Astrocyte-to-microglia communication via Sema4B-Plexin-B2 modulates injury-induced reactivity of microglia.

After central nervous system injury, a rapid cellular and molecular response is induced. This response can be both beneficial and detrimental to neuronal survival in the first few days and increases the risk for neurodegeneration if persistent. Semaphorin4B (Sema4B), a transmembrane protein primarily expressed by cortical astrocytes, has been shown to play a role in neuronal cell death following injury. Our study shows that after cortical stab wound injury, cytokine expression is attenuated in Sema4B-/- mice, and microglia/macrophage reactivity is altered. In vitro, Sema4B enhances the reactivity of microglia following injury, suggesting astrocytic Sema4B functions as a ligand. Moreover, injury-induced microglia reactivity is attenuated in the presence of Sema4B-/- astrocytes compared to Sema4B+/- astrocytes. In vitro experiments indicate that Plexin-B2 is the Sema4B receptor on microglia. Consistent with this, in microglia/macrophage-specific Plexin-B2-/- mice, similar to Sema4B-/- mice, microglial/macrophage reactivity and neuronal cell death are attenuated after cortical injury. Finally, in Sema4B/Plexin-B2 double heterozygous mice, microglial/macrophage reactivity is also reduced after injury, supporting the idea that both Sema4B and Plexin-B2 are part of the same signaling pathway. Taken together, we propose a model in which following injury, astrocytic Sema4B enhances the response of microglia/macrophages via Plexin-B2, leading to increased reactivity.

Effects of the SEMA4B gene on hexavalent chromium [Cr(VI)]-induced malignant transformation of human bronchial epithelial cells.

Our previous study identified the potential of SEMA4B methylation level as a biomarker for hexavalent chromium [Cr(VI)] exposure. This study aimed to investigate the role of the SEMA4B gene in Cr(VI)-mediated malignant transformation of human bronchial epithelial (BEAS-2B) cells. In our population survey of workers, the geometric mean [95% confidence intervals (CIs)] of Cr in blood was 3.80 (0.42, 26.56) µg/L. Following treatment with various doses of Cr(VI), it was found that 0.5 µM had negligible effects on the cell viability of BEAS-2B cells. The expression of SEMA4B was observed to decrease in BEAS-2B cells after 7 days of treatment with 0.5 µM Cr(VI), and this downregulation continued with increasing passages of Cr(VI) treatment. Chronic exposure to 0.5 µM Cr(VI) enhanced the anchorage-independent growth ability of BEAS-2B cells. Furthermore, the use of a methylation inhibitor suppressed the Cr(VI)-mediated anchorage-independent growth in BEAS-2B cells. Considering that Cr levels exceeding 0.5 µM can be found in human blood due to occupational exposure, the results suggested a potential carcinogenic risk associated with occupational Cr(VI) exposure through the promotion of malignant transformation. The in vitro study further demonstrated that Cr(VI) exposure might inhibit the expression of the SEMA4B gene to promote the malignant transformation of BEAS-2B cells.

Semaphorin 4B is an ADAM17-cleaved adipokine that inhibits adipocyte differentiation and thermogenesis.

OBJECTIVE: The metalloprotease ADAM17 (also called TACE) plays fundamental roles in homeostasis by shedding key signaling molecules from the cell surface. Although its importance for the immune system and epithelial tissues is well-documented, little is known about the role of ADAM17 in metabolic homeostasis. The purpose of this study was to determine the impact of ADAM17 expression, specifically in adipose tissues, on metabolic homeostasis. METHODS: We used histopathology, molecular, proteomic, transcriptomic, in vivo integrative physiological and ex vivo biochemical approaches to determine the impact of adipose tissue-specific deletion of ADAM17 upon adipocyte and whole organism metabolic physiology. RESULTS: ADAM17adipoq-creΔ/Δ mice exhibited a hypermetabolic phenotype characterized by elevated energy consumption and increased levels of adipocyte thermogenic gene expression. On a high fat diet, these mice were more thermogenic, while exhibiting elevated expression levels of genes associated with lipid oxidation and lipolysis. This hypermetabolic phenotype protected mutant mice from obesogenic challenge, limiting weight gain, hepatosteatosis and insulin resistance. Activation of beta-adrenoceptors by the neurotransmitter norepinephrine, a key regulator of adipocyte physiology, triggered the shedding of ADAM17 substrates, and regulated ADAM17 expression at the mRNA and protein levels, hence identifying a functional connection between thermogenic licensing and the regulation of ADAM17. Proteomic studies identified Semaphorin 4B (SEMA4B), as a novel ADAM17-shed adipokine, whose expression is regulated by physiological thermogenic cues, that acts to inhibit adipocyte differentiation and dampen thermogenic responses in adipocytes. Transcriptomic data showed that cleaved SEMA4B acts in an autocrine manner in brown adipocytes to repress the expression of genes involved in adipogenesis, thermogenesis, and lipid uptake, storage and catabolism. CONCLUSIONS: Our findings identify a novel ADAM17-dependent axis, regulated by beta-adrenoceptors and mediated by the ADAM17-cleaved form of SEMA4B, that modulates energy balance in adipocytes by inhibiting adipocyte differentiation, thermogenesis and lipid catabolism.

Improved neuron protection following cortical injury in the absence of Semaphorin4B.

Injury to the central nervous system induces neuronal cell death and astrogliosis, an astrocyte-mediated response that has both a beneficial and detrimental impact on surrounding neuronal cells. The circumstance however, in which astrogliosis improves neuronal survival after an injury is not fully characterized. We have recently shown that Semaphorin4B (Sema4B) in the cortex is mostly expressed by astrocytes, and in its absence, astrocyte activation after an injury is altered. Here we find that in Sema4B knockout mice, neuronal cell death is reduced; as a result, more neurons survive near the injury site. Sema4B protein applied directly to neurons does not affect neuronal survival. In contrast, survival of wild-type neurons is increased when plated on glial culture isolated from the Sema4B knockout mice, as compared to Sema4B heterozygous cultures. Furthermore, this increased survival is also observed with conditioned medium collected from glial cultures of Sema4B knockout mice compared to heterozygous mice. This indicates that the increased survival is glial cell-dependent and mediated by a secreted factor(s). Together, our results imply that following injury, the lack of Sema4B expression in glial cells improves neuronal survival either as a result of reduced toxic factors, or perhaps increased survival factors under these conditions.

Semaphorin 4B promotes tumor progression and associates with immune infiltrates in lung adenocarcinoma.

BACKGROUND: Semaphorins have been found to play important roles in multiple malignancy-related processes. However, the role of Semaphorin 4B (SEMA4B) in lung cancer remains unclear. Here, we aimed to explore the biological functions of SEMA4B in through bioinformatic analysis, in vitro and in vivo assays. In the present study, the possible mechanism by which SEMA4B affected the tumor growth and microenvironment of lung adenocarcinoma (LUAD) were investigated. METHODS: The expression of SEMA4B in LUAD was analyzed by bioinformatic analysis and verified by the immunohistochemistry staining. The prognostic value of SEMA4B in LUAD was investigated using the Kaplan-Meier survival and Cox's regression model. After silencing SEMA4B expression, the functions of SEMA4B in LUAD cells were investigated by in vitro experiments, including CCK-8 and plate clone formation. And the effect of SEMA4B on tumor growth and immune infiltration was explored in C57BL/6 mice tumor-bearing models. RESULTS: SEMA4B expression was upregulated in LUAD tissues and correlated with later pathological stages and poor prognosis of LUAD patients. Further study found that SEMA4B silencing suppressed the proliferation of lung cancer cells both in vitro and in vivo. Bioinformatic analysis showed that SEMA4B expression was correlated with the increased infiltration of myeloid-derived suppressor cells (MDSCs), T-regs and the decreased infiltration of CD8+ T cell in LUAD. Importantly, in vivo study verified that the infiltration of T-regs and MDSCs in tumor microenvironment (TME) of Xenograft tissues was decreased after SEMA4B silencing. CONCLUSIONS: These findings demonstrated SEMA4B might play an oncogenic role in LUAD progression, and be a promising therapeutic target for lung cancer.

Long non-coding RNA NEAT1 promotes the malignancy of laryngeal squamous cell carcinoma by regulating the microRNA-204-5p/SEMA4B axis.

Laryngeal squamous cell carcinoma (LSCC) is a highly invasive malignant tumor in the head and neck area. As an oncogene, long non-coding RNA (lncRNA) nuclear enriched abundant transcript 1 (NEAT1) promotes cell proliferation, migration and invasion several types of cancer. The present study aimed to reveal the effects of NEAT1 on the progression of LSCC. Reverse transcription-quantitative PCR (RT-qPCR) was used to detect relative mRNA expression levels of NEAT1, microRNA (miR)-204-5p and semaphorin (SEMA) 4B. Kaplan-Meier analysis was used to analyze overall survival times. RNA in-situ hybridization (ISH) exhibited the distribution of NEAT1 and miR-204-5p in tissues. RNA fluorescence ISH was used to analyze the distribution of NEAT1 and miR-204-5p in the cells. Western blot analysis was used to detect the expression level of target proteins. Cell viability was analyzed using a MTT assay, while flow cytometry was used to determine cell apoptosis. Wound healing and Transwell invasion assays were used to value cell migration and invasion, respectively. RNA immunoprecipitation assay, bioinformatics prediction and a dual luciferase reporter assay were used to analyze the target relationship. The RT-qPCR results showed that NEAT1 was highly expressed and miR-204-5p had decreased expression in LSCC tissues and cells compared with that in the normal tissue and the 16HBE-14o cell line, respectively. Knockdown of NEAT1 using small interfering (si) RNA and overexpressed miR-204-5p both effectively inhibited the proliferation, migration and invasion of LSCC cells. Besides, further experiments revealed that miR-204-5p was a target of NEAT1. At the same time, silenced miR-204-5p reversed the anti-tumor effects of si-NEAT1. In addition, SEMA4B was targeted by miR-204-5p in LSCC cells and upregulated SEMA4B weakened the antitumor effects of miR-204-5p in LSCC cells. NEAT1 regulated the expression of SEMA4B by targeting miR-204-5p in LSCC cells. Overall, NEAT1 promoted the proliferation and invasion of LSCC cells by regulating the miR-204-5p/SEMA4B axis.

CircSEMA4B targets miR-431 modulating IL-1ß-induced degradative changes in nucleus pulposus cells in intervertebral disc degeneration via Wnt pathway.

Intervertebral disc (IVD) degeneration (IDD), characterized by elevated levels of proinflammatory mediators, increased Aggrecan and collagen degradation, and increased degradation of extracellular matrix (ECM), has been widely regarded as a significant contributor to low back pain. Genetics are significant factors contribute to IDD. Based on previous data, circular RNA SEMA4B (circSEMA4B) is down-regulated in IDD specimens; herein, we demonstrated circSEMA4B overexpression could attenuate the effect of IL-1ß on nucleus pulposus cell (NPC) proliferation, senescence, and ECM and Aggrecan degradation in IDD via Wnt signaling. Moreover, miR-431, a direct target of circSEMA4B, could bind to the 3'UTR of SFRP1 or GSK-3ß, two inhibitory regulators of Wnt signaling, to inhibit their expression thus playing a role similar to the activator of Wnt signaling in NPCs. The effect of circSEMA4B knockdown on NPCs was partially reversed by miR-431 inhibition; circSEMA4B serves as a miR-431 sponge to compete with SFRP1 or GSK-3ß for miR-431 binding, thus inhibiting IL-1ß-induced degenerative process in NPCs through Wnt signaling. Rescuing circSEMA4B expression in NPCs in IDD might present a potential strategy for IDD improvement.

Astrogliosis Induced by Brain Injury Is Regulated by Sema4B Phosphorylation

Injury to the CNS induces astrogliosis, an astrocyte-mediated response that has both beneficial and detrimental impacts on surrounding neural and non-neural cells. The precise signaling events underlying astrogliosis are not fully characterized. Here, we show that astrocyte activation was altered and proliferation was reduced in Semaphorin 4B (Sema4B)-deficient mice following injury. Proliferation of cultured Sema4B(-/-) astrocytes was also significantly reduced. In contrast to its expected role as a ligand, the Sema4B ectodomain was not able to rescue Sema4B(-/-) astrocyte proliferation but instead acted as an antagonist against Sema4B(+/-) astrocytes. Furthermore, the effects of Sema4B on astrocyte proliferation were dependent on phosphorylation of the intracellular domain at Ser825. Our results suggest that Sema4B functions as an astrocyte receptor, defining a novel signaling pathway that regulates astrogliosis after CNS injury.

SEMA4B inhibits growth of non-small cell lung cancer in vitro and in vivo.

We have recently shown that Semaphorin 4B (SEMA4B) inhibits the invasion of non-small cell lung cancer (NSCLC) through PI3K-dependent suppression of MMP9 activation. In the current study, we evaluated whether SEMA4B may also affect the growth of NSCLC. We thus used two human NSCLC lines, A549 and Calu-3, to examine our hypothesis. We found that overexpression of SEMA4B significantly decreased NSCLC cell growth, while SEMA4B inhibition significantly increased NSCLC cell growth, both in vitro and in vivo in an implanted NSCLC model. Adaptation of SEMA4B in NSCLC cells did not alter cell apoptosis, but changed the cell proliferation. Further analyses show that SEMA4B may induce FoxO1 nuclear retention through suppressing PI3K/Akt signaling pathway, which subsequently inhibited cell growth through the direct nuclear target of FoxO1, p21. Our study thus demonstrate a role of SEMA4B in suppressing NSCLC growth, besides its role in inhibiting cell metastasis, and highlights SEMA4B as a promising therapeutic target for NSCLC.