Adenovirus-mediated expression of SIK1 improves hepatic glucose and lipid metabolism in type 2 diabetes mellitus rats

Abstract

2 AIM: In this study, we investigated the role and mechanism of Salt-induced kinase 3 1 (SIK1) in regulation of hepatic glucose and lipid metabolism in a high-fat food 4 (HFD) and streptozocin (STZ)-induced type 2 diabetes mellitus (T2DM) rat model. 5 Methods: A diabetic rat model treated with HFD plus low-dose STZ was 6 developed and was transduced to induce a high expression of SIK1 in vivo via a 7 tail-vein injection of a recombinant adenoviral vector. The effects on hepatic 8 glucogenetic and lipogenic gene expression, systemic metabolism and pathological 9 changes were then determined.10 Results: In T2DM rats, SIK1 expression was reduced in the liver. Overexpression 11 of SIK1 improved hyperglycaemia, hyperlipidaemia and fatty liver, reduced 12 the expression of cAMP-response element binding protein (CREB)-regulated 13 transcription co-activator 2 (CRTC2), phosphoenolpyruvate carboxykinase (PEPCK), 14 glucose-6-phosphatase (G6Pase), pS577 SIK1, sterol regulatory element 15 binding-protein-1c (SREBP-1c) and its target genes, including acetyl-CoA 16 carboxylase (ACC) and fatty acid synthase (FAS), and increased the expression of 17 SIK1, pT182 SIK1 and pS171 CRTC2 in diabetic rat livers with the suppression of 18 gluconeogenesis and lipid deposition.19 Conclusion: SIK1 plays a crucial role in the regulation of glucose and lipid 20 metabolism in the livers of HFD/STZ-induced T2DM rats, where it suppresses hepatic 21 gluconeogenesis and lipogenesis by regulating the SIK1/CRTC2 and SIK1/SREBP-1c 22 signalling pathways. Strategies to activate SIK1 kinase in liver would likely have 3 / 28 23 beneficial effects in patients with T2DM and nonalcoholic fatty liver disease 24 (NAFLD). 25 26 2 diabetes mellitus; diabetic rats 27 42 (PKA) makes SIK1 translocate to the cytoplasm and lose its repressive properties[3, 43 8]. Knockdown of SIK1 in mice promoted both fasting hyperglycaemia and 44 gluconeogenic gene expression. Conversely, mice treated with adenovirus-expressed 4 / 28 45 SIK1 (Ad-SIK1) exhibited fasting hypoglycaemia and reduce gluconeogenic gene 46 expression [9]. Ad-SIK1 was also effective in reducing blood glucose levels in fasted 47 db/db diabetic mice [9]. These observations demonstrate a key role of SIK1 on 48 glucose metabolism in vivo. 49The liver is the major organ responsible for glucose production. Hepatic glucose 50 production mainly comes from gluconeogenesis and is critical for maintaining 51 normoglycemia in the fasting state [10]. The cAMP response element binding protein 52 (CREB) and its co-activator, CRTC2, play crucial roles in signal-dependent 53 transcriptional regulation of hepatic gluconeogenesis. CREB transcriptional activity is 54 required for fasting gluconeogenesis [11]. CRTC2 is a key regulator of fasting glucose 55 metabolism that acts through the CREB to modulate glucose output. Phosphorylation 56 of CRTC2 at Ser171 by AMPK results in the inhibition of the nuclear translocation of 57 CRTC2; subsequently, the cytoplasmic localization of CRTC2 prevents its 58 combination with CREB el...