An in situ and in vitro investigation of cytoplasmic TDP-43 inclusions reveals the absence of a clear amyloid signature

Introduction: Several neurodegenerative conditions are associated with a common histopathology within neurons of the central nervous system, consisting of the deposition of cytoplasmic inclusions of TAR DNA-binding protein 43 (TDP-43). Such inclusions have variably been described as morphologically and molecularly ordered aggregates having amyloid properties, as filaments without the cross-β-structure and dye binding specific for amyloid, or as amorphous aggregates with no defined structure and fibrillar morphology.Aims and Methods: Here we have expressed human full-length TDP-43 in neuroblastoma x spinal cord 34 (NSC-34) cells to investigate the morphological, structural, and tinctorial properties of TDP-43 inclusions in situ. We have used last-generation amyloid diagnostic probes able to cross the cell membrane and detect amyloid in the cytoplasm and have adopted Raman and Fourier transform infrared microspectroscopies to study in situ the secondary structure of the TDP-43 protein in the inclusions. We have then used transmission electron microscopy to study the morphology of the TDP-43 inclusions.Results: The results show the absence of amyloid dye binding, the lack of an enrichment of cross-β structure in the inclusions, and of a fibrillar texture in the round inclusions. The aggregates formed in vitro from the purified protein under conditions in which it is initially native also lack all these characteristics, ruling out a clear amyloid-like signature.Conclusions: These findings indicate a low propensity of TDP-43 to form amyloid fibrils and even non-amyloid filaments, under conditions in which the protein is initially native and undergoes its typical nucleus-to-cell mislocalization. It cannot be excluded that filaments emerge on the long time scale from such inclusions, but the high propensity of the protein to form initially other types of inclusions appear to be an essential characteristic of TDP-43 proteinopathies.KEY MESSAGESCytoplasmic inclusions of TDP-43 formed in NSC-34 cells do not stain with amyloid-diagnostic dyes, are not enriched with cross-β structure, and do not show a fibrillar morphology.TDP-43 assemblies formed in vitro from pure TDP-43 do not have any hallmarks of amyloid.

Synthesis of benzylidene-benzofuranone derivatives as probes for detection of amyloid fibrils in cells

Aggregated protein is the common cause of a wide variety of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease, etc. It is proven that protein aggregation like amyloid β (Aβ) is one of the critical factors causing AD and, its diagnosis in the early stages of the disease is important for the treatment or prevention of AD. To have a better understanding of protein aggregation and its pathologies, there is a huge need to design and develop new and more trustworthy probe molecules for in vitro amyloid quantification and in vivo amyloid imaging. In this study, 17 new biomarker compounds, have been synthesized from benzofuranone derivatives, to detect and identify amyloid in vitro (dye-binding assay) as well as in the cell by staining method. According to the results, some of these synthetic derivatives can be considered suitable identifiers and quantifiers to detect amyloid fibrils in vitro. Compared to thioflavin T, 4 probes out of 17 probes have shown good results in selectivity and detectability of Aβ depositions, and their binding properties were also confirmed with in silico analysis. The drug-likeness prediction results for selected compounds by the Swiss ADME server show a satisfactory percentage of blood-brain barrier (BBB) permeability and gastrointestinal (GI) absorption. Among all of them, compound 10 was able to show better binding properties than others, and in vivo study showed that this compound was capable of detecting intracellular amyloid.Communicated by Ramaswamy H. Sarma.

Synthesis of benzylidene-indandione derivatives as quantification of amyloid fibrils

The formation of amyloid fibrils due to its association with fatal diseases, including Alzheimer's, has been investigated by many researchers. These common diseases, mostly become verified when it is too late to be treated. Currently, no cure is available for neurodegenerative diseases, and the process of diagnosing amyloid fibrils in the early stages, while there are fewer amyloid fibrils, has become an issue of interest. To do so, determining new probes with the highest binding affinity to the lowest number of amyloid fibrils is necessary. In this study, we proposed to employ new synthesized benzylidene-indandione derivatives as amyloid fibrils fluorescent detection probes. Native soluble proteins of insulin, bovine serum albumin (BSA), BSA amorphous aggregation, and insulin amyloid fibrils were used to evaluate our compounds' specificity to the amyloid structure. While ten synthesized compounds were examined individually, four of them including 3d, 3g, 3i, and 3j showed a high binding affinity with selectivity and specificity to amyloid fibrils, and their binding properties were also confirmed with in silico analysis. The drug-likeness prediction results for selected compounds by Swiss ADME server shows a satisfactory percentage of blood-brain barrier (BBB) permeability and gastrointestinal (GI) absorption for the compounds 3g, 3i, and 3j. More evaluation is needed to determine all properties of compounds in vitro and in vivo.

Inhibiting mTTR Aggregation/Fibrillation by a Chaperone-like Hydrophobic Amino Acid-Conjugated SPION

Transthyretin (TTR) aggregation via misfolding of a mutant or wild-type protein leads to systemic or partial amyloidosis (ATTR). Here, we utilized variable biophysical assays to characterize two distinct aggregation pathways for mTTR (a synthesized monomer TTR incapable of association into a tetramer) at pH 4.3 and also pH 7.4 with agitation, referred to as mTTR aggregation and fibrillation, respectively. The findings suggest that early-stage conformational changes termed monomer activation here determine the aggregation pathway, resulting in developing either amorphous aggregates or well-organized fibrils. Less packed partially unfolded monomers consisting of more non-regular secondary structures that were rapidly produced via a mildly acidic condition form amorphous aggregates. Meanwhile, more hydrophobic and packed monomers consisting of rearranged β sheets and increased helical content developed well-organized fibrils. Conjugating superparamagnetic iron oxide nanoparticles (SPIONs) with leucine and glutamine (L-SPIONs and G-SPIONs in order) via a trimethoxysilane linker provided the chance to study the effect of hydrophobic/hydrophilic surfaces on mTTR aggregation. The results indicated a powerful inhibitory effect of hydrophobic L-SPIONs on both mTTR aggregation and fibrillation. Monomer depletion was introduced as the governing mechanism for inhibiting mTTR aggregation, while a chaperone-like property of L-SPIONs by maintaining an mTTR native structure and adsorbing oligomers suppressed the progression of further fibril formation.

The albumin-based nanoparticle formation in relation to protein aggregation

Albumin is an attractive protein for the preparation of nanoparticle with possible therapeutic applications, due to its biodegradable, nontoxic, non-immunogenic, and metabolizable properties. Many studies have investigated the formation of albumin nanoparticles, generally by the desolvation or coacervation approaches. One of the most important parameters that should be considered in the formation of nanoparticles is their morphology (size and shape). There are many proposals to control the nanoparticle size, but it remains a challenge for researchers yet. In this study, we showed that control of BSA-based nanoparticles/microparticles size could be achieved by varying the temperature and pH and therefore controlling the rate of aggregation. The aggregation behavior was monitored by UV-Vis spectroscopy, SEM, and dye-binding assay. Our results provide more options for the size and shape control of BSA-based nanoparticle in natural buffer systems. The aggregation of BSA at different temperatures within the range of 50-80 °C were studied under the effect of different pHs in the range of 4.7-6.2. In this research, we found that protein aggregation under extreme conditions of pH and temperature, or at the pH near to pI appears to be amorphous, and at the pH above the pI seems to be the amyloid fibril structure. In some instances where the aggregation is neither too fast nor too slow, in the initial phase of the aggregation process, nanoparticle structures can be identified and separated by mechanistic approaches. This observation suggests that the best condition for monitoring the formation of albumin-based nanoparticles could be pH 5.7, 70 °C. Satisfactory rationalization of all aspects of our experimental observation requires further and more detailed study.

Chicken Interspecies Chimerism Unveils Human Pluripotency

Human pluripotent stem cells (hPSCs) are commonly kept in a primed state but also able to acquire a more immature naive state under specific conditions in vitro. Acquisition of naive state changes several properties of hPSCs and might affect their contribution to embryonic development in vivo. However, the lack of an appropriate animal test system has made it difficult to assess potential differences for chimera formation between naive and primed hPSCs. Here, we report that the developing chicken embryo is a permissive host for hPSCs, allowing analysis of the pluripotency potential of hPSCs. Transplantation of naive-like and primed hPSCs at matched developmental stages resulted in robust chimerism. Importantly, the ability of naive-like but not of primed hPSCs to form chimera was substantially reduced when injected at non-matched developmental stages. We propose that contribution to chick embryogenesis is an informative and versatile test to identify different pluripotent states of hPSCs.

Synthesis and in vitro quantification of amyloid fibrils by barbituric and thiobarbituric acid-based chromene derivatives

Neurodegenerative disease is caused by the abnormal build-up of proteins in and around cells called amyloid. The amyloid fibril formation and its mechanism have been investigated with various techniques, including dye-binding assay. Thioflavin T (ThT) has been one of the most widely used dyes for quantifying amyloid deposits, but ThT has a weak fluorescence signal especially at low concentration of amyloid fibrils, low lipophilicity and positive charge that makes it unable to cross the blood-brain barrier (BBB) to detect amyloid fibrils in vivo. Hence, there is a strong motivation for designing and developing the new compounds for in vitro amyloid quantification and in vivo amyloid imaging. The need for new probes to detect amyloid fibrils, especially within the cell, is highlighted by the fact that an accurate understanding of the molecular details of amyloid fibril formation is required to design and develop strategies for controlling the amyloid formation, and this needs more reliable probes for amyloid identification. In this work, we synthesized and applied barbituric and thiobarbituric acid-based chromene derivatives, as new fluorescent dyes to quantitatively detect the amyloid fibrils of bovine serum albumin (BSA) and human insulin in comparison with native soluble proteins or amorphous aggregation. Our results showed that among the 14 synthesized compounds, five compounds 4a, 4h, 4j, 4k, and 4l could selectively and specifically bind to amyloid fibrils while other compounds demonstrated a low-affinity binding. Furthermore, according to the cell viability experiment, compounds 4a, 4j and 4l at low concentration of compounds are not toxic, especially compound 4j which could be used as a suitable candidate for in vivo study. Further studies are needed to determine all the properties of compounds, especially in vivo experiments.

Transthyretin Inhibits Primary and Secondary Nucleations of Amyloid-β Peptide Aggregation and Reduces the Toxicity of Its Oligomers

Alzheimer’s disease is associated with the deposition of the amyloid-β peptide (Aβ) into extracellular senile plaques in the brain. In vitro and in vivo observations have indicated that transthyretin (TTR) acts as an Aβ scavenger in the brain, but the mechanism has not been fully resolved. We have monitored the aggregation process of Aβ₄₀ by thioflavin T fluorescence, in the presence or absence of different concentrations of preformed seed aggregates of Aβ₄₀, of wild-type tetrameric TTR (WT-TTR), and of a variant engineered to be stable as a monomer (M-TTR). Both WT-TTR and M-TTR were found to inhibit specific steps of the process of Aβ₄₀ fibril formation, which are primary and secondary nucleations, without affecting the elongation of the resulting fibrils. Moreover, the analysis shows that both WT-TTR and M-TTR bind to Aβ₄₀ oligomers formed in the aggregation reaction and inhibit their conversion into the shortest fibrils able to elongate. Using biophysical methods, TTR was found to change some aspects of its overall structure following such interactions with Aβ₄₀ oligomers, as well as with oligomers of Aβ₄₂, while maintaining its overall topology. Hence, it is likely that the predominant mechanism by which TTR exerts its protective role lies in the binding of TTR to the Aβ oligomers and in inhibiting primary and secondary nucleation processes, which limits both the toxicity of Aβ oligomers and the ability of the fibrils to proliferate.

FRET studies of various conformational states adopted by transthyretin

Transthyretin (TTR) is an extracellular protein able to deposit into well-defined protein aggregates called amyloid, in pathological conditions known as senile systemic amyloidosis, familial amyloid polyneuropathy, familial amyloid cardiomyopathy and leptomeningeal amyloidosis. At least three distinct partially folded states have been described for TTR, including the widely studied amyloidogenic state at mildly acidic pH. Here, we have used fluorescence resonance energy transfer (FRET) experiments in a monomeric variant of TTR (M-TTR) and in its W41F and W79F mutants, taking advantage of the presence of a unique, solvent-exposed, cysteine residue at position 10, that we have labelled with a coumarin derivative (DACM, acceptor), and of the two natural tryptophan residues at positions 41 and 79 (donors). Trp41 is located in an ideal position as it is one of the residues of β-strand C, whose degree of unfolding is debated. We found that the amyloidogenic state at low pH has the same FRET efficiency as the folded state at neutral pH in both M-TTR and W79F-M-TTR, indicating an unmodified Cys10-Trp41 distance. The partially folded state populated at low denaturant concentrations also has a similar FRET efficiency, but other spectroscopic probes indicate that it is distinct from the amyloidogenic state at acidic pH. By contrast, the off-pathway state accumulating transiently during refolding has a higher FRET efficiency, indicating non-native interactions that reduce the Cys10-Trp41 spatial distance, revealing a third distinct conformational state. Overall, our results clarify a negligible degree of unfolding of β-strand C in the formation of the amyloidogenic state and establish the concept that TTR is a highly plastic protein able to populate at least three distinct conformational states.

An in vitro model for spontaneous angiogenesis using rat mesenteric endothelial cells: possible therapeutic perspective for obesity and related disorders

CONTEXT

Abnormal obesity and the related diseases, such as diabetes and cardiovascular disease, are the main causes of mortality, around the world. A key feature of the adipogenesis and obesity is angiogenesis-dependent tissue growth accompanied with extracellular remodeling. In this way, suppression of angiogenesis may be a key point for preventing the adipogenesis.

OBJECTIVE

In the present study, to provide a deeper insight to understand obesity and screening for more effective therapeutics, we have developed a three-dimensional in vitro model of microvessel formation under collagen matrix culture using endothelial cells, extracted from a suitable tissue.

MATERIALS AND METHODS

In a successful approach for developing an angiogenesis model, the rat mesenteric microvascular endothelial cells (RMMECs) were isolated, coated on dextran beads and then suspended in collagen gel. Additionally, the proliferation as well as migration of endothelial cells were analyzed and compared with human umbilical vein endothelial cells (HUVECs).

RESULTS

RMMECs showed remarkable migration ability and had higher growth during the logarithmic growth phase, when compared with HUVECs. Also, no significance differences in morphogenesis were observed between HUVECs and RMMECs.

DISCUSSION AND CONCLUSION

The model may be useful in providing insights to develop potential intervention strategies in vivo against obesity-related disorders. Targeting endothelial cells is an interesting and exciting possibility that may be raised in further investigations.

Comparative study of immunological and structural properties of two recombinant vaccine candidates against botulinum neurotoxin type E

BACKGROUND

Recently, botulinum neurotoxin (BoNT)-derived recombinant proteins have been suggested as potential botulism vaccines. Here, with concentrating on BoNT type E (BoNT/E), we studied two of these binding domain-based recombinant proteins: a multivalent chimer protein, which is composed of BoNT serotypes A, B and E binding subdomains, and a monovalent recombinant protein, which contains 93 amino acid residues from recombinant C-terminal heavy chain of BoNT/E (rBoNT/E-HCC). Both proteins have an identical region (48 aa) that contains one of the most important BoNT/E epitopes (YLTHMRD sequence).

METHODS

The recombinant protein efficiency in antibody production, their structural differences, and their BoNT/E-epitope location were compared by using ELISA, circular dichroism, computational modeling, and hydrophobicity predictions.

RESULTS

Immunological studies indicated that the antibody yield against rBoNT/E-HCC was higher than chimer protein. Cross ELISA confirmed that the antibodies against the chimer protein recognized rBoNT/E-HCC more efficiently. However, both antibody groups (anti-chimer and anti-rBoNT/E-HCC antibodies) were able to recognize other proteins. Structural studies with circular dichroism showed that chimer proteins have slightly more secondary structures than rBoNT/E-HCC.

CONCLUSION

The immunological results suggested that the above-mentioned identical region in rBoNT/E-HCC is more exposed. Circular dichroism, computational protein modeling and hydrophobicity predictions indicated a more exposed location for the identical region in rBoNT/E-HCC than the chimer protein, which is strongly in agreement with immunological results.

Comparative spectroscopic studies on drug binding characteristics and protein surface hydrophobicity of native and modified forms of bovine serum albumin: possible relevance to change in protein structure/function upon non-enzymatic glycation

The interaction between serum albumin (SA) and drugs has provided an interesting ground for understanding of drug effects, especially in drug distribution and drug-drug interaction on SA, in the case of multi-drug therapy. Determination of the impact of various factors on drug-protein interaction is especially important upon significant binding of drug to albumin. In the present study, the interaction of two drugs (furosemide and indomethacin) with native and modified albumins were investigated by using various spectroscopic methods. Fluorescence data indicated that 1:1 binding of drugs to bovine serum albumin (BSA) is associated with quenching of albumin intrinsic fluorescence. The Job's plot also confirmed that drug binds to BSA via mentioned stoichiometry. Analysis of the quenching and thermodynamic parameters indicated that intermolecular interactions between drug and albumin may change upon protein modification. The theoretical analyses also suggested some conformational changes of interacting side chains in subdomain IIA binding site (at the vicinity of W237), which were in good agreement with experimental data. Decrease of protein surface hydrophobicity (PSH) was also observed upon both albumin modification and drug binding.