Elevated hepatic glucose output during fasting is a major contributor to type 2 diabetes, which affects 10-25% of Americans. The cAMP response element binding protein CREB and its co-activator CRTC2 regulate hepatic glucose output by transcriptional induction of rate-limiting gluconeogenic enzymes during fasting. Given that CREB activity becomes aberrantly activated in diabetic rodents, we aim to identify molecular mechanisms by which this pathway can be inhibited. Recent studies in mouse models and cultured hepatocytes implicated a family of AMPK-related kinases called Salt-Inducible Kinases (SIK1-3), in the control of CRTC co-activator function during fasting and re-feeding. Among these, SIK1 is unique in that fasting stimuli induce hepatic SIK1 mRNA transcription. SIK1 protein then feeds back to inhibit CREB/CRTC2 and glucose output after a meal. This cycle is reset during the postprandial period, during which SIK1 protein levels decline, thus allowing re- activation of CREB at the onset of the next fast. Based on the temporal nature of SIK1 expression and its potent inhibitory effects on hepatic glucose output, we hypothesize that the timing of SIK1 activity is limited by regulated degradation during the fasting to feeding transition. We propose to test this hypothesis using a variety of molecular and genetic techniques. We will investigate the dynamics of SIK1 activity in hepatocytes and liver tissue and explore the structural determinants of SIK1 that regulate its degradation. We will also test the role of a candidate E3 ubiquitin ligase in limiting SIK1 activity during the postprandial period. Finally, we will characterize metabolic phenotypes resulting from liver-specific deletion of the Sik1 gene in mice. We have generated several transgenic animal strains for these studies, including transgenic luciferase reporter mice to visualize CREB-dependent transcription in vivo. The goal of this work is to determine how dynamic regulation of SIK1 contributes to maintenance of glucose homeostasis and identify new molecular mechanisms by which SIK1 activity is regulated. Molecular insight into this pathway will reveal new therapeutic strategies for inhibition of hepatic glucose output in diabetic patients.
Inappropriate regulation of blood glucose is the hallmark of diabetes mellitus, which is a growing public health problem in the United States. The liver is a major organ in which glucose regulation occurs. This project addresses the molecular regulation of an enzyme that normally functions in the liver to turn off glucose production. This study aims to identify novel therapeutic targets for treatment of diabetes.
|Fekry, Baharan; Ribas-Latre, Aleix; Baumgartner, Corrine et al. (2018) Incompatibility of the circadian protein BMAL1 and HNF4? in hepatocellular carcinoma. Nat Commun 9:4349|
|Kim, Eun Ran; Fan, Shengjie; Akhmedov, Dmitry et al. (2017) Red blood cell ?-adrenergic receptors contribute to diet-induced energy expenditure by increasing O2 supply. JCI Insight 2:|
|Akhmedov, Dmitry; Mendoza-Rodriguez, Maria G; Rajendran, Kavitha et al. (2017) Gs-DREADD Knock-In Mice for Tissue-Specific, Temporal Stimulation of Cyclic AMP Signaling. Mol Cell Biol 37:|
|Valera, Juliana M; Diaz, Tatyana; Petty, Lauren E et al. (2017) Prevalence of spinocerebellar ataxia 36 in a US population. Neurol Genet 3:e174|
|Nixon, Mark; Stewart-Fitzgibbon, Randi; Fu, Jingqi et al. (2016) Skeletal muscle salt inducible kinase 1 promotes insulin resistance in obesity. Mol Metab 5:34-46|
|Akhmedov, Dmitry; Rajendran, Kavitha; Mendoza-Rodriguez, Maria G et al. (2016) Knock-in Luciferase Reporter Mice for In Vivo Monitoring of CREB Activity. PLoS One 11:e0158274|
|Wong, Ching-On; Palmieri, Michela; Li, Jiaxing et al. (2015) Diminished MTORC1-Dependent JNK Activation Underlies the Neurodevelopmental Defects Associated with Lysosomal Dysfunction. Cell Rep 12:2009-20|
|Clark, Rebecca I; Tan, Sharon W S; Péan, Claire B et al. (2013) MEF2 is an in vivo immune-metabolic switch. Cell 155:435-47|
|Fu, Jingqi; Akhmedov, Dmitry; Berdeaux, Rebecca (2013) The short isoform of the ubiquitin ligase NEDD4L is a CREB target gene in hepatocytes. PLoS One 8:e78522|
|Luo, Jialie; Stewart, Randi; Berdeaux, Rebecca et al. (2012) Tonic inhibition of TRPV3 by Mg2+ in mouse epidermal keratinocytes. J Invest Dermatol 132:2158-65|