Recognition of neurokinin 1 receptor (NK1-R): an antibody to a peptide sequence from the third extracellular region binds to brain NK1-R

Prophylactic and therapeutic targeting of the neurokinin-1 receptor limits neuroinflammation in a murine model of pneumococcal meningitis

There is increasing evidence that the tachykinin substance P (SP) can augment inflammatory immune responses within the CNS. We have recently demonstrated that resident CNS cells express high-affinity receptors for this neuropeptide (neurokinin-1 receptors [NK-1R]), and we have shown that SP can significantly augment glial inflammatory responses to clinically relevant Gram-negative bacteria. Furthermore, we provided evidence that endogenous SP/NK-1R interactions are an essential component in the initiation and/or progression of CNS inflammation following in vivo exposure to these pathogens. In this study, we demonstrate that SP similarly enhances inflammatory glial responses to the major Gram-positive causative agent of bacterial meningitis, Streptococcus pneumoniae, and show that endogenous SP/NK-1R interactions play a critical role in the development of CNS inflammation in an in vivo model of pneumococcal meningitis. Importantly, we provide the first demonstration, to our knowledge, that pharmacological targeting of the NK-1R not only prevents the development of damaging inflammation when administered prophylactically, but can also limit or reverse neuroinflammation associated with an established streptococcal CNS infection when delivered therapeutically. We show that an NK-1R antagonist attenuates increases in CNS inflammatory cytokine levels and decreases in immunosuppressive cytokine production associated with an ongoing S. pneumoniae infection. Furthermore, we demonstrate that such a therapeutic intervention reverses infection-associated gliosis and demyelination in the absence of changes in CNS bacterial burden. Together, these results suggest that targeting SP/NK-1R interactions is a strategy worthy of further study for the treatment of microbially induced neuroinflammation.

Neurogenic exacerbation of microglial and astrocyte responses to Neisseria meningitidis and Borrelia burgdorferi

Although glial cells are recognized for their roles in maintaining neuronal function, there is growing appreciation of the ability of resident CNS cells to initiate and/or augment inflammation following trauma or infection. The tachykinin, substance P (SP), is well known to augment inflammatory responses at peripheral sites and its presence throughout the CNS raises the possibility that this neuropeptide might serve a similar function within the brain. In support of this hypothesis, we have recently demonstrated the expression of high affinity receptors for SP (Neurokinin-1 (NK-1) receptors) on microglia and shown that this tachykinin can significantly elevate bacterially induced inflammatory prostanoid production by isolated cultures of these cells. In the present study, we demonstrate that endogenous SP/NK-1R interactions are an essential component in the initiation and/or progression of CNS inflammation in vivo following exposure to two clinically relevant bacterial CNS pathogens, Neisseria meningitidis and Borrelia burgdorferi. We show that in vivo elevations in inflammatory cytokine production and decreases in the production of an immunosuppressive cytokine are markedly attenuated in mice genetically deficient in the expression of the NK-1R or in mice treated with a specific NK-1R antagonist. Furthermore, we have used isolated cultures of microglia and astrocytes to demonstrate that SP can augment inflammatory cytokine production by these resident CNS cell types following exposure to either of these bacterial pathogens. Taken together, these studies indicate a potentially important role for neurogenic exacerbation of resident glial immune responses in CNS inflammatory diseases, such as bacterial meningitis.

Airway smooth muscle cells express functional neurokinin-1 receptors and the nerve-derived preprotachykinin-a gene: regulation by passive sensitization

Preprotachykinin-A (PPT-A) gene-derived neuropeptides, namely substance P (SP) and neurokinin (NK)A, and their receptors participate in allergen-induced airway responses. Whether airway smooth muscle cells (ASMC) may react directly to SP through expression of the NK-1 receptor or express the gene for the synthesis of SP, the PPT-A gene, is unknown. We demonstrated using reverse transcription-polymerase chain reaction that tracheal SMC (TSMC) from atopic Brown Norway rats contained mRNA transcripts for the full-length isoform of the NK-1 receptor. Flow cytometric analysis indicated that the NK-1 receptor was expressed on the surface of TSMC. This receptor was functional as demonstrated by calcium mobilization in response to SP stimulation. The expression of the NK-1 receptor was not altered in passively sensitized TSMC in response to antigenic stimulation, although this stimulation increased the expression of the chemokine RANTES (regulated on activation, normal T cells expressed and secreted). Using different sets of PCR primers, we showed that TSMC also express the beta, alpha, and its alternative splicing product delta, and possibly the gamma mRNA transcript isoforms of the PPT-A gene. Gene sequencing of the PCR-amplified beta isoform confirmed that it is a transcript product of the rat PPT-A gene, and the production of SP by TSMC was confirmed by enzyme immunoassay. We also showed the beta isoform increased after cell stimulation with rat sera, whether sensitized or not. In conclusion, both the PPT-A gene and NK-1 receptors are expressed by TSMC, which suggests the possibility of autocrine neuropeptidergic mechanisms in these cells. However, these mechanisms are not upregulated by passive sensitization.

Tachykinins and tachykinin receptors in bone

Tachykinins are neuropeptides that are widely distributed in the body and function as neurotransmitters and neuromodulators. Five tachykinin subtypes: substance P (SP), neurokinin A, neurokinin B, neuropeptide K, and neuropeptide gamma; and three receptor subtypes: neurokinin-1, -2, and -3 receptors, have been identified. SP was the first peptide of the tachykinin family to be identified. It is considered to be an important neuropeptide, and to function in the nervous system and intestine. However, recent advances in the analysis of SP receptors, particularly neurokinin-1 receptors (NK(1)-Rs) that have high affinity for SP, have demonstrated that NK(1)-Rs are distributed not only in neurons and immune cells, but also in other peripheral cells, including bone cells. This article reviews the current understanding of the distribution of SP and other tachykinins in bone, and the function of tachykinins, through neurokinin receptors. The distribution of tachykinin-immunoreactive axons and neurokinin receptors suggests that tachykinins may directly modulate bone metabolism through neurokinin receptors.

Spontaneously hypertensive rat: cholera toxin converts suppression to immunity through a Th2 cell-IL-4 pathway

The spontaneously hypertensive rat (SHR) exhibits a number of T cell dysfunctions that develop concurrently with elevated blood pressure. Studies have shown a mitogen-induced lymphocyte suppression mediated in part by the production of interferon-gamma (IFN-gamma), which stimulated NO production by macrophages. To assess whether this immune suppression is reversible, SHR were immunized with diphtheria toxoid (DT) with or without cholera toxin (CT) as adjuvant. SHR immunized with DT only displayed weak serum immunoglobulin G (IgG) anti-DT titers, tenfold less than similarly treated normotensive Wistar-Kyoto rats (WKYR). SHR CD4+ T cells failed to proliferate upon in vitro stimulation with DT. In contrast, SHR coimmunized with DT and CT showed serum IgG antibody titers similar to WKYR and Brown Norway rats. Coimmunization with CT rescued SHR CD4+ T cells from suppression and supported DT- or B subunit of CT-specific proliferative responses, and these cells produced more interleukin-4 (IL-4) than IFN-gamma, and anti-IFN-gamma antibody treatment enhanced IL-4 production. Exogenous IL-4 increased the proliferation of antigen-specific CD4+ T cells, whereas IFN-gamma was inhibitory. This study shows that the adjuvant CT induces T helper 2-type responses, reversing the T cell dysfunction in the SHR.

A monoclonal antibody to the ligand-binding domain of the neurokinin 1 receptor (NK1-R) for the neuropeptide substance P

Monoclonal antibodies to the binding site of the NK1 receptor for the neuropeptide substance P were produced in mice using the complementary or antisense peptide methodology. Among several anti-peptide monoclonal antibodies, we selected the mAb12 antibody which specifically crossreacted, through its paratope, with a binding site present on membranes from rat parotid gland cells, with an affinity close to 2 x 10(-7) M and with membranes from CHO cells expressing human brain NK1 receptors. Immunocytochemical investigations using mAb12 revealed immunostaining whose distribution in the dorsal horns of rat spinal cord fits well with the known location of NK1 receptors. In both biochemical and immunocytochemical experiments, the competition occurring between the antibody and substance P, or a substance P-protein conjugate, indicates that mAb12 recognizes a membrane epitope located at or near the substance P binding domain on the NK1 receptor. Immunization of mice with mAb12 led to the production of specific anti-substance P antibodies, again suggesting that mAb12 shares common structural features with the neuropeptide. This monoclonal antibody can now be used in further biochemical or cytochemical characterizations of NK1 receptors. Owing to its fine specificity, mAb12 could also serve as a molecular model for designing peptides, possibly displaying pharmacological properties in the various processes in which substance P is involved, e.g. immunomodulation, inflammation or chronic pain.