Maternal high-fat diet disrupted one-carbon metabolism in offspring, contributing to nonalcoholic fatty liver disease.

BACKGROUND & AIMS: Pregnant women may transmit their metabolic phenotypes to their offspring, enhancing the risk for nonalcoholic fatty liver disease (NAFLD); however, the molecular mechanisms remain unclear. METHODS: Prior to pregnancy female mice were fed either a maternal normal-fat diet (NF-group, "no effectors"), or a maternal high-fat diet (HF-group, "persistent effectors"), or were transitioned from a HF to a NF diet before pregnancy (H9N-group, "effectors removal"), followed by pregnancy and lactation, and then offspring were fed high-fat diets after weaning. Offspring livers were analysed by functional studies, as well as next-generation sequencing for gene expression profiles and DNA methylation changes. RESULTS: The HF, but not the H9N offspring, displayed glucose intolerance and hepatic steatosis. The HF offspring also displayed a disruption of lipid homeostasis associated with an altered methionine cycle and abnormal one-carbon metabolism that caused DNA hypermethylation and L-carnitine depletion associated with deactivated AMPK signalling and decreased expression of PPAR-α and genes for fatty acid oxidation. These changes were not present in H9N offspring. In addition, we identified maternal HF diet-induced genes involved in one-carbon metabolism that were associated with DNA methylation modifications in HF offspring. Importantly, the DNA methylation modifications and their associated gene expression changes were reversed in H9N offspring livers. CONCLUSIONS: Our results demonstrate for the first time that maternal HF diet disrupted the methionine cycle and one-carbon metabolism in offspring livers which further altered lipid homeostasis. CpG islands of specific genes involved in one-carbon metabolism modified by different maternal diets were identified.

Fatty acid sensing GPCR (GPR84) signaling safeguards cartilage homeostasis and protects against osteoarthritis.

It is well known that free fatty acids (FFAs) have beneficial effects on the skeletal system, however, which fatty acid sensing GPCR(s) and how the GPCR(s) regulating cartilage development and osteoarthritis (OA) pathogenesis is largely unknown. In this study, we found Gpr84, a receptor for medium-chain FFAs (MCFA), was the only FFA-sensing GPCR in human and mouse chondrocytes that exhibited elevated expression when stimulated by interleukin (IL)-1ß. Gpr84-deficiency upregulated cartilage catabolic regulator expression and downregulated anabolic factor expression in the IL-1ß-induced cell model and the destabilization of the medial meniscus (DMM)-induced OA mouse model. Gpr84-/- mice exhibited an aggravated OA phenotype characterized by severe cartilage degradation, osteophyte formation and subchondral bone sclerosis. Moreover, activating Gpr84 directly enhanced cartilage extracellular matrix (ECM) generation while knockout of Gpr84 suppressed ECM-related gene expression. Especially, the agonists of GPR84 protected human OA cartilage explants against degeneration by inducing cartilage anabolic factor expression. At the molecular level, GPR84 activation inhibited IL-1ß-induced NF-κB signaling pathway. Furthermore, deletion of Gpr84 had little effect on articular and spine cartilaginous tissues during skeletal growth. Together, all of our results demonstrated that fatty acid sensing GPCR (Gpr84) signaling played a critical role in OA pathogenesis, and activation of GPR84 or MCFA supplementation has potential in preventing the pathogenesis and progression of OA without severe cartilaginous side effect.

Sex and Race-Related DNA Methylation Changes in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is the sixth most common cancer and fourth leading cause of cancer-related death worldwide. The number of HCC cases continues to rise despite advances in screening and therapeutic inventions. More importantly, HCC poses two major health disparity issues. First, HCC occurs more commonly in men than women. Second, with the global increase in non-alcoholic fatty liver diseases (NAFLD), it has also become evident that HCC is more prevalent in some races and/or ethnic groups compared to others, depending on its predisposing etiology. Most studies on HCC in the past have been focused on genetic factors as the driving force for HCC development, and the results revealed that genetic mutations associated with HCC are often heterogeneous and involve multiple pathogenic pathways. An emerging new research field is epigenetics, in which gene expression is modified without altering DNA sequences. In this article, we focus on reviewing current knowledge on HCC-related DNA methylation changes that show disparities among different sexes or different racial/ethnic groups, in an effort to establish a point of departure for resolving the broader issue of health disparities in gastrointestinal malignancies using cutting-edge epigenetic approaches.

UHRF2 promotes intestinal tumorigenesis through stabilization of TCF4 mediated Wnt/ß-catenin signaling.

Intestinal tumors mainly originate from transformed crypt stem cells supported by Wnt signaling, which functions through downstream critical factors enriched in the intestinal stem/progenitor compartment. Here, we show Uhrf2 is predominantly expressed in intestinal crypts and adenomas in mice and is transcriptionally regulated by Wnt signaling. Upregulated UHRF2 correlates with poor prognosis in colorectal cancer patients. Although loss of Uhrf2 did not affect intestinal homeostasis and regeneration, tumor initiation and progression were inhibited, leading to a markedly prolonged life span in Uhrf2 null mice on an ApcMin background. Uhrf2 deficiency also strongly reduced primary tumor organoid formation suggesting impairment of tumor stem cells. Moreover, ablation of Uhrf2 suppressed tumor cell proliferation through downregulation of the Wnt/ß-catenin pathway. Mechanistically, Uhrf2 directly interacts with and sumoylates Tcf4, a critical intranuclear effector of the Wnt pathway. Uhrf2 mediated SUMOylation stabilized Tcf4 and further sustained hyperactive Wnt signaling. Together, we demonstrate that Wnt-induced Uhrf2 expression promotes tumorigenesis through modulation of the stability of Tcf4 for maintaining oncogenic Wnt/ß-catenin signaling. This is a new reciprocal feedforward regulation between Uhrf2 and Wnt signaling in tumor initiation and progression.

Loss of Lgr4 inhibits differentiation, migration and apoptosis, and promotes proliferation in bone mesenchymal stem cells.

The key signaling networks regulating bone marrow mesenchymal stem cells (BMSCs) are poorly defined. Lgr4, which belongs to the leucine-rich repeat-containing G protein-coupled receptor (LGR) family, is widely expressed in multiple tissues from early embryogenesis to adulthood. We investigated whether Lgr4 functions in BMSCs and in osteogenesis, adipogenesis, and skeletal myoblasts, using mice with a ß-geo gene trap inserted into the Lgr4 gene. Abundant Lgr4 expression was detected in skeletal, adipose and muscular tissue of Lgr4+/- mice at E16.5 by ß-gal staining, and Lgr4-deficiency promoted BMSC proliferation (16 ± 4 in wild-type [WT] and 28 ± 2 in Lgr4-/- ) using colony forming units-fibroblast assay, while suppressing BMSC migration (from 103 ± 18 in WT to 57 ± 10 in Lgr4-/- ) by transwell migration assay and apoptosis ratio (from 0.0720 ± 0.0123 to 0.0189 ± 0.0051) by annexin V staining assay. Deletion of Lgr4 decreased bone mass (BV/TV from 19.16 ± 2.14 in WT mice to 10.36 ± 1.96 in KO) and fat mass through inhibiting BMSC differentiation to osteoblasts or adipocytes. Furthermore, LGR4-regulated osteogenic, adipogenic, and myogenic gene expression. Importantly, our data showed that loss of Lgr4-inhibited fracture healing by suppressing osteoblast differentiation. Moreover, deletion of Lgr4 in BMSCs-delayed fracture healing following stem cell therapy by BMSC transplantation. Together, our results demonstrated that LGR4 is essential for mesoderm-derived tissue development and BMSC differentiation, demonstrating that LGR4 could be a promising drug target for related diseases and a critical protein for stem cell therapy.

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/ß-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/ß-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.

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.

Leucine-rich repeat-containing G protein-coupled receptor 4 facilitates vesicular stomatitis virus infection by binding vesicular stomatitis virus glycoprotein.

Vesicular stomatitis virus (VSV) and rabies and Chandipura viruses belong to the Rhabdovirus family. VSV is a common laboratory virus to study viral evolution and host immune responses to viral infection, and recombinant VSV-based vectors have been widely used for viral oncolysis, vaccination, and gene therapy. Although the tropism of VSV is broad, and its envelope glycoprotein G is often used for pseudotyping other viruses, the host cellular components involved in VSV infection remain unclear. Here, we demonstrate that the host protein leucine-rich repeat-containing G protein-coupled receptor 4 (Lgr4) is essential for VSV and VSV-G pseudotyped lentivirus (VSVG-LV) to infect susceptible cells. Accordingly, Lgr4-deficient mice had dramatically decreased VSV levels in the olfactory bulb. Furthermore, Lgr4 knockdown in RAW 264.7 cells also significantly suppressed VSV infection, and Lgr4 overexpression in RAW 264.7 cells enhanced VSV infection. Interestingly, only VSV infection relied on Lgr4, whereas infections with Newcastle disease virus, influenza A virus (A/WSN/33), and herpes simplex virus were unaffected by Lgr4 status. Of note, assays of virus entry, cell ELISA, immunoprecipitation, and surface plasmon resonance indicated that VSV bound susceptible cells via the Lgr4 extracellular domain. Pretreating cells with an Lgr4 antibody, soluble LGR4 extracellular domain, or R-spondin 1 blocked VSV infection by competitively inhibiting VSV binding to Lgr4. Taken together, the identification of Lgr4 as a VSV-specific host factor provides important insights into understanding VSV entry and its pathogenesis and lays the foundation for VSV-based gene therapy and viral oncolytic therapeutics.

SH479, a Betulinic Acid Derivative, Ameliorates Experimental Autoimmune Encephalomyelitis by Regulating the T Helper 17/Regulatory T Cell Balance.

CD4+ T helper cells, especially T helper 17 (TH17) cells, combined with immune regulatory network dysfunction, play key roles in autoimmune diseases including multiple sclerosis (MS). Betulinic acid (BA), a natural pentacyclic triterpenoid, has been reported to be involved in anti-inflammation, in particular having an inhibitory effect on proinflammatory cytokine interleukin 17 (IL-17) and interferon-γ (IFN-γ) production. In this study, we screened BA derivatives and found a BA derivative, SH479, that had a greater inhibitory effect on TH17 differentiation. Our further analysis showed that SH479 had a greater inhibitory effect on TH17 and TH1, and a more stimulatory effect on regulatory T (Treg) cells. To evaluate the effects of SH479 on autoimmune diseases in vivo, we employed the extensively used MS mouse model experimental autoimmune encephalomyelitis (EAE). Our results showed that SH479 ameliorated clinical and histologic signs of EAE in both prevention and therapeutic protocols by regulating the TH17/Treg balance. SH479 dose-dependently reduced splenic lymphocyte proinflammatory factors and increased anti-inflammatory factors. Moreover, SH479 specifically inhibited splenic lymphocyte viability from EAE mice but not normal splenic lymphocyte viability. At the molecular level, SH479 inhibited TH17 differentiation by regulating signal transducer and activator of transcription-3 (STAT3) phosphorylation, DNA binding activity, and recruitment to the Il-17a promoter in CD4+ T cells. Furthermore, SH479 promoted the STAT5 signaling pathway and inhibited the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway. Together, our data demonstrated that SH479 ameliorated EAE by regulating the TH17/Treg balance through inhibiting the STAT3 and NF-κB pathways while activating the STAT5 pathway, suggesting that SH479 is a potential novel drug candidate for autoimmune diseases including MS.

Repression of Mammalian Target of Rapamycin Complex 1 Inhibits Intestinal Regeneration in Acute Inflammatory Bowel Disease Models.

The mammalian target of rapamycin (mTOR) signaling pathway integrates environmental cues to regulate cell growth and survival through various mechanisms. However, how mTORC1 responds to acute inflammatory signals to regulate bowel regeneration is still obscure. In this study, we investigated the role of mTORC1 in acute inflammatory bowel disease. Inhibition of mTORC1 activity by rapamycin treatment or haploinsufficiency of Rheb through genetic modification in mice impaired intestinal cell proliferation and induced cell apoptosis, leading to high mortality in dextran sodium sulfate- and 2,4,6-trinitrobenzene sulfonic acid-induced colitis models. Through bone marrow transplantation, we found that mTORC1 in nonhematopoietic cells played a major role in protecting mice from colitis. Reactivation of mTORC1 activity by amino acids had a positive therapeutic effect in mTORC1-deficient Rheb(+/-) mice. Mechanistically, mTORC1 mediated IL-6-induced Stat3 activation in intestinal epithelial cells to stimulate the expression of downstream targets essential for cell proliferation and tissue regeneration. Therefore, mTORC1 signaling critically protects against inflammatory bowel disease through modulation of inflammation-induced Stat3 activity. As mTORC1 is an important therapeutic target for multiple diseases, our findings will have important implications for the clinical usage of mTORC1 inhibitors in patients with acute inflammatory bowel disease.

LGR4/GPR48 inactivation leads to aniridia-genitourinary anomalies-mental retardation syndrome defects.

AGR syndrome (the clinical triad of aniridia, genitourinary anomalies, and mental retardation, a subgroup of WAGR syndrome for Wilm's tumor, aniridia, genitourinary anomalies, and mental retardation) is a rare syndrome caused by a contiguous gene deletion in the 11p13-14 region. However, the mechanisms of WAGR syndrome pathogenesis are elusive. In this study we provide evidence that LGR4 (also named GPR48), the only G-protein-coupled receptor gene in the human chromosome 11p12-11p14.4 fragment, is the key gene responsible for the diseases of AGR syndrome. Deletion of Lgr4 in mouse led to aniridia, polycystic kidney disease, genitourinary anomalies, and mental retardation, similar to the pathological defects of AGR syndrome. Furthermore, Lgr4 inactivation significantly increased cell apoptosis and decreased the expression of multiple important genes involved in the development of WAGR syndrome related organs. Specifically, deletion of Lgr4 down-regulated the expression of histone demethylases Jmjd2a and Fbxl10 through cAMP-CREB signaling pathways both in mouse embryonic fibroblast cells and in urinary and reproductive system mouse tissues. Our data suggest that Lgr4, which regulates eye, kidney, testis, ovary, and uterine organ development as well as mental development through genetic and epigenetic surveillance, is a novel candidate gene for the pathogenesis of AGR syndrome.

Lgr4 regulates mammary gland development and stem cell activity through the pluripotency transcription factor Sox2.

The key signaling networks regulating mammary stem cells are poorly defined. The leucine-rich repeat containing G protein-coupled receptor (Lgr) family has been implicated in intestinal, gastric, and epidermal stem cell functions. We investigated whether Lgr4 functions in mammary gland development and mammary stem cells. We found that Lgr4(-/-) mice had delayed ductal development, fewer terminal end buds, and decreased side-branching. Crucially, the mammary stem cell repopulation capacity was severely impaired. Mammospheres from Lgr4(-/-) mice showed decreased Wnt signaling. Wnt3a treatment prevented the adverse effects of Lgr4 loss on organoid formation. Chromatin immunoprecipitation analysis indicated that Sox2 expression was controlled by the Lgr4/Wnt/ß-catenin/Lef1 pathway. Importantly, Sox2 overexpression restored the in vivo mammary regeneration potential of Lgr4(-/-) mammary stem cells. Therefore, Lgr4 activates Sox2 to regulate mammary development and stem cell functions via Wnt/ß-catenin/Lef1.

Lgr4 is a key regulator of prostate development and prostate stem cell differentiation.

Mechanisms modulating prostate cell fate determination remain unexplored. The leucine-rich repeat containing G-protein-coupled receptors (Lgr) have been identified as important stem cell markers in various tissues. Here, we investigated the roles of Lgr4/Gpr48 in prostate stem cells (PSCs) and development. Lgr4 was ubiquitously expressed during early prostate development prior to lineage specification, with adult expression restricted to a few basal cells (principally Lin(-)Sca1(+)CD49f(+)). Lgr4(-/-) mice had compromised branching morphogenesis and delayed epithelial differentiation, leading to decreased prostate size and impaired luminal cell function. In vitro prostate sphere culture revealed that Lgr4(-/-) Lin(-)/Sca1(+)/CD49f(+) cells failed to generate p63(low) cells, indicating a differentiation deficiency. Furthermore, Lgr4 ablation arrested PSC differentiation of in vivo kidney capsule prostate grafts, suggesting that Lgr4 modulates PSC properties independent of hormonal and mesenchymal effects. Analysis of neonatal prostates and prostate spheres revealed a decrease in Wnt, Sonic Hedgehog, and Notch1 expression in Lgr4(-/-) cells. Lgr4 loss blocked differentiation of prostate sphere p63(hi) cells to p63(low). Treatment with exogenous Sonic Hedgehog partially restored the differentiation of p63(hi) cells in Lgr4(-/-) spheres. Taken together, our data revealed the roles of Lgr4 in early prostate development and in stem cell differentiation through regulation of the Wnt, Notch, and Sonic Hedgehog signaling pathways.

Kisspeptin-10 binding to Gpr54 in osteoclasts prevents bone loss by activating Dusp18-mediated dephosphorylation of Src.

Osteoclasts are over-activated as we age, which results in bone loss. Src deficiency in mice leads to severe osteopetrosis due to a functional defect in osteoclasts, indicating that Src function is essential in osteoclasts. G-protein-coupled receptors (GPCRs) are the targets for ∼35% of approved drugs but it is still unclear how GPCRs regulate Src kinase activity. Here, we reveal that GPR54 activation by its natural ligand Kisspeptin-10 (Kp-10) causes Dusp18 to dephosphorylate Src at Tyr 416. Mechanistically, Gpr54 recruits both active Src and the Dusp18 phosphatase at its proline/arginine-rich motif in its C terminus. We show that Kp-10 binding to Gpr54 leads to the up-regulation of Dusp18. Kiss1, Gpr54 and Dusp18 knockout mice all exhibit osteoclast hyperactivation and bone loss, and Kp-10 abrogated bone loss by suppressing osteoclast activity in vivo. Therefore, Kp-10/Gpr54 is a promising therapeutic target to abrogate bone resorption by Dusp18-mediated Src dephosphorylation.

KiSS1 and its G-protein-coupled receptor GPR54 in cancer development and metastasis.

KiSS1 and its cognate G-protein-coupled receptor, GPR54, have diverse functions. While KiSS1 and GPR54 have been intensively studied in physiology, their role in cancer is still unclear. In cancer, KiSS1 and GPR54 have been known to suppress metastasis by inhibiting cancer cell motility. However, recent studies suggest that KiSS1 and GPR54 have varied roles even in cancer development and metastasis. Here, we examine recent advances in understanding the roles of KiSS1 and GPR54 in cancer development and metastasis.

Re-engineering the adenine deaminase TadA-8e for efficient and specific CRISPR-based cytosine base editing.

Cytosine base editors (CBEs) efficiently generate precise C·G-to-T·A base conversions, but the activation-induced cytidine deaminase/apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like (AID/APOBEC) protein family deaminase component induces considerable off-target effects and indels. To explore unnatural cytosine deaminases, we repurpose the adenine deaminase TadA-8e for cytosine conversion. The introduction of an N46L variant in TadA-8e eliminates its adenine deaminase activity and results in a TadA-8e-derived C-to-G base editor (Td-CGBE) capable of highly efficient and precise C·G-to-G·C editing. Through fusion with uracil glycosylase inhibitors and further introduction of additional variants, a series of Td-CBEs was obtained either with a high activity similar to that of BE4max or with higher precision compared to other reported accurate CBEs. Td-CGBE/Td-CBEs show very low indel effects and a background level of Cas9-dependent or Cas9-independent DNA/RNA off-target editing. Moreover, Td-CGBE/Td-CBEs are more efficient in generating accurate edits in homopolymeric cytosine sites in cells or mouse embryos, suggesting their accuracy and safety for gene therapy and other applications.

Aberrant DNA hydroxymethylation reshapes transcription factor binding in myeloid neoplasms.

Epigenetic abnormalities in DNA hydroxymethylation (5hmC) have been detected in patients with myeloid neoplasms, suggesting that 5hmC might act as a valuable epigenetic mark to reflect the disease status of myeloid neoplasms. Here, we report systematic genome-wide mapping of the DNA hydroxymethylomes in over 70 patients with myeloid neoplasms. Our integrative analysis leads to the identification of distinct 5hmC signatures that can sensitively discriminate patients from healthy individuals. At the molecular level, we unveiled dynamic 5hmC changes within key transcription factor (e.g., the CEBP family) binding motifs that are essential for hematopoiesis and myeloid lineage specification. 5hmC redistribution was found to alter the genome-wide binding of CEBP-α, thereby reprogramming transcriptional outputs to affect leukemia cell survival and stemness. Taken together, we provide a comprehensive 5hmC atlas representative of myeloid neoplasms, which sets the stage for future exploration on the epigenetic etiology of hematological malignancies. Mechanistically, our study further furnishes important insights into how abnormal 5hmC distribution in patients directly interrupts the binding of transcription factors to reshape transcriptional landscapes and aggravate leukemogenesis.

The proton-activated G protein-coupled receptor GPR4 regulates the development of osteoarthritis via modulating CXCL12/CXCR7 signaling.

Inflammatory diseases decrease the extracellular environmental pH. However, whether proton-activated G protein-coupled receptors (GPCRs) can regulate the development of osteoarthritis (OA) is largely unknown. In this study, we report that proton-activated GPR4 is essential for OA development. We found a marked increase in expression of the proton-activated GPR4 in human and mouse OA cartilage. Lentivirus-mediated overexpression of GPR4 in mouse joints accelerated the development of OA, including promotion of articular cartilage damage, synovial hyperplasia, and osteophyte formation, while Gpr4 knockout effectively attenuated the development of posttraumatic and aging-associated OA in mice. We also found that inhibition of GPR4 with the antagonist NE52-QQ57 ameliorated OA progression in mice, promoted extracellular matrix (ECM) production, and protected cartilage from degradation in human articular cartilage explants. Moreover, GPR4 overexpression upregulated matrix-degrading enzymes' expression and inflammation factors under pro-inflammatory and slightly acidic conditions. Mechanistically, GPR4 suppressed chondrocyte differentiation and upregulated cartilage homeostasis through NF-κB/MAPK signaling activation by regulating CXCR7/CXCL12 expression. Together, our results take the lead to illustrate that proton-activated GPCR acts as a key regulator for OA pathogenesis in vivo, and support that GPR4 could be a promising therapeutic target for OA treatment.

Identification of a STIM1 Splicing Variant that Promotes Glioblastoma Growth.

Deregulated store-operated calcium entry (SOCE) mediated by aberrant STIM1-ORAI1 signaling is closely implicated in cancer initiation and progression. Here the authors report the identification of an alternatively spliced variant of STIM1, designated STIM1ß, that harbors an extra exon to encode 31 additional amino acids in the cytoplasmic domain. STIM1ß, highly conserved in mammals, is aberrantly upregulated in glioma tissues to perturb Ca2+ signaling. At the molecular level, the 31-residue insertion destabilizes STIM1ß by perturbing its cytosolic inhibitory domain and accelerating its activation kinetics to efficiently engage and gate ORAI calcium channels. Functionally, STIM1ß depletion affects SOCE in glioblastoma cells, suppresses tumor cell proliferation and growth both in vitro and in vivo. Collectively, their study establishes a splicing variant-specific tumor-promoting role of STIM1ß that can be potentially targeted for glioblastoma intervention.

RSPO2 and RANKL signal through LGR4 to regulate osteoclastic premetastatic niche formation and bone metastasis.

Therapeutics targeting osteoclasts are commonly used treatments for bone metastasis; however, whether and how osteoclasts regulate premetastatic niche and bone tropism are largely unknown. In this study, we report that osteoclast precursors (OPs) can function as a premetastatic niche component that facilitates breast cancer (BCa) bone metastasis at early stages. At the molecular level, unbiased GPCR ligand/agonist screening in BCa cells suggested that R-spondin 2 (RSPO2) and RANKL, through interaction with their receptor LGR4, promoted osteoclastic premetastatic niche formation and enhanced BCa bone metastasis. This was achieved by RSPO2/RANKL-LGR4 signal modulating the WNT inhibitor DKK1 through Gαq and ß-catenin signaling. DKK1 directly facilitated OP recruitment through suppression of its receptor LDL receptor-related protein 5 (LRP5) but not LRP6, upregulating Rnasek expression via inhibition of canonical WNT signaling. In clinical samples, RSPO2, LGR4, and DKK1 expression showed a positive correlation with BCa bone metastasis. Furthermore, soluble LGR4 extracellular domain (ECD) protein, acting as a decoy receptor for RSPO2 and RANKL, significantly alleviated bone metastasis and osteolytic lesions in a mouse bone metastasis model. These findings provide unique insights into the functional role of OPs as key components of the premetastatic niche for BCa bone metastasis and identify RSPO2/RANKL-LGR4 signaling as a promising target for inhibiting BCa bone metastasis.