Neuropilin (NRPs) Related Pathological Conditions and Their Modulators

The role of neuropilin in bone/cartilage diseases

Bone remodeling is the balance between osteoblasts and osteoclasts. Bone diseases such as osteoporosis and osteoarthritis are associated with imbalanced bone remodeling. Skeletal injury leads to limited motor function and pain. Neurophilin was initially identified in axons, and its various ligands and roles in bone remodeling, angiogenesis, neuropathic pain and immune regulation were later discovered. Neurophilin promotes osteoblast mineralization and inhibits osteoclast differentiation and its function. Neuropolin-1 provides channels for immune cell chemotaxis and cytokine diffusion and leads to pain. Neuropolin-1 regulates the proportion of T helper type 17 (Th17) and regulatory T cells (Treg cells), and affects bone immunity. Vascular endothelial growth factors (VEGF) combine with neuropilin and promote angiogenesis. Class 3 semaphorins (Sema3a) compete with VEGF to bind neuropilin, which reduces angiogenesis and rejects sympathetic nerves. This review elaborates on the structure and general physiological functions of neuropilin and summarizes the role of neuropilin and its ligands in bone and cartilage diseases. Finally, treatment strategies and future research directions based on neuropilin are proposed.

Neuropilin-1 is a co-receptor for NGF and TrkA-evoked pain

Nerve growth factor (NGF) monoclonal antibodies (mAb) are one of the few patient-validated non-opioid treatments for chronic pain, despite failing to gain FDA approval due to worsened joint damage in some osteoarthritis patients. Herein, we demonstrate that neuropilin-1 (NRP1) is a nociceptor-enriched co-receptor for NGF that is necessary for tropomyosin-related kinase A (TrkA) signaling of pain. NGF binds NRP1 with nanomolar affinity. NRP1 and G Alpha Interacting Protein C-terminus 1 (GIPC1), a NRP1/TrkA adaptor, are coexpressed with TrkA in human and mouse nociceptors. NRP1 small molecule inhibitors and blocking mAb prevent NGF-stimulated action potential firing and activation of Na+ and Ca2+ channels in human and mouse nociceptors and abrogate NGF-evoked and inflammatory nociception in mice. NRP1 knockdown blunts NGF-stimulated TrkA phosphorylation, kinase signaling and transcription, whereas NRP1 overexpression enhances NGF and TrkA signaling. As well as interacting with NGF, NRP1 forms a heteromeric complex with TrkA. NRP1 thereby chaperones TrkA from the biosynthetic pathway to the plasma membrane and then to signaling endosomes, which enhances NGF-induced TrkA dimerization, endocytosis and signaling. Knockdown of GIPC1, a PDZ-binding protein that scaffolds NRP1 and TrkA to myosin VI, abrogates NGF-evoked excitation of nociceptors and pain-like behavior in mice. We identify NRP1 as a previously unrecognized co-receptor necessary for NGF/TrkA pain signaling by direct NGF binding and by chaperoning TrkA to the plasma membrane and signaling endosomes via the adaptor protein GIPC1. Antagonism of NRP1 and GIPC1 in nociceptors offers a long-awaited alternative to systemic sequestration of NGF with mAbs for the treatment of pain.

Orchestrating Resilience: How Neuropilin-2 and Macrophages Contribute to Cardiothoracic Disease

Immunity has evolved to balance the destructive nature of inflammation with wound healing to overcome trauma, infection, environmental insults, and rogue malignant cells. The inflammatory response is marked by overlapping phases of initiation, resolution, and post-resolution remodeling. However, the disruption of these events can lead to prolonged tissue damage and organ dysfunction, resulting long-term disease states. Macrophages are the archetypic phagocytes present within all tissues and are important contributors to these processes. Pleiotropic and highly plastic in their responses, macrophages support tissue homeostasis, repair, and regeneration, all while balancing immunologic self-tolerance with the clearance of noxious stimuli, pathogens, and malignant threats. Neuropilin-2 (Nrp2), a promiscuous co-receptor for growth factors, semaphorins, and integrins, has increasingly been recognized for its unique role in tissue homeostasis and immune regulation. Notably, recent studies have begun to elucidate the role of Nrp2 in both non-hematopoietic cells and macrophages with cardiothoracic disease. Herein, we describe the unique role of Nrp2 in diseases of the heart and lung, with an emphasis on Nrp2 in macrophages, and explore the potential to target Nrp2 as a therapeutic intervention.

Synovial mesenchymal stem cell-derived exosomal miR-485-3p relieves cartilage damage in osteoarthritis by targeting the NRP1-mediated PI3K/Akt pathway: Exosomal miR-485-3p relieves cartilage damage

Osteoarthritis (OA) is an age-related musculoskeletal disease that results in pain and functional disability. Stem cell therapy has been considered as a promising treatment for OA. In this study, the therapeutic action and potential mechanism of synovial mesenchymal stem cells (SMSCs)-derived exosomes (Exos) in OA cartilage damage were investigated. Cartilage cells were stimulated with IL-1β to establish an in vitro model of OA cartilage damage. Cartilage cell functions were detected by CCK-8, scratch assay, and flow cytometry, respectively. Inflammatory cytokine levels were assessed by ELISA. Target molecule levels were measured by qRT‒PCR and Western blotting. Exos-induced differential expression of miRNAs in cartilage cells were analyzed by microarray analysis. The interaction between miR-485-3p and neuropilin-1 (NRP1) was validated by dual luciferase reporter and RIP assays. We found that treatment with Exos promoted proliferation, migration, and ECM secretion, but restrained apoptosis and inflammation of IL-1β-exposed cartilage cells via up-regulation of miR-485-3p. Additionally, miR-485-3p directly targeted NRP1 to repress NRP1 expression, which subsequently caused inactivation of the PI3K/Akt pathway. The protective effect of Exos on cartilage damage was counteracted by NRP1 overexpression-mediated activation of the PI3K/Akt pathway. In conclusion, Exos delivered miR-485-3p to attenuate IL-1β-induced cartilage degradation by targeting NRP1 and succedent inactivation of the PI3K/Akt pathway. Our findings shed light on the novel protective mechanism of Exos in OA, which suggest that the restoration of miR-485-3p by Exos might be a novel approach for OA treatment.

Neuropilin 1 promotes unilateral ureteral obstruction-induced renal fibrosis via RACK1 in renal tubular epithelial cells

Neuropilin 1 (NRP1) is a single-channel transmembrane glycoprotein whose role and mechanism in renal fibrosis remain incompletely elucidated. Therefore, we investigated the effect of NRP1 on renal fibrosis and its potential mechanism. NRP1 expression in the renal sections from patients with chronic kidney disease (CKD) and a unilateral ureteral obstruction (UUO) mouse model was detected. Nrp1 overexpression or knockdown plasmid was transfected into mice, TKPTS mouse kidney proximal tubular epithelial cells (TECs), and rat kidney fibroblasts, after which pathological injury evaluation and fibrosis marker detection were conducted. The direct interaction of the receptor of activated protein C kinase 1 (RACK1) with NRP1 was validated by immunoprecipitation and Western blot analysis. We found that the upregulated renal NRP1 expression in patients with CKD was located in proximal TECs, consistent with the degree of interstitial fibrosis. In the UUO mouse model, NRP1 expression was upregulated in the kidney, and overexpression of Nrp1 increased the mRNA and protein expression of fibronectin (Fn) and α-smooth muscle actin (α-SMA), whereas Nrp1 knockdown significantly reduced Fn and α-SMA expression and downregulated the inflammatory response. NRP1 promoted transforming growth factor β1 (TGF-β1)-induced profibrotic responses in the TKPTS cells and fibroblasts, and Nrp1 knockdown partially reversed these responses. Immunoprecipitation combined with liquid chromatography-tandem mass spectrometry verified that NRP1 can directly bind to RACK1, and Rack1 knockdown reversed the NRP1-induced fibrotic response. In summary, NRP1 may enhance the TGF-β1 pathway by binding to RACK1, thus promoting renal fibrosis.NEW & NOTEWORTHY Although a few studies have confirmed the correlation between neuropilin 1 (NRP1) and renal diseases, the mechanism of NRP1 in renal fibrosis remains unclear. Here, we investigated the effects of NRP1 on renal fibrosis through in vitro and in vivo experiments and explored the possible downstream mechanisms. We found that NRP1 can stimulate the TGF-β1 signaling pathway, possibly by binding to RACK1, thereby promoting renal fibrosis.

New Biosensor for Determination of Neuropilin-1 with Detection by Surface Plasmon Resonance Imaging

Neuropilin-1 is transmembrane protein with soluble isoforms. It plays a pivotal role in both physiological and pathological processes. NRP-1 is involved in the immune response, formation of neuronal circuits, angiogenesis, survival and migration of cells. The specific SPRI biosensor for the determination of neuropilin-1 was constructed using mouse monoclonal antibody that captures unbound NRP-1 form body fluids. The biosensor exhibits linearity of the analytical signal between 0.01 and 2.5 ng/mL, average precision value 4.7% and recovery between 97% and 104%. The detection limit is 0.011 ng/mL, and the limit of quantification is 0.038 ng/mL. The biosensor was validated by parallel determination of NRP-1 in serum and saliva samples using the ELISA test, with good agreement of the results.

NRP1 promotes prostate cancer progression via modulating EGFR-dependent AKT pathway activation

Prostate cancer (PCa) is the most common malignant tumor with a high global incidence in males. The mechanism underlying PCa progression is still not clear. This study observed that NRP1 was highly expressed in PCa and associated with poor prognosis in PCa patients. Functionally, NRP1 depletion attenuated the proliferation and migration ability of PCa cells in vitro and in vivo, while NRP1 overexpression promoted PCa cell proliferation and migration. Moreover, it was observed that NRP1 depletion induced G1 phase arrest in PCa cells. Mechanistically, HIF1α is bound to the specific promoter region of NRP1, thereby regulating its transcriptional activation. Subsequently, NRP1 interacted with EGFR, leading to EGFR phosphorylation. This study also provided evidence that the b1/b2 domain of NRP1 was responsible for the interaction with the extracellular domain of EGFR. Moreover, EGFR mediated NRP1-induced activation of the AKT signaling pathway, which promoted the malignant progression of PCa. In addition, the administration of NRP1 inhibitor EG01377 significantly inactivated the EGFR/AKT signaling axis, thereby suppressing PCa progression. In conclusion, the findings from this study highlighted the molecular mechanism underlying NRP1 expression in PCa and provide a potential predictor and therapeutic target for clinical prognosis and treatment of PCa.