SirT1 knockdown in liver decreases basal hepatic glucose production and increases hepatic insulin responsiveness in diabetic rats

Abstract

Hepatic gluconeogenesis is a major contributing factor to hyperglycemia in the fasting and postprandial states in type 2 diabetes mellitus (T2DM). Because Sirtuin 1 (SirT1) induces hepatic gluconeogenesis during fasting through the induction of phosphoenolpyruvate carboxylase kinase (PEPCK), fructose-1,6-bisphosphatase (FBPase), and glucose-6-phosphatase (G6Pase) gene transcription, we hypothesized that reducing SirT1, by using an antisense oligonucleotide (ASO), would decrease fasting hyperglycemia in a rat model of T2DM. SirT1 ASO lowered both fasting glucose concentration and hepatic glucose production in the T2DM rat model. Whole body insulin sensitivity was also increased in the SirT1 ASO treated rats as reflected by a 25% increase in the glucose infusion rate required to maintain euglycemia during the hyperinsulinemiceuglycemic clamp and could entirely be attributed to increased suppression of hepatic glucose production by insulin. The reduction in basal and clamped rates of glucose production could in turn be attributed to decreased expression of PEPCK, FBPase, and G6Pase due to increased acetylation of signal transducer and activator of transcription 3 (STAT3), forkhead box O1 (FOXO1), and peroxisome proliferator-activated receptor-␥ coactivator 1␣ (PGC-1␣), known substrates of SirT1. In addition to the effects on glucose metabolism, SirT1 ASO decreased plasma total cholesterol, which was attributed to increased cholesterol uptake and export from the liver. These results indicate that inhibition of hepatic SirT1 may be an attractive approach for treatment of T2DM. gluconeogenesis ͉ glucose 6 phosphatase ͉ phosphoenolpyruvate carboxykinase ͉ type 2 diabetes mellitus ͉ hepatic insulin resistance T ype 2 diabetes mellitus (T2DM) is associated with an increased rate of hepatic glucose production that contributes to fasting hyperglycemia (1-3). Specifically, increased endogenous glucose production can be accounted for by increased rates of hepatic gluconeogenesis (4). Inhibition of hepatic gluconeogenesis has been shown to improve fasting plasma glucose levels and decrease endogenous glucose production in T2DM patients (5). Furthermore, inhibition of transcriptional gluconeogenic activators, such as forkhead box O1 (FOXO1), and peroxisome proliferator-activated receptor-␥ coactivator 1␣ (PGC-1␣), in turn improved hepatic insulin resistance in rodent models of diabetes (6, 7). Therefore inhibitors of gluconeogenesis are potentially excellent targets for treatment of poorly controlled T2DM.Sirtuin1 (SirT1) is a NAD ϩ -dependent deacetylase activated in response to fasting and caloric restriction (8). In the ␤-cells of the pancreas, SirT1 has been shown to increase insulin secretion through repression of uncoupling protein 2 (UCP2) (9). In adipose tissue, SirT1 has been shown to inhibit adipogenesis and decrease lipolysis through inhibition of peroxisome proliferator-activated receptor-␥ (PPAR␥) (10). In liver tissue, SirT1 activates gluconeogenesis transcription through deacetylation of PGC-1␣, FOXO1, and signa...

Identification of the Aryl Hydrocarbon Receptor Target Gene TiPARP as a Mediator of Suppression of Hepatic Gluconeogenesis by 2,3,7,8-Tetrachlorodibenzo-p-dioxin and of Nicotinamide as a Corrective Agent for This Effect

“…S6B). A role for SIRT1 in these effects is supported by a report that SIRT1 knockdown in the rat increased hepatic PGC1␣ acetylation and decreased gluconeogenic gene expression and glucose production (37). The ability of NAM to enhance GO and gluconeogenic gene expression (seen in both CEH and mammalian (H4IIE) cells) appears to involve both increased NAD ϩ production, and suppression of AHR action, resulting in decreased NAD ϩ utilization.…”

Inhibition of STAT3 acetylation is associated with attenuated renal fibrosis in the obstructed kidney

“…SIRT1 has been proven to be the major enzyme that removes acetyl groups from STAT3 lysine residues [38,39,41] . As a SIRT1 activator [42,43] , resveratrol was used to identify whether acetylated STAT3 is involved in the activation of STAT3 signaling.…”

“…One of the best characterized deacetylases is sirtuin 1 (SIRT1), a member of nicotinamide adenine dinucleotide (NAD + )-dependent class III protein deacetylases, which can be inhibited by nicotinamide [35,36] . SIRT1, which mediates the deacetylation of STAT3 Lys685 site [37][38][39][40][41] , can be activated by resveratrol (trans-3,4',5-trihydroxystilbene) [42,43] , a natural polyphenol with renal protective effects that depend on deacetylation of Smad3 [44] , p53 [45] , and NF-κB p65 [46] . However, the role of STAT3 acetylation in the antifibrotic activity of resveratrol has yet to be clarified.…”

Feedback regulation of hepatic gluconeogenesis through modulation of SHP/Nr0b2 gene expression by Sirt1 and FoxO1

“…CRTC2 has been shown to play a critical role in short-term gluconeogenesis in response to glucagon (25). Intriguingly, Sirt1 has been shown to confer both positive and negative effects on hepatic gluconeogenesis through differential modulation of the above mentioned factors (2,13,15,28,30,39,40). For example, on the one hand, Sirt1 activates FoxO1 and PGC-1␣ for the promotion of hepatic gluconeogenesis; on the other hand, Sirt1 suppresses the activity of CRTC2 and HNF-4␣ to downregulate gluconeogenic gene expression (25,51).…”