cells

AIM

Our previous study has shown that leucine-rich repeat containing GPCR-4 (LGR4, or GPR48) LGR4 plays a role in cell migration, invasion, proliferation and apoptosis of prostate cancer (PCa). In this study, we aimed to explore whether LGR4 would affect radiation response in PCa.

MATERIALS AND METHODS

LGR4 expression was silenced by shRNA transfection. qRT-PCR was employed to determine mRNA expression of LGR4 and DNA damage repair genes. Western blot was used to evaluate protein expression of LGR4, RSPO1-4, androgen receptor (AR), cyclic AMP response-element binding protein (CREB1), γH2A.X, and H2A.X. Cell proliferation was detected by CCK-8 assay and apoptosis was assayed by flow cytometry. Additionally, a xenograft model was also established to validate the role of LGR4 in PCa cells after radiation.

KEY FINDINGS

LGR4 expression was enhanced in PCa cells by radiation treatment in dose- and time-dependent means. RSPO1-4 were also upregulated post-radiation. Furthermore, LGR4 knockdown exacerbated apoptosis, reduced cell viabilities and strengthened nuclear γH2A.X staining in AR positive PCa cells but not in AR negative cells in the presence of radiation. Likewise, LGR4 ablation diminished AR and CREB1 expression induced by radiation. In contrast, RSPO1 stimulation augmented cell viabilities, promoted AR and CREB1 expression, and upregulated DNA repair gene expression, which could be reversed by enzalutamide, except for AR expression. Additionally, LGR4 knockdown further suppressed tumor growth and AR/CREB1 expression but enhanced γH2A.X expression in xenografts.

SIGNIFICANCE

In all, our study suggested that LGR4 might serve as an important regulator of radiation sensitivity in PCa.

LGR5 constitutively activates NF-κB signaling to regulate the growth of intestinal crypts

Mammalian LGR5 and LGR4, markers of adult stem cells, are involved in many physiological functions by enhancing WNT signaling. However, whether LGR5 and LGR4 are coupled to other intracellular signaling pathways to regulate stem cell function remains unknown. Here, we show that LGR5 and LGR4 can constitutively activate NF-κB signaling in a ligand-independent manner, which is dependent on their C-termini, but independent of receptor endocytosis. Moreover, the C-termini of LGR5/4 interact with TROY, which is required for activating NF-κB signaling. In small intestinal crypt organoids, overexpression of a C-terminal deletion mutant of LGR5 inhibits the growth and bud formation of organoids, whereas overexpression of the R-spondin-binding mutant of LGR5 that is defective for WNT signaling can still promote organoid growth. Our study reveals that NF-κB signaling, regulated by LGR5 and LGR4, plays an important role in the survival of colon cancer cells and the growth of intestinal crypts. Our findings also suggest that LGR5/4-induced NF-κB signaling and WNT signaling may co-regulate the growth of LGR5⁺ adult stem cells and intestinal crypts.

Lgr4 Governs a Pro-Inflammatory Program in Macrophages to Antagonize Post-Infarction Cardiac Repair

RATIONALE

Macrophages are critically involved in wound healing following myocardial infarction (MI). Lgr4, a member of LGR (leucine-rich repeat-containing G protein-coupled receptor) family, is emerging as a regulator of macrophage-associated immune responses. However, the contribution of Lgr4 to macrophage phenotype and function in the context of MI remains unclear.

OBJECTIVE

To determine the role of macrophage Lgr4 in MI and to dissect the underlying mechanisms.

METHODS AND RESULTS

During early inflammatory phase of MI, infarct macrophages rather than neutrophils expressed high level of Lgr4. Macrophage-specific Lgr4 knockout mice had no baseline cardiovascular defects but manifested improved heart function, modestly reduced infarct size, decreased early mortality due to cardiac rupture, and ameliorated adverse remodeling after MI. Improved outcomes in macrophage-specific Lgr4 knockout mice subjected to MI were associated with mitigated ischemic injury and optimal infarct healing, as determined by reduction of cardiac apoptosis in the peri-infarct zone, attenuation of local myocardial inflammatory response, decrease of matrix metalloproteinase expression in the infarct, enhancement of angiogenesis, myofibroblast proliferation, and collagen I deposition in reparative granulation tissue as well as formation of collagen-rich scar. More importantly, macrophage-specific Lgr4 knockout infarcts had reduced numbers of infiltrating leukocytes and inflammatory macrophages but harbored abundant reparative macrophage subsets. Lgr4-null infarct macrophages exhibited a less inflammatory transcriptional signature. These findings were further supported by transcriptomic profiling data showing repression of multiple pathways and broad-spectrum genes associated with proinflammatory responses in macrophage-specific Lgr4 knockout infarcts. Notably, we discovered that Lgr4-mediated functional phenotype programing in infarct macrophages was at least partly attributed to regulation of AP (activator protein)-1 activity. We further demonstrated that the synergistic effects of Lgr4 on AP-1 activation in inflammatory macrophages occurred via enhancing CREB (cAMP response element-binding protein)-mediated c-Fos, Fosl1, and Fosb transactivation.

CONCLUSIONS

Together, our data highlight the significance of Lgr4 in governing proinflammatory phenotype of infarct macrophages and postinfarction repair.

The lysophospholipase D enzyme Gdpd3 is required to maintain chronic myelogenous leukaemia stem cells

Although advanced lipidomics technology facilitates quantitation of intracellular lipid components, little is known about the regulation of lipid metabolism in cancer cells. Here, we show that disruption of the Gdpd3 gene encoding a lysophospholipase D enzyme significantly decreased self-renewal capacity in murine chronic myelogenous leukaemia (CML) stem cells in vivo. Sophisticated lipidomics analyses revealed that Gdpd3 deficiency reduced levels of certain lysophosphatidic acids (LPAs) and lipid mediators in CML cells. Loss of Gdpd3 also activated AKT/mTORC1 signalling and cell cycle progression while suppressing Foxo3a/β-catenin interaction within CML stem cell nuclei. Strikingly, CML stem cells carrying a hypomorphic mutation of Lgr4/Gpr48, which encodes a leucine-rich repeat (LRR)-containing G-protein coupled receptor (GPCR) acting downstream of Gdpd3, displayed inadequate disease-initiating capacity in vivo. Our data showing that lysophospholipid metabolism is required for CML stem cell maintenance in vivo establish a new, biologically significant mechanism of cancer recurrence that is independent of oncogene addiction.

How lipid metabolism can affect cancer recurrence is still unclear. Here, the authors show that the lysophospholipase D Gdpd3 maintains self-renewal capacity of CML stem cells by regulating the quiescence, and AKT/mTORC1 and Foxo3a/β-catenin signalling in an oncogene-independent manner.

Rspo1/Rspo3-LGR4 signaling inhibits hepatic cholesterol synthesis through the AMPKα-SREBP2 pathway

R-spondins (Rspos) are endogenous ligands of leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4). Rspos-LGR4 signaling plays important roles in embryogenesis, gastrointestinal homeostasis, and food intake. Here, we investigated the impacts of Rspos-LGR4 on hepatic cholesterol synthesis. Rspo1/3 and Lgr4 knockdown mice were used to investigate the impacts of Rspo1/3-LGR4 on hepatic cholesterol synthesis. AMPKα agonist, antagonist, and shRNA were used to explore the downstream targets of Rspos-LGR4 signaling. In our study, we reported that LGR4, Rspo1, and Rspo3 were highly expressed in hepatocytes and their expressions were sensitive to energy states. Rspo1 and Rspo3 reversed OA-induced cholesterol synthesis, accompanying with increased the phosphorylation of AMPKα Thr172, reduced SREBP2 nuclear translocation, and Srebf2 mRNA expression. Conversely, hepatic LGR4 knockdown increased hepatic cholesterol synthesis and decreased the phosphorylation of AMPKα both in vitro and in vivo. Activation or inhibition of AMPKα significantly abolished the effects of LGR4 deficiency or Rspos, respectively, on cholesterol synthesis. Knockdown of AMPKα1 or/and AMPKα2 repressed Rspos-induced inhibition on cholesterol synthesis. Our study indicates that Rspo1/Rspo3-LGR4 signaling in hepatocytes suppresses cholesterol synthesis via the AMPKα-SREBP2 pathway.

Targeting RSPO3-LGR4 Signaling for Leukemia Stem Cell Eradication in Acute Myeloid Leukemia

Signals driving aberrant self-renewal in the heterogeneous leukemia stem cell (LSC) pool determine aggressiveness of acute myeloid leukemia (AML). We report that a positive modulator of canonical WNT signaling pathway, RSPO-LGR4, upregulates key self-renewal genes and is essential for LSC self-renewal in a subset of AML. RSPO2/3 serve as stem cell growth factors to block differentiation and promote proliferation of primary AML patient blasts. RSPO receptor, LGR4, is epigenetically upregulated and works through cooperation with HOXA9, a poor prognostic predictor. Blocking the RSPO3-LGR4 interaction by clinical-grade anti-RSPO3 antibody (OMP-131R10/rosmantuzumab) impairs self-renewal and induces differentiation in AML patient-derived xenografts but does not affect normal hematopoietic stem cells, providing a therapeutic opportunity for HOXA9-dependent leukemia.

A novel function of R-spondin1 in regulating estrogen receptor expression independent of Wnt/β-catenin signaling

R-spondin1 (Rspo1) has been featured as a Wnt agonist, serving as a potent niche factor for stem cells in many tissues. Here we unveil a novel role of Rspo1 in promoting estrogen receptor alpha (Esr1) expression, hence regulating the output of steroid hormone signaling in the mouse mammary gland. This action of Rspo1 relies on the receptor Lgr4 and intracellular cAMP-PKA signaling, yet is independent of Wnt/β-catenin signaling. These mechanisms were reinforced by genetic evidence. Luminal cells-specific knockout of Rspo1 results in decreased Esr1 expression and reduced mammary side branches. In contrast, luminal cells-specific knockout of Wnt4, while attenuating basal cell Wnt/β-catenin signaling activities, enhances Esr1 expression. Our data reveal a novel Wnt-independent role of Rspo1, in which Rspo1 acts as a bona fide GPCR activator eliciting intracellular cAMP signaling. The identification of Rspo1-ERα signaling axis may have a broad implication in estrogen-associated diseases.

Discovery of polypeptide ligand-receptor pairs based on their co-evolution

Sequencing diverse genomes allowed the tracing of orthologous and paralogous genes to understand the co-evolution of polypeptide ligands and receptors. This review documents the discovery of several polypeptide ligands and their cognate receptors mainly expressed in the reproductive tissue using evolutionary genomics. We discussed the sub-functionization of paralogs and co-evolution of ligand-receptor families. Based on the conserved signaling among paralogous receptors and common knock-out phenotypes of ligand-receptor pairs, relationships between relaxin family peptides and leucine-rich repeat-containing, G protein-coupled receptors (LGR) were revealed. We also described the identification of a novel paralogous glycoprotein hormone thyrostimulin and design of a long-acting FSH. Human stresscopin and stresscopin-related peptide, paralogous to CRH, were also identified based on the conserved signaling pathways. Recently, a novel ligand placensin expressed in human placenta was found based on the paralogous relationship with a metabolic hormone asprosin. Placensin likely contributes to stage-dependent increases in insulin resistance during human pregnancy and its elevated secretion was associated with gestational diabetes mellitus. Although many ligands were predicted based on sequence signatures, ligands of shorter sequences have not been identified, together with many "orphan" receptors without known ligands. Future development of tools for predicting ligands and high throughput assays to identify ligand-receptor pairs based on ligand binding and/or signal transduction could advance hormone-based physiology and pathophysiology.

MicroRNA-34 Family Enhances Wound Inflammation by Targeting LGR4

Venous ulcers are the most common type of human chronic nonhealing wounds and are stalled in a constant and excessive inflammatory state. The molecular mechanisms underlying the chronic wound inflammation remain elusive. Moreover, little is known about the role of regulatory RNAs, such as microRNAs, in the pathogenesis of venous ulcers. We found that both microRNA (miR)-34a and miR-34c were upregulated in the wound-edge epidermal keratinocytes of venous ulcers compared with normal wounds or the skin. In keratinocytes, miR-34a and miR-34c promoted inflammatory chemokine and cytokine production. In wounds of wild-type mice, miR-34a-mimic treatment enhanced inflammation and delayed healing. To further explore how miR-34 functions, LGR4 was identified as a direct target mediating the proinflammatory function of miR-34a and miR-34c. Interestingly, impaired wound closure with enhanced inflammation was also observed in Lgr4 knockout mice. Mechanistically, the miR-34-LGR4 axis regulated GSK-3β-induced p65 serine 468 phosphorylation, changing the activity of the NF-κB signaling pathway. Collectively, the miR-34-LGR4 axis was shown to regulate keratinocyte inflammatory response, the deregulation of which may play a pathological role in venous ulcers.

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.

The nucleoside-diphosphate kinase NME3 associates with nephronophthisis proteins and is required for ciliary function during renal development

Nephronophthisis (NPH) is an autosomal recessive renal disease leading to kidney failure in children and young adults. The protein products of the corresponding genes (NPHPs) are localized in primary cilia or their appendages. Only about 70% of affected individuals have a mutation in one of 100 renal ciliopathy genes, and no unifying pathogenic mechanism has been identified. Recently, some NPHPs, including NIMA-related kinase 8 (NEK8) and centrosomal protein 164 (CEP164), have been found to act in the DNA-damage response pathway and to contribute to genome stability. Here, we show that NME/NM23 nucleoside-diphosphate kinase 3 (NME3) that has recently been found to facilitate DNA-repair mechanisms binds to several NPHPs, including NEK8, CEP164, and ankyrin repeat and sterile α motif domain-containing 6 (ANKS6). Depletion of nme3 in zebrafish and Xenopus resulted in typical ciliopathy-associated phenotypes, such as renal malformations and left-right asymmetry defects. We further found that endogenous NME3 localizes to the basal body and that it associates also with centrosomal proteins, such as NEK6, which regulates cell cycle arrest after DNA damage. The ciliopathy-typical manifestations of NME3 depletion in two vertebrate in vivo models, the biochemical association of NME3 with validated NPHPs, and its localization to the basal body reveal a role for NME3 in ciliary function. We conclude that mutations in the NME3 gene may aggravate the ciliopathy phenotypes observed in humans.

Evidence for Lgr6 as a Novel Marker of Osteoblastic Progenitors in Mice

Bone marrow-derived mesenchymal stem cells are an important source of osteoblasts critical for both bone homeostasis and repair. The ability to isolate, or specifically target, mesenchymal stem cells committed to the osteogenic lineage is necessary for orthopedic translational therapy efforts; however the precise molecular signature of these cells remains elusive. Previously, we identified a population of osteoprogenitor cells expressing the Wnt signaling agonist Lgr6, which contributes to the development and regeneration of the mouse digit tip bone. In our present study we build upon this data and investigate the expression of Lgr6 more broadly in the skeleton. We find that Lgr6, and closely related Lgr4, are expressed in mouse primary calvarial cells, bone marrow cells, and bone marrow-derived mesenchymal stem cells. In addition, our data demonstrates that Lgr4 expression is modestly increased throughout the differentiation and mineralization of mesenchymal stem cells. In contrast, we find Lgr6 expression to be strikingly increased upon osteogenic induction and subsequently decreased upon differentiation and mineralization. These findings provide evidence for Lgr6 as a novel marker of osteoprogenitor cells in bone marrow, which could prove useful for isolation of this population toward future research and clinical applications.

Myocardial-specific R-spondin3 drives proliferation of the coronary stems primarily through the Leucine Rich Repeat G Protein coupled receptor LGR4

Coronary artery anomalies are common congenital disorders with serious consequences in adult life. Coronary circulation begins when the coronary stems form connections between the aorta and the developing vascular plexus. We recently identified the WNT signaling modulator R-spondin 3 (Rspo3), as a crucial regulator of coronary stem proliferation. Using expression analysis and tissue-specific deletion we now demonstrate that Rspo3 is primarily produced by cardiomyocytes. Moreover, we have employed CRISPR/Cas9 technology to generate novel Lgr4-null alleles that showed a significant decrease in coronary stem proliferation and thus phenocopied the coronary artery defects seen in Rspo3 mutants. Interestingly, Lgr4 mutants displayed slightly hypomorphic right ventricles, an observation also made after myocardial specific deletion of Rspo3. These results shed new light on the role of Rspo3 in heart development and demonstrate that LGR4 is the principal R-spondin 3 receptor in the heart.

Targeting LGR5 in Colorectal Cancer: therapeutic gold or too plastic?

Leucine-rich repeat-containing G-protein coupled receptor (LGR5 or GPR49) potentiates canonical Wnt/β-catenin signalling and is a marker of normal stem cells in several tissues, including the intestine. Consistent with stem cell potential, single isolated LGR5⁺ cells from the gut generate self-organising crypt/villus structures in vitro termed organoids or 'mini-guts', which accurately model the parent tissue. The well characterised deregulation of Wnt/β-catenin signalling that occurs during the adenoma-carcinoma sequence in colorectal cancer (CRC) renders LGR5 an interesting therapeutic target. Furthermore, recent studies demonstrating that CRC tumours contain LGR5⁺ subsets and retain a degree of normal tissue architecture has heightened translational interest. Such reports fuel hope that specific subpopulations or molecules within a tumour may be therapeutically targeted to prevent relapse and induce long-term remissions. Despite these observations, many studies within this field have produced conflicting and confusing results with no clear consensus on the therapeutic value of LGR5. This review will recap the various oncogenic and tumour suppressive roles that have been described for the LGR5 molecule in CRC. It will further highlight recent studies indicating the plasticity or redundancy of LGR5⁺ cells in intestinal cancer progression and assess the overall merit of therapeutically targeting LGR5 in CRC.

RSPO2 inhibition of RNF43 and ZNRF3 governs limb development independently of LGR4/5/6

The four R-spondin secreted ligands (RSPO1-RSPO4) act via their cognate LGR4, LGR5 and LGR6 receptors to amplify WNT signalling^1-3. Here we report an allelic series of recessive RSPO2 mutations in humans that cause tetra-amelia syndrome, which is characterized by lung aplasia and a total absence of the four limbs. Functional studies revealed impaired binding to the LGR4/5/6 receptors and the RNF43 and ZNRF3 transmembrane ligases, and reduced WNT potentiation, which correlated with allele severity. Unexpectedly, however, the triple and ubiquitous knockout of Lgr4, Lgr5 and Lgr6 in mice did not recapitulate the known Rspo2 or Rspo3 loss-of-function phenotypes. Moreover, endogenous depletion or addition of exogenous RSPO2 or RSPO3 in triple-knockout Lgr4/5/6 cells could still affect WNT responsiveness. Instead, we found that the concurrent deletion of rnf43 and znrf3 in Xenopus embryos was sufficient to trigger the outgrowth of supernumerary limbs. Our results establish that RSPO2, without the LGR4/5/6 receptors, serves as a direct antagonistic ligand to RNF43 and ZNRF3, which together constitute a master switch that governs limb specification. These findings have direct implications for regenerative medicine and WNT-associated cancers.

R-spondin3-LGR4 signaling protects hepatocytes against DMOG-induced hypoxia/reoxygenation injury through activating β-catenin

BACKGROUND & AIMS

Leucine-rich repeat G-protein-coupled receptor 4 (LGR4) and its ligands R-spondin1-4 (Rspos) have been vastly investigated in embryonic development. The biological functions of Rspos-LGR4 system in liver remains largely unknown. Here, we explored whether it protects hepatocytes against hypoxia/reoxygenation (H/R) induced damage.

METHODS

H/R injury was induced by dimethyloxalylglycine (DMOG) in AML12 cells and the effects of Rspo3 on cell proliferation and apoptosis were assessed. Specific shRNAs were used to interfere LGR4 or β-catenin.

RESULTS

DMOG caused hepatocytes damage evidenced by increase in HIF-1α, cell death and apoptosis genes p27 and Bax, with concurrent decrease of cell proliferation genes PCNA and CyclinD1. Of all the Rspos, Rspo3 is predominantly expressed in AML12 hepatocytes. Importantly, Rspo3 demonstrated an alteration in a manner similar to proliferation-related genes during H/R injury. Rspo3 pretreatment rendered hepatocytes less vulnerable to DMOG induced H/R injury. Ablation of LGR4 using shRNA attenuated the protective effects of Rspo3. Wnt3a also protected AML12 cells from damages caused by H/R, showing enhanced proliferation activity. Notably, knockdown of β-catenin in hepatocytes completely abolished the effect of Rspo3 pretreatment on the expression levels of PCNA and CyclinD1.

CONCLUSION

Rspo3-LGR4 axis protects hepatocytes from H/R injury via activating β-catenin.

Wnt, RSPO and Hippo Signalling in the Intestine and Intestinal Stem Cells

In this review, we address aspects of Wnt, R-Spondin (RSPO) and Hippo signalling, in both healthy and transformed intestinal epithelium. In intestinal stem cells (ISCs), the Wnt pathway is essential for intestinal crypt formation and renewal, whereas RSPO-mediated signalling mainly affects ISC numbers. In human colorectal cancer (CRC), aberrant Wnt signalling is the driving mechanism initiating this type of neoplasia. The signalling role of the RSPO-binding transmembrane proteins, the leucine-rich-repeat-containing G-protein-coupled receptors (LGRs), is possibly more pleiotropic and not only limited to the enhancement of Wnt signalling. There is growing evidence for multiple crosstalk between Hippo and Wnt/β-catenin signalling. In the ON state, Hippo signalling results in serine/threonine phosphorylation of Yes-associated protein (YAP1) and tafazzin (TAZ), promoting formation of the β-catenin destruction complex. In contrast, YAP1 or TAZ dephosphorylation (and YAP1 methylation) results in β-catenin destruction complex deactivation and β-catenin nuclear localization. In the Hippo OFF state, YAP1 and TAZ are engaged with the nuclear β-catenin and participate in the β-catenin-dependent transcription program. Interestingly, YAP1/TAZ are dispensable for intestinal homeostasis; however, upon Wnt pathway hyperactivation, the proteins together with TEA domain (TEAD) transcription factors drive the transcriptional program essential for intestinal cell transformation. In addition, in many CRC cells, YAP1 phosphorylation by YES proto-oncogene 1 tyrosine kinase (YES1) leads to the formation of a transcriptional complex that includes YAP1, β-catenin and T-box 5 (TBX5) DNA-binding protein. YAP1/β-catenin/T-box 5-mediated transcription is necessary for CRC cell proliferation and survival. Interestingly, dishevelled (DVL) appears to be an important mediator involved in both Wnt and Hippo (YAP1/TAZ) signalling and some of the DVL functions were assigned to the nuclear DVL pool. Wnt ligands can trigger alternative signalling that directly involves some of the Hippo pathway components such as YAP1, TAZ and TEADs. By upregulating Wnt pathway agonists, the alternative Wnt signalling can inhibit the canonical Wnt pathway activity.

Novel Genetic Variants Associated with Lumbar Spondylosis in Koreans : A Genome-Wide Association Study

Objective

The aim of this study was to identify the susceptibility genes responsible for lumbar spondylosis (LS) in Korean patients.

Methods

Data from 1427 subjects were made available for radiographic grading and genome wide association studies (GWAS) analysis. Lateral lumbar spine radiographs were obtained and the various degrees of degenerative change were semi-quantitatively scored. A pilot GWAS was performed using the AffymetrixGenome-Wide Human single-nucleotide polymorphisms (SNPs), 500K array. A total of 352228 SNPs were analyzed and the association between the SNPs and case-control status was analyzed by stepwise logistic regression analyses.

Results

The top 100 SNPs with a cutoff p-value of less than 3.7×10^-4 were selected for joint space narrowing, while a cutoff p-value of 6.0×10^-4 was applied to osteophytes and the Kellgren-Lawrence (K-L) osteoarthritis grade. The SNPs with the strongest effect on disc space narrowing, osteophytes, and K-L grade were serine incorporator 1 (rs155467, odds ratio [OR]=17.58, p=1.6×10^-4), stromal interaction molecule 2 (STIM1, rs210781, OR=5.53, p=5×10^-4), and transient receptor potential cation channel, subfamily C (rs11224760, OR=3.99, p=4.8×10^-4), respectively. Leucine-rich repeat-containing G protein-coupled receptor 4 was significantly associated with both disc space narrowing and osteophytes (rs1979400, OR=2.01, p=1.1×10^-4 for disc space narrowing, OR=1.79, p=3×10^-4 for osteophytes), while zinc finger and BTB domain containing 7C was significantly and negatively associated with both osteophytes and a K-L grade >2 (rs12457004,OR=0.25, p=5.8×10^-4 and OR=0.27, p=5.3×10^-4, respectively).

Conclusion

We identified SNPs that potentially contribute to the pathogenesis of LS. This is the first report of a GWAS in an Asian population.

LGR4 modulates breast cancer initiation, metastasis, and cancer stem cells

The fourth member of the leucine-rich repeat-containing GPCR family (LGR4, frequently referred to as GPR48) and its cognate ligands, R-spondins (RSPOs) play crucial roles in the development of multiple organs as well as the survival of adult stem cells by activation of canonical Wnt signaling. Wnt/β-catenin signaling acts to regulate breast cancer; however, the molecular mechanisms determining its spatiotemporal regulation are largely unknown. In this study, we identified LGR4 as a master controller of Wnt/β-catenin signaling-mediated breast cancer tumorigenesis, metastasis, and cancer stem cell (CSC) maintenance. LGR4 expression in breast tumors correlated with poor prognosis. Either Lgr4 haploinsufficiency or mammary-specific deletion inhibited mouse mammary tumor virus (MMTV)- PyMT- and MMTV- Wnt1-driven mammary tumorigenesis and metastasis. Moreover, LGR4 down-regulation decreased in vitro migration and in vivo xenograft tumor growth and lung metastasis. Furthermore, Lgr4 deletion in MMTV- Wnt1 tumor cells or knockdown in human breast cancer cells decreased the number of functional CSCs by ∼90%. Canonical Wnt signaling was impaired in LGR4-deficient breast cancer cells, and LGR4 knockdown resulted in increased E-cadherin and decreased expression of N-cadherin and snail transcription factor -2 ( SNAI2) (also called SLUG), implicating LGR4 in regulation of epithelial-mesenchymal transition. Our findings support a crucial role of the Wnt signaling component LGR4 in breast cancer initiation, metastasis, and breast CSCs.-Yue, Z., Yuan, Z., Zeng, L., Wang, Y., Lai, L., Li, J., Sun, P., Xue, X., Qi, J., Yang, Z., Zheng, Y., Fang, Y., Li, D., Siwko, S., Li, Y., Luo, J., Liu, M. LGR4 modulates breast cancer initiation, metastasis, and cancer stem cells.

MiR-449a regulates caprine endometrial stromal cell apoptosis and endometrial receptivity

In this study, an RT-qPCR analysis showed that the expression levels of miR-449a in the pre-receptive endometrium were lower compared to the receptive endometrium, which is consistent with previous sequencing data (previous investigations). To detect the role of miR-449a in endometrial receptivity, we transfected caprine endometrial stromal cells (ESCs) cultured in vitro with miR-449a mimics. The results revealed that miR-449a decreased the mRNA and protein levels of LGR4 by targeting its 3′-untranslated region. The miR-449a mimics significantly reduced the G₁ cell population from 52.56% (mimic NC) to 42.19% with a concordant increase in the G₂ and S cell populations from 47.44% (mimic NC) to 57.81%, suggesting that miR-449a caused ESC cell cycle arrest. In addition, the number of apoptotic cells was significantly higher in ESCs transfected with miR-449a mimics (P < 0.05) than in ESCs transfected with mimic NC. In vivo, rich pinopodes were observed on the endometrial surface in the miR-449a agomir group compared with the miR-449a antagomir group. The results of hematoxylin-eosin staining showed that endometrial thickness was significantly increased in the miR-449a agomir group compared with the miR-449a antagomir group. These results suggest that miR-449a could enhance endometrial receptivity.

Alteration of Wnt5a expression and of the non-canonical Wnt/PCP and Wnt/PKC-Ca2+ pathways in human osteoarthritis osteoblasts

Objective

Clinical and in vitro studies suggest that subchondral bone sclerosis due to abnormal osteoblasts (Ob) is involved in the progression and/or onset of osteoarthritis (OA). Human Ob isolated from sclerotic subchondral OA bone tissue show an altered phenotype, a decreased canonical Wnt/β-catenin signaling pathway (cWnt), and a reduced mineralization in vitro. In addition to the cWnt pathway, at least two non-canonical signaling pathways, the Wnt/PKC and Wnt/PCP pathway have been described. However, there are no reports of either pathway in OA Ob. Here, we studied the two non-canonical pathways in OA Ob and if they influence their phenotype.

Methods

Human primary subchondral Ob were isolated from the subchondral bone plate of tibial plateaus of OA patients undergoing total knee arthroplasty, or of normal individuals at autopsy. The expression of genes involved in non-canonical Wnt signaling was evaluated by qRT-PCR and their protein production by Western blot analysis. Alkaline phosphatase activity and osteocalcin secretion (OC) were determined with substrate hydrolysis and EIA, respectively. Mineralization levels were evaluated with Alizarin Red Staining, Wnt/PKC and Wnt/PCP pathways by target gene expression and their respective activity using the NFAT and AP-1 luciferase reporter assays.

Results

OA Ob showed an altered phenotype as illustrated by an increased alkaline phosphatase activity and osteocalcin release compared to normal Ob. The expression of the non-canonical Wnt5a ligand was increased in OA Ob compared to normal. Whereas, the expression of LGR5 was significantly increased in OA Ob compared to normal Ob, the expression of LGR4 was similar. Wnt5a directly stimulated the expression and production of LGR5, contrasting, Wnt5a did not stimulate the expression of LGR4. Wnt5a also stimulated the phosphorylation of both JNK and PKC, as well as the activity of both NFAT and AP-1 transcription factors. The inhibition of Wnt5a expression partially corrects the abnormal mineralization, OC secretion and ALPase activity of OA Ob.

Conclusion

These data indicate that the alteration of Wnt5a, a non-canonical Wnt signaling activator, is implicated in the modified signalisation and phenotype observed in OA Ob.

Leucine-rich repeat-containing G protein-coupled receptor 4 (Lgr4) is necessary for prostate cancer metastasis via epithelial-mesenchymal transition

Prostate cancer is a highly penetrant disease among men in industrialized societies, but the factors regulating the transition from indolent to aggressive and metastatic cancer remain poorly understood. We found that men with prostate cancers expressing high levels of the G protein-coupled receptor LGR4 had a significantly shorter recurrence-free survival compared with patients with cancers having low LGR4 expression. LGR4 expression was elevated in human prostate cancer cell lines with metastatic potential. We therefore generated a novel transgenic adenocarcinoma of the mouse prostate (TRAMP) mouse model to investigate the role of Lgr4 in prostate cancer development and metastasis in vivo TRAMP Lgr4^-/- mice exhibited an initial delay in prostate intraepithelial neoplasia formation, but the frequency of tumor formation was equivalent between TRAMP and TRAMP Lgr4^-/- mice by 12 weeks. The loss of Lgr4 significantly improved TRAMP mouse survival and dramatically reduced the occurrence of lung metastases. LGR4 knockdown impaired the migration, invasion, and colony formation of DU145 cells and reversed epithelial-mesenchymal transition (EMT), as demonstrated by up-regulation of E-cadherin and decreased expression of the EMT transcription factors ZEB, Twist, and Snail. Overexpression of LGR4 in LNCaP cells had the opposite effects. Orthotopic injection of DU145 cells stably expressing shRNA targeting LGR4 resulted in decreased xenograft tumor size, reduced tumor EMT marker expression, and impaired metastasis, in accord with our findings in TRAMP Lgr4^-/- mice. In conclusion, we propose that Lgr4 is a key protein necessary for prostate cancer EMT and metastasis.

Establishment of a tagged variant of Lgr4 receptor suitable for functional and expression studies in the mouse

Leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4) is produced in a broad spectrum of mouse embryonic and adult tissues and its deficiency results in embryonal or perinatal lethality. The LGR4 function was mainly related to its potentiation of canonical Wnt signaling; however, several recent studies associate LGR4 with additional signaling pathways. To obtain a suitable tool for studying the signaling properties of Lgr4, we generated a tagged variant of the Lgr4 receptor using gene targeting in the mouse oocyte. The modified Lgr4 allele expresses the Lgr4 protein fused with a triple hemagglutinin (3HA) tag located at the extracellular part of the protein. The allele is fully functional, enabling tracking of Lgr4 expression in the mouse tissues. We also show that via surface labeling, the 3HA tag allows direct isolation and analysis of living Lgr4-positive cells obtained from the small intestinal crypts. Finally, the HA tag-specific antibody can be employed to characterize the biochemical features of Lgr4 and to identify possible biding partners of the protein in cells derived from various mouse tissues.

Regeneration of thyroid follicles from primordial cells in a murine thyroidectomized model

The functional unit of the thyroid gland, the thyroid follicle, dynamically responds to various stimuli to maintain thyroid hormone homeostasis. However, thyroid follicles in the adult human thyroid gland have a very limited regenerative capacity following partial resection of the thyroid gland. To gain insight into follicle regeneration in the adult thyroid gland, we observed the regeneration processes of murine thyroid follicles after partial resection of the lower third of the thyroid gland in 10-week-old male C57BL/6 mice. Based on sequential observation of the partially resected thyroid lobe, we found primitive follicles forming in the area corresponding to the central zone of the intact lateral thyroid lobe. The primitive thyroid follicles were multiciliated and had coarsely vacuolated cytoplasm and large vesicular nuclei. Consistently, these primitive follicular cells did not express the differentiation markers paired box gene-8 and thyroid transcription factor-1 (clone SPT24), but were positive for forkhead box protein A2 and leucine-rich repeat-containing G-protein-coupled receptor 4/GPR48. Follicles newly generated from the primitive follicles had clear or vacuolar cytoplasm with dense, darkly stained nuclei. At day 21 after partial thyroidectomy, the tall cuboidal follicular epithelial cells had clear or vacuolar cytoplasm, and the intraluminal colloid displayed pale staining. Smaller activated follicles were found in the central zone of the lateral lobe, whereas larger mature follicles were located in the peripheral zone. Based on these observations, we propose that the follicle regeneration process in the partially resected adult murine thyroid gland associated with the appearance of primitive follicular cells may be a platform for the budding of differentiated follicles in mice.

On the development of the hepatopancreatic ductal system

The hepatopancreatic ductal system is the collection of ducts that connect the liver and pancreas to the digestive tract. The formation of this system is necessary for the transport of exocrine secretions, for the correct assembly of the pancreatobiliary ductal system, and for the overall function of the digestive system. Studies on endoderm organ formation have significantly advanced our understanding of the molecular mechanisms that govern organ induction, organ specification and morphogenesis of the major foregut-derived organs. However, little is known about the mechanisms that control the development of the hepatopancreatic ductal system. Here, we provide a description of the different components of the system, summarize its development from the endoderm to a complex system of tubes, list the pathologies produced by anomalies in its development, as well as the molecules and signaling pathways that are known to be involved in its formation. Finally, we discuss its proposed potential as a multipotent cell reservoir and the unresolved questions in the field.

MicroRNA-34c promotes osteoclast differentiation through targeting LGR4

MicroRNAs have emerged as important regulators of osteoclast differentiation in recent years. Of these, miR-34c has been reported to play an important role in bone development. However, its role and the underlying mechanism in osteoclast differentiation remains poorly understood. In this study, we aimed to investigate the precise role and molecular mechanism of miR-34c in osteoclast differentiation. We found an obvious increase in miR-34c expression during osteoclast differentiation in osteoclast precursors induced by receptor activator of nuclear factor κB (NF-κB) ligand and macrophage colony-stimulating factor in vitro. Further experiments showed that overexpression of miR-34c significantly promoted osteoclast differentiation while suppression of miR-34c showed the opposite effect. Interestingly, bioinformatics analysis and dual-luciferase reporter assays showed that miR-34c targets the 3'-untranslated region of leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4). The expression of LGR4 was regulated by miR-34c in osteoclasts. Moreover, miR-34c regulated NF-κB and glycogen synthase kinase 3-β signaling during osteoclast differentiation. Overexpression of LGR4 partially reversed the promoting effect of miR-34c overexpression on osteoclast differentiation. Taken together, our study suggests that miR-34c contributes to osteoclast differentiation by targeting LGR4, providing novel insights into understanding the molecular mechanism underlying osteoclast differentiation.

Intrinsic disorder in spondins and some of their interacting partners

Spondins, which are proteins that inhibit and promote adherence of embryonic cells so as to aid axonal growth are part of the thrombospondin-1 family. Spondins function in several important biological processes, such as apoptosis, angiogenesis, etc. Spondins constitute a thrombospondin subfamily that includes F-spondin, a protein that interacts with Aβ precursor protein and inhibits its proteolytic processing; R-spondin, a 4-membered group of proteins that regulates Wnt pathway and have other functions, such as regulation of kidney proliferation, induction of epithelial proliferation, the tumor suppressant action; M-spondin that mediates mechanical linkage between the muscles and apodemes; and the SCO-spondin, a protein important for neuronal development. In this study, we investigated intrinsic disorder status of human spondins and their interacting partners, such as members of the LRP family, LGR family, Frizzled family, and several other binding partners in order to establish the existence and importance of disordered regions in spondins and their interacting partners by conducting a detailed analysis of their sequences, finding disordered regions, and establishing a correlation between their structure and biological functions.

Lgr4 promotes prostate tumorigenesis through the Jmjd2a/AR signaling pathway

Lgr4 (leucine-rich repeat domain containing G protein-coupled receptor 4) is implicated in the transcriptional regulation of multiple histone demethylases in the progression of diverse cancers, but there are few reports concerning the molecular mechanism by which Lgr4 regulates histone demethylase activation in prostate cancer (PCa) progression. As Jmjd2a is a histone demethylase, in the current study, we investigated the relationship between interaction Lgr4 with Jmjd 2a and Jmjd2a/androgen receptor (AR) signaling pathway in PCa progression. Firstly, Lgr4 was overexpressed by transfecting pcDNA3.1(+)/Lgr4 plasmids into PCa (LNCaP and PC-3) cell lines. Next, we found that Lgr4 overexpression promoted Jmjd2a mRNA expression, reduced cell apoptosis and arrested cell cycle in the S phase, these effects were reversed by Jmjd2a silencing. Moreover, Lgr4 overexpression markedly elevated AR levels and its interaction with Jmjd2a, which was tested by co-immunoprecipitation and luciferase reporter assays. Furthermore, interaction AR with PSA promoter (containing an AR response element) was obviously improved by Lgr4 overexpression, and PSA silencing reduced Lgr4-induced cell apoptosis and cell cycle arrest in PCa cells. Taken together, Lgr4 may be a novel tumor marker providing new mechanistic insights into PCa progression. Lgr4 activates Jmjd2a/AR signaling pathway to promote interaction AR with PSA promoter, causing reduction of PCa apoptosis and cell cycle arrest.

Lgr4 is crucial for skin carcinogenesis by regulating MEK/ERK and Wnt/β-catenin signaling pathways

Lgr4 is a member of the leucine-rich, G protein-coupled receptor family of proteins, and has recently been shown to augment Wnt/β-catenin signaling via binding to Wnt agonists R-spondins. It plays an important role in skin development, but its involvement in skin tumorigenesis is unclear. Here, we report that mice deficient for Lgr4 are resistant to 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced keratinocyte proliferation and papilloma formation. We show that TPA treatment activates MEK1, ERK1/2 and downstream effector AP-1 in wild-type (WT) epidermal cells and mice, but not in cells or mice where Lgr4 is depleted. Wnt/β-catenin signaling is also dramatically activated by TPA treatment, and this activation is abolished when Lgr4 is deleted. We provide evidences that blocking both MEK1/ERK1/2 and Wnt/β-catenin pathways prevents TPA-induced increase in the expression of Ccnd1 (cyclin D1), a known Wnt/β-catenin target gene, and that the activation of MEK1/ERK1/2 pathway lies upstream of Wnt/β-catenin signal pathway. Collectively, our findings identify Lgr4 as a critical positive factor for skin tumorigenesis by mediating the activation of MEK1/ERK1/2 and Wnt/β-catenin pathways.

G Protein-Coupled Receptor Signaling in Stem Cells and Cancer

G protein-coupled receptors (GPCRs) are a large superfamily of cell-surface signaling proteins that bind extracellular ligands and transduce signals into cells via heterotrimeric G proteins. GPCRs are highly tractable drug targets. Aberrant expression of GPCRs and G proteins has been observed in various cancers and their importance in cancer stem cells has begun to be appreciated. We have recently reported essential roles for G protein-coupled receptor 84 (GPR84) and G protein subunit Gαq in the maintenance of cancer stem cells in acute myeloid leukemia. This review will discuss how GPCRs and G proteins regulate stem cells with a focus on cancer stem cells, as well as their implications for the development of novel targeted cancer therapies.

BMP-2 Enhances Lgr4 Gene Expression in Osteoblastic Cells

Osteoporosis is one of the most prevalent diseases and the number of patients suffering from this disease is soaring due to the increase in the aged population in the world. The severity of bone loss in osteoporosis is based on the levels of impairment in the balance between bone formation and bone resorption, two arms of the bone metabolism, and bone remodeling. However, determination of bone formation levels is under many layers of control that are as yet fully defined. Bone morphogenetic protein (BMP) plays a key role in regulation of bone formation while its downstream targets are still incompletely understood. Lgr4 gene encodes an orphan receptor and has been identified as a genetic determinant for bone mass in osteoporotic patients. Here, we examine the effects of BMP on the expression of Lgr4 in osteoblastic cells. Lgr4 gene is expressed in an osteoblastic cell line, MC3T3E1 in a time dependent manner during the culture. BMP treatment enhances Lgr4 mRNA expression at least in part via transcriptional event. When Lgr4 mRNA is knocked down, the levels of BMP-induced increase in alkaline phosphatase (Alp) activity and Alp mRNA are suppressed. BMP enhancement of Lgr4 gene expression is suppressed by FGF and reversed by dexamethasone. BMP also enhances Lgr4 expression in primary cultures of calvarial osteoblasts. These data indicate that Lgr4 gene is regulated by BMP and is required for BMP effects on osteoblastic differentiation. J. Cell. Physiol. 231: 887-895, 2016. © 2015 Wiley Periodicals, Inc.

Targeted deletion of the murine Lgr4 gene decreases lens epithelial cell resistance to oxidative stress and induces age-related cataract formation

Oxidative stress contributes to the formation of cataracts. The leucine rich repeat containing G protein-coupled receptor 4 (LGR4, also known as GPR48), is important in many developmental processes. Since deletion of Lgr4 has previously been shown to lead to cataract formation in mice, we sought to determine the specific role that Lgr4 plays in the formation of cataracts. Initially, the lens opacities of Lgr4(-/-) mice at different ages without ocular anterior segment dysgenesis (ASD) were evaluated with slit-lamp biomicroscopy. Lenses from both Lgr4(-/-) and wild-type mice were subjected to oxidation induced protein denaturation to assess the ability of the lens to withstand oxidation. The expression of antioxidant enzymes was evaluated with real-time quantitative PCR. Phenotypically, Lgr4(-/-) mice showed earlier onset of lens opacification and higher incidence of cataract formation compared with wild-type mice of similar age. In addition, Lgr4(-/-) mice demonstrated increased sensitivity to environmental oxidative damage, as evidenced by altered protein expression. Real-time quantitative PCR showed that two prominent antioxidant defense enzymes, catalase (CAT) and superoxidase dismutase-1 (SOD1), were significantly decreased in the lens epithelial cells of Lgr4(-/-) mice. Our results suggest that the deletion of Lgr4 can lead to premature cataract formation, as well as progressive deterioration with aging. Oxidative stress and altered expression of several antioxidant defense enzymes contribute to the formation of cataracts.

Unveiling the mysteries of the genetics of osteoporosis

INTRODUCTION

Osteoporosis is a common disease characterised by low bone mineral density and an increased risk of fragility fractures.

METHODS

We conducted a literature review of relevant studies relating to the genetics of osteoporosis.

RESULTS

Family studies have revealed that bone density and fractures have a strong heritable component but environmental factors also play an important role. This makes identification of the causative genetic variants challenging. Linkage analysis has been successful in identifying the genes responsible for rare inherited diseases associated with abnormalities of bone mass but has been of limited value in osteoporosis. In contrast, genome-wide association studies in large cohort studies have identified 56 loci with robust evidence of association with bone density and 14 loci that predispose to fractures. Although the effect size of the implicated variants is small, many of the loci contain genes known to be involved in regulating bone cell activity through the RANK and Wnt signalling pathways, whereas others contain novel genes not previously implicated in bone metabolism. In a few instances, whole genome and exome sequencing have been successfully used to identify rare variants of large effect size that influence susceptibility to osteoporosis.

CONCLUSION

A future challenge will be to conduct fine mapping and functional analysis of the loci implicated in osteoporosis in order to identify the causal genetic variants and examine the mechanisms by which they influence bone cell function and bone mass. Ultimately this may lead to the identification of biomarkers for susceptibility to osteoporosis and fractures or new therapeutic targets.