A Dynamic Stochastic Model of Frequency-Dependent Stress Fiber Alignment Induced by Cyclic Stretch

BACKGROUND: Actin stress fibers (SFs) are mechanosensitive structural elements that respond to forces to affect cell morphology, migration, signal transduction and cell function. Cells are internally stressed so that SFs are extended beyond their unloaded lengths, and SFs tend to self-adjust to an equilibrium level of extension. While there is much evidence that cells reorganize their SFs in response to matrix deformations, it is unclear how cells and their SFs determine their specific response to particular spatiotemporal changes in the matrix. METHODOLOGY/PRINCIPAL FINDINGS: Bovine aortic endothelial cells were subjected to cyclic uniaxial stretch over a range of frequencies to quantify the rate and extent of stress fiber alignment. At a frequency of 1 Hz, SFs predominantly oriented perpendicular to stretch, while at 0.1 Hz the extent of SF alignment was markedly reduced and at 0.01 Hz there was no alignment at all. The results were interpreted using a simple kinematic model of SF networks in which the dynamic response depended on the rates of matrix stretching, SF turnover, and SF self-adjustment of extension. For these cells, the model predicted a threshold frequency of 0.01 Hz below which SFs no longer respond to matrix stretch, and a saturation frequency of 1 Hz above which no additional SF alignment would occur. The model also accurately described the dependence of SF alignment on matrix stretch magnitude. CONCLUSIONS: The dynamic stochastic model was capable of describing SF reorganization in response to diverse temporal and spatial patterns of stretch. The model predicted that at high frequencies, SFs preferentially disassembled in the direction of stretch and achieved a new equilibrium by accumulating in the direction of lowest stretch. At low stretch frequencies, SFs self-adjusted to dissipate the effects of matrix stretch. Thus, SF turnover and self-adjustment are each important mechanisms that cells use to maintain mechanical homeostasis

Stretch-Induced Stress Fiber Remodeling and the Activations of JNK and ERK Depend on Mechanical Strain Rate, but Not FAK

BACKGROUND: Cells within tissues are subjected to mechanical forces caused by extracellular matrix deformation. Cells sense and dynamically respond to stretching of the matrix by reorienting their actin stress fibers and by activating intracellular signaling proteins, including focal adhesion kinase (FAK) and the mitogen-activated proteins kinases (MAPKs). Theoretical analyses predict that stress fibers can relax perturbations in tension depending on the rate of matrix strain. Thus, we hypothesized stress fiber organization and MAPK activities are altered to an extent dependent on stretch frequency. PRINCIPAL FINDINGS: Bovine aortic endothelial cells and human osteosarcoma cells expressing GFP-actin were cultured on elastic membranes and subjected to various patterns of stretch. Cyclic stretching resulted in strain rate-dependent increases in stress fiber alignment, cell retraction, and the phosphorylation of the MAPKs JNK, ERK and p38. Transient step changes in strain rate caused proportional transient changes in the levels of JNK and ERK phosphorylations without affecting stress fiber organization. Disrupting stress fiber contractile function with cytochalasin D or Y27632 decreased the levels of JNK and ERK phosphorylation. Previous studies indicate that FAK is required for stretch-induced cell alignment and MAPK activations. However, cyclic uniaxial stretching induced stress fiber alignment and the phosphorylation of JNK, ERK and p38 to comparable levels in FAK-null and FAK-expressing mouse embryonic fibroblasts. CONCLUSIONS: These results indicate that cyclic stretch-induced stress fiber alignment, cell retraction, and MAPK activations occur as a consequence of perturbations in fiber strain. These findings thus shed new light into the roles of stress fiber relaxation and reorganization in maintenance of tensional homeostasis in a dynamic mechanical environment

In Silico Searching for Alternative Lead Compounds to Treat Type 2 Diabetes through a QSAR and Molecular Dynamics Study

Free fatty acid receptor 1 (FFA1) stimulates insulin secretion in pancreatic β-cells. An advantage of therapies that target FFA1 is their reduced risk of hypoglycemia relative to common type 2 diabetes treatments. In this work, quantitative structure–activity relationship (QSAR) approach was used to construct models to identify possible FFA1 agonists by applying four different machine-learning algorithms. The best model (M2) meets the Tropsha’s test requirements and has the statistics parameters R2 = 0.843, Q2CV = 0.785, and Q2ext = 0.855. Also, coverage of 100% of the test set based on the applicability domain analysis was obtained. Furthermore, a deep analysis based on the ADME predictions, molecular docking, and molecular dynamics simulations was performed. The lipophilicity and the residue interactions were used as relevant criteria for selecting a candidate from the screening of the DiaNat and DrugBank databases. Finally, the FDA-approved drugs bilastine, bromfenac, and fenofibric acid are suggested as potential and lead FFA1 agonists

International Social Survey Programme: Work Orientations IV - ISSP 2015

Attitude towards work. Work orientation. Conflict and social exclusion. Subjective experience of job. Work satisfaction. Non-standard employment. Work life balance. Job and working flexibility. Human capital. Outcome of work. Employability, new job. Topics: work centrality (a job is just a way of earning money vs. would enjoy having a paid job even if the money is not needed); importance of selected demands of a job like job security, high income, etc. (work values); work life balance: willingness to give up good job opportunities for the benefit of the family; willingness to remain in a job that is not satisfying for the benefit of the family; conflict and social exclusion: experience of discrimination with regard to work, for instance when applying for a job; main reason for the discrimination; experience of harassment at the workplace by superiors or co-workers (for example bullying, physical or psychological abuse); solidarity and conflict with regard to trade unions (workers need strong trade unions to protect their interests vs. strong trade unions are bad for the country´s economy); preferred employment arrangements (full-time, part-time, less than 10 hours a week, no paid job at all); currently working for pay (employment status); preference for more work (and money) or for reduction in working hours (work longer hours and earn more money, work the same number of hours and earn the same money, or work fewer hours and earn less money); characteristics (social dimension) of own job; subjective experience of job: frequency of hard physical work and stressful work; non-standard employment: frequency of working at home during the usual working hours and working on weekends; job and working flexibility concerning starting and finishing times; non-standard employment: usual working schedule in the main job; job and working flexibility: organisation of daily work (free decision, decision within certain limits, no free decision); work life balance: difficult to take an hour off during working hours to take care of personal or family matters; demands of the job interfere with the family life and the demands of family life interfere with the job; human capital: usefulness of the abilities learned from past work experience for the present job; job training over the past twelve months to improve job skills; judgement on the relations between management and employees and the relations between workmates/ colleagues (working atmosphere); outcome of work: work satisfaction in the main job; identification with firm or organisation; occupational commitment (would change the present type of work for something different, proud of the present type of work); employability/ new job: expected difficulties in finding a new job at least as good as the current one; likeliness of job search in the next twelve months; worried about the possibility of losing own job; job and working flexibility: accepted concessions to avoid unemployment (acceptance of a job that requires new skills, acceptance of a lower paid position, acceptance of temporary employment, longer travel to reach the place of work, movement within the country, movement to a different country); existence of a side job in addition to the main job; earning from the additional job(s) in total compared with the main job. Respondents who are not currently employed were asked: ever worked for pay for one year or more; month and year the last paid job ended; work satisfaction in the last job; main reason for the end of last employment; interest in finding a paid job; expected difficulties in finding a new job; worried about the possibility of not finding a job; accepted concessions in order to get a job (acceptance of a job that requires new skills, acceptance of a lower paid position, acceptance of temporary employment, longer travel to reach the place of work, movement within the country, movement to a different country); job seeking activities in the past twelve months and training to improve own job skills; currently looking for a job; main source of economic support; worried about the possibility of losing this main economic support. Optional items: recent work histories: ever worked for pay over the past five years; experience of selected changes in working life (unemployment for a period longer than three months, change of the employer, change of the occupation, started own business/ became self-employed, took up an additional job); self-assessment of current financial situation; change of current financial situation compared to five years ago; expected financial situation in five years; attitude towards senior citizens´ work (good for the country´s economy, employed people aged 60 and over take jobs away from younger people). Optional background variable: self-assessment of physical and mental health. Additional compulsory background variable: age of the youngest child in the household. Demography: sex; age; year of birth; years in school; education (country specific); highest completed degree; work status; hours worked weekly; employment relationship; number of employees; supervision of employees; number of supervised employees; type of organisation: for-profit vs. non profit and public vs. private; occupation (ISCO-08); main employment status; living in steady partnership; union membership; religious affiliation or denomination (country specific); groups of religious denominations; attendance of religious services; top-bottom self-placement; vote in last general election; country specific party voted in last general election; party voted (left-right); self-assessed affiliation of ethnic group 1 and 2 (country specific); number of children; number of toddlers; size of household; earnings of respondent (country specific); family income (country specific); father´s and mother´s country of birth; marital status; place of living: urban – rural; region (country specific). Information about spouse/ partner on: work status; hours worked weekly; employment relationship; supervises other employees; occupation (ISCO-08); main employment status. Additionally encoded: respondent-ID number; date of interview (year, month, day); case substitution flag; mode of data collection; weight