Supramolecular polymer networks are non-covalently crosslinked soft materials that exhibit unique mechanical features such as self-healing, high toughness and stretchability. Previous studies have ...focused on optimizing such properties using fast-dissociative crosslinks (that is, for an aqueous system, dissociation rate constant k
> 10 s
). Herein, we describe non-covalent crosslinkers with slow, tuneable dissociation kinetics (k
< 1 s
) that enable high compressibility to supramolecular polymer networks. The resultant glass-like supramolecular networks have compressive strengths up to 100 MPa with no fracture, even when compressed at 93% strain over 12 cycles of compression and relaxation. Notably, these networks show a fast, room-temperature self-recovery (< 120 s), which may be useful for the design of high-performance soft materials. Retarding the dissociation kinetics of non-covalent crosslinks through structural control enables access of such glass-like supramolecular materials, holding substantial promise in applications including soft robotics, tissue engineering and wearable bioelectronics.
Purpose
– Although a substantial body of research has examined the effects of job characteristics on job attitudes, there is a paucity of work on individual difference moderators of these ...relationships. Based in selective optimization with compensation theory and socio-emotional selectivity theory, the purpose of this paper is to show that age moderated the relationship between task variety and two key job attitudes, job satisfaction and engagement.
Design/methodology/approach
– Data were collected through self-report questionnaires (n=152), using a time-lagged design with two waves (two to three weeks between T
1 and T
2).
Findings
– The authors found that task variety had a stronger relationship with job satisfaction and work engagement for younger workers compared to older workers.
Research limitations/implications
– Although there was good age variance in the sample, it had fewer late-career workers and more workers who are in their early and mid-career.
Practical implications
– To have workers of all ages satisfied and engaged at work, we need to understand which work characteristics are the best for them. For example, it may be a competitive gain for organizations to challenge younger workers with different tasks, and to challenge older workers in ways that utilize their experience.
Social implications
– The study addresses a societal issue related to profound demographic changes in the age composition of the workforce, gaining a better knowledge of differences between workers of different ages to promote effective interventions and policies.
Originality/value
– This is the first study to show that task variety differentially affects worker satisfaction and engagement depending on the age of the worker.
The diet and habitat of eight danionin species (Danio and Devario) from 18 sites in India and Thailand are reported. At every site, habitat characteristics, including pH, light penetration, water ...temperature, current speed, stream dimensions, canopy cover and substratum type, were recorded. Danionins were found primarily in warm (24–35° C), moving water of moderate clarity and pH (6·6–8·2) and there were significant differences among species in water temperature, pH and current speed. Deep‐bodied Devario species were generally associated with faster water currents than more slender‐bodied Danio species. Gut content analyses of 327 individuals representing 17 populations showed that insects were the primary food resource for the eight Danio and Devario species. Crustaceans, fish scales, algae and detritus were also important supplements for particular species. Stable isotope data from syntopic species indicated long‐term differences in consumption of terrestrial v. aquatic insects in one of two population pairs.
The mitochondrial phospholipid cardiolipin is required for optimal mitochondrial respiration. In this study, cardiolipin molecular species and cytochrome oxidase (COx) activity were studied in ...interfibrillar (IF) and subsarcolemmal (SSL) cardiac mitochondria from Spontaneously Hypertensive Heart Failure (SHHF) and Sprague-Dawley (SD) rats throughout their natural life span. Fisher Brown Norway (FBN) and young aortic-constricted SHHF rats were also studied to investigate cardiolipin alterations in aging versus pathology. Additionally, cardiolipin was analyzed in human hearts explanted from patients with dilated cardiomyopathy. A loss of tetralinoleoyl cardiolipin (L4CL), the predominant species in the healthy mammalian heart, occurred during the natural or accelerated development of heart failure in SHHF rats and humans. L4CL decreases correlated with reduced COx activity (no decrease in protein levels) in SHHF cardiac mitochondria, but with no change in citrate synthase (a matrix enzyme) activity. The fraction of cardiac cardiolipin containing L4CL became much lower with age in SHHF than in SD or FBN mitochondria. In summary, a progressive loss of cardiac L4CL, possibly attributable to decreased remodeling, occurs in response to chronic cardiac overload, but not aging alone, in both IF and SSL mitochondria. This may contribute to mitochondrial respiratory dysfunction during the pathogenesis of heart failure.
Abstract Small molecule histone deacetylase (HDAC) inhibitors block adverse cardiac remodeling in animal models of heart failure. The efficacious compounds target class I, class IIb and, to a lesser ...extent, class IIa HDACs. It is hypothesized that a selective inhibitor of a specific HDAC class (or an isoform within that class) will provide a favorable therapeutic window for the treatment of heart failure, although the optimal selectivity profile for such a compound remains unknown. Genetic studies have suggested that class I HDACs promote pathological cardiac remodeling, while class IIa HDACs are protective. In contrast, nothing is known about the function or regulation of class IIb HDACs in the heart. We developed assays to quantify catalytic activity of distinct HDAC classes in left and right ventricular cardiac tissue from animal models of hypertensive heart disease. Class I and IIa HDAC activity was elevated in some but not all diseased tissues. In contrast, catalytic activity of the class IIb HDAC, HDAC6, was consistently increased in stressed myocardium, but not in a model of physiologic hypertrophy. HDAC6 catalytic activity was also induced by diverse extracellular stimuli in cultured cardiac myocytes and fibroblasts. These findings suggest an unforeseen role for HDAC6 in the heart, and highlight the need for pre-clinical evaluation of HDAC6-selective inhibitors to determine whether this HDAC isoform is pathological or protective in the setting of cardiovascular disease.
During the development of heart failure (HF), the chief myocardial energy substrate switches from fatty acids to glucose. This metabolic switch, which recapitulates fetal cardiac energy substrate ...preferences, is thought to maintain aerobic energetic balance. The regulatory mechanisms involved in this metabolic response are unknown.
To characterize the expression of genes involved in mitochondrial fatty acid beta-oxidation (FAO) in the failing heart, levels of mRNA encoding enzymes that catalyze the first and third steps of the FAO cycle were delineated in the left ventricles (LVs) of human cardiac transplant recipients. FAO enzyme and mRNA levels were coordinately downregulated (> 40%) in failing human LVs compared with controls. The temporal pattern of this alteration in FAO enzyme gene expression was characterized in a rat model of progressive LV hypertrophy (LVH) and HF SHHF/Mcc-facp (SHHF) rat. FAO enzyme mRNA levels were coordinately downregulated (> 70%) during both the LVH and HF stages in the SHHF rats compared with controls. In contrast, the activity and steady-state levels of medium-chain acyl-CoA dehydrogenase, which catalyzes a rate-limiting step in FAO, were not significantly reduced until the HF stage, indicating additional control at the translational or post-translational levels in the hypertrophied but nonfailing ventricle.
These findings identify a gene regulatory pathway involved in the control of cardiac energy production during the development of HF.
Electrospray ionization mass spectrometry has previously been used to probe qualitative changes in the phospholipid cardiolipin (CL), but it has rarely been used in a quantitative manner. We assessed ...changes in the amount of individual molecular species of cardiac CL present in a model of congestive heart failure using 1,1',2,2'-tetramyristoyl cardiolipin as an internal standard. There was a linear relationship between the ratio of the negative molecular ion (M-H⁻) current from four different CL reference standards and the M-H⁻ from the internal standard, as a function of the concentration of CL molecular species. Therefore, this internal standard can be used to quantitate many naturally occurring CL molecular species over a wide range of CL concentrations. Using this method, changes to individual molecular species of CL in failing hearts from male spontaneously hypertensive heart failure rats were examined. CL isolated from cardiac mitochondria was compared with left ventricular tissue to demonstrate the feasibility of extracting and quantitating CL from either mitochondrial or tissue samples. The acyl chain composition of individual CL molecular species was identified using tandem mass spectrometry. In animals with heart failure, the major cardiac CL species (tetralinoloyl) decreased significantly, whereas other minor CL species were significantly increased.
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