Biology subjects

Masaki, H.

Publications and source records attributed to Masaki, H..

8 recordsLinked to original sources

bioRxiv2026

TorPause: Efficient Static Organ Preservation for Transplants

Transplantation is limited by how long organs survive outside the body. Existing preservation methods slow metabolism or sustain physiological support, but neither eliminates ischemia-reperfusion injury (IRI), which shortens storage and drives organ discard. Embryonic diapause and hibernation show that mammalian cells retain a latent capacity for reversible metabolic arrest. Screening the PI3K-mTOR axis, we identified a dual inhibitor that pauses embryonic stem cells reversibly at ambient oxygen and holds intact mouse embryos in arrest for 11 days. Combined with a mitochondria-targeted hydrogen sulfide donor, this yields TorPause: a two-component flush pairing metabolic pausing with mitochondrial protection, compatible with existing preservation protocols. In a rat liver transplantation model, TorPause reduced structural injury and improved recipient survival after severe warm ischemic storage, potentially expanding the usable donor pool.

developmental biology↗

bioRxiv2025

Xenophagocytosis blockade enhances interspecies chimerism

Organ shortage remains a major challenge in transplantation medicine. Interspecies blastocyst complementation is a promising approach to generate human organs in livestock hosts. However, getting xenogeneic donor cells to engraft and expand at early stages remains challenging. Here we identify an innate immune barrier, wherein host macrophages selectively recognize and eliminate viable xenogeneic donor cells. These events represent a form of phagoptosis and highlight a xenogeneic clearance process that we term xenophagocytosis. We identify the mechanism by which host macrophages selectively phagocytize xenogeneic donor cells: xenogeneic cells display elevated phosphatidylserine, an "eat-me" signal recognized by host macrophages through phagocytic receptor Axl. Xenophagocytosis blockade improves both rat and human donor chimerism in mouse embryos, indicating a conserved mechanism. These findings reveal potential mechanisms by which innate immune cells eliminate xenogeneic cells in early embryogenesis to preserve species integrity and offer improved strategies for generating human organs in livestock.

immunology↗

bioRxiv2025

The generation of viable, structurally integrated human-mouse chimaeras through enhanced hPSCs proliferation

The generation of human organs in animals through blastocyst complementation offers a promising solution to the shortage of transplantable organs. While human pluripotent stem cells (hPSCs) can contribute to interspecies chimaeric embryos when injected into preimplantation embryos of mice, pigs, or monkeys, their integration is often limited due to low chimaerism and segregation from host tissues, significantly impeding progress toward exogenic organ generation. Here, we demonstrate that co-overexpression of the anti-apoptotic gene BCL2 and the proto-oncogene MYCL, along with various cell cycle regulators significantly enhances human cell chimaerism by promoting cell proliferation. This strategy facilitates the generation of viable mouse pups containing hPSC-derived tissues without tumorigenesis. scRNA-seq analysis revealed that hPSCs already exit pluripotent by early post-implantation stage yet hPSCs with enhanced proliferation were able to integrate effectively into the cardiomyocytes and vasculature of both embryonic and extraembryonic tissues with gene expression profiles reflecting their structural integration. These findings highlight the critical role of cell cycle regulation in overcoming xenogeneic barriers. Our findings offer new insights into strategies for enhancing interspecies organogenesis and advancing the field of regenerative medicine. HighlightO_LIEnhancing hPSC proliferation increases human cell contribution in interspecies chimaeras C_LIO_LIAchieving the generation of viable human-mouse chimaeras without tumour formation C_LIO_LIhPSCs in post-implantation mouse epiblast exit pluripotency but retain the capacity to integrate into mouse embryogenesis C_LIO_LIhPSCs derivatives integrate into vasculature and cardiac tissues with lineage-matched transcriptional profiles C_LI

developmental biology↗

bioRxiv2023

Heart generation via blastocyst complementation in Mesp1/2-deficient mice

Heart transplantation is the only curative option available for patients with advanced heart failure. However, donor organ shortage and graft rejection remain critical challenges in heart transplantation. Blastocyst complementation using pluripotent stem cells (PSCs) can be used to generate organs such as the pancreas and kidneys in animal models with abnormalities in essential developmental genes. Nonetheless, whether functional adult hearts can be generated with blastocyst complementation remains unclear, and it is unknown if parenchyma, blood vessels, and stroma can be generated concomitantly from PSCs using blastocyst complementation to avoid graft rejection. Here, we show the generation of functional adult hearts in acardiac Mesp1 and Mesp2 double-knockout (Mesp1/2-DKO) mice via blastocyst complementation using mouse PSCs. Our result shows that the generated hearts were structurally and functionally normal and restored embryonic lethality in Mesp1/2-DKO mice. All four cardiovascular lineages, including cardiomyocytes, vascular endothelial cells, smooth muscle cells, and cardiac fibroblasts, were virtually entirely derived from exogenous PSCs in the myocardium. Exogenous rat PSCs also generated rat-derived xenogeneic hearts in Mesp1/2-DKO mice via interspecies blastocyst complementation. Thus, blastocyst complementation is a viable technique for generating hearts derived from PSCs and may represent significant progress toward generating rejection-free hearts.

cell biology↗

bioRxiv2023

Relationship Between Domain and Function of the Yeast RNase T2, Rny1p, Which Mediates rRNA Degradation upon Starvation

RNase T2 is ubiquitous across diverse organisms, playing essential roles despite its simple enzymatic activity. In Saccharomyces cerevisiae, RNase T2, known as Rny1p, localizes in vacuoles and mediates rRNA degradation during autophagy of ribosomes. In this study, we elucidated novel aspects of ribosome degradation mechanisms and the function of Rny1p. First, we discovered that most ribosomes are degraded by selective autophagy, where Rsa1p is the specific receptor of ribosomes to be degraded. Complex structure prediction suggested that Rsa1p also interacts with Atg8p. Furthermore, we observed that the accumulation of rRNA in vacuoles, due to the lack of Rny1p, leads to a decrease in bulk autophagic activity. This decrease in autophagic activity may explain the inability of Rny1p-deficient strains to adapt to starvation conditions. Second, our structural prediction and biochemical analyses indicate that a C-terminal extension, characteristic in fungal RNase T2 including Rny1p, is not necessary for rRNA degradation but for anchoring to the cell wall. Together with molecular phylogenetic analysis, a species-specific role of RNase T2 conferred by the C-terminal extension is suggested.

molecular biology↗

bioRxiv2021

Nasal delivery of single-domain antibodies improve symptoms of SARS-CoV-2 infection in an animal model

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the disease COVID-19 can lead to serious symptoms, such as severe pneumonia, in the elderly and those with underlying medical conditions. While vaccines are now available, they do not work for everyone and therapeutic drugs are still needed particularly for treating life-threatening conditions. Here, we showed nasal delivery of a new, unmodified camelid single-domain antibody (VHH), termed K-874A, effectively inhibited SARS-CoV-2 titers in infected lungs of Syrian hamsters without causing weight loss and cytokine induction. In vitro studies demonstrated that K-874A neutralized SARS-CoV-2 in both VeroE6/TMPRSS2 and human lung-derived alveolar organoid cells. Unlike other drug candidates, K-874A blocks viral membrane fusion rather than viral attachment. Cryo-electron microscopy revealed K-874A bound between the receptor binding domain and N-terminal domain of the virus S protein. Further, infected cells treated with K-874A produced fewer virus progeny that were less infective. We propose that direct administration of K-874A to the lung via a nebulizer could be a new treatment for preventing the reinfection of amplified virus in COVID-19 patients. Author summaryVaccines for COVID-19 are now available but therapeutic drugs are still needed to treat life-threatening cases and those who cannot be vaccinated. We discovered a new heavy-chain single-domain antibody that can effectively neutralize the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes COVID-19. Unlike other drug candidates, which prevent the virus from attaching to the receptor on the host cell, this new antibody acts by blocking the virus membrane from fusing with the host cell membrane. We studied the behavior of the new antibody in vitro using VeroE6/TMPRSS2 cells and human lung organoids. When delivered through the nose to infected Syrian hamsters, we found that this antibody could prevent the typical symptoms caused by SARS-CoV-2. Our results are significant because delivering simple drugs directly to infected lungs using a nebulizer could increase the potency of the drugs while reducing the risk of immune reaction that could occur if the drugs escape or are delivered through the blood stream.

microbiology↗

bioRxiv2017

Transcriptomes and Raman spectra are linked linearly through a shared low-dimensional subspace

Raman spectroscopy is an imaging technique that can reflect whole-cell molecular compositions in vivo, and has been applied recently in cell biology to characterize different cell types and states. However, due to the complex molecular compositions and spectral overlaps, the interpretation of cellular Raman spectra have remained unclear. In this report, we compared cellular Raman spectra to transcriptomes of Schizosaccharomyces pombe and Escherichia coli, and provide firm evidence that they can be computationally connected and interpreted. Specifically, we find that the dimensions of high-dimensional Raman spectra and transcriptomes measured by RNA-seq can be effectively reduced and connected linearly through a shared low-dimensional subspace. Accordingly, we were able to reconstruct global gene expression profiles by applying the calculated transformation matrix to Raman spectra, and vice versa. Strikingly, highly expressed ncRNAs contributed to the Raman-transcriptome linear correspondence more significantly than mRNAs in S. pombe, which implies their major role in coordinating molecular compositions. This compatibility between whole-cell Raman spectra and transcriptomes marks an important and promising step towards establishing spectroscopic live-cell omics studies.

systems biology↗

bioRxiv2017

Establishment In Culture Of Expanded Potential Stem Cells

Mouse embryonic stem cells are derived from in vitro explantation of blastocyst epiblasts1,2 and contribute to both the somatic lineage and germline when returned to the blastocyst3 but are normally excluded from the trophoblast lineage and primitive endoderm4-6. Here, we report that cultures of expanded potential stem cells (EPSCs) can be established from individual blastomeres, by direct conversion of mouse embryonic stem cells (ESCs) and by genetically reprogramming somatic cells. Remarkably, a single EPSC contributes to the embryo proper and placenta trophoblasts in chimeras. Critically, culturing EPSCs in a trophoblast stem cell (TSC) culture condition permits direct establishment of TSC lines without genetic modification. Molecular analyses including single cell RNA-seq reveal that EPSCs share cardinal pluripotency features with ESCs but have an enriched blastomere transcriptomic signature and a dynamic DNA methylome. These proof-of-concept results open up the possibility of establishing cultures of similar stem cells in other mammalian species.

developmental biology↗