Conversion of β-amyloid (Aβ) peptides from soluble random-coil to aggregated protein enriched with β-sheet-rich intermediates has been suggested to play a role in the degeneration of neurons and development of Alzheimer’s disease (AD) pathology. Aggregation of Aβ peptide can be prompted by a variety of environmental factors including temperature which can influence disease pathogenesis. Recently, we reported that FDA-approved unconjugated poly (d,l-lactide-co-glycolide) (PLGA) nanoparticles can have beneficial effects in cellular and animal models of AD by targeting different facets of the Aβ axis. In this study, using biochemical, structural and spectroscopic analyses, we evaluated the effects of native PLGA on temperature-dependent Aβ aggregation and its ability to protect cultured neurons from degeneration. Our results show that the rate of spontaneous Aβ1–42 aggregation increases with a rise in temperature from 27 to 40 °C and PLGA with 50:50 resomer potently inhibits Aβ aggregation at all temperatures, but the effect is more profound at 27 °C than at 40 °C. It appears that native PLGA, by interacting with the hydrophobic domain of Aβ1–42, prevents a conformational shift towards β-sheet structure, thus precluding the formation of Aβ aggregates. Additionally, PLGA triggers disassembly of matured Aβ1–42 fibers at a faster rate at 40 °C than at 27 °C. PLGA-treated Aβ samples can significantly enhance viability of cortical cultured neurons compared to neurons treated with Aβ alone by attenuating phosphorylation of tau protein. Injection of native PLGA is found to influence the breakdown/clearance of Aβ peptide in the brain. Collectively, these results suggest that PLGA nanoparticles can inhibit Aβ aggregation and trigger disassembly of Aβ aggregates at temperatures outside the physiological range and can protect neurons against Aβ-mediated toxicity thus validating its unique therapeutic potential in the treatment of AD pathology. Graphical Abstract
Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders affecting key enzymes of cortisol biosynthesis. In the majority of cases the underlying cause are detrimental mutations in the steroidogenic cytochrome P450 enzyme 21-hydroxylase (CYP21A2). Early diagnosis via newborn screening programs in most Western countries and lifelong oral cortisol replacement therapy enable survival, however quality of life often is reduced and co-morbidities are substantially increased. Treatment is a major challenge as disease control can only be achieved with supraphysiological glucocorticoid doses. In addition, the currently available drugs cannot ideally mimic the circadian rhythm and stress adaption of cortisol secretion. Currently, disease severity is classified by residual enzyme activity. The goal of our research is to better understand the specific biophysico-chemical pathomechanism of 21-hydroxylase deficiency in order to enable causative therapeutic approaches. To this end, we investigated the structural and stability properties of six clinically relevant mutant variants of CYP21A2 (V282G/L, P31L, D323G, R484Q/W). Difficulty in purification of these CYP21A2 variants and various biophysical studies suggest that the proteins were less stable than wild-type (WT). Structural and thermal stability assessment by circular dichroism (CD) spectroscopy of recombinant, purified CYP21A2 mutant variants revealed high α-helical content for the WT (65% α-helix) and the mutants at the position 282 (V282G: 60.6 %, V282L: 57.6%). Other mutations (P31L, D323G, R484Q/W) disrupt the α-helical organization of CYP21A2 in exchange for a slight increase in ß-sheet content but mainly for random coil. Temperature dependent CD spectroscopy showed that all mutant variants have reduced thermal stability (Tm: 41.3 - 45,6°C) compared to the WT (Tm: 47.1°C). Tryptophane fluorescence showed that mutant variants of the protein were more prone to local unfolding at the hydrophobic core compared to WT using urea as denaturant. Furthermore, in UV/Vis spectroscopy at 280 nm and 418 nm we could demonstrate that all mutant variants had a reduced heme incorporation (A418/A280: 0.20 - 0.63) compared to WT (A418/A280: 0.88). Our results show that correct structural folding and stability pose a major problem in specific mutations involved in CAH. Therefore we propose that structural protein instability, play a key role in the pathophysiology of CAH and thus might constitute a novel tailored therapeutic target for the treatment of affected patients.
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