Introduction and Objective: Recent studies highlight the essential role of amino acids in α cell function, with cysteine (Cys) showing the strongest stimulation of glucagon secretion. Diabetic conditions not only elevate glucagon secretion but also alter plasma Cys levels. Hence, the objective was to decipher the mechanistic role of Cys in modulating α cell function.Methods: The impact of Cys deficiency on glucagon secretion was investigated using islets from C57BL/6 mice and human donors briefly cultured (<12h) in cysteine-free media. Glucagon levels were measured through immunoassays. Intracellular calcium signaling ([Ca2+]i) and electrophysiological properties of cys-deprived islet α cells expressing fluorescence Ca2+ indicators. In some experiments Cys-deprived islets were treated with L-cysteine (2mM), sodium mercaptopyruvate (1mM), and DTT (1mM).Results: Cys deprivation significantly decreased glucagon secretion under hypoglycemic conditions in both human (81 ± 1.2%, P < 0.0001) and mouse islets (68 ± 6.5%, P < 0.01). The defect in secretion was accompanied by reduced total Ca2+ influx (60.5 ± 5.7%, P < 0.001) and whole-cell K+ current (36 ± 11%, P < 0.01) in mouse α cells. L-cysteine supplementation in mouse islets rapidly restored glucagon secretion (428 ± 64%, P < 0.01) and enhanced Ca2+ influx (288 ± 33%, P < 0.05). Furthermore, sodium channel amplitude, crucial for glucagon exocytosis, was reduced (47 ± 6 % at 10mV, P < 0.0001) in Cys-deficient mouse α cells and partially restored with sodium mercaptopyruvate (generates H2S gas) (245 ± 54%, P < 0.001at 10mV) as well as dithiothreitol (reducing agent) (400± 132% at 10mV, P < 0.001).Conclusion: Cysteine deficiency leads to oxidative suppression of islet α cell sodium channels, which impairs action potential firing, Ca2+ influx and glucagon secretion. This work suggests Cys control of α cell electrical activity is critical for glucagon secretion and amino acid sensing.
S. Behera: None. M. Dickerson: None. P. Dadi: None. J. Dobson: None. S. Peachee: None. S. Gibson: None. D. Jacobson: None.
Helmsley Charitable Trust, 602987
Source link
Leave a Reply