The differential solvent exposure of N-terminal residues provides "fingerprints" of alpha-synuclein fibrillar polymorphs.

Synucleinopathies are neurodegenerative diseases characterized by the presence of intracellular deposits containing the protein alpha-synuclein (aSYN) within patients' brains. It has been shown that aSYN can form structurally distinct fibrillar assemblies, also termed polymorphs. We previously showed that distinct aSYN polymorphs assembled in vitro, named fibrils, ribbons, and fibrils 91, differentially bind to and seed the aggregation of endogenous aSYN in neuronal cells, which suggests that distinct synucleinopathies may arise from aSYN polymorphs. In order to better understand the differential interactions of aSYN polymorphs with their partner proteins, we mapped aSYN polymorphs surfaces. We used limited proteolysis, hydrogen-deuterium exchange, and differential antibody accessibility to identify amino acids on their surfaces. We showed that the aSYN C-terminal region spanning residues 94 to 140 exhibited similarly high solvent accessibility in these three polymorphs. However, the N-terminal amino acid residues 1 to 38 of fibrils were exposed to the solvent, while only residues 1 to 18 within fibrils 91 were exposed, and no N-terminal residues within ribbons were solvent-exposed. It is likely that these differences in surface accessibility contribute to the differential binding of distinct aSYN polymorphs to partner proteins. We thus posit that the polypeptides exposed on the surface of distinct aSYN fibrillar polymorphs are comparable to fingerprints. Our findings have diagnostic and therapeutic potential, particularly in the prion-like propagation of fibrillar aSYN, as they can facilitate the design of ligands that specifically bind and distinguish between fibrillar polymorphs.

Novel potent liposome agonists of triggering receptor expressed on myeloid cells 2 phenocopy antibody treatment in cells.

The receptor Triggering Receptor Expressed on Myeloid cells 2 (TREM2) is associated with several neurodegenerative diseases including Alzheimer's Disease and TREM2 stimulation represents a novel therapeutic opportunity. TREM2 can be activated by antibodies targeting the stalk region, most likely through receptor dimerization. Endogenous ligands of TREM2 are suggested to be negatively charged apoptotic bodies, mimicked by phosphatidylserine incorporated in liposomes and other polyanionic molecules likely binding to TREM2 IgV fold. However, there has been much discrepancy in the literature on the nature of phospholipids (PLs) that can activate TREM2 and on the stability of the corresponding liposomes over time. We describe optimized liposomes as robust agonists selective for TREM2 over TREM1 in cellular system. The detailed structure/activity relationship studies of lipid polar heads indicate that negatively charged lipid heads are required for activity and we identified the shortest maximally active PL sidechain. Optimized liposomes are active on both TREM2 common variant and TREM2 R47H mutant. Activity and selectivity were further confirmed in different native TREM2 expressing cell types including on integrated cellular responses such as stimulation of phagocytic activity. Such tool agonists will be useful in further studies of TREM2 biology in cellular systems alongside antibodies, and in the design of small molecule synthetic TREM2 agonists.

Cerebrospinal fluid neurogranin in an inducible mouse model of neurodegeneration: A translatable marker of synaptic degeneration.

Synapse impairment is thought to be an early event in Alzheimer's disease (AD); dysfunction and loss of synapses are linked to cognitive symptoms that precede neuronal loss and neurodegeneration. Neurogranin (Ng) is a somatodendritic protein that has been shown to be reduced in brain tissue but increased in the cerebrospinal fluid (CSF) of AD patients compared to age-matched controls. High levels of CSF Ng have been shown to reflect a more rapid AD progression. To gauge the translational value of Ng as a biomarker, we developed a new, highly sensitive, digital enzyme-linked immunosorbent assay (ELISA) on the Simoa platform to measure Ng in both mouse and human CSF. We investigated and confirmed that Ng levels are increased in the CSF of patients with AD compared to controls. In addition, we explored how Ng is altered in the brain and CSF of transgenic mice that display progressive neuronal loss and synaptic degeneration following the induction of p25 overexpression. In this model, we found that Ng levels increased in CSF when neurodegeneration was induced, peaking after 2 weeks, while they decreased in brain. Our data suggest that CSF Ng is a biomarker of synaptic degeneration with translational value.

Tetravalent Bispecific Tandem Antibodies Improve Brain Exposure and Efficacy in an Amyloid Transgenic Mouse Model.

Most antibodies display very low brain exposure due to the blood-brain barrier (BBB) preventing their entry into brain parenchyma. Transferrin receptor (TfR) has been used previously to ferry antibodies to the brain by using different formats of bispecific constructs. Tetravalent bispecific tandem immunoglobulin Gs (IgGs) (TBTIs) containing two paratopes for both TfR and protofibrillar forms of amyloid-beta (Aß) peptide were constructed and shown to display higher brain penetration than the parent anti-Aß antibody. Additional structure-based mutations on the TfR paratopes further increased brain exposure, with maximal enhancement up to 13-fold in wild-type mice and an additional 4-5-fold in transgenic (Tg) mice harboring amyloid plaques, the main target of our amyloid antibody. Parenchymal target engagement of extracellular amyloid plaques was demonstrated using in vivo and ex vivo fluorescence imaging as well as histological methods. The best candidates were selected for a chronic study in an amyloid precursor protein (APP) Tg mouse model showing efficacy at reducing brain amyloid load at a lower dose than the corresponding monospecific antibody. TBTIs represent a promising format for enhancing IgG brain penetration using a symmetrical construct and keeping bivalency of the payload antibody.

A cellular microRNA mediates antiviral defense in human cells.

In eukaryotes, 21- to 24-nucleotide-long RNAs engage in sequence-specific interactions that inhibit gene expression by RNA silencing. This process has regulatory roles involving microRNAs and, in plants and insects, it also forms the basis of a defense mechanism directed by small interfering RNAs that derive from replicative or integrated viral genomes. We show that a cellular microRNA effectively restricts the accumulation of the retrovirus primate foamy virus type 1 (PFV-1) in human cells. PFV-1 also encodes a protein, Tas, that suppresses microRNA-directed functions in mammalian cells and displays cross-kingdom antisilencing activities. Therefore, through fortuitous recognition of foreign nucleic acids, cellular microRNAs have direct antiviral effects in addition to their regulatory functions.

The Ets-1 transcription factor is required for complete pre-T cell receptor function and allelic exclusion at the T cell receptor beta locus.

The pre-T cell receptor (TCR) functions as a critical checkpoint during alphabeta T cell development. Signaling through the pre-TCR controls the differentiation of immature CD4(-)CD8(-)CD25(+)CD44(-) [double-negative (DN)3] thymocytes into CD4(+)CD8(+) double-positive (DP) cells through the CD4(-)CD8(-)CD25(-)CD44(-)(DN4) stage. In addition, pre-TCR activity triggers expansion and survival of thymocytes and inhibits TCRbeta gene rearrangement through a process referred to as allelic exclusion. Whereas many proteins involved in the pre-TCR transduction cascade have been identified, little is known about the nuclear factors associated with receptor function. Here, we use gene targeting to inactivate the Ets-1 transcription factor in mice and analyze pre-TCR function in developing Ets-1-deficient (Ets-1(-/-)) thymocytes. We find that inactivation of Ets-1 impairs the development of DN3 into DP thymocytes and induces an elevated rate of cell death in the DN4 subset. This defect appears specific to the alphabeta lineage because gammadelta T cells maturate efficiently. Finally, the percentage of thymocytes coexpressing two different TCRbeta chains is increased in the Ets-1(-/-) background and, in contrast with wild type, forced activation of pre-TCR signaling does not block endogenous TCRbeta gene rearrangement. These data identify Ets-1 as a critical transcription factor for pre-TCR functioning and for allelic exclusion at the TCRbeta locus.

Disruption of the lineage restriction of TCR beta gene rearrangements.

Despite a common lymphoid recombinase, assembly of Ig genes is restricted to B cells, whereas TCR loci rearrange in T cells. Transcriptional promoters and enhancers are critical for the regulation of the recombination process. However, the specific function of such elements in conferring the lineage-restriction of V(D)J recombination remains poorly understood. To gain further insights into the mechanism restricting TCR beta-chain rearrangements to T cells, we generated mice in which an 11 kb region--containing the beta-chain constant region 2 and the TCR beta enhancer (E beta)--was replaced with the B cell specific Ig heavy-chain enhancer (E mu). Unlike the simple E mu to E beta replacement, this mutation allowed significant levels of D beta to J beta as well as V beta to DJ beta rearrangements in both T and B cells. Although the lineage restriction was disrupted, TCR beta allelic exclusion was still efficient in mutated T cells. Together these results demonstrate that changes in the activity of regulatory elements located at the TCR beta constant regions are sufficient to redirect the recombination pattern of TCR beta variable gene segments.

The development of early and mature B cells is impaired in mice deficient for the Ets-1 transcription factor.

The Ets-1 transcription factor is essential for normal development of the natural killer and T cell lineages; however, its role in B cell development remains poorly understood. To address this issue, we used gene targeting to inactivate Ets-1 in mice (Ets-1(-/-)). We show here that the development of B cell precursors, particularly steps requiring pre-B cell receptor function, is defective in Ets-1(-/-) mice. Peripheral B cell subsets were analyzed in RAG2-deficient mice reconstituted with Ets-1(-/-) fetal liver cells. In such Ets-1(-/-) chimeric mice, B cell precursors develop into IgM/IgD-bearing cells, but B-1a cells as well as transitional-2 and marginal zone B cell subsets of the spleen are absent. In response to B cell receptor stimulation, Ets-1(-/-) splenic B cells fail to express the CD69 and CD25 activation markers. Furthermore, despite activation of ERK and JNK signaling pathways, Ets-1-deficient B cells do not proliferate and die following BCR engagement. These findings demonstrate that the effect of Ets-1 inactivation is not restricted to the terminal B cell differentiation stage, but also affects the development and function of earlier B cell subsets.

Transgenic expression of the p16(INK4a) cyclin-dependent kinase inhibitor leads to enhanced apoptosis and differentiation arrest of CD4-CD8- immature thymocytes.

In the thymus, T cell development proceeds by successive steps of differentiation, expansion, and selection. Control of thymocyte proliferation is critical to insure the full function of the immune system and to prevent T cells from transformation. Deletion of the cell cycle inhibitor p16(INK4a) is frequently observed in human T cell neoplasias and, in mice, gene targeted inactivation of the Ink4a locus enhances thymocyte expansion and predisposes mutant animal to tumorigenesis. Here, we investigate the mechanism by which p16(Ink4a) controls thymocyte development by analyzing transgenic mice expressing the human p16(INK4a) into the T cell lineage. We show that forced expression of p16(INK4a) in thymocytes blocked T cell differentiation at the early CD4-CD8-CD3-CD25+ stage without significantly affecting the development of gammadelta T cells. Pre-TCR function was mimicked by the induction of CD3 signaling in thymocytes of recombinase activating gene (RAG)-2-deficient mice (RAG-2(-/-)). Upon anti-CD3epsilon treatment in vivo, p16(INK4a)-expressing RAG-2(-/-) thymocytes were not rescued from apoptosis, nor could they differentiate. Our data demonstrate that expression of p16(INK4a) prevents the pre-TCR-mediated expansion and/or survival of differentiating thymocytes.