Binding of vasoactive intestinal polypeptide to dispersed enterocytes results in rapid removal of the NH2-terminal histidyl residue

The G Protein-Coupled Receptor, VPAC1, Mediates Vasoactive Intestinal Peptide-Dependent Functional Homeostasis of the Gut Microbiota

BACKGROUND AND AIMS

Vasoactive intestinal peptide (VIP) is a neuropeptide involved in the regulation of feeding behavior and circadian rhythms, metabolism, and immunity. Previous studies revealed the homeostatic effects of VIP signaling on the gut microbiota. VIP-deficient mice demonstrate a gut microbiota dysbiosis characterized by reduced α-diversity and decreased relative abundance (RA) of Gram-positive Firmicutes. However, the mechanism by which VIP signaling affects changes in the microbiota is unknown.

METHODS

To investigate the role of the 2 cognate G protein-coupled receptors for VIP (VPAC1 and VPAC2) in VIP-mediated homeostasis of the microbiota, fecal samples from VPAC1- and VPAC2-deficient, heterozygous, and wild-type littermate mice were assessed via targeted amplicon sequencing. Their microbiota profiles were additionally compared with microbiota from VIP-deficient, heterozygous, and wild-type littermates, where genotype-dependent changes in the composition and predicted function of each cohort were compared.

RESULTS

While wild-type mice in each line differed in α-diversity and β-diversity, consistent changes in both metrics were observed in VIP-deficient and VPAC1-deficient mice. This includes a dramatic reduction in α-diversity, increased RA of Proteobacteria and Bacteroidetes, and decreased RA of Lachnospiraceae, Ruminococcaceae, Muribaculaceae, and Rikenellaceae. Specific amplicon sequence variants and predicted functions found to differ significantly based on VIP or VPAC1 genotype were concordant in their directions of change. Multiplatform predicted functional profiling suggested a defective VIP-VPAC1 axis was associated with reduced amino acid degradation along with reduced quinol and quinone biosynthesis. Furthermore, alterations in predicted functions include increased sugar degradation, nitrate reduction, and fatty acid biosynthetic pathways, among other changes.

CONCLUSION

We conclude that VIP signaling through VPAC1 is critical for the maintenance of normal function of the gut microbiota.

Interaction of lipophilic VIP derivatives with recombinant VIP1/PACAP and VIP2/PACAP receptors

Stearyl vasoactive intestinal polypeptide has been reported to be a VIP (vasoactive intestinal polypeptide) receptor agonist of high potency with an original bioavailability and action. We synthesized three fatty acyl derivatives, myristyl-, palmityl- and stearyl-[Nle17]VIP, and tested their capacity to recognize recombinant rat- and human VIP1- and VIP2/PACAP (pituitary adenylate cyclase-activating polypeptide) receptors and to stimulate adenylate cyclase activity. The three lipophilic analogues bound with high affinity (from 0.5 to 20 nM) to both receptor subtypes but did not distinguish between them. In preparations expressing a high density of human VIP1/PACAP receptors, the three lipophilic analogues had the same efficacy as VIP and [Nle17]VIP. In preparations expressing the rat receptors, stearyl-[Nle17]VIP had a lower efficacy than the other peptides tested. In preparations expressing a low level of VIP1/PACAP receptors and in those expressing VIP2/PACAP receptors, all analogues behaved like partial agonists. The lowest efficacy was observed for stearyl-[Nle17]VIP on the VIP2/PACAP receptor subclass. Based on our results, a complex pattern of in vivo biological effects of the lipophilic VIP derivatives should be expected: these compounds might behave as full agonists, partial agonists, or antagonists of the VIP response, depending on the number and the subtype of receptor expressed.

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP-27, but not PACAP-38) degradation by the neutral endopeptidase EC 3.4.24.11

VIP (vasoactive intestinal polypeptide) and PACAP (pituitary adenylate cyclase-activating polypeptide), which are potent relaxing agents in the airways, were submitted to in vitro degradation by the neutral endopeptidase EC 3.4.24.11 (NEP), one of the most active peptidase in the lung, to test their relative resistance to proteolysis. Both VIP and PACAP(1-27) were cleaved by NEP, but PACAP(1-38) was not. The main fragments produced were VIP(1-22) and VIP(1-25), and PACAP(1-22) and PACAP(1-25), respectively. The degradation of VIP(1-27), PACAP(6-27), and PACAP(13-27) was also hindered by extending their C-terminal ends with the (28-38) sequence of PACAP(1-38). The sensitivity to enzyme degradation was gradually reduced when the C-terminal extension was increased from PACAP(1-27) to PACAP(1-29), PACAP(1-32) and PACAP(1-38). The biological activities of the degradation products were evaluated on the three classes of PACAP/VIP receptors, with VIP(1-25) and PACAP(1-25) retaining an important part of their activities on the VIP1 receptor. Thus, the degradation of VIP and PACAP(1-27) by the neutral endopeptidase 24.11 might produce a VIP1 receptor-selective active metabolite, provided that very high VIP or PACAP(1-27) concentrations are achieved in the receptor vicinity.

Characterization of VIP receptor-effector system antagonists in rat and mouse peritoneal macrophages

In the present study we show that the synthetic peptides [4-Cl-D-Phe6,Leu17]VIP and the growth hormone releasing factor (GRF) analog [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 inhibit in a competitive manner the specific [125I]VIP binding to both rat and mouse peritoneal macrophages. In rat peritoneal macrophages, the order of potency of the different peptides, as expressed by the IC50 values was: VIP (IC50 = 1.90 +/- 0.16 nM) > [4-Cl-D-Phe6,Leu17]VIP (IC50 = 125.8 +/- 13.2 nM) > [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 (IC50 = 354.8 +/- 21.2 nM). In mouse peritoneal macrophages a similar pattern of potency was observed: VIP (IC50 = 1.58 +/- 0.12 nM) > [4-Cl-D-Phe6,Leu17]VIP (IC50 = 110.8 +/- 10.7 nM) > [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 (IC50 = 251 +/- 19.2 nM). The behavior as VIP receptor antagonists of both [4-Cl-D-Phe6,Leu17]VIP and [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 in rat and mouse peritoneal macrophages was confirmed by: (a) the shift to the right of VIP dose-stimulated cyclic AMP production curves in the presence of the two antagonists; (b) the agreement between the order of efficacy of the two peptides in competition experiments with the corresponding inhibition of cyclic AMP production; (c) the inefficiency of the two antagonists on the stimulation of cyclic AMP production by the beta-adrenoceptor agonist isoproterenol, which indicates the specificity of the interaction; (d) the synergic effect of VIP on isoproterenol-stimulated cyclic AMP production was completely abolished by [4-Cl-D-Phe6,Leu17]VIP or [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2, suggesting that both antagonists acted via specific VIP receptors. Moreover, propranolol, a beta-adrenoceptor antagonist, did not affect the VIP-stimulated cyclic AMP production and the antagonist role of [4-Cl-D-Phe6,Leu17]VIP or [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2; (e) in cross-linking experiments, the intensity of the labeling of the [125I]VIP/receptor complexes was significantly lower with the antagonists than in the control experimental situation in both mouse and rat peritoneal macrophage membranes.

Thymosin alpha 1 interacts with the VIP receptor-effector system in rat and mouse immunocompetent cells

Thymic peptide thymosin alpha 1 (10(-11) to 10(-6) M) is shown to interact with the VIP receptor-effector system in rat and mouse peritoneal macrophages, and both rat peripheral blood lymphocytes and spleen lymphocytes. In all models, thymosin alpha 1 inhibits 125I-VIP binding with a potency that is in a range 1000-1700 times lower than that of the native VIP. Interaction of thymosin alpha 1 with VIP receptors is compared with that of some structurally VIP-related peptides such as helodermin, PHI, secretin, and glucagon. The order of potency in inhibiting 125I-VIP binding was VIP > helodermin > PHI > secretin > thymosin alpha 1. Thymosin alpha 1 (10(-10) to 10(-6) M) was weak in stimulating adenylyl cyclase activity. Its efficacy is in a range 900-1800 times lower than that of native VIP in all cell types studied. The analysis of the sequence of both complete and N-terminal portion of thymosin alpha 1 reveals close structural and physicochemical similarities with the members of the so-called VIP family of polypeptides. Taken together, experimental data support that thymosin alpha 1 must be included like the lowest partial agonist of the VIP family of polypeptides and it is a VIP receptor antagonist with weak intrinsic activity.

Jejunal toxin inactivation regulates susceptibility of the immature rat to STa

The immature rat jejunum demonstrates an increased response, sensitivity, and susceptibility to heat-stable enterotoxin. In the present study, the hypothesis that this increased secretory response results from diminished jejunal toxin inactivation and persistence of biologically active toxin was tested. A modification of toxin injected into ligated jejunal loops was observed in both adult and immature rats. However, in the immature jejunum there was also persistence of biologically active toxin and continued toxin-induced secretion. In contrast, in the adult jejunum there was inactivation of toxin and cessation of secretion. Incubation of toxin with luminal fluid, pancreatic fluid, or jejunal brush border membranes resulted in toxin alteration. However, a completely inactive toxin species was generated only after incubation with jejunal organ culture slices. It is concluded that (a) incomplete toxin inactivation in the immature rat jejunum contributes to prolonged intestinal secretion and that (b) the inactivation process is multifactorial, but it is likely that final toxin inactivation requires the participation of the enterocyte. These findings may help explain the increased responsiveness of the immature intestine to heat-stable enterotoxin.

High affinity receptors for vasoactive intestinal peptide on a human glioma cell line

Vasoactive intestinal peptide (VIP) bound with high affinity (Kd 0.13 nmol/l) to receptors on the human glioma cell line U-343 MG Cl 2:6. The receptors bound the related peptides helodermin, PHM and secretin with 10, 400 and 5000 times lower affinity, respectively. Deamidated VIP (VIP-COOH) and [des-His1]VIP bound with 10 and 100 times lower affinity. The fragment VIP(7-28) displaced 25% of the receptor-bound 125I-VIP whereas VIP(16-28) and VIP(1-22-NH2) were inactive. The binding of 125I-VIP could be completely inhibited by 10 mumol/l of the antagonists [N-Ac-Tyr1,D-Phe2]GRF(1-29)-NH2, [pCl-D-Phe6,Leu17]VIP and VIP(10-28); in contrast, the antagonist L-8-K was inactive. Affinity labeling showed that VIP bound to proteins with Mr's of 75 kDa, 66 kDa and 50 kDa, respectively. Following binding, the peptide was rapidly internalized, and at steady-state only 20% of cell-associated 125I-VIP was bound to receptors on the cell surface. The internalized 125I-VIP was completely degraded to 125I-tyrosine which was released from the cells. Degradation of internalized 125I-VIP was significantly reduced by chloroquine phenanthroline and pepstatin-A. Surface binding and internalization of 125I-VIP was increased 3 times by phenanthroline, and pepstatin-A caused a 5 times increase in surface binding. Chloroquine reduced surface-bound 125I-VIP, but caused retention of internalized 125I-VIP.

Effects of preprovasoactive intestinal polypeptide-derived peptides on ileal output

Tumors associated with the Verner Morrison syndrome secrete peptide histidine methionine, its C-terminally extended variant peptide histidine valine, and vasoactive intestinal peptide. There is evidence that vasoactive intestinal peptide mediates diarrhea, but recent evidence suggested that peptide histidine methionine and peptide histidine valine may be at least as important. Infusion of vasoactive intestinal peptide, peptide histidine methionine, and peptide histidine valine into patients with ileostomies produced mean plateau plasma levels of 163, 1301, and 2106 pM, respectively, which are within the range seen in the Verner Morrison syndrome. Vasoactive intestinal peptide produced an integrated ileal output of 174 (53) g (mean [SEM]), compared with only 20 (7) g with peptide histidine methionine and 10 (3) g with peptide histidine valine. These results suggest that vasoactive intestinal peptide is substantially more important than peptide histidine methionine or peptide histidine valine in mediating diarrhea in the Verner Morrison syndrome.

The isolation and chemical characterization of a novel vasoactive intestinal peptide-related peptide from a teleost fish, the cod, Gadus morhua

An octacosapeptide that shows sequence homology to porcine vasoactive intestinal peptide (VIP) has been isolated from a teleost fish, the cod, Gadus morhua. The full primary sequence is His-Ser-Asp-Ala-Val-Phe-Thr-Asp-Asn-Tyr-Ser-Arg-Phe-Arg-Lys-Gln-Met-Ala-Ala- Lys-Lys-Tyr-Leu-Asn-Ser-Val-Leu-Ala. This peptide contains four, or five substitutions, compared with dogfish and porcine VIP, respectively. The residues in positions 13, 26 and 28 are different in all three species. These substitutions seem to have little effect on bioactivity, since cod VIP was virtually equipotent with porcine VIP in stimulating amylase release from guinea-pig pancreatic acini. During the isolation procedure an N-terminally modified form of VIP (Des-His, or 2-28 cod VIP) was also isolated. The available data suggest the sequence of VIP is well conserved in vertebrates which is consistent with an important biological role.

Binding sites for peptide-histidine-isoleucine (PHI) on rat insulinoma-derived RINm5F cells

Specific binding sites for 125I-labelled rat peptide-histidine-isoleucine (PHI) were identified on rat insulinoma-derived RINm5F cells. The concentrations of peptides producing half-maximal displacement of label were rat PHI, 0.36 +/- 0.14 nM, vasoactive intestinal polypeptide (VIP), 0.38 +/- 0.13 nM and secretin, approximately 0.2 microM. Glucagon and glucagon-like peptide-1(7-36)amide were without effect on binding. PHI and VIP produced dose-dependent increases in cAMP production in the cells that were significantly (P less than 0.05) above unstimulated rates for ligand concentrations between 10(-8) and 10(-6) M. Both PHI and VIP produced a small but significant (P less than 0.05) enhancement in the rate of release of immunoreactive insulin from the cells but the effect was not dose dependent.