The stimulation of gastric acid secretion from parietal cells involves both intracellular
calcium and cAMP signaling. To understand the effect of increased cAMP on parietal cell function, we engineered transgenic mice expressing
cholera toxin (Ctox), an irreversible stimulator of
adenylate cyclase. The parietal cell-specific H(+),K(+)-
ATPase beta-subunit promoter was used to drive expression of the
cholera toxin A1 subunit (CtoxA1). Transgenic lines were established and tested for Ctox expression,
acid content, plasma
gastrin, tissue morphology, and cellular composition of the gastric mucosa. Four lines were generated, with Ctox-7 expressing approximately 50-fold higher Ctox than the other lines. Enhanced cAMP signaling in parietal cells was confirmed by observation of hyperphosphorylation of the
protein kinase A-regulated
proteins LASP-1 and CREB. Basal
acid content was elevated and circulating
gastrin was reduced in Ctox transgenic lines. Analysis of gastric morphology revealed a progressive cellular transformation in Ctox-7. Expanded patches of mucous neck cells were observed as early as 3 mo of age, and by 15 mo, extensive mucous cell
metaplasia was observed in parallel with almost complete loss of parietal and chief cells. Detection of anti-parietal cell
antibodies, inflammatory cell infiltrates, and increased expression of the Th1
cytokine IFN-gamma in Ctox-7 mice suggested that autoimmune destruction of the tissue caused
atrophic gastritis. Thus constitutively high parietal cell cAMP results in high
acid secretion and a compensatory reduction in circulating
gastrin. High Ctox in parietal cells can also induce progressive changes in the cellular architecture of the gastric glands, corresponding to the development of anti-parietal cell
antibodies and autoimmune
gastritis.