Nogo-B is associated with cytoskeletal structures in human monocyte-derived macrophages

Protective effects of Nogo-B deficiency in NAFLD mice and its multiomics analysis of gut microbiology and metabolism

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a prevalent chronic liver ailment that can lead to serious conditions such as cirrhosis and hepatocellular carcinoma. Hepatic Nogo-B regulates glucose and lipid metabolism, and its inhibition has been shown to be protective against metabolic syndrome. Increasing evidence suggests that imbalances in the gut microbiota (GM) and lipid metabolism disorders are significant contributors to NAFLD progression. Nevertheless, it is not yet known whether Nogo-B can affect NAFLD by influencing the gut microbiota and metabolites. Hence, the aim of the present study was to characterize this process and explore its possible underlying mechanisms.

METHODS

A NAFLD model was constructed by administering a high-fat diet (HFD) to Nogo-B-/- and WT mice from the same litter, and body weight was measured weekly in each group. The glucose tolerance test (GTT) and insulin tolerance test (ITT) were performed to assess blood glucose levels. At the end of the 12-week period, samples of serum, liver, and intestinal contents were collected and used for serum biochemical marker and inflammatory factor detection; pathology evaluation; and gut microbiome and metabolomics analysis. Spearman's correlation analysis was performed to determine possible correlations between differential gut microbiota and differential serum metabolites between groups.

RESULTS

Nogo-B deficiency attenuated the effects of the HFD, including weight gain, liver weight gain, impaired glucose tolerance, hepatic steatosis, elevated serum lipid biochemicals levels, and liver function. Nogo-B deficiency suppressed M1 polarization and promoted M2 polarization, thus inhibiting inflammatory responses. Furthermore, Nogo-B-/--HFD-fed mice presented increased gut microbiota richness and diversity, decreased Firmicutes/Bacteroidota (F/B) ratios, and altered serum metabolites compared with those of WT-HFD-fed mice. During analysis, several differential gut microbiota, including Lachnoclostridium, Harryflintia, Odoribacter, UCG-009, and unclassified_f_Butyricoccaceae, were screened between groups. These microbiota were found to be positively correlated with upregulated purine metabolism and bile acid metabolites in Nogo-B deficiency, while they were negatively correlated with downregulated corticosterone and tricarboxylic acid cyclic metabolites in Nogo-B deficiency.

CONCLUSION

Nogo-B deficiency delayed NAFLD progression, as demonstrated by reduced hepatocellular lipid accumulation, attenuated inflammation and liver injury, and ameliorated gut microbiota dysbiosis and metabolic disorders. Importantly, Odoribacter was strongly positively correlated with ALB and taurodeoxycholic acid, suggesting that it played a considerable role in the influence of Nogo-B on the progression of NAFLD, a specific feature of NAFLD in Nogo-B-/- mice. The regulation of bile acid metabolism by the gut microbiota may be a potential target for Nogo-B deficiency to ameliorate NAFLD.

A Novel Role of Nogo Proteins: Regulating Macrophages in Inflammatory Disease

Nogo proteins, also known as Reticulon-4, have been identified as myelin-derived inhibitors of neurite outgrowth in the central nervous system (CNS). There are three Nogo variants, Nogo-A, Nogo-B and Nogo-C. Recent studies have shown that Nogo-A/B is abundant in macrophages and may have a wider effect on inflammation. In this review, we focus mainly on the possible roles of Nogo-A/B on polarization and recruitment of macrophages and their involvement in a variety of inflammatory diseases. We then discuss the Nogo receptor1 (NgR1), a common receptor for Nogo proteins that is also abundant in microglia/macrophage in the CNS. Interaction of Nogo and NgR1 in microglia/macrophage may affect the adhesion and polarization of macrophages that are involved in multiple neurodegenerative diseases, including Alzheimer's disease and multiple sclerosis. Overall, this review provides insights into the roles of Nogo proteins in regulating macrophage functions and suggests that, potentially, Nogo proteins maybe a new target in the treatment of inflammatory diseases.

Interoperability of RTN1A in dendrite dynamics and immune functions in human Langerhans cells

Skin is an active immune organ where professional antigen-presenting cells such as epidermal Langerhans cells (LCs) link innate and adaptive immune responses. While Reticulon 1A (RTN1A) was recently identified in LCs and dendritic cells in cutaneous and lymphoid tissues of humans and mice, its function is still unclear. Here, we studied the involvement of this protein in cytoskeletal remodeling and immune responses toward pathogens by stimulation of Toll-like receptors (TLRs) in resident LCs (rLCs) and emigrated LCs (eLCs) in human epidermis ex vivo and in a transgenic THP-1 RTN1A+ cell line. Hampering RTN1A functionality through an inhibitory antibody induced significant dendrite retraction of rLCs and inhibited their emigration. Similarly, expression of RTN1A in THP-1 cells significantly altered their morphology, enhanced aggregation potential, and inhibited the Ca2+ flux. Differentiated THP-1 RTN1A+ macrophages exhibited long cell protrusions and a larger cell body size in comparison to wild-type cells. Further, stimulation of epidermal sheets with bacterial lipoproteins (TLR1/2 and TLR2 agonists) and single-stranded RNA (TLR7 agonist) resulted in the formation of substantial clusters of rLCs and a significant decrease of RTN1A expression in eLCs. Together, our data indicate involvement of RTN1A in dendrite dynamics and structural plasticity of primary LCs. Moreover, we discovered a relation between activation of TLRs, clustering of LCs, and downregulation of RTN1A within the epidermis, thus indicating an important role of RTN1A in LC residency and maintaining tissue homeostasis.

A proximity-labeling proteomic approach to investigate invadopodia molecular landscape in breast cancer cells

Metastatic progression is the leading cause of mortality in breast cancer. Invasive tumor cells develop invadopodia to travel through basement membranes and the interstitial matrix. Substantial efforts have been made to characterize invadopodia molecular composition. However, their full molecular identity is still missing due to the difficulty in isolating them. To fill this gap, we developed a non-hypothesis driven proteomic approach based on the BioID proximity biotinylation technology, using the invadopodia-specific protein Tks5α fused to the promiscuous biotin ligase BirA* as bait. In invasive breast cancer cells, Tks5α fusion concentrated to invadopodia and selectively biotinylated invadopodia components, in contrast to a fusion which lacked the membrane-targeting PX domain (Tks5β). Biotinylated proteins were isolated by affinity capture and identified by mass spectrometry. We identified known invadopodia components, revealing the pertinence of our strategy. Furthermore, we observed that Tks5 newly identified close neighbors belonged to a biologically relevant network centered on actin cytoskeleton organization. Analysis of Tks5β interactome demonstrated that some partners bound Tks5 before its recruitment to invadopodia. Thus, the present strategy allowed us to identify novel Tks5 partners that were not identified by traditional approaches and could help get a more comprehensive picture of invadopodia molecular landscape.

Overexpression of Circulating Soluble Nogo-B Improves Diabetic Kidney Disease by Protecting the Vasculature

Damage to the vasculature is the primary mechanism driving chronic diabetic microvascular complications such as diabetic nephropathy, which manifests as albuminuria. Therefore, treatments that protect the diabetic vasculature have significant therapeutic potential. Soluble neurite outgrowth inhibitor-B (sNogo-B) is a circulating N-terminus isoform of full-length Nogo-B, which plays a key role in vascular remodeling following injury. However, there is currently no information on the role of sNogo-B in the context of diabetic nephropathy. We demonstrate that overexpression of sNogo-B in the circulation ameliorates diabetic kidney disease by reducing albuminuria, hyperfiltration, and abnormal angiogenesis and protecting glomerular capillary structure. Systemic sNogo-B overexpression in diabetic mice also associates with dampening vascular endothelial growth factor-A signaling and reducing endothelial nitric oxide synthase, AKT, and GSK3β phosphorylation. Furthermore, sNogo-B prevented the impairment of tube formation, which occurred when human endothelial cells were exposed to sera from patients with diabetic kidney disease. Collectively, these studies provide the first evidence that sNogo-B protects the vasculature in diabetes and may represent a novel therapeutic target for diabetic vascular complications.

RTN4 Knockdown Dysregulates the AKT Pathway, Destabilizes the Cytoskeleton, and Enhances Paclitaxel-Induced Cytotoxicity in Cancers

Reticulon-4 (RTN4), commonly known as a neurite outgrowth inhibitor (Nogo), is emerging as an important player in human cancers. Clinically, we found lower RTN4 expression in patient-derived tumors was associated with significantly better survival in lung, breast, cervical, and renal cancer patients. To identify the role of RTN4 in cancer biology, we performed mass spectrometry-based quantitative proteomic analysis on cancer cells following RTN4 knockdown and found its link with pro-survival as well as cytoskeleton-related processes. Subsequent mechanistic investigations revealed that RTN4 regulates lipid homeostasis, AKT signaling, and cytoskeleton modulation. In particular, downregulation of RTN4 reduced sphingomyelin synthesis and impaired plasma membrane localization of AKT, wherein AKT phosphorylation, involved in many cancers, was significantly reduced without any comparable effect on AKT-related upstream kinases, in a sphingolipid-dependent manner. Furthermore, knockdown of RTN4 retarded proliferation of cancer cells in vitro as well as tumor xenografts in mice. Finally, RTN4 knockdown affected tubulin stability and promoted higher cytotoxic effects with chemotherapeutic paclitaxel in cancer cells both in vitro and in vivo. In summary, RTN4 is involved in carcinogenesis and represents a molecular candidate that may be targeted to achieve desired antitumor effects in clinics.

The Reticulum-Associated Protein RTN1A Specifically Identifies Human Dendritic Cells

RTN1 is an endoplasmic reticulum-associated protein that was initially identified in neuronal tissues. Here we show that the main isoform RTN1A is a marker for dendritic cells. In the skin, HLA-DR⁺CD1a^highCD207⁺CD11c^weak Langerhans cells were the only cells in the epidermis, and HLA-DR⁺CD11c⁺ dendritic cells were the main cells in the dermis, expressing this protein. RTN1A⁺ dendritic cells were also found in gingiva, trachea, tonsil, thymus, and peripheral blood. During differentiation of MUTZ-3 cells into Langerhans cells, expression of RTN1A mRNA and protein preceded established Langerhans cell markers CD1a and CD207, and RTN1A protein partially co-localized with the endoplasmic reticulum marker protein disulfide isomerase. In line with this observation, we found that RTN1A was expressed by around 80% of Langerhans cell precursors in human embryonic skin. Our findings show that RTN1A is a marker for cells of the dendritic lineage, including Langerhans cells and dermal dendritic cells. This unexpected finding will serve as a starting point for the elucidation of the, until now, elusive functional roles of RTN1A in both the immune and the nervous system.

Identification of reliable biomarkers of human papillomavirus 16 methylation in cervical lesions based on integration status using high-resolution melting analysis

BACKGROUND

The dynamic methylation of human papillomavirus (HPV) 16 DNA is thought to be associated with the progression of cervical lesions. Previous studies that did not consider the physical status of HPV 16 may have incorrectly mapped HPV 16 methylomes. In order to identify reliable biomarkers for squamous cervical cancer (SCC), we comprehensively evaluated the methylation of HPV 16 depending on the integration incidence of each sample.

METHODS

Based on the integration status of 115 HPV 16-infected patients (50 SCC, 30 high-grade squamous intraepithelial lesion [HSIL], and 35 low-grade squamous intraepithelial lesion [LSIL]) and HPV 16-infected Caski cell lines by PCR detection of integrated papillomavirus sequences, we designed a series of primers that would not be influenced by breakpoints for a high-resolution melting (HRM) PCR method to detect the genome methylation.

RESULTS

A few regions with recurrent interruptions were identified in E1, E2/E4, L1, and L2 despite scattering of breakpoints throughout all eight genes of HPV 16. Frequent integration sites often occurred concomitantly with methylated CpG sites. The HRM PCR method showed 100% agreement with pyrosequencing when 3% was set as the cutoff value. A panel of CpG sites such as nt5606, nt5609, nt5615, and nt5378 can be combined in reweighing calculations to distinguish SCC from HSIL and LSIL patients which have high sensitivity and specificity (88% and 92.31%, respectively).

CONCLUSIONS

Our research shows that combination of CpG sites nt5606, nt5609, nt5615, and nt5378 can be used as potential diagnosis biomarkers for SCC, and the HRM PCR method is suitable for clinical methylation analysis.

NOGO-A/RTN4A and NOGO-B/RTN4B are simultaneously expressed in epithelial, fibroblast and neuronal cells and maintain ER morphology

Reticulons (RTNs) are a large family of membrane associated proteins with various functions. NOGO-A/RTN4A has a well-known function in limiting neurite outgrowth and restricting the plasticity of the mammalian central nervous system. On the other hand, Reticulon 4 proteins were shown to be involved in forming and maintaining endoplasmic reticulum (ER) tubules. Using comparative transcriptome analysis and qPCR, we show here that NOGO-B/RTN4B and NOGO-A/RTN4A are simultaneously expressed in cultured epithelial, fibroblast and neuronal cells. Electron tomography combined with immunolabelling reveal that both isoforms localize preferably to curved membranes on ER tubules and sheet edges. Morphological analysis of cells with manipulated levels of NOGO-B/RTN4B revealed that it is required for maintenance of normal ER shape; over-expression changes the sheet/tubule balance strongly towards tubules and causes the deformation of the cell shape while depletion of the protein induces formation of large peripheral ER sheets.

Impact of RTN3 deficiency on expression of BACE1 and amyloid deposition

Reticulon 3 (RTN3) has previously been shown to interact with BACE1 and negatively regulate BACE1 activity. To what extent RTN3 deficiency affects BACE1 activity is an intriguing question. In this study, we aimed to address this by generating RTN3-null mice. Mice with complete deficiency of RTN3 grow normally and have no obviously discernible phenotypes. Morphological analyses of RTN3-null mice showed no significant alterations in cellular structure, although RTN3 is recognized as a protein contributing to the shaping of tubular endoplasmic reticulum. Biochemical analysis revealed that RTN3 deficiency increased protein levels of BACE1. This elevation of BACE1 levels correlated with enhanced processing of amyloid precursor protein at the β-secretase site. We also demonstrated that RTN3 deficiency in Alzheimer's mouse models facilitates amyloid deposition, further supporting an in vivo role of RTN3 in the regulation of BACE1 activity. Since it has been shown that RTN3 monomer is reduced in brains of Alzheimer's patients, our results suggest that long-lasting reduction of RTN3 levels has adverse effects on BACE1 activity and may contribute to Alzheimer's pathogenesis.

The Nogo-B-PirB axis controls macrophage-mediated vascular remodeling

Objective

Nogo-B mediates vascular protection and facilitates monocyte- and macrophage-dependent vascular remodeling. PirB is an alternate receptor for Nogo-B, but a role for the Nogo-PirB axis within the vascular system has not been previously reported. We examined whether Nogo-B or PirB play a role in regulating macrophage-mediated vascular remodeling and hypothesized that endothelial Nogo-B regulates vein graft macrophage infiltration via its alternate receptor PirB.

Methods

Vein grafts were performed using Nogo and PirB wild type and knockout mice. Human vein grafts were similarly analyzed. The hindlimb ischemia model was performed in PirB wild type and knockout mice. Accompanying in vitro work included isolation of macrophages from PirB wild type and knockout mice.

Results

Increased Nogo-B and PirB mRNA transcripts and protein expression were observed within mouse and human vein grafts. Both Nogo knockout and PirB knockout vein grafts showed increased wall thickness and increased numbers of F4/80-positive macrophages. Macrophages derived from PirB knockout mice had increased adhesion to fibronectin, increased EC-specific binding, and increased numbers of mRNA transcripts of M2 markers as well as MMP3 and MMP9. PirB knockout vein grafts had increased active MMP9 compared to wild type vein grafts. PirB knockout mice had increased recovery from hindlimb ischemia and increased macrophage infiltration compared to wild type mice.

Conclusions

Vein graft adaptation shows increased expression of both Nogo-B and PirB. Loss of PirB, or its endothelial ligand Nogo-B, results in increased inflammatory cell infiltration and vein graft wall thickening. These findings suggest that PirB regulates macrophage activity in vein grafts and that Nogo-B in the vein graft limits macrophage infiltration and vein graft thickening. PirB may play a more general role in regulating macrophage responses to vascular injury. Macrophage inhibition via Nogo-PirB interactions may be an important mechanism regulating vein graft adaptation to the arterial circulation.

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.

Nogo-receptors NgR1 and NgR2 do not mediate regulation of CD4 T helper responses and CNS repair in experimental autoimmune encephalomyelitis

Myelin-associated inhibition of axonal regrowth after injury is considered one important factor that contributes to regeneration failure in the adult central nervous system (CNS). Blocking strategies targeting this pathway have been successfully applied in several nerve injury models, including experimental autoimmune encephalomyelitis (EAE), suggesting myelin-associated inhibitors (MAIs) and functionally related molecules as targets to enhance regeneration in multiple sclerosis. NgR1 and NgR2 were identified as interaction partners for the myelin proteins Nogo-A, MAG and OMgp and are probably mediating their growth-inhibitory effects on axons, although the in vivo relevance of this pathway is currently under debate. Recently, alternative functions of MAIs and NgRs in the regulation of immune cell migration and T cell differentiation have been described. Whether and to what extent NgR1 and NgR2 are contributing to Nogo and MAG-related inhibition of neuroregeneration or immunomodulation during EAE is currently unknown. Here we show that genetic deletion of both receptors does not promote functional recovery during EAE and that NgR1 and NgR2-mediated signals play a minor role in the development of CNS inflammation. Induction of EAE in Ngr1/2-double mutant mice resulted in indifferent disease course and tissue damage when compared to WT controls. Further, the development of encephalitogenic CD4⁺ Th1 and Th17 responses was unchanged. However, we observed a slightly increased leukocyte infiltration into the CNS in the absence of NgR1 and NgR2, indicating that NgRs might be involved in the regulation of immune cell migration in the CNS. Our study demonstrates the urgent need for a more detailed knowledge on the multifunctional roles of ligands and receptors involved in CNS regeneration failure.