Mammalian D-Cysteine controls insulin secretion in the pancreas

• Published in: Molecular metabolism (Germany) Vol. 90; p. 102043
• Main Authors: Roychaudhuri, Robin, West, Timothy, Bhattacharya, Soumyaroop, Saavedra, Harry G., Lee, Hangnoh, Albacarys, Lauren, Gadalla, Moataz M., Amzel, Mario, Yang, Peixin, Snyder, Solomon H.
• Format: Journal Article
• Language: English
• Published: Germany Elsevier GmbH 01.12.2024; Elsevier
• Subjects: cAMP; D-cysteine; DNA methylation; Insulin; Islets; Luciferase assay; Original; Serine racemase; D-cysteine; DNA methylation; Luciferase assay; Islets; cAMP; Serine racemase; Insulin
• ISSN: 2212-8778; 2212-8778
• DOI: 10.1016/j.molmet.2024.102043

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. [Display omitted] •Serine Racemase (SR) is also a cysteine racemase.•Lack of SR results in high levels of insulin in the pancreas and plasma.•D-cysteine shows greater inhibition of insulin secretion compared to D-serine.•Endogenous D-cysteine signals via cyclic AMP mediated by CREB-DNMT1 interaction.•Hypomethylation of Ins1 promoter is rescued by high methyl donor diet rescuing high insulin levels.