Disruption of Ninjurin1 Leads to Repetitive and Anxiety-Like Behaviors in Mice

NINJ1 in Cell Death and Ferroptosis: Implications for Tumor Invasion and Metastasis

NINJ1 was initially recognized for its role in nerve regeneration and cellular adhesion. Subsequent studies have uncovered its participation in cancer progression, where NINJ1 regulates critical steps in tumor metastasis, such as cell migration and invasion. More recently, NINJ1 has emerged as a multifunctional protein mediating plasma membrane rupture (PMR) in several lytic cell death processes, including apoptosis, necroptosis, and pyroptosis. However, its role in ferroptosis-an iron-dependent form of lytic cell death characterized by lipid peroxidation-remained unclear until 2024. Ferroptosis is a tumor suppression mechanism that may be particularly relevant to detached and metastatic cancer cells. This review explores the role of NINJ1 in tumor invasion and metastasis, focusing on its regulation of ferroptosis via a non-canonical mechanism distinct from other cell deaths. We discuss the process of ferroptosis and its implications for cancer invasion and metastasis. Furthermore, we review recent studies highlighting the diverse roles of NINJ1 in ferroptosis regulation, including its canonical function in PMR and its non-canonical function of modulating intracellular levels of glutathione (GSH) and coenzyme A (CoA) via interaction with xCT anti-porter. Given that ferroptosis has been associated with tumor suppression, metastasis, the elimination of treatment-resistant cancer cells, and tumor dormancy, NINJ1's modulation of ferroptosis presents a promising therapeutic target for inhibiting metastasis. Understanding the dual role of NINJ1 in promoting or restraining ferroptosis depending on cellular context could open avenues for novel anti-cancer strategies to enhance ferroptotic vulnerability in metastatic tumors.

Multifaceted roles of ninjurin1 in immunity, cell death, and disease

Ninjurin1 (NINJ1) is initially identified as a nerve injury-induced adhesion molecule that facilitates axon growth. It is initially characterized to promote nerve regeneration and mediate the transendothelial transport of monocytes/macrophages associated with neuroinflammation. Recent evidence indicates that NINJ1 mediates plasma membrane rupture (PMR) in lytic cell death. The absence or inhibition of NINJ1 can delay PMR, thereby mitigating the spread of inflammation resulting from cell lysis and preventing the progression of various cell death-related pathologies, suggesting a conserved regulatory mechanism across these processes. Further research elucidated the structural basis and mechanism of NINJ1-mediated PMR. Although the role of NINJ1 in PMR is established, the identity of its activating factors and its implications in diseases remain to be fully explored. This review synthesizes current knowledge regarding the structural basis and mechanism of NINJ1-mediated PMR and discusses its significance and therapeutic targeting potential in inflammatory diseases, neurological disorders, cancer, and vascular injuries.

NINJ1: A new player in multiple sclerosis pathogenesis and potential therapeutic target

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) characterized by demyelination. Current treatment options for MS focus on immunosuppression, but their efficacy can be limited. Recent studies suggest a potential role for nerve injury-induced protein 1 (NINJ1) in MS pathogenesis. NINJ1, a protein involved in cell death and inflammation, may contribute to the infiltration and activation of inflammatory cells in the CNS, potentially through enhanced blood-brain barrier crossing; enhancing plasma membrane rupture during cell death, leading to the release of inflammatory mediators and further tissue damage. This review explores the emerging evidence for NINJ1's involvement in MS. It discusses how NINJ1 might mediate the migration of immune cells across the blood-brain barrier, exacerbate neuroinflammation, and participate in plasma membrane rupture-related damage. Finally, the review examines potential therapeutic strategies targeting NINJ1 for improved MS management. Abbreviations: MS, Multiple sclerosis; CNS, Central nervous system; BBB, Blood-brain barrier; GSDMD, Gasdermin-D; EAE, Experimental autoimmune encephalitis; HMGB-1, High mobility group box-1 protein; LDH, Lactate dehydrogenase; PMR, Plasma membrane rupture; DMF, Dimethyl fumarate; DUSP1, Dual-specificity phosphatase 1; PAMPs, Pathogen-associated molecular patterns; DAMPs, Danger-associated molecular patterns; PRRs, Pattern recognition receptors; GM-CSF, Granulocyte-macrophage colony stimulating factor; IFN-γ, Interferon gamma; TNF, Tumor necrosis factor; APCs, Antigen-presenting cells; ECs, Endothelial cells; TGF-β, Transforming growth factor-β; PBMCs, Peripheral blood mononuclear cells; FACS, Fluorescence-activated cell sorting; MCP-1, Monocyte chemoattractant protein-1; NLRP3, Pyrin domain-containing 3; TCR, T cell receptor; ROS, Reactive oxygen species; AP-1, Activator protein-1; ANG1, Angiopoietin 1; BMDMs, Bone marrow-derived macrophages; Arp2/3, actin-related protein 2/3; EMT, epithelial-mesenchymal transition; FAK, focal adhesion kinase; LIMK1, LIM domain kinase 1; PAK1, p21-activated kinases 1; Rac1, Ras-related C3 botulinum toxin substrate 1; β-cat, β-caten; MyD88, myeloid differentiation primary response gene 88; TIRAP, Toll/interleukin-1 receptor domain-containing adapter protein; TLR4, Toll-like receptor 4; IRAKs, interleukin-1 receptor-associated kinases; TRAF6, TNF receptor associated factor 6; TAB2/3, TAK1 binding protein 2/3; TAK1, transforming growth factor-β-activated kinase 1; JNK, c-Jun N-terminal kinase; ERK1/2, Extracellular Signal Regulated Kinase 1/2; IKK, inhibitor of kappa B kinase; IκB, inhibitor of NF-κB; NF-κB, nuclear factor kappa-B; AP-1, activator protein-1; ASC, Apoptosis-associated Speck-like protein containing a CARD; NEK7, NIMA-related kinase 7; NLRP3, Pyrin domain-containing 3; CREB, cAMP response element-binding protein.

A guide to cell death pathways

Regulated cell death mediated by dedicated molecular machines, known as programmed cell death, plays important roles in health and disease. Apoptosis, necroptosis and pyroptosis are three such programmed cell death modalities. The caspase family of cysteine proteases serve as key regulators of programmed cell death. During apoptosis, a cascade of caspase activation mediates signal transduction and cellular destruction, whereas pyroptosis occurs when activated caspases cleave gasdermins, which can then form pores in the plasma membrane. Necroptosis, a form of caspase-independent programmed necrosis mediated by RIPK3 and MLKL, is inhibited by caspase-8-mediated cleavage of RIPK1. Disruption of cellular homeostatic mechanisms that are essential for cell survival, such as normal ionic and redox balance and lysosomal flux, can also induce cell death without invoking programmed cell death mechanisms. Excitotoxicity, ferroptosis and lysosomal cell death are examples of such cell death modes. In this Review, we provide an overview of the major cell death mechanisms, highlighting the latest insights into their complex regulation and execution, and their relevance to human diseases.

Drugging the NLRP3 inflammasome: from signalling mechanisms to therapeutic targets

Diseases associated with chronic inflammation constitute a major health burden across the world. As central instigators of the inflammatory response to infection and tissue damage, inflammasomes - and the NACHT, LRR and PYD domain-containing protein 3 (NLRP3) inflammasome in particular - have emerged as key regulators in diverse rheumatic, metabolic and neurodegenerative diseases. Similarly to other inflammasome sensors, NLRP3 assembles a cytosolic innate immune complex that activates the cysteine protease caspase-1, which in turn cleaves gasdermin D (GSDMD) to induce pyroptosis, a regulated mode of lytic cell death. Pyroptosis is highly inflammatory, partly because of the concomitant extracellular release of the inflammasome-dependent cytokines IL-1β and IL-18 along with a myriad of additional danger signals and intracellular antigens. Here, we discuss how NLRP3 and downstream inflammasome effectors such as GSDMD, apoptosis-associated speck-like protein containing a CARD (ASC) and nerve injury-induced protein 1 (NINJ1) have gained significant traction as therapeutic targets. We highlight the recent progress in developing small-molecule and biologic inhibitors that are advancing into the clinic and serving to harness the broad therapeutic potential of modulating the NLRP3 inflammasome.

Dopaminergic organization of striatum is linked to cortical activity and brain expression of genes associated with psychiatric illness

Dopamine signaling is constrained to discrete tracts yet has brain-wide effects on neural activity. The nature of this relationship between local dopamine signaling and brain-wide neuronal activity is not clearly defined and has relevance for neuropsychiatric illnesses where abnormalities of cortical activity and dopamine signaling coexist. Using simultaneous PET-MRI in healthy volunteers, we find strong evidence that patterns of striatal dopamine signaling and cortical blood flow (an index of local neural activity) contain shared information. This shared information links amphetamine-induced changes in gradients of striatal dopamine receptor availability to changes in brain-wide blood flow and is informed by spatial patterns of gene expression enriched for genes implicated in schizophrenia, bipolar disorder, and autism spectrum disorder. These results advance our knowledge of the relationship between cortical function and striatal dopamine, with relevance for understanding pathophysiology and treatment of diseases in which simultaneous aberrations of these systems exist.

The Role of Ninjurin1 and Its Impact beyond the Nervous System

Ninjurin1 (Ninj1) is a double-transmembrane cell surface protein that could promote nerve regeneration in the process of the peripheral nervous system injury and repairment. Nonetheless, the accurate function of Ninj1 in the central nervous system and outside the nervous system is not completely clear. According to the recent studies, we found that Ninj1 is also aberrantly expressed in various pathophysiological processes in vivo, including inflammation, tumorigenesis, and vascular, bone, and muscle homeostasis. These findings suggest that Ninj1 may play an influential role during these pathophysiological processes. Our review summarizes the diverse roles of Ninj1 in multiple pathophysiological processes inside and outside the nervous system. Ninj1 should be considered as an important and novel therapeutic target in certain diseases, such as inflammatory diseases and ischemic diseases. Our study provided a better understanding of Ninj1 in different pathophysiological processes and thereby provided the theoretical support for further research.

Neural Mechanisms Underlying Repetitive Behaviors in Rodent Models of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is comprised of several conditions characterized by alterations in social interaction, communication, and repetitive behaviors. Genetic and environmental factors contribute to the heterogeneous development of ASD behaviors. Several rodent models display ASD-like phenotypes, including repetitive behaviors. In this review article, we discuss the potential neural mechanisms involved in repetitive behaviors in rodent models of ASD and related neuropsychiatric disorders. We review signaling pathways, neural circuits, and anatomical alterations in rodent models that display robust stereotypic behaviors. Understanding the mechanisms and circuit alterations underlying repetitive behaviors in rodent models of ASD will inform translational research and provide useful insight into therapeutic strategies for the treatment of repetitive behaviors in ASD and other neuropsychiatric disorders.

Ninjurin 1 dodecamer peptide containing the N-terminal adhesion motif (N-NAM) exerts proangiogenic effects in HUVECs and in the postischemic brain

Nerve injury-induced protein 1 (Ninjurin 1, Ninj1) is a cell adhesion molecule responsible for cell-to-cell interactions between immune cells and endothelial cells. In our previous paper, we have shown that Ninj1 plays an important role in the infiltration of neutrophils in the postischemic brain and that the dodecamer peptide harboring the Ninj1 N-terminal adhesion motif (N-NAM, Pro²⁶-Asn³⁷) inhibits infiltration of neutrophils in the postischemic brain and confers robust neuroprotective and anti-inflammatory effects. In the present study, we examinedt the pro-angiogenic effect of N-NAM using human umbilical vein endothelial cells (HUVECs) and rat MCAO (middle cerebral artery occlusion) model of stroke. We found that N-NAM promotes proliferation, migration, and tube formation of HUVECs and demonstrate that the suppression of endogenous Ninj1 is responsible for the N-NAM-mediated pro-angiogenic effects. Importantly, a pull-down assay revealed a direct binding between exogenously delivered N-NAM and endogenous Ninj1 and it is N-terminal adhesion motif dependent. In addition, N-NAM activated the Ang1-Tie2 and AKT signaling pathways in HUVECs, and blocking those signaling pathways with specific inhibitors suppressed N-NAM-induced tube formation, indicating critical roles of those signaling pathways in N-NAM-induced angiogenesis. Moreover, in a rat MCAO model, intranasal administration of N-NAM beginning 4 days post-MCAO (1.5 µg daily for 3 days) augmented angiogenesis in the penumbra of the ipsilateral hemisphere of the brain and significantly enhanced total vessel lengths, vessel densities, and pro-angiogenic marker expression. These results demonstrate that the 12-amino acid Ninj1 peptide, which contains the N-terminal adhesion motif of Ninj1, confers pro-angiogenic effects and suggest that those effects might contribute to its neuroprotective effects in the postischemic brain.

Ninjurin1 deficiency aggravates colitis development by promoting M1 macrophage polarization and inducing microbial imbalance

Disruption of colonic homeostasis caused by aberrant M1/M2 macrophage polarization and dysbiosis contributes to inflammatory bowel disease (IBD) pathogenesis. However, the molecular factors mediating colonic homeostasis are not well characterized. Here, we found that Ninjurin1 (Ninj1) limits colon inflammation by regulating macrophage polarization and microbiota composition under homeostatic conditions and during colitis development. Ninj1 deletion in mice induced hypersusceptibility to colitis, with increased prevalence of colitogenic Prevotellaceae strains and decreased immunoregulatory Lachnospiraceae strains. Upon co-housing (CoH) with WT mice, Ninj1^-/- mice showed increased Lachnospiraceae and decreased Prevotellaceae abundance, with subsequent improvement of colitis. Under homeostatic conditions, M1 macrophage frequency was higher in the Ninj1^-/- mouse colons than wild-type (WT) mouse colons, which may contribute to increased basal colonic inflammation and microbial imbalance. Following colitis induction, Ninj1 expression was increased in macrophages; meanwhile Ninj1^-/- mice showed severe colitis development and impaired recovery, associated with decreased M2 macrophages and escalated microbial imbalance. In vitro, Ninj1 knockdown in mouse and human macrophages activated M1 polarization and restricted M2 polarization. Finally, the transfer of WT macrophages ameliorated severe colitis in Ninj1^-/- mice. These findings suggest that Ninj1 mediates colonic homeostasis by modulating M1/M2 macrophage balance and preventing extensive dysbiosis, with implications for IBD prevention and therapy.

Abnormal repetitive behaviors in zebrafish and their relevance to human brain disorders

Abnormal repetitive behaviors (ARBs) are a prominent symptom of numerous human brain disorders and are commonly seen in rodent models as well. While rodent studies of ARBs continue to dominate the field, mounting evidence suggests that zebrafish (Danio rerio) also display ARB-like phenotypes and may therefore be a novel model organism for ARB research. In addition to clear practical research advantages as a model species, zebrafish share high genetic and physiological homology to humans and rodents, including multiple ARB-related genes and robust behaviors relevant to ARB. Here, we discuss a wide spectrum of stereotypic repetitive behaviors in zebrafish, data on their genetic and pharmacological modulation, and the overall translational relevance of fish ARBs to modeling human brain disorders. Overall, the zebrafish is rapidly emerging as a new promising model to study ARBs and their underlying mechanisms.