Expression of IL-12 receptor by neurons

Neurogenesis is disrupted in human hippocampal progenitor cells upon exposure to serum samples from hospitalized COVID-19 patients with neurological symptoms

Coronavirus disease 2019 (COVID-19), represents an enormous new threat to our healthcare system and particularly to the health of older adults. Although the respiratory symptoms of COVID-19 are well recognized, the neurological manifestations, and their underlying cellular and molecular mechanisms, have not been extensively studied yet. Our study is the first one to test the direct effect of serum from hospitalised COVID-19 patients on human hippocampal neurogenesis using a unique in vitro experimental assay with human hippocampal progenitor cells (HPC0A07/03 C). We identify the different molecular pathways activated by serum from COVID-19 patients with and without neurological symptoms (i.e., delirium), and their effects on neuronal proliferation, neurogenesis, and apoptosis. We collected serum sample twice, at time of hospital admission and approximately 5 days after hospitalization. We found that treatment with serum samples from COVID-19 patients with delirium (n = 18) decreased cell proliferation and neurogenesis, and increases apoptosis, when compared with serum samples of sex- and age-matched COVID-19 patients without delirium (n = 18). This effect was due to a higher concentration of interleukin 6 (IL6) in serum samples of patients with delirium (mean ± SD: 229.9 ± 79.1 pg/ml, vs. 32.5 ± 9.5 pg/ml in patients without delirium). Indeed, treatment of cells with an antibody against IL6 prevented the decreased cell proliferation and neurogenesis and the increased apoptosis. Moreover, increased concentration of IL6 in serum samples from delirium patients stimulated the hippocampal cells to produce IL12 and IL13, and treatment with an antibody against IL12 or IL13 also prevented the decreased cell proliferation and neurogenesis, and the increased apoptosis. Interestingly, treatment with the compounds commonly administered to acute COVID-19 patients (the Janus kinase inhibitors, baricitinib, ruxolitinib and tofacitinib) were able to restore normal cell viability, proliferation and neurogenesis by targeting the effects of IL12 and IL13. Overall, our results show that serum from COVID-19 patients with delirium can negatively affect hippocampal-dependent neurogenic processes, and that this effect is mediated by IL6-induced production of the downstream inflammatory cytokines IL12 and IL13, which are ultimately responsible for the detrimental cellular outcomes.

Inhibition of IL-12/IL-23 signaling reduces Alzheimer's disease-like pathology and cognitive decline

The pathology of Alzheimer's disease has an inflammatory component that is characterized by upregulation of proinflammatory cytokines, particularly in response to amyloid-β (Aβ). Using the APPPS1 Alzheimer's disease mouse model, we found increased production of the common interleukin-12 (IL-12) and IL-23 subunit p40 by microglia. Genetic ablation of the IL-12/IL-23 signaling molecules p40, p35 or p19, in which deficiency of p40 or its receptor complex had the strongest effect, resulted in decreased cerebral amyloid load. Although deletion of IL-12/IL-23 signaling from the radiation-resistant glial compartment of the brain was most efficient in mitigating cerebral amyloidosis, peripheral administration of a neutralizing p40-specific antibody likewise resulted in a reduction of cerebral amyloid load in APPPS1 mice. Furthermore, intracerebroventricular delivery of antibodies to p40 significantly reduced the concentration of soluble Aβ species and reversed cognitive deficits in aged APPPS1 mice. The concentration of p40 was also increased in the cerebrospinal fluid of subjects with Alzheimer's disease, which suggests that inhibition of the IL-12/IL-23 pathway may attenuate Alzheimer's disease pathology and cognitive deficits.

Disruption of IFN-gamma- mediated antiviral activity in neurons: the role of cannabinoids

Interferon-gamma (IFN-gamma) has potent antiviral activity in neurons which is affected by the production of nitric oxide (NO). This study examines the interactions between cannabinoid receptor-1 (CB(1)), IFNgamma-induced pathways, and inhibition of vesicular stomatitis virus (VSV) replication in neuronal cells. CB(1) is abundantly expressed in neurons of the CNS and the NB41A3 neuroblastoma cell line. CB(1) activation of NB41A3 cells by the synthetic cannabinoid, WIN55,212-2, is associated with an inhibition of Ca(2+) mobilization, leading to diminished nitric oxide synthase (NOS)-1 activity and the production of NO, in vitro. This ultimately results in antagonism of IFN-gamma-mediated antiviral activity and enhanced viral replication. Therefore, activation of cells expressing CB(1) by endogenous (or exogenous) ligands may contribute to decreased inflammation and to increased viral replication in neurons and disease in the CNS.

Peripheral, but not central nervous system, type I interferon expression in mice in response to intranasal vesicular stomatitis virus infection

Type I interferon (IFN) is critical for resistance of mice to infection with vesicular stomatitis virus (VSV). Wild type (wt) VSV infection did not induce type I IFN production in vitro or in the central nervous system (CNS) of mice; however IFN-beta was detected in lungs, spleen, and serum within 24 h. The M protein mutant VSV, T1026R1 (also referred to as M51R), induced type I IFN production in vitro and in the CNS, with poor expression in spleens. In addition, VSV T1026R1 was not pathogenic to mice after intranasal infection, illustrating the importance of IFN in controlling VSV replication in the CNS. Experiments with chemical sympathectomy, sRAGE, and neutralizing antibody to VSV were performed to investigate the mechanism(s) utilized for induction of peripheral IFN; neither sRAGE infusion nor chemical sympathectomy had an effect on peripheral IFN production. In contrast, administration of neutralizing antibody (Ab) readily blocked the response. Infectious VSV was transiently present in lungs and spleens at 24 h post infection. The results are consistent with VSV traffic from the olfactory neuroepithelium to peripheral lymphoid organs hematogenously or via lymphatic circulation. These results suggest that VSV replicates to high titers in the brains of mice because of the lack of IFN production in the CNS after intranasal VSV infection. In contrast, replication of VSV in peripheral organs is controlled by the production of large amounts of IFN.

Gene expression contributing to recruitment of circulating cells in response to vesicular stomatitis virus infection of the CNS

During acute Vesicular Stomatitis Virus (VSV) infection of the mouse central nervous system, neutrophils, natural killer (NK) cells, macrophages, and CD4+ and CD8+ T cells are recruited from the circulation in response to chemokines and cytokines. This study elucidated the production of these factors and infiltration of these peripheral cells. Chemokines that were observed included CCL1, CXCL10 (IP-10), CCL5 (RANTES), CCL3 (MIP-1alpha), CCL4 (MIP-1beta), CXCL1 (MIP-2), CCL2 (MCP-1), and CCL11 (eotaxin). Cytokines produced in response to the infection include IL-1 and interferon-gamma, but not type I interferons. Neutrophils are the first recruited cell type, appearing as early as 24 h after intranasal application of the virus. NK cells follow, but T cells are not detected until 6 days postinfection.

Interleukin (IL)-12 receptor beta1 or IL-12 receptor beta 2 deficiency in mice indicates that IL-12 and IL-23 are not essential for host recovery from viral encephalitis

Vesicular stomatitis virus (VSV), a negative-sense, single-stranded RNA rhabdovirus, causes acute viral encephalitis when administered intranasally to mice. Interleukin-12 (IL-12) is a key pro-inflammatory cytokine that is produced largely by the antigen presenting cells (APC) and that bridges the innate and acquired immune responses. IL-12 is efficacious in enhancing recovery from VSV infection of the murine central nervous system. This effect is mediated by nitric oxide (NO) produced by the neuronal isoform of nitric oxide synthase (NOS-1), and is independent of the pro-inflammatory cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). These data implied a link between IL-12 and NOS-1. Here we investigate the role of the IL-12R during VSV pathogenesis, using IL-12R beta2 and IL-12R beta1-deficient mice. We showed that a deficiency in either IL-12R beta2 or IL-12R beta1 had no effect on the outcome of VSV infection of the CNS or on the clearance of VSV from the CNS. Furthermore, these data indicate that IL-23 is not acting redundantly in the absence of IL-12 during VSV-induced encephalitis.