CFTR channel insertion to the apical surface in rat duodenal villus epithelial cells is upregulated by VIP in vivo

Abstract

cAMP activated insertion of the cystic fibrosis transmembrane conductance regulator (CFTR) channels from endosomes to the apical plasma membrane has been hypothesized to regulate surface expression and CFTR function although the physiologic relevance of this remains unclear. We previously identified a subpopulation of small intestinal villus epithelial cells or CFTR high expressor (CHE) cells possessing very high levels of apical membrane CFTR in association with a prominent subapical vesicular pool of CFTR. We have examined the subcellular redistribution of CFTR in duodenal CHE cells in vivo in response to the cAMP activated secretagogue vasoactive intestinal peptide (VIP). Using anti-CFTR antibodies against the C terminus of rodent CFTR and indirect immunofluorescence, we show by quantitative confocal microscopy that CFTR rapidly redistributes from the cytoplasm to the apical surface upon cAMP stimulation by VIP and returns to the cytoplasm upon removal of VIP stimulation of intracellular cAMP levels. Using ultrastructural and confocal immunofluorescence examination in the presence or absence of cycloheximide, we also show that redistribution was not dependent on new protein synthesis, changes in endocytosis, or rearrangement of the apical cytoskeleton. These observations suggest that physiologic cAMP activated apical membrane insertion and recycling of CFTR channels in normal CFTR expressing epithelia contributes to the in vivo regulation of CFTR mediated anion transport.

Loss of Serum Glucocorticoid-Inducible Kinase 1 SGK1 Worsens Malabsorption and Diarrhea in Microvillus Inclusion Disease (MVID)

“…Unlike villus enterocytes of the small intestine, CHEs lack the typical absorptive markers that are present on the brush border, including sucrase isomaltase, lactase, alkaline phosphatase, but they express high levels of the vATPase (vacuolar H + -ATPase proton pump) and CFTR. Interestingly, villus CHEs display robust trafficking of endosomal associated CFTR into the brush border upon cAMP, cGMP, Ca 2+ stimulation, and low pH consistent with a secretory profile [ 41 , 42 , 43 , 44 ]. We observed high levels of CFTR on the brush border of villus CHE cells in human MVID duodenal tissues resulting from loss of MYO5B mutations [ 15 ].…”

“…CFTR High Expresser (CHE) Cells Are Present in cMYO5BKO and cMYO5B-SGK1-DKO Mice CHE cells were first reported in localization studies of CFTR in the human and rat intestine in 1995 [39] but were not found in mice under homeostatic conditions [40]. CHEs are unique rare enterocytes (~1-2% total epithelial cells) found both in crypts and villi but more predominantly found scattered along the villi of duodenum and jejunum where they express unusually high levels of CFTR both in subapical endosomes and on the brush border [39,[41][42][43][44]. Unlike villus enterocytes of the small intestine, CHEs lack the typical absorptive markers that are present on the brush border, including sucrase isomaltase, lactase, alkaline phosphatase, but they express high levels of the vATPase (vacuolar H + -ATPase proton pump) and CFTR.…”

“…Consistent with our observations in human MVID, here we observed CHE cells with a normal subcellular distribution of CFTR on the villi (Figure 11B,C) and in superficial crypts (Figure 11E,F) of cMYO5BKO (Figure 11B,E) and also in the cMYO5B-SGK1-DKO (Figure 11C,F) mouse jejunum. unusually high levels of CFTR both in subapical endosomes and on the brush border [39,[41][42][43][44]. Unlike villus enterocytes of the small intestine, CHEs lack the typical absorptive markers that are present on the brush border, including sucrase isomaltase, lactase, alkaline phosphatase, but they express high levels of the vATPase (vacuolar H + -ATPase proton pump) and CFTR.…”

Novel insights in the pathomechanism of Brugada syndrome and fever‐related type 1 ECG changes in a preclinical study using human‐induced pluripotent stem cell‐derived cardiomyocytes

“…It is also known that the G‐protein‐cAMP‐PKA signalling, as downstream factors of adrenergic and muscarinic receptors, mediate sympathetic and parasympathetic effects on cardiomyocytes. The activation of PKA via neurohumoral stimulation of β‐adrenergic receptors could increase the conduction in normal ventricular myocardium and modulate cardiac electrophysiology, 33 indicating the possible roles of alterations of PKA and adrenergic stimulation in arrhythmic events. 34 , 35 Moreover, catecholamine level in blood can be increased by fever, 36 suggesting an involvement of activation of adrenoceptor/cAMP/PKA signalling at febrile state.…”

CFTR High Expresser Cells in cystic fibrosis and intestinal diseases

“…High levels of intracellular cAMP results in the activation of downstream targets that leads to CFTR activation and secretory diarrhea. [ 77 , 102 ] Traveler's diarrhea Escherichia coli heat-stable enterotoxins (STa) binds to GC-C receptor in the membrane of enterocytes resulting in cGMP increase and consequent activation of downstream targets, including PKGII, that promotes CFTR activation and secretory diarrhea. [ 91 ] 2.…”