Methods to attach polypeptides to lipid bilayers are often indirect, ineffective and can represent a substantial bottleneck in the formation of functionalized lipid-based materials. Although the polyhistidine tag (his-tag) has been transformative in its simplicity and efficacy in binding to immobilized metals, the successful application of this approach has been challenging in physiological settings. Here we show that lipid bilayers containing porphyin-phospholipid that is chelated with cobalt, but not other metals, can effectively capture his-tagged proteins and peptides. The binding follows a Co(II) to Co(III) transition and occurs within the sheltered hydrophobic bilayer, resulting in essentially irreversible attachment in serum or in million-fold excess of competing imidazole. Using this approach we anchored homing peptides into the bilayer of preformed and cargo-loaded liposomes to enable tumour-targeting without disrupting the bilayer integrity. As a further demonstration, a synthetic HIV-derived protein fragment was bound to immunogenic liposomes for potent antibody generation for an otherwise non-antigenic peptide.

Background: The Wnt signaling pathway is a cellular communication pathway that plays critical roles in development and disease. A major class of Wnt signaling regulators is the Dickkopf (Dkk) family of secreted glycoproteins. Although the biological properties of Dickkopf 1 (Dkk1) and Dickkopf 2 (Dkk2) are well characterized, little is known about the function of the related Dickkopf 3 (Dkk3) protein in vivo or in cell lines. We recently demonstrated that Dkk3 transcripts are upregulated during photoreceptor death in a mouse model of retinal degeneration. In this study, we characterized the activity of Dkk3 in Wnt signaling and cell death.

This study is the first demonstration that Wnt signaling is activated in the degenerating retina and that it protects retinal cultures from oxidative stress. These data suggest that Wnt signaling is a component of the glial protective response during photoreceptor injury. Therefore, inducing Wnt activation, alone or in combination with growth factors, may increase the threshold for apoptosis and halt or delay further photoreceptor degeneration.

BDNF is a well-characterized neurotrophin that mediates a wide variety of activities in the central nervous system (CNS), including neuronal differentiation, neuroprotection and synaptic plasticity. The canonical Wnt signaling pathway is a critical regulator of embryonic development and homeostasis in adult tissues. Our group and others recently demonstrated that Wnt signaling induces BDNF expression in neurons and glia. However, the precise relationship between BDNF and Wnt signaling pathways is not understood. Here, we investigated Wnt signaling regulation of BDNF at the transcriptional level by using a combination of bioinformatics and molecular analyses. Analysis of the BDNF gene promoter identified seven binding motifs for Wnt-dependent TCF/LEF transcription factors. Furthermore, specific BDNF promoters were induced by the Wnt3a ligand using chloramphenicol acetyl transferase (CAT) reporter assays, and a dominant-negative TCF4 gene reduced Wnt3a-mediated induction. Finally, Wnt3a induced expression of BDNF and other members of the BDNF signaling pathway in glia cells. Therefore, these data indicate that BDNF is a direct target of Wnt signaling, which provides new insight into the interaction between two essential signaling pathways.

Wnt/β-catenin signaling is an essential pathway that regulates numerous cellular processes, including cell survival. The molecular mechanisms contributing to pro-survival Wnt signaling are mostly unknown. Signal transducer and activator of transcription proteins (STATs) are a well-described family of transcription factors. STAT3 induces expression of anti-apoptotic genes in many tissues and is a downstream mediator of protective growth factors and cytokines. In this study, we investigated whether pro-survival Wnt signaling is mediated by STAT3. The Wnt3a ligand activated Wnt signaling in the retinal pigment epithelium ARPE-19 cell line and significantly increased the viability of cells exposed to oxidative stress. Furthermore, Wnt3a increased STAT3 activation and nuclear translocation, as measured by an antibody against phosphorylated STAT3. Reducing STAT3 levels with siRNA eliminated Wnt3a-dependent protection from oxidative stress. Together, these data demonstrate a previously unknown link between Wnt3a-mediated activation of STAT3 and cell survival, and indicate cross-talk between two important pro-survival signaling pathways.