Maria G. Juarranz

Vasoactive intestinal peptide in the immune system: potential therapeutic role in inflammatory and autoimmune diseases

Abstract. Vasoactive intestinal peptide (VIP), a neuropeptide that is produced by lymphoid as well as neural cells, exerts a wide spectrum of immunological functions, controlling the homeostasis of the immune system through different receptors expressed in various immunocompetent cells. In the last decade, VIP has been clearly identified as a potent anti-inflammatory factor, which acts by regulating the production of both anti- and pro-inflammatory mediators. In this sense, VIP has been described to prevent death by septic shock, an acute inflammatory disease with a high mortality. In addition, VIP regulates the expression of co-stimulatory molecules, this being an action that may be related to modulating the shift toward Th1 and Th2 differentiation. We have recently reported that VIP prevents the deleterious effects of an experimental model of rheumatoid arthritis, by downregulating both inflammatory and autoimmune components of the disease. Therefore, VIP has been proposed as a promising candidate alternative treatment for acute and chronic inflammatory and autoimmune diseases such as septic shock, arthritis, multiple sclerosis, Crohn disease, or autoimmune diabetes.

Anti-inflammatory role in septic shock of pituitary adenylate cyclase-activating polypeptide receptor

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are two mediators synthesized by immune cells, specially under inflammatory and antigen stimulation conditions. Reports have shown that neuropeptides attenuate the deleterious consequences of septic shock both by down-regulating the production of proinflammatory mediators and by stimulating the production of anti-inflammatory cytokines by activated macrophages. In this study, we used a knockout for the PACAP receptor (PAC1−/−) to demonstrate an important protective role for PAC1 receptor in endotoxic shock. Moreover, our results indicate that PAC1 receptor acts in vivo as an anti-inflammatory receptor, at least in part, by attenuating lipopolysaccharide (LPS)-induced production of proinflammatory IL-6, which appears to be the main cytokine regulating the expression of the majority of the acute phase protein genes, which are an important deleterious component of septic shock. Besides, our findings point to endogenously produced VIP and PACAP as participants of the natural anti-inflammatory machinery. Because VIP and PACAP are two attractive candidates for the development of therapies against acute and chronic inflammatory diseases, septic shock, and autoimmune diseases, this paper represents a contribution to the understanding of the mechanism of action of these anti-inflammatory agents.

VIP and PACAP are autocrine factors that protect the androgen‐independent prostate cancer cell line PC‐3 from apoptosis induced by serum withdrawal

In the present study, we describe the expression of the neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase‐activating polypeptide (PACAP) as well as their receptors in PC‐3 cells, a human prostate cancer cell line. In addition, we have investigated their role in apoptosis induced by serum starvation. By RT–PCR and immunocytochemistry assays, we have demonstrated the production of VIP and PACAP in PC‐3 cells. We have demonstrated by RT–PCR and binding assays the expression of common PACAP/VIP (VPAC1 and VPAC2) receptors, but not PACAP‐specific (PAC1) receptors. The pharmacological profile of [125I]‐VIP binding assays was as follows: VPAC1 antagonist=VPAC1 agonist>VIP>VPAC2 agonist (IC50=1.2, 1.5, 2.3 and 30 nM, respectively). In addition, both receptor subtypes are functional since VIP, PACAP‐27 or VPAC1 and VPAC2 agonists all increased the intracellular levels of cAMP. The expression of both peptides and their receptors is similar in serum‐cultured and serum‐deprived PC‐3 cells. The treatment of serum‐deprived PC‐3 cells with exogenous VIP or PACAP‐27 increases cell number and viability in a dose‐dependent manner, as demonstrated by cellular counting and MTT assays. The increased cell survival is exerted through the VPAC1 receptor, since a VPAC1, but not VPAC2, receptor agonist, mimics the effects and a VPAC1 receptor antagonist blocks it. Moreover, VIP and PACAP‐27 inhibit genomic DNA fragmentation in PC‐3 cells triggered by serum starvation, and increase the immunoreactivity of the antiapoptotic protein bcl‐2. Our results suggest that VIP and PACAP are autocrine/paracrine factors that protect PC‐3 cells from apoptosis through VPAC1 receptors.

Pituitary Adenylate-Cyclase-Activating Polypeptide Expression in the Immune System

Although pituitary adenylate-cyclase-activating polypeptide (PACAP) is a multifunctional and pleiotropic neuropeptide with many different immunomodulatory properties, investigations of its source in lymphoid organs are scarce. The present report contributes to the knowledge on the origin and synthesis of this peptide in immune cells of the lymphoid organs and peritoneum using immunohistochemistry, immunocytochemical staining, Western blot and RT-PCR methods. Our study reveals PACAP immunoreactivity in the thymus, spleen and lymph nodes. Cytochemical results show that PACAP is present in thymocytes, lymphocytes and plasma cells from the spleen and lymph nodes. Western blot analysis showed a band corresponding to PACAP for all lymphoid organs studied. mRNA appears in both double (CD4+CD8+)- and single-positive (CD4+CD8–, CD4–CD8+) thymocytes and in T subsets and B cells from the spleen and lymph nodes. In addition, PACAP mRNA is expressed in lymphocytes, but not in macrophages from peritoneal suspensions. Our findings show that PACAP produced by lymphocytes could be added to the growing list of mediators shared by nervous, endocrine and immune systems. Moreover, PACAP could be considered as a lymphocyte-derived cytokine in the central and peripheral lymphoid organs acting on lymphocytes and stromal cells.

Neuroendocrine differentiation of the LNCaP prostate cancer cell line maintains the expression and function of VIP and PACAP receptors

The molecular mechanisms involved in differentiation of prostate cancer cells to a neuroendocrine (NE) cell phenotype are not well understood. Here we used the androgen-dependent human prostate cancer cell line LNCaP to perform a systematic and broad analysis of the expression, pharmacology, and functionality of vasoactive intestinal peptide (VIP)/pituitary adenylate cyclase-activating peptide (PACAP) receptors. Reverse transcription polymerase chain reaction experiments, together with pharmacological approaches with a set of specific agonists and antagonists, demonstrated the presence of the three VIP/PACAP receptor subtypes (PAC1, VPAC1, and VPAC2 with a major role for VPAC1, acting through adenylate cyclase (AC) stimulation. An essentially similar pattern was observed by NE differentiated cells (4 days after serum deprivation) in spite of the important morphological changes observed. However, the expression of the prostate-specific antigen (PSA) decreased in NE cells (and increased again by dihydrotestosterone, DHT, treatment). The present demonstration of the induction of NE transdifferentiation in LNCaP cells by increasing concentrations of VIP adds value to previous observations on the role of cAMP in this process, an interesting topic in the comprehension of the molecular changes that are involved in the progression of prostate cancer to androgen independence.

Expression of vasoactive intestinal peptide (VIP) receptors in human uterus.

We show the existence of functional vasoactive intestinal peptide (VIP) receptors in normal human female genital tract (endometrium, myometrium, ovary and Fallopian tube) as well as in leiomyoma (a frequent uterine pathology). The correlation between VIP binding and stimulation of adenylyl cyclase activity for all studied tissues was linear (r = 0.86) suggesting the expression of VIP receptors throughout the human female genital tract. Immunodetection of VIP receptor subtypes gave different molecular weights for VPAC(1) (47 kDa primarily) and VPAC(2) (65 kDa), which may be due to different glycosylation extents. In conclusion, this study demonstrates the expression of both subtypes of VIP receptors and their functionality in human female genital tract, suggesting that this neuropeptide could play an important physiological and pathophysiological role at this level.

Analysis of vasoactive intestinal peptide receptors and the G protein regulation of adenylyl cyclase in seminal vesicle membranes from streptozotocin-diabetic rats

The present report describes the status of the vasoactive intestinal peptide (VIP) receptor/effector system of signal transduction in seminal vesicle from streptozotocin (STZ)-treated rats. STZ-treatment modified the binding parameters of the high-affinity sites for VIP in seminal vesicle: 0.78 +/- 0.10 and 2.54 +/- 0.30 nM for the dissociation constant (Kd) in control and diabetic rats, respectively; 0.07 +/- 0.01 and 0.15 +/- 0.03 pmol VIP/mg protein for the maximum binding capacity (Bmax) in control and diabetic rats, respectively. It was associated with a reduced potency of VIP on the stimulation of adenylyl cyclase activity in the diabetic state (ED50 = 64.0 +/- 20.0 nM) as compared to control (ED50 = 9.5 +/- 4.3 nM). In contrast, the stimulatory effects of GTP, Gpp[NH]p and forskolin on the enzyme activity were not modified in diabetic rats. The levels of G-protein subunits in rat seminal vesicle were studied by immunoblot of alpha s and alpha i subunits: whereas alpha i-subunit levels did not vary, those corresponding to alpha s subunit decreased after STZ treatment. In diabetic rats, low concentrations of Gpp[NH]p failed to inhibit forskolin-stimulated adenylyl cyclase activity, suggesting the absence of functional Gi in this condition. In conclusion, present results show a decrease in the sensitivity of the VIP receptor/effector system in seminal vesicle membranes from STZ-treated rats suggesting a physiopathological role for VIP in the seminal neuropathy observed in diabetes.

Stimulation of the Adenylyl Cyclase Activity in Human Endometrial Membranes by VIP and Related Peptides

Vasoactive intestinal peptide (VIP) has been shown to stimulate adenylyl cyclase activity in human endometrial membranes. The effect was dependent on the time and temperature of incubation as well as on the concentration of endometrial membrane proteins in the medium. In the presence of 1 μM GTP, half-maximal stimulation of adenylyl cyclase activity was observed at 25.0±7.0 nM VIP, whereas the maximal activity (at 1 μM VIP)corresponded to an increase of about 140% with respect to basal values (7.5±0.6 pmol cyclic AMP/min/mg of protein). However, the maximal stimulation of adenylyl cyclase activity was obtained with helodermin (1 μM) that increased the activity by 170% over the basal. The relative potency of VIP-related peptides upon the adenylyl cyclase activity was: helodermin (ED50=1.8±1.4 nM)>VIP(ED50=25.0±7.0 nM)>PHI (ED50=725.0±127.2 nM). Secretin had a faint effect upon the adenylyl cyclase activity and glucagon was completely inefficient at this level. The presence of αs and αi subunits of G proteins in human endometrium was detected by immunoblot. Preliminary results showed the presence of two classes of125I-VIP receptors in human endometrial membranes with the following stoichoimetric parameters: high affinity receptor (Kd=2.0 nM, binding capacity 0.1 pmol VIP/mg protein) and low affinity receptor (Kd=0.43 μM, binding capacity 13.1 pmol VIP/mg protein). The present results together with the known presence of VIP in human uterus and the actions of this neuropeptide in the adjacent myometrial tissue support the idea that VIP and related peptides may have a role in human endometrium.

G-protein regulation of adenylate cyclase activity in rat prostatic membranes after chronic ethanol ingestion

The possibility that long‐term ethanol ingestion might alter either vasoactive intestinal peptide (VIP) content, VIP binding to membrane receptors, G‐protein levels or adenylate cyclase activity in rat prostate was tested, as ethanol produces serious alterations in the hypothalamic‐pituitary‐gonadal axis and several modifications on different elements on signal transduction pathways in other systems.

Ontogenic Development of the Adenylyl Cyclase Enzyme and the αs, αi1 and αi2 G-protein Regulatory Subunits from Rat Prostate

Abstract The expression of α s , α i1 and α i2 G-protein subunits measured by immunoblot increased in the rat prostate during sexual maturation, supporting their involvement in proliferation/differentiation. Northern blotting gave transcripts of 1.8 and 4 kb for α s , 1.4 and 4.5 kb (mainly) for α i1 , and 2.4 kb for α i2 with levels suggesting a differential regulation (at transcription or post-transcription for α s , transcription for α i1 , and translation for α i2 ). The stimulatory effects of forskolin, vasoactive intestinal peptide (VIP) and isoproterenol on adenylyl cyclase activity increased between 0.5–3 mo, remained constant up to 12 mo and decreased thereafter, conceivably following the expression of VIP and β-adrenergic receptors. However, G-protein activation of adenylyl cyclase (by GTP and Gpp[NH]p) was maximal at 0.5 mo and then decreased as it occurred with toxin-catalyzed ADP-ribose incorporation to α subunits suggesting that other factors are also involved in the regulation of G-protein activity during rat prostatic development.