Munc18c: a controversial regulator of peripheral insulin action

Ramalingam, Latha; Yoder, Stephanie M.; Oh, Eunjin; Thurmond, Debbie C.

doi:10.1016/j.tem.2014.06.010

Cited by 9 publications

(10 citation statements)

References 81 publications

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“…Indeed, DOC2B may play both roles by virtue of dual cellular compartmentalisationexisting in two pools, one at the PM, the other in the cytosolic space. We and others have speculated that SNARE assembly occurs in parallel with GLUT4 vesicle translocation, orchestrating the preparation of the plasma-membrane-localised t-SNARE proteins for the arrival of the vesicle-associated SNARE (v-SNARE)-loaded GLUT4 vesicle for seamless vesicle docking and fusion events [22,54]. KLC1 is also localised to the cytoplasm under basal conditions, consistent with its role in microtubule-based GLUT4 vesicle trafficking [55], and hence insulin-stimulated enhancement of DOC2B-KLC1 interaction may represent an early event in the process of GLUT4 vesicle translocation to the PM.…”

Section: Discussionmentioning

confidence: 99%

DOC2B promotes insulin sensitivity in mice via a novel KLC1-dependent mechanism in skeletal muscle

Zhang

Merz

et al. 2019

Diabetologia

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Aims/hypothesis Skeletal muscle accounts for >80% of insulin-stimulated glucose uptake; dysfunction of this process underlies insulin resistance and type 2 diabetes. Insulin sensitivity is impaired in mice deficient in the double C2 domain β (DOC2B) protein, while whole-body overexpression of DOC2B enhances insulin sensitivity. Whether insulin sensitivity in the skeletal muscle is affected directly by DOC2B or is secondary to an effect on other tissues is unknown; the underlying molecular mechanisms also remain unclear. Methods Human skeletal muscle samples from non-diabetic or type 2 diabetic donors were evaluated for loss of DOC2B during diabetes development. For in vivo analysis, new doxycycline-inducible skeletal-muscle-specific Doc2b-overexpressing mice fed standard or high-fat diets were evaluated for insulin and glucose tolerance, and insulin-stimulated GLUT4 accumulation at the plasma membrane (PM). For in vitro analyses, a DOC2B-overexpressing L6-GLUT4-myc myoblast/myotube culture system was coupled with an insulin resistance paradigm. Biochemical and molecular biology methods such as site-directed mutagenesis, coimmunoprecipitation and mass spectrometry were used to identify the molecular mechanisms linking insulin stimulation to DOC2B. Results We identified loss of DOC2B (55% reduction in RNA and 40% reduction in protein) in the skeletal muscle of human donors with type 2 diabetes. Furthermore, inducible enrichment of DOC2B in skeletal muscle of transgenic mice enhanced whole-body glucose tolerance (AUC decreased by 25% for female mice) and peripheral insulin sensitivity (area over the curve increased by 20% and 26% for female and male mice, respectively) in vivo, underpinned by enhanced insulin-stimulated GLUT4 accumulation at the PM. Moreover, DOC2B enrichment in skeletal muscle protected mice from high-fat-diet-induced peripheral insulin resistance, despite the persistence of obesity. In L6-GLUT4-myc myoblasts, DOC2B enrichment was sufficient to preserve normal insulin-stimulated GLUT4 accumulation at the PM in cells exposed to diabetogenic stimuli. We further identified that DOC2B is phosphorylated on insulin stimulation, enhancing its interaction with a microtubule motor protein, kinesin light chain 1 (KLC1). Mutation of Y301 in DOC2B blocked the insulin-stimulated phosphorylation of DOC2B and interaction with KLC1, and it blunted the ability of DOC2B to enhance insulin-stimulated GLUT4 accumulation at the PM. Conclusions/interpretation These results suggest that DOC2B collaborates with KLC1 to regulate insulin-stimulated GLUT4 accumulation at the PM and regulates insulin sensitivity. Our observation provides a basis for pursuing DOC2B as a novel drug target in the muscle to prevent/treat type 2 diabetes. Karla E. Merz and Arianne Aslamy contributed equally to this work.Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00125-019-4824-2) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

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Section: Discussionmentioning

confidence: 99%

DOC2B promotes insulin sensitivity in mice via a novel KLC1-dependent mechanism in skeletal muscle

Zhang

Merz

et al. 2019

Diabetologia

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“…The fusion of GLUT4 containing vesicles (GSVs) with the plasma membrane is an essential aspect in GLUT4 translocation upon insulin stimulation and has been extensively reviewed . This process has been shown to require Munc18c in 3T3‐L1 adipocytes .…”

Section: Regulation Of Glucose and Lipid Metabolism Through The Endosmentioning

confidence: 99%

Metabolic regulation through the endosomal system

Gilleron

Gerdes

Zeigerer

2019

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The endosomal system plays an essential role in cell homeostasis by controlling cellular signaling, nutrient sensing, cell polarity and cell migration. However, its place in the regulation of tissue, organ and whole body physiology is less well understood. Recent studies have revealed an important role for the endosomal system in regulating glucose and lipid homeostasis, with implications for metabolic disorders such as type 2 diabetes, hypercholesterolemia and non‐alcoholic fatty liver disease. By taking insights from in vitro studies of endocytosis and exploring their effects on metabolism, we can begin to connect the fields of endosomal transport and metabolic homeostasis. In this review, we explore current understanding of how the endosomal system influences the systemic regulation of glucose and lipid metabolism in mice and humans. We highlight exciting new insights that help translate findings from single cells to a wider physiological level and open up new directions for endosomal research.

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“…Munc18c and cognate Syn-4 have been well studied to mediate GLUT4 vesicle translocation to PM and exocytosis in adipose tissue and muscle and also some aspects of GSIS [18,19] . Optimal levels of Munc18c play a pivotal role in maintaining peripheral insulin sensitivity and glucose uptake [20] . A transgenic mouse model of Munc18c protein overexpression in adipose, skeletal muscle, and pancreas, exhibits peripheral insulin resistance resulting from impaired insulin-stimulated glucose uptake and GLUT4 vesicle exocytosis, and decreased GSIS [21] .…”

Section: Introductionmentioning

confidence: 99%

Munc18c mediates exocytosis of pre-docked and newcomer insulin granules underlying biphasic glucose stimulated insulin secretion in human pancreatic beta-cells

Zhu

Xie

Karimian

et al. 2015

Molecular Metabolism

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ObjectivePancreatic beta-cells express three Munc18 isoforms. Much is known about the roles of Munc18a (pre-docked secretory granules-SGs) and Munc18b (newcomer SGs and SG–SG fusion) in insulin exocytosis. Although shown to influence glucose-stimulated insulin secretion (GSIS) in rodents the precise role of Munc18c in insulin SG exocytosis has not been elucidated. We here examined the role of Munc18c in human pancreatic beta-cells.MethodsMunc18c-shRNA/RFP lenti-virus (versus control virus) was used to knock down the expression level of Munc18c in human islets or single beta-cells. Insulin secretion and granule exocytosis were measured by performing islets perifusion, single-cell patch clamp capacitance measurements and total internal reflection fluorescence microscopy (TIRFM).ResultsMunc18c is most abundant in the cytosol of human beta-cells. Endogenous function of Munc18c was assessed by knocking down (KD) its islet expression by 70% employing lenti-shRNA virus. Munc18c-KD caused reduction in cognate syntaxin-4 islet expression but not in other exocytotic proteins, resulting in the reduction in GSIS in first- (by 42%) and second phases (by 35%). Single cell analyses of RFP-tagged Munc18c-KD beta-cells by patch clamp capacitance measurements showed inhibition in both readily-releasable pool (by 52%) and mobilization from the reserve pool (by 57%). TIRFM to assess single SG behavior showed that Munc18c-KD inhibition of first phase GSIS was attributed to reduction in exocytosis of pre-docked and newcomer SGs, and second phase inhibition attributed entirely to reduction in newcomer SG fusion (SGs that undergo minimal residence or docking time at the plasma membrane before fusion).ConclusionMunc18c is involved in the distinct molecular machineries that affect exocytosis of both predocked and newcomer SG pools that underlie Munc18c's role in first and second phases of GSIS, respectively.

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Munc18c: a controversial regulator of peripheral insulin action

Cited by 9 publications

References 81 publications

DOC2B promotes insulin sensitivity in mice via a novel KLC1-dependent mechanism in skeletal muscle

DOC2B promotes insulin sensitivity in mice via a novel KLC1-dependent mechanism in skeletal muscle

Metabolic regulation through the endosomal system

Munc18c mediates exocytosis of pre-docked and newcomer insulin granules underlying biphasic glucose stimulated insulin secretion in human pancreatic beta-cells

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