The G protein-coupled receptor GPR34 - The past 20 years of a grownup

GPR34 senses demyelination to promote neuroinflammation and pathologies

Sterile neuroinflammation is a major driver of multiple neurological diseases. Myelin debris can act as an inflammatory stimulus to promote inflammation and pathologies, but the mechanism is poorly understood. Here, we showed that lysophosphatidylserine (LysoPS)-GPR34 axis played a critical role in microglia-mediated myelin debris sensing and the subsequent neuroinflammation. Myelin debris-induced microglia activation and proinflammatory cytokine expression relied on its lipid component LysoPS. Both myelin debris and LysoPS promoted microglia activation and the production of proinflammatory cytokines via GPR34 and its downstream PI3K-AKT and ERK signaling. In vivo, reducing the content of LysoPS in myelin or inhibition of GPR34 with genetic or pharmacological approaches reduced neuroinflammation and pathologies in the mouse models of multiple sclerosis and stroke. Thus, our results identify GPR34 as a key receptor to sense demyelination and CNS damage and promote neuroinflammation, and suggest it as a potential therapeutic target for demyelination-associated diseases.

Reliable detection of RNA in hippocampus sections of mice by FISH up to a post-mortem delay of 24 h

Proteins can be successfully localized in post-mortem (PM) brain tissue sections if the time until PM tissue sampling is not too long. In this study, we show that this also applies to the localization of RNA and in particular to the RNA of microglia-specific receptor proteins using the probes and the RNAscope™ Multiplex Fluorescent Detection Kit v2 from Advanced Cell Diagnostics. Brains were removed from killed mice after different PM delays and processed into paraffin sections. In sections of brains from animals whose cadavers had been kept at room temperature (21 °C) before tissue removal, ubiquitously expressed RNAs of genes with low to high expression levels (Polr2a, PPIB, and UBC) were reliably detected in the brain sections even if tissue removal was delayed by up to 48 h. In addition, microglia-specific G protein-coupled receptor RNA (Gpr34, P2ry12) could be reliably assigned to microglia by simultaneous labeling of the microglia with microglia-specific antibodies (Iba1 or P2ry12). Only after a delay of 48 h until tissue removal were the receptor RNA signals significantly lower. The reduction in receptor RNA signals could be delayed if the animal cadavers were stored at 4 °C until the brains were removed. Tissue sections of PM brain samples allow the spatial and cellular localization of specific RNA, at least if the sampling takes place within the first 24 h of PM.

Longitudinal Neuropathological Consequences of Extracranial Radiation Therapy in Mice

Cancer-related cognitive impairment (CRCI) is a consequence of chemotherapy and extracranial radiation therapy (ECRT). Our prior work demonstrated gliosis in the brain following ECRT in SKH1 mice. The signals that induce gliosis were unclear. Right hindlimb skin from SKH1 mice was treated with 20 Gy or 30 Gy to induce subclinical or clinical dermatitis, respectively. Mice were euthanized at 6 h, 24 h, 5 days, 12 days, and 25 days post irradiation, and the brain, thoracic spinal cord, and skin were collected. The brains were harvested for spatial proteomics, immunohistochemistry, Nanostring nCounter® glial profiling, and neuroinflammation gene panels. The thoracic spinal cords were evaluated by immunohistochemistry. Radiation injury to the skin was evaluated by histology. The genes associated with neurotransmission, glial cell activation, innate immune signaling, cell signal transduction, and cancer were differentially expressed in the brains from mice treated with ECRT compared to the controls. Dose-dependent increases in neuroinflammatory-associated and neurodegenerative-disease-associated proteins were measured in the brains from ECRT-treated mice. Histologic changes in the ECRT-treated mice included acute dermatitis within the irradiated skin of the hindlimb and astrocyte activation within the thoracic spinal cord. Collectively, these findings highlight indirect neuronal transmission and glial cell activation in the pathogenesis of ECRT-related CRCI, providing possible signaling pathways for mitigation strategies.

Lysophosphatidylserine: A Signaling Lipid with Implications in Human Diseases

Lysophosphatidylserine (lyso-PS) has emerged as yet another important signaling lysophospholipid in mammals, and deregulation in its metabolism has been directly linked to an array of human autoimmune and neurological disorders. It has an indispensable role in several biological processes in humans, and therefore, cellular concentrations of lyso-PS are tightly regulated to ensure optimal signaling and functioning in physiological settings. Given its biological importance, the past two decades have seen an explosion in the available literature toward our understanding of diverse aspects of lyso-PS metabolism and signaling and its association with human diseases. In this Review, we aim to comprehensively summarize different aspects of lyso-PS, such as its structure, biodistribution, chemical synthesis, and SAR studies with some synthetic analogs. From a biochemical perspective, we provide an exhaustive coverage of the diverse biological activities modulated by lyso-PSs, such as its metabolism and the receptors that respond to them in humans. We also briefly discuss the human diseases associated with aberrant lyso-PS metabolism and signaling and posit some future directions that may advance our understanding of lyso-PS-mediated mammalian physiology.

SorLA restricts TNFα release from microglia to shape a glioma-supportive brain microenvironment

SorLA, encoded by the gene SORL1, is an intracellular sorting receptor of the VPS10P domain receptor gene family. Although SorLA is best recognized for its ability to shuttle target proteins between intracellular compartments in neurons, recent data suggest that also its microglial expression can be of high relevance for the pathogenesis of brain diseases, including glioblastoma (GBM). Here, we interrogated the impact of SorLA on the functional properties of glioma-associated microglia and macrophages (GAMs). In the GBM microenvironment, GAMs are re-programmed and lose the ability to elicit anti-tumor responses. Instead, they acquire a glioma-supporting phenotype, which is a key mechanism promoting glioma progression. Our re-analysis of published scRNA-seq data from GBM patients revealed that functional phenotypes of GAMs are linked to the level of SORL1 expression, which was further confirmed using in vitro models. Moreover, we demonstrate that SorLA restrains secretion of TNFα from microglia to restrict the inflammatory potential of these cells. Finally, we show that loss of SorLA exacerbates the pro-inflammatory response of microglia in the murine model of glioma and suppresses tumor growth.

The role of orphan G protein-coupled receptors in pain

G protein-coupled receptors (GPCRs), which form the largest family of membrane protein receptors in humans, are highly complex signaling systems with intricate structures and dynamic conformations and locations. Among these receptors, a specific subset is referred to as orphan GPCRs (oGPCRs) and has garnered significant interest in pain research due to their role in both central and peripheral nervous system function. The diversity of GPCR functions is attributed to multiple factors, including allosteric modulators, signaling bias, oligomerization, constitutive signaling, and compartmentalized signaling. This review primarily focuses on the recent advances in oGPCR research on pain mechanisms, discussing the role of specific oGPCRs including GPR34, GPR37, GPR65, GPR83, GPR84, GPR85, GPR132, GPR151, GPR160, GPR171, GPR177, and GPR183. The orphan receptors among these receptors associated with central nervous system diseases are also briefly described. Understanding the functions of these oGPCRs can contribute not only to a deeper understanding of pain mechanisms but also offer a reference for discovering new targets for pain treatment.

Discovery of (S)-3-(4-(benzyloxy)phenyl)-2-(2-phenoxyacetamido)propanoic acid derivatives as a new class of GPR34 antagonists

GPR34 is a rhodopsin-like class G protein-coupled receptor (GPCR) that is involved in the development and progression of several diseases. Despite its importance, effective targeting strategies are lacking. We herein report a series of (S)-3-(4-(benzyloxy)phenyl)-2-(2-phenoxyacetamido)propanoic acid derivatives as a new class of GPR34 antagonists. Structure-activity relationship (SAR) studies led to the identification of the most potent compound, 5e, which displayed an IC50 value of 0.680 μM in the GloSensor cAMP assay and 0.059 μM in the Tango assay. 5e demonstrated low cytotoxicity and high selectivity in vitro, and it was able to dose-dependently inhibit Lysophosphatidylserine-induced ERK1/2 phosphorylation in CHO cells expressing GPR34. Furthermore, 5e displayed excellent efficacy in a mouse model of neuropathic pain without any apparent signs of toxicity. Collectively, this study has identified a promising compound, which shows great potential in the development of potent antagonists with a new chemical scaffold targeting GPR34.

Structural basis for ligand recognition and signaling of the lysophosphatidylserine receptors GPR34 and GPR174

Lysophosphatidylserine (LysoPS) is a naturally occurring lipid mediator involved in various physiological and pathological processes especially those related to the immune system. GPR34, GPR174, and P2Y10 have been identified as the receptors for LysoPS, and its analogues have been developed as agonists or antagonists for these receptors. However, the lack of structural information hinders the drug development with novel characteristics, such as nonlipid ligands and allosteric modulators. Here, we determined the structures of human GPR34 and GPR174 in complex with LysoPS and G protein by cryo-EM. Combined with structural analysis and functional studies, we elucidated the lipid-binding modes of these receptors. By structural comparison, we identified the structural features of GPR34 and GPR174 in active state. Taken together, our findings provide insights into ligand recognition and signaling of LysoPS receptors and will facilitate the development of novel therapeutics for related inflammatory diseases and autoimmune diseases.

Characterization of cancer-associated fibroblasts (CAFs) and development of a CAF-based risk model for triple-negative breast cancer

Triple-negative breast Cancer (TNBC) is a highly malignant cancer with unclear pathogenesis. Within the tumor microenvironment (TME), cancer-associated fibroblasts (CAFs) vitally influence tumor onset and progression. Thus, this research aimed to identify distinct subgroups of CAF using single-cell and TNBC-related information from the GEO and TCGA databases, respectively. The primary aim was to establish a novel predictive model based on the CAF features and their clinical relevance. Moreover, the CAFs were analyzed for their immune characteristics, response to immunotherapy, and sensitivity to different drugs. The developed predictive model demonstrated significant effectiveness in determining the prognosis of patients with TNBC, TME, and the immune landscape of the tumor. Of note, the expression of GPR34 was significantly higher in TNBC tissues compared to that in other breast cancer (non-TNBC) tissues, indicating that GPR34 plays a crucial role in the onset and progression of TNBC. In summary, this research has yielded a novel predictive model for TNBC that holds promise for the accurate prediction of prognosis and response to immunotherapy in patients with TNBC.

From clinical variables to multiomics analysis: a margin morphology-based gross classification system for hepatocellular carcinoma stratification

OBJECTIVE

Selecting interventions for patients with solitary hepatocellular carcinoma (HCC) remains a challenge. Despite gross classification being proposed as a potential prognostic predictor, its widespread use has been restricted due to inadequate studies with sufficient patient numbers and the lack of established mechanisms. We sought to investigate the prognostic impacts on patients with HCC of different gross subtypes and assess their corresponding molecular landscapes.

DESIGN

A prospective cohort of 400 patients who underwent hepatic resection for solitary HCC was reviewed and analysed and gross classification was assessed. Multiomics analyses were performed on tumours and non-tumour tissues from 49 patients to investigate the mechanisms underlying gross classification. Inverse probability of treatment weight (IPTW) was used to control for confounding factors.

RESULTS

Overall 3-year survival rates varied significantly among the four gross subtypes (type I: 91%, type II: 80%, type III: 74.6%, type IV: 38.8%). Type IV was found to be independently associated with poor prognosis in both the entire cohort and the IPTW cohort. The four gross subtypes exhibited three distinct transcriptional modules. Particularly, type IV tumours exhibited increased angiogenesis and immune score as well as decreased metabolic pathways, together with highest frequency of TP53 mutations. Patients with type IV HCC may benefit from adjuvant intra-arterial therapy other than the other three subtypes. Accordingly, a modified trichotomous margin morphological gross classification was established.

CONCLUSION

Different gross types of HCC showed significantly different prognosis and molecular characteristics. Gross classification may aid in development of precise individualised diagnosis and treatment strategies for HCC.

Cryo-EM structures of human GPR34 enable the identification of selective antagonists

GPR34 is a functional G-protein-coupled receptor of Lysophosphatidylserine (LysoPS), and has pathogenic roles in numerous diseases, yet remains poorly targeted. We herein report a cryo-electron microscopy (cryo-EM) structure of GPR34 bound with LysoPS (18:1) and Gi protein, revealing a unique ligand recognition mode with the negatively charged head group of LysoPS occupying a polar cavity formed by TM3, 6 and 7, and the hydrophobic tail of LysoPS residing in a lateral open hydrophobic groove formed by TM3-5. Virtual screening and subsequent structural optimization led to the identification of a highly potent and selective antagonist (YL-365). Design of fusion proteins allowed successful determination of the challenging cryo-EM structure of the inactive GPR34 complexed with YL-365, which revealed the competitive binding of YL-365 in a portion of the orthosteric binding pocket of GPR34 and the antagonist-binding-induced allostery in the receptor, implicating the inhibition mechanism of YL-365. Moreover, YL-365 displayed excellent activity in a neuropathic pain model without obvious toxicity. Collectively, this study offers mechanistic insights into the endogenous agonist recognition and antagonist inhibition of GPR34, and provides proof of concept that targeting GPR34 represents a promising strategy for disease treatment.

The molecular features of chronic lung allograft dysfunction in lung transplant airway mucosa

BACKGROUND

Many lung transplants fail due to chronic lung allograft dysfunction (CLAD). We recently showed that transbronchial biopsies (TBBs) from CLAD patients manifest severe parenchymal injury and dedifferentiation, distinct from time-dependent changes. The present study explored time-selective and CLAD-selective transcripts in mucosal biopsies from the third bronchial bifurcation (3BMBs), compared to those in TBBs.

METHODS

We used genome-wide microarray measurements in 324 3BMBs to identify CLAD-selective changes as well as time-dependent changes and develop a CLAD classifier. CLAD-selective transcripts were identified with linear models for microarray data (limma) and were used to build an ensemble of 12 classifiers to predict CLAD. Hazard models and random forests were then used to predict the risk of graft loss using the CLAD classifier, transcript sets associated with rejection, injury, and time.

RESULTS

T cell-mediated rejection and donor-specific antibody were increased in CLAD 3BMBs but most had no rejection. Like TBBs, 3BMBs showed a time-dependent increase in transcripts expressed in inflammatory cells that was not associated with CLAD or survival. Also like TBBs, the CLAD-selective transcripts in 3BMBs reflected severe parenchymal injury and dedifferentiation, not inflammation or rejection. While 3BMBs and TBBs did not overlap in their top 20 CLAD-selective transcripts, many CLAD-selective transcripts were significantly increased in both for example LOXL1, an enzyme controlling matrix remodeling. In Cox models for one-year survival, the 3BMB CLAD-selective transcripts and CLAD classifier predicted graft loss and correlated with CLAD stage. Many 3BMB CLAD-selective transcripts were also increased by injury in kidney transplants and correlated with decreased kidney survival, including LOXL1.

CONCLUSIONS

Mucosal and transbronchial biopsies from CLAD patients reveal a diffuse molecular injury and dedifferentiation state that impacts prognosis and correlates with the physiologic disturbances. CLAD state in lung transplants shares features with failing kidney transplants, indicating elements shared by the injury responses of distressed organs.

Transcriptomic Regulation of Macrophages by Matrix-Bound Nanovesicle-Associated Interleukin-33

The innate immune response, particularly the phenotype of responding macrophages, has significant clinical implications in the remodeling outcome following implantation of biomaterials and engineered tissues. In general, facilitation of an anti-inflammatory (M2-like) phenotype is associated with tissue repair and favorable outcomes, whereas pro-inflammatory (M1-like) activation can contribute to chronic inflammation and a classic foreign body response. Biologic scaffolds composed of extracellular matrix (ECM) and, more recently, matrix-bound nanovesicles (MBV) embedded within the ECM are known to direct macrophages toward an anti-inflammatory phenotype and stimulate a constructive remodeling outcome. The mechanisms of MBV-mediated macrophage activation are not fully understood, but interleukin-33 (IL-33) within the MBV appears critical for M2-like activation. Previous work has shown that IL-33 is encapsulated within the lumen of MBV and stimulates phenotypical changes in macrophages independent of its canonical surface receptor stimulation-2 (ST2). In the present study, we used next-generation RNA sequencing to determine the gene signature of macrophages following exposure to MBV with and without intraluminal IL-33. MBV-associated IL-33 instructed an anti-inflammatory phenotype in both wild-type and st2-/- macrophages by upregulating M2-like and downregulating M1-like genes. The repertoire of genes regulated by ST2-independent IL-33 signaling were broadly related to the inflammatory response and crosstalk between cells of both the innate and adaptive immune systems. These results signify the importance of the MBV intraluminal protein IL-33 in stimulating a pro-remodeling M2-like phenotype in macrophages and provides guidance for the designing of next-generation biomaterials and tissue engineering strategies. Impact statement The phenotype of responding macrophages is predictive of the downstream remodeling response to an implanted biomaterial. The clinical impact of macrophage phenotype has motivated studies to investigate the factors that regulate macrophage activation. Matrix-bound nanovesicles (MBV) embedded within the extracellular matrix direct macrophages toward an anti-inflammatory (M2)-like phenotype that is indicative of a favorable remodeling response. Although the mechanisms of MBV-mediated macrophage activation are not fully understood, the intraluminal protein interleukin-33 (IL-33) is clearly a contributing signaling molecule. The present study identifies those genes regulated by MBV-associated IL-33 that promote a pro-remodeling M2-like macrophage activation state and can guide future therapies in regenerative medicine.

Neuroinflammation: A Possible Link Between Chronic Vascular Disorders and Neurodegenerative Diseases

Various age-related diseases involve systemic inflammation, i.e. a stereotyped series of acute immune system responses, and aging itself is commonly associated with low-grade inflammation or inflamm’aging. Neuroinflammation is defined as inflammation-like processes inside the central nervous system, which this review discusses as a possible link between cardiovascular disease-related chronic inflammation and neurodegenerative diseases. To this aim, neuroinflammation mechanisms are first summarized, encompassing the cellular effectors and the molecular mediators. A comparative survey of the best-known physiological contexts of neuroinflammation (neurodegenerative diseases and transient ischemia) reveals some common features such as microglia activation. The recently published transcriptomic characterizations of microglia have pointed a marker core signature among neurodegenerative diseases, but also unraveled the discrepancies with neuroinflammations related with acute diseases of vascular origin. We next review the links between systemic inflammation and neuroinflammation, beginning with molecular features of respective pro-inflammatory cells, i.e. macrophages and microglia. Finally, we point out a gap of knowledge concerning the atherosclerosis-related neuroinflammation, which is for the most surprising given that atherosclerosis is established as a major risk factor for neurodegenerative diseases.

G-protein coupled receptor 34 regulates the proliferation and growth of LS174T cells through differential expression of PI3K subunits and PTEN

Purpose

G-protein coupled receptor (GPR 34) has been found to play important roles in some cancers and regulates the proliferation, apoptosis, and migration of these cancer cells. However, the mechanisms underlying how GPR34 functions to regulate growth and proliferation of colorectal cancer cells remains to be clarified.

Methods

We employed stable GPR34 knockdown LS174T cell models, GPR34 Mab blocking, a CCK-8 kit, and a colony formation assay to characterize the effect of GPR34 on the proliferation of LS174T in vitro and xenograft tumor growth in vivo. The mRNA level of GPR34 was detected by RT-PCR in tumor tissues and adjacent normal tissues from 34 CRC patients.

Results

Based on RT-PCR results, GPR34 exhibited high level in tumor samples compared with adjacent normal samples. Increased expression of GPR34 is more associated with poor prognosis of CRC as shown in The Cancer Genome Atlas (TCGA) dataset by Kaplan–Meier survival analysis. Furthermore, we showed that GPR34 knockdown inhibited the proliferation of LS174T colon cancer cells and related xenograft tumor growth. Searching for the distinct molecular mechanism, we identified several contributors to proliferation of LS174T colon cancer cells: PI3K subunits/PTEN, PDK1/AKT, and Src/Raf/Ras/ERK. GPR34 knockdown inhibited the proliferation of LS174T cells by upregulating expression of PTEN, and downregulating expression of PI3K subunits p110-beta.

Conclusion

Our findings provide direct evidence that GPR34 regulates the proliferation of LS174T cells and the growth of LS174T tumor xenografts by regulating different pathways. High expression of GPR34 mRNA could then be used to predict poor prognosis of CRC.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11033-021-07068-4.

G-protein Coupled Receptor 34 Promotes Gliomagenesis by Inducing Proliferation and Malignant Phenotype via TGF-Beta/Smad Signaling Pathway

Background: G-protein coupled receptor 34 (GPR34) is involved in cell motility, differentiation, and mitosis. GPR34 was reported to be highly expressed and play an oncogenic role in several solid tumors. Here, we investigated the mechanisms underlying how GPR34 promotes glioma progression. Methods: Bioinformatic analysis was performed on RNA-seq and clinical data from the gene expression omnibus (GEO), cancer genome atlas (TCGA), and Genotype-Tissue Expression (GTEx) databases. TIMER database and single-sample GSEA (ssGAEA) method were used to investigate the association between the GPR34 expression and immune infiltration level in glioma. Cox regression analysis was employed to ascertain whether the risk signature was an independent prognostic indicator for glioma. The viability and migratory/invasive potential of glioma cells were assessed using Cell Counting Kit-8, colony formation, wound healing, and Transwell assays. Results: We found that GPR34 expression was positively correlated with immune infiltration level and that high GPR34 level may be associated with poor prognosis in glioma. We further found that GPR34 may serve as an independent prognostic marker and prediction factor for the clinicopathological features of glioma. We showed that knocking down GPR34 attenuated the viability and migratory/invasive capacity of glioma cells (U251 and LN229), while GPR34 overexpression exerted the opposite effects. Additionally, core enrichment in the GSEA analysis indicated that GPR34-mediated gliomagenesis was associated with the cell cycle arrest, epithelial–mesenchymal transition (EMT), and activation of the TGF-β/Smad pathway; furthermore, inhibiting TGF-β/Smad signaling using LY2157299, a TGF-β inhibitor, reversed the oncogenic effects and malignant phenotype associated with GPR34 overexpression. Conclusion: GPR34 enhances the malignancy and carcinogenesis of glioma by promoting an EMT-like process, G1/S phase cell cycle transition, and TGF-β/Smad signaling. Accordingly, GPR34 likely functions as an oncogene in glioma and may represent a potential therapeutic target for this cancer.

MicroRNA-300 Inhibits the Proliferation and Metastasis of Cervical Cancer Cells via Posttranscriptional Suppression of G Protein-Coupled Receptor 34 (GPR34)

Cervical cancer is one of the dominant gynecological disorders which has poor prognosis and often diagnosed at advanced stages where it becomes nearly impossible to effectively manage this disorder. MicroRNA-300 (miR-300) has dual role in human tumorogenesis. However, characterization of its regulatory action has not been made in cervical cancer. The molecular role of miR-300 in cervical cancer was thus explored in the present study with prime focus on elucidating its mechanism of action. The results showed significant (P < 0.05) downregulation of miR-300 in cervical cancer. Overexpression of miR-300 in cervical cancer cells inhibited their proliferation in vitro by inducing apoptosis. Cervical cancer cells overexpressing miR-300 also showed decreased rates of migration and invasion. G protein-coupled receptor 34 (GPR34) was found to be the functional regulatory target of miR-300 in cervical cancer. GPR34 was found to be significantly (P < 0.05) overexpressed in cervical cancer tissues and cell lines. Silencing of GPR34 inhibited the growth of the cervical cancer cells. However, overexpression of GPR34 could prevent the tumor-suppressive effects of miR-300 on cervical cancer cells. Collectively, the results of the current study are indicative of the tumor-suppressive regulatory role of miR-300 in cervical cancer and suggestive of the potential therapeutic value of miR-300/GPR34 molecular axis.

Mirtronic miR-4646-5p promotes gastric cancer metastasis by regulating ABHD16A and metabolite lysophosphatidylserines

The aberrant classical miRNAs are considered to play significant roles in tumor progression. However, it remains unclear for nonclassical miRNAs, a set of Drosha-independent miRNAs in the process of various biology. Here, we reveal that a nonclassical miR-4646-5p plays a pivotal role in gastric cancer (GC) metastasis. MiR-4646-5p, one of Drosha-independent mirtronic miRNA, is aberrant up-regulated in Drosha-low expressed GC and Drosha-knockdown gastric cancer cells. Mirtronic miR-4646-5p is a specific transcription splicing product of intron 3 of the host gene Abhd16a with the aid of SRSF2. The enhanced miR-4646-5p can stabilize HIF1A by targeting PHD3 to positive feedback regulate Abhd16a and miR-4646-5p itself expressions. ABHD16A, as an emerging phosphatidylserine-specific lipase, involves in lipid metabolism leading to lysophosphatidylserines (lyso-PSs) accumulation, which stimulates RhoA and downstream LIMK/cofilin cascade activity through GPR34/Gi subunit, thus causes metastasis of gastric cancer. In addition, miR-4646-5p/PHD3/HIF1A signaling can also up-regulate RhoA expression and synergistically promote gastric cancer cell invasion and metastasis. Our study provides new insights of nonclassical mirtronic miRNA on tumor progress and may serve as a new diagnostic biomarker for gastric cancer. MiR-4646-5p and its host gene Abhd16a mediated abnormal lipid metabolism may be a new target for clinical treatment of gastric cancer.

Beyond Activation: Characterizing Microglial Functional Phenotypes

Classically, the following three morphological states of microglia have been defined: ramified, amoeboid and phagocytic. While ramified cells were long regarded as “resting”, amoeboid and phagocytic microglia were viewed as “activated”. In aged human brains, a fourth, morphologically novel state has been described, i.e., dystrophic microglia, which are thought to be senescent cells. Since microglia are not replenished by blood-borne mononuclear cells under physiological circumstances, they seem to have an “expiration date” limiting their capacity to phagocytose and support neurons. Identifying factors that drive microglial aging may thus be helpful to delay the onset of neurodegenerative diseases, such as Alzheimer’s disease (AD). Recent progress in single-cell deep sequencing methods allowed for more refined differentiation and revealed regional-, age- and sex-dependent differences of the microglial population, and a growing number of studies demonstrate various expression profiles defining microglial subpopulations. Given the heterogeneity of pathologic states in the central nervous system, the need for accurately describing microglial morphology and expression patterns becomes increasingly important. Here, we review commonly used microglial markers and their fluctuations in expression in health and disease, with a focus on IBA1 low/negative microglia, which can be found in individuals with liver disease.

Increase in Cellular Lysophosphatidylserine Content Exacerbates Inflammatory Responses in LPS-Activated Microglia

Mutations in alpha/beta-hydrolase domain containing (ABHD) 12 gene, which encodes lysophosphatidylserine (LysoPS) lipase, cause the neurodegenerative disease PHARC (Polyneuropathy, Hearing loss, Ataxia, Retinitis pigmentosa, Cataract). Since ABHD12 is expressed by microglia in the central nervous system and is localized to the endoplasmic reticulum, accumulation of intracellular LysoPS by ABHD12 mutations is assumed to be one of the pathological mechanisms associated with microglial activation in PHARC. However, the role of microglia in the PHARC brain and the relationship between microglial function and cellular LysoPS content remains unclear. Therefore, we explored the influence of cellular LysoPS content in microglial inflammatory responses. We evaluated the effects of inhibitors of cellular LysoPS metabolism, KC01 and DO-264, on inflammatory responses using a lipopolysaccharide (LPS)-stimulated mouse microglial cell line, BV-2 and primary microglia. Treatment of DO-264, an inhibitor of cellular LysoPS degradation, enhanced LPS-induced phagocytosis concomitant with the increase in cellular LysoPS content in BV-2 cells. On the other hand, treatment with KC01, an agent had been developed as an inhibitor of LysoPS synthase, reduced phagocytosis without affecting cellular LysoPS content. Such effects of both inhibitors on phagocytosis were also confirmed using primary microglia. KC01 treatment decreased nitric oxide (NO) production, accompanied by a reduction in inducible NO synthase expression in BV-2 microglia. KC01 also suppressed LPS-induced generation of intracellular reactive oxygen species and cytokines such as interleukin-6. Our results suggest that increase in cellular LysoPS levels can exacerbate microglial inflammatory responses. Treatment to prevent the increase in cellular LysoPS in microglia may have therapeutic potential for PHARC.

GPR34-mediated sensing of lysophosphatidylserine released by apoptotic neutrophils activates type 3 innate lymphoid cells to mediate tissue repair

Neutrophils migrate rapidly to damaged tissue and play critical roles in host defense and tissue homeostasis. Here we investigated the mechanisms whereby neutrophils participate in tissue repair. In an intestinal epithelia injury model, neutrophil depletion exacerbated colitis and associated with reduced interleukin (IL)-22 and limited activation of type 3 innate lymphoid cells (ILC3s). Co-culture with neutrophils activated ILC3s in a manner dependent on neutrophil apoptosis. Metabolomic analyses revealed that lysophosphatidylserine (LysoPS) from apoptotic neutrophils directly stimulated ILC3 activation. ILC3-specific deletion of Gpr34, encoding the LysoPS receptor GPR34, or inhibition of downstream PI3K-AKT or ERK suppressed IL-22 production in response to apoptotic neutrophils. Gpr34-/- mice exhibited compromised ILC3 activation and tissue repair during colon injury, and neutrophil depletion abrogated these defects. GPR34 deficiency in ILC3s limited IL-22 production and tissue repair in vivo in settings of colon and skin injury. Thus, GPR34 is an ILC3-expressed damage-sensing receptor that triggers tissue repair upon recognition of dying neutrophils.

PRISM: recovering cell-type-specific expression profiles from individual composite RNA-seq samples

MOTIVATION

A major challenge in analyzing cancer patient transcriptomes is that the tumors are inherently heterogeneous and evolving. We analyzed 214 bulk RNA samples of a longitudinal, prospective ovarian cancer cohort and found that the sample composition changes systematically due to chemotherapy and between the anatomical sites, preventing direct comparison of treatment-naive and treated samples.

RESULTS

To overcome this, we developed PRISM, a latent statistical framework to simultaneously extract the sample composition and cell-type-specific whole-transcriptome profiles adapted to each individual sample. Our results indicate that the PRISM-derived composition-free transcriptomic profiles and signatures derived from them predict the patient response better than the composite raw bulk data. We validated our findings in independent ovarian cancer and melanoma cohorts, and verified that PRISM accurately estimates the composition and cell-type-specific expression through whole-genome sequencing and RNA in situ hybridization experiments.

AVAILABILITYAND IMPLEMENTATION

https://bitbucket.org/anthakki/prism.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

A human cell atlas of fetal gene expression

The gene expression program underlying the specification of human cell types is of fundamental interest. We generated human cell atlases of gene expression and chromatin accessibility in fetal tissues. For gene expression, we applied three-level combinatorial indexing to >110 samples representing 15 organs, ultimately profiling ~4 million single cells. We leveraged the literature and other atlases to identify and annotate hundreds of cell types and subtypes, both within and across tissues. Our analyses focused on organ-specific specializations of broadly distributed cell types (such as blood, endothelial, and epithelial), sites of fetal erythropoiesis (which notably included the adrenal gland), and integration with mouse developmental atlases (such as conserved specification of blood cells). These data represent a rich resource for the exploration of in vivo human gene expression in diverse tissues and cell types.

Mutations in G Protein-Coupled Receptors: Mechanisms, Pathophysiology and Potential Therapeutic Approaches

There are approximately 800 annotated G protein-coupled receptor (GPCR) genes, making these membrane receptors members of the most abundant gene family in the human genome. Besides being involved in manifold physiologic functions and serving as important pharmacotherapeutic targets, mutations in 55 GPCR genes cause about 66 inherited monogenic diseases in humans. Alterations of nine GPCR genes are causatively involved in inherited digenic diseases. In addition to classic gain- and loss-of-function variants, other aspects, such as biased signaling, trans-signaling, ectopic expression, allele variants of GPCRs, pseudogenes, gene fusion, and gene dosage, contribute to the repertoire of GPCR dysfunctions. However, the spectrum of alterations and GPCR involvement is probably much larger because an additional 91 GPCR genes contain homozygous or hemizygous loss-of-function mutations in human individuals with currently unidentified phenotypes. This review highlights the complexity of genomic alteration of GPCR genes as well as their functional consequences and discusses derived therapeutic approaches. SIGNIFICANCE STATEMENT: With the advent of new transgenic and sequencing technologies, the number of monogenic diseases related to G protein-coupled receptor (GPCR) mutants has significantly increased, and our understanding of the functional impact of certain kinds of mutations has substantially improved. Besides the classical gain- and loss-of-function alterations, additional aspects, such as biased signaling, trans-signaling, ectopic expression, allele variants of GPCRs, uniparental disomy, pseudogenes, gene fusion, and gene dosage, need to be elaborated in light of GPCR dysfunctions and possible therapeutic strategies.

Non-naturally Occurring Regio Isomer of Lysophosphatidylserine Exhibits Potent Agonistic Activity toward G Protein-Coupled Receptors

Lysophosphatidylserine (LysoPS), an endogenous ligand of G protein-coupled receptors, consists of l-serine, glycerol, and fatty acid moieties connected by phosphodiester and ester linkages, respectively. An ester linkage of phosphatidylserine can be hydrolyzed at the 1-position or at the 2-position to give 2-acyl lysophospholipid or 1-acyl lysophospholipid, respectively. 2-Acyl lysophospholipid is in nonenzymatic equilibrium with 1-acyl lysophospholipid in vivo. On the other hand, 3-acyl lysophospholipid is not found, at least in mammals, raising the question of whether the reason for this might be that the 3-acyl isomer lacks the biological activities of the other isomers. Here, to test this idea, we designed and synthesized a series of new 3-acyl lysophospholipids. Structure-activity relationship studies of more than 100 "glycol surrogate" derivatives led to the identification of potent and selective agonists for LysoPS receptors GPR34 and P2Y10. Thus, the non-natural 3-acyl compounds are indeed active and appear to be biologically orthogonal with respect to the physiologically relevant 1- and 2-acyl lysophospholipids.

Genetic basis of functional variability in adhesion G protein-coupled receptors

The enormous sizes of adhesion G protein-coupled receptors (aGPCRs) go along with complex genomic exon-intron architectures giving rise to multiple mRNA variants. There is a need for a comprehensive catalog of aGPCR variants for proper evaluation of the complex functions of aGPCRs found in structural, in vitro and animal model studies. We used an established bioinformatics pipeline to extract, quantify and visualize mRNA variants of aGPCRs from deeply sequenced transcriptomes. Data analysis showed that aGPCRs have multiple transcription start sites even within introns and that tissue-specific splicing is frequent. On average, 19 significantly expressed transcript variants are derived from a given aGPCR gene. The domain architecture of the N terminus encoded by transcript variants often differs and N termini without or with an incomplete seven-helix transmembrane anchor as well as separate seven-helix transmembrane domains are frequently derived from aGPCR genes. Experimental analyses of selected aGPCR transcript variants revealed marked functional differences. Our analysis has an impact on a rational design of aGPCR constructs for structural analyses and gene-deficient mouse lines and provides new support for independent functions of both, the large N terminus and the transmembrane domain of aGPCRs.

GPR34 in spinal microglia exacerbates neuropathic pain in mice

Background

Neuropathic pain is caused by sensory nerve injury, but effective treatments are currently lacking. Microglia are activated in the spinal dorsal horn after sensory nerve injury and contribute to neuropathic pain. Accordingly, molecules expressed by these cells are considered potential targets for therapeutic strategies. Our previous gene screening study using a mouse model of motor nerve injury showed that the G-protein-coupled receptor 34 gene (GPR34) is induced by nerve injury. Because GPR34 is now considered a microglia-enriched gene, we explored the possibility that it might be involved in microglial activation in the dorsal horn in a mouse model of neuropathic pain.

Methods

mRNA expression of GPR34 and pro-inflammatory molecules was determined by quantitative real-time PCR in wild-type and GPR34-deficient mice with L4 spinal nerve injury. In situ hybridization was used to identify GPR34 expression in microglia, and immunohistochemistry with the microglial marker Iba1 was performed to examine microglial numbers and morphology. Mechanical sensitivity was evaluated by the von Frey hair test. Liquid chromatography–tandem mass spectrometry quantified expression of the ligand for GPR34, lysophosphatidylserine (LysoPS), in the dorsal horn, and a GPR34 antagonist was intrathecally administrated to examine the effect of inhibiting LysoPS-GPR34 signaling on mechanical sensitivity.

Results

GPR34 was predominantly expressed by microglia in the dorsal horn after L4 nerve injury. There were no histological differences in microglial numbers or morphology between WT and GPR34-deficient mice. However, nerve injury-induced pro-inflammatory cytokine expression levels in microglia and pain behaviors were significantly attenuated in GPR34-deficient mice. Furthermore, the intrathecal administration of the GPR34 antagonist reduced neuropathic pain.

Conclusions

Inhibition of GPR34-mediated signal by GPR34 gene deletion reduced nerve injury-induced neuropathic pain by suppressing pro-inflammatory responses of microglia without affecting their morphology. Therefore, the suppression of GPR34 activity may have therapeutic potential for alleviating neuropathic pain.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1458-8) contains supplementary material, which is available to authorized users.