Search

Hypothalamic leptin receptor (LR) signaling regulates body weight by balancing food intake and energy expenditure. It is well established that the human LR undergoes ectodomain shedding, but little is known about the fate of the remaining cytosolic domain. This study demonstrates that regulated intramembrane proteolysis (RIP) releases the LR intracellular domain (LR ICD), which translocates to the mitochondria where it binds to SOCS6. This LR ICD-SOCS6 interaction stabilizes both proteins on the mitochondrial outer membrane and requires a functional BC box in SOCS6 for mitochondrial association and a central motif in the LR ICD for SOCS6 binding. The LR ICD prevents CCCP-induced mitochondrial depolarization and mitophagy as shown by lowered Parkin translocation and p62 accumulation. Strict regulation of mitochondrial dynamics in the hypothalamus is known to be essential for body weight homeostasis. This is the first study showing that the LR can directly modulate mitochondrial biology. [ABSTRACT FROM AUTHOR]

After its discovery in 1994, it soon became clear that leptin acts as an adipocyte-derived hormone with a central role in the control of body weight and energy homeostasis. However, a growing body of evidence has revealed that leptin is a pleiotropic cytokine with activities on many peripheral cell types. Inappropriate leptin signaling can promote autoimmunity, certain cardiovascular diseases, elevated blood pressure and cancer, which makes leptin and the leptin receptor interesting targets for antagonism. Profound insights in the leptin receptor (LR) activation mechanisms are a prerequisite for the rational design of these antagonists. In this review, we focus on the molecular mechanisms underlying leptin receptor activation and signaling. We also discuss the current strategies to interfere with leptin signaling and their therapeutic potential. [ABSTRACT FROM AUTHOR]

Introduction: Metabolic dysfunction is now recognized as a pivotal component of Alzheimer's disease (AD), the most common dementia worldwide. However, the precise molecular mechanisms linking metabolic dysfunction to AD remain elusive. Objective: Here, we investigated the direct impact of soluble oligomeric amyloid beta (Aβ) peptides, the main molecular hallmark of AD, on the leptin system, a major component of central energy metabolism regulation. Methods: We developed a new time-resolved fluorescence resonance energy transfer-based Aβ binding assay for the leptin receptor (LepR) and studied the effect of Aβ on LepR function in several in vitro assays. The in vivo effect of Aβ on LepR function was studied in an Aβ-specific AD mouse model and in pro-opiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus. Results: We revealed specific and high-affinity (Ki = 0.1 nM) binding of Aβ to LepR. Pharmacological characterization of this interaction showed that Aβ binds allosterically to the extracellular domain of LepR and negatively affects receptor function. Negative allosteric modulation of LepR by Aβ was detected at the level of signaling pathways (STAT-3, AKT, and ERK) in vitroand in vivo. Importantly, the leptin-induced response of POMC neurons, key players in the regulation of metabolic function, was completely abolished in the presence of Aβ. Conclusion: Our data indicate that Aβ is a negative allosteric modulator of LepR, resulting in impaired leptin action, and qualify LepR as a new and direct target of Aβ oligomers. Preventing the interaction of Aβ with LepR might improve both the metabolic and cognitive dysfunctions in AD condition. [ABSTRACT FROM AUTHOR]

Leptin links body energy stores to high energy demanding processes like reproduction and immunity. Based on leptin's role in autoimmune diseases and cancer, several leptin and leptin receptor (LR) antagonists have been developed, but these intrinsically lead to unwanted weight gain. Here, we report on the uncoupling of leptin's metabolic and immune functions based on the cross talk with the epidermal growth factor receptor (EGFR). We show that both receptors spontaneously interact and, remarkably, that this complex can partially overrule the lack of LR activation by a leptin antagonistic mutein. Moreover, this leptin mutant induces EGFR phosphorylation comparable to wild-type leptin. Exploiting this non-canonical leptin signalling pathway, we identified a camelid single-domain antibody that selectively inhibits this LR-EGFR cross talk without interfering with homotypic LR signalling. Administration in vivo showed that this single-domain antibody did not interfere with leptin's metabolic functions, but could reverse the leptin-driven protection against starvation-induced thymic and splenic atrophy. These findings offer new opportunities for the design and clinical application of selective leptin and LR antagonists that avoid unwanted metabolic side effects. [ABSTRACT FROM AUTHOR]

The adipocyte-derived cytokine leptin acts as a metabolic switch, connecting the body's metabolism to high-energy consuming processes such as reproduction and immune responses. We here provide genetic and biochemical evidence that the metabolic and immune functions of leptin can be uncoupled at the receptor level. First, homozygous mutant fatt/fatt mice carry a spontaneous splice mutation causing deletion of the leptin receptor (LR) immunoglobulin-like domain (IGD) in all LR isoforms. These mice are hyperphagic and morbidly obese, but display only minimal changes in size and cellularity of the thymus, and cellular immune responses are unaffected. These animals also displayed liver damage in response to concavalin A comparable to wild-type and heterozygous littermates. Second, treatment of healthy mice with a neutralizing nanobody targeting IGD induced weight gain and hyperinsulinaemia, but completely failed to block development of experimentally induced autoimmune diseases. These data indicate that leptin receptor deficiency or antagonism profoundly affects metabolism, with little concomitant effects on immune functions. [ABSTRACT FROM AUTHOR]

Leptin plays a central role in the control of body weight and energy homeostasis, but is a pleiotropic cytokine with activities on many peripheral cell types. In this review, we discuss the interaction of leptin with its receptor, and focus on the structural and mechanistic aspects of the extracellular aspects of leptin receptor (LR) activation. We provide an extensive overview of all structural information that has been obtained for leptin and its receptor via X-ray crystallography, electron microscopy, small-angle X-ray scattering, homology modeling, and mutagenesis studies. The available knowledge is integrated into putative models toward a recapitulation of the LR activation mechanism [ABSTRACT FROM AUTHOR]

Despite the impact of the leptin system on body weight and other physiologic processes, little is known about the binding of leptin to its receptor. The extracellular domain of the leptin receptor consists of two cytokine receptor homology (CRH) domains separated by an immunoglobulin-like domain, and followed by two juxtamembrane fibronectin type HI modules. The CRH2 domain functions as a high-affinity binding site for leptin, and we previously demonstrated interaction with helices A and C of leptin. In this work, we constructed a homology model for the leptin/CRH2 complex and performed a detailed mutation analysis of the CRH2/leptin interface. Using both cell-based and in vitro binding assays using the isolated CRH2 domain, we show the critical role of hydrophobic interactions between Leu 13 and Leu 86 of leptin and Leu 504 in CRH2 in leptin binding and signalling. This binding pattern closely resembles the interaction of other four-helix bundle long chain cytokines with the CRH domain of their cognate receptors. [ABSTRACT FROM AUTHOR]

The leptin receptor (LEPR) is a class I cytokine receptor signalling via both the janus kinase/signal transducer and activator of transcription (JAK/STAT) and the MAP kinase pathways. In addition, leptin has been shown previously to activate AMP-activated kinase (AMPK) in skeletal muscle. To enable a detailed analysis of leptin signalling in pancreatic beta cells, LEPR point mutants with single or combined exchanges of the three intracellular tyrosines were expressed in HIT-T15 insulinoma cells. Western blots with activation state-specific antibodies recognizing specific signalling molecules revealed that the wild-type receptor activated STAT1, STAT3, STAT5 and ERK1/2 but failed to alter the phosphorylation of AMPK. Each of the three intracellular tyrosine residues in LEPR exhibited different signalling capacities: Tyr985 was necessary and sufficient for leptin-induced activation of ERK1/2; Tyr1077 induced tyrosyl phosphorylation of STAT5; and Tyr1138 was capable of activating STAT1, STAT3 and STAT5. Consistent results were obtained in reporter gene assays with STAT3 or STAT5-responsive promoter constructs, respectively. Furthermore, the sequence motifs surrounding the three tyrosine residues are conserved in LEPR from mammals, birds and in a LEPR-like cytokine receptor from pufferfish. Mutational analysis of the box3 motif around Tyr1138 identified Met1139 and Gln1141 as important determinants that define specificity towards the different STAT factors. These data indicate that all three conserved tyrosines are involved in LEPR function and define the pleiotropy of signal transduction via STAT1/3, STAT5 or ERK kinases. Activation and inhibition of AMPK appears to require additional components of the signalling pathways that are not present in beta cells. [ABSTRACT FROM AUTHOR]

The adipocyte-derived hormone leptin signals the status of body energy stores by activating its receptor in hypothalamic nuclei. In contrast to the initial expectations, leptin treatment of human obesity was largely unsuccessful. One explanation for this is the marked leptin resistance, which likely operates in part at the receptor level. The leptin receptor is a member of the class I cytokine receptor family, which uses the Janus kinase/signal transducer and activator of transcription pathway as a major signaling route. In this review, we focus on the molecular mechanisms underlying leptin receptor activation. Different modes of leptin-induced clustering of the ectodomains and the subsequent signaling events will be discussed. [Copyright &y& Elsevier]

Hypothalamic leptin receptor signalling plays a central role in weight regulation by controlling fat storage and energy expenditure. In addition, leptin also has direct effects on peripheral cell types involved in regulation of diverse body functions including immune response, bone formation and reproduction. Previous studies have demonstrated the important role of SOCS3 (suppressor of cytokine signalling 3) in leptin physiology. Here, we show that CIS (cytokine-inducible SH2 protein) and SOCS2 can also interact with the leptin receptor. Using MAPPIT (mammalian protein-protein interaction trap), a cytokine receptor-based two-hybrid method operating in intact cells, we show specific binding of CIS with the conserved Y985 and Y1077 motifs in the cytosolic domain of the leptin receptor. SOCS2 only interacts with the Y1077 motif, but with higher binding affinity and can interfere with CIS and STAT5a prey recruitment at this site. Furthermore, although SOCS2 does not associate with Y985 of the leptin receptor, we find that SOCS2 can block interaction of CIS with this position. This unexpected interference can be explained by the direct binding of SOCS2 on the CIS SOCS box, whereby elongin B/C recruitment is crucial to suppress CIS activity. [ABSTRACT FROM AUTHOR]