“Role of LANCL1 and LANCL2 in the physiology and biochemistry of myocytes and cardiomyocytes.”

Background. Abscisic acid (ABA) is an isoprenoid hormone present in unicellular organisms and conserved across kingdoms in modern plants and animals. In mammals, ABA is produced by different cell types and is involved in tissue-specific physiological functions, such as inflammation, hemopoietic stem cell regeneration and control of blood glucose levels. The latter occurs through the insulin-independent stimulation of glucose uptake and metabolism in adipose tissue and skeletal muscle through its receptor LANCL2. The aim of this study was to investigate whether: • LANCL1, another member of the LANCL protein family, also behaves as an ABA receptor, sharing signalling pathway and functional properties with LANCL2 in the control of muscle glucose uptake; • ABA could improve glycemic control in a murine model of (insulin-deficient) type 1 diabetes. Methods. Rat L6 myoblasts overexpressing or silenced for LANCL1 and LANCL2, treated or not with ABA, were used to investigate the signalling pathway downstream of LANCL1 by Western Blot and qPCR experiments. Energy metabolism was studied in H9C2 cardiomyoblasts overexpressing or silenced for LANCL1/2 by monitoring the mitochondrial proton gradient. Finally, experiments were performed on LANCL2 knock-out mice, which overexpress LANCL1 in skeletal muscle, to investigate whether ABA could improve glucose tolerance after induction of insulin deficiency with streptozotocin. Results. In L6 cells, both LANCL1 and LANCL2 mediate basal and ABA-stimulated glucose uptake (4-fold), activate transcription and protein expression of the glucose transporters GLUT4 and GLUT1 (4-6-fold) and the AMPK/PGC-1a/Sirt1 signalling proteins (2-fold). In H9c2, overexpression of LANCL1 and LANCL2 increases, while their combined silencing almost abrogates, the mitochondrial proton gradient. LANCL2 knock-out mice have a reduced glucose tolerance compared to WT, but they do respond to chronic ABA treatment (1 µg/kg BW/day) with an improved glycemia response to glucose load and an increased skeletal muscle transcription of GLUT4, GLUT1 (20-fold) and of the AMPK/PGC-1a/Sirt1 axis. In mice rendered diabetic with low dose streptozotocin, chronic treatment with ABA improves glycemia control. In mice treated with high-dose streptozotocin (causing complete insulin deficiency) treatment with ABA improves the effect of low-dose insulin on glycemia control. In diabetic mice, ABA treatment increases skeletal muscle expression of the AMPK/PGC-1a/Sirt1 axis, of glucose transporters GLUT1/4, of the insulin receptor and of glycolytic enzymes. Conclusions. Having regard to the results of this study, the conclusions are: • LANCL1 shares with LANCL2 similar properties as an ABA receptor, stimulating glucose transport in skeletal muscle, mitochondrial function in cardiomyoblasts and whole-body glucose disposal. • ABA supplementation in conjunction with insulin holds promise as a means to reduce the dose of insulin required for glycemia control, reducing the risk of hypoglycaemia, and improving skeletal muscle insulin sensitivity and glucose consumption as well as cardiomyocyte mitochondrial function.