scholarly journals C-terminal truncation of Pik3r1 in mice models human lipodystrophic insulin resistance uncoupled from dyslipidemia

2017 ◽  
Author(s):  
Albert Kwok ◽  
Ilona Zvetkova ◽  
Sam Virtue ◽  
Isabel Huang-Doran ◽  
Patsy Tomlinson ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Tyrosine Kinases ◽  
Target Genes ◽  
Ex Vivo ◽  
Liver Weight ◽  
Postnatal Growth ◽  
Regulatory Subunit ◽  
Severe Insulin Resistance ◽  
Triglyceride Content ◽  
Short Syndrome

SummaryHeterodimeric class IA phosphatidylinositol-3-kinases (PI3K) transduce signals from many receptor tyrosine kinases including the insulin receptor. PI3K recruitment to phosphotyrosines is mediated by Pik3r1 gene products including the most intensely studied PI3K regulatory subunit, p85α, which also binds and regulates the PIP3 phosphatase Pten, and the lipogenic transcription factor Xbp1. Mutations in human PIK3R1 cause SHORT syndrome, featuring lipodystrophy and severe insulin resistance which, uniquely, are uncoupled from fatty liver and dyslipidemia. We describe a novel mouse model of SHORT syndrome made by knock in of the Pik3r1 Y657X mutation. Homozygous embryos die at E11.5, while heterozygous mice exhibit pre-and postnatal growth impairment with diminished placental vascularity. Adipose tissue accretion on high fat feeding was reduced, however adipocyte size was unchanged and preadipocyte differentiation ex vivo unimpaired. Despite severe insulin resistance, heterozygous mice were hypolipidemic, and plasma adiponectin, liver weight, cholesterol, glycogen and triglyceride content were unchanged. Mild downregulation of lipogenic Srebp1, Srebp2 and Chrebp transcriptional activity but no suppression of Xbp1 target genes was seen after fasting. These findings give new insights into the developmental role of Pik3r1, and establish a model of lipodystrophic insulin resistance dissociated from dyslipidemia as seen in SHORT syndrome.

scholarly journals In Vivo Targeting of the Growth Hormone Receptor (GHR) Box1 Sequence Demonstrates that the GHR Does Not Signal Exclusively through JAK2

2010 ◽  
Vol 24 (1) ◽  
pp. 204-217 ◽  
Author(s):  
Johanna L. Barclay ◽  
Linda M. Kerr ◽  
Leela Arthur ◽  
Jennifer E. Rowland ◽  
Caroline N. Nelson ◽  
...  
Keyword(s):  
Tyrosine Kinases ◽  
Growth Hormone Receptor ◽  
Target Genes ◽  
Postnatal Growth ◽  
Signal Transducers ◽  
Phenotypic Differences ◽  
Protein Levels ◽  
Igf Binding ◽  
Transcript Profiles

Abstract GH is generally believed to signal exclusively through Janus tyrosine kinases (JAK), particularly JAK2, leading to activation of signal transducers and activators of transcription (STAT), ERK and phosphatidylinositol 3-kinase pathways, resulting in transcriptional regulation of target genes. Here we report the creation of targeted knock-in mice wherein the Box1 motif required for JAK2 activation by the GH receptor (GHR) has been disabled by four Pro/Ala mutations. These mice are unable to activate hepatic JAK2, STAT3, STAT5, or Akt in response to GH injection but can activate Src and ERK1/2. Their phenotype is identical to that of the GHR−/− mouse, emphasizing the key role of JAK2 in postnatal growth and the minimization of obesity in older males. In particular, they show dysregulation of the IGF-I/IGF-binding protein axis at transcript and protein levels and decreased bone length. Because no gross phenotypic differences were evident between GHR−/− and Box1 mutants, we undertook transcript profiling in liver from 4-month-old males. We compared their transcript profiles with our 391-GHR truncated mice, which activate JAK2, ERK1/2, and STAT3 in response to GH but not STAT5a/b. This has allowed us for the first time to identify in vivo Src/ERK-regulated transcripts, JAK2-regulated transcripts, and those regulated by the distal part of the GHR, particularly by STAT5.

scholarly journals OR20-07 Placentas from Obese Women Are Resistant to the Effect of Insulin on Triglyceride Content Ex Vivo

2020 ◽  
Vol 4 (Supplement_1) ◽  
Author(s):  
Anika K Anam ◽  
Katherine Cooke ◽  
Jane O’Bryan ◽  
Pavithra Vijayakumar ◽  
Daniel Vatner ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Ex Vivo ◽  
Insulin Dose ◽  
Fold Increase ◽  
Maximal Response ◽  
Obese Women ◽  
Peripheral Tissues ◽  
High Insulin ◽  
Triglyceride Content ◽  
The Difference

Abstract Background: Obesity affects 25% of pregnant women and is associated with a higher risk of neonatal complications, such as macrosomia and increased adiposity. The placenta may contribute to neonatal adiposity by accumulating and transferring excess lipid in response to maternal hyperinsulinemia. We previously found that insulin promotes a 3-fold increase in placental triglyceride (TG) content in lean women. We hypothesized that obese women have higher placental insulin resistance compared to lean women[FC1] with respect to TG content. Methods: Healthy, lean women (n=12; mean age 34±1 yrs; BMI 22±0.4 kg/m2) and non-diabetic, obese women (n=9; mean age 32±2 yrs; BMI 33±0.4 kg/m2, p<0.0001) consented for placenta collection at elective c-section under fasting conditions. Placental villous explants were immediately flash frozen or cultured for 24 hours, starved, then treated for 48 hours with 0.1nM, 1nM, 10nM, or 100nM of insulin, or vehicle. Lipids were extracted from basal and treated explants using a chloroform-methanol separation protocol. TG content was quantified by spectrophotometer and normalized to weight. Data were analyzed by two-way ANOVA. Results: Basal placenta tissue from obese women contained a 1.5-fold higher level of TG compared to lean women (9.4±0.5 vs 5.7±0.5 mcg/mg, p=0.001). Placental response to insulin in lean women peaked at 1nM insulin (20.2±3.3 mcg/mg), and plateaued at higher doses of 10nM (18.6±3.3 mcg/mg) and 100nM (22.8±2.8 mcg/mg, p=NS respectively). In contrast, placenta explants from obese women required the highest insulin dose of 100 nM for maximal response (23.6±3.2 mcg/mg), and showed a gradual dose response from 0.1 nM insulin (9.5±2), 1nM (14.8±2), 10 nM (16.9±3). At 100nM insulin, the difference in TG content was variable, but on average was 2-fold higher than vehicle treated placenta (vs 11.8±2.5[FC2] [AA3] mcg/mg, p=0.002). Conclusion: Our findings indicate that placenta from obese women develop insulin resistance similar to peripheral tissues, which can be overcome by high insulin doses. This placental insulin resistance likely occurs in response to chronic hyperinsulinemia, leading to interference of insulin signaling pathways, and may protect the neonate from excessive nutrient flux.

scholarly journals Human Placental Growth Hormone Increases Expression of the P85 Regulatory Unit of Phosphatidylinositol 3-Kinase and Triggers Severe Insulin Resistance in Skeletal Muscle

Endocrinology ◽  
2004 ◽  
Vol 145 (3) ◽  
pp. 1144-1150 ◽  
Author(s):  
Linda A. Barbour ◽  
Jianhua Shao ◽  
Liping Qiao ◽  
Wayne Leitner ◽  
Marianne Anderson ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Normal Pregnancy ◽  
Dominant Negative ◽  
Regulatory Subunit ◽  
Phosphatidylinositol 3 Kinase ◽  
Cellular Mechanisms ◽  
Severe Insulin Resistance ◽  
Placental Growth Hormone ◽  
Glut 4 Translocation ◽  
Phosphatidylinositol 3

Abstract The insulin resistance of normal pregnancy is necessary to divert fuels to the fetus to meet fetal growth demands and is mediated by placental hormones. We recently demonstrated that human placental GH (hPGH) can trigger severe insulin resistance in transgenic (TG) mice. In this study we sought to elucidate the cellular mechanisms by which hPGH interferes with insulin signaling in muscle in TG mice. Insulin-stimulated GLUT-4 translocation to the plasma membrane (PM) was reduced in the TG compared with wild-type (WT) mice (P = 0.05). Insulin receptor (IR) levels were modestly reduced by 19% (P < 0.01) in TG mice, but there were no changes in phosphorylation of IR or IR substrate-1 (IRS-1) between WT and TG mice. A singular finding was a highly significant increase in the p85α regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase; P < 0.001), yet a reduced ability of insulin to stimulate IRS-1-associated PI 3-kinase activity (P < 0.05). Although the levels of the p110 catalytic subunit protein of PI 3-kinase and IRS-1 were unchanged in the TG mice, insulin’s ability to stimulate p110 association with IRS-1 was markedly reduced (P < 0.0001). We demonstrate a unique mechanism of insulin resistance and suggest that hPGH may contribute to the insulin resistance of normal pregnancy by increasing the expression of the p85α monomer, which competes in a dominant negative fashion with the p85-p110 heterodimer for binding to IRS-1 protein.

In vivo chloroquine-induced inhibition of insulin degradation in a diabetic patient with severe insulin resistance

Diabetes ◽  
1984 ◽  
Vol 33 (12) ◽  
pp. 1133-1137 ◽  
Author(s):  
B. R. Blazar ◽  
C. B. Whitley ◽  
A. E. Kitabchi ◽  
M. Y. Tsai ◽  
J. Santiago ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Diabetic Patient ◽  
Insulin Degradation ◽  
Severe Insulin Resistance

Drosophila Gain-of-Function Mutant RTK Torso Triggers Ectopic Dpp and STAT Signaling

Genetics ◽  
2003 ◽  
Vol 164 (1) ◽  
pp. 247-258 ◽  
Author(s):  
Jinghong Li ◽  
Willis X Li
Keyword(s):  
Tyrosine Kinases ◽  
Target Genes ◽  
Tor Signaling ◽  
Gain Of Function ◽  
Essential Requirement ◽  
Downstream Target ◽  
Rtk Signaling ◽  
Genome Wide ◽  
A Genome ◽  
Genomic Regions

Abstract Overactivation of receptor tyrosine kinases (RTKs) has been linked to tumorigenesis. To understand how a hyperactivated RTK functions differently from wild-type RTK, we conducted a genome-wide systematic survey for genes that are required for signaling by a gain-of-function mutant Drosophila RTK Torso (Tor). We screened chromosomal deficiencies for suppression of a gain-of-function mutation tor (torGOF), which led to the identification of 26 genomic regions that, when in half dosage, suppressed the defects caused by torGOF. Testing of candidate genes in these regions revealed many genes known to be involved in Tor signaling (such as those encoding the Ras-MAPK cassette, adaptor and structural molecules of RTK signaling, and downstream target genes of Tor), confirming the specificity of this genetic screen. Importantly, this screen also identified components of the TGFβ (Dpp) and JAK/STAT pathways as being required for TorGOF signaling. Specifically, we found that reducing the dosage of thickveins (tkv), Mothers against dpp (Mad), or STAT92E (aka marelle), respectively, suppressed torGOF phenotypes. Furthermore, we demonstrate that in torGOF embryos, dpp is ectopically expressed and thus may contribute to the patterning defects. These results demonstrate an essential requirement of noncanonical signaling pathways for a persistently activated RTK to cause pathological defects in an organism.

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