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Identification of the leptin receptor sequences crucial for the STAT3-Independent control of metabolism.

ABSTRACT: BACKGROUND:Leptin acts via its receptor, LepRb, on specialized neurons in the brain to modulate energy balance and glucose homeostasis. LepRb?STAT3 signaling plays a crucial role in leptin action, but LepRb also mediates an additional as-yet-unidentified signal (Signal 2) that is important for leptin action. Signal 2 requires LepRb regions in addition to those required for JAK2 activation but operates independently of STAT3 and LepRb phosphorylation sites. METHODS:To identify LepRb sequences that mediate Signal 2, we used CRISPR/Cas9 to generate five novel mouse lines containing COOH-terminal truncation mutants of LepRb. We analyzed the metabolic phenotype and measures of hypothalamic function for these mouse lines. RESULTS:We found that deletion of LepRb sequences between residues 921 and 960 dramatically worsens metabolic control and alters hypothalamic function relative to smaller truncations. We also found that deletion of the regions including residues 1013-1053 and 960-1013 each decreased obesity compared to deletions that included additional COOH-terminal residues. CONCLUSIONS:LepRb sequences between residues 921 and 960 mediate the STAT3 and LepRb phosphorylation-independent second signal that contributes to the control of energy balance and metabolism by leptin/LepRb. In addition to confirming the inhibitory role of the region (residues 961-1013) containing Tyr985, we also identified the region containing residues 1013-1053 (which contains no Tyr residues) as a second potential mediator of LepRb inhibition. Thus, the intracellular domain of LepRb mediates multiple Tyr-independent signals.

SUBMITTER: Barnes TM

PROVIDER: S-EPMC6992902 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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Identification of the leptin receptor sequences crucial for the STAT3-Independent control of metabolism.

Barnes Tammy M TM Shah Kimi K Allison Margaret B MB Steinl Gabrielle K GK Gordian Desiree D Sabatini Paul V PV Tomlinson Abigail J AJ Cheng Wenwen W Jones Justin C JC Zhu Qing Q Faber Chelsea C Myers Martin G MG

Molecular metabolism 20200103

<h4>Background</h4>Leptin acts via its receptor, LepRb, on specialized neurons in the brain to modulate energy balance and glucose homeostasis. LepRb→STAT3 signaling plays a crucial role in leptin action, but LepRb also mediates an additional as-yet-unidentified signal (Signal 2) that is important for leptin action. Signal 2 requires LepRb regions in addition to those required for JAK2 activation but operates independently of STAT3 and LepRb phosphorylation sites.<h4>Methods</h4>To identify LepR ...[more]

PMID: 32029227

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Project description:Population based studies have established that androgen deficiency in males correlates with type 2 diabetes, visceral adiposity, and metabolic syndrome. Androgen therapy has been investigated as a possible treatment regime to combat these disorders. However, the molecular mechanism of androgen effects on these diseases still remain poorly understood. The zucker diabetic fatty (ZDF) rat, containing a mutation in the leptin receptor, is a well-investigated model of obesity and type 2 diabetes. Male rats are characterized as androgen deficient and spontaneously develop obese, hyperlipidemia, hyperglycemia and hyperinsulinemia. In this study, we used ZDF male rats as a model of metabolic syndrome to investigate the effects of testosterone administration on the development of the metabolic conditions. Methods: Male ZDF rats at six week of age were randomly divided into two groups and administered testosterone undecanoate(TU) or vehicle alone every three days for three weeks. After three weeks, overnight fasted blood glucose and insulin concentrations were significantly higher and glucose tolerance and insulin sensitivity were impaired in TU treated ZDF rats compared to vehicle controls. Moreover, increased serum triglycerides and VLDL were observed in TU treated rats. To further explore the observed metabolic changes in TU treated ZDF rats, whole-genome microarray analysis were performed on isolated liver mRNA. Results: Array analysis revealed that many hepatic lipogenic genes were increased in male ZDF rat livers treated with TU. Interestingly, SREBP-1c, a key transcriptional activator of lipogenic genes and PGC-1 , an activator of SREBP-1c were induced while small heterodimer partner, a transcriptional inhibitor of lipogenic genes was suppressed by TU treatment. Exploring signaling pathways for these effects, we observed that the hepatic activated forms of STAT3 and AMPK, two known inhibitors of hepatic lipogenesis, were decreased in TU treated rat. Moreover, we observed that DHT could block the induction of STAT3 and AMPK phosphorylation in treated primary human hepatocytes. Preliminarily, in the leptin receptor positive zucker diabetic lean male rats, we observed that TU treatment has an oppose effect on the hepatic lipogenic genes, suggesting that hepatic leptin signaling may influence androgen signaling. Further insight into the relationship between androgen deficiency and the leptin system may help improve treatment of the metabolic syndrome. Population based studies have established that androgen deficiency in males correlates with type 2 diabetes, visceral adiposity, and metabolic syndrome. Androgen therapy has been investigated as a possible treatment regime to combat these disorders. However, the molecular mechanism of androgen effects on these diseases still remain poorly understood. The zucker diabetic fatty (ZDF) rat, containing a mutation in the leptin receptor, is a well-investigated model of obesity and type 2 diabetes. Male rats are characterized as androgen deficient and spontaneously develop obese, hyperlipidemia, hyperglycemia and hyperinsulinemia. In this study, we used ZDF male rats as a model of metabolic syndrome to investigate the effects of testosterone administration on the development of the metabolic conditions. Two-condition experiment. (1) lean ZDF rats (control) vs. lean ZDF rats (testosterone treated). (2) obese ZDF rats (control) vs. obese ZDF rats (testosterone treated). Biological replicates: 4 control replicates, 4 treated replicates.

Project description:Differentiated articular chondrocytes express a functional bisoform of the leptin receptor (LRb); however, leptin-LRb signaling in these cells is poorly understood. We hypothesized that leptin-LRb signaling in articular chondrocytes functions to modulate canonical Wnt signaling events by altering the expression of Frizzled (FZD) receptors.Human chondrocyte cell lines and primary articular chondrocytes were grown in serum containing growth media for 24h, followed by a media change to Dulbecco's modified Eagle's medium (DMEM) containing 1% Nutridoma-SP to obtain a serum-deficient environment for 24h before treatment. Treatments included recombinant human leptin (10-100nM), recombinant human IL-6 (0.3-3nM), or recombinant human erythropoietin (Epo) (10mU/ml). Cells were harvested 30min-48h after treatment and whole cell lysates were analyzed using immunoblots or luciferase assays.Treatment of cells with leptin resulted in activation of Janus kinase 2 (JAK2) and subsequent phosphorylation of specific tyrosine residues on LRb, followed by dose- and time-dependent increases in the expression of Frizzled-1 (FZD1) and Frizzled-7 (FZD7). Leptin-mediated increases in the expression of FZD1 were blocked by pre-treatment with the protein synthesis inhibitor cycloheximide or the JAK2 inhibitor AG490. Experiments using a series of hybrid Epo extracellular domain-leptin intracellular domain receptors (ELR) harboring mutations of specific tyrosine residues in the cytoplasmic tail showed that increases in the expression of FZD1 were dependent on LRb-mediated phosphorylation of STAT3, but not ERK1/2 or STAT5. Leptin pre-treatment of chondrocytes prior to Wnt3a stimulation resulted in an increased magnitude of canonical Wnt signaling.These experiments show that leptin-LRb signaling in articular chondrocytes modulates expression of canonical Wnt signaling receptors and suggests that direct cross-talk between these pathways is important in determining chondrocyte homeostasis.

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Identification of the leptin receptor sequences crucial for the STAT3-Independent control of metabolism.

Publications

Identification of the leptin receptor sequences crucial for the STAT3-Independent control of metabolism.

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