Different expressions of Nogo-B1 and Nogo-B2 in mouse heart microvascular endothelial cell dysfunction induced by lysophosphatidylcholine

Nogo-B promotes angiogenesis and improves cardiac repair after myocardial infarction via activating Notch1 signaling

Nogo-B (Reticulon 4B) is reportedly a regulator of angiogenesis during the development and progression of cancer. However, whether Nogo-B regulates angiogenesis and post-myocardial infarction (MI) cardiac repair remains elusive. In the present study, we aimed to explore the role and underlying mechanisms of Nogo-B in cardiac repair during MI. We observed an increased expression level of Nogo-B in the heart of mouse MI models, as well as in isolated cardiac microvascular endothelial cells (CMECs). Moreover, Nogo-B was significantly upregulated in CMECs exposed to oxygen-glucose deprivation (OGD). Nogo-B overexpression in the endothelium via cardiotropic adeno-associated virus serotype 9 (AAV9) with the mouse endothelial-specific promoter Tie2 improved heart function, reduced scar size, and increased angiogenesis. RNA-seq data indicated that Notch signaling is a deregulated pathway in isolated CMECs along the border zone of the infarct with Nogo-B overexpression. Mechanistically, Nogo-B activated Notch1 signaling and upregulated Hes1 in the MI hearts. Inhibition of Notch signaling using a specific siRNA and γ-secretase inhibitor abolished the promotive effects of Nogo-B overexpression on network formation and migration of isolated cardiac microvascular endothelial cells (CMECs). Furthermore, endothelial Notch1 heterozygous deletion inhibited Nogo-B-induced cardioprotection and angiogenesis in the MI model. Collectively, this study demonstrates that Nogo-B is a positive regulator of angiogenesis by activating the Notch signaling pathway, suggesting that Nogo-B is a novel molecular target for ischemic disease.

Nogo-B receptor modulates angiogenesis response of pulmonary artery endothelial cells through eNOS coupling

Nogo-B, a reticulon-4 isoform, modulates the motility and adhesion of vascular endothelial cells after binding to its receptor, Nogo-B receptor (NgBR). Nogo-B/NgBR pathway contributes to vascular remodeling and angiogenesis, but the role of this pathway in the angiogenesis of developing lungs remains unknown. We previously reported that angiogenesis function of pulmonary artery endothelial cells (PAECs) is impaired by increased reactive oxygen species formation in a fetal lamb model of intrauterine pulmonary hypertension (IPH). Here, we report that Nogo-B/NgBR pathway is altered in IPH, and that decreased NgBR expression contributes to impaired angiogenesis in IPH. We observed a decrease in NgBR levels in lysates of whole lung or PAECs from fetal lambs with IPH compared with controls. Overexpression of NgBR in IPH PAECs rescued the in vitro angiogenesis defects and increased the phosphorylation of both Akt and endothelial nitric oxide synthase at serine(1179) as well as the levels of both manganese superoxide dismutase and GTP cyclohydrolase-1. Consistent with the phenotype of IPH PAECs, knockdown of NgBR in control PAECs decreased the levels of nitric oxide, increased the levels of reactive oxygen species, and impaired in vitro angiogenesis. Our data demonstrate that NgBR mediates PAEC angiogenesis response through the modulation of Akt/endothelial nitric oxide synthase functions, and its decreased expression is mechanistically linked to IPH-related angiogenesis defects in the developing lungs.

Nogo-B regulates migration and contraction of airway smooth muscle cells by decreasing ARPC 2/3 and increasing MYL-9 expression

BACKGROUND

Abnormal proliferation, apoptosis, migration and contraction of airway smooth muscle (ASM) cells in airway remodeling in asthma are basically excessive repair responses to a network of inflammatory mediators such as PDGF, but the mechanisms of such responses remain unclear. Nogo-B, a member of the reticulum family 4(RTN4), is known to play a key role in arteriogenesis and tissue repair. Further studies are needed to elucidate the role of Nogo-B in airway smooth muscle abnormalities.

METHODS

A mouse model of chronic asthma was established by repeated OVA inhalation and subjected to Nogo-B expression analysis using immunohistochemistry and Western Blotting. Then, primary human bronchial smooth muscle cells (HBSMCs) were cultured in vitro and a siRNA interference was performed to knockdown the expression of Nogo-B in the cells. The effects of Nogo-B inhibition on PDGF-induced HBSMCs proliferation, migration and contraction were evaluated. Finally, a proteomic analysis was conducted to unveil the underlying mechanisms responsible for the function of Nogo-B.

RESULTS

Total Nogo-B expression was approximately 3.08-fold lower in chronic asthmatic mice compared to naïve mice, which was obvious in the smooth muscle layer of the airways. Interference of Nogo-B expression by siRNA resulted nearly 96% reduction in mRNA in cultured HBSMCs. In addition, knockdown of Nogo-B using specific siRNA significantly decreased PDGF-induced migration of HBSMCs by 2.3-fold, and increased the cellular contraction by 16% compared to negative controls, but had limited effects on PDGF-induced proliferation. Furthermore, using proteomic analysis, we demonstrate that the expression of actin related protein 2/3 complex subunit 5 (ARPC 2/3) decreased and, myosin regulatory light chain 9 isoform a (MYL-9) increased after Nogo-B knockdown.

CONCLUSIONS

These data define a novel role for Nogo-B in airway remodeling in chronic asthma. Endogenous Nogo-B, which may exert its effects through ARPC 2/3 and MYL-9, is necessary for the migration and contraction of airway smooth muscle cells.

Analysis of RTN4 3'UTR insertion/deletion polymorphisms in ventricular septal defect in a Chinese Han population

Congenital heart disease is the most common type of birth defect and the leading cause of infant mortality in the first year of life. Ventricular septal defect (VSD) is one of the most general congenital heart defects and is a defect in the wall between the right and left ventricles of the heart. The pathogenesis of VSD has been extensively investigated for many years, but it remains uncertain. To determine whether reticulon 4 gene (RTN4) 3'UTR insertion/deletion polymorphisms are associated with VSD, we genotyped the TATC and CAA insertion/deletion polymorphisms of RTN4 by polymerase chain reaction-polyacrylamide gel electrophoresis in 151 VSD patients and 308 unrelated healthy subjects in a Chinese Han population. No significant differences in 3'UTR TATC and CAA insertion/deletion polymorphisms genotype and allele frequencies were observed between the VSD and controls. These data indicate that, for the first time, RTN4 3'UTR insertion/deletion polymorphisms may not appear to play a role in the susceptibility of VSD in Chinese Han population.

Localization of an axon growth inhibitory molecule Nogo and its receptor in the spinal cord of mouse embryos

The localization of an axon growth inhibitory molecule Nogo and its receptor (NgR) was investigated in the mouse spinal cord during prenatal development of the commissural pathway. Using the antibody N18, an intense signal for Nogo was localized largely on radial glia processes that are immunoreactive to RC2 antibody during the major period of commissural axon growth and was gradually reduced towards the end of gestation. The glial processes ramified extensively in the ventral funiculus and resided within the interfascicular space between the longitudinally projecting axons. Axonal localization of Nogo was observed on the premidline segment of commissural axons and on axons in the dorsal and ventral funiculi, but only at the earliest stage of pathway development. Nogo signals were initially weak on the glial processes during the period of axon crossing in the floor plate but was elevated when the decussation is finished. NgR was expressed on the commissural axons; the expression pattern is spatially regulated, being low in the premidline and midline courses but is upregulated when the axons leave the floor plate. These expression patterns raise the possibilities that the glial-specific form of Nogo may be involved in the guidance of commissural axons by (i) preventing recrossing of axons across the midline through an upregulation of axonal NgR and (ii) partitioning axons in the ventral funiculus into longitudinal fascicles.

Identification of Nogo as a novel indicator of heart failure

Numerous genetically engineered animal models of heart failure (HF) exhibit multiple characteristics of human HF, including aberrant beta-adrenergic signaling. Several of these HF models can be rescued by cardiac-targeted expression of the Gbetagamma inhibitory carboxy-terminus of the beta-adrenergic receptor kinase (betaARKct). We recently reported microarray analysis of gene expression in multiple animal models of HF and their betaARKct rescue, where we identified gene expression patterns distinct and predictive of HF and rescue. We have further investigated the muscle LIM protein knockout model of HF (MLP-/-), which closely parallels human dilated cardiomyopathy disease progression and aberrant beta-adrenergic signaling, and their betaARKct rescue. A group of known and novel genes was identified and validated by quantitative real-time PCR whose expression levels predicted phenotype in both the larger HF group and in the MLP-/- subset. One of these novel genes is herein identified as Nogo, a protein widely studied in the nervous system, where it plays a role in regeneration. Nogo expression is altered in HF and normalized with rescue, in an isoform-specific manner, using left ventricular tissue harvested from both animal and human subjects. To investigate cell type-specific expression of Nogo in the heart, immunofluorescence and confocal microscopy were utilized. Nogo expression appears to be most clearly associated with cardiac fibroblasts. To our knowledge, this is the first report to demonstrate the relationship between Nogo expression and HF, including cell-type specificity, in both mouse and human HF and phenotypic rescue.

Regulation of Nogo-B expression in the lesion of aortic aneurysms

1. Our previous study showed that Nogo-B was highly expressed in endothelial cells and downregulated in endothelial cells following induction by lysophosphatidylcholine, which contributed to atherosclerotic lesions. However, the role of Nogo-B in the development of aortic aneurysms remains unclear. 2. In the present study, segments of thoracic aortic aneurysms (TAA) and adjacent normal thoracic aortic tissues (NTA) without aneurysmal changes were obtained from 31 patients undergoing graft surgery. The mRNA and protein expression levels of Nogo-B were measured with semiquantitative reverse transcription-polymerase chain reaction, western blotting and immunohistochemistry. 3. The results demonstrate that Nogo-B mRNA expression levels in TAA lesions decreased to 45% compared with levels in NTA lesions and that protein levels in TAA decreased to 35%. Tissue Nogo immunohistochemical staining in aortic specimens suggested the involvement of Nogo in neovascularization and smooth muscle cell proliferation. The weaker brown staining of endothelial cells in TAA lesions suggested the lower expression of Nogo-B in TAA lesions. 4. These results demonstrate that Nogo-B mRNA and protein expression are downregulated in TAA lesions. It is concluded that the reduction of Nogo-B protein expression in TAA lesions is closely correlated to the formation of aneurysm and that Nogo-B may play a protective role in the pathological process of aneurysms.