ISSN: 2377-3634 Chaves et al. Int J Diabetes Clin Res 2018, 5:080 DOI: 10.23937/2377-3634/1410080 Volume 5 | Issue 1 International Journal of Open Access Diabetes and Clinical Research REVIEW ARTICLE Role of TXNIP Biology in Glucose Metabolism Alec B Chaves1, Jacob M Haus2 and Joseph A Houmard1* 1 Check for Department of Kinesiology, East Carolina University, Greenville, USA updates 2Department of Kinesiology and Nutrition, University of Illinois Chicago, Chicago, USA *Corresponding author: Joseph A Houmard, Ph.D, Department of Kinesiology, Human Performance Laboratory East Carolina University, Greenville, NC, USA, Tel: 252-737-4617, E-mail: [email protected] Abstract Protein; P300: Histone Acetyltransferase p300; PA: Palmi- tic Acid; NAC: N-Acetyl-L-cysteine; AMPK: AMP-Activated Skeletal muscle insulin resistance is a major contributor to Protein Kinase; SIRT1: Sirtuin 1; NLRP3: NOD-Like Recep- the natural history of type 2 diabetes mellitus. A common tor P3; PERK: PKR-like ER Resident Kinase; ATF6: Activa- underpinning that exists behind the mechanisms of insulin ting Transcription Factor 6 resistance is the overproduction of reactive oxygen species, which may be exacerbated by a protein target known as thioredoxin-interacting protein (TXNIP). TXNIP is a member Introduction of the α-arrestin protein family that is capable of suppres- sing glucose metabolism in several tissues. Cross sectio- Type II diabetes (T2DM) is a debilitating disease that nal analysis reveals that individuals with insulin resistance, places significant economic burden on the healthcare impaired glucose tolerance, and type II diabetes have ele- system with over $245 billion in annual costs affecting vated protein and mRNA expression of TXNIP in skeletal muscle compared to lean healthy controls, which negatively over 30 million Americans [1]. T2DM is characterized by correlates with insulin sensitivity. The goal of this review is chronic hyperglycemia which promotes oxidative stress to explore TXNIP’s role in glucose metabolism and provide and inflammation in multiple tissues. If left untreated, mechanisms through which it can be regulated to provide T2DM can lead to an increased risk of heart disease, potential targets for future research and therapeutic inter- kidney failure, and augmented cognitive decline [2-5]. ventions for the treatment of insulin resistance. Although T2DM requires the coordinated dysfunction Keywords of several tissues, understanding the molecular mecha- Diabetes, Insulin resistance, TXNIP, Exercise nisms that promote insulin resistance in skeletal muscle should be a chief concern, as this tissue is the primary List of Abbreviations site for insulin-mediated glucose metabolism [6]. A pro- T2DM: Type II Diabetes; TXNIP: Thioredoxin Interacting Pro- tein that has gained recent attention in relation to the tein; REDD1: Regulated in Development and DNA Damage regulation of insulin action at the level of the skeletal Responses 1; TRX: Thioredoxin; NGT: Normal Glucose Tolerant; IGT: Impaired Glucose Tolerant; ASK1: Apopto- muscle, is thioredoxin-interacting protein (TXNIP). tic Signaling Kinase; PTEN: Phosphatase Tensin Homolog TXNIP description and domain analysis 10; REF-1: Redox Factor-1; HIF-1: Hypoxia-Inducible Fac- tor-1a; NF-κB: Nuclear Factor Kappa-Light-Chain-Enhan- TXNIP, also referred to as Vitamin-D upregulated cer of Activated B Cells; AP-1: Activator Protein-1; NRF-2: protein 1 (VDUP-1), was first discovered in HL-60 leu- Nuclear Factor E2-Related Factor 2; GR: Glucocorticoid Receptor; ER: Estrogen Receptor; ETC: Electron Transport kemia cells and shown to be upregulated in response Chain; AICAR: 5-Aminoimidazole-4-Carboxamide Ribo- to treatment with 1,25-dihydroxyvitamin D3 [7]. Subse- nucleotide; PBMC: Peripheral Blood Mononuclear Cells; quent investigations utilizing two-hybrid yeast analysis PP2A: Protein Phosphatase 2; AKT: Protein Kinase B; P38 revealed that TXNIP is capable of binding to cysteine MAPK: P38 Mitogen-Activated Protein Kinase; FOXO1: For- khead Box 01 Transcriptional Factor; CCP: Clathrin Coated residues located within the active site of antioxidan- Pits; CHREBP: Carbohydrate Response Element Binding ts Thioredoxin-1 (TRX-1) and 2 (TRX-2) and inhibiting Citation: Chaves AB, Haus JM, Houmard JA (2018) Role of TXNIP Biology in Glucose Metabolism. Int J Diabetes Clin Res 4:080. doi.org/10.23937/2377-3634/1410080 Received: November 17, 2017: Accepted: January 06, 2018: Published: January 08, 2018 Copyright: © 2018 Chaves AB, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Chaves et al. Int J Diabetes Clin Res 2018, 5:080 • Page 1 of 5 • DOI: 10.23937/2377-3634/1410080 ISSN: 2377-3634 their ability to scavenge reactive oxygen species thus cellular level, a preclinical model with liver-specific de- promoting oxidative stress [8]. Although TXNIP belon- letion of TXNIP was developed. With TXNIP deletion, he- gs to the α-arrestin protein family, the active cysteine patic glucose production was blunted which led to hypo- residues that enable its interaction with TRX are not glycemia during the fasted state. However, in response present in other members of the family, indicating that to a glucose challenge, liver-specific TXNIP knockout TXNIP has the distinct ability to bind to the active site mice were incapable of achieving greater glucose clea- of TRX and affect the redox environment [9]. Spindel, rance rates compared to their wildtype littermates. This et al. [10] conducted three-dimensional (3D) analysis of finding is in contrast with systemic knockout models TXNIP and determined that TXNIP contains several do- indicating that although fasting glucose homeostasis mains that are conserved amongst other members of is modulated by hepatocyte TXNIP levels; postprandial the α-arrestin family and are necessary for its redox-in- glucose tolerance may require modulation of TXNIP bio- dependent functions. Within the n-terminus there are logy in other tissues and cell types [19]. two SH3-binding domains which are known to interact with non-tyrosine kinase Src, and a mitogen activated DeBalsi, et al. [20] developed a skeletal muscle-spe- protein kinase kinase kinase 5 (MAP3K-5) [10-12]. Con- cific TXNIP knockout (SKM-/-) murine model. Compari- versely, within the C-terminus lies three SH3-binding sons between the whole-body knockout, skeletal mu- domains and two PPxY motifs. The PPxY motifs are ne- scle-specific knockout, and wild type revealed that glu- cessary for TXNIP to interact with E3 Ubiqutin Ligase, cose tolerance was enhanced (i.e. lowered circulating Itch, enabling it to undergo polyubiquitination and sub- glucose concentrations) in the whole-body knockout sequent proteasome degradation [13]. Recent evidence model following an intraperitoneal glucose tolerance suggests that following phosphorylation of a specific se- test. Interestingly, these improvements were preserved rine residue, ser308, TXNIP undergoes a conformational in the SKM (-/-) specific knockout indicating that skele- change that increases its susceptibility to ubiquitination tal muscle expression of TXNIP contributes significantly via Itch, augmenting its rate of proteasome degrada- to whole-body glucose homeostasis. Although SKM (-/-) tion [14]. TXNIP also contains two additional domains specific TXNIP deficiency improved glucose tolerance, including immune-receptor tyrosine-based inhibition the mice also experienced reduced mitochondrial respi- domain (ITIM) and chromatin maintenance region 1 ration, substrate oxidation, mitochondrial protein mar- (CRM1) [10]. ITIM mediates TXNIP’s interaction with kers, and aerobic exercise capacity. These data suggest tyrosine phosphatases in order to regulate the intracel- that TXNIP serves as a metabolic switch between oxida- lular activity of membrane-bound receptors [15]. CRM1 tive and glycolytic metabolism, and must be regulated mediates the interaction with hypoxia-inducible factor appropriately to achieve proper balance between ener- 1-α (HIF1-α) and ubiquitin ligase von Hippel-Lindau pro- gy systems. tein (pVHL), leading to the exclusion of HIF1-α from the Despite extensive work conducted on TXNIP expres- nucleus and degradation in the cytosol [16]. sion and glucose metabolism, the mechanism through Role of TXNIP in glucose metabolism which TXNIP exerted these effects was still largely un- known. Oslowski, et al. [21] provided some initial insi- TXNIP’s role in regulating metabolism was first inve- ght by demonstrating in pancreatic β-cells that TXNIP stigated in HcB-19 mice used as a preclinical model to can interact and mediate the activation of the nod like study familial hypercholesterolemia in humans. Intere- receptor P3 (NLRP3) inflammasome, which is a large stingly, the hypocholesteremia was a result of a sponta- multimeric protein complex, capable of inducing en- neous mutation on the TXNIP gene leading to systemic doplasmic reticulum (ER) stress, IL-1β expression, and reductions at the mRNA levels. As a result, HcB-19 mice apoptotic cell death. These findings were substantiated had lower basal CO2 production, increased triglyceride in microvascular endothelial cells by demonstrating that synthesis, and decreased flux of free fatty acids (FFA) silencing of TXNIP ameliorated NLRP3 activation in -re through the tricarboxylic acid (TCA) cycle [17]. Conside- sponse to oxidative stress [22]. Further,