記述言語：英語   掲載種別：研究論文（学術雑誌）  

The contractile apparatus, stress fiber (SF), is connected to the cell adhesion machinery, focal adhesion (FA), at the termini of SF. The SF-FA complex is essential for various mechanical activities of cells, including cell adhesion to the extracellular matrix (ECM), ECM rigidity sensing, and cell migration. This mini-review highlights the importance of SF mechanics in these cellular activities. Actin-crosslinking proteins solidify SFs by attenuating myosin-driven flows of actin and myosin filaments within the SF. In the solidified SFs, viscous slippage between actin filaments in SFs and between the filaments and the surrounding cytosol is reduced, leading to efficient transmission of myosin-generated contractile force along the SFs. Hence, SF solidification via actin crosslinking ensures exertion of a large force to FAs, enabling FA maturation, ECM rigidity sensing and cell migration. We further discuss intracellular mechanisms for tuning crosslinker-modulated SF mechanics and the potential relationship between the aberrance of SF mechanics and pathology including cancer.

DOI： 10.3389/fcell.2024.1444827

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Contractile force generated in actomyosin stress fibers (SFs) is transmitted along SFs to the extracellular matrix (ECM), which contributes to cell migration and sensing of ECM rigidity. In this study, we show that efficient force transmission along SFs relies on actin crosslinking by α-actinin. Upon reduction of α-actinin-mediated crosslinks, the myosin II activity induced flows of actin filaments and myosin II along SFs, leading to a decrease in traction force exertion to ECM. The fluidized SFs maintained their cable integrity probably through enhanced actin polymerization throughout SFs. A computational modeling analysis suggested that lowering the density of actin crosslinks caused viscous slippage of actin filaments in SFs and, thereby, dissipated myosin-generated force transmitting along SFs. As a cellular scale outcome, α-actinin depletion attenuated the ECM-rigidity-dependent difference in cell migration speed, which suggested that α-actinin-modulated SF mechanics is involved in the cellular response to ECM rigidity.

DOI： 10.1016/j.isci.2023.106090

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Harmful health effects of exposure to low-frequency noise (LFN) defined as noise with frequencies at ≤100 Hz on the circulatory system have been a concern. However, there has been no study on the effects of exposure to LFN on the circulatory system with consideration of its frequencies and decibels. In this study, the effects of short-term exposure to broad-band LFNs and their pure-tone components (pure-tone LFNs) on cutaneous blood flow in the extremities including the hands were investigated. In our fieldwork study, we first sampled some kinds of common broad-band LFNs. Our human study then showed that broad-band LFN with a narrower frequency range more strongly increased cutaneous blood flow than did broad-band LFN with a wider frequency range. Pure-tone LFNs of 70-100 Hz at ≤85 dB(Z), but not pure-tone LFNs exceeding 100 Hz, further increased levels of cutaneous blood flow. Our wavelet-transform spectrum analysis of cutaneous blood flow next revealed that the nitric oxide (NO)-dependent and -independent vascular activities of the vascular endothelium were specifically increased by exposure to pure-tone LFN. Our animal study again indicated that exposure to pure-tone LFN increased cutaneous blood flow in mice with impairments of bilateral inner ears as well as cutaneous blood flow in control mice, suggesting a limited effect of inner ear function on the LFN-mediated increase in cutaneous blood flow. The NO-dependent suppressive effect of pure-tone LFN on cutaneous blood flow was confirmed by inhibition of vascular endothelial activity through intravenous injection of an NO inhibitor in wild-type mice. Taken together, the results of this study demonstrated that the vascular endothelium is a target tissue of LFN and that NO is an effector of the LFN-mediated increase in cutaneous blood flow. Since improvement of peripheral circulation could generally promote human health, short-term exposure to LFN may be beneficial for health.

DOI： 10.1016/j.scitotenv.2022.158828

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

The bacterial mechanosensitive channel, MscL, is activated by membrane tension, acting as a safety valve to prevent cell lysis against hypotonic challenge. It has been established that its activation threshold decreases with membrane thickness, while the underlying mechanism remains to be solved. We performed all-atom molecular dynamics (MD) simulations for the initial opening process of MscL embedded in four different types of lipid bilayers with different thicknesses: 1,2-dilauroyl- sn-glycero-3-phosphocholine (DLPC)), 1,2-dimyristoyl-glycero-3-phosphorylcholine (DMPC), 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC), and 1,2-distearoyl- sn-glycero-3-phosphocholine (DSPC). In response to membrane stretching, channel opening occurred only in the thinner membranes (DLPC and DMPC) in a thickness-dependent way. We found that the MscL opening was governed by the rate and degree of membrane thinning and that the channel opening was tightly associated with the tilting of transmembrane (TM) helices of MscL toward the membrane plane. Upon membrane stretching, the order parameter of acyl chains of thinner membranes (DLPC and DMPC) became smaller, whereas other thicker membranes (DPPC and DSPC) showed interdigitation with little changes in the order parameter. The decreased order parameter contributed much more to membrane thinning than did interdigitation. We conclude that the membrane-thickness-dependent MscL opening mainly arises from structural changes in MscL to match the altered membrane thickness by stretching.

DOI： 10.1021/acs.langmuir.8b02074

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

BACKGROUND: Fabry disease is an X-linked lysosomal storage disorder and shows globotriosylceramide (Gb3) accumulation in multiple organs, resulting from a deficiency of α-galactosidase. In patients with Fabry disease, cardiovascular disease occurs at an early age. Previous studies have shown that serum levels of high-density lipoprotein-cholesterol (HDL-C) increase in this disease, yet its clinical significance for cardiovascular disease remains unclear. Methods and Results: In order to determine why the serum HDL-cholesterol is high in various cardiovascular diseases of Fabry disease patients, we evaluated the serum lipid profiles, ocular vascular lesions, and levels of serum vascular endothelial growth factor (VEGF) and intercellular adhesion molecule-1 in 69 patients with Fabry disease diagnosed by genetic examination. The serum HDL-C/total cholesterol (T-Chol) ratio was significantly high, especially in male patients (41.5±1.7%) regardless of body mass index. Ocular vascular lesions were more likely to occur in female patients with a high HDL-C/T-Chol ratio compared with most male patients. Female patients with a high HDL-C/T-Chol ratio also presented a high serum VEGF level, suggesting that vascular endothelium dysfunction and arteriosclerotic changes progress more severely than in patients with a normal HDL-C/T-Chol ratio. In most patients, enzyme replacement therapy improved serum Gb3 and lyso-Gb3 levels, but these Gb3 and lyso-Gb3 still remained higher than in healthy controls, which appears to result in continuous vascular arteriosclerotic changes. CONCLUSIONS: We concluded that increased low-density lipoprotein-cholesterol uptake to the vascular wall caused by endothelial dysfunction is likely to contribute to the high HDL-C/T-Chol ratio observed in Fabry disease patients.

DOI： 10.1253/circj.CJ-18-0378

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