USP8 Deubiquitinates the Leptin Receptor and Is Necessary for Leptin-Mediated Synapse Formation

Abstract

Leptin has neurotrophic actions in the hippocampus to increase synapse formation and stimulate neuronal plasticity. Leptin also enhances cognition and has antidepressive and anxiolytic-like effects, two hippocampal-dependent behaviors. In contrast, mice lacking leptin or the long form of the leptin receptor (LepRb) have lower cortical volume and decreased memory and exhibit depressive-like behaviors. A number of the signaling pathways regulated by LepRb are known, but how membrane LepRb levels are regulated in the central nervous system is not well understood. Here, we show that the lysosomal inhibitor chloroquine increases LepRb expression in hippocampal cultures, suggesting that LepRb is degraded in the lysosome. Furthermore, we show that leptin increases surface expression of its own receptor by decreasing the level of ubiquitinated LepRbs. This decrease is mediated by the deubiquitinase ubiquitin-specific protease 8 (USP8), which we show is in complex with LepRb. Acute leptin stimulation increases USP8 activity. Moreover, leptin stimulates USP8 gene expression through cAMP response element–binding protein (CREB)–dependent transcription, an effect blocked by expression of a dominant-negative CREB or with short hairpin RNA knockdown of CREB. Increased expression of USP8 causes increased surface localization of LepRb, which in turn enhances leptin-mediated activation of the MAPK kinase/extracellular signal–regulated kinase pathway and CREB activation. Lastly, increased USP8 expression increases glutamatergic synapse formation in hippocampal cultures, an effect dependent on expression of LepRbs. Leptin-stimulated synapse formation also requires USP8. In conclusion, we show that USP8 deubiquitinates LepRb, thus inhibiting lysosomal degradation and enhancing surface localization of LepRb, which are essential for leptin-stimulated synaptogenesis in the hippocampus.

Ubiquitin-specific protease 8 (USP8/UBPy): a prototypic multidomain deubiquitinating enzyme with pleiotropic functions

“…Besides the EGFR, the ubiquitination, endosomal lysosomal trafficking, and/or stability of many other transmembrane proteins have been shown to be regulated by USP8. These include the hepatocyte growth factor receptor MET [19], ERBB2 [35], the G protein-coupled receptor protease-activated receptor 2 [36]; chemokine receptor 4 [37], the Wg/Wnt receptor Frizzled [38],the calcium-activated potassium channel KCa3.1 [39], the epithelial Na+ channel ENaC [40], the low-density lipoprotein receptor (LDLR) [41,42], leucine-rich repeats and Ig-like domains 1 (LRIG1, a negative regulator of RTKs) [22,23], AMPA receptors [43], Tropomyosin related kinase A (TrkA) [44], vascular endothelial growth factor receptor 2 (VEGFR2) [45], β-site amyloid precursor protein-cleaving enzyme (BACE1) [46], connexin-43 [47], and leptin receptor [48]. Despite suggesting a common mode of action, conclusions on the impact of USP8 on protein stability in these studies are highly diverse and the precise molecular mechanisms remain elusive.…”

Leptin increases GABAergic synaptogenesis through the Rho guanine exchange factor β-PIX in developing hippocampal neurons

“…There is growing evidence that leptin receptor signaling is multifaceted and that the leptin receptor is capable of interacting with a number of different receptors and signaling molecules to form a complex interactome, suggesting that multiple signaling cascades can be activated in a coordinated manner (16,17,34,(51)(52)(53)(54). Our finding that -PIX is part of the leptin receptor interactome and that the association transiently increases with leptin-more specifically upon phosphorylation of Tyr 985 residue-suggests that scaffolding proteins can be activated and recruited to the plasma membrane locally to stabilize GABA A receptors in response to leptin, potentially by remodeling and stabilizing the actin cytoskeleton.…”

Deubiquitinases in Neurodegeneration

“…The leptin receptor (LEPR) regulates synapses, neuronal plasticity, cognition, and cortical volume, and has been associated with memory maintenance and depression. USP8 also deubiquitinates LEPR, and USP8 overexpression increases glutamatergic synapse formation in hippocampal areas and the maintenance of brain development in a LEPRdependent manner [152]. USP8 also has a regulatory function in AD.…”