Gastrin, secreted by stomach G cells in response to ingested sodium, stimulates the renal cholecystokinin B receptor (CCKBR) to increase renal sodium excretion. It is not known how dietary sodium, independent of food, can increase gastrin secretion in human G cells. However, fenofibrate (FFB), a peroxisome proliferator-activated receptor-α (PPAR-α) agonist, increases gastrin secretion in rodents and several human gastrin-secreting cells, via a gastrin transcriptional promoter. We tested the following hypotheses: (1.) the sodium sensor in G cells plays a critical role in the sodium-mediated increase in gastrin expression/secretion, and (2.) dopamine, via the D1R and PPAR-α, is involved. Intact human stomach antrum and G cells were compared with human gastrin-secreting gastric and ovarian adenocarcinoma cells. When extra- or intracellular sodium was increased in human antrum, human G cells, and adenocarcinoma cells, gastrin mRNA and protein expression/secretion were increased. In human G cells, the PPAR-α agonist FFB increased gastrin protein expression that was blocked by GW6471, a PPAR-α antagonist, and LE300, a D1-like receptor antagonist. LE300 prevented the ability of FFB to increase gastrin protein expression in human G cells via the D1R, because the D5R, the other D1-like receptor, is not expressed in human G cells. Human G cells also express tyrosine hydroxylase and DOPA decarboxylase, enzymes needed to synthesize dopamine. G cells in the stomach may be the sodium sensor that stimulates gastrin secretion, which enables the kidney to eliminate acutely an oral sodium load. Dopamine, via the D1R, by interacting with PPAR-α, is involved in this process.
Supplemental Figure 1.Human G and ovarian adenocarcinoma SW626 cells express the appropriate molecular (Mol) size of gastrin mRNA, ~300 base pairs (bp), expected from the primers used. Actin is used for control.
Supplemental Figure 2. Effect of NaCl concentration in the incubation medium on gastrin expression in gastrin-secreting tumor cells, SW626 and AGS. Increasing the sodium concentration in the buffer from 135 to 170 mM NaCl (4 hrincubation) increases gastrin protein expression in both SW626 and AGS cells (*, #, P<0.01 vs 135 mM NaCl, n=6/group, one-way ANOVA, Holm-Sidaktest). IF = immunofluorescence, RFU = relative fluorescence unit
Supplemental Figure 3.
Supplemental Figure 4. There is no D5R expression in human stomach antrum. Gastrin is stained red and nucleus stained blue with DAPI.
Supplemental Figure 5. Both D1R and D5R are expressed in AGS and SW626 cells.
Supplemental Figure 6. PPAR-α silencing in G cells.
Supplemental Figure 7. Gastrin synthesis, D1-like receptor, and the PPAR-α pathway in SW626 cells.
Supplemental Figure 8. Expression of tyrosine hydroxylase in G cells in stomach antrum and isolated G cells in culture.
Supplemental Figure 9. Expression of DOPA decarboxylase in G cells in stomach antrum and isolated G cells in culture.