Interactions between semaphorins and plexin-neuropilin receptor complexes in the membranes of live cells

SEMA3B inhibits TGFβ-induced extracellular matrix protein production and its reduced levels are associated with a decline in lung function in IPF

Idiopathic pulmonary fibrosis (IPF) is marked by the activation of fibroblasts, leading to excessive production and deposition of extracellular matrix (ECM) within the lung parenchyma. Despite the pivotal role of ECM overexpression in IPF, potential negative regulators of ECM production in fibroblasts have yet to be identified. Semaphorin class 3B (SEMA3B), a secreted protein highly expressed in lung tissues, has established roles in axonal guidance and tumor suppression. However, the role of SEMA3B in ECM production by fibroblasts in the pathogenesis of IPF remains unexplored. Here, we show the downregulation of SEMA3B and its cognate binding receptor, neuropilin 1 (NRP1), in IPF lungs compared with healthy controls. Notably, the reduced expression of SEMA3B and NRP1 is associated with a decline in lung function in IPF. The downregulation of SEMA3B and NRP1 transcripts was validated in the lung tissues of patients with IPF, and two alternative mouse models of pulmonary fibrosis. In addition, we show that transforming growth factor-β (TGFβ) functions as a negative regulator of SEMA3B and NRP1 expression in lung fibroblasts. Furthermore, we demonstrate the antifibrotic effects of SEMA3B against TGFβ-induced ECM production in IPF lung fibroblasts. Overall, our findings uncovered a novel role of SEMA3B in the pathogenesis of pulmonary fibrosis and provided novel insights into modulating the SEMA3B-NRP1 axis to attenuate pulmonary fibrosis.NEW & NOTEWORTHY The excessive production and secretion of collagens and other extracellular matrix proteins by fibroblasts lead to the scarring of the lung in severe fibrotic lung diseases. This study unveils an antifibrotic role for semaphorin class 3B (SEMA3B) in the pathogenesis of idiopathic pulmonary fibrosis. SEMA3B functions as an inhibitor of transforming growth factor-β-driven fibroblast activation and reduced levels of SEMA3B and its receptor, neuropilin 1, are associated with decreased lung function in idiopathic pulmonary fibrosis.

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.

Sema3C signaling is an alternative activator of the canonical WNT pathway in glioblastoma

The Wnt pathway is frequently dysregulated in many cancers, underscoring it as a therapeutic target. Wnt inhibitors have uniformly failed in clinical trials. Here, we report a mechanism of WNT pathway activation through the Semaphorin 3 C neurodevelopmental program in glioma stem-like cells. Sema3C directs β-catenin nuclear accumulation in a Rac1-dependent process, leading to transactivation of Wnt target genes. Sema3C-driven Wnt signaling occurred despite suppression of Wnt ligand secretion, suggesting that Sema3C drives canonical Wnt signaling independent of Wnt ligand binding. In a mouse model of glioblastoma, combined depletion of Sema3C and β-catenin partner TCF1 extended animal survival more than single target inhibition alone. In human glioblastoma, Sema3C expression and Wnt pathway activation were highly concordant. Since Sema3C is frequently overexpressed in glioblastoma, Sema3C signaling may be a significant mechanism of resistance to upstream Wnt pathway inhibitors. Dual targeting of Sema3C and Wnt pathways may achieve clinically significant Wnt pathway inhibition.

Plexin-A2 enables the proliferation and the development of tumors from glioblastoma derived cells

The semaphorin guidance factors receptor plexin-A2 transduces sema6A and sema6B signals and may mediate, along with plexin-A4, the anti-angiogenic effects of sema6A. When associated with neuropilins plexin-A2 also transduces the anti-angiogenic signals of sema3B. Here we show that inhibition of plexin-A2 expression in glioblastoma derived cells that express wild type p53 such as U87MG and A172 cells, or in primary human endothelial cells, strongly inhibits cell proliferation. Inhibition of plexin-A2 expression in U87MG cells also results in strong inhibition of their tumor forming ability. Knock-out of the plexin-A2 gene in U87MG cells using CRISPR/Cas9 inhibits cell proliferation which is rescued following plexin-A2 re-expression, or expression of a truncated plexin-A2 lacking its extracellular domain. Inhibition of plexin-A2 expression results in cell cycle arrest at the G2/M stage, and is accompanied by changes in cytoskeletal organization, cell flattening, and enhanced expression of senescence associated β-galactosidase. It is also associated with reduced AKT phosphorylation and enhanced phosphorylation of p38MAPK. We find that the pro-proliferative effects of plexin-A2 are mediated by FARP2 and FYN and by the GTPase activating (GAP) domain located in the intracellular domain of plexin-A2. Point mutations in these locations inhibit the rescue of cell proliferation upon re-expression of the mutated intracellular domain in the knock-out cells. In contrast re-expression of a plexin-A2 cDNA containing a point mutation in the semaphorin binding domain failed to inhibit the rescue. Our results suggest that plexin-A2 may represent a novel target for the development of anti-tumorigenic therapeutics.

Motor neurons use push-pull signals to direct vascular remodeling critical for their connectivity

The nervous system requires metabolites and oxygen supplied by the neurovascular network, but this necessitates close apposition of neurons and endothelial cells. We find motor neurons attract vessels with long-range VEGF signaling, but endothelial cells in the axonal pathway are an obstacle for establishing connections with muscles. It is unclear how this paradoxical interference from heterotypic neurovascular contacts is averted. Through a mouse mutagenesis screen, we show that Plexin-D1 receptor is required in endothelial cells for development of neuromuscular connectivity. Motor neurons release Sema3C to elicit short-range repulsion via Plexin-D1, thus displacing endothelial cells that obstruct axon growth. When this signaling pathway is disrupted, epaxial motor neurons are blocked from reaching their muscle targets and concomitantly vascular patterning in the spinal cord is altered. Thus, an integrative system of opposing push-pull cues ensures detrimental axon-endothelial encounters are avoided while enabling vascularization within the nervous system and along peripheral nerves.

Single-virus tracking reveals variant SARS-CoV-2 spike proteins induce ACE2-independent membrane interactions

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) became a global health crisis after its emergence in 2019. Replication of the virus is initiated by binding of the viral spike (S) protein to human angiotensin-converting enzyme 2 (ACE2) on the target cell surface. Mutations acquired by SARS-CoV-2 S variants likely influence virus-target cell interaction. Here, using single-virus tracking to capture these initial steps, we observe how viruses carrying variant S interact with target cells. Specificity for ACE2 occurs for viruses with the reference sequence or D614G mutation. Analysis of the Alpha, Beta, and Delta SARS-CoV-2 variant S proteins revealed a progressive altered cell interaction with a reduced dependence on ACE2. Notably, the Delta variant S affinity was independent of ACE2. These enhanced interactions may account for the increased transmissibility of variants. Knowledge of how mutations influence cell interaction is essential for vaccine development against emerging variants of SARS-CoV-2.

Multiomics analysis reveals that hepatocyte nuclear factor 1β regulates axon guidance genes in the developing mouse kidney

The transcription factor hepatocyte nuclear factor 1β (HNF-1β) is essential for normal development of the kidney and other epithelial organs. In the developing mouse kidney, HNF-1β is required for the differentiation and patterning of immature nephrons and branching morphogenesis of the ureteric bud (UB). Here, we used ChIP-sequencing (ChIP-seq) and RNA sequencing (RNA-seq) to identify genes that are regulated by HNF-1β in embryonic mouse kidneys. ChIP-seq revealed that HNF-1β binds to 8284 sites in chromatin from E14.5 mouse kidneys. Comparison with previous ATAC-seq and histone modification studies showed that HNF-1β binding peaks colocalized with open chromatin and epigenetic marks of transcriptional activation (H3K27 acetylation, H3K4 trimethylation, H3K4 monomethylation), indicating that the binding sites were functional. To investigate the relationship between HNF-1β binding and HNF-1β-dependent gene regulation, RNA-seq was performed on UB cells purified from wild-type and HNF-1β mutant embryonic kidneys. A total of 1632 genes showed reduced expression in HNF-1β-deficient UB cells, and 485 genes contained nearby HNF-1β binding sites indicating that they were directly activated by HNF-1β. Conversely, HNF-1β directly repressed the expression of 526 genes in the UB. Comparison with snATAC-seq analysis of UB-derived cells showed that both HNF-1β-dependent activation and repression correlated with chromatin accessibility. Pathway analysis revealed that HNF-1β binds near 68 axon guidance genes in the developing kidney. RNA-seq analysis showed that Nrp1, Sema3c, Sema3d, Sema6a, and Slit2 were activated by HNF-1β, whereas Efna1, Epha3, Epha4, Epha7, Ntn4, Plxna2, Sema3a, Sema4b, Slit3, Srgap1, Unc5c and Unc5d were repressed by HNF-1β. RNAscope in situ hybridization showed that Nrp1, Sema3c, Sema3d, Sema6a, and Slit2 were expressed in wild-type UB and were dysregulated in HNF-1β mutant UB. These studies show that HNF-1β directly regulates the expression of multiple axon guidance genes in the developing mouse kidney. Dysregulation of axon guidance genes may underlie kidney defects in HNF-1β mutant mice.

Regulation of Semaphorin3A in the process of cutaneous wound healing

Semaphorin 3A (Sema3A) has been recognized as a crucial regulator of morphogenesis and homeostasis over a wide range of organ systems. However, its function in cutaneous wound healing is poorly understood. In our study, we demonstrated that Sema3A adenovirus plasmids transfection limited keratinocyte proliferation and decreased migrative capacity as assessed by in vitro wound healing assay. Sema3A transduction inhibited TGF-β1-mediated keratinocyte migration and EMT process. Besides, we applied mice with K14-Cre-mediated deletion of Sema3A and found that Sema3A depletion postponed wound closure with decreased re-epithelialization and matrix growth. Contrary to the results obtained with full-length Sema3A plasmids transfection, increased keratinocyte migration with recombinant Sema3A proteins resulted in quicker closure of the wounding area after a scratch. Further, exogenously applied recombinant Sema3A worked with EGF to maintain the activation of EGFR by interacting with NRP1 and thereby regulated the internalization of the EGFR-NRP1 complex. Taken together, these results indicated a paradoxical role of autonomous and non-autonomous Sema3A expression during wound healing. Combined administration of recombinant EGF and Sema3A proteins could accelerate the process of wound repair, thus providing promising treatment prospects in the future.