Reticulon 4B (Nogo-B) facilitates hepatocyte proliferation and liver regeneration in mice

Intestinal Nogo-B reduces GLP1 levels by binding to proglucagon on the endoplasmic reticulum to inhibit PCSK1 cleavage

Glucagon-like peptide 1 (GLP1), which is mainly processed and cleaved from proglucagon in enteroendocrine cells (EECs) of the intestinal tract, acts on the GLP1 receptor in pancreatic cells to stimulate insulin secretion and to inhibit glucagon secretion. However, GLP1 processing is not fully understood. Here, we show that reticulon 4B (Nogo-B), an endoplasmic reticulum (ER)-resident protein, interacts with the major proglucagon fragment of proglucagon to retain proglucagon on the ER, thereby inhibiting PCSK1-mediated cleavage of proglucagon in the Golgi. Intestinal Nogo-B knockout in male type 2 diabetes mellitus (T2DM) mice increases GLP1 and insulin levels and decreases glucagon levels, thereby alleviating pancreatic injury and insulin resistance. Finally, we identify aberrantly elevated Nogo-B expression and inhibited proglucagon cleavage in EECs from diabetic patients. Our study reveals the subcellular regulatory processes involving Nogo-B during GLP1 production and suggests intestinal Nogo-B as a potential therapeutic target for T2DM.

6-Methyl flavone inhibits Nogo-B expression and improves high fructose diet-induced liver injury in mice

Excessive fructose consumption increases hepatic de novo lipogenesis, resulting in cellular stress, inflammation and liver injury. Nogo-B is a resident protein of the endoplasmic reticulum that regulates its structure and function. Hepatic Nogo-B is a key protein in glycolipid metabolism, and inhibition of Nogo-B has protective effects against metabolic syndrome, thus small molecules that inhibit Nogo-B have therapeutic benefits for glycolipid metabolism disorders. In this study we tested 14 flavones/isoflavones in hepatocytes using dual luciferase reporter system based on the Nogo-B transcriptional response system, and found that 6-methyl flavone (6-MF) exerted the strongest inhibition on Nogo-B expression in hepatocytes with an IC50 value of 15.85 μM. Administration of 6-MF (50 mg· kg-1 ·d-1, i.g. for 3 weeks) significantly improved insulin resistance along with ameliorated liver injury and hypertriglyceridemia in high fructose diet-fed mice. In HepG2 cells cultured in a media containing an FA-fructose mixture, 6-MF (15 μM) significantly inhibited lipid synthesis, oxidative stress and inflammatory responses. Furthermore, we revealed that 6-MF inhibited Nogo-B/ChREBP-mediated fatty acid synthesis and reduced lipid accumulation in hepatocytes by restoring cellular autophagy and promoting fatty acid oxidation via the AMPKα-mTOR pathway. Thus, 6-MF may serve as a potential Nogo-B inhibitor to treat metabolic syndrome caused by glycolipid metabolism dysregulation.

Reticulons 1 and 3 are essential for axonal growth and synaptic maintenance associated with intellectual development

Reticulon (RTN) proteins are a family of proteins biochemically identified for shaping tubular endoplasmic reticulum, a subcellular structure important for vesicular transport and cell-to-cell communication. In our recent study of mice with knockout of both reticulon 1 (Rtn1) and Rtn3, we discovered that Rtn1-/-;Rtn3-/- (brief as R1R3dKO) mice exhibited neonatal lethality, despite the fact that mice deficient in either RTN1 or RTN3 alone exhibit no discernible phenotypes. This has been the first case to find early lethality in animals with deletion of partial members of RTN proteins. The complete penetrance for neonatal lethality can be attributed to multiple defects including the impaired neuromuscular junction found in the diaphragm. We also observed significantly impaired axonal growth in a regional-specific manner, detected by immunohistochemical staining with antibodies to neurofilament light chain and neurofilament medium chain. Ultrastructural examination by electron microscopy revealed a significant reduction in synaptic active zone length in the hippocampus. Mechanistic exploration by unbiased proteomic assays revealed reduction of proteins such as FMR1, Staufen2, Cyfip1, Cullin-4B and PDE2a, which are known components in the fragile X mental retardation pathway. Together, our results reveal that RTN1 and RTN3 are required to orchestrate neurofilament organization and intact synaptic structure of the central nervous system.

Nogo-B inhibition restricts ulcerative colitis via inhibiting p68/miR-155 signaling pathway

BACKGROUND & AIMS

Ulcerative colitis (UC) is a main type of inflammatory bowel diseases which spreads globally during the westernization of lifestyle over the past few decades. However, the cause of UC is still not fully understood. We aimed to disclose the role of Nogo-B in the development of UC.

METHODS

Nogo-deficiency (Nogo^-/-) and wild-type male mice were treated with dextran sodium sulfate (DSS) to conduct a UC model, followed by determination of colon and serum inflammatory cytokines level. RAW264.7, THP1 and NCM460 cells were used to determine macrophage inflammation as well as proliferation and migration of NCM460 cells under Nogo-B or miR-155 intervention.

RESULTS

Nogo deficiency significantly reduced DSS-induced weight loss, colon length and weight reduction, and inflammatory cells accumulation in the intestinal villus, while increased the expression of tight junctions (TJs) proteins (Zonula occludens-1, Occludin) and adherent junctions (AJs) proteins (E-cadherin, α-catenin), implying that Nogo deficiency attenuated DSS-induced UC. Mechanistically, Nogo-B deficiency reduced TNFα, IL-1β and IL-6 levels in the colon, serum, RAW264.7 cells and THP1-derived macrophages. Furthermore, we identified that Nogo-B inhibition can reduce the maturation of miR-155, which is essential for Nogo-B-affected inflammatory cytokines expression. Interestingly, we determined that Nogo-B and p68 can interact with each other to promote the expression and activation of Nogo-B and p68, thus facilitating miR-155 maturation to induce macrophage inflammation. Blocking p68 inhibited Nogo-B, miR-155, TNFα, IL-1β and IL-6 expression. Moreover, the culture medium collected from Nogo-B overexpressed macrophages can inhibit enterocytes NCM460 cells proliferation and migration.

CONCLUSION

We disclose that Nogo deficiency reduced DSS-induced UC via inhibiting p68-miR-155-activated inflammation. Our results indicate that Nogo-B inhibition serves as a new potential therapeutic candidate for the prevention and treatment of UC.

Increased RTN3 phenocopies nonalcoholic fatty liver disease by inhibiting the AMPK-IDH2 pathway

Reticulon 3 (RTN3), an endoplasmic reticulum protein, is crucial in neurodegenerative and kidney diseases. However, the role of RTN3 in liver tissues has not been described. Here, we employed public datasets, patients, and several animal models to explore the role of RTN3 in nonalcoholic fatty liver disease (NAFLD). The underlying mechanisms were studied in primary hepatocytes and L02 cells in vitro. We found an increased expression of RTN3 in NAFLD patients, high-fat diet mice, and oxidized low-density lipoprotein-treated L02 cells. The RTN3 transgenic mice exhibited the phenotypes of fatty liver and lipid accumulation. Single-cell RNA sequencing analysis indicated that increased RTN3 might induce mitochondrial dysfunction. We further showed this in primary hepatocytes, the L02 cell line, and the Caenorhabditis elegans strain. Mechanistically, RTN3 regulated these events through its interactions with glucose-regulated protein 78 (GRP78), which further inhibited the adenosine 5 monophosphate-activated protein kinase (AMPK)-isocitrate dehydrogenase 2 (IDH2) pathway. In the end, knockout of RTN3 relieved fatty liver and mitochondrial dysfunction. Our study indicated that RTN3 was important in NAFLD and lipid catabolism and that an increase in RTN3 in the liver might be a risk factor for nonalcoholic steatohepatitis and NAFLD.

O-GlcNAcylation of SPOP promotes carcinogenesis in hepatocellular carcinoma

Aberrantly elevated O-GlcNAcylation level is commonly observed in human cancer patients, and has been proposed as a potential therapeutic target. Speckle-type POZ protein (SPOP), an important substrate adaptor of cullin3-RING ubiquitin ligase, plays a key role in the initiation and development of various cancers. However, the regulatory mechanisms governing SPOP and its function during hepatocellular carcinoma (HCC) progression remain unclear. Here, we show that, in HCC, SPOP is highly O-GlcNAcylated by O-GlcNAc transferase (OGT) at Ser96. In normal liver cells, the SPOP protein mainly localizes in the cytoplasm and mediates the ubiquitination of the oncoprotein neurite outgrowth inhibitor-B (Nogo-B) (also known as reticulon 4 B) by recognizing its N-terminal SPOP-binding consensus (SBC) motifs. However, O-GlcNAcylation of SPOP at Ser96 increases the nuclear positioning of SPOP in hepatoma cells, alleviating the ubiquitination of the Nogo-B protein, thereby promoting HCC progression in vitro and in vivo. In addition, ablation of O-GlcNAcylation by an S96A mutation increased the cytoplasmic localization of SPOP, thereby inhibiting the Nogo-B/c-FLIP cascade and HCC progression. Our findings reveal a novel post-translational modification of SPOP and identify a novel SPOP substrate, Nogo-B, in HCC. Intervention with the hyper O-GlcNAcylation of SPOP may provide a novel strategy for HCC treatment.

Role of serum Nogo-B as a biomarker for diagnosis of chronic liver diseases and its severity

Background

Nogo-B is one of the members of the reticulon family. Nogo-B influences the proliferation of the hepatic stellate cells inducing liver fibrotic changes. We aimed at measuring the serum levels of Nogo-B in patients with chronic liver disease (CLD) with different etiologies. Ninety subjects were included, 18 of them were normal healthy individuals and 72 had liver disease (fibrosis/cirrhosis) with different etiologies: post-hepatitis C infection, post-hepatitis B infection, NASH, and autoimmune hepatitis. Serum Nogo-B was assessed using ELISA. Patients were subdivided according to the Child-Pugh score into 3 groups: group 1—Child A (24 patients); group 2—Child B (24 patients); and group 3—Child C (24 patients).

Results

Serum Nogo-B levels were found to be significantly higher in patients (1477.92 ± 1113.50) when compared with healthy control (301.28 ± 180.87) (p < 0.001). There was a statistically significant difference in serum Nogo-B level between the three sub-groups of patients (p < 0.001). A positive correlation was found between serum Nogo-B and MELD score (r = 0.46, p-value < 0.001). However, there was no correlation found between Nogo-B and FIB-4 index or APRI score. There was a significant positive correlation between serum Nogo-B level and coagulation profile and serum bilirubin. An inverse correlation was found between serum Nogo-B with serum albumin. A ROC curve was done to examine the validity of Nogo-B in the diagnosis of liver cirrhosis, and the area under the curve was found to be 0.979, a cutoff value of 600 with a sensitivity of 97.2% and a specificity of 94.4% (p-value < 0.001).

Conclusion

Nogo-B had a high value in the identification of patients with any severity of CLD. There is a highly significant correlation between Nogo-B and the synthetic function of the liver; it could be used as a measure of hepatic functional reserve.

Upregulation of Nogo-B by hypoxia inducible factor-1 and activator protein-1 in hepatocellular carcinoma

Nogo-B is an important regulator of tumor angiogenesis. Expression of Nogo-B is remarkably upregulated in multiple tumor types, especially hepatocellular carcinoma (HCC). Here, we show the transcriptional regulation mechanisms of Nogo-B in liver cancer. In response to hypoxia, expression of Nogo-B significantly increased in HCC tissues and cells. The distal hypoxia-responsive element in the promoter was essential for transcriptional activation of Nogo-B under hypoxic conditions, which is the specific site for hypoxia inducible factor-1α (HIF-1α) binding. In addition, Nogo-B expression was associated with c-Fos expression in HCC tissues. Nogo-B expression was induced by c-Fos, yet inhibited by a dominant negative mutant A-Fos. Deletion and mutation analysis of the predicted activator protein-1 binding sites revealed that functional element mediated the induction of Nogo-B promoter activity, which was confirmed by ChIP. These results indicate that HIF-1α and c-Fos induce the expression of Nogo-B depending on tumor microenvironments, such as hypoxia and low levels of nutrients, and play a role in upregulation of Nogo-B in tumor angiogenesis.

Nogo-B promotes epithelial-mesenchymal transition in lung fibrosis via PERK branch of the endoplasmic reticulum stress pathway

Background

Idiopathic pulmonary fibrosis (IPF) is a fatal chronic pulmonary fibrosis disease and pathological mechanisms of fibrogenesis in IPF are still to be elucidated. Here, we investigated the potential role of Nogo-B in pulmonary fibrogenesis.

Methods

A mouse model of pulmonary fibrosis was established by intratracheal injection of bleomycin (BLM). Lung epithelial cells MLE-12 and TC-1 JHU-1 were cultured for TGF-β treatment. The extent of lung fibrosis was evaluated using hematoxylin and eosin (HE) staining and Masson staining in model mice and Nogo-B knockout mice. The protein levels of Nogo-B, endoplasmic reticulum stress (ERS) sensors including PERK, IRE1α, ATF6 and epithelial-mesenchymal transition (EMT) markers including E-cadherin and N-cadherin, vimentin were assayed by Western blotting respectively after Nogo-B knockdown or overexpression with lentivirus. Enzyme-linked immunosorbent assay (ELISA) was used to evaluate cytokine levels of TGF-β, TNF-α, IL-1β, IL-6 and IL-10 in bronchoalveolar lavage fluid (BALF).

Results

Nogo-B expression was up-regulated in lung tissues of fibrosis model mice and alveolar epithelial cells. Nogo-B knockdown significantly attenuated lung fibrogenesis, downregulated the levels of inflammatory cytokines, inhibited EMT as well as decreased the level of phosphor-PERK/PERK but not the levels of phosphor-IRE1α/IRE1α and c-ATF6. Additionally, a potential efficacy of PERK blockade was demonstrated in improving the extent of lung fibrosis in model mice.

Conclusions

This study discovered that involvement of Nogo-B in pulmonary fibrogenesis was associated with the PERK branch of ERS pathway and EMT. Nogo-B could be considered as a potential therapeutic target for the treatment of IPF.

Reduced Nogo expression inhibits diet-induced metabolic disorders by regulating ChREBP and insulin activity

BACKGROUND & AIMS

Chronic overconsumption of a high-carbohydrate diet leads to steatosis and its associated metabolic disorder and, eventually, to non-alcoholic fatty liver disease. Carbohydrate-responsive element binding protein (ChREBP) and insulin regulate de novo lipogenesis from glucose. Herein, we studied the effect of reticulon-4 (Nogo) expression on diet-induced metabolic disorders in mice.

METHODS

Nogo-deficient (Nogo^-/-) and littermate control [wild-type (WT)] mice were fed a high-glucose or high-fructose diet (HGD/HFrD) to induce metabolic disorders. The effects of Nogo small interfering (si) RNA (siRNA) on HFrD-induced metabolic disorders were investigated in C57BL/6J mice.

RESULTS

HGD/HFrD induced steatosis and its associated metabolic disorders in WT mice by activating ChREBP and impairing insulin sensitivity. They also activated Nogo-B expression, which in turn inhibited insulin activity. In response to HGD/HFrD feeding, Nogo deficiency enhanced insulin sensitivity and energy metabolism to reduce the expression of ChREBP and lipogenic molecules, activated AMP-activated catalytic subunit α, peroxisome proliferator activated receptor α and fibroblast growth factor 21, and reduced endoplasmic reticulum (ER) stress and inflammation, thereby blocking HGD/HFrD-induced hepatic lipid accumulation, insulin resistance and other metabolic disorders. Injection of Nogo siRNA protected C57BL/6J mice against HFrD-induced metabolic disorders by ameliorating insulin sensitivity, ChREBP activity, ER stress and inflammation.

CONCLUSIONS

Our study identified Nogo as an important mediator of insulin sensitivity and ChREBP activity. Reduction of Nogo expression is a potential strategy for the treatment of high-carbohydrate diet-induced metabolic complications.

LAY SUMMARY

Nogo deficiency blocks high-carbohydrate diet-induced glucose intolerance and insulin resistance, while increasing glucose/lipid utilisation and energy expenditure. Thus, reduction of Nogo expression protects against high-carbohydrate diet-induced body-weight gain, hepatic lipid accumulation and the associated metabolic disorders, indicating that approaches inhibiting Nogo expression can be applied for the treatment of diseases associated with metabolic disorders.

Nogo-B is a key mediator of hepatic ischemia and reperfusion injury

Nogo-B is an endoplasmic reticulum-residential protein with distinctive functions in different diseases. However, it remains unclear the role of Nogo-B in liver sterile inflammatory injury. This study aims to elucidate the functions and mechanisms in liver ischemia and reperfusion injury (IRI). The Nogo-B expression and liver function were analyzed in biopsy/serum specimens from 36 patients undergoing ischemia-related hepatectomy and in a mouse model of liver IRI. Human specimens were harvested prior to ischemia and post-reperfusion. The Nogo-B knockout (Nogo-B^KO) and myeloid-specific Nogo-B knockout (Nogo-B^MKO) mice were used to analyze the function and mechanism of Nogo-B in a mouse model of liver IRI. In human specimens, the Nogo-B expression was positively correlated with higher levels of serum transaminase (sALT) and severe histopathological injury at one day post-hepatectomy. Moreover, Nogo-B is mainly expressed on macrophages in normal and ischemic liver tissues from human and mice. Unlike in controls, the Nogo-B^KO or Nogo-B^MKO livers was protected against IRI, with reduced reactive oxygen species (ROS) production and liver inflammation in ischemic livers. In parallel in vitro studies, Nogo-B deficiency reduced M1 macrophage polarization and inhibited proinflammatory cytokines (TNF-α, IL-6, MCP-1 and iNOS) in response to LPS or HMGB-1 stimulation. Mechanistic studies showed that Nogo-B bound to MST1/2, increased MST1/2, LAST1, and YAP phosphorylation, leading to reduced YAP activity. Interestingly, disruption of macrophage YAP abolished Nogo-B deficiency-mediated cytoprotective effects in vitro and in vivo. Thus, YAP is crucial for the regulation of macrophage Nogo-B-triggered liver inflammation. Nogo-B promotes macrophage-related innate inflammation and contributes to IR-induced liver injury by activating the MST-mediated Hippo/YAP pathway, which provides a potential therapeutic target for clinical management in liver IRI.

Nogo-B fosters HCC progression by enhancing Yap/Taz-mediated tumor-associated macrophages M2 polarization

Tumor-associated macrophages (TAMs) and their M2-type extremely promote tumor angiogenesis, invasion and metastasis, including hepatocellular carcinoma (HCC). Nogo-B is expressed in most tissues and participates in macrophage polarization. However, whether Nogo-B is involved in the polarization and the effects of TAMs has been unclear. The expression of Nogo-B in TAMs of HCC patients is significantly increased, which correlated with the poor prognosis of the patients with HCC. Coincidentally, HCC conditioned medium (HCM) facilitated Nogo-B expression and the M2 phenotype of macrophages. Nogo-B knockdown Nogo-B significantly suppressed the M2-type polarization of macrophages and inhibited HCC cells proliferation both in vivo and in vitro. Furthermore, interference of Nogo-B facilitates macrophage-mediated apoptosis of tumor cells. Nogo-B meaningfully enhanced IL4-stimulated the alternative activation of macrophages as well as expression of the transcriptional regulators Yes-associated protein (Yap)/transcriptional coactivator with PDZ-binding motif (Taz). An inhibitor of Yap, Verteporfin, could block Nogo-B-Yap/Taz-mediated macrophages M2 polarization. Nogo-B expression in macrophages facilitates tumor-associated macrophages M2 polarization and protumoral effects of TAMs in HCC. Targeting Nogo-B/Yap/Taz in macrophages could provide a new therapeutic strategy in HCC therapy.

Rosiglitazone alleviates intrahepatic cholestasis induced by α-naphthylisothiocyanate in mice: The role of circulating 15-deoxy-Δ12,14 -PGJ2 and Nogo

BACKGROUND AND PURPOSE

Intrahepatic cholestasis is mainly caused by dysfunction of bile secretion and has limited effective treatment. Rosiglitazone is a synthetic agonist of PPARγ, whose endogenous agonist is 15-deoxy-Δ^12,14 -PGJ₂ (15d-PGJ₂ ). Reticulon 4B (Nogo-B) is the detectable Nogo protein family member in the liver and secreted into circulation. Here, we determined if rosiglitazone can alleviate intrahepatic cholestasis in mice.

EXPERIMENTAL APPROACH

Wild-type, hepatocyte-specific PPARγ or Nogo-B knockout mice received intragastric administration of α-naphthylisothiocyanate (ANIT) and/or rosiglitazone, followed by determination of intrahepatic cholestasis and the involved mechanisms. Serum samples from primary biliary cholangitis (PBC) patients and non-PBC controls were analysed for cholestasis-related parameters.

KEY RESULTS

Rosiglitazone prevented wild type, but not hepatocyte-specific PPARγ deficient mice from developing ANIT-induced intrahepatic cholestasis by increasing expression of bile homeostatic proteins, reducing hepatic necrosis, and correcting abnormal serum parameters and enterohepatic circulation of bile. Nogo-B knockout provided protection similar to that of rosiglitazone treatment. ANIT-induced intrahepatic cholestasis decreased 15d-PGJ₂ but increased Nogo-B in serum, and both were corrected by rosiglitazone. Nogo-B deficiency in the liver increased 15d-PGJ₂ production, thereby activating expression of PPARγ and bile homeostatic proteins. Rosiglitazone and Nogo-B deficiency also alleviated cholestasis-associated dyslipidemia. In addition, rosiglitazone reduced symptoms of established intrahepatic cholestasis in mice. In serum from PBC patients, the decreased 15d-PGJ₂ and increased Nogo-B levels were significantly correlated with classical cholestatic markers.

CONCLUSIONS AND IMPLICATIONS

Levels of 15d-PGJ₂ and Nogo are important biomarkers for intrahepatic cholestasis. Synthetic agonists of PPARγ could be used for treatment of intrahepatic cholestasis and cholestasis-associated dyslipidemia.

Identification of Nogo-B as a new molecular target of peroxisome proliferator-activated receptor gamma

Nonalcoholic fatty liver disease (NAFLD) is a fast-growing chronic liver disease worldwide which can lead to liver cirrhosis. Peroxisome proliferator-activated receptor γ (PPARγ), a ligand-activated transcription factor, plays an important role in lipogenesis. Increased Nogo-B expression can be determined in the liver of cirrhosis patients. However, the effect of PPARγ activation on hepatic Nogo-B expression remains unknown. In this study, we found PPARγ activation by rosiglitazone or dephosphorylation increased Nogo-B expression at mRNA and protein levels in HepG2 cells and mouse primary hepatocytes. Furthermore, we identified a PPARγ response element (PPRE) in Nogo-B promoter and found PPARγ enhanced Nogo-B transcription in a PPRE-dependent manner. ChIP assay further confirms rosiglitazone enhanced the binding of PPARγ to Nogo-B promoter. Using a liver specific PPARγ deficient mice, we determined the critical role of PPARγ expression in regulating hepatic Nogo-B expression. Increased glucose and palmitate in culture medium activated Nogo-B and PPARγ expression in mouse primary hepatocytes, and corresponding, high-fat diet (HFD) induced fatty liver associated with increased hepatic Nogo-B and PPARγ expression in mice. Similarly, serum Nogo-B levels in patients with NAFLD were increased. However, rosiglitazone treatment reduced HFD-induced fatty liver and Nogo-B expression. In summary, our study identifies Nogo-B as a new molecular target of PPARγ, and suggests increased Nogo-B might be a potential indicator for NAFLD.

Transplantation of HUVECs with genetically modified Nogo-B accelerates wound-healing in nude mice

Wound repair is an intractable problem in clinic, with limited treatment options. Previous studies have demonstrated the therapeutic potential of Nogo-B in tissue repairs. However, the therapeutic effect of Nogo-B in HUVEC is still unknown. In this study, we examined the benefit of genetically modified Human Umbilical Vein Endothelial Cells (HUVECs) and found that down regulation of Nogo-B significantly promoted secretion of growth factors involving in wound healing and greatly boosted the proliferation, migration of fibroblasts and epithelial cells. Moreover, using an excisional wound splinting model, we showed that injection of exogenous HUVEC-siNogo-B around the wound significantly enhanced angiogenesis and wound healing in nude mice. Thus, our data suggests that genetically modified HUVECs support microenvironment suitable for wound healing and systemically demonstrates the beneficial effect of HUVECs in wound healing.

Nogo-B promotes tumor angiogenesis and provides a potential therapeutic target in hepatocellular carcinoma

Tumor angiogenesis is one of the hallmarks of cancer as well as an attractive target for cancer therapy. Characterization of novel pathways that act in parallel with the VEGF/VEGFR axis to promote tumor angiogenesis may provide insights into novel anti‐angiogenic therapeutic targets. We found that the expression level of Nogo‐B is positively correlated with tumor vessel density in hepatocellular carcinoma (HCC). While Nogo‐B depletion inhibited tumor angiogenesis, Nogo‐B overexpression promoted tumor angiogenesis in a tumor xenograft subcutaneous model of the human HCC cell line. Mechanically, Nogo‐B regulates tumor angiogenesis based on its association with integrin α_vβ₃ and activation of focal adhesion kinase. Moreover, Nogo‐B antibody successfully abolished the function of Nogo‐B in tumor angiogenesis in vitro and in vivo. Collectively, our results strongly suggest that Nogo‐B is an important tumor angiogenic factor and blocking Nogo‐B selectively inhibits tumor angiogenesis.

Nogo-B (Reticulon-4B) functions as a negative regulator of the apoptotic pathway through the interaction with c-FLIP in colorectal cancer cells

Nogo-B is a member of the Nogo/Reticulon-4 family and has been reported to be an inducer of apoptosis in certain types of cancer cells. However, the role of Nogo-B in human cancer remains less understood. Here, we demonstrated the functions of Nogo-B in colorectal cancer cells. In clinical colorectal cancer specimens, Nogo-B was obviously overexpressed, as determined by immunohistochemistry; and Western blot analysis showed its expression level to be significantly up-regulated. Furthermore, knockdown of Nogo-B in two colorectal cancer cell lines, SW480 and DLD-1, by transfection with si-RNA (siR) resulted in significantly reduced cell viability and a dramatic increase in apoptosis with insistent overexpression of cleaved caspase-8 and cleaved PARP. The transfection with Nogo-B plasmid cancelled that apoptosis induced by siRNogoB in SW480 cells. Besides, combinatory treatment with siR-Nogo-B/staurosporine (STS) or siR-Nogo-B/Fas ligand (FasL) synergistically reduced cell viability and increased the expression of apoptotic signaling proteins in colorectal cancer cells. These results strongly support our contention that Nogo-B most likely played an oncogenic role in colorectal cancer cells, mainly by negatively regulating the extrinsic apoptotic pathway in them. Finally, we revealed that suppression of Nogo-B caused down-regulation of c-FLIP, known as a major anti-apoptotic protein, and activation of caspase-8 in the death receptor pathway. Interaction between Nogo-B and c-FLIP was shown by immunoprecipitation and immunofluorescence studies. In conclusion, Nogo-B was shown to play an important negative role in apoptotic signaling through its interaction with c-FLIP in colorectal cancer cells, and may thus become a novel therapeutic target for colorectal cancer.

The Inhibition of Indoleamine 2,3-Dioxygenase Accelerates Early Liver Regeneration in Mice After Partial Hepatectomy

BACKGROUND AND AIM

The inflammatory response accelerates early liver regeneration after liver injury and resection. Recent studies have demonstrated that indoleamine 2,3-dioxygenase-1 (IDO1) suppresses the activation of inflammatory cells and induces immune tolerance. In this study, we examined the role of IDO1 in liver regeneration after partial hepatectomy (PHx).

METHODS

WT or IDO1-knockout (IDO1-KO) mice received 70% PHx. The liver-body weight ratio after PHx was measured and hepatocyte growth was assessed by immunostaining. The expression of cell cycle genes and pro-inflammatory cytokines in the liver was analyzed by quantitative RT-PCR. In addition, 1-methyl-DL-tryptophan (1-MT), which is an IDO1 inhibitory agent, was given to WT mice and the liver-body weight ratio was measured after PHx.

RESULTS

The liver-body weight ratio was significantly increased in IDO1-KO mice compared with that in WT mice after PHx. More Ki-67-positive cells were present in IDO1-KO mice than in WT mice after PHx. The expression of cell cycle genes (cyclin D1, cyclin E) and pro-inflammatory cytokines (IL-1β, TNF-α and IL-6) was up-regulated in the remnant liver of IDO1-KO mice compared with WT mice. Moreover, treatment with 1-MT promoted liver regeneration.

CONCLUSION

IDO1 deficiency promoted early liver regeneration after PHx, indicating that IDO1 suppresses the production of inflammatory cytokines and subsequently inhibits hepatocyte proliferation during liver regeneration.

Knockout of the Nogo-B Gene Attenuates Tumor Growth and Metastasis in Hepatocellular Carcinoma

Human hepatocellular carcinoma (HCC) is a malignant cancer. It is a challenge to develop anti-HCC drugs due to HCC's extreme aggressiveness and with the sensitivity of the liver to show severe adverse effects. More importantly, the precise mechanisms causing HCC pathogenicity are not known. Our previous study disclosed Nogo-B as a reticulon 4 (Rtn4) family member. In the present study, we first identified that Nogo-B played a critical role in HCC progression. We found, via in vitro and in vivo assays, that Nogo-B was expressed aberrantly in primary HCC tumor tissues and immortal HCC cells but was relatively scarce in the normal liver tissues or cells. Nogo-B knockout, via the CRISPR-Cas9 technique, resulted in significant suppression of HCC cell proliferation and tumor growth. Next-generation sequencing analysis showed that Nogo-B knockout have effects on interleukin-6 (IL-6) signaling pathway. Furthermore, we observed that IL-6 induced phosphorylation of STAT3 (pSTAT3) in wild-type HCC cells, but Nogo-B knockout could reduce IL-6-induced increase of pSTAT3, supporting that Nogo-B affects HCC tumor progression possibly via regulating the IL-6/STAT3 signaling pathway. In conclusion, Nogo-B is expressed aberrantly in HCCs and plays an oncogenic role. These findings support that Nogo-B may be a novel anti-HCC therapeutic target.

An endoplasmic reticulum protein, Nogo-B, facilitates alcoholic liver disease through regulation of kupffer cell polarization

Nogo-B (Reticulon 4B) is an endoplasmic reticulum (ER) resident protein that regulates ER structure and function. Because ER stress is known to induce M2 macrophage polarization, we examined whether Nogo-B regulates M1/M2 polarization of Kupffer cells and alters the pathogenesis of alcoholic liver disease (ALD). M1 and M2 phenotypes were assessed in relation to Nogo-B expression and disease severity in liver specimens from ALD patients (NCT01875211). Liver specimens from wild-type (WT) and Nogo-B knockout (KO) mice fed a control or Lieber-DeCarli ethanol liquid diet (5% ethanol) for 6 weeks were analyzed for liver injury and steatosis. Kupffer cells isolated from WT and Nogo-B KO mice were assessed for M1 and M2 activation. A significant positive correlation was observed between Nogo-B positive Kupffer cells and disease severity in ALD patients (n = 30, r = 0.66, P = 0.048). Furthermore, Nogo-B-positive Kupffer cells were correlated with M1 activation (inducible nitric oxide synthase) (r = 0.50, P = 0.05) and negatively with markers of M2 status (CD163) (r = -0.48, P = 0.07) in these patients. WT mice exhibited significantly increased liver injury (P < 0.05) and higher hepatic triglyceride levels (P < 0.01) compared with Nogo-B KO mice in response to chronic ethanol feeding. Nogo-B in Kupffer cells promoted M1 polarization, whereas absence of Nogo-B increased ER stress and M2 polarization in Kupffer cells.

CONCLUSION

Nogo-B is permissive of M1 polarization of Kupffer cells, thereby accentuating liver injury in ALD in humans and mice. Nogo-B in Kupffer cells may represent a new therapeutic target for ALD. (Hepatology 2017;65:1720-1734).

Dissecting the role of epidermal growth factor receptor catalytic activity during liver regeneration and hepatocarcinogenesis

Different data support a role for the epidermal growth factor receptor (EGFR) pathway during liver regeneration and hepatocarcinogenesis. However, important issues, such as the precise mechanisms mediating its actions and the unique versus redundant functions, have not been fully defined. Here, we present a novel transgenic mouse model expressing a hepatocyte-specific truncated form of human EGFR, which acts as negative dominant mutant (ΔEGFR) and allows definition of its tyrosine kinase-dependent functions. Results indicate a critical role for EGFR catalytic activity during the early stages of liver regeneration. Thus, after two-thirds partial hepatectomy, ΔEGFR livers displayed lower and delayed proliferation and lower activation of proliferative signals, which correlated with overactivation of the transforming growth factor-β pathway. Altered regenerative response was associated with amplification of cytostatic effects of transforming growth factor-β through induction of cell cycle negative regulators. Interestingly, lipid synthesis was severely inhibited in ΔEGFR livers after partial hepatectomy, revealing a new function for EGFR kinase activity as a lipid metabolism regulator in regenerating hepatocytes. In spite of these profound alterations, ΔEGFR livers were able to recover liver mass by overactivating compensatory signals, such as c-Met. Our results also indicate that EGFR catalytic activity is critical in the early preneoplastic stages of the liver because ΔEGFR mice showed a delay in the appearance of diethyl-nitrosamine-induced tumors, which correlated with decreased proliferation and delay in the diethyl-nitrosamine-induced inflammatory process.

CONCLUSION

These studies demonstrate that EGFR catalytic activity is critical during the initial phases of both liver regeneration and carcinogenesis and provide key mechanistic insights into how this kinase acts to regulate liver pathophysiology. (Hepatology 2016;63:604-619).

Down-Regulation of Nogo-B Expression as a Newly Identified Feature of Intrahepatic Cholangiocarcinoma

Nogo-B, located in the endoplasmic reticulum, is an isoform belonging to the reticulon protein family, which is expressed specifically in cholangiocytes and non-parenchymal cells in the liver. Nogo-B expression is down-regulated with the progression of liver fibrosis, but its distinct function in liver malignancies has not been fully clarified. We have hypothesized that Nogo-B expression may be altered in intrahepatic cholangiocarcinoma (ICC), a relatively rare type of primary liver cancer with highly malignant behavior. The present study aimed to investigate the relationship between Nogo-B expression, assessed by immunohistochemical staining, and clinicopathological factors and prognosis in 34 ICC patients. Positive expression was observed in 19 (56%) of 34 ICC specimens: 6 patients (18%) with positivity levels of 1+ (positive cells in 10-50% of cancer cells) and 13 patients (38%) with 2+ (positive cells over 50%). Importantly, the remaining 15 patients (44%) were categorized as negative expression (Nogo-B-positive cells, less than 10%). Conversely, the mass-forming type of ICC tended to express Nogo-B with the degree of 2+ positivity, compared to the periductal infiltration type (p = 0.064), and the mass-forming type showed a better 5-year survival rate (66% vs. 5%) after hepatectomy (p < 0.05). However, the degree of positivity was not associated with tumor relapse rate, disease-free and overall survival, although each of the periductal infiltration type, intrahepatic metastasis, larger tumor size, and lower microvessel counts was associated with lower survival rates. We propose that Nogo-B expression is down-regulated in ICC, the implication of which, however, remains to be investigated.

PI-88 inhibits postoperative recurrence of hepatocellular carcinoma via disrupting the surge of heparanase after liver resection

Phosphomannopentaose sulfate (PI-88), an effective inhibitor of heparanase (HPSE), exhibited anti-recurrence and anti-metastasis activity in preliminary clinical trials of hepatocellular carcinoma (HCC); however, the underlying mechanisms remain uncertain. Our aim was to reveal the mechanism by which PI-88 inhibits recurrence and intrahepatic metastasis. A tissue microarray containing samples from 352 HCC patients was used to determine HPSE expression. We performed enzyme-linked immunosorbent assay (ELISA) to detect plasma levels of HPSE in 40 HCC patients. We also used quantitative polymerase chain reaction, western blot analysis, and immunohistochemical staining to assess HPSE expression of HCC cell lines and tissues. The in vitro effects of PI-88 were examined by cell proliferation and migration assays. In vivo PI-88 activity was assessed using murine orthotopic HCC models. Intratumoral HPSE was an independent prognostic marker for postsurgical overall survival (P = 0.001) and time to recurrence (P < 0.001) of HCC patients with hepatectomy. Elevated levels of HPSE were detected both in postsurgical plasma of HCC patients and an orthotopic mouse model after hepatectomy. PI-88 inhibited tumor recurrence and metastasis after liver resection in the mouse model. In vitro expression of HPSE was up-regulated by overexpression of early growth response 1 (EGR1), which is induced after hepatectomy. Up-regulation of HPSE enhanced the sensitivity of HCC cells to PI-88 and the inhibitive effect of PI-88 on cell proliferation and migration. Our data show that PI-88 effectively inhibits postoperative recurrence and intrahepatic metastasis of HCC, providing an experimental basis for the clinical application of PI-88 in HCC patients who have undergone hepatectomy.

Nogo-B protects mice against lipopolysaccharide-induced acute lung injury

Nogo-B, a member of the reticulon 4 protein family, plays a critical role in tissue repair and acute inflammation. Its role in acute lung injury (ALI) remains unclear. Here, we assessed the function of Nogo-B during tissue injury in a lipopolysaccharide (LPS)-induced ALI mouse model. We found that pulmonary Nogo-B was significantly repressed after LPS instillation in C57BL/6 mice. Over-expression of pulmonary Nogo-B using an adenovirus vector carrying the Nogo-B-RFP-3flag gene (Ad-Nogo-B) significantly prolonged the survival of mice challenged with a lethal dose of LPS. The Ad-Nogo-B-treated mice also had less severe lung injury, less alveolar protein exudation, and a higher number of macrophages but less neutrophil infiltration compared with Ad-RFP-treated mice. Interestingly, microarray analysis showed that the Ad-Nogo-B-treated mice had different gene expression profiles compared with the controls and the prominent expression of genes related to wound healing and the humoral immune response after LPS induction. Of the 49 differently expressed genes, we found that the expression of PTX3 was significantly up-regulated following Nogo-B over-expression as observed in lung tissues and RAW264.7 cells. In conclusion, Nogo-B plays a protective role against LPS-induced ALI, and this effect might be exerted through the modulation of alveolar macrophage recruitment and PTX3 production.

In vitro culture of isolated primary hepatocytes and stem cell-derived hepatocyte-like cells for liver regeneration

Various liver diseases result in terminal hepatic failure, and liver transplantation, cell transplantation and artificial liver support systems are emerging as effective therapies for severe hepatic disease. However, all of these treatments are limited by organ or cell resources, so developing a sufficient number of functional hepatocytes for liver regeneration is a priority. Liver regeneration is a complex process regulated by growth factors (GFs), cytokines, transcription factors (TFs), hormones, oxidative stress products, metabolic networks, and microRNA. It is well-known that the function of isolated primary hepatocytes is hard to maintain; when cultured in vitro, these cells readily undergo dedifferentiation, causing them to lose hepatocyte function. For this reason, most studies focus on inducing stem cells, such as embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), hepatic progenitor cells (HPCs), and mesenchymal stem cells (MSCs), to differentiate into hepatocyte-like cells (HLCs) in vitro. In this review, we mainly focus on the nature of the liver regeneration process and discuss how to maintain and enhance in vitro hepatic function of isolated primary hepatocytes or stem cell-derived HLCs for liver regeneration. In this way, hepatocytes or HLCs may be applied for clinical use for the treatment of terminal liver diseases and may prolong the survival time of patients in the near future.

Loss of α1,6-fucosyltransferase suppressed liver regeneration: implication of core fucose in the regulation of growth factor receptor-mediated cellular signaling

Core fucosylation is an important post-translational modification, which is catalyzed by α1,6-fucosyltransferase (Fut8). Increased expression of Fut8 has been shown in diverse carcinomas including hepatocarcinoma. In this study, we investigated the role of Fut8 expression in liver regeneration by using the 70% partial hepatectomy (PH) model, and found that Fut8 is also critical for the regeneration of liver. Interestingly, we show that the Fut8 activities were significantly increased in the beginning of PH (~4d), but returned to the basal level in the late stage of PH. Lacking Fut8 led to delayed liver recovery in mice. This retardation mainly resulted from suppressed hepatocyte proliferation, as supported not only by a decreased phosphorylation level of epidermal growth factor (EGF) receptor and hepatocyte growth factor (HGF) receptor in the liver of Fut8^−/− mice in vivo, but by the reduced response to exogenous EGF and HGF of the primary hepatocytes isolated from the Fut8^−/− mice. Furthermore, an administration of L-fucose, which can increase GDP-fucose synthesis through a salvage pathway, significantly rescued the delayed liver regeneration of Fut8^+/− mice. Overall, our study provides the first direct evidence for the involvement of Fut8 in liver regeneration.

Nogo-B: A potential indicator for hepatic cirrhosis and regulator in hepatic stellate cell activation

AIM

To evaluate plasma Nogo-B levels in liver cirrhotic patients and declare a novel molecular basis by which Nogo-B modulates hepatic stellate cell (HSC) activation.

METHODS

Plasma Nogo-B levels from liver cirrhotic patients were detected by enzyme-linked immunosorbent assay. Rat primary HSC were culture activated or stimulated with transforming growth factor (TGF)-β. Activated HSC were transfected for 48 h with Nogo-B shRNA to inhibit Nogo-B expression. Gene expressions of Nogo-B, α-smooth muscle actin (SMA), collagen type I, TGF-β, endoplasmic reticulum (ER) stress key molecules, including C/EBP homologous protein (CHOP), glucose-regulated protein 78 (GRP78), activating transcription factor (ATF)4, ATF6, X-box binding protein 1 (Xbp-1) and calnexin, and the marker of autophagy beclin 1, were detected by quantitative reverse transcription polymerase chain reaction. The protein expressions of Nogo-B, α-SMA, collagen type I, CHOP, GRP78 and the marker of autophagy LC3B were evaluated by western blot.

RESULTS

Liver cirrhotic patients showed a much higher level of plasma Nogo-B compared with the healthy controls. Nogo-B expression and ER stress could be induced during the process of cultured HSC activation. TGF-β treatment increased Nogo-B expression time- and dose-dependently. Knockdown of Nogo-B in HSC reduced the activation of HSC. After Nogo-B gene knockdown, there was a decline of expression of ER stress markers and autophagic markers. Agonist or antagonist of ER stress could regulate autophagy level.

CONCLUSION

Circulating Nogo-B may be an effective indicator for liver cirrhosis. Nogo-B inhibition could diminish HSC activation, in which alleviating ER stress may be one of the mechanisms, suggesting a potential approach to interference Nogo-B in liver fibrosis.

Suppression of autophagy during liver regeneration impairs energy charge and hepatocyte senescence in mice

Autophagy is a homeostatic mechanism that regulates protein and organelle turnover and uses the amino acids from degraded proteins to produce adenosine 5'-triphosphate (ATP). We investigated the activity of autophagy-associated pathways in liver regeneration after partial hepatectomy (PHx) in liver-specific autophagy-related gene 5 (Atg5) knockout (KO) mice. Liver regeneration was severely impaired by 70% PHx, with a reduction in postoperative mitosis, but a compensating increase in hepatocyte size. PHx induced intracellular adenosine triphosphate and β-oxidation reduction as well as injured cellular mitochondria. Furthermore, PHx in Atg5 KO mice enhanced hepatic accumulation of p62 and ubiquitinated proteins. These results indicated that reorganization of intracellular proteins and organelles during autophagy was impaired in the regenerating liver of these mice. Up-regulation of p21 was associated with hepatocyte senescence, senescence-associated β-galactosidase expression, irreversible growth arrest, and secretion of senescence-associated molecules, including interleukin (IL)-6 and IL-8.

CONCLUSION

These findings indicate that autophagy plays a critical role in liver regeneration and in the preservation of cellular quality, preventing hepatocytes from becoming fully senescent and hypertrophic.

The role of reticulons in neurodegenerative diseases

Reticulons (RTNs) are a group of membrane-associated proteins mainly responsible for shaping the tubular endoplasmic reticulum network, membrane trafficking, inhibition of axonal growth, and apoptosis. These proteins share a common sequence feature, the reticulon homology domain, which consists of paired hydrophobic stretches that are believed to induce membrane curvature by acting as a wedge in bilayer membranes. RTNs are ubiquitously expressed in all tissues, but each RTN member exhibits a unique expression pattern that prefers certain tissues or even cell types. Recently, accumulated evidence has suggested additional and unexpected roles for RTNs, including those on DNA binding, autophagy, and several inflammatory-related functions. These manifold actions of RTNs account for their ever-growing recognition of their involvement in neurodegenerative diseases like Alzheimer's disease, amyotrophic lateral sclerosis, multiple sclerosis, as well as hereditary spastic paraplegia. This review summarizes the latest discoveries on RTNs in human pathophysiology, and the engagement of these in neurodegeneration, along with the implications of these findings for a better understanding of the molecular events triggered by RTNs and their potential exploitation as next-generation therapeutics.