ABSTRACT
At high altitudes, the hypoxic atmosphere decreases the oxygen partial pressure in the body, inducing several metabolic changes in tissues and cells. Furthermore, it exerts potent anorectic effects, thus causing an energy deficit. Two decades ago, a marked increase in the resting level of plasma cholecystokinin (CCK) was observed in humans at the Mt. Kanchenjunga basecamp, located at 5100 m above the sea level, compared to sea-level control values. Interestingly, acute exercise also raises plasma CCK and exerts potent anorectic effects under normoxic conditions. However, the transcriptional regulations of Cck gene underlying these effects have not yet been established. Here, we employed acute electrical pulse stimulation (EPS) followed by microarray analysis to discover novel myokines in 3D-engineered muscle. Acute EPS affects the contractile function, inducing a decline in the contractile force. Surprisingly, microarray analysis revealed an EPS-induced activation of cholecystokinin receptor (CCKR)-mediated signaling. Furthermore, Cck was constitutively upregulated in 3D-engineered muscle, and its expression increased under hypoxic conditions. Notably, a hypoxia-responsive element was detected in the Cck promoters of mice and humans. Our results suggested that hypoxia transactivated Cck expression in 3D-engineered muscle. Furthermore, the elevation in plasma CCK levels following acute exercise or at high altitude might be partly attributed to myogenic cells.