Identification of a new RTN3 transcript, RTN3-A1, and its distribution in adult mouse brain

Nogo-B Silencing Expedites the Senescence of Platelet-Derived Growth Factor-BB-Induced Human Hepatic Stellate Cells Via Autophagy

Liver fibrosis is a severe liver pathology in response to chronic or iterative liver injury. Senescence has emerged as a protective mechanism against liver fibrosis. Nogo-B has been well established as a significant contributor to liver fibrosis. Nonetheless, researches regarding the role of Nogo-B in cell senescence during liver fibrosis are few. In platelet-derived growth factor-BB (PDGF-BB)-treated human hepatic stellate cell line LX-2, cell proliferation was assayed by CCK-8 method. Western blotting estimated the expression of Nogo-B and fibrosis markers. After Nogo-B was silenced in LX-2 cells pretreated by an autophagy activator Rapamycin and PDGF-BB, CCK-8 method was used to assess cell proliferation. Fibrosis was measured by western blotting and immunofluorescence. Cell cycle was subjected to flow cytometry analysis and cell senescence was evaluated by SA-β-gal staining. Immunofluorescence staining assessed autophagy. Nogo-B was elevated in PDGF-BB-exposed LX-2 cells. Nogo-B silencing suppressed the proliferation, fibrosis, and autophagy while induced cell cycle arrest and senescence of LX-2 cells. Additionally, pretreatment with Rapamycin partially restored the effects of Nogo-B knockdown on the autophagy, proliferation, fibrosis, cell cycle, and senescence of LX-2 cells upon exposure to PDGF-BB. Collectively, inactivation of autophagy mediated by Nogo-B deficiency might elicit protective activities against the development of liver fibrosis.

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.

Overexpression of Reticulon 3 Enhances CNS Axon Regeneration and Functional Recovery after Traumatic Injury

CNS neurons are generally incapable of regenerating their axons after injury due to several intrinsic and extrinsic factors, including the presence of axon growth inhibitory molecules. One such potent inhibitor of CNS axon regeneration is Reticulon (RTN) 4 or Nogo-A. Here, we focused on RTN3 as its contribution to CNS axon regeneration is currently unknown. We found that RTN3 expression correlated with an axon regenerative phenotype in dorsal root ganglion neurons (DRGN) after injury to the dorsal columns, a well-characterised model of spinal cord injury. Overexpression of RTN3 promoted disinhibited DRGN neurite outgrowth in vitro and dorsal column axon regeneration/sprouting and electrophysiological, sensory and locomotor functional recovery after injury in vivo. Knockdown of protrudin, however, ablated RTN3-enhanced neurite outgrowth/axon regeneration in vitro and in vivo. Moreover, overexpression of RTN3 in a second model of CNS injury, the optic nerve crush injury model, enhanced retinal ganglion cell (RGC) survival, disinhibited neurite outgrowth in vitro and survival and axon regeneration in vivo, an effect that was also dependent on protrudin. These results demonstrate that RTN3 enhances neurite outgrowth/axon regeneration in a protrudin-dependent manner after both spinal cord and optic nerve injury.

Tumor angiogenesis: causes, consequences, challenges and opportunities

Tumor vascularization occurs through several distinct biological processes, which not only vary between tumor type and anatomic location, but also occur simultaneously within the same cancer tissue. These processes are orchestrated by a range of secreted factors and signaling pathways and can involve participation of non-endothelial cells, such as progenitors or cancer stem cells. Anti-angiogenic therapies using either antibodies or tyrosine kinase inhibitors have been approved to treat several types of cancer. However, the benefit of treatment has so far been modest, some patients not responding at all and others acquiring resistance. It is becoming increasingly clear that blocking tumors from accessing the circulation is not an easy task to accomplish. Tumor vessel functionality and gene expression often differ vastly when comparing different cancer subtypes, and vessel phenotype can be markedly heterogeneous within a single tumor. Here, we summarize the current understanding of cellular and molecular mechanisms involved in tumor angiogenesis and discuss challenges and opportunities associated with vascular targeting.

Role of Endoplasmic Reticulum-Associated Proteins in Flavivirus Replication and Assembly Complexes

Flavivirus replication in host cells requires the formation of replication and assembly complexes on the cytoplasmic side of the endoplasmic reticulum (ER) membrane. These complexes consist of an ER membrane, viral proteins, and host proteins. Genome-wide investigations have identified a number of ER multiprotein complexes as vital factors for flavivirus replication. The detailed mechanisms of the role of ER complexes in flavivirus replication are still largely elusive. This review highlights the fact that the ER multiprotein complexes are crucial for the formation of flavivirus replication and assembly complexes, and the ER complexes could be considered as a target for developing successful broad-spectrum anti-flavivirus drugs.

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 αv β3 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.

Effects of altered RTN3 expression on BACE1 activity and Alzheimer's neuritic plaques

Reticulon 3 (RTN3), which is a member of the reticulon family of proteins, has a biochemical function of shaping tubular endoplasmic reticulum. RTN3 has also been found to interact with β-site amyloid precursor protein cleaving enzyme 1 (BACE1), which initiates the generation of β-amyloid peptides (Aβ) from amyloid precursor protein. Aβ is the major proteinaceous component in neuritic plaques, which constitute one of the major pathological features in brains of Alzheimer's disease (AD) patients. Mice deficient in or overexpressing RTN3 have altered amyloid deposition through effects on BACE1 expression and activity. In this review, we will summarize the current findings concerning the role of RTN3 in AD pathogenesis and demonstrate that RTN3 protein levels act as age-dependent modulators of BACE1 activity and Aβ deposition during the pathogenic progression of AD.

RTN3 Regulates the Expression Level of Chemokine Receptor CXCR4 and is Required for Migration of Primordial Germ Cells

CXCR4 is a crucial chemokine receptor that plays key roles in primordial germ cell (PGC) homing. To further characterize the CXCR4-mediated migration of PGCs, we screened CXCR4-interacting proteins using yeast two-hybrid screening. We identified reticulon3 (RTN3), a member of the reticulon family, and considered an apoptotic signal transducer, as able to interact directly with CXCR4. Furthermore, we discovered that the mRNA and protein expression levels of CXCR4 could be regulated by RTN3. We also found that RTN3 altered CXCR4 translocation and localization. Moreover, increasing the signaling of either CXCR4b or RTN3 produced similar PGC mislocalization phenotypes in zebrafish. These results suggested that RTN3 modulates PGC migration through interaction with, and regulation of, CXCR4.

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 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.

Sequencing of hippocampal and cerebellar transcriptomes provides new insights into the complexity of gene regulation in the human brain

The hippocampus and cerebellum represent anatomically and functionally distinct parts of the human brain. The RNA-Seq technique makes it possible to investigate the human transcriptome with unprecedented resolution, allowing identification of differential mRNA splicing and promoter usage on a genome-wide scale. We undertook whole-mRNA sequencing of samples from the human hippocampus and cerebellum. A bioinformatic analysis revealed distinct expression patterns of genes related to the molecular physiology of neurons and glial cells. Upregulated genes in hippocampal tissue included serpin peptidase inhibitor, clade A (SERPINA3), lymphocyte antigen 6 complex, locus H (LY6H) and transthyretin (TTR). In cerebellum, the cerebellin 3 precursor (CLBN3) and Zic family member 4 (ZIC4) genes were significantly upregulated. These changes were validated in independent donor samples by qRT-PCR. The hippocampus and the cerebellum showed striking differences in splicing patterns and promoter usage. A notable example of this was the gene for NGFI-A binding protein 2 (NAB2), which displayed tissue-specific isoforms which may affect its function as a transcriptional repressor.

RTN/Nogo in forming Alzheimer's neuritic plaques

One of the pathological hallmarks in brains of patients with Alzheimer's disease (AD) is the presence of neuritic plaques, in which amyloid deposits are surrounded by reactive gliosis and dystrophic neurites. Within neuritic plaques, reticulon 3 (RTN3), a homolog of Nogo protein, appears to regulate the formation of both amyloid deposition via negative modulation of BACE1 activity and dystrophic neurites via the formation of RTN3 aggregates. Transgenic mice over-expressing RTN3, but not the other known markers of dystrophic neurites in AD brain, spontaneously develop RTN3-immunoreactive dystrophic neurites. The presence of dystrophic neurites impairs cognition. Blocking abnormal RTN3 aggregation will increase the available RTN3 monomer and is therefore a promising therapeutic strategy for enhancing cognitive function in AD patients.

The proteome of the presynaptic active zone: from docked synaptic vesicles to adhesion molecules and maxi-channels

The presynaptic proteome controls neurotransmitter release and the short and long term structural and functional dynamics of the nerve terminal. Using a monoclonal antibody against synaptic vesicle protein 2 we immunopurified a presynaptic compartment containing the active zone with synaptic vesicles docked to the presynaptic plasma membrane as well as elements of the presynaptic cytomatrix. Individual protein bands separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were subjected to nanoscale-liquid chromatography electrospray ionization-tandem mass spectrometry. Combining this method with 2-dimensional benzyldimethyl-n-hexadecylammonium chloride/sodium dodecyl sulfate-polyacrylamide gel electrophoresis and matrix-assisted laser desorption ionization time of flight and immunodetection we identified 240 proteins comprising synaptic vesicle proteins, components of the presynaptic fusion and retrieval machinery, proteins involved in intracellular signal transduction, a large variety of adhesion molecules and proteins potentially involved in regulating the functional and structural dynamics of the pre-synapse. Four maxi-channels, three isoforms of voltage-dependent anion channels and the tweety homolog 1 were co-isolated with the docked synaptic vesicles. As revealed by in situ hybridization, tweety homolog 1 reveals a distinct expression pattern in the rodent brain. Our results add novel information to the proteome of the presynaptic active zone and suggest that in particular proteins potentially involved in the short and long term structural modulation of the mature presynaptic compartment deserve further detailed analysis.

EST-based identification of genes expressed in perch (Perca fluviatilis, L.)

Perch are promising species for freshwater aquaculture and, differently from other fish, have not yet been domesticated through artificial selection; therefore, they show a wide genetic variability that is undesirable for aquaculture. In addition to the more traditional methods of aquatic biotechnology, the most recently developed molecular biological techniques can augment the overall efficiency of aquaculture. To help these new molecular techniques find their place in the everyday management of fish farming, we should make an effort to reduce the gap in genomic resources that separates farming species from "model organisms." We performed single-pass sequencing on 1237 randomly selected clones from a perch liver cDNA expression library, 350 clones of a brain-minus-liver, and 639 clones of a liver-minus-brain subtraction library. The sequences were deposited in the NCBI Expressed Sequence Tags database (www.ncbi.nlm.nih.gov/projects/dbEST). In the three libraries we identified 108, 46, and 104 genes, respectively. EST cataloguing and profiling of perch will provide a basis for functional genomic research in this species, but will also promote studies in comparative and environmental genomics, for identifying polymorphic markers that are useful, for example, to survey the disease resistance of fish and for discovering of new molecular markers of exposure. Using these genomic resources, micro- and macroarrays can be produced that will give immediate and practical benefits in the field of aquaculture, allowing early diagnosis of the fish conditions and helping in the generation of new mechanistic data on the nature of fish responses to different farming conditions.