Differentiation of columnar epithelia: the hensin pathway

Apical cell expansion maintained by Dusky-like establishes a scaffold for corneal lens morphogenesis

The biconvex shape of the Drosophila corneal lens, which enables it to focus light onto the retina, arises by organized assembly of chitin and other apical extracellular matrix components. We show here that the Zona Pellucida domain-containing protein Dusky-like is essential for normal corneal lens morphogenesis. Dusky-like transiently localizes to the expanded apical surfaces of the corneal lens-secreting cells, and in its absence, these cells undergo apical constriction and apicobasal contraction. Dusky-like also controls the arrangement of two other Zona Pellucida-domain proteins, Dumpy and Piopio, external to the developing corneal lens. Loss of either dusky-like or dumpy delays chitin accumulation and disrupts the outer surface of the corneal lens. Artificially inducing apical constriction with constitutively active Myosin light chain kinase is sufficient to similarly alter chitin deposition and corneal lens morphology. These results demonstrate the importance of cell shape for the morphogenesis of overlying apical extracellular matrix structures.

Nrf2 deficiency causes hepatocyte dedifferentiation and reduced albumin production in an experimental extrahepatic cholestasis model

The transcription factor Nrf2 modulates the initiation and progression of a number of diseases including liver disorders. We evaluated whether Nrf2 mediates hepatic adaptive responses to cholestasis. Wild-type and Nrf2-null mice were subjected to bile duct ligation (BDL) or a sham operation. As cholestasis progressed to day 15 post-BDL, hepatocytes in the wild-type mice exhibited a tendency to dedifferentiate, indicated by the very weak expression of hepatic progenitor markers: CD133 and tumor necrosis factor-like weak induced apoptosis receptor (Fn14). During the same period, Nrf2 deficiency augmented this tendency, manifested by higher CD133 expression, earlier, stronger, and continuous induction of Fn14 expression, and markedly reduced albumin production. Remarkably, as cholestasis advanced to the late stage (40 days after BDL), hepatocytes in the wild-type mice exhibited a Fn14+ phenotype and strikingly upregulated the expression of deleted in malignant brain tumor 1 (DMBT1), a protein essential for epithelial differentiation during development. In contrast, at this stage, hepatocytes in the Nrf2-null mice entirely inhibited the upregulation of DMBT1 expression, displayed a strong CD133+/Fn14+ phenotype indicative of severe dedifferentiation, and persistently reduced albumin production. We revealed that Nrf2 maintains hepatocytes in the differentiated state potentially via the increased activity of the Nrf2/DMBT1 pathway during cholestasis.

The Salivary Scavenger and Agglutinin (SALSA) in Healthy and Complicated Pregnancy

Pre-eclampsia is a leading cause of maternal and perinatal morbidity and mortality worldwide. The etiology is not clear, but an immune attack towards components of placenta or fetus has been indicated. This involves activation of the complement system in the placenta. We have previously described the presence of the complement-regulating protein salivary scavenger and agglutinin (SALSA) in amniotic fluid. In this study we investigated the potential role of SALSA in pregnancy by analyzing its presence in amniotic fluid and placental tissue during healthy and complicated pregnancies. SALSA levels in amniotic fluid increased during pregnancy. Before 20 weeks of gestation the levels were slightly higher in patients who later developed pre-eclampsia than in gestation age-matched controls. In the placenta of pre-eclamptic patients syncytial damage is often followed by the formation of fibrinoid structures. SALSA was found clustered into these fibrinoid structures in partial co-localization with complement C1q and fibronectin. In vitro analysis showed direct protein binding of SALSA to fibronectin. SALSA binds also to fibrin/fibrinogen but did not interfere with the blood clotting process in vitro. Thus, in addition to antimicrobial defense and epithelial differentiation, the data presented here suggest that SALSA, together with fibronectin and C1q, may be involved in the containment of injured placental structures into fibrinoids.

Uriniferous tubule: structural and functional organization

The uriniferous tubule is divided into the proximal tubule, the intermediate (thin) tubule, the distal tubule and the collecting duct. The present chapter is based on the chapters by Maunsbach and Christensen on the proximal tubule, and by Kaissling and Kriz on the distal tubule and collecting duct in the 1992 edition of the Handbook of Physiology, Renal Physiology. It describes the fine structure (light and electron microscopy) of the entire mammalian uriniferous tubule, mainly in rats, mice, and rabbits. The structural data are complemented by recent data on the location of the major transport- and transport-regulating proteins, revealed by morphological means(immunohistochemistry, immunofluorescence, and/or mRNA in situ hybridization). The structural differences along the uriniferous tubule strictly coincide with the distribution of the major luminal and basolateral transport proteins and receptors and both together provide the basis for the subdivision of the uriniferous tubule into functional subunits. Data on structural adaptation to defined functional changes in vivo and to genetical alterations of specified proteins involved in transepithelial transport importantly deepen our comprehension of the correlation of structure and function in the kidney, of the role of each segment or cell type in the overall renal function,and our understanding of renal pathophysiology.

Proteomic profiling of paraffin-embedded samples identifies metaplasia-specific and early-stage gastric cancer biomarkers

Early diagnosis and curative resection are the predominant factors associated with increased survival in patients with gastric cancer. However, most gastric cancer cases are still diagnosed at later stages. Since most pathologic specimens are archived as FFPE samples, the ability to use them to generate expression profiles can greatly improve cancer biomarker discovery. We sought to uncover new biomarkers for stomach preneoplastic metaplasias and neoplastic lesions by generating proteome profiles using FFPE samples. We combined peptide isoelectric focusing and liquid chromatography-tandem mass spectrometry analysis to generate proteomic profiles from FFPE samples of intestinal-type gastric cancer, metaplasia, and normal mucosa. The expression patterns of selected proteins were analyzed by immunostaining first in single tissue sections from normal stomach, metaplasia, and gastric cancer and later in larger tissue array cohorts. We detected 60 proteins up-regulated and 87 proteins down-regulated during the progression from normal mucosa to metaplasia to gastric cancer. Two of the up-regulated proteins, LTF and DMBT1, were validated as specific markers for spasmolytic polypeptide-expressing metaplasia and intestinal metaplasia, respectively. In cancers, significantly lower levels of DMBT1 or LTF correlated with more advanced disease and worse prognosis. Thus, proteomic profiling using FFPE samples has led to the identification of two novel markers for stomach metaplasias and gastric cancer prognosis.

Terminal differentiation in epithelia: the role of integrins in hensin polymerization

Epithelia, the most abundant cell type, differentiate to protoepithelia from stem cells by developing apical and basolateral membrane domains and form sheets of cells connected by junctions. Following this differentiation step, the cells undergo a second step (terminal differentiation), during which they acquire a mature phenotype, which unlike the protoepithelial one is tissue and organ specific. An extracellular matrix (ECM) protein termed hensin (DMBT1) mediates this differentiation step in the kidney intercalated cells. Although hensin is secreted as a soluble monomer, it requires polymerization and deposition in the ECM to become active. The polymerization step is mediated by the activation of inside-out signaling by integrins and by the secretion of two proteins: cypA (a cis-trans prolyl isomerase) and galectin 3.

Deletion of hensin/DMBT1 blocks conversion of beta- to alpha-intercalated cells and induces distal renal tubular acidosis

Acid-base transport in the renal collecting tubule is mediated by two canonical cell types: the β-intercalated cell secretes HCO(3) by an apical Cl:HCO(3) named pendrin and a basolateral vacuolar (V)-ATPase. Acid secretion is mediated by the α-intercalated cell, which has an apical V-ATPase and a basolateral Cl:HCO(3) exchanger (kAE1). We previously suggested that the β-cell converts to the α-cell in response to acid feeding, a process that depended on the secretion and deposition of an extracellular matrix protein termed hensin (DMBT1). Here, we show that deletion of hensin from intercalated cells results in the absence of typical α-intercalated cells and the consequent development of complete distal renal tubular acidosis (dRTA). Essentially all of the intercalated cells in the cortex of the mutant mice are canonical β-type cells, with apical pendrin and basolateral or diffuse/bipolar V-ATPase. In the medulla, however, a previously undescribed cell type has been uncovered, which resembles the cortical β-intercalated cell in ultrastructure, but does not express pendrin. Polymerization and deposition of hensin (in response to acidosis) requires the activation of β1 integrin, and deletion of this gene from the intercalated cell caused a phenotype that was identical to the deletion of hensin itself, supporting its critical role in hensin function. Because previous studies suggested that the conversion of β- to α-intercalated cells is a manifestation of terminal differentiation, the present results demonstrate that this differentiation proceeds from HCO(3) secreting to acid secreting phenotypes, a process that requires deposition of hensin in the ECM.

gp340 promotes transcytosis of human immunodeficiency virus type 1 in genital tract-derived cell lines and primary endocervical tissue

The human scavenger receptor gp340 has been identified as a binding protein for the human immunodeficiency virus type 1 (HIV-1) envelope that is expressed on the cell surface of female genital tract epithelial cells. This interaction allows such epithelial cells to efficiently transmit infective virus to susceptible targets and maintain viral infectivity for several days. Within the context of vaginal transmission, HIV must first traverse a normally protective mucosa containing a cell barrier to reach the underlying T cells and dendritic cells, which propagate and spread the infection. The mechanism by which HIV-1 can bypass an otherwise healthy cellular barrier remains an important area of study. Here, we demonstrate that genital tract-derived cell lines and primary human endocervical tissue can support direct transcytosis of cell-free virus from the apical to basolateral surfaces. Further, this transport of virus can be blocked through the addition of antibodies or peptides that directly block the interaction of gp340 with the HIV-1 envelope, if added prior to viral pulsing on the apical side of the cell or tissue barrier. Our data support a role for the previously described heparan sulfate moieties in mediating this transcytosis but add gp340 as an important facilitator of HIV-1 transcytosis across genital tract tissue. This study demonstrates that HIV-1 actively traverses the protective barriers of the human genital tract and presents a second mechanism whereby gp340 can promote heterosexual transmission.

Functional regulation of H+-ATPase-rich cells in zebrafish embryos acclimated to an acidic environment

It is important to maintain internal pH homeostasis in biological systems. In our previous studies, H(+)-ATPase-rich (HR) cells were found to be responsible for proton secretion in the skin of zebrafish embryos during development. In this study, zebrafish embryos were exposed to acidic and basic waters to investigate the regulation of HR cell acid secretion during pH disturbances. Our results showed that the function of HR cells on the skin of zebrafish embryos can be upregulated in pH 4 water not only by increasing the cell number but also by enlarging the acid-secreting function of single cells. We also identified an "alveolar-type" apical opening under scanning electron microscopy observations of the apical membrane of HR cells, and the density and size of the alveolar type of apical openings were also increased in pH 4 water. p63 and PCNA immunostaining results also showed that additional HR cells in pH 4 water may be differentiated not only from ionocyte precursor cells but also newly proliferating epithelial stem cells.

Dry eye and designer ophthalmics

Expressed sequence tag (EST), proteomic, and antibody capture assays are revealing a level of tear film protein complexity far greater than previously appreciated. A systems biology approach will be needed to fully appreciate function as tear protein doses fluctuate in time through different conditions. Although consensus is growing on what fully constitutes the human tear proteome, questions remain about the source and significance of the approximately 256 tear proteins designated as "intracellular." Many of these may derive from normal cellular turnover and could therefore be informative. A further >183 are designated as "extracellular." Surprisingly, only 4 to 5% of these appear to be dysregulated in the three forms of dry eye preliminarily examined to date. Some differ and a couple overlap, suggesting that disease-specific signatures could be identified. Future dry eye treatment might include recombinant tear protein rescue as a personalized ophthalmic approach to ocular surface disease.

Role of integrins in the assembly and function of hensin in intercalated cells

Epithelial differentiation proceeds in at least two steps: Conversion of a nonepithelial cell into an epithelial sheet followed by terminal differentiation into the mature epithelial phenotype. It was recently discovered that the extracellular matrix (ECM) protein hensin is able to convert a renal intercalated cell line from a flat, squamous shape into a cuboidal or columnar epithelium. Global knockout of hensin in mice results in embryonic lethality at the time that the first columnar cells appear. Here, antibodies that either activate or block integrin beta1 were used to demonstrate that activation of integrin alpha v beta 1 causes deposition of hensin in the ECM. Once hensin polymerizes and deposits into the ECM, it binds to integrin alpha 6 and mediates the conversion of epithelial cells to a cuboidal phenotype capable of apical endocytosis; therefore, multiple integrins play a role in the terminal differentiation of the intercalated cell: alpha v beta 1 generates polymerized hensin, and another set of integrins (containing alpha 6) mediates signals between hensin and the interior of the cells.

Effects of Muclin (Dmbt1) deficiency on the gastrointestinal system

The Dmbt1 gene encodes alternatively spliced glycoproteins that are either membrane-associated or secreted epithelial products. Functions proposed for Dmbt1 include it being a tumor suppressor, having roles in innate immune defense and inflammation, and being a Golgi-sorting receptor in the exocrine pancreas. The heavily sulfated membrane glycoprotein mucin-like glycoprotein (Muclin) is a Dmbt1 product that is strongly expressed in organs of the gastrointestinal (GI) system. To explore Muclin's functions in the GI system, the Dmbt1 gene was targeted to produce Muclin-deficient mice. Muclin-deficient mice have normal body weight gain and are fertile. The Muclin-deficient mice did not develop GI tumors, even when crossed with mice lacking the known tumor suppressor p53. When colitis was induced by dextran sulfate sodium, there was no significant difference in disease severity in Muclin-deficient mice. Also, when acute pancreatitis was induced with supraphysiological caerulein, there was no difference in disease severity in the Muclin-deficient mice. Exocrine pancreatic function was impaired, as measured by attenuated neurohormonal-stimulated amylase release from Muclin-deficient acinar cells. Also, by [(35)S]Met/Cys pulse-chase analysis, traffic of newly synthesized protein to the stimulus-releasable pool was significantly retarded in Muclin-deficient cells compared with wild type. Thus Muclin deficiency impairs trafficking of regulated proteins to a stimulus-releasable pool in the exocrine pancreas.