Biology subjects

Yamazaki, N.

Publications and source records attributed to Yamazaki, N..

4 recordsLinked to original sources

bioRxiv2024

Metabolic resistance of Abeta3pE-42, epitope of the anti-Alzheimer therapeutic antibody, donanemab.

The amyloid {beta} peptide (A{beta}) starting with pyroglutamate (pE) at position 3 and ending at position 42 (A{beta}3pE-42) is a dominant species that accumulates in the Alzheimers disease (AD) brain. Consistently, a therapeutic antibody raised against this species, donanemab, has been shown to be effective in recent clinical trials. While the primary A{beta} species produced physiologically is A{beta}1-40/42, an explanation for how and why this physiological A{beta} is converted to the pathological form has remained elusive. The conversion of A{beta}1-42 to A{beta}3pE-42 is likely to take place after deposition of A{beta}1-42 given that A{beta}3pE-42 plaques arise significantly later than A{beta}1-42 deposition in the brains of single App knock-in and APP-transgenic mice. Here, we present experimental evidence that accounts for the aging-associated A{beta}3pE-42 deposition: [1] A{beta}3pE-42 is metabolically more stable than other A{beta}X-42 species; [2] Deficiency of neprilysin (NEP), the major A{beta}-degrading enzyme, induces a relatively selective deposition of A{beta}3pE-42 in APP-Tg mice. [3] A{beta}3pE-42 deposition always colocalizes with cored plaques in both APP-Tg and App knock-in mouse brains; [4] A{beta}3E-42, an immediate precursor of A{beta}3pE-42, as well as A{beta}2A-42 and A{beta}4F-42 are more short-lived than A{beta}1-42 in vivo, indicating that simple N-terminal truncation that can arise enzymatically or spontaneously makes A{beta}X-42 easier to catabolize. Consistently, newly generated knock-in mice, AppNL-({Delta}DA)-F and AppNL-({Delta}DA)-Q-F, showed no detectable A{beta} pathology even after aging, indicating that the A{beta}3E-42 and A{beta}3Q-42 species are extremely labile to the in vivo catabolic system and that the E/Q cyclase activity present in mouse brain is insufficient for A{beta}3pE-42 generation. In addition, a deficiency of NEP facilitated A{beta}3pE-42 deposition. Of note, we identified a trace amount of A{beta}3pE-42 and its immediate precursor, A{beta}3E-42, in the insoluble fraction of NEP-deficient APP-Tg mouse brains. A{beta}3pE-42 is thus likely to be a probabilistic by-product of A{beta}1-42 metabolism that selectively accumulates over a long-time range of brain aging. It is likely produced in the solid state or at the solid-liquid interface. Our findings suggest that anti-A{beta} therapies will probably be most effective if given before A{beta}3pE-42 deposition takes place.

neuroscience↗

bioRxiv2023

Bidirectional feedforward regulatory loop of Dicer-like 4 and flavonoids causes floral bicolor patterning in petunia and dahlia

Floral bicolor pigmentation is caused by naturally occurring RNA interference (RNAi) in some cultivars of petunia and dahlia. In both plants, the chalcone synthase gene is highly expressed only in the pigmented region of bicolor petals. However, it remains unknown why RNAi is induced only in the unpigmented region. To elucidate the mechanism of this clear bicolor pattern formation, we examined the dicing activity of Dicer-like 4 (DCL4), which produces small interfering RNAs essential for the induction of RNAi. We showed that the crude extract in the pigmented petal region inhibits dicing activity of DCL4, but not when flavonoids were depleted from the extract. Moreover, we showed the inhibitory activity was associated with flavonoid aglycons. The in vivo dicing activities were detected in the intact protoplasts prepared from the unpigmented region but not from the pigmented region. These results suggest that in the unpigmented region, flavonoids that inhibit DCL4 are not synthesized, and RNAi is maintained, whereas in the pigmented region, DCL4 is inhibited by flavonoids, RNAi is not induced, and anthocyanin biosynthesis is maintained, which ensures RNAi inhibition. Therefore, a clear bicolor pattern is generated by the bidirectional feedforward mechanism of antagonizing DCL4 and flavonoids.

plant biology↗

bioRxiv2021

An isogenic panel of single App knock-in mouse models of Alzheimer's disease confers differential profiles of β-secretase inhibition and endosomal abnormalities

We previously developed single App knock-in mouse models of Alzheimers disease (AD) that harbor the Swedish and Beyreuther/Iberian mutations with or without the Arctic mutation (AppNL- G-F and AppNL-F mice). These models showed the development of amyloid {beta} peptide (A{beta}) pathology, neuroinflammation and cognitive impairment with aging. We have now generated App knock-in mice devoid of the Swedish mutations (AppG-F mice) and some additional mutants to address the following two questions: [1] Do the Swedish mutations influence the mode of {beta}-secretase inhibitor action in vivo? [2] Does the quantity of C-terminal fragment of amyloid precursor protein (APP) generated by {beta}-secretase (CTF-{beta}) affect endosomal properties as previously reported as well as other pathological events? A{beta} pathology was exhibited by AppG-F mice from 6 to 8 months of age, and was accompanied by microglial and astrocyte activation. We found that a {beta}-secretase inhibitor, verubecestat, inhibited A{beta} production in AppG-F mice, but not in AppNL-G-F mice, indicating that the AppG-F mice are more suitable for preclinical studies of {beta}-secretase inhibition given that most AD patients do not carry Swedish mutations. We also found that the quantity of CTF-{beta} generated by various App knock-in mutants failed to correlate with endosomal alterations or enlargement, implying that CTF-{beta}, endosomal abnormalities, or both are unlikely to play a major role in AD pathogenesis. This is the first AD mouse model ever described that recapitulates amyloid pathology in the brain without the presence of Swedish mutations and without relying on the overexpression paradigm. Thus, experimental comparisons between different App knock-in mouse lines will potentially provide new insights into our understanding of the etiology of AD.

neuroscience↗

bioRxiv2021

Neprilysin-sensitive amyloidogenic Aβ versus IDE-sensitive soluble Aβ: a probable mechanistic cause for sporadic Alzheimer's disease

Neprilysin (NEP) and insulin-degrading enzyme (IDE) are considered the two major catabolic enzymes that degrade amyloid {beta} peptide (A{beta}), the primary cause of Alzheimers disease (AD). However, their roles in A{beta} metabolism in vivo have never been compared in an impartial and side-by-side manner. Here, we crossbred single App knock-in mice with NEP (Mme) KO mice and with IDE (Ide) KO mice to generate double mutants that were analyzed for their biochemical and A{beta} pathology properties. We found that NEP is responsible for the metabolism of amyloidogenic insoluble A{beta} whereas IDE affects soluble A{beta}. A deficiency of NEP, but not of IDE, augmented the formation of A{beta} plaques, dystrophic neurites, and astrocytic and microglial activation, all of which are key pathological events in the development of AD. In addition, a deficiency of NEP had no significant impact on the levels of various neuropeptides (somatostatin, substance P, cholecystokinin, and neuropeptide Y), well known to be in vitro substrates for NEP, presumably because NEP is expressed in secretory vesicles and on the presynaptic membranes of excitatory neurons while most if not all neuropeptides are secreted from inhibitory neurons. This argues against the concern that NEP up-regulation for treatment of preclinical AD would reduce the levels of these neuropeptides. These findings indicate that NEP relatively selectively degrades A{beta} in the brain. Whereas familial AD (FAD) is unambiguously caused by an increased anabolism of A{beta}, and of A{beta} 42 and A{beta} 43 in particular, the anabolism of A{beta} appears unaffected before its deposition in the brain that subsequently leads to the onset of sporadic AD (SAD). These observations thus suggest that NEP-sensitive amyloidogenic A{beta} likely plays a primary pathogenic role in the etiology of SAD. Our findings are consistent with the aging-dependent decline of NEP expression in human brain and with recent genome-wide association studies (GWAS) indicating that variants of the gene encoding NEP (MME) are associated with the risk of SAD development. Taken together, our results imply that the aging-associated decrease in NEP expression is a primary cause of SAD and could thus be a target for the treatment of preclinical AD once other factors such as apolipoprotein E genotypes have also been considered.

neuroscience↗