Myosin-induced F-actin fragmentation facilitates contraction of actin networks.

Mechanical forces play a crucial role in diverse physiological processes, such as cell migration, cytokinesis, and morphogenesis. The actin cytoskeleton generates a large fraction of the mechanical forces via molecular interactions between actin filaments (F-actins) and myosin motors. Recent studies have shown that the common tendency of actomyosin networks to contract into a smaller structure deeply involves F-actin buckling induced by motor activities, fragmentation of F-actins, and the force-dependent unbinding of cross-linkers that inter-connect F-actins. The fragmentation of F-actins was shown to originate from either buckling or tensile force from previous single-molecule experiments. While the role of buckling in network contraction has been studied extensively, to date, the role of tension-induced F-actin fragmentation in network contraction has not been investigated. In this study, we employed in vitro experiments and an agent-based computational model to illuminate when and how the tension-induced F-actin fragmentation facilitates network contraction. Our experiments demonstrated that F-actins can be fragmented due to tensile forces, immediately followed by catastrophic rupture and contraction of networks. Using the agent-based model, we showed that F-actin fragmentation by tension results in distinct rupture dynamics different from that observed in networks only with cross-linker unbinding. Moreover, we found that tension-induced F-actin fragmentation is particularly important for the contraction of networks with high connectivity. Results from our study shed light on an important regulator of the contraction of actomyosin networks which has been neglected. In addition, our results provide insights into the rupture mechanisms of polymeric network structures and bio-inspired materials.

Effect of temperature on actin filament corkscrewing driven by nonprocessive myosin IC.

Myosin family proteins are ATP-driven, actin filament-based motor proteins that generate force along actin filaments. In in vitro actin filament gliding assays, certain myosins generate rotation of gliding actin filaments around their long axes. In this study, we assessed the effects of temperature on the corkscrewing motion of actin filaments, including factors like gliding and rotational velocities and corkscrewing pitch. The corkscrewing motion was driven by a nonprocessive, full-length single-headed Drosophila myosin IC attached to an antibody adsorbed onto a cover glass. We performed an in vitro actin filament corkscrewing assay at temperatures ranging from 25 °C to 35 °C. We found that the gliding and rotational velocities and the pitch of corkscrewing actin filaments generated by myosin IC molecules increased with increasing temperature. Since the pitch is determined by dividing the gliding velocity by the rotational velocity, an increase in the pitch indicates that the gliding velocity increased faster than the rotational velocity with increasing temperature. These results suggest that temperature has distinct effects on the gliding and rotational forces produced by myosin IC, with implications for interpreting the temperature effect on torque-generation mechanisms driven by myosins on actin filaments at physiological temperatures.

Membrane-bound myosin IC drives the chiral rotation of the gliding actin filament around its longitudinal axis.

Myosin IC, a single-headed member of the myosin I family, specifically interacts with anionic phosphatidylinositol 4,5-bisphosphate (PI[4,5]P2) in the cell membrane via the pleckstrin homology domain located in the myosin IC tail. Myosin IC is widely expressed and physically links the cell membrane to the actin cytoskeleton; it plays various roles in membrane-associated physiological processes, including establishing cellular chirality, lipid transportation, and mechanosensing. In this study, we evaluated the motility of full-length myosin IC of Drosophila melanogaster via the three-dimensional tracking of quantum dots bound to actin filaments that glided over a membrane-bound myosin IC-coated surface. The results revealed that myosin IC drove a left-handed rotational motion in the gliding actin filament around its longitudinal axis, indicating that myosin IC generated a torque perpendicular to the gliding direction of the actin filament. The quantification of the rotational motion of actin filaments on fluid membranes containing different PI(4,5)P2 concentrations revealed that the rotational pitch was longer at lower PI(4,5)P2 concentrations. These results suggest that the torque generated by membrane-bound myosin IC molecules can be modulated based on the phospholipid composition of the cell membrane.

The importance of psychosocial support in youth dilated cardiomyopathy patient who underwent cardiac rehabilitation.

Poor health-related quality of life (HR-QOL) and anxiety status in younger patients living with heart failure and dilated cardiomyopathy (DCM) may be caused by the illness itself or the numerous life events that traditionally occur earlier in life, such as establishing a career, meaningful relationships, family, and financial security. The present case involved a 26-year-old man diagnosed with DCM who participated in an outpatient cardiac rehabilitation (CR) program once a week. No cardiovascular events were observed during CR. At follow-up after 12 months, exercise tolerance improved from 18.4 to 24.9 mL/kg/min. Regarding HR-QOL, the Short-Form Health Survey showed that only general health, social function, and physical component summary were improved during follow-up. However, other components showed no significant increasing trend. The State-Trait Anxiety Inventory showed a better improvement in trait anxiety (from 59 to 54 points) than state anxiety (from 46 to 45 points). For young patients with DCM, it is crucial to consider not only physical status but also psychosocial status even with improved exercise tolerance. Learning objective: Younger adults with dilated cardiomyopathy (DCM) had strikingly worse health-related quality of life with both the emotional and physical components of the scale. Beyond physical symptoms alone, living with heart failure and DCM at a younger age negatively impacts role fulfillment, autonomy, perception, and psychological well-being. Cardiac rehabilitation (CR) comprised medical evaluation of patients, exercise therapy, education for secondary prevention, and support for psychosocial factors including counseling and cognitive-behavioral therapy. Therefore, early detection of the psychosocial problem and providing further support by participating in CR is important.

Nutritional Status in Patients Undergoing Phase II Cardiac Rehabilitation by Mini Nutritional Assessment.

Background: Malnutrition impairs quality of life and prognosis of patients with cardiovascular disease. The Mini Nutritional Assessment (MNA) is a screening tool developed for the nutritional assessment of older adults. However, usefulness of MNA for patients undergoing cardiac rehabilitation (CR) has not been fully investigated. Methods: From March 2017 to September 2019, the MNA-short form (MNA-SF) and the MNA total score in patients undergoing phase II CR at the Juntendo University Hospital were evaluated. Results: A total of 336 patients (mean age 70.1 ± 11.4 years; males: 209) were analyzed. In the MNA-SF, 157 patients (47%) were found to be malnourished or at risk of malnutrition. In MNA total score, 168 patients (50%) were found to be malnourished or at risk of malnutrition. The MNA-SF < 12 group had significantly lower body mass index (BMI), hemoglobin level, low MNA scores for protein/water intake, self-evaluation of nutrition and health, and upper arm and calf circumferences compared to the MNA-SF ≥ 12 group. Assuming BMI < 18.5 as malnutrition, the sensitivity and specificity for malnutrition were 100% and 58.9% for MNA-SF, and 96.9% and 54.9% for MNA total score, respectively. Conclusions: MNA is useful in screening for malnutrition in patients undergoing CR. Approximately 50% of them were determined to be malnourished or at risk of malnutrition, suggesting the need for detailed evaluation regarding their food intake and dietary intervention.

AFI Corp. PixeeMo™ for Enumeration of Aerobic Bacteria in Drinking Water: AOAC Performance Tested MethodSM 012002.

BACKGROUND: PixeeMo™ is a compact instrument that enables bacterial cell counting using microfluidic chips instead of counting of colonies on culture media. Chips containing electrodes, based on fluid, electric filtering and sorting technology (FES), allow the selection of bacterial cells from other components in the sample. In the United States (US), surface water or ground water affected by surface water must be treated to reduce the total microbial load to less than 500 CFU/mL. In Japan, drinking water regulations limit the total bacterial load to 100 CFU/mL. OBJECTIVE: To validate the PixeeMoTM aerobic bacteria method based on the Japanese regulation in the range of 30-300 CFU/mL in drinking water. METHOD: PixeeMoTM aerobic bacteria method was compared to the Standard Method for the Examination of Water and Wastewater (SMEWW) 9215B (2017) using naturally contaminated drinking water. RESULTS: The maximum repeatability standard deviation of the PixeeMoTM method was 14.8%. The difference of mean log10 values between the PixeeMoTM and SMEWW 9215B methods ranged from -0.015 to 0.258. Similar results were obtained in the independent laboratory study. CONCLUSIONS: The PixeeMoTM method is equivalent to that of the SMEWW 9215B methods. The product consistency and stability study demonstrated no significant difference within the expiration date. The robustness study confirmed that there was no effect within the expected range. The instrument variation study also demonstrated no significant difference among the data of three PixeeMoTM instruments. HIGHLIGHTS: Total counts of bacteria in drinking water can be determined accurately within 1 h with PixeeMoTM.