Substance P in nerve tissue in the gut

Identification of different types of spinal afferent nerve endings that encode noxious and innocuous stimuli in the large intestine using a novel anterograde tracing technique

In mammals, sensory stimuli in visceral organs, including those that underlie pain perception, are detected by spinal afferent neurons, whose cell bodies lie in dorsal root ganglia (DRG). One of the major challenges in visceral organs has been how to identify the different types of nerve endings of spinal afferents that transduce sensory stimuli into action potentials. The reason why spinal afferent nerve endings have been so challenging to identify is because no techniques have been available, until now, that can selectively label only spinal afferents, in high resolution. We have utilized an anterograde tracing technique, recently developed in our laboratory, which facilitates selective labeling of only spinal afferent axons and their nerve endings in visceral organs. Mice were anesthetized, lumbosacral DRGs surgically exposed, then injected with dextran-amine. Seven days post-surgery, the large intestine was removed. The characteristics of thirteen types of spinal afferent nerve endings were identified in detail. The greatest proportion of nerve endings was in submucosa (32%), circular muscle (25%) and myenteric ganglia (22%). Two morphologically distinct classes innervated myenteric ganglia. These were most commonly a novel class of intraganglionic varicose endings (IGVEs) and occasionally rectal intraganglionic laminar endings (rIGLEs). Three distinct classes of varicose nerve endings were found to innervate the submucosa and circular muscle, while one class innervated internodal strands, blood vessels, crypts of lieberkuhn, the mucosa and the longitudinal muscle. Distinct populations of sensory endings were CGRP-positive. We present the first complete characterization of the different types of spinal afferent nerve endings in a mammalian visceral organ. The findings reveal an unexpectedly complex array of different types of primary afferent endings that innervate specific layers of the large intestine. Some of the novel classes of nerve endings identified must underlie the transduction of noxious and/or innocuous stimuli from the large intestine.

Substance P induces CCN1 expression via histone deacetylase activity in human colonic epithelial cells

We have shown that substance P (SP) and its neurokinin-1 receptor (NK-1R) regulate intestinal angiogenesis by increasing expression of protein CYR61 (the cysteine-rich angiogenic inducer 61, or CCN1) in colonic epithelial cells. However, the mechanism involved in SP-induced CCN1 expression has not been studied, and the outcome of increased CCN1 expression in the development of colitis is not fully understood. Because histone deacetylase (HDAC) modulates transcription of several genes involved in inflammation, we investigated participation of HDAC in SP-induced CCN1 expression in human colonic epithelial NCM460 cells overexpressing NK-1R (NCM460-NK-1R) and in primary colonocytes. SP increased HDAC activity with deacetylation and dephosphorylation of nucleosome protein histone H3 in NCM460-NK-1R and/or primary colonocytes. Histone deacetylation and dephosphorylation was observed in colonic mucosa from irritable bowel disease patients. Similarly, colonic mucosal tissues from mice exposed to dextran sulfate sodium showed histone H3 deacetylation and dephosphorylation and increased HDAC activity that was reversed by the NK-1R antagonist CJ-12255. SP-induced increased CCN1 expression in NCM460-NK-1R cells was abolished by pharmacological HDAC inhibition. HDAC overexpression activated basal and SP-induced CCN1 promoter activity. Intracolonic CCN1 overexpression significantly ameliorated dextran sulfate sodium-induced colitis, with reduction of proinflammatory cytokine expression in mice. Thus, SP-mediated CCN1 expression in the inflamed human and mouse colon involves increased HDAC activity. Our results strongly suggest that increased CCN1 expression may be involved in mucosal healing during colitis.

Substance P modulates colitis-associated fibrosis

Substance P (SP) and the neurokinin-1 receptor (NK-1R) are involved in the development of colitis and mucosal healing after colonic inflammation. We studied whether SP modulates colonic fibrosis by using a chronic model of trinitrobenzenesulfonic acid (TNBS)-induced colitis in wild-type (WT) and NK-1R-deficient (NK-1R KD) mice. We found increased mRNA expression levels of collagen, vimentin, and the fibrogenic factors transforming growth factor β1 and insulin-like growth factor 1 in the chronically inflamed colons of WT mice treated with repeated intracolonic TNBS administrations. Fibrosis in TNBS-treated mice was also evident immunohistochemically by collagen deposition in the colon. Treatment of TNBS-exposed WT mice with the NK-1R antagonist CJ-12255 reduced colonic inflammation, colonic fibrosis, fibroblast accumulation, and expression levels of the fibrogenic factors. NK-1R knockout mice chronically exposed to TNBS had similar colonic inflammation compared with WT, but reduced colonic fibrosis, fibroblast accumulation, and expression levels of fibrogenic factors. Immunohistochemical staining also showed co-localization of NK-1R with fibroblasts in inflamed colons of mice and in colonic mucosa of patients with Crohn's disease. Exposure of human colonic CCD-18Co fibroblasts to SP (10 nmol/L) increased cell migration. SP stimulated collagen synthesis in CCD-18Co fibroblasts in the presence of transforming growth factor β1 and insulin-like growth factor 1, and this effect was reduced by Akt inhibition. Thus, SP, via NK-1R, promotes intestinal fibrogenesis after chronic colitis by stimulating fibrotic responses in fibroblasts.

Substance P-mediated expression of the pro-angiogenic factor CCN1 modulates the course of colitis

Substance P (SP) regulates important intestinal functions, such as mucosal permeability, motility, chloride secretion, and inflammation via the neurokinin-1 receptor (NK-1R). Previous reports showed that vascularization and expression of angiogenic factors are evident in the colonic mucosa of rats with colitis and patients with inflammatory bowel disease. Here we determined whether SP is associated with angiogenesis. Human NCM460 colonocytes stably transfected with the human NK-1R (NCM460-NK-1R cells) and mice with dextran sodium sulfate-induced colitis were used. We found that expression of the angiogenic factor CCN1 was increased in the colons of patients with Crohn's disease and ulcerative colitis. Mucosal extracts from inflammatory bowel disease patients induced human intestinal microvascular endothelial cell migration that was inhibited by blockade of CCN1 and its receptor integrin alphavbeta3. Both the degree of angiogenesis and CCN1 expression were elevated in the colons of mice with dextran sodium sulfate-induced colitis, which was reduced by treatment with the NK-1R antagonist CJ-12255. SP also increased CCN1 expression in NCM460-NK-1R colonocytes. SP exposure to human intestinal microvascular endothelial cells co-cultured with NCM460-NK-1R cells induced angiogenic activity that was inhibited by CCN1 silencing. In addition, intracolonic overexpression of CCN1 induced angiogenesis in mouse colon. Thus, SP mediates angiogenesis via CCN1 during colitis.

Distribution of substance P in brain and periphery and its possible role as a co-transmitter

Substance P is widely distributed in the nervous system. In brain and spinal cord it may act as a transmitter, for example at the central branches of primary sensory neurons. It may also be released from the sensory nerve endings and is thought to be involved in antidromic vasodilatation and in synaptic transmission in autonomic ganglia. In some central neurons substance P is stored together with 5-hydroxytryptamine and thyrotropin-releasing hormone. These neurons project to the ventral horn of the spinal cord, amongst other places. In another system substance P coexists with a cholecystokinin-like peptide. These neurons are localized in the periaqueductal central grey matter and also project to the spinal cord. Finally, injection of a substance P antagonist into the ventral mesencephalon causes marked morphological changes in neurons that contain dopamine, substance P and gamma-aminobutyric acid (GABA).

Substance P stimulates cyclooxygenase-2 and prostaglandin E2 expression through JAK-STAT activation in human colonic epithelial cells

Substance P (SP) via its neurokinin-1 receptor (NK-1R) regulates several gastrointestinal functions. We previously reported that NK-1R-mediated chloride secretion in the colon involves formation of PG. PGE2 biosynthesis is controlled by cyclooxygenase-1 (COX-1) and COX-2, whose induction involves the STATs. In this study, we examined whether SP stimulates PGE2 production and COX-2 expression in human nontransformed NCM460 colonocytes stably transfected with the human NK-1R (NCM460-NK-1R cells) and identified the pathways involved in this response. SP exposure time and dose dependently induced an early (1-min) phosphorylation of JAK2, STAT3, and STAT5, followed by COX-2 expression and PGE2 production by 2 h. Pharmacologic experiments showed that PGE2 production is dependent on newly synthesized COX-2, but COX-1 protein. Inhibition of protein kinase Ctheta (PKCtheta), but not PKCepsilon and PKCdelta, significantly reduced SP-induced COX-2 up-regulation, and JAK2, STAT3, and STAT5 phosphorylation. Pharmacological blockade of JAK inhibited SP-induced JAK2, STAT3, and STAT5 phosphorylation; COX-2 expression; and PGE2 production. Transient transfection with JAK2 short-interferring RNA reduced COX-2 promoter activity and JAK2 phosphorylation, while RNA interference of STAT isoforms showed that STAT5 predominantly mediates SP-induced COX-2 promoter activity. Site-directed mutation of STAT binding sites on the COX-2 promoter completely abolished COX-2 promoter activity. Lastly, COX-2 expression was elevated in colon of mice during experimental colitis, and this effect was normalized by administration of the NK-1R antagonist CJ-12,255. Our results demonstrate that SP stimulates COX-2 expression and PGE2 production in human colonocytes via activation of the JAK2-STAT3/5 pathway.

Substance P recognition by a subset of human T lymphocytes

The interaction of substance P with human blood T-lymphocytes, which stimulates T-lymphocyte proliferation, was quantified by both flow cytometric and direct binding assays. Fluorescence-detection flow cytometry recorded the binding of dichlorotriazinylamino-fluorescein-labeled substance P to 21 +/- 10% (mean +/- SD, n = 6) and 35 +/- 8% (n = 2) of human blood T-lymphocytes before and after stimulation with 10 micrograms/ml of phytohemagglutinin, respectively. The suppressor-cytotoxic (leu 2a) and helper-inducer (leu 3a) subsets identified by phycoerythrin-labeled monoclonal antibodies contained substance P-reactive T-lymphocytes at respective mean frequencies of 10 and 18%. [3H]substance P bound rapidly and reversibly to a mean of 7035 +/- 2850 sites/T-lymphocyte, which exhibited a dissociation constant (KD) of 1.85 +/- 0.70 X 10(-7) M (mean +/- SD, n = 5). [D-Pro2,D-Phe7,D-Trp9]substance P inhibited the binding of dichlorotriazinylamino-fluorescein-labeled substance P and [3H]substance P to T-lymphocytes at concentrations that suppressed the proliferative response to substance P. Substance P, eledoisin, and substance K (alpha-neurokinin), which all share with substance P the carboxy-terminal substituent -Gly-Leu-Met-NH2, were more potent than substance P in inhibiting the binding of [3H]substance P to T-lymphocytes, suggesting the importance of this sequence in the interaction. Purified human blood B-lymphocytes, monocytes, polymorphonuclear leukocytes, and platelets, and cultured Hut 78 cutaneous lymphoma T-cells, Jurkat cells, Molt-4 lymphoblasts, and HL-60 and U-937 monocyte-like cells all showed only minimal specific binding of [3H]substance P. The recognition of substance P by T-lymphocytes provides one mechanism for selective modulation of immunity by sensory nerves.