Wnt plays important role during development and in various diseases. Because Wnts are lipidated and highly hydrophobic, they can only be purified in the presence of detergents, limiting their use in various in vitro and in vivo assays. We purified N-terminally tagged recombinant Wnt3a secreted from cells and accidentally discovered that Wnt3a co-purified with a glycoprotein afamin derived from the bovine serum included in the media. Wnt3a forms a 1:1 complex with afamin, which remains soluble in aqueous buffer after isolation, and can induce signaling in various cellular systems including the intestical stem cell growth assay. By co-expressing with afamin, biologically active afamin-Wnt complex can be easily obtained in large quantity. As afamin can also solubilize Wnt5a, Wnt3, and many more Wnt subtypes, afamin complexation will open a way to put various Wnt ligands and their signaling mechanisms under a thorough biochemical scrutiny that had been difficult for years.

The amyloid precursor protein (APP) and its neurotoxic cleavage product Aβ are key players in the development of Alzheimer's disease (AD) and appear to be essential for neuronal development and cell homeostasis. Proteolytic processing of APP and its physiological function depend on its interaction with heparin and are influenced by the binding of metal ions and sorLA. We created various mutations of metal binding site M1 residing within the extracellular E2 domain of APP. Using isothermal titration calorimetry and circular dichroism spectroscopy, we analyzed the binding of Cu(2+) and Zn(2+) to APP E2 and identified two mutations that are most suited for functional studies to dissect ion specific effects of metal binding. The H313A mutation abrogates only copper-based effects, whereas the H382A mutation weakens any metal binding at M1 of APP E2. Subsequently, we tested the effect of Cu(2+) and Zn(2+) on the binding of heparin and sorLA to APP E2 using a chromatographic technique and surface plasmon resonance. We show that Zn(2+) and to a larger degree also Cu(2+) enhance the binding of heparin to APP E2, consistent with an extracellular regulation of the function of APP by both metal ions. In contrast, neither ion seemed to affect the interaction between APP E2 and sorLA. This supports an intracellular interaction between the latter two partners that would not sense extracellular variations of metal ions upon synaptic activity.

Progranulin (PGRN), a widely secreted growth factor, is involved in multiple biological functions, and mutations located within the PGRN gene (GRN) are a major cause of frontotemporal lobar degeneration with TDP-43-positive inclusions (FLTD-TDP). In light of recent reports suggesting PGRN functions as a protective neurotrophic factor and that sortilin (SORT1) is a neuronal receptor for PGRN, we used a Sort1-deficient (Sort1-/-) murine primary hippocampal neuron model to investigate whether PGRN's neurotrophic effects are dependent on SORT1. We sought to elucidate this relationship to determine what role SORT1, as a regulator of PGRN levels, plays in modulating PGRN's neurotrophic effects.

Recombinant adeno-associated virus (rAAV) vectors have emerged as the safe vehicles of choice for long-term gene transfer in mammalian nervous system. Recombinant adeno-associated virus-mediated localized gene transfer in adult nervous system following direct inoculation, that is, intracerebral or intrathecal, is well documented. However, recombinant adeno-associated virus delivery in defined neuronal populations in adult animals using less-invasive methods as well as avoiding ectopic gene expression following systemic inoculation remain challenging. Harnessing the capability of some recombinant adeno-associated virus serotypes for retrograde transduction may potentially address such limitations (Note: The term retrograde transduction in this manuscript refers to the uptake of injected recombinant adeno-associated virus particles at nerve terminals, retrograde transport, and subsequent transduction of nerve cell soma). In some studies, recombinant adeno-associated virus serotypes 2/6, 2/8, and 2/9 have been shown to exhibit transduction of connected neuroanatomical tracts in adult animals following lower limb intramuscular recombinant adeno-associated virus delivery in a pattern suggestive of retrograde transduction. However, an extensive side-by-side comparison of these serotypes following intramuscular delivery regarding tissue viral load, and the effect of promoter on transgene expression, has not been performed. Hence, we delivered recombinant adeno-associated virus serotypes 2/6, 2/8, or 2/9 encoding enhanced green fluorescent protein (eGFP), under the control of either cytomegalovirus (CMV) or human synapsin (hSyn) promoter, via a single unilateral hindlimb intramuscular injection in the bicep femoris of adult C57BL/6J mice. Four weeks post injection, we quantified viral load and transgene (enhanced green fluorescent protein) expression in muscle and related nervous tissues. Our data show that the select recombinant adeno-associated virus serotypes transduce sciatic nerve and groups of neurons in the dorsal root ganglia on the injected side, indicating that the intramuscular recombinant adeno-associated virus delivery is useful for achieving gene transfer in local neuroanatomical tracts. We also observed sparse recombinant adeno-associated virus viral delivery or eGFP transduction in lumbar spinal cord and a noticeable lack thereof in brain. Therefore, further improvements in recombinant adeno-associated virus design are warranted to achieve efficient widespread retrograde transduction following intramuscular and possibly other peripheral routes of delivery.

The human epidermal growth factor receptor 2 (HER2) is an oncogene targeted by several kinase inhibitors and therapeutic antibodies. While the endosomal trafficking of many other receptor tyrosine kinases is known to regulate their oncogenic signalling, the prevailing view on HER2 is that this receptor is predominantly retained on the cell surface. Here, we find that sortilin-related receptor 1 (SORLA; SORL1) co-precipitates with HER2 in cancer cells and regulates HER2 subcellular distribution by promoting recycling of the endosomal receptor back to the plasma membrane. SORLA protein levels in cancer cell lines and bladder cancers correlates with HER2 levels. Depletion of SORLA triggers HER2 targeting to late endosomal/lysosomal compartments and impairs HER2-driven signalling and in vivo tumour growth. SORLA silencing also disrupts normal lysosome function and sensitizes anti-HER2 therapy sensitive and resistant cancer cells to lysosome-targeting cationic amphiphilic drugs. These findings reveal potentially important SORLA-dependent endosomal trafficking-linked vulnerabilities in HER2-driven cancers.

Whether and how the pathogenic disruptions in endosomal trafficking observed in Alzheimer's disease (AD) are linked to its anatomical vulnerability remain unknown. Here, we began addressing these questions by showing that neurons are enriched with a second retromer core, organized around VPS26b, differentially dedicated to endosomal recycling. Next, by imaging mouse models, we show that the trans-entorhinal cortex, a region most vulnerable to AD, is most susceptible to VPS26b depletion-a finding validated by electrophysiology, immunocytochemistry, and behavior. VPS26b was then found enriched in the trans-entorhinal cortex of human brains, where both VPS26b and the retromer-related receptor SORL1 were found deficient in AD. Finally, by regulating glutamate receptor and SORL1 recycling, we show that VPS26b can mediate regionally selective synaptic dysfunction and SORL1 deficiency. Together with the trans-entorhinal's unique network properties, hypothesized to impose a heavy demand on endosomal recycling, these results suggest a general mechanism that can explain AD's regional vulnerability.

Here we report de novo macrocyclic peptide binders to Wnt3a, a member of the Wnt protein family. By means of the Random non-standard Peptides Integrated Discovery (RaPID) system, we have performed in vitro selection against the complex of mouse Wnt3a (mWnt3a) with human afamin (hAFM) to discover macrocyclic peptides that bind mWnt3a with K D values as tight as 110 nM. One of these peptides, WAp-D04 (Wnt-AFM-peptide-D04), was able to inhibit the receptor-mediated signaling process, which was demonstrated in a Wnt3a-dependent reporter cell-line. Based on this initial hit, we applied a block-mutagenesis scanning display to identify a mutant inhibitor, WAp-D04-W10P, with 5-fold greater potency in a reporter assay. This work represents the first instance of molecules capable of inhibiting Wnt signaling through direct interaction with a Wnt protein, a molecular class for which targeting has been challenging due its highly hydrophobic nature.

SORL1 is strongly associated with both sporadic and familial forms of Alzheimer's disease (AD), but a lack of information about alternatively spliced transcripts currently limits our understanding of the role of SORL1 in AD. Here, we describe a SORL1 transcript (SORL1-38b) characterized by inclusion of a novel exon (E38b) that encodes a truncated protein. We identified E38b-containing transcripts in several brain regions, with the highest expression in the cerebellum and showed that SORL1-38b is largely located in neuronal dendrites, which is in contrast to the somatic distribution of transcripts encoding the full-length SORLA protein (SORL1-fl). SORL1-38b transcript levels were significantly reduced in AD cerebellum in three independent cohorts of postmortem brains, whereas no changes were observed for SORL1-fl. A trend of lower 38b transcript level in cerebellum was found for individuals carrying the risk variant at rs2282649 (known as SNP24), although not reaching statistical significance. These findings suggest synaptic functions for SORL1-38b in the brain, uncovering novel aspects of SORL1 that can be further explored in AD research.

SARS-CoV-2 has mutated during the global pandemic leading to viral adaptation to medications and vaccinations. Here we describe an engineered human virus receptor, ACE2, by mutagenesis and screening for binding to the receptor binding domain (RBD). Three cycles of random mutagenesis and cell sorting achieved sub-nanomolar affinity to RBD. Our structural data show that the enhanced affinity comes from better hydrophobic packing and hydrogen-bonding geometry at the interface. Additional disulfide mutations caused the fixing of a closed ACE2 conformation to avoid off-target effects of protease activity, and also improved structural stability. Our engineered ACE2 neutralized SARS-CoV-2 at a 100-fold lower concentration than wild type; we also report that no escape mutants emerged in the co-incubation after 15 passages. Therapeutic administration of engineered ACE2 protected hamsters from SARS-CoV-2 infection, decreased lung virus titers and pathology. Our results provide evidence of a therapeutic potential of engineered ACE2.

The established causal genes in Alzheimer's disease (AD), APP, PSEN1, and PSEN2, are functionally characterized using biomarkers, capturing an in vivo profile reflecting the disease's initial preclinical phase. Mutations in SORL1, encoding the endosome recycling receptor SORLA, are found in 2%-3% of individuals with early-onset AD, and SORL1 haploinsufficiency appears to be causal for AD. To test whether SORL1 can function as an AD causal gene, we use CRISPR-Cas9-based gene editing to develop a model of SORL1 haploinsufficiency in Göttingen minipigs, taking advantage of porcine models for biomarker investigations. SORL1 haploinsufficiency in young adult minipigs is found to phenocopy the preclinical in vivo profile of AD observed with APP, PSEN1, and PSEN2, resulting in elevated levels of β-amyloid (Aβ) and tau preceding amyloid plaque formation and neurodegeneration, as observed in humans. Our study provides functional support for the theory that SORL1 haploinsufficiency leads to endosome cytopathology with biofluid hallmarks of autosomal dominant AD.

The Omicron (B.1.1.529) SARS-CoV-2 variant contains an unusually high number of mutations in the spike protein, raising concerns of escape from vaccines, convalescent serum, and therapeutic drugs. Here, we analyzed the degree to which Omicron pseudo-virus evades neutralization by serum or therapeutic antibodies. Serum samples obtained 3 months after two doses of BNT162b2 vaccination exhibited 18-fold lower neutralization titers against Omicron than parental virus. Convalescent serum samples from individuals infected with the Alpha and Delta variants allowed similar frequencies of Omicron breakthrough infections. Domain-wise analysis using chimeric spike proteins revealed that this efficient evasion was primarily achieved by mutations clustered in the receptor binding domain but that multiple mutations in the N-terminal domain contributed as well. Omicron escaped a therapeutic cocktail of imdevimab and casirivimab, whereas sotrovimab, which targets a conserved region to avoid viral mutation, remains effective. Angiotensin-converting enzyme 2 (ACE2) decoys are another virus-neutralizing drug modality that are free, at least in theory, from complete escape. Deep mutational analysis demonstrated that an engineered ACE2 molecule prevented escape for each single-residue mutation in the receptor binding domain, similar to immunized serum. Engineered ACE2 neutralized Omicron comparably to the Wuhan strain and also showed a therapeutic effect against Omicron infection in hamsters and human ACE2 transgenic mice. Similar to previous SARS-CoV-2 variants, some sarbecoviruses showed high sensitivity against engineered ACE2, confirming the therapeutic value against diverse variants, including those that are yet to emerge.

The SORL1 gene has recently emerged as a strong Alzheimer's Disease (AD) risk gene. Over 500 different variants have been identified in the gene and the contribution of individual variants to AD development and progression is still largely unknown. Here, we describe a family consisting of 2 parents and 5 offspring. Both parents were affected with dementia and one had confirmed AD pathology with an age of onset >75 years. All offspring were affected with AD with ages at onset ranging from 53yrs-74yrs. DNA was available from the parent with confirmed AD and 5 offspring. We identified a coding variant, p.(Arg953Cys), in SORL1 in 5 of 6 individuals affected by AD. Notably, variant carriers had severe AD pathology, and the SORL1 variant segregated with TDP-43 pathology (LATE-NC). We further characterized this variant and show that this Arginine substitution occurs at a critical position in the YWTD-domain of the SORL1 translation product, SORL1. Functional studies further show that the p.R953C variant leads to retention of the SORL1 protein in the endoplasmic reticulum which leads to decreased maturation and shedding of the receptor and prevents its normal endosomal trafficking. Together, our analysis suggests that p.R953C is a pathogenic variant of SORL1 and sheds light on mechanisms of how missense SORL1 variants may lead to AD.

Cytosine arabinoside (AraC) is one of the main therapeutic treatments for several types of cancer, including acute myeloid leukaemia. However, after a high-dose AraC chemotherapy regime, patients develop severe neurotoxicity and cell death in the central nervous system leading to cerebellar ataxia, dysarthria, nystagmus, somnolence and drowsiness. AraC induces apoptosis in dividing cells. However, the mechanism by which it leads to neurite degeneration and cell death in mature neurons remains unclear. We hypothesise that the upregulation of the death receptor p75NTR is responsible for AraC-mediated neurodegeneration and cell death in leukaemia patients undergoing AraC treatment. To determine the role of AraC-p75NTR signalling in the cell death of mature neurons, we used mature cerebellar granule neurons' primary cultures from p75NTR knockout and p75NTRCys259 mice. Evaluation of neurite degeneration, cell death and p75NTR signalling was done by immunohistochemistry and immunoblotting. To assess the interaction between AraC and p75NTR, we performed cellular thermal shift and AraTM assays as well as Homo-FRET anisotropy imaging. We show that AraC induces neurite degeneration and programmed cell death of mature cerebellar granule neurons in a p75NTR-dependent manner. Mechanistically, Proline 252 and Cysteine 256 residues facilitate AraC interaction with the transmembrane domain of p75NTR resulting in uncoupling of p75NTR from the NFκB survival pathway. This, in turn, exacerbates the activation of the cell death/JNK pathway by recruitment of TRAF6 to p75NTR. Our findings identify p75NTR as a novel molecular target to develop treatments for counteract AraC-mediated cell death of mature neurons.

Semaphorin 4A (Sema4A) has an essential role in photoreceptor survival. In humans, mutations in Sema4A are thought to contribute to retinal degenerative diseases. Here we generate a series of knock-in mouse lines with corresponding mutations (D345H, F350C or R713Q) in the Sema4A gene and find that Sema4A(F350C) causes retinal degeneration phenotypes. The F350C mutation results in abnormal localization of the Sema4A protein, leading to impaired endosomal sorting of molecules indispensable for photoreceptor survival. Additionally, protein structural modelling reveals that the side chain of the 350th amino acid is critical to retain the proper protein conformation. Furthermore, Sema4A gene transfer successfully prevents photoreceptor degeneration in Sema4A(F350C/F350C) and Sema4A(-/-) mice. Thus, our findings not only indicate the importance of the Sema4A protein conformation in human and mouse retina homeostasis but also identify a novel therapeutic target for retinal degenerative diseases.

Conformational communication across the plasma membrane between the extracellular and intracellular domains of integrins is beginning to be defined by structural work on both domains. However, the role of the alpha and beta subunit transmembrane domains and the nature of signal transmission through these domains have been elusive. Disulfide bond scanning of the exofacial portions of the integrin alpha(IIbeta) and beta(3) transmembrane domains reveals a specific heterodimerization interface in the resting receptor. This interface is lost rather than rearranged upon activation of the receptor by cytoplasmic mutations of the alpha subunit that mimic physiologic inside-out activation, demonstrating a link between activation of the extracellular domain and lateral separation of transmembrane helices. Introduction of disulfide bridges to prevent or reverse separation abolishes the activating effect of cytoplasmic mutations, confirming transmembrane domain separation but not hinging or piston-like motions as the mechanism of transmembrane signaling by integrins.

The ADAMTS9 rs4607103 C allele is one of the few gene variants proposed to increase the risk of type 2 diabetes through an impairment of insulin sensitivity. We show that the variant is associated with increased expression of the secreted ADAMTS9 and decreased insulin sensitivity and signaling in human skeletal muscle. In line with this, mice lacking Adamts9 selectively in skeletal muscle have improved insulin sensitivity. The molecular link between ADAMTS9 and insulin signaling was characterized further in a model where ADAMTS9 was overexpressed in skeletal muscle. This selective overexpression resulted in decreased insulin signaling presumably mediated through alterations of the integrin β1 signaling pathway and disruption of the intracellular cytoskeletal organization. Furthermore, this led to impaired mitochondrial function in mouse muscle-an observation found to be of translational character because humans carrying the ADAMTS9 risk allele have decreased expression of mitochondrial markers. Finally, we found that the link between ADAMTS9 overexpression and impaired insulin signaling could be due to accumulation of harmful lipid intermediates. Our findings contribute to the understanding of the molecular mechanisms underlying insulin resistance and type 2 diabetes and point to inhibition of ADAMTS9 as a potential novel mode of treating insulin resistance.

Apolipoprotein E receptor 2 (ApoER2) is a close homologue of low-density lipoprotein receptor (LDLR) that mediates the endocytosis of ligands, including LDL particles. LDLR family members have been presumed to explore a large conformational space to capture ligands in the extended conformation at the cell surface. Ligands are subsequently released through a pH-titrated structural transition to a self-docked, contracted-closed conformation. In addition to lipoprotein uptake, ApoER2 is implicated in signal transduction during brain development through capture of the extracellular protein reelin. From crystallographic analysis, we determine that the full-length ApoER2 ectodomain adopts an intermediate contracted-open conformation when complexed with the signaling-competent reelin fragment, and we identify a previously unappreciated auxiliary low-affinity binding interface. Based on mutational analyses, we propose that the pH shift during endocytosis weakens the affinity of the auxiliary interface and destabilizes the ligand-receptor complex. Furthermore, this study elucidates that the contracted-open conformation of ligand-bound ApoER2 at neutral pH resembles the contracted-closed conformation of ligand-unbound LDLR at acidic pH in a manner suggestive of being primed for ligand release even prior to internalization.

Circumstantial evidence points to a pathological role of alpha-synuclein (aSyn; gene symbol SNCA), conferred by aSyn misfolding and aggregation, in Parkinson disease (PD) and related synucleinopathies. Several findings in experimental models implicate perturbations in the tissue homeostatic mechanisms triggered by pathological aSyn accumulation, including impaired redox homeostasis, as significant contributors in the pathogenesis of PD. The nuclear factor erythroid 2-related factor (NRF2/Nrf2) is recognized as 'the master regulator of cellular anti-oxidant response', both under physiological as well as in pathological conditions. Using immunohistochemical analyses, we show a robust nuclear NRF2 accumulation in post-mortem PD midbrain, detected by NRF2 phosphorylation on the serine residue 40 (nuclear active p-NRF2, S40). Curated gene expression analyses of four independent publicly available microarray datasets revealed considerable alterations in NRF2-responsive genes in the disease affected regions in PD, including substantia nigra, dorsal motor nucleus of vagus, locus coeruleus and globus pallidus. To further examine the putative role of pathological aSyn accumulation on nuclear NRF2 response, we employed a transgenic mouse model of synucleionopathy (M83 line, expressing the mutant human A53T aSyn), which manifests widespread aSyn pathology (phosphorylated aSyn; S129) in the nervous system following intramuscular inoculation of exogenous fibrillar aSyn. We observed strong immunodetection of nuclear NRF2 in neuronal populations harboring p-aSyn (S129), and found an aberrant anti-oxidant and inflammatory gene response in the affected neuraxis. Taken together, our data support the notion that pathological aSyn accumulation impairs the redox homeostasis in nervous system, and boosting neuronal anti-oxidant response is potentially a promising approach to mitigate neurodegeneration in PD and related diseases.

Mutations in CHCHD2 have been identified in some Parkinson's disease (PD) cases. To understand the physiological and pathological roles of CHCHD2, we manipulated the expression of CHCHD2 in Drosophila and mammalian cells. The loss of CHCHD2 in Drosophila causes abnormal matrix structures and impaired oxygen respiration in mitochondria, leading to oxidative stress, dopaminergic neuron loss and motor dysfunction with age. These PD-associated phenotypes are rescued by the overexpression of the translation inhibitor 4E-BP and by the introduction of human CHCHD2 but not its PD-associated mutants. CHCHD2 is upregulated by various mitochondrial stresses, including the destabilization of mitochondrial genomes and unfolded protein stress, in Drosophila. CHCHD2 binds to cytochrome c along with a member of the Bax inhibitor-1 superfamily, MICS1, and modulated cell death signalling, suggesting that CHCHD2 dynamically regulates the functions of cytochrome c in both oxidative phosphorylation and cell death in response to mitochondrial stress.

In this study, we develop an approach termed "2D hybrid analysis" for building atomic models by image matching from electron microscopy (EM) images of biological molecules. The key advantage is that it is applicable to flexible molecules, which are difficult to analyze by 3DEM approach. In the proposed approach, first, a lot of atomic models with different conformations are built by computer simulation. Then, simulated EM images are built from each atomic model. Finally, they are compared with the experimental EM image. Two kinds of models are used as simulated EM images: the negative stain model and the simple projection model. Although the former is more realistic, the latter is adopted to perform faster computations. The use of the negative stain model enables decomposition of the averaged EM images into multiple projection images, each of which originated from a different conformation or orientation. We apply this approach to the EM images of integrin to obtain the distribution of the conformations, from which the pathway of the conformational change of the protein is deduced.