Biology subjects

Komatsu, H.

Publications and source records attributed to Komatsu, H..

8 recordsLinked to original sources

bioRxiv2026

Distinct viability and oxygen-sensing responses to hypoxia and reoxygenation in pancreatic islets

Early graft hypoxia limits the efficiency and success of islet transplantation. Defining the relationships among oxygen availability, exposure duration, islet survival, and oxygen sensing is therefore critical, but these relationships remain incompletely understood. We examined adult primary rat islets under continuous exposure to 1%, 5%, or 18% O2 for 48 or 96 h and under reoxygenation conditions comprising 48 h at 1% O2 followed by 48 h at 18% O2. We assessed islet size-dependent viability, morphology, mass recovery, estimated viable mass, and targeted hypoxia-responsive gene-expression signatures. Overall, 6,699 individual islets were analyzed. At 1% O2, viability decreased significantly, with most loss occurring within the first 48 h (93.0% at 0 h, 70.8% at 48 h, and 65.0% at 96 h). Overall viability remained largely preserved at 5% and 18% O2 (92.8 and 95.0% at 96h, respectively), although larger islets showed vulnerability at 5% O2. Exposure to 1% O2 caused deformation, particularly in larger islets, and reduced estimated viable mass compared with 5% and 18% O2. Reoxygenation did not fully restore viability or estimated viable mass (76.0% at 96h). Gene-expression analyses revealed sustained hypoxia-responsive signatures at both 1% and 5% O2, distinct from those at 18% O2. Reoxygenation shifted gene-expression profiles toward a normoxia-like signature. These findings suggest divergent viability and oxygen-sensing responses to hypoxia and reoxygenation. The 5% O2 condition may represent a marginal oxygen environment that preserves short-term overall survival despite sustained molecular responses to hypoxia. These data inform the oxygen targets and timing of early graft oxygenation strategies.

cell biology↗

bioRxiv2026

Oxygen-permeable microwell plates for high-throughput spheroid culture

Oxygen (O2) transport is a major limitation in high-density cell culture, particularly as three-dimensional (3D) spheroids are increasingly used to better mimic in vivo tissue environments. Here, we developed a poly(4-methyl-1-pentene) (PMP)-based microwell platform, leveraging its lower molecular absorption and greater mechanical stability than the commonly used O2-permeable polydimethylsiloxane (PDMS), while retaining high O2 permeability. We measured O2 permeability in 50-m-thick PMP membranes and found approximately 200-fold greater O2 permeability than the conventional 1-mm polystyrene culture-plate material. PMP membrane-based microwell plates with 350-m-diameter wells maintained spatial separation of pre-formed hepatocyte spheroids while supplying O2 from the plate bottom, synergistically enhancing spheroid oxygenation. Compared with non-O2-permeable plates, the platform reduced localized hypoxia and hypoxia-associated cell injury while improving spheroid viability and growth. Collectively, PMP-based O2-permeable microwell plates provide a promising, scalable, high-throughput platform for spheroid culture with multiple applications in tissue engineering, drug screening and beyond.

bioengineering↗

bioRxiv2026

Optimizing 3D Spheroid Formation in Microwells via a Simple Pluronic F127 Coating

Three-dimensional (3D) spheroid culture provides a physiologically relevant alternative to conventional two-dimensional culture, but reliable spheroid formation in microwells depends on limiting cell-substrate adhesion. Pluronic F127 is an amphiphilic triblock copolymer that forms a hydrated surface layer, reducing protein adsorption. Here, we evaluated whether this intrinsic anti-fouling property could restore an anti-adhesive surface in used microwell plates to promote spheroid formation. Using chondrogenic ATDC5 and pancreatic {beta}-cell INS-1 cells, we characterized spheroid assembly kinetics, F127 cytotoxicity, surface hydrophilicity, protein adsorption, and spheroid morphology including size and shape factor. Both cell types formed compact spheroids within 24 hours on commercial anti-adhesive microwells. F127 coating markedly reduced water contact angle and protein adsorption, confirming increased surface hydrophilicity and reduced protein fouling. In microwells stripped of their original surface coating, F127 coating amounts of approximately 0.011-0.045 mg/cm2 consistently promoted spheroid formation across both cell types. Soluble F127 concentrations were confirmed to be non-cytotoxic up to 0.625% (w/v), while even complete dissolution of the highest tested coating amount would correspond to only 0.025% (w/v) F127. This simple, reproducible, and low-cost surface-modification strategy may provide an accessible approach for re-functionalizing microwell platforms for 3D cell culture.

bioengineering↗

bioRxiv2025

Non-DNA-damaging DNA-PK activation improving hearing and prolonging life due to NAD+ and SIRT upregulation

Emerging evidence strongly supports a close relationship between age-related hearing loss and frailty, highlighting the importance of early detection and intervention. Recently, we invented a mitochondria-homing drug named mitochonic acid 5 (MA-5), that increases the adenosine triphosphate (ATP) levels, rescue mitochondrial function, and protect tissue damages. Currently, the phase I clinical trial has been finished in Japan (jRCT2031210495) and the phase 2 clinical trial has already been approved by PMDA. Here we show that MA-5 improved various types of hearing loss in mouse models. Structural chemical bioanalysis revealed that MA-5 is a mixture of equal amount of S- and R- enantiomer and both S- and R- enantiomer increase ATP by binding mitochondrial protein, mitofilin. However, S-enantiomer significantly increased the NAD+ levels by binding to the NAD+-producing key enzyme nicotinamide phosphoribosyltransferase (NAMPT). Moreover, the S-enantiomer increased the sirtuin 1 protein by suppressing polyubiquitination induced by tripartite motif containing 28 (TRIM28) phosphorylation which was triggered by DNA-dependent protein kinase (DNA-PK) activation in the absence of DNA damage. Transcriptomic signatures showed that the signature of MA-5 shows an inverse correlation with aging and mortality and is oriented in the same direction as the OSKM-related iPSCs, suggesting the modification of aging pathways. Oral administration of MA-5 to mitochondrial disease model mouse showed increased survival. Our findings suggest that, in addition to enhancing ATP levels, the coordinated regulation of NAD+ metabolism, SIRT protein expression, and DNA-PK activity-constituting a novel therapeutic triad may contribute to the amelioration of hearing impairment and mitochondrial dysfunction, thereby improving life prognosis.

cell biology↗

bioRxiv2023

Injectable microcapillary network hydrogels engineered by liquid-liquid phase separation for stem cell transplantation

Injectable hydrogels are promising carriers for cell delivery in regenerative medicine. However, injectable hydrogels composed of crosslinked polymer networks are often non porous and prevent biological communication with host tissues through signals, nutrients, oxygen, and cells, thereby limiting graft survival and tissue integration. Here we report injectable hydrogels with liquid-liquid phase separation-induced microcapillary networks ({micro}CN) as stem cell-delivering scaffolds. The molecular modification of gelatin with hydrogen bonding moieties induced liquid-liquid phase separation when mixed with unmodified gelatin to form {micro}CN structures in the hydrogels. Through spatiotemporally controlled covalent crosslinking and dissolution processes, porous {micro}CN structures were formed in the hydrogels, which can enhance mass transport and cellular activity. The encapsulation of cells with injectable {micro}CN hydrogels improved cellular adhesion, spreading, migration, and proliferation. Transplantation of mesenchymal stem cells with injectable {micro}CN hydrogels enhanced graft survival and recovered hindlimb ischemia by enhancing material-tissue communication with biological signals and cells through {micro}CN. This facile approach may serve as an advanced scaffold for improving stem cell transplantation therapies in regenerative medicine.

bioengineering↗

bioRxiv2023

Effect of microstimulation of the inferior temporal cortex on color judgment behavior

Within the anterior inferior temporal cortex (AIT) there is a cluster of color selective neurons whose activities correlate with color discrimination behavior. To examine the causal relationship between the activities of these neurons and behavior, we applied electrical microstimulation to modulate neuronal activities within the AIT. We trained monkeys to perform a color judgment task and evaluated the effect of microstimulation in terms of the horizontal shift of the psychometric function. We found large effects of microstimulation on color discrimination behavior, predominantly within a subregion of the AIT. The cortical extent where microstimulation modulated behavior correlated with the presence of color-selective neurons. Unexpectedly, the direction of the modulation of color judgment evoked by microstimulation correlated negatively with the preference of the neurons around the stimulation site. These results support the existence of an anterior inferior temporal color-selective area (AITC) and its causal relationship with the color perception of these animals.

neuroscience↗

bioRxiv2018

Computational model for human 3D shape perception from a single specular image

In natural conditions the human visual system can estimate the 3D shape of specular objects even from a single image. Although previous studies suggested that the orientation field plays a key role for 3D shape perception from specular reflections, its computational plausibility and possible mechanisms have not been investigated. In this study, to complement the orientation field information, we first add prior knowledge that objects are illuminated from above and utilize the vertical polarity of the intensity gradient. Then we construct an algorithm that incorporates these two image cues to estimate 3D shapes from a single specular image. We evaluated the algorithm with glossy and mirrored surfaces and found that 3D shapes can be recovered with a high correlation coefficient of around 0.8 with true surface shapes. Moreover, under a specific condition, the algorithms errors resembled those made by human observers. These findings show that the combination of the orientation field and the vertical polarity of the intensity gradient is computationally sufficient and probably reproduces essential representations used in human shape perception from specular reflections.

neuroscience↗

bioRxiv2017

Context-Dependent Attractor Dynamics in Visual Cortex

The capacity for flexible sensory-action association in animals has been related to context-dependent attractor dynamics outside the sensory cortices. Here we report a line of evidence that flexibly modulated attractor dynamics during task switching are already present in the higher visual cortex in macaque monkeys. With a nonlinear decoding approach, we can extract the particular aspect of the neural population response that reflects the task-induced emergence of bistable attractor dynamics in a neural population, which could be obscured by standard unsupervised dimensionality reductions such as PCA. The dynamical modulation selectively increases the information relevant to task demands, indicating that such modulation is beneficial for perceptual decisions. A computational model that features nonlinear recurrent interaction among neurons with a task-dependent background input replicates the key properties observed in the experimental data. These results suggest that the context-dependent attractor dynamics involving the sensory cortex can underlie flexible perceptual abilities.

neuroscience↗