Pancreatic exocrine insufficiency in LXRbeta-/- mice is associated with a reduction in aquaporin-1 expression - PubMed (original) (raw)

Pancreatic exocrine insufficiency in LXRbeta-/- mice is associated with a reduction in aquaporin-1 expression

Chiara Gabbi et al. Proc Natl Acad Sci U S A. 2008.

Abstract

Liver X receptors (LXRs) alpha and beta are nuclear oxysterol receptors with a key role in cholesterol, triglyceride, and glucose metabolism. In LXRbeta(-/-) mice on a normal diet, there is a reduction in size of perigonadal fat pad and, on high-fat diet there is resistance to obesity. In the present study, we investigated the reason for the resistance of LXRbeta(-/-) mice to weight gain. In LXRbeta(-/-) mice we found pancreatic exocrine insufficiency with reduced serum levels of amylase and lipase, reduced proteolytic activity in feces, chronic inflammatory infiltration, and, in the ductal epithelium, an increased apoptosis without compensatory proliferation. Electron microscopy revealed ductal dilatation with intraductal laminar structures characteristic of cystic fibrosis. To investigate the relationship between LXRbeta and pancreatic secretion, we studied the expression of LXRbeta and the water channel, aquaporin-1 (AQP1), in the ductal epithelium of the pancreas. In WT mice, ductal epithelial cells expressed LXRbeta in the nuclei and AQP1 on the plasma membrane. In LXRbeta(-/-) mice neither LXRbeta nor AQP1 was detectable. Moreover, in WT mice the LXR agonist (T2320) increased AQP1 gene expression. These data demonstrate that in LXRbeta(-/-) mice dietary resistance to weight gain is caused by pancreatic insufficiency and that LXRbeta regulates pancreatic exocrine secretion through the control of AQP1 expression. Pancreatic exocrine insufficiency is the main cause of malabsorption syndrome responsible for weight loss in adults and growth failure in children. Several genes are known to be involved in the pathogenesis and susceptibility to pancreatic insufficiency. LXRbeta should be included in that list.

PubMed Disclaimer

Conflict of interest statement

Conflict of interest statement: J.-Å.G. is a shareholder and consultant of KaroBio AB.

Figures

Fig. 1.

Fig. 1.

Serum lipase, α-amylase, and fecal total protease in 11-month-old male and female mice. (A and B) Levels of lipase (U/l) (A) and α-amylase (U/l) (B) in serum are significantly lower in LXRβ−/− male and female mice than in WT mice. LXRα−/−β−/− serum α-amylase but not lipase is reduced. (C) Total proteases (units/mg) in feces are lower in male LXRβ−/− mice and female mice of all of the knockout genotypes. Data represent the mean ± SEM. *, P < 0.05 versus WT.

Fig. 2.

Fig. 2.

Immuno-morphological study of 11-month-old female pancreas. (A and B) Hematoxylin-eosin staining demonstrates a large infiltration of immune cells all around medium-sized pancreatic ducts of LXRβ−/− mice (B) compared with WT mice (A). (C and D) TUNEL staining (green) shows more apoptotic epithelial cells in the pancreatic ducts in LXRβ−/− mice (D) than in WT mice (C). Nuclei are counterstained with DAPI. (E and F) There are no detectable differences between WT mice (E) and LXRβ−/− mice (F) in BrdU-positive cells in pancreatic ducts. (Scale bars: 10 μm.)

Fig. 3.

Fig. 3.

Pancreatic electron microscopy study of 11-month-old male mice. (A and B) Laminar structures, characteristic of sticky secretions in luminal region of pancreatic ducts, are detectable in LXRβ−/− mice (B) where a dilatation of the ducts is also evident compared with WT mice (A). (C and D) Cisternae of Golgi apparatus are more dilated in LXRβ−/− mice (D) than in WT mice (C). (Scale bars: 1 μm.)

Fig. 4.

Fig. 4.

Study of LXRβ localization in pancreatic ducts. (A) LXRβ-positive immunoreactivity is detectable in the nuclear region of pancreatic ductal epithelial cells. (B and C) The staining is eliminated after preadsorption of the antibody with LXRβ protein (B), and there is no nuclear staining in the ductal cells of LXRβ−/− mice (C). (D) Nuclear fractions isolated from WT, LXRβ−/− mice and LXRα−/−β−/− mice were examined on Western blots probed with LXRβ antibody. A band of 56 kDa, the same molecular mass as the LXRβ standard protein, is detectable in WT mice but not in LXRβ−/− or LXRα−/−β−/− mice. (Scale bars: 10 μm.)

Fig. 5.

Fig. 5.

Expression of AQP1 in pancreas of WT and LXRβ−/− mice. (A) mRNA levels of AQP-1 are significantly decreased in 11-month-old LXRβ−/− female mice. Values of WT mice were taken as 1, and the knockout mouse values are expressed relative to WT mice. Data represent the mean ± SE. *, P < 0.05 versus WT. (B and C) Protein levels detected with immunohistochemistry are markedly reduced in pancreatic ducts of LXRβ−/− female mice (C) compared with WT mice (B). Positive staining is detectable on the luminal membrane of ductal epithelial cells in WT mice. Staining of AQP-1 in endothelial cells of small blood vessels is still detectable in the knockout animal. (Scale bars: 10 μm.)

Fig. 6.

Fig. 6.

AQP1 mRNA levels after LXR agonist treatment. After 7 days of LXR agonist (T2320 Sigma–Aldrich) treatment (20 mg/kg), AQP1 mRNA relative expression, quantified with real-time RT-PCR, is significantly increased. Values of vehicle-treated mice were taken as 1, and T2320-treated mouse values are expressed relative to vehicle. Data represent the mean ± SE. *, P < 0.05 versus vehicle.

Similar articles

Cited by

References

    1. Owens SR, Greenson JK. The pathology of malabsorption: Current concepts. Histopathology. 2007;50:64–82. - PubMed
    1. Witt H. Chronic pancreatitis and cystic fibrosis. Gut. 2003;52(Suppl 2):ii31–41. - PMC - PubMed
    1. Witt H, Apte MV, Keim V, Wilson JS. Chronic pancreatitis: Challenges and advances in pathogenesis, genetics, diagnosis, and therapy. Gastroenterology. 2007;132:1557–1573. - PubMed
    1. Balog A, et al. Polymorphism of the TNF-α, HSP70–2, and CD14 genes increases susceptibility to severe acute pancreatitis. Pancreas. 2005;30:e46–e50. - PubMed
    1. Janowski BA, et al. Structural requirements of ligands for the oxysterol liver X receptors LXRα and LXRβ. Proc Natl Acad Sci USA. 1999;96:266–271. - PMC - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources