Peptide YY stimulates the expression of apolipoprotein A-IV gene in Caco-2 intestinal cells

Modulatory role of PYY in transport and metabolism of cholesterol in intestinal epithelial cells

Background

Gastrointestinal peptides are involved in modulating appetite. Other biological functions attributed to them include the regulation of lipid homeostasis. However, data concerning PYY remain fragmentary. The objectives of the study were: (i) To determine the effect of PYY on intestinal transport and synthesis of cholesterol, the biogenesis of apolipoproteins (apos) and assembly of lipoproteins and (ii) To analyze whether the effects of PYY are similar according to whether cells are exposed to PYY on apical or basolateral surface.

Methodology/Principal Findings

Caco-2/15 cells were incubated with PYY (1–36) administered either to the apical or basolateral medium, at concentrations of 50 or 200 nM for 24 hours. De novo synthesis of cholesterol, cholesterol uptake, and assembly of lipoproteins were evaluated through the incorporation of [¹⁴C]-acetate, [¹⁴C]-cholesterol, and [¹⁴C]-oleate, respectively. Biogenesis of apos (A-I, A-IV, E, B-48 and B-100) was examined by the incorporation of [³⁵S]-methionine. The influence of PYY on protein and mRNA levels of many key mediators of lipid metabolism was analyzed by Western blot and PCR, respectively. Our results show that PYY influenced cholesterol metabolism in Caco-2/15 cells depending on the site of PYY delivery. Apical addition of PYY significantly lowered the incorporation of [¹⁴C]-cholesterol likely via the reduction of NPC1L1, stimulated intracellular cholesterol synthesis probably through an increase in SREBP-2 expression, whereas it concomitantly increased apo A-I synthesis and decreased LDL secretion. In contrast, basolateral PYY reduced the production of chylomicrons (CM) as well as the biogenesis of apos B-48 and B-100, while lowering the expression of the transcription factors RXRα and PPAR(α,β).

Conclusions/Significance

PYY is capable of influencing cholesterol homeostasis in intestinal Caco-2/15 cells depending on the site delivery. Apical PYY was able to decrease cholesterol uptake via NPC1L1 downregulation, whereas basolateral PYY diminished CM output through the biogenesis decline of apos B-48 and B-100.

Peptide YY and Neuropeptide Y Induce Villin Expression, Reduce Adhesion, and Enhance Migration in Small Intestinal Cells through the Regulation of CD63, Matrix Metalloproteinase-3, and Cdc42 Activity

Peptide YY (PYY) and neuropeptide Y (NPY) are regulatory peptides synthesized in the intestine and brain, respectively, that modify physiological functions affecting nutrient assimilation and feeding behavior. Because PYY and NPY also alter the expression of intestine-specific differentiation marker proteins and the tetraspanin CD63, which is involved in cell adhesion, we investigated whether intestinal cell differentiation could be linked to mucosal cell adhesion and migration through these peptides. PYY and NPY significantly decreased cell adhesion and increased cell migration in a dose-dependent manner prior to cell confluency in our model system, non-tumorigenic small intestinal hBRIE 380i cells. Both peptides reduced CD63 expression and CD63-dependent cell adhesion. CD63 overexpression increased and antisense CD63 cDNA decreased intestinal cell adhesion. In parallel, both PYY and NPY increased expression of matrix metalloproteinase-3 (MMP-3) to a level sufficient to induce cell migration by activating the Rho GTPase Cdc42. The effects of both peptides on cell migration were blocked in cells constitutively overexpressing dominant-negative Cdc42. PYY and NPY also significantly induced the expression of the differentiation marker villin, which could be eliminated by an MMP inhibitor at a concentration that inhibits cell migration. Increased MMP-3 activity, which enhanced cell migration, also induced villin mRNA levels. Therefore, these data indicate that the alteration of adhesion and migration by PYY and NPY occurs in part by synchronous modulation of three proteins that are involved in extracellular matrix-basolateral membrane interactions, CD63, MMP-3 and Cdc42, and that PYY/NPY regulation of expression of mucosal proteins such as villin is linked to the process of cell migration and adhesion.

Further evidence for the association between obesity-related traits and the apolipoprotein A-IV gene

OBJECTIVE

To investigate associations and gene-environment interactions of APOA-IV gene polymorphisms with obesity-related phenotypes in a Brazilian population.

METHODS

A total of 391 individuals (171 men and 220 women) were genotyped for Xbal, Thr347Ser and Gln360His polymorphisms by PCR-RFLP methods. Adjusted body mass index (BMI) and waist circumference (WC) were compared among genotypes/haplotypes by unpaired t-test or analysis of variance. Gene-environment interactions were tested by analysis of variance using a general linear model.

RESULTS

Analysis of the APOA-IV gene variants separately showed that X*2 and 347Ser alleles were associated with higher BMI (P=0.02 for both polymorphisms). Haplotype analysis confirmed this association. For these polymorphisms, the effect on BMI appeared to depend on smoking status (test for interaction, P=0.007 and 0.02, respectively), the Thr347Ser variant was associated with a BMI increase in smokers only (P=0.002). At the single-locus level no association was observed between 360His allele and BMI; however, haplotype analyses showed an association of this gene variant and higher BMI. A trend for association with WC (P=0.05) was observed in male carriers of the 360His allele. The effect of this polymorphism also depended on smoking status (test for interaction, P=0.018). Nonsmoker male carriers of the 360His allele had a larger waist circumference than homozygotes for the Gln allele (P=0.003).

CONCLUSION

Our data suggest that the APOA-IV gene polymorphisms investigated are associated with obesity-related traits. The effects of X*2 and 347Ser variants on BMI and the 360His variant on waist circumference depended on smoking status.

Non-effect of hexamethonium, a ganglionic blocker, on the response of ileal apolipoprotein A-IV mRNA following a massive small bowel resection in rats

An intravenous infusion of hexamethonium, a ganglionic blocker, did not affect the increase in the apolipoprotein A-IV mRNA level in the residual ileum following a massive small bowel resection in unrestrained conscious rats. The result suggests that upregulation of the apolipoprotein A-IV gene in the residual ileum is not mediated by a neural pathway, including the nicotinic synapse route.

Intravenous infusion of hexamethonium and atropine but not propranolol diminishes apolipoprotein A-IV gene expression in rat ileum

To clarify the role of neural factors in the regulation of apolipoprotein (apo) A-IV expression in the small intestine, we investigated the effect of neural blockers on mRNA levels of apo A-IV in rat small intestine. Either ganglionic blocker (hexamethonium), cholinergic blocker (atropine) or beta-adrenergic blocker (propranolol) was infused intravenously to unrestrained conscious rats for 8 h, and then total RNA was isolated from the small intestine and analyzed using Northern hybridization. Apo A-IV mRNA levels in the ileum were significantly lower in hexamethonium- or atropine-infused rats than in saline- (control) or propranolol-infused rats. Immunoblot analysis showed no difference in plasma apo A-IV concentrations between hexamethonium- and saline-infused groups. The lower mRNA levels of apo A-IV in the ileum of hexamethonium-infused rats were observed even in bile-drained rats, indicating that the lower expression was not due to any changes in bile availability. The ileal apo A-IV mRNA levels were significantly higher in rats infused with lipid emulsion into the ileum than in rats infused with glucose-saline, and the concomitant infusion of intravenous hexamethonium did not affect the higher levels of apo A-IV mRNA. These results suggest that the basal expression of the ileal A-IV gene is at least partially regulated in a site-specific manner by cholinergic neurons.