Myosin Sequestration Regulates Sarcomere Function, Cardiomyocyte Energetics, and Metabolism, Informing the Pathogenesis of Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is caused by pathogenic variants in sarcomere protein genes that evoke hypercontractility, poor relaxation, and increased energy consumption by the heart and increased patient risks for arrhythmias and heart failure. Recent studies show that pathogenic missense variants in myosin, the molecular motor of the sarcomere, are clustered in residues that participate in dynamic conformational states of sarcomere proteins. We hypothesized that these conformations are essential to adapt contractile output for energy conservation and that pathophysiology of HCM results from destabilization of these conformations.

METHODS

We assayed myosin ATP binding to define the proportion of myosins in the super relaxed state (SRX) conformation or the disordered relaxed state (DRX) conformation in healthy rodent and human hearts, at baseline and in response to reduced hemodynamic demands of hibernation or pathogenic HCM variants. To determine the relationships between myosin conformations, sarcomere function, and cell biology, we assessed contractility, relaxation, and cardiomyocyte morphology and metabolism, with and without an allosteric modulator of myosin ATPase activity. We then tested whether the positions of myosin variants of unknown clinical significance that were identified in patients with HCM, predicted functional consequences and associations with heart failure and arrhythmias.

RESULTS

Myosins undergo physiological shifts between the SRX conformation that maximizes energy conservation and the DRX conformation that enables cross-bridge formation with greater ATP consumption. Systemic hemodynamic requirements, pharmacological modulators of myosin, and pathogenic myosin missense mutations influenced the proportions of these conformations. Hibernation increased the proportion of myosins in the SRX conformation, whereas pathogenic variants destabilized these and increased the proportion of myosins in the DRX conformation, which enhanced cardiomyocyte contractility, but impaired relaxation and evoked hypertrophic remodeling with increased energetic stress. Using structural locations to stratify variants of unknown clinical significance, we showed that the variants that destabilized myosin conformations were associated with higher rates of heart failure and arrhythmias in patients with HCM.

CONCLUSIONS

Myosin conformations establish work-energy equipoise that is essential for life-long cellular homeostasis and heart function. Destabilization of myosin energy-conserving states promotes contractile abnormalities, morphological and metabolic remodeling, and adverse clinical outcomes in patients with HCM. Therapeutic restabilization corrects cellular contractile and metabolic phenotypes and may limit these adverse clinical outcomes in patients with HCM.

High-performance chemical- and light-inducible recombinases in mammalian cells and mice

Site-specific DNA recombinases are important genome engineering tools. Chemical- and light-inducible recombinases, in particular, enable spatiotemporal control of gene expression. However, inducible recombinases are scarce due to the challenge of engineering high performance systems, thus constraining the sophistication of genetic circuits and animal models that can be created. Here we present a library of >20 orthogonal inducible split recombinases that can be activated by small molecules, light and temperature in mammalian cells and mice. Furthermore, we engineer inducible split Cre systems with better performance than existing systems. Using our orthogonal inducible recombinases, we create a genetic switchboard that can independently regulate the expression of 3 different cytokines in the same cell, a tripartite inducible Flp, and a 4-input AND gate. We quantitatively characterize the inducible recombinases for benchmarking their performances, including computation of distinguishability of outputs. This library expands capabilities for multiplexed mammalian gene expression control.

Effect of a Combined Tai Chi, Resistance Training and Dietary Intervention on Cognitive Function in Obese Older Women

Cognitive decline in older adults is a major public health problem and can compromise independence and quality of life. Exercise and diet have been studied independently and have shown to be beneficial for cognitive function, however, a combined Tai Chi, resistance training, and diet intervention and its influence on cognitive function has not been undertaken. The current study used a 12-week non-randomized research design with experiment and control groups to examine the effect of a combined Tai Chi, resistance training, and diet intervention on cognitive function in 25 older obese women. Results revealed improvements in domain specific cognitive function in our sample. Baseline cognitive function was correlated with changes in dietary quality. These findings suggest that Tai Chi and resistance training combined with diet intervention might be beneficial for community-based programs aiming to improve cognitive function.

Electrospun Nanofiber Scaffolds and Their Hydrogel Composites for the Engineering and Regeneration of Soft Tissues

Electrospinning has emerged as a simple, elegant, and scalable technique that can be used to fabricate polymeric nanofibers. Pure polymers as well as blends and composites of both natural and synthetic ones have been successfully electrospun into nanofiber matrices for many biomedical applications. Tissue-engineered medical implants, such as polymeric nanofiber scaffolds, are potential alternatives to autografts and allografts, which are short in supply and carry risks of disease transmission. These scaffolds have been used to engineer various soft tissues, including connective tissues, such as skin, ligament, and tendon, as well as nonconnective ones, such as vascular, muscle, and neural tissue. Electrospun nanofiber matrices show morphological similarities to the natural extracellular matrix (ECM), characterized by ultrafine continuous fibers, high surface-to-volume ratios, high porosities, and variable pore-size distributions. The physiochemical properties of nanofiber matrices can be controlled by manipulating electrospinning parameters so that they meet the requirements of a specific application.Nanostructured implants show improved biological performance over bulk materials in aspects of cellular infiltration and in vivo integration, taking advantage of unique quantum, physical, and atomic properties. Furthermore, the topographies of such scaffolds has been shown to dictate cellular attachment, migration, proliferation, and differentiation, which are critical in engineering complex functional tissues with improved biocompatibility and functional performance. This chapter discusses the use of the electrospinning technique in the fabrication of polymer nanofiber scaffolds utilized for the regeneration of soft tissues. Selected scaffolds will be seeded with human mesenchymal stem cells (hMSCs), imaged using scanning electron and confocal microscopy, and then evaluated for their mechanical properties as well as their abilities to promote cell adhesion, proliferation , migration, and differentiation.

Impact of heat stress on Mytilus edulis: contaminants affect survival and HSP 70 proteoform expression

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The glue-clot technique: a new technique description for small calyceal stone fragments removal

During the last 20 years, the technology advancement of small flexible ureterorenoscopes has dramatically changed the management of renal calculi. Retrograde intrarenal surgery (RIRS) has currently a high impact on active stone treatment, and it is increasingly used worldwide. Nevertheless, kidney stone fragmentation and direct removal of fragments require many passages of the ureteroscope, is often time-consuming, and may be very difficult through anatomical and technical factors. We describe a simple, feasible and efficient technique for small stone fragments retrieval, which are often difficult to remove during RIRS.

Oropharyngeal dysphagia in patients with oculopharyngeal muscular dystrophy

Sixteen patients with an established diagnosis of oculopharyngeal muscular dystrophy underwent clinical, radiologic and manometric assessment. Secondary pharyngo-oral and pharyngonasal regurgitations are usually associated with this condition and chronic aspiration with consequent bronchorrhea is common. Such patients may present with marked oropharyngeal dysphagia. Cineradiologic findings correlated well with the mamometric results. The pharynx showed very weak contractions of longer duration than those observed in normal subjects. The proximal esophageal sphincter had a normal resting and closing pressure; however, relaxation and coordination of the sphincter were substantially different from those in a control group. Eleven patients underwent cricopharyngeal myotomy. All had notable improvement of their symptoms. Surgery on the sphincter results in a substantial decrease in its resting pressure; pharyngeal contraction remains unaltered.