Targeting Wnt signaling at the neuroimmune interface for dopaminergic neuroprotectionJrepair in Parkinson＇s disease

During the past three decades, the Wingless-type MMTV integration site （Wnt） signaling cascade has emerged as an essential system regulating multiple processes in developing and adult brain. Accumulating evidence points to a dysregulation of Wnt signaling in major neurodegenerative pathologies including Parkinson＇s disease （PD）, a common neurodegenerative disorder characterized by the pro- gressive loss of midbrain dopaminergic （mDA） neurons and deregulated activation of astrocytes and microglia. This review highlights the emerging link between Wnt signaling and key inflammatory pathways during mDA neuron damage/repair in PD progression. In particular, we summarize recent evidence documenting that aging and neurotoxicant exposure strongly antagonize Wnt/β-catenin signaling in mDA neurons and subventricular zone （SVZ） neuroprogenitors via astrocyte-microglial interactions. Dysregulation of the crosstalk between Wnt/β-catenin signaling and anti-oxidant/anti-inflammatory pathways delineate novel mechanisms driving the decline of SVZ plasticity with age and the limited nigrostriatal dopaminergic self-repair in PD. These findings hold a promise in devetoping therapies that target Wnt/β-catenin signaling to enhance endogenous restoration and neuronal outcome in age-dependent diseases, such as PD.     

nhe regulation and deregulation of Wnt signaling by PARK genes in health and disease

Wingless/Int （Wnt） signaling pathways are signal transduction mechanisms that have been widely studied In the field of embryogen- esis. Recent work has established a critical role for these pathways in brain development, especially of midbrain dopaminergic neu- rones, However, the fundamental importance of Wnt signaling for the normal function of mature neurones in the adult central nervous system has also lately been demonstrated by an increasing number of studies. Parkinson＇s disease （PD） is the second most prevalent neurodegenerative disease worldwide and is currently incurable. This debilitating disease is characterized by the progres- sive loss of a subset of midbrain dopaminergic neurones in the substontla nigm leadingto typical extrapyramidal motor symptoms. The aetiology of PD is poorly understood but work performed over the Last two decades has identified a growing number of genetic defects that underlie this condition. Herewe review a growing body of data connecting genes implicated in PD--most notablythe PARKgenes-- with Wnt signaling. These observations provide clues to the normal function of these proteins in healthy neurones and suggest that deregulated Wnt signaling might be a frequent pathomechanlsm leading to PD. These observations have implications for the patho- genesis and treatment of neurodegenerative diseases in general.     

The coiled-coil domain containing protein Ccdc136b antagonizes maternal Wnt/β-catenin activity during zebrafish dorsoventral axial patterning

The coiled-coil domain containing protein CCDC136 is a putative tumor suppressor and significantly down-regulated in gastric and colorectal cancer tissues.However,little is known about its biological functions during vertebrate embryo development.Zebrafish has two CCDC136 orthologs,ccdcl36 a and ccdc136 b,but only ccdc136 b is highly expressed during early embryonic development.In this study,we demonstrate that ccdc136 b is required for dorsal-ventral axial patterning in zebrafish embryos.ccdc136 b morphants display strongly dorsalized phenotypes.Loss- and gain-of-function experiments in zebrafish embryos and mammalian cells show that Ccdc136 b is a crucial negative regulator of the Wnt/β-catenin signaling pathway,and plays a critical role in the establishment of the dorsal-ventral axis.We further find that Ccdc136 b interacts with APC,promotes the binding affinity of APC with β-catenin and then facilitates the turnover of β-catenin.These results provide the first evidence that CCDC136 regulates zebrafish dorsal-ventral patterning by antagonizing Wnt/β-catenin signal transduction and suggest a potential mechanism underlying its suppressive activity in carcinogenesis.     

Role of Lef1 in sustaining self-renewal in mouse embryonic stem cells

Embryonic stem cells (ESCs) can self-renew indefinitely while maintaining the ability to generate all three germ-layer derivatives.Despite the importance of ESCs in developmental biology and their potential impact on regenerative medicine,the molecular mechanisms controlling ESC behavior are incompletely understood.Previously,activation of the canonical Wnt signaling pathway has been shown to contribute to mouse ESC self-renewal.Here we report that ectopic expression of Lef1,a component of the Wnt signaling pathway,has a positive effect on the self-renewal of mouse ESCs.Lef1 up-regulates Oct4 promoter activity and physically interacts with Nanog,two key components of the ESC pluripotency machinery.Moreover,siRNA for Lef1 induced mouse ESC differentiation.Our results thus suggest that in response to Wnt signaling Lef1 binds to stabilized β-catenin and helps maintain the undifferentiated status of ESCs through modulation of Oct4 and Nanog.     

Novel functions of GABA signaling in adult neurogenesis

Neurotransmitter gamma-aminobutiric acid （GABA） through ionotropic GABAA and metabotropic GABAB receptors plays key roles in modulating the development, plasticity and function of neuronal networks. GABA is inhibitory in mature neurons but excitatory in immature neurons, neuroblasts and neural stem/progenitor cells （NSCs/ NPCs）. The switch from excitatory to inhibitory occurs following the development of glutamatergic synaptic input and results from the dynamic changes in the expression of Na＋/K＋/2CF co-transporter NKCC1 driving CF influx and neuron-specific K＋/Cl co-transporter KCC2 driving Cl efflux. The developmental transition of KCC2 expression is regulated by Disrupted-in-Schizophrenia 1 （DISC1） and brain-derived neurotrophic factor （BDNF） signaling. The excitatory GABA signaling during early neurogenesis is important to the activity/experience-induced regulation of NSC quiescence, NPC proliferation, neuroblast migration and new-born neuronal maturation/functional integration. The inhibitory GABA signaling allows for the sparse and static functional networking essential for learning/memory development and maintenance.     

Receptor-Like Kinases in Plant Innate Immunity

Plants employ a highly effective surveillance system to detect potential pathogens, which is critical for the success of land plants in an environment surrounded by numerous microbes. Recent efforts have led to the identification of a number of immune receptors and components of immune receptor complexes. It is now clear that receptor-like kinases （RLKs） and receptor-like proteins （RLPs） are key pattern-recognition receptors （PRRs） for microbe- and plant-derived molecular patterns that are associated with pathogen invasion. RLKs and RLPs involved in immune signaling belong to large gene families in plants and have undergone lineage specific expansion. Molecular evolution and population studies on phytopathogenic molecular signatures and their receptors have provided crucial insight into the co-evolution between plants and pathogens.     

Dynamic expression of Wnt signaling molecules and stem-cell marker CK15 in the growth cycle of rat whisker hair follicles

Objective To investigate the distribution and dynamic changes of both Wnt signaling molecules and CK15 throughoutthe three phases of the follicular cycle,and to explore the relationship between Wnt/β-catenin signaling and CK15 in rat whisker hair follicle(HF)growth cycles.Methods Hematoxylin-Eosin(HE)and immunofluorescence stains were used to characterize the expression patterns,including sites and levels of some representative proteins of both canonical and non-canonical Wnt signaling molecules,as well as HF epithelial stem cell marker CK15.Results The expression patterns of bothβ-catenin and Wnt5a were correlated with that of CK15.CK15 was only expressed in anagen.In catagen,β-catenin showed a massive depletion while Wnt5a noticeably increased.In telogen,high level expression ofβ-catenin and low level of Wnt5a were detected.Wnt10b and TCF3 were detected during the entire HF growth cycle.Conclusion These results suggest that Wnt5a is associated with the transition of anagen-catagen phase,accompanied by broad deletion ofβ-catenin and loss of CK15.WntlOb is important for the maintenance of HF activity and is related to the telogenanagen transition.     

miR-199b-5p enhances the proliferation of medullary thymic epithelial cells via regulating Wnt signaling by targeting Fzd6

Thymic epithelial cells (TECs) are essential regulators of T-cell development and selection. miRNAs play critical roles in regulating TEC proliferation during the process of thymic aging. Our previous studies revealed that miR-199b-5p was upregulated in TECs from 1- to 3-month-old mice. But its function and potential mechanism are not clear. We hypothesized that miR-199b-5p may play an important role in age-related thymus involution via targeting some genes. To confirm it, the murine thymic epithelial cell line 1 (MTEC1) cells were used. Our results showed that overexpression of miR-199b-5p can enhance MTEC1 cell proliferation. On the contrary, repression of miR-199b-5p can inhibit MTEC1 cell proliferation. Meanwhile, it was confirmed that frizzled receptor 6 (Fzd6) is the direct target gene of miR-199b-5p. Furthermore, overexpression of miR-199b-5p can upregulate the expressions of β-catenin, Tcf7, Wnt4, and C-myc to activate Wnt signaling and cell cycle signaling. Silence of Fzd6 and co-transfection with siFzd6 and miR-199b-5p mimic/inhibitor confirmed that the biological function of miR-199b-5p is indeed by targeting Fzd6 in medullary TECs. Overall, miR-199b-5p is an important regulator in medullary TEC proliferation through targeting Fzd6 to activate Wnt signaling and cell cycle signaling. Our data indicate that miR-199b-5p may block the process of thymic aging and be a potential therapeutic target for thymus involution.     

Wnt signaling in disease and in development

The highly conserved Wnt secreted proteins are critical mediators of cell-to-cell signaling during development of animals. Recent biochemical and genetic analyses have led to significant insight into understanding how Wnt signals work. The catalogue of Wnt signaling components has exploded. We now realize that multiple extracellular, cytoplasmic, and nuclear components modulate Wnt signaling. Moreover, receptor-ligand specificity and multiple feedback loops determine Wnt signaling outputs. It is also clear that Wnt signals are required for adult tissue maintenance. Perturbations in Wnt signaling cause human degenerative diseases as well as cancer.     

Regulation of hematopoiesis and the hematopoietic stem cell niche by Wnt signaling pathways

Hematopoietic stem cells （HSCs） are a rare population of cells that are responsible for life-long generation of blood cells of all lineages. In order to maintain their numbers, HSCs must establish a balance between the opposing cell fates of self-renewal （in which the ability to function as HSCs is retained） and initiation of hematopoietic differentiation. Multiple signaling pathways have been implicated in the regulation of HSC cell fate. One such set of pathways are those activated by the Wnt family of ligands. Wnt signaling pathways play a crucial role during embryogenesis and deregulation of these pathways has been implicated in the formation of solid tumors. Wnt signaling also plays a role in the regulation of stem cells from multiple tissues, such as embryonic, epidermal, and intestinal stem cells. However, the function of Wnt signaling in HSC biology is still controversial. In this review, we will discuss the basic characteristics of the adult HSC and its regulatory microenvironment, the ＂niche＂, focusing on the regulation of the HSC and its niche by the Wnt signaling pathways.