WLS/wntless is essential in controlling dendritic cell homeostasis via a WNT signaling-independent mechanism

We propose that beyond its role in WNT secretion, WLS/GPR177 (wntless, WNT ligand secretion mediator) acts as an essential regulator controlling protein glycosylation, endoplasmic reticulum (ER) homeostasis, and dendritic cell (DC)-mediated immunity. WLS deficiency in bone marrow-derived DCs (BMDCs) resulted in poor growth and an inability to mount cytokine and T-cell responses in vitro, phenotypes that were irreversible by the addition of exogenous WNTs. In fact, WLS was discovered to integrate a protein complex in N-glycan-dependent and WLS domain-selective manners, comprising ER stress sensors and lectin chaperones. WLS deficiency in BMDCs led to increased ER stress response and macroautophagy/autophagy, decreased calcium efflux from the ER, and the loss of CALR (calreticulin)-CANX (calnexin) cycle, and hence protein hypo-glycosylation. Consequently, DC-specific wls-null mice were unable to develop both Th1-, Th2- and Th17-associated responses in the respective autoimmune and allergic disease models. These results suggest that WLS is a critical chaperone in maintaining ER homeostasis, glycoprotein quality control and calcium dynamics in DCs.Abbreviations: ATF6: activating transcription factor 6; ATG5: autophagy related 5; ATG12: autophagy related 12; ATG16L1: autophagy related 16 like 1; ATP2A1/SERCA1: ATPase sarcoplasmic/endoplasmic reticulum Ca2+ transporting 1; BALF: bronchoalveolar lavage fluid; BFA: brefeldin A; BMDC: bone marrow-derived dendritic cell; CALR: calreticulin; CANX: calnexin; CCL2/MCP-1: C-C motif chemokine ligand 2; CNS: central nervous system; CT: C-terminal domain; DTT: dithiothreitol; DNAJB9/ERDJ4: DnaJ heat shock protein family (Hsp40) member B9; EAE: experimental autoimmune encephalomyelitis; EIF2A/eIF2α: eukaryotic translation initiation factor 2A; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; ERN1/IRE1: endoplasmic reticulum (ER) to nucleus signaling 1; GFP: green fluorescent protein; HSPA5/GRP78/BiP: heat shock protein A5; IFNA: interferon alpha; IFNAR1: interferon alpha and beta receptor subunit 1; IFNB: interferon beta; IFNG/INFγ: interferon gamma; IFNGR2: interferon gamma receptor 2; IL6: interleukin 6; IL10: interleukin 10; IL12A: interleukin 12A; IL23A: interleukin 23 subunit alpha; ITGAX/CD11c: integrin subunit alpha X; ITPR1/InsP3R1: inositol 1,4,5-trisphosphate receptor type 1; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; OVA: ovalbumin; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PLF: predicted lipocalin fold; PPP1R15A/GADD34: protein phosphatase 1 regulatory subunit 15A; RYR1/RyanR1: ryanodine receptor 1, skeletal muscle; SD: signal domain; TGFB/TGF-β: transforming growth factor beta family; Th1: T helper cell type 1; Th17: T helper cell type 17; TM: tunicamycin; TNF/TNF-α: tumor necrosis factor; UPR: unfolded protein response; WLS/wntless: WNT ligand secretion mediator.

Gpr177, a novel locus for bone mineral density and osteoporosis, regulates osteogenesis and chondrogenesis in skeletal development

Human genetic analysis has recently identified Gpr177 as a susceptibility locus for bone mineral density and osteoporosis. Determining the unknown function of this gene is therefore extremely important to furthering our knowledge base of skeletal development and disease. The protein encoded by Gpr177 exhibits an ability to modulate the trafficking of Wnt, similar to the Drosophila Wls/Evi/Srt. Because it plays a critical role in Wnt regulation, Gpr177 might be required for several key steps of skeletogenesis. To overcome the early lethality associated with the inactivation of Gpr177 in mice, conditional gene deletion is used to assess its functionality. Here we report the generation of four different mouse models with Gpr177 deficiency in various skeletogenic cell types. The loss of Gpr177 severely impairs development of the craniofacial and body skeletons, demonstrating its requirement for intramembranous and endochondral ossifications, respectively. Defects in the expansion of skeletal precursors and their differentiation into osteoblasts and chondrocytes suggest that Wnt production and signaling mediated by Gpr177 cannot be substituted. Because the Gpr177 ablation impairs Wnt secretion, we therefore identify the sources of Wnt proteins essential for osteogenesis and chondrogenesis. The intercross of Wnt signaling between distinct cell types is carefully orchestrated and necessary for skeletogenesis. Our findings lead to a proposed mechanism by which Gpr177 controls skeletal development through modulation of autocrine and paracrine Wnt signals in a lineage-specific fashion.

Ultrastructural relationship between the mu opioid receptor and its interacting protein, GPR177, in striatal neurons

GPR177, the mammalian ortholog of Drosophila Wntless/Evi/Sprinter, was recently identified as a novel mu-opioid receptor (MOR) interacting protein. GPR177 is a trans-membrane protein pivotal to mediating the secretion of Wnt signaling proteins. Wnt proteins, in turn, are essential in regulating neuronal development, a phenomenon inhibited upon chronic exposure to MOR agonists such as morphine and heroin. We previously showed that GPR177 and MOR are co-localized in the mouse dorsolateral striatum; however, the nature of this interaction was not fully elucidated. Therefore, in the present study, we examined cellular substrates for interactions between GPR177 and MOR using a combined immunogold-silver and peroxidase detection approach in coronal sections in the dorsolateral segment of the striatum. Semi-quantitative analysis of the ultrastructural distribution of GPR177 and MOR in striatal somata and in dendritic processes showed that, of the somata and dendritic processes exhibiting GPR177, 32% contained MOR immunolabeling while for profiles exhibiting MOR, 37% also contained GPR177 immunoreactivity. GPR177-labeled particles were localized predominantly along both the plasma membrane and within the cytoplasm of MOR-labeled dendrites. Somata and dendritic processes that contained both GPR177 and MOR more often received symmetric (inhibitory-type) synapses from unlabeled axon terminals. To further define the phenotype of GPR177 and MOR-containing cellular profiles, triple immunofluorescence detection showed that GPR177 and MOR are localized in neurons containing the opioid peptide, enkephalin, within the dorsolateral striatum. The results provide an anatomical substrate for interactions between MOR and its interacting protein, GPR177, in striatal opioid-containing neurons that may underlie the morphological alterations produced in neurons by chronic opiate use.