Piezo1/2 regulates gastric pepsinogen secretion of mandarin fish

Pepsinogen plays a crucial role in the gastric digestion of carnivorous fish. Piezo signals in the stomach, which are typically associated with digestion through mechanical forces resulting from food intake, have been extensively investigated in mammals but have received comparatively limited attention in fish. To explore the physiological characteristics of gastric digestion and the regulatory mechanism of pepsinogen and piezo secretion in carnivorous fish, we investigated the gastric contents of juvenile mandarin fish (5.83 ± 1.32 g, 6.60 ± 0.46 cm) following feeding and developed a mathematical model for gastric emptying (feeding live baits at 26 °C) to briefly describe changes in gastric pressure. The expression patterns of piezo1/2 and pepsinogens were examined under normal feeding and water gavage (only gastric pressure) conditions. The results indicated that the weight of gastric contents gradually decreased over time, and the most appropriate model describing this trend was the square root model with a fitted equation of Y = - 0.0006t² - 0.0130t + 0.6163 (R² = 0.9599) of mandarin fish. The percentage of wet weight decreased significantly after 6 hpf (hour post-feeding) (P < 0.05), meaning that the stomach pressure decreased significantly at 6 hpf. During gastric digestion, there was a significant increase in piezo1/2 expression at 6 hpf (P < 0.05), followed by a gradual plateau (P > 0.05). Pepsinogen (PG A and PG C) content exhibited a similar trend to piezo1/2, showing a rising trend and peaking at 6 hpf (P < 0.05). The relative expression levels of gas, pg a1/2, pg c, and hk α demonstrated an "upward and then downward" trajectory and peak levels at 6 hpf (P < 0.05). In the water gavage group, piezo1/2 increased significantly (P < 0.05) and peaked at 1-2 h. Similarly, the rises in PG A and PG C contents, gas, pg a2, and hk α mRNA relative expression levels were also observed with a peak at 1-2 h (P < 0.05), while no distinct peaks of piezo and pepsinogen were observed in the starved group. Our results suggested that piezo1/2 is activated by intragastric pressure and up-regulated the pepsinogen expression in juvenile mandarin fish (5.83 ± 1.32 g, 6.60 ± 0.46 cm).