Biology subjects

Sasahara, T.

Publications and source records attributed to Sasahara, T..

4 recordsLinked to original sources

bioRxiv2024

How Alzheimer's Abeta propagates and triggers tau pathology in intact neurons

Alzheimers disease begins with A{beta} accumulation, progresses to tau aggregates and results in widespread neurodegeneration1-3. Simultaneous propagation of A{beta} aggregates from very limited to wide and distant brain regions is one of the outstanding events in the early stage. Here, we demonstrate that the neurovascular unit4,5 comprising capillaries and pericytes, the machinery supplying oxygen and glucose to neurons, is also the machinery for propagating effector molecules that impose Alzheimers pathologies on intact neurons. We discovered two distinct signaling cascades, one activated in capillary endothelial cells and the other in pericytes. At the origin of either cascade, we identified amylospheroid (ASPD)6,7, a highly toxic 30-mer assembly of A{beta}, and its sole target NKA38, a neuron-specific isoform of Na+,K+-ATPase9,10 but present in endothelial cells and pericytes. In endothelial cells, ASPD binding to NKA3 releases angiotensin II, which increases {beta}-secretase in intact neurons, causing a huge increase of A{beta}42and resultant accumulation. In pericytes, ASPD binding to NKA3 releases an unknown effector molecule that activates {delta}-secretase in intact neurons, further augmenting A{beta}42and producing pathogenic tau1-368 fragment. Thus, A{beta} and tau pathologies are directly linked. Stopping the signaling cascades near the origin by inhibiting ASPD-NKA3 interaction8 may provide a new therapeutic approach.

neuroscience↗

bioRxiv2020

Alzheimer's Aβ assembly binds sodium pump and blocks endothelial NOS activity via ROS-PKC pathway

Amyloid {beta}-protein (A{beta}) may contribute to worsening of Alzheimers disease (AD) through vascular dysfunction, but the actual molecular mechanisms remain controversial. Using ex-vivo blood vessels and primary endothelial cells derived from human brain microvessels, we revealed that patient-derived A{beta} assemblies, termed amylospheroids (ASPD), exist on the microvascular surface in patient brains and inhibit vasorelaxation through binding to the 3 subunit of sodium, potassium-ATPase (NAK3) on endothelial cells. Interestingly, NAK3 also serves as the toxic target of ASPD in neurons. ASPD elicit neurodegeneration through calcium overload, while ASPD suppress vasorelaxation by inhibiting nitric oxide (NO) production. ASPD-NAK3 interaction on cerebrovascular endothelial cells disturbs the NO release by inactivating endothelial NO synthase through mitochondrial reactive oxygen species and protein kinase C. The findings suggest that ASPD may dually contribute to neuronal and vascular pathologies through binding to NAK3. Thus, blocking the ASPD-NAK3 interaction may be a useful target for AD therapy.

biochemistry↗

bioRxiv2019

Development of CRISPR-Cas13a-based antimicrobials capable of sequence-specific killing of target bacteria

Emergence of antimicrobial-resistant bacteria is an increasingly serious threat to global health, necessitating the development of innovative antimicrobials. We established a series of CRISPR-Cas13a-based antibacterial nucleocapsid, termed CapsidCas13a(s), capable of sequence-specific killing of carbapenem-resistant Escherichia coli and methicillin-resistant Staphylococcus aureus through promiscuous RNA cleavage after recognizing corresponding antimicrobial resistance genes. CapsidCas13a constructs were generated by packaging CRISPR-Cas13a into a bacteriophage capsid to target antimicrobial resistance genes. Contrary to Cas9-based antimicrobials that lack bacterial killing capacity when the target genes are located on a plasmid, the CapsidCas13a(s) exhibited strong bacterial killing activities upon recognizing target genes regardless of their location. The antimicrobials treatment efficacy was confirmed using a Galleria mellonella larvae model. Further, we demonstrated that the CapsidCas13a(s) can assist in bacterial gene detection without employing nucleic acid amplification and optical devices.

microbiology↗

bioRxiv2019

Composition and Diversity of CRISPR-Cas13a systems in the genus Leptotrichia

Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas13a, previously known as CRISPR-C2c2, is the most recently identified RNA-guided RNA-targeting CRISPR-Cas system and has the unique characteristics of both targeted and collateral single-stranded RNA (ssRNA) cleavage activities, which was first identified in Leptotrichia shahii CRISPR-Cas13a. Here, the complete whole genome sequences of 11 Leptotrichia strains were determined and compared with 18 publicly available Leptotrichia genomes in regard to the composition, occurrence and diversity of the CRISPR-Cas13a and other CRISPR-Cas systems. Various types of CRISPR-Cas systems, I-B, II-C, III-A, III-D, III-like and VI-A, were unevenly distributed among the Leptotrichia genomes, accounting for 10 (34.4%), 1 (2.6%), 6 (15.4%), 6 (15.4%), 3 (7.7%) and 11 (37.9%) of the 29 strains, respectively, while 8 (20.5%) strains had no CRISPR-Cas system. The Cas13a effectors were highly divergent with amino acid sequence similarities ranging from 61% to 90% to that of L. shahii and their collateral ssRNA cleavage activities, resulting in cytotoxicity to host cell, were found to be maintained. CRISPR-Cas spacers represent a sequential achievement of former intruder encounters, and the retained spacers reflect the evolutionary phylogeny or relatedness of strains. Analysis of spacer contents and numbers among Leptotrichia species showed considerable diversity with only 2 (0.5%) of 400 spacers through CRIPSR-Cas I-VI were shared by two strains. The organisation and distribution of CRISPR-Cas systems (type I-VI) encoded by all registered Leptotrichia species revealed that effector or spacer sequences of the CRISPR-Cas systems were very divergent, and the prevalence of types I, III and VI was almost equal. There was only one strain carrying type II, while none carried type IV or V. These results provide new insights into the characteristics and divergences of CRISPR-Cas systems among Leptotrichia species.

microbiology↗