8 research outputs found
Novel <i>trans</i>-Stilbene-based Fluorophores as Probes for Spectral Discrimination of Native and Protofibrillar Transthyretin
Accumulation
of misfolded transthyretin (TTR) as amyloid fibrils causes various
human disorders. Native transthyretin is a neurotrophic protein and
is a putative extracellular molecular chaperone. Several fluorophores
have been shown <i>in vitro</i> to bind selectively to native
TTR. Other compounds, such as thioflavin T, bind TTR amyloid fibrils.
The probe 1-anilinonaphthalene-8-sulfonate (ANS) binds to both native
and fibrillar TTR, becoming highly fluorescent, but with indistinguishable
emission spectra for native and fibrillar TTR. Herein we report our
efforts to develop a fluorescent small molecule capable of binding
both native and misfolded protofibrillar TTR, providing distinguishable
emission spectra. We used microwave synthesis for efficient production
of a small library of <i>trans</i>-stilbenes and fluorescence
spectral screening of their binding properties. We synthesized and
tested 22 <i>trans</i>-stilbenes displaying a variety of
functional groups. We successfully developed two naphthyl-based <i>trans</i>-stilbenes probes that detect both TTR states at physiological
concentrations. The compounds bound with nanomolar to micromolar affinities
and displayed distinct emission maxima upon binding native or misfolded
protofibrillar TTR (>100 nm difference). The probes were mainly
responsive to environment polarity providing evidence for the divergent
hydrophobic structure of the binding sites of these protein conformational
states. Furthermore, we were able to successfully use one of these
probes to quantify the relative amounts of native and protofibrillar
TTR in a dynamic equilibrium. In conclusion, we identified two <i>trans</i>-stilbene-based fluorescent probes, (<i>E</i>)-4-(2-(naphthalen-1-yl)vinyl)benzene-1,2-diol (<b>11</b>)
and (<i>E</i>)-4-(2-(naphthalen-2-yl)vinyl)benzene-1,2-diol
(<b>14</b>), that bind native and protofibrillar TTR, providing
a wide difference in emission maxima allowing conformational discrimination
by fluorescence spectroscopy. We expect these novel molecules to serve
as important chemical biology research tools in studies of TTR folding
and misfolding
Derivatization of a Bioorthogonal Protected Trisaccharide LinkerToward Multimodal Tools for Chemical Biology
When cross-linking biomolecules to surfaces or to other
biomolecules,
the use of appropriate spacer molecules is of great importance. Mimicking
the naturally occurring spacer molecules will give further insight
into their role and function, possibly unveil important issues regarding
the importance of the specificity of carbohydrate-based anchor moieties,
in e.g., glycoproteins and glycosylphosphatidylinositols. Herein,
we present the synthesis of a lactoside-based trisaccharide, potentially
suitable as a heterobifunctional bioorthogonal linker molecule whereon
valuable chemical handles have been conjugated. An amino-derivative
having thiol functionality shows promise as novel SPR-surfaces. Furthermore,
the trisaccharide has been conjugated to a cholesterol moiety in combination
with a fluorophore which successfully assemble on the cell surface
in lipid microdomains, possibly lipid-rafts. Finally, a Cu<sup>I</sup>-catalyzed azide–alkyne cycloaddition reaction (CuAAC) confirms
the potential use of oligosaccharides as bioorthogonal linkers in
chemical biology
Divergent Age-Dependent Conformational Rearrangement within Aβ Amyloid Deposits in APP23, APPPS1, and <i>App</i><sup><i>NL‑F</i></sup> Mice
Amyloid plaques composed of fibrils of misfolded Aβ
peptides
are pathological hallmarks of Alzheimer’s disease (AD). Aβ
fibrils are polymorphic in their tertiary and quaternary molecular
structures. This structural polymorphism may carry different pathologic
potencies and can putatively contribute to clinical phenotypes of
AD. Therefore, mapping of structural polymorphism of Aβ fibrils
and structural evolution over time is valuable to understanding disease
mechanisms. Here, we investigated how Aβ fibril structures in
situ differ in Aβ plaque of different mouse models expressing
familial mutations in the AβPP gene. We imaged frozen brains
with a combination of conformation-sensitive luminescent conjugated
oligothiophene (LCO) ligands and Aβ-specific antibodies. LCO
fluorescence mapping revealed that mouse models APP23, APPPS1, and AppNL‑F have different
fibril structures within Aβ-amyloid plaques depending on the
AβPP-processing genotype. Co-staining with Aβ-specific
antibodies showed that individual plaques from APP23 mice expressing
AβPP Swedish mutation have two distinct fibril polymorph regions
of core and corona. The plaque core is predominantly composed of compact
Aβ40 fibrils, and the corona region is dominated by diffusely
packed Aβ40 fibrils. Conversely, the AβPP knock-in mouse AppNL‑F, expressing the
AβPP Iberian mutation along with Swedish mutation has tiny,
cored plaques consisting mainly of compact Aβ42 fibrils, vastly
different from APP23 even at elevated age up to 21 months. Age-dependent
polymorph rearrangement of plaque cores observed for APP23 and APPPS1
mice >12 months, appears strongly promoted by Aβ40 and was
hence
minuscule in AppNL‑F. These structural studies of amyloid plaques in situ can map
disease-relevant fibril polymorph distributions to guide the design
of diagnostic and therapeutic molecules
Multimodal Chemical Imaging of Amyloid Plaque Polymorphism Reveals Aβ Aggregation Dependent Anionic Lipid Accumulations and Metabolism
Amyloid plaque formation
constitutes one of the main pathological
hallmarks of Alzheimer’s disease (AD) and is suggested to be
a critical factor driving disease pathogenesis. Interestingly, in
patients that display amyloid pathology but remain cognitively normal,
Aβ deposits are predominantly of diffuse morphology suggesting
that cored plaque formation is primarily associated with cognitive
deterioration and AD pathogenesis. Little is known about the molecular
mechanism responsible for conversion of monomeric Aβ into neurotoxic
aggregates and the predominantly cored deposits observed in AD. The
structural diversity among Aβ plaques, including cored/compact-
and diffuse, may be linked to their distinct Aβ profile and
other chemical species including neuronal lipids. We developed a novel,
chemical imaging paradigm combining matrix assisted laser desorption/ionization
imaging mass spectrometry (MALDI IMS) and fluorescent amyloid staining.
This multimodal imaging approach was used to probe the lipid chemistry
associated with structural plaque heterogeneity in transgenic AD mice
(tgAPP<sub>Swe</sub>) and was correlated to Aβ profiles determined
by subsequent laser microdissection and immunoprecipitation-mass spectrometry.
Multivariate image analysis revealed an inverse localization of ceramides
and their matching metabolites to diffuse and cored structures within
single plaques, respectively. Moreover, phosphatidylinositols implicated
in AD pathogenesis, were found to localize to the diffuse Aβ
structures and correlate with Aβ1–42. Further, lysophospholipids
implicated in neuroinflammation were increased in all Aβ deposits.
The results support previous clinical findings on the importance of
lipid disturbances in AD pathophysiology and associated sphingolipid
processing. These data highlight the potential of multimodal imaging
as a powerful technology to probe neuropathological mechanisms
<sup>11</sup>C and <sup>18</sup>F Radiolabeling of Tetra- and Pentathiophenes as PET-Ligands for Amyloid Protein Aggregates
Three oligothiophenes were evaluated
as PET ligands for the study
of local and systemic amyloidosis <i>ex vivo</i> using tissue
from patients with amyloid deposits and <i>in vivo</i> using
healthy animals and PET-CT. The <i>ex vivo</i> binding studies
revealed that all three labeled compounds bound specifically to human
amyloid deposits. Specific binding was found in the heart, kidney,
liver, and spleen. To verify the specificity of the oligothiophenes
toward amyloid deposits, tissue sections with amyloid pathology were
stained using the fluorescence exhibited by the compounds and evaluated
with multiphoton microscopy. Furthermore, a <i>in vivo</i> monkey PET-CT study showed very low uptake in the brain, pancreas,
and heart of the healthy animal indicating low nonspecific binding
to healthy tissue. The biological evaluations indicated that this
is a promising group of compounds for the visualization of systemic
and localized amyloidosis
Binding of Polythiophenes to Amyloids: Structural Mapping of the Pharmacophore
Luminescent
conjugated polythiophenes bind to amyloid proteins
with high affinity. Their fluorescence properties, which are modulated
by the detailed conformation in the bound state, are highly sensitive
to structural features of the amyloid. Polythiophenes therefore represent
diagnostic markers for the detection and differentiation of pathological
amyloid aggregates. We clarify the binding site and mode of two different
polythiophenes to fibrils of the prion domain of the HET-s protein
by solid-state NMR and correlate these findings with their fluorescence
properties. We demonstrate how amyloid dyes recognize distinct binding
sites with specific topological features. Regularly spaced surface
charge patterns and well-accessible grooves on the fibril surface
define the pharmacophore of the amyloid, which in turn determines
the binding mode and fluorescence wavelength of the polythiophene
Evidence for Age-Dependent <i>in Vivo</i> Conformational Rearrangement within Aβ Amyloid Deposits
Deposition
of aggregated Aβ peptide in the brain is one of the major hallmarks
of Alzheimer’s disease. Using a combination of two structurally
different, but related, hypersensitive fluorescent amyloid markers,
LCOs, reporting on separate ultrastructural elements, we show that
conformational rearrangement occurs within Aβ plaques of transgenic
mouse models as the animals age. This important mechanistic insight
should aid the design and evaluation of experiments currently using
plaque load as readout
Evidence for Age-Dependent <i>in Vivo</i> Conformational Rearrangement within Aβ Amyloid Deposits
Deposition
of aggregated Aβ peptide in the brain is one of the major hallmarks
of Alzheimer’s disease. Using a combination of two structurally
different, but related, hypersensitive fluorescent amyloid markers,
LCOs, reporting on separate ultrastructural elements, we show that
conformational rearrangement occurs within Aβ plaques of transgenic
mouse models as the animals age. This important mechanistic insight
should aid the design and evaluation of experiments currently using
plaque load as readout