Pulmonary pericytes regulate lung morphogenesis.

Blood vessels are essential for blood circulation but also control organ growth, homeostasis, and regeneration, which has been attributed to the release of paracrine signals by endothelial cells. Endothelial tubules are associated with specialised mesenchymal cells, termed pericytes, which help to maintain vessel wall integrity. Here we identify pericytes as regulators of epithelial and endothelial morphogenesis in postnatal lung. Mice lacking expression of the Hippo pathway components YAP and TAZ in pericytes show defective alveologenesis. Mutant pericytes are present in normal numbers but display strongly reduced expression of hepatocyte growth factor leading to impaired activation of the c-Met receptor, which is expressed by alveolar epithelial cells. YAP and TAZ are also required for expression of angiopoietin-1 by pulmonary pericytes, which also controls hepatocyte growth factor expression and thereby alveologenesis in an autocrine fashion. These findings establish that pericytes have important, organ-specific signalling properties and coordinate the behavior of epithelial and vascular cells during lung morphogenesis.

Inflammation increases cells expressing ZSCAN4 and progenitor cell markers in the adult pancreas.

We have recently identified the zinc finger and SCAN domain containing 4 (Zscan4), which is transiently expressed and regulates telomere elongation and genome stability in mouse embryonic stem (ES) cells. The aim of this study was to examine the expression of ZSCAN4 in the adult pancreas and elucidate the role of ZSCAN4 in tissue inflammation and subsequent regeneration. The expression of ZSCAN4 and other progenitor or differentiated cell markers in the human pancreas was immunohistochemically examined. Pancreas sections of alcoholic or autoimmune pancreatitis patients before and under maintenance corticosteroid treatment were used in this study. In the adult human pancreas a small number of ZSCAN4-positive (ZSCAN4⁺) cells are present among cells located in the islets of Langerhans, acini, ducts, and oval-shaped cells. These cells not only express differentiated cell markers for each compartment of the pancreas but also express other tissue stem/progenitor cell markers. Furthermore, the number of ZSCAN4⁺ cells dramatically increased in patients with chronic pancreatitis, especially in the pancreatic tissues of autoimmune pancreatitis actively regenerating under corticosteroid treatment. Interestingly, a number of ZSCAN4⁺ cells in the pancreas of autoimmune pancreatitis returned to the basal level after 1 yr of maintenance corticosteroid treatment. In conclusion, coexpression of progenitor cell markers and differentiated cell markers with ZSCAN4 in each compartment of the pancreas may indicate the presence of facultative progenitors for both exocrine and endocrine cells in the adult pancreas.

Molecular mechanisms of pancreatic stone formation in chronic pancreatitis.

Chronic pancreatitis (CP) is a progressive inflammatory disease in which the pancreatic secretory parenchyma is destroyed and replaced by fibrosis. The presence of intraductal pancreatic stone(s) is important for the diagnosis of CP; however, the precise molecular mechanisms of pancreatic stone formation in CP were left largely unknown. Cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel expressed in the apical plasma membrane of pancreatic duct cells and plays a central role in [Formula: see text] secretion. In previous studies, we have found that CFTR is largely mislocalized to the cytoplasm of pancreatic duct cells in all forms of CP and corticosteroids normalizes the localization of CFTR to the proper apical membrane at least in autoimmune pancreatitis. From these observations, we could conclude that the mislocalization of CFTR is a cause of protein plug formation in CP, subsequently resulting in pancreatic stone formation. Considering our observation that the mislocalization of CFTR also occurs in alcoholic or idiopathic CP, it is very likely that these pathological conditions can also be treated by corticosteroids, thereby preventing pancreatic stone formation in these patients. Further studies are definitely required to clarify these fundamental issues.

Effects of CFTR gene silencing by siRNA or the luminal application of a CFTR activator on fluid secretion from guinea-pig pancreatic duct cells.

AIMS: The cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP regulated chloride channel expressed in the apical plasma membrane of pancreatic duct cells where it plays an important role in fluid secretion. The purpose of this study was to elucidate the role of the CFTR chloride channel on ion and fluid secretion from the guinea-pig pancreas by manipulating the expression of CFTR by RNA interference or by luminal application of a CFTR selective activator, MPB91, in isolated cultured pancreatic ducts. MATERIALS AND METHODS: Using cDNA isolated from the guinea-pig small intestine, fragments of the CFTR gene were generated by polymerase chain reaction and directly sequenced. Two different RNA duplexes for small interference RNA (siRNA) were designed from the sequence obtained. Fluid secretion from the isolated guinea-pig pancreatic ducts was measured using video-microscopy. The amount of CFTR chloride channel or AQP1 water channel expressed in pancreatic ducts was examined by immunoblotting with antibodies against CFTR or AQP1, respectively. RESULTS: Guinea-pig CFTR consists of 1481 amino acid residues. An additional glutamine residue was found to be inserted between amino acid residues 403 and 404 of human CFTR. Forskolin-stimulated fluid secretion from intact pancreatic ducts was significantly higher in the presence of MPB91 compared to fluid secretion in the absence of MPB91. Both basal and forskolin-stimulated fluid secretion in pancreatic ducts transfected with CFTR specific siRNAs were reduced by ∼50% compared to fluid secretion from ducts transfected with scrambled negative control dsRNAs. The amount of CFTR and AQP1 proteins was reduced to 34% and 45% of control, respectively. CONCLUSIONS: The activity of the CFTR chloride channel or the amount of CFTR protein expressed determines the rate of fluid secretion from the isolated guinea-pig pancreatic ducts.

Corticosteroids correct aberrant CFTR localization in the duct and regenerate acinar cells in autoimmune pancreatitis.

BACKGROUND & AIMS: Corticosteroids are now widely accepted as a treatment for autoimmune pancreatitis (AIP). However, the molecular mechanism by which steroid treatment improves AIP remains largely unknown. The aim of this study was to elucidate cellular mechanisms by which corticosteroids improve both pancreatic exocrine function and histopathology in AIP. METHODS: Pancreatic exocrine function was evaluated by the secretin-stimulated function test and pancreatic biopsy specimens were processed for histologic analysis at the time of diagnosis and 3 months after initiation of steroid treatment. Expression and localization of proteins was assayed by immunohistochemistry. Analysis of immunoglobulin (Ig)G4-positive plasma cells was used to verify inflammation in AIP. RESULTS: The number of IgG4-positive plasma cells in pancreatic sections was decreased by steroid treatment, indicating reduced inflammation. Fluid, bicarbonate (HCO(3)(-)), and digestive enzyme secretions all were impaired in most patients with AIP. Corticosteroids improved both HCO(3)(-) and digestive enzyme secretion. A large fraction of the cystic fibrosis transmembrane conductance regulator (CFTR), which plays a central role in pancreatic duct HCO(3)(-) secretion, was mislocalized to the cytoplasm of duct cells before treatment. Corticosteroids corrected the localization of CFTR to the apical membrane, accounting for the improved HCO(3)(-) secretion. Steroid treatment resulted in regeneration of acinar cells, accounting for restored digestive enzyme secretion. CONCLUSIONS: Corticosteroids reduce inflammation and restore both digestive enzyme and HCO(3)(-) secretion in patients with AIP by regenerating acinar cells and correcting CFTR localization in pancreatic duct cells. Mislocalization of CFTR may explain aberrant HCO(3)(-) secretion in other forms of pancreatitis.

Aquaporin 1 water channel is overexpressed in the plasma membranes of pancreatic ducts in patients with autoimmune pancreatitis.

Chronic pancreatitis with all kinds of etiologies is characterized by pancreatic exocrine dysfunction especially impaired fluid secretion from pancreatic ducts. However, the molecular mechanism of this impaired fluid secretion in chronic pancreatitis is largely unknown. Aquaporin water channels are intrinsic membrane proteins expressed most of the cell types which have high osmotic water permeability. Among them aquaporin 1 (AQP1) is a predominant water channel expressed in the plasma membranes of human pancreatic ducts. Exocrine function test revealed that fluid secretion was severely impaired in AIP. immunohistochemical analysis revealed that AQP1 is localized mainly in the apical and lateral membranes of small pancreatic ducts in control subjects. AQP1 expression was significantly increased in plasma membranes of pancreatic ducts in AIP. Upregulation of AQP1 expression seen in pancreatic ducts of patient with AIP may be caused by the reduced fluid secretion from the pancreas as compensation. Further study would be required to elucidate the precise molecular mechanism for the role of AQP1 in pancreatic fluid secretion from the pancreas in diseases characterized by the impaired ductal fluid secretion such as cystic fibrosis.