Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Obstetrics, Gynecology and Reproductive Sciences, Center for Birth Defects, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Mol Metab. 2024 Dec;90:102043. doi: 10.1016/j.molmet.2024.102043. Epub 2024 Oct 3.
D-amino acids are being recognized as important molecules in mammals with function. This is a first identification of endogenous D-cysteine in mammalian pancreas.
Using a novel stereospecific bioluminescent assay, chiral chromatography, enzyme kinetics and a transgenic mouse model we identify endogenous D-cysteine. We elucidate its function in two mice models of type 1 diabetes (STZ and NOD), and in tests of Glucose Stimulated Insulin Secretion in isolated mouse and human islets and INS-1 832/13 cell line.
D-cysteine is synthesized by serine racemase (SR) and SR mice produce 6-10 fold higher levels of insulin in the pancreas and plasma including higher glycogen and ketone bodies in the liver. The excess insulin is stored as amyloid in secretory vesicles and exosomes. In glucose stimulated insulin secretion in mouse and human islets, equimolar amount of D-cysteine showed higher inhibition of insulin secretion compared to D-serine, another closely related stereoisomer synthesized by SR. In mouse models of diabetes (Streptozotocin (STZ) and Non Obese Diabetes (NOD) and human pancreas, the diabetic state showed increased expression of D-cysteine compared to D-serine followed by increased expression of SR. SR mice show decreased cAMP in the pancreas, lower DNA methyltransferase enzymatic and promoter activities followed by reduced phosphorylation of CREB (S133), resulting in decreased methylation of the Ins1 promoter. D-cysteine is efficiently metabolized by D-amino acid oxidase and transported by ASCT2 and Asc1. Dietary supplementation with methyl donors restored the high insulin levels and low DNMT enzymatic activity in SR mice.
Our data show that endogenous D-cysteine in the mammalian pancreas is a regulator of insulin secretion.
D-氨基酸在哺乳动物中被认为是具有功能的重要分子。这是首次在哺乳动物胰腺中鉴定出内源性 D-半胱氨酸。
使用新型立体特异性生物发光测定法、手性色谱法、酶动力学和转基因小鼠模型，我们鉴定了内源性 D-半胱氨酸。我们在 1 型糖尿病（STZ 和 NOD）的两种小鼠模型中以及在分离的小鼠和人胰岛和 INS-1 832/13 细胞系中的葡萄糖刺激胰岛素分泌测试中阐明了其功能。
D-半胱氨酸由丝氨酸 racemase（SR）合成，SR 小鼠的胰腺和血浆中胰岛素水平升高 6-10 倍，包括肝脏中的糖原和酮体增加。多余的胰岛素作为淀粉样体储存在分泌小泡和外泌体中。在小鼠和人胰岛的葡萄糖刺激胰岛素分泌中，等摩尔量的 D-半胱氨酸显示出比由 SR 合成的另一种密切相关的立体异构体 D-丝氨酸更高的抑制胰岛素分泌作用。在糖尿病小鼠模型（链脲佐菌素（STZ）和非肥胖糖尿病（NOD）和人胰腺中，与 D-丝氨酸相比，糖尿病状态下 D-半胱氨酸的表达增加，随后 SR 的表达增加。SR 小鼠的胰腺中 cAMP 减少，DNA 甲基转移酶酶活性和启动子活性降低，随后 CREB（S133）磷酸化减少，导致 Ins1 启动子的甲基化减少。D-半胱氨酸被 D-氨基酸氧化酶有效代谢，并通过 ASCT2 和 Asc1 转运。膳食补充甲基供体可恢复 SR 小鼠的高胰岛素水平和低 DNMT 酶活性。
我们的数据表明，哺乳动物胰腺中的内源性 D-半胱氨酸是胰岛素分泌的调节剂。
