Biology subjects

Karasawa, T.

Publications and source records attributed to Karasawa, T..

9 recordsLinked to original sources

bioRxiv2026

Inflammasome activation drives gasdermin-independent plasma membrane rupture by clustering ninjurin-1 in macrophages

Inflammasome assembly rapidly triggers caspase-1 activation to initiate pyroptosis, an inflammatory cell death characterized by the release of cytosolic contents, including interleukin (IL)-1{beta}/. Here, we report that inflammasome activation drives necrotic cell death independent of gasdermin D (GSDMD) and GSDME, which are essential executors of pyroptosis by forming a pore on the plasma membrane and increasing membrane permeability. NLRP3 inflammasome activation induced necrotic cell death, coupled with IL-1{beta}/ release in Gsdmd-/-Gsdme-/- macrophages. Mechanistically, the oligomerization of ninjurin-1 (NINJ1) was caused by inflammasome activation even in the absence of GSDMD and GSDME. Concordantly, glycine, an inhibitor of NINJ1, blocked plasma membrane permeabilization triggered by inflammasome activation in Gsdmd-/-Gsdme-/- macrophages, but not in WT macrophages. The dimerizer-mediated ASC oligomerization promoted NINJ1-mNeonGreen cluster formation in the absence of GSDMD and GSDME. Moreover, NINJ1 deficiency prevented membrane permeabilization initiated by ASC oligomerization in Gsdmd-/-Gsdme-/- immortalized bone marrow-derived macrophages (iBMDM). Blocking of phosphatidylserine (PtdSer) exposure, a feature of inflammasome-driven necrotic cell death, by Xkr8 deficiency inhibited plasma membrane permeabilization in Gsdmd-/-Gsdme-/- iBMDM. These results suggest that inflammasome-triggered activation of caspase-1 itself drives inflammatory necrotic cell death independent of gasdermins.

cell biology↗

bioRxiv2026

Females are protected from semaglutide-induced muscle loss in ob/ob mice

Obesity is a major contributor to cardiometabolic disease, and pharmacological therapies such as semaglutide are increasingly used to induce weight loss. However, the commonly used diet-induced obesity model in C57BL/6J mice is limited by relative resistance to weight gain in females, complicating the study of sex-specific effects. Here, we used leptin-deficient ob/ob mice, which develop severe early-onset obesity in both sexes, to investigate sex-specific responses to semaglutide on skeletal muscle mass, function, and mitochondrial metabolism. The ob/ob mice were treated daily with semaglutide or vehicle for three weeks, followed by assessments of body composition, muscle and organ mass, muscle contractile function, and mitochondrial efficiency. Semaglutide induced comparable reductions in body weight and food intake in both sexes but elicited distinct sex-specific changes in body composition. Male mice exhibited losses in both skeletal muscle and organ mass, whereas female mice preferentially lost fat and organ mass while preserving skeletal muscle. Despite these divergent structural adaptations, muscle force generation remained intact in both sexes. Collectively, these findings reveal pronounced sexual dimorphism in skeletal muscle and metabolic remodeling during pharmacologically induced weight loss, highlighting the importance of considering biological sex when evaluating the metabolic and therapeutic effects of anti-obesity interventions. Article HighlightO_LIC57BL/6J mice are limited by relative resistance to weight gain in females, complicating the study of sex-specific effects. So, we wanted to determine the sex-specific effect of semaglutide on skeletal muscle function, and mitochondrial metabolism in ob/ob mice. C_LIO_LIWe assessed body composition and ex-vivo muscle force following the treatment and found that the female ob/ob mice are protected from semaglutide-induced skeletal muscle mass loss. C_LIO_LIThese findings demonstrate sex-specific effects of semaglutide, highlighting the need to consider biological sex in GLP-1RA-based therapies. C_LI

physiology↗

bioRxiv2025

N-acetylcarnosine attenuates age-associated declines in multi-organ systems to improve survival

Histidine containing dipeptides (HCDs) such as N-acetylcarnosine are endogenous metabolites that are ergogenic and mitigate metabolic dysfunction. We previously demonstrated that short-term N-acetylcarnosine treatment is highly efficacious in protecting muscle atrophy induced by disuse. Here we demonstrate that a 6-months treatment of N-acetylcarnosine attenuates a broad spectrum of age-associated maladies and improved survival by [~]50% in female mice. A comprehensive survey of organ systems revealed that N-acetylcarnosine prevents decline in adiposity, diastolic function, vasodilation, muscle strength, and bone density. Together, N-acetylcarnosine substantially delays the onset of system-wide end-stage pathology to prolong lifespan. As an endogenously present metabolite, treatment with N-acetylcarnosine may be a safe and promising intervention to promote healthy aging in humans.

physiology↗

bioRxiv2024

Semaglutide-induced weight loss improves mitochondrial energy efficiency in skeletal muscle

ObjectiveGlucagon-like peptide 1 receptor agonists (e.g. semaglutide) potently induce weight loss and thereby reducing obesity-related complications. However, weight regain occurs when treatment is discontinued. An increase in skeletal muscle oxidative phosphorylation (OXPHOS) efficiency upon diet-mediated weight loss has been described, which may contribute to reduced systemic energy expenditure and weight regain. We set out to determine the unknown effect of semaglutide on muscle OXPHOS efficiency. MethodsC57BL/6J mice were fed a high-fat diet for 12 weeks before receiving semaglutide or vehicle for 1 or 3 weeks. The rate of ATP production and O2 consumption were measured by a high-resolution respirometry and fluorometry to determine OXPHOS efficiency in skeletal muscle at these 2 timepoints. ResultsSemaglutide treatment led to significant reductions in fat and lean mass. Semaglutide improved skeletal muscle OXPHOS efficiency, measured as ATP produced per O2 consumed (P/O) in permeabilized muscle fibers. Mitochondrial proteomic analysis revealed changes restricted to two proteins linked to complex III assembly (Lyrm7 and Ttc1, p <0.05 without multiple corrections) without substantial changes in the abundance of OXPHOS subunits. ConclusionsThese data indicate that weight loss with semaglutide treatment increases skeletal muscle mitochondrial efficiency. Future studies could test whether it contributes to weight regain.

physiology↗

bioRxiv2024

Muscle-specific Keap1 deletion enhances force production but does not prevent inactivity-induced muscle atrophy in mice

Immobilization-associated muscle atrophy and weakness appear to be driven in part by oxidative stress. Nuclear Factor Erythroid 2-Related Factor 2 (NRF2) is a critical redox rheostat that regulates oxidative stress responses, and its deletion is known to accelerate muscle atrophy and weakness during aging (sarcopenia) or denervation. Conversely, pharmacologic activation of NRF2 extends mouse lifespan and attenuates sarcopenia. Similarly, deletion of Kelch-like ECH-associated Protein 1 (Keap1), negative regulator of NRF2, enhances exercise capacity. The purpose of this study was to determine whether muscle-specific Keap1 deletion is sufficient to prevent muscle atrophy and weakness in mice following 7-days of hindlimb unloading (HU). To test this hypothesis, control (Ctrl) and tamoxifen inducible, muscle-specific Keap1 knockout (mKO) mice were subjected to either normal housing (Sham) or HU for 7 days. Activation of NRF2 in muscle was confirmed by increased mRNA of NRF2 targets thioredoxin 1 (Txn1) and NAD(P)H quinone dehydrogenase 1 (NQO1) in mKO mice. Keap1 deletion had an effect to increase force-generating capacity at baseline. However, muscle masses, cross sectional area, and ex vivo force were not different between mKO and Ctrl HU mice. In addition, muscle 4-hydroxynonenal-modified proteins and protein carbonyls were unaffected by Keap1 deletion. These data suggest NRF2 activation improves muscle force production during ambulatory conditions but is not sufficient prevent muscle atrophy or weakness following 7-days of HU. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=95 SRC="FIGDIR/small/616570v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@433d1eorg.highwire.dtl.DTLVardef@61996dorg.highwire.dtl.DTLVardef@19fe734org.highwire.dtl.DTLVardef@104205f_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2024

Skeletal muscle PGC-1α remodels mitochondrial phospholipidome but does not alter energy efficiency for ATP synthesis

BackgroundExercise training is thought to improve the mitochondrial energy efficiency of skeletal muscle. Some studies suggest exercise training increases the efficiency for ATP synthesis by oxidative phosphorylation (OXPHOS), but the molecular mechanisms are unclear. We have previously shown that exercise remodels the lipid composition of mitochondrial membranes, and some of these changes could contribute to improved OXPHOS efficiency (ATP produced by O2 consumed or P/O). Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1) is a transcriptional co-activator that coordinately regulates exercise-induced adaptations including mitochondria. We hypothesized that increased PGC-1 activity is sufficient to remodel mitochondrial membrane lipids and promote energy efficiency. MethodsMice with skeletal muscle-specific overexpression of PGC-1 (MCK-PGC-1) and their wildtype littermates were used for this study. Lipid mass spectrometry and quantitative PCR were used to assess muscle mitochondrial lipid composition and their biosynthesis pathway. The abundance of OXPHOS enzymes was determined by western blot assay. High-resolution respirometry and fluorometry analysis were used to characterize mitochondrial bioenergetics (ATP production, O2 consumption, and P/O) for permeabilized fibers and isolated mitochondria. ResultsLipidomic analyses of skeletal muscle mitochondria from wildtype and MCK-PGC-1 mice revealed that PGC-1 increases the concentrations of cone-shaped lipids such as phosphatidylethanolamine (PE), cardiolipin (CL), and lysophospholipids, while decreases the concentrations of phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidic acid (PA). However, while PGC-1 overexpression increased the abundance of OXPHOS enzymes in skeletal muscle and the rate of O2 consumption (JO2), P/O values were unaffected with PGC-1 in permeabilized fibers or isolated mitochondria. ConclusionsCollectively, overexpression of PGC-1 promotes the biosynthesis of mitochondrial PE and CL but neither PGC-1 nor the mitochondrial membrane lipid remodeling induced in MCK-PGC-1 mice is sufficient to increase the efficiency for mitochondrial ATP synthesis. These findings suggest that exercise training may increase OXPHOS efficiency by a PGC-1-independent mechanism, and question the hypothesis that mitochondrial lipids directly affect OXPHOS enzymes to improve efficiency for ATP synthesis.

physiology↗

bioRxiv2023

Cis-regulatory evolution that caused change in wingless expression pattern associated with wing pigmentation pattern of Drosophila

Genetic mechanisms underlying the acquisition of new traits are an important topic in evolutionary developmental biology. Especially, the co-option of important regulatory genes potentially plays an important role in the gain of new traits. However, how the co-option occurs at the sequence level is still elusive. Drosophila guttifera has a unique wing pigmentation pattern and this is newly gained via the evolution of the expression pattern of wingless, which induces the pigmentation pattern formation. In this study, to reveal the changes in the cis-regulatory sequence which caused the co-option of wingless that lead to the expression in a new place, we conducted transgenic EGFP reporter assays of altered cis-regulatory sequences. As a result, the sequence was divided into regions needed to activate expression in the entire wing veins and a region required for repressing expression in excess parts. Comparisons with the homologous sequence of Drosophila melanogaster showed that the repressive function of the cis-regulatory region is also possessed by D. melanogaster while the activating function is newly gained in a lineage leading to D. guttifera. Furthermore, a putative binding site of SMAD transcription factors is shown to be essential for activating expression but also existing in the homologous region of D. melanogaster. Our results suggest that the pre-existing regulatory sequences in the cis-regulatory region coordinate with the newly gained sequences to acquire the new expression pattern of wingless. Graphical Abstract O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

developmental biology↗

bioRxiv2022

DHCR7 as a novel regulator of ferroptosis in hepatocytes

Recent evidence indicates that ferroptosis is implicated in the pathophysiology of various liver diseases; however, the mechanism of ferroptosis regulation in the liver is poorly understood. Here, using the whole-genome screening approach, we identified 7-dehydrocholesterol reductase (DHCR7), the terminal enzyme of cholesterol biosynthesis, as a novel regulator of ferroptosis in hepatocytes. Genetic and pharmacological inhibition (with AY9944) of DHCR7 suppressed lipid peroxidation and ferroptosis in human hepatocellular carcinoma Huh-7 cells. DHCR7 inhibition increased its substrate, 7-dehydrocholesterol (7-DHC), and extrinsic 7-DHC supplementation in turn suppressed ferroptosis. On the other hand, cholesterol deprivation had no effect on ferroptosis. A 7-DHC-derived oxysterol metabolite, 3{beta},5-dihydroxycholest-7-en-6-one (DHCEO), was increased by a ferroptosis inducer RSL-3 in DHCR7-deficient cells, suggesting that the ferroptosis-suppressive effect of DHCR7 inhibition was driven by intracellular 7-DHC as a radical scavenger. While extrinsic 7-DHC supplementation suppressed ferroptosis in various cancer cells, pharmacological DHCR7 inhibition by AY9944 showed cell-type specific effects, which could be explained by high DHCR7 expression in Huh-7 cells. We further showed that AY9944 suppressed ferroptosis in murine primary hepatocytes in vitro and systemic administration of AY9944 inhibited hepatic ischemia-reperfusion injury in vivo. These findings provide new insights into the regulatory mechanism of liver ferroptosis and suggest that DHCR7 inhibition is a potential therapeutic option for ferroptosis-related liver diseases.

molecular biology↗

bioRxiv2021

Cryo-sensitive aggregation triggers NLRP3 inflammasome assemblyin cryopyrin-associated periodic syndrome

Cryopyrin-associated periodic syndrome (CAPS) is an autoinflammatory syndrome caused by mutations of NLRP3, which was originally identified as cryopyrin. Familial cold autoinflammatory syndrome (FCAS), the mildest form of CAPS, is characterized by cold-induced inflammation induced by the overproduction of IL-1{beta}. However, the molecular mechanism of how mutated NLRP3 causes inflammasome activation in CAPS remains unclear. Here, we found that CAPS-associated NLRP3 mutants form cryo-sensitive aggregates that function as a scaffold for inflammasome activation. Cold exposure promoted inflammasome assembly and subsequent IL-1{beta} release triggered by mutated NLRP3. While K+ efflux was dispensable, Ca2+ was indispensable for mutated NLRP3-mediated inflammasome assembly. Notably, Ca2+ influx was induced during mutated NLRP3-mediated inflammasome assembly. Furthermore, caspase-1 inhibition prevented Ca2+ influx and inflammasome assembly induced by the mutated NLRP3, suggesting a feed-forward Ca2+ influx loop triggered by mutated NLRP3. Thus, the mutated NLRP3 forms cryo-sensitive aggregates to promote inflammasome assembly distinct from canonical NLRP3 inflammasome activation.

immunology↗