Isolation, culture and adenoviral transduction of parietal cells from mouse gastric mucosa

Splicing variation of Long-IRBIT determines the target selectivity of IRBIT family proteins

IRBIT [inositol 1,4,5-trisphosphate receptor (IP₃R) binding protein released with inositol 1,4,5-trisphosphate (IP₃)] is a multifunctional protein that regulates several target molecules such as ion channels, transporters, polyadenylation complex, and kinases. Through its interaction with multiple targets, IRBIT contributes to calcium signaling, electrolyte transport, mRNA processing, cell cycle, and neuronal function. However, the regulatory mechanism of IRBIT binding to particular targets is poorly understood. Long-IRBIT is an IRBIT homolog with high homology to IRBIT, except for a unique N-terminal appendage. Long-IRBIT splice variants have different N-terminal sequences and a common C-terminal region, which is involved in multimerization of IRBIT and Long-IRBIT. In this study, we characterized IRBIT and Long-IRBIT splice variants (IRBIT family). We determined that the IRBIT family exhibits different mRNA expression patterns in various tissues. The IRBIT family formed homo- and heteromultimers. In addition, N-terminal splicing of Long-IRBIT changed the protein stability and selectivity to target molecules. These results suggest that N-terminal diversity of the IRBIT family and various combinations of multimer formation contribute to the functional diversity of the IRBIT family.

Helicobacter suis affects the health and function of porcine gastric parietal cells

The stomach of pigs at slaughter age is often colonized by Helicobacter (H.) suis, which is also the most prevalent gastric non-H. pylori Helicobacter (NHPH) species in humans. It is associated with chronic gastritis, gastric ulceration and other gastric pathological changes in both hosts. Parietal cells are highly specialized, terminally differentiated epithelial cells responsible for gastric acid secretion and regulation. Dysfunction of these cells is closely associated with gastric pathology and disease. Here we describe a method for isolation and culture of viable and responsive parietal cells from slaughterhouse pigs. In addition, we investigated the interactions between H. suis and gastric parietal cells both in H. suis-infected six-month-old slaughter pigs, as well as in our in vitro parietal cell model. A close interaction of H. suis and parietal cells was observed in the fundic region of stomachs from H. suis positive pigs. The bacterium was shown to be able to directly interfere with cultured porcine parietal cells, causing a significant impairment of cell viability. Transcriptional levels of Atp4a, essential for gastric acid secretion, showed a trend towards an up-regulation in H. suis positive pigs compared to H. suis-negative pigs. In addition, sonic hedgehog, an important factor involved in gastric epithelial differentiation, gastric mucosal repair, and stomach homeostasis, was also significantly up-regulated in H. suis positive pigs. In conclusion, this study describes a successful approach for the isolation and culture of porcine gastric parietal cells. The results indicate that H. suis affects the viability and function of this cell type.

Seven transmembrane G protein-coupled receptor repertoire of gastric ghrelin cells

The molecular mechanisms regulating secretion of the orexigenic-glucoregulatory hormone ghrelin remain unclear. Based on qPCR analysis of FACS-purified gastric ghrelin cells, highly expressed and enriched 7TM receptors were comprehensively identified and functionally characterized using in vitro, ex vivo and in vivo methods. Five Gαs-coupled receptors efficiently stimulated ghrelin secretion: as expected the β1-adrenergic, the GIP and the secretin receptors but surprisingly also the composite receptor for the sensory neuropeptide CGRP and the melanocortin 4 receptor. A number of Gαi/o-coupled receptors inhibited ghrelin secretion including somatostatin receptors SSTR1, SSTR2 and SSTR3 and unexpectedly the highly enriched lactate receptor, GPR81. Three other metabolite receptors known to be both Gαi/o- and Gαq/11-coupled all inhibited ghrelin secretion through a pertussis toxin-sensitive Gαi/o pathway: FFAR2 (short chain fatty acid receptor; GPR43), FFAR4 (long chain fatty acid receptor; GPR120) and CasR (calcium sensing receptor). In addition to the common Gα subunits three non-common Gαi/o subunits were highly enriched in ghrelin cells: GαoA, GαoB and Gαz. Inhibition of Gαi/o signaling via ghrelin cell-selective pertussis toxin expression markedly enhanced circulating ghrelin. These 7TM receptors and associated Gα subunits constitute a major part of the molecular machinery directly mediating neuronal and endocrine stimulation versus metabolite and somatostatin inhibition of ghrelin secretion including a series of novel receptor targets not previously identified on the ghrelin cell.

Independent trafficking of the KCNQ1 K+ channel and H+-K+-ATPase in gastric parietal cells from mice

Gastric acid secretion by the H(+)-K(+)-ATPase at the apical surface of activated parietal cells requires luminal K(+) provided by the KCNQ1/KCNE2 K(+) channel. However, little is known about the trafficking and relative spatial distribution of KCNQ1 and H(+)-K(+)-ATPase in resting and activated parietal cells and the capacity of KCNQ1 to control acid secretion. Here we show that inhibition of KCNQ1 activity quickly curtails gastric acid secretion in vivo, even when the H(+)-K(+)-ATPase is permanently anchored in the apical membrane, demonstrating a key role of the K(+) channel in controlling acid secretion. Three-dimensional imaging analysis of isolated mouse gastric units revealed that the majority of KCNQ1 resides in an intracytoplasmic, Rab11-positive compartment in resting parietal cells, distinct from H(+)-K(+)-ATPase-enriched tubulovesicles. Upon activation, there was a significant redistribution of H(+)-K(+)-ATPase and KCNQ1 from intracytoplasmic compartments to the apical secretory canaliculi. Significantly, high Förster resonance energy transfer was detected between H(+)-K(+)-ATPase and KCNQ1 in activated, but not resting, parietal cells. These findings demonstrate that H(+)-K(+)-ATPase and KCNQ1 reside in independent intracytoplasmic membrane compartments, or membrane domains, and upon activation of parietal cells, both membrane proteins are transported, possibly via Rab11-positive recycling endosomes, to apical membranes, where the two molecules are closely physically opposed. In addition, these studies indicate that acid secretion is regulated by independent trafficking of KCNQ1 and H(+)-K(+)-ATPase.

The Golgi apparatus in the endomembrane-rich gastric parietal cells exist as functional stable mini-stacks dispersed throughout the cytoplasm

Background information. Acid-secreting gastric parietal cells are polarized epithelial cells that harbour highly abundant and specialized, H⁺,K⁺ ATPase-containing, tubulovesicular membranes in the apical cytoplasm. The Golgi apparatus has been implicated in the biogenesis of the tubulovesicular membranes; however, an unanswered question is how a typical Golgi organization could regulate normal membrane transport within the membrane-dense cytoplasm of parietal cells.

Results. Here, we demonstrate that the Golgi apparatus of parietal cells is not the typical juxta-nuclear ribbon of stacks, but rather individual Golgi units are scattered throughout the cytoplasm. The Golgi membrane structures labelled with markers of both cis- and trans-Golgi membrane, indicating the presence of intact Golgi stacks. The parietal cell Golgi stacks were closely aligned with the microtubule network and were shown to participate in both anterograde and retrograde transport pathways. Dispersed Golgi stacks were also observed in parietal cells from H⁺,K⁺ ATPase-deficient mice that lack tubulovesicular membranes.

Conclusions. These results indicate that the unusual organization of individual Golgi stacks dispersed throughout the cytoplasm of these terminally differentiated cells is likely to be a developmentally regulated event.

Nucleic acid delivery using magnetic nanoparticles: the Magnetofection™ technology

In recent years, gene therapy has received considerable interest as a potential method for the treatment of numerous inherited and acquired diseases. However, successes have so far been hampered by several limitations, including safety issues of viral-based nucleic acid vectors and poor in vivo efficiency of nonviral vectors. Magnetofection™ has been introduced as a novel and powerful tool to deliver genetic material into cells. This technology is defined as the delivery of nucleic acids, either ‘naked’ or packaged (as complexes with lipids or polymers, and viruses) using magnetic nanoparticles under the guidance of an external magnetic field. This article first discusses the principles of the Magnetofection technology and its benefits as compared with standard transfection methods. A number of relevant examples of its use, both in vitro and in vivo, will then be highlighted. Future trends in the development of new magnetic nanoparticle formulations will also be outlined.