Nonhematopoietic β-Arrestin-1 inhibits inflammation in a murine model of polymicrobial sepsis

ARRB1 downregulates acetaminophen-induced hepatoxicity through binding to p-eIF2α to inhibit ER stress signaling

Acetaminophen (APAP) stands as the predominant contributor to drug-induced liver injury (DILI), and limited options are available. β-Arrestin1 (ARRB1) is involved in numerous liver diseases. However, the role of ARRB1 in APAP-induced liver injury remained uncertain. Wild-type (WT) and ARRB1 knockout (KO) mice were injected with APAP and sacrificed at the indicated times. The histological changes, inflammation, endoplasmic reticulum (ER) stress, and apoptosis were then evaluated. Hepatic cell lines AML-12 and primary hepatocytes were used for in vitro analyses. Systemic ARRB1-KO mice were susceptible to APAP-induced hepatotoxicity, as indicated by larger areas of centrilobular necrosis area and higher levels of ALT, AST, and inflammation level. Moreover, ARRB1-KO mice exhibited increased ER stress (indicated by phosphorylated α subunit of eukaryotic initiation factor 2 (p-eIF2α)-activating transcription factor 4 (ATF4)-CCAAT-enhancer-binding protein homologous protein (CHOP)) and apoptosis (indicated by cleaved caspase 3). Further rescue experiments demonstrated that the induction of apoptosis was partially mediated by ER stress. Overexpression of ARRB1 alleviated APAP-induced ER stress and apoptosis. Moreover, co-IP analysis revealed that ARRB1 directly bound to p-eIF2α and eIF2α. ARRB1 protected against APAP-induced hepatoxicity through targeting ER stress and apoptosis. ARRB1 is a prospective target for treating APAP-induced DILI.

Characterization of lncRNA-Based ceRNA Network and Potential Prognostic Hub Genes for Sepsis

Objective

Sepsis is one of the most common reasons for hospitalization and in-hospital mortality each year. Noncoding RNAs have been reported not only as diagnostic and prognostic indicators but also as therapeutic targets of sepsis. Herein, we used an integrative computational approach to identify miRNA-mediated ceRNA crosstalk between lncRNAs and genes in sepsis based on the “ceRNA hypothesis” and investigated prognostic roles of hub genes in sepsis.

Methods

Two good-quality gene expression datasets with more than 10 patient samples, GSE89376 and GSE95233, were employed to obtain differentially expressed lncRNAs (DElncRNAs) and genes (DEGs) in sepsis. The DElncRNA-miRNA-DEG regulatory network was constructed using a combination of DElncRNA-miRNA pairs and miRNA-DEmRNA pairs. The protein-protein interaction (PPI) network was constructed by mapping DEGs into the STRING database to identify hub genes in sepsis. The clinical and prognostic significance of hub genes was validated in 89 patients with post-traumatic sepsis.

Results

The integrative computational approach identified 311 DEGs and 19 DElncRNAs between septic patients and healthy volunteers. Results yielded 122 downDElncRNA-miRNA-downDEG networks based on two lncRNAs, HCP5, and HOTAIRM1, and 36 upDElncRNA-miRNA-upDEG network based on BASP1-AS1. The PPI network identified serum/glucocorticoid regulated kinase 1 (SGK1), arrestin beta 1 (ARRB1), and G protein-coupled receptor 183 (GPR183) as located at the core of the network, and three of them were downregulated in sepsis. SGK1, ARRB1, and GPR183 were all involved in lncRNA HCP5-based ceRNA network. The quantitative real-time PCR revealed that the patients with post-traumatic sepsis exhibited reduced relative mRNA levels of SGK1, ARRB1, and GPR183 compared to the patients without sepsis. The nonsurvivor group, according to the 28-day mortality, showed lower relative mRNA levels of SGK1, ARRB1, and GPR183 than the survivor group. We also demonstrated reduced mRNA levels of SGK1, ARRB1, and GPR183 were associated with sepsis-related death after trauma.

Conclusion

Our integrative analysis and clinical validation suggest lncRNA HCP5-based ceRNA networks with SGK1, ARRB1, and GPR183 involved were associated with the occurrence and progression of sepsis.

ARRB1 suppresses the activation of hepatic macrophages via modulating endoplasmic reticulum stress in lipopolysaccharide-induced acute liver injury

Acute liver injury (ALI) caused by multiple inflammatory responses is a monocyte-/macrophage-mediated liver injury that is associated with high morbidity and mortality. Liver macrophage activation is a vital event that triggers ALI. However, the mechanism of liver macrophage activation has not been fully elucidated. This study examined the role of β-arrestin1 (ARRB1) in wild-type (WT) and ARRB1-knockout (ARRB1-KO) mouse models of ALI induced by lipopolysaccharide (LPS), and ARRB1-KO mice exhibited more severe inflammatory injury and liver macrophage activation compared to WT mice. We found that LPS treatment reduced the expression level of ARRB1 in Raw264.7 and THP-1 cell lines, and mouse primary hepatic macrophages. Overexpression of ARRB1 in Raw264.7 and THP-1 cell lines significantly attenuated LPS-induced liver macrophage activation, such as transformation in cell morphology and enhanced expression of proinflammatory cytokines (tumor necrosis factor-α, interleukin-1β, and interleukin-6), while downregulation of ARRB1 by small interfering RNA and ARRB1 deficiency in primary hepatic macrophages both aggravated macrophage activation. Moreover, overexpression of ARRB1 suppressed LPS-induced endoplasmic reticulum (ER) stress in liver macrophages, and inhibition of ER stress impeded excessive hepatic macrophage activation induced by downregulation of ARRB1. Our data demonstrate that ARRB1 relieves LPS-induced ALI through the ER stress pathway to regulate hepatic macrophage activation and that ARRB1 may be a potential therapeutic target for ALI.

Arrestin domain containing 3 promotes Helicobacter pylori-associated gastritis by regulating protease-activated receptor 1

Arrestin domain containing 3 (ARRDC3) represents a newly discovered α-arrestin involved in obesity, inflammation, and cancer. Here, we demonstrate a proinflammation role of ARRDC3 in Helicobacter pylori–associated gastritis. Increased ARRDC3 was detected in gastric mucosa of patients and mice infected with H. pylori. ARRDC3 in gastric epithelial cells (GECs) was induced by H. pylori, regulated by ERK and PI3K-AKT pathways in a cagA-dependent manner. Human gastric ARRDC3 correlated with the severity of gastritis, and mouse ARRDC3 from non-BM–derived cells promoted gastric inflammation. This inflammation was characterized by the CXCR2-dependent influx of CD45⁺CD11b⁺Ly6C^–Ly6G⁺ neutrophils, whose migration was induced via the ARRDC3-dependent production of CXCL2 by GECs. Importantly, gastric inflammation was attenuated in Arrdc3^–/– mice but increased in protease-activated receptor 1^–/– (Par1^–/–) mice. Mechanistically, ARRDC3 in GECs directly interacted with PAR1 and negatively regulated PAR1 via ARRDC3-mediated lysosomal degradation, which abrogated the suppression of CXCL2 production and following neutrophil chemotaxis by PAR1, thereby contributing to the development of H. pylori–associated gastritis. This study identifies a regulatory network involving H. pylori, GECs, ARRDC3, PAR1, and neutrophils, which collectively exert a proinflammatory effect within the gastric microenvironment. Efforts to inhibit this ARRDC3-dependent pathway may provide valuable strategies in treating of H. pylori–associated gastritis.

A regulatory network including H. pylori, GECs, ARRDC3, PAR1, and neutrophils collectively exerts a pro-inflammatory effect within the gastric microenvironment.

β-Arrestin1 alleviates acute pancreatitis via repression of NF-κBp65 activation

BACKGROUND AND AIM

β-Arrestins (β-arrs) are regulators and mediators of G protein-coupled receptor signaling that are functionally involved in inflammation. Nuclear factor-κB p65 (NF-κBp65) activation has been observed early in the onset of pancreatitis. However, the effect of β-arrs in acute pancreatitis (AP) is unclear. The aim of this study is to investigate whether β-arrs are involved in AP through activation of NF-κBp65.

METHODS

Acute pancreatitis was induced by either caerulein injection or choline-deficient supplemented with ethionine diet (CDE). β-arr1 wild-type and β-arr1 knockout mice were used in the experiment. The survival rate was calculated in the CDE model mice. Histological and western blot analyses were performed in the caerulein model. Inflammatory mediators were detected by real-time polymerase chain reaction in the caerulein-induced AP mice. Furthermore, AR42J and PANC-1 cell lines were used to further study the effects of β-arr1 in caerulein-induced pancreatic cells.

RESULTS

β-Arr1 but not β-arr2 is significantly downregulated in caerulein-induced AP in mice. Targeted deletion of β-arr1 notably upregulated expression of the pancreatic inflammatory mediators including tumor necrosis factor α and interleukin 1β as well as interleukin 6 and aggravated AP in caerulein-induced mice. β-Arr1 deficiency increased mortality in mice with CDE-induced AP. Further, β-arr1 deficiency enhanced caerulein-induced phosphorylation of NF-κBp65 both in vivo and in vitro.

CONCLUSION

β-Arr1 alleviates AP via repression of NF-κBp65 activation, and it is a potentially therapeutic target for AP.

Poly(I:C) Priming Exacerbates Cecal Ligation and Puncture-Induced Polymicrobial Sepsis in Mice

Sepsis continues to be a major healthcare issue with one of the highest mortality rates in intensive care units. Toll-like receptors are pattern recognition receptors that are intricately involved in the pathogenesis of sepsis. TLR3 is a major receptor for double-stranded RNA and is largely associated with immunity to viral infection. In this study, we examined the role of TLR3 priming in the immunopathology of sepsis using cecal-ligation and puncture (CLP) model of sepsis in mice. Mice injected with vehicle or poly(I:C) were subjected to sham or CLP surgery and various parameters of sepsis, including mortality, inflammation, and bacterial clearance were assessed. Poly(I:C) pre-treatment significantly enhanced mortality in mice subjected to CLP. Consistent with this, inflammatory cytokines including TNFα, IL-12p40, IFNγ, and MCP-1 were enhanced both systemically and locally in the poly(I:C)-treated group compared to the vehicle control. In addition, bacterial load was significantly higher in the poly(I:C)-treated septic mice. These changes were associated with reduced macrophage activation (but not neutrophils) in the peritoneal cavity of poly(I:C) pre-treated mice compared to vehicle pre-treatment. Together our results demonstrate that poly(I:C) priming in sepsis is likely to be detrimental to the host due to effects on systemic inflammatory cytokines and bacterial clearance.

Inflammatory cytokine expression in patients with sepsis at an intensive care unit

Sepsis is a systemic inflammatory response syndrome caused by infection of bacteria, fungi and/or viruses in clinical patients. It is known that inflammatory cytokine levels have an essential role in the progression of sepsis. The present study investigated the role of inflammatory markers in human peripheral blood mononuclear cells (hPBMCs) of patients with sepsis at an intensive care unit. In addition, the plasma levels of inflammatory cytokines were compared between sepsis patients and healthy individuals. The results demonstrated that the serum levels of interleukin-1, -17 and -6, as well as tumor necrosis factor-α, were upregulated in sepsis patients. The serum levels of high mobility group box 1 and C-reactive protein were increased in sepsis patients compared with those in healthy individuals. The expression levels of nuclear factor-κB-p65 and its inhibitor IκBα, as well as the ratio of CD25⁺ cells, and the levels of neutrophil gelatinase-associated lipocalin and peptidoglycan recognition protein were higher in hPBMCs in sepsis patients compared with those in healthy individuals. It was also indicated that balance of T helper type 1/2 cytokines was also disturbed in patients with sepsis compared with that in healthy individuals. In conclusion, these results indicated that inflammation is involved in the progression of sepsis by interfering with the expression of various molecules, suggesting a potential therapeutic strategy for the treatment of sepsis patients.

G protein-coupled receptor kinase-2-deficient mice are protected from dextran sodium sulfate-induced acute colitis

G protein-coupled receptor kinase 2 (GRK2) is a serine/threonine kinase and plays a key role in different disease processes. Previously, we showed that GRK2 knockdown enhances wound healing in colonic epithelial cells. Therefore, we hypothesized that ablation of GRK2 would protect mice from dextran sodium sulfate (DSS)-induced acute colitis. To test this, we administered DSS to wild-type (GRK2^+/+) and GRK2 heterozygous (GRK^+/-) mice in their drinking water for 7 days. As predicted, GRK2^+/- mice were protected from colitis as demonstrated by decreased weight loss (20% loss in GRK2^+/+ vs. 11% loss in GRK2^+/-). lower disease activity index (GRK2^+/+ 9.1 vs GRK2^+/- 4.1), and increased colon lengths (GRK2^+/+ 4.7 cm vs GRK2^+/- 5.3 cm). To examine the mechanisms by which GRK2^+/- mice are protected from colitis, we investigated expression of inflammatory genes in the colon as well as immune cell profiles in colonic lamina propria, mesenteric lymph node, and in bone marrow. Our results did not reveal differences in immune cell profiles between the two genotypes. However, expression of inflammatory genes was significantly decreased in DSS-treated GRK2^+/- mice compared with GRK2^+/+. To understand the mechanisms, we generated myeloid-specific GRK2 knockout mice and subjected them to DSS-induced colitis. Similar to whole body GRK2 heterozygous knockout mice, myeloid-specific knockout of GRK2 was sufficient for the protection from DSS-induced colitis. Together our results indicate that deficiency of GRK2 protects mice from DSS-induced colitis and further suggests that the mechanism of this effect is likely via GRK2 regulation of inflammatory genes in the myeloid cells.

β-Arrestin1 inhibits chemotherapy-induced intestinal stem cell apoptosis and mucositis

The mechanism of chemotherapy-induced gastrointestinal (GI) syndrome (CIGIS) is still controversial, and it is unclear whether chemotherapy induces intestinal stem cell (ISC) apoptosis. β-Arrestins are regulators and mediators of G protein-coupled receptor signaling in cell apoptosis, division and growth. In this study, we aimed to investigate whether chemotherapy induces ISC apoptosis to contribute to mucositis in CIGIS and whether β-arrestin1 (β-arr1) is involved in this apoptosis. Different chemotherapeutic agents were used to generate a CIGIS model. Lgr5-EGFP-IRES-creERT2^+/− knock-in mice were used as a CIGIS model to investigate ISC apoptosis. β-arr1 knockout mice were used to determine whether β-arr1 is involved in the apoptosis in CIGIS. Intestinal histology was performed, the ISC apoptosis was analyzed and the mucosal barrier was examined. The effects of β-arr1 in apoptosis were investigated in the samples from humans and mice as well as in cell lines. Here, we demonstrate that chemotherapy induced intestinal mucositis by promoting crypt cell apoptosis, especially in Lgr5+ stem cells and Paneth cells but not in goblet cells, epithelial cells or vascular endothelial cells. Furthermore, β-arr1 deficiency exacerbated the Lgr5+ stem cell apoptosis, but not Paneth cell apoptosis, in CIGIS. In addition, the data showed that β-arr1 reduced the chemotherapy-induced Lgr5+ stem cell apoptosis by inhibiting endoplasmic reticulum stress-mediated mitochondrial apoptotic signaling. Our study indicates that β-arr1 inhibits chemotherapy-induced ISC apoptosis to alleviate intestinal mucositis in CIGIS.

Bacterial Dose-Dependent Role of G Protein-Coupled Receptor Kinase 5 in Escherichia coli-Induced Pneumonia

G protein-coupled receptor kinase 5 (GRK5) is a serine/threonine kinase previously shown to mediate polymicrobial sepsis-induced inflammation. The goal of the present study was to examine the role of GRK5 in monomicrobial pulmonary infection by using an intratracheal Escherichia coli infection model of pneumonia. We used sublethal and lethal doses of E. coli to examine the mechanistic differences between low-grade and high-grade inflammation induced by E. coli infection. With a sublethal dose of E. coli, GRK5 knockout (KO) mice exhibited higher plasma CXCL1/KC levels and enhanced lung neutrophil recruitment early after infection, and lower bacterial loads, than wild-type (WT) mice. The inflammatory response was also diminished, and resolution of inflammation advanced, in the lungs of GRK5 KO mice. In contrast to the reduced bacterial loads in GRK5 KO mice following a sublethal dose, at a lethal dose of E. coli, the bacterial burdens remained high in GRK5 KO mice relative to those in WT mice. This occurred in spite of enhanced plasma CXCL1 levels as well as neutrophil recruitment in the KO mice. But the recruited neutrophils (following high-dose infection) exhibited decreased CD11b expression and reduced reactive oxygen species production, suggesting decreased neutrophil activation or increased neutrophil exhaustion in the GRK5 KO mice. In agreement with the increased bacterial burden, KO mice showed poorer survival than WT mice following E. coli infection at a lethal dose. Overall, our data suggest that GRK5 negatively regulates CXCL1/KC levels during bacterial pneumonia but that the role of GRK5 in the clinical outcome in this model is dependent on the bacterial dose.

Multifaceted role of β-arrestins in inflammation and disease

Arrestins are intracellular scaffolding proteins known to regulate a range of biochemical processes including G protein-coupled receptor (GPCR) desensitization, signal attenuation, receptor turnover and downstream signaling cascades. Their roles in regulation of signaling network have lately been extended to receptors outside of the GPCR family, demonstrating their roles as important scaffolding proteins in various physiological processes including proliferation, differentiation and apoptosis. Recent studies have demonstrated a critical role for arrestins in immunological processes including key functions in inflammatory signaling pathways. In this review, we provide a comprehensive analysis of the different functions of the arrestin family of proteins especially related to immunity and inflammatory diseases.

Non-Hematopoietic β-Arrestin1 Confers Protection Against Experimental Colitis

β-Arrestins are multifunctional scaffolding proteins that modulate G protein-coupled receptor (GPCR)-dependent and -independent cell signaling pathways in various types of cells. We recently demonstrated that β-arrestin1 (β-arr1) deficiency strikingly attenuates dextran sodium sulfate (DSS)-induced colitis in mice. Since DSS-induced colitis is in part dependent on gut epithelial injury, we examined the role of β-arr1 in intestinal epithelial cells (IECs) using a colon epithelial cell line, SW480 cells. Surprisingly, we found that knockdown of β-arr1 in SW480 cells enhanced epithelial cell death via a caspase-3-dependent process. To understand the in vivo relevance and potential cell type-specific role of β-arr1 in colitis development, we generated bone marrow chimeras with β-arr1 deficiency in either the hematopoietic or non-hematopoietic compartment. Reconstituted chimeric mice were then subjected to DSS-induced colitis. Similar to our previous findings, β-arr1 deficiency in the hematopoietic compartment protected mice from DSS-induced colitis. However, consistent with the role of β-arr1 in epithelial apoptosis in vitro, non-hematopoietic β-arr1 deficiency led to an exacerbated colitis phenotype. To further understand signaling mechanisms, we examined the effect of β-arr1 on TNF-α-mediated NFκB and MAPK pathways. Our results demonstrate that β-arr1 has a critical role in modulating ERK, JNK and p38 MAPK pathways mediated by TNF-α in IECs. Together, our results show that β-arr1-dependent signaling in hematopoietic and non-hematopoietic cells differentially regulates colitis pathogenesis and further demonstrates that β-arr1 in epithelial cells inhibits TNF-α-induced cell death pathways.