Computational insights into the cross-talk between medin and Aß: implications for age-related vascular risk factors in Alzheimer's disease.

The aggregation of medin forming aortic medial amyloid is linked to arterial wall degeneration and cerebrovascular dysfunction. Elevated levels of arteriolar medin are correlated with an increased presence of vascular amyloid-ß (Aß) aggregates, a hallmark of Alzheimer's disease (AD) and vascular dementia. The cross-interaction between medin and Aß results in the formation of heterologous fibrils through co-aggregation and cross-seeding processes both in vitro and in vivo. However, a comprehensive molecular understanding of the cross-interaction between medin and Aß-two intrinsically disordered proteins-is critically lacking. Here, we employed atomistic discrete molecular dynamics simulations to systematically investigate the self-association, co-aggregation and also the phenomenon of cross-seeding between these two proteins. Our results demonstrated that both Aß and medin were aggregation prone and their mixture tended to form ß-sheet-rich hetero-aggregates. The formation of Aß-medin hetero-aggregates did not hinder Aß and medin from recruiting additional Aß and medin peptides to grow into larger ß-sheet-rich aggregates. The ß-barrel oligomer intermediates observed in the self-aggregations of Aß and medin were also present during their co-aggregation. In cross-seeding simulations, preformed Aß fibrils could recruit isolated medin monomers to form elongated ß-sheets. Overall, our comprehensive simulations suggested that the cross-interaction between Aß and medin may contribute to their pathological aggregation, given the inherent amyloidogenic tendencies of both medin and Aß. Targeting medin, therefore, could offer a novel therapeutic approach to preserving brain function during aging and AD by improving vascular health.

Deciphering the influence of Y12L and N17H substitutions on the conformation and oligomerization of human calcitonin.

The abnormal aggregation of human calcitonin (hCT) hormone peptides impairs their physiological function, leading to harmful immune responses and cytotoxicity, which limits their clinical utility. Interestingly, a representative hCT analog incorporating Y12L and N17H substitutions (DM-hCT) has shown reduced aggregation tendencies while maintaining bioactivity. But the molecular mechanism of Y12L and N17H substitutions on the conformational dynamics of hCT remains unclear. Here, we systematically investigated the folding and self-assembly dynamics of hCT and DM-hCT using atomistic discrete molecular dynamics (DMD) simulations. Our findings revealed that hCT monomers predominantly adopted unstructured conformations with dynamic helices. Oligomerization of hCT resulted in the formation of ß-sheet-rich aggregates and ß-barrel intermediates. The Y12L and N17H substitutions enhanced helical conformations and suppressed ß-sheet formation in both monomers and oligomers. These substitutions stabilized the dynamic helices and disrupted aromatic interactions responsible for ß-sheet formation at residue 12. Notably, DM-hCT assemblies still exhibited ß-sheets in phenylalanine-rich and C-terminal hydrophobic regions, suggesting that future optimizations should focus on these areas. Our simulations provide insights into the molecular mechanisms underlying hCT aggregation and the amyloid-resistant effects of Y12L and N17H substitutions. These findings have valuable implications for the development of clinical hCT analogs.

Computational Investigation of Coaggregation and Cross-Seeding between Aß and hIAPP Underpinning the Cross-Talk in Alzheimer's Disease and Type 2 Diabetes.

The coexistence of amyloid-ß (Aß) and human islet amyloid polypeptide (hIAPP) in the brain and pancreas is associated with an increased risk of Alzheimer's disease (AD) and type 2 diabetes (T2D) due to their coaggregation and cross-seeding. Despite this, the molecular mechanisms underlying their interaction remain elusive. Here, we systematically investigated the cross-talk between Aß and hIAPP using atomistic discrete molecular dynamics (DMD) simulations. Our results revealed that the amyloidogenic core regions of both Aß (Aß10-21 and Aß30-41) and hIAPP (hIAPP8-20 and hIAPP22-29), driving their self-aggregation, also exhibited a strong tendency for cross-interaction. This propensity led to the formation of ß-sheet-rich heterocomplexes, including potentially toxic ß-barrel oligomers. The formation of Aß and hIAPP heteroaggregates did not impede the recruitment of additional peptides to grow into larger aggregates. Our cross-seeding simulations demonstrated that both Aß and hIAPP fibrils could mutually act as seeds, assisting each other's monomers in converting into ß-sheets at the exposed fibril elongation ends. The amyloidogenic core regions of Aß and hIAPP, in both oligomeric and fibrillar states, exhibited the ability to recruit isolated peptides, thereby extending the ß-sheet edges, with limited sensitivity to the amino acid sequence. These findings suggest that targeting these regions by capping them with amyloid-resistant peptide drugs may hold potential as a therapeutic approach for addressing AD, T2D, and their copathologies.

Unveiling Medin Folding and Dimerization Dynamics and Conformations via Atomistic Discrete Molecular Dynamics Simulations.

Medin is a principal component of localized amyloid found in the vasculature of individuals over 50 years old. Its amyloid aggregation has been linked to endothelial dysfunction and vascular inflammation, contributing to the pathogenesis of various vascular diseases. Despite its significance, the structures of the medin monomer, oligomer, and fibril remain elusive, and the dynamic processes of medin aggregation are not fully understood. In this study, we comprehensively investigated the medin folding and dimerization dynamics and conformations using atomistic discrete molecular dynamics simulations. Our simulation results suggested that the folding initiation of the medin involved the formation of ß-sheets around medin30-41 and medin42-50, with subsequent capping of other segments to their ß-sheet edges. Medin monomers typically consisted of three or four ß-strands, along with a dynamic N-terminal helix. Two isolated medin peptides readily aggregated into a ß-sheet-rich dimer, displaying a strong aggregation propensity. Dimerization of medin not only enhanced the ß-sheet conformations but also led to the formation of ß-barrel oligomers. The aggregation tendencies of medin1-18 and medin19-29 were relatively weak. However, the segments of medin30-41 and medin42-50 played a crucial role as they primarily formed a ß-sheet core and facilitated medin1-18 and medin19-29 to form intra- and interpeptide ß-sheets. The findings highlight the critical role of the medin30-41 and medin42-50 regions in stabilizing the monomer structure and driving the medin amyloid aggregation. These regions could potentially serve as promising targets for designing antiamyloid inhibitors against amyloid aggregation of medin. Additionally, our study provides a full picture of the monomer conformations and dimerization dynamics for medin, which will help better understand the pathology of medin aggregation.

SEVI Inhibits Aß Amyloid Aggregation by Capping the ß-Sheet Elongation Edges.

Inhibiting the aggregation of amyloid peptides with endogenous peptides has broad interest due to their intrinsically high biocompatibility and low immunogenicity. Here, we investigated the inhibition mechanism of the prostatic acidic phosphatase fragment SEVI (semen-derived enhancer of viral infection) against Aß42 fibrillization using atomistic discrete molecular dynamic simulations. Our result revealed that SEVI was intrinsically disordered with dynamic formation of residual helices. With a high positive net charge, the self-aggregation tendency of SEVI was weak. Aß42 had a strong aggregation propensity by readily self-assembling into ß-sheet-rich aggregates. SEVI preferred to interact with Aß42, rather than SEVI themselves. In the heteroaggregates, Aß42 mainly adopted ß-sheets buried inside and capped by SEVI in the outer layer. SEVI could bind to various Aß aggregation species─including monomers, dimers, and proto-fibrils─by capping the exposed ß-sheet elongation edges. The aggregation processes Aß42 from the formation of oligomers to conformational nucleation into fibrils and fibril growth should be inhibited as their ß-sheet elongation edges are being occupied by the highly charged SEVI. Overall, our computational study uncovered the molecular mechanism of experimentally observed inhibition of SEVI against Aß42 aggregation, providing novel insights into the development of therapeutic strategies against Alzheimer's disease.