Potential Down-Regulation of Salivary Gland AQP5 by LPS via Cross-Coupling of NF-κB and p-c-Jun/c-Fos

Abstract

The mRNA and protein levels of aquaporin (AQP)5 in the parotid gland were found to be potentially decreased by lipopolysaccharide (LPS) in vivo in C3H/HeN mice, but only weakly in C3H/HeJ, a TLR4 mutant mouse strain. In the LPS-injected mice, pilocarpine-stimulated saliva production was reduced by more than 50%. In a tissue culture system, the LPS-induced decrease in the AQP5 mRNA level was blocked completely by pyrrolidine dithiocarbamate, MG132, tyrphostin AG126, SP600125, and partially by SB203580, which are inhibitors for IkappaB kinase, 26S proteasome, ERK1/2, JNK, and p38 MAPK, respectively. In contrast, the expression of AQP1 mRNA was down-regulated by LPS and such down-regulation was blocked only by SP600125. The transcription factors NF-kappaB (p65 subunit), p-c-Jun, and c-Fos were increased by LPS given in vivo, whereas the protein-binding activities of the parotid gland extract toward the sequences for NF-kappaB but not AP-1-responsive elements present at the promoter region of the AQP5 gene were increased by LPS injection. Co-immunoprecipitation by using antibody columns suggested the physical association of the three transcription factors. These results suggest that LPS-induced potential down-regulation of expression of AQP5 mRNA in the parotid gland is mediated via a complex(es) of these two classes of transcription factors, NF-kappaB and p-c-Jun/c-Fos.

The laxative effect of bisacodyl is attributable to decreased aquaporin-3 expression in the colon induced by increased PGE2secretion from macrophages

“…sacodyl activates macrophages in the colon (24,29). Furthermore, TNF-␣ (9,19,38) and PGE 2 (25,39) decrease the expression levels of AQPs. Based on this, we examined whether bisacodyl directly activated macrophages and caused the secretion of TNF-␣ and PGE 2 using Raw264.7 cells.…”

Effects of isoproterenol on aquaporin 5 levels in the parotid gland of mice in vivo

“…The Bio-Rad protein assay kit was purchased from Bio-Rad Laboratories (Hercules, CA). Goat polyclonal anti-human -calpain antibody and goat anti-mouse amylase antibody, as well as their blocking solutions, were purchased from Santa Cruz Biotechnology (Santa Cruz, CA), whereas rabbit anti-AQP5 antibody was prepared in our laboratory (31). Donkey anti-goat and donkey anti-rabbit IgGs conjugated with FITC were from Jackson ImmunoResearch laboratories, (West Grove, PA).…”

“…The Fuji RX X-ray film was a product of Fuji Film (Kanagawa, Japan). All other reagents were procured as described previously (31).…”

“…Studies of the AQP5-mutant rat (18) and AQP5-knockout mice (13) as well as the model mouse of Sjögren's syndrome (26) have indicated that AQP5 plays a pivotal role in maintaining the normal physiological function of the salivary gland; i.e., some of these animals produce significantly hypertonic, viscous, and smaller volumes of saliva (13,18). The parotid gland (PG) belongs to one of the major salivary glands and expresses abundant AQP5 in the luminal membrane of its serous acinar cells (20,31). It was reported previously that isolated and disaggregated PG acinar cells prepared from AQP5-knockout mice showed a significant decrease in transmembrane water transport (9).…”

Role of aquaporins in saliva secretion

“…In some animal models for SS, altered SG AQP5 distribution appears to be concomitant with the presence of inflammatory infiltrates and acinar destruction 54 . Toll-like receptor activation and tumour necrosis factor α decreased AQP5 expression in SG 57,58 , while interferon α (improving xerostomia in SS patients) increased AQP5 expression 59 . Besides, auto-antibodies against M3 receptors, present in SS patients, inhibited AQP5 trafficking in SG cells 60 .…”