Titin Research Articles

Increase in Efficiency of End Milling of Titanium Alloys Due to Tools with Multilayered Composite Nano-Structured Zr-ZrN-(Zr,Al)N and Zr-ZrN-(Zr,Cr,Al)N Coatings

The study deals with an increase in the tool life parameter for metal-cutting tools and efficiency of end milling for titanium alloys, due to the use of tools with multilayered composite nano-structured Zr–ZrN–(Zr,Al)N and Zr–ZrN–(Zr,Cr,Al)N coatings, deposited through the technology of the filtered cathodic vacuum arc deposition (FCVAD). The studies included the microstructured investigations using SEM, the analysis of chemical composition (Energy-dispersive X-ray spectroscopy, EDXS), the determination of the value of critical failure force (with the use of scratch testing), and the measurement of the microhardness of the coatings under study. The cutting tests were conducted in end milling of titanium alloys at various cutting speeds. The mechanisms of wear and failure for end milling cutters with the coatings under study were studied in milling. The studies determined the advantages of using a tool with the coatings under study compared to an uncoated tool, as well as to tools with the commercial Ti–TiN coating and the nano-structured Ti–TiN–(Ti,Al)N coating. Adding Cr to the composition of the coating can significantly increase the hardness, while the coating retains sufficient ductility and brittle fracture resistance, which allows for a best result when milling titanium alloys.

Rare truncating variants in the sarcomeric protein titin associate with familial and early-onset atrial fibrillation

A family history of atrial fibrillation constitutes a substantial risk of developing the disease, however, the pathogenesis of this complex disease is poorly understood. We perform whole-exome sequencing on 24 families with at least three family members diagnosed with atrial fibrillation (AF) and find that titin-truncating variants (TTNtv) are significantly enriched in these patients (P = 1.76 × 10−6). This finding is replicated in an independent cohort of early-onset lone AF patients (n = 399; odds ratio = 36.8; P = 4.13 × 10−6). A CRISPR/Cas9 modified zebrafish carrying a truncating variant of titin is used to investigate TTNtv effect in atrial development. We observe compromised assembly of the sarcomere in both atria and ventricle, longer PR interval, and heterozygous adult zebrafish have a higher degree of fibrosis in the atria, indicating that TTNtv are important risk factors for AF. This aligns with the early onset of the disease and adds an important dimension to the understanding of the molecular predisposition for AF.

Towards Dynamic but Supertough Healable Polymers through Biomimetic Hierarchical Hydrogen-Bonding Interactions.

A biomimetic (titin protein molecular structure) strategy is reported for preparing transparent and healable elastomers featuring supertoughness (345 MJ m-3 ) and high tensile strength (44 MPa) after self-healing enabled by hierarchical (single, double, and quadruple) hydrogen-bonding moieties in the polymer backbone. The rigid domain containing hierarchical H-bonds formed with urethane, urea, and 2-ureido-4[1H]-pyrimidinone groups leads to a durable network structure that has enhanced mechanical properties and is also dynamic for rapid self-healing. Healable polymers with hierarchical hydrogen-bonding interactions show excellent recoverability and high energy dissipation owing to the durable interaction between polymer chains. This biomimetic strategy of using hierarchical hydrogen bonds as building blocks is an alternative approach for obtaining dynamic, strong, yet smart self-healing polymers for heavy-duty protection materials and wearable electronics.

Towards Dynamic but Supertough Healable Polymers through Biomimetic Hierarchical Hydrogen‐Bonding Interactions

AbstractA biomimetic (titin protein molecular structure) strategy is reported for preparing transparent and healable elastomers featuring supertoughness (345 MJ m−3) and high tensile strength (44 MPa) after self‐healing enabled by hierarchical (single, double, and quadruple) hydrogen‐bonding moieties in the polymer backbone. The rigid domain containing hierarchical H‐bonds formed with urethane, urea, and 2‐ureido‐4[1H]‐pyrimidinone groups leads to a durable network structure that has enhanced mechanical properties and is also dynamic for rapid self‐healing. Healable polymers with hierarchical hydrogen‐bonding interactions show excellent recoverability and high energy dissipation owing to the durable interaction between polymer chains. This biomimetic strategy of using hierarchical hydrogen bonds as building blocks is an alternative approach for obtaining dynamic, strong, yet smart self‐healing polymers for heavy‐duty protection materials and wearable electronics.

Uncertain Skies. Forecasting Typhoons in Hong Kong, ca. 1874-1906

This paper explores the conceptualisation of “uncertainty” in late nineteenth-century meteorological thought. By investigating the story of meteorological forecasting in nineteenth and early twentieth century Hong Kong, it considers the changing ways in which forecasting was judged historically. In the early nineteenth century forecasting the weather was considerar impossible. By the end of the century, it was confidently expected that the much improved understanding of weather paterns would lead to the ability to better predict them. During the intervenint period “uncertainty” competed with “certainty” and “prediction” was mistaken for “predictability”. The shift in perception of what science could achieve and pressure to accurately predict typhoons. Such concerns helped sahpe the course of meteorology globally from a series of subjective teories into an objective pragmatic science based on observational analysis. This article seeks to highlight the practices, places and experiences that contributed knowledgement to the burgeoning field overseas whilst also connectin with others in this volume by considerin the circumstances that contributed to chaging perceptions of forecasting. In particular, it also explores how the qualification of wheather phenomenon- in this case the typhoon- as “unpredictable” or “uncertain” opened the door to innovation and discovery.

The effect of layer thickness ratio on the plastic deformation mechanisms of nanoindented Ti/TiN nanolayered composite

Molecular dynamics simulations were performed to identify the underlying deformation mechanisms controlling the plastic behavior of nanoindented nanoscale multilayered Ti/TiN. MD simulations were conducted on pure Ti and pure TiN as well as on four different layer-thickness ratios of Ti/TiN multilayers, Ti:TiN = 1, 2.5, 4, and 7.5. The Ti layer thickness varied from 2 nm to 15 nm while the TiN layer thickness is kept constant of 2 nm. The plastic deformation of nanoindented pure Ti was dominated by the formation of dislocation loops resulting from basal partial dislocations, while very few perfect dislocations that tie dislocation loops together were observed. The plastic deformation of nanoindented pure TiN was controlled by the activation of perfect dislocation propagation along the (111) plane that dissociates into two partials. Depending on the thickness ratio, either dislocation pile-up or single dislocation crossing through the interface was the controlling plastic deformation mechanism of nanoindented Ti/TiN multilayers. For metal layer thicknesses above 5 nm, significant dislocation pile-ups were observed at the interface of the multi-layered samples. The Ti/TiN multilayer with a thickness ratio of 1:1 with individual layer thickness of 2 nm exhibited the highest strain-hardening rate. At this length scale, the activation of dislocation sources requires very high stresses, and the single dislocation crossing process is the most dominant deformation mechanism. The initiation of plasticity in the TiN layer occurs at a high level of stress since there is no dislocation pile-up at the interface.

Positive End-Expiratory Pressure Ventilation Induces Longitudinal Atrophy in Diaphragm Fibers.

Diaphragm weakness in critically ill patients prolongs ventilator dependency and duration of hospital stay and increases mortality and healthcare costs. The mechanisms underlying diaphragm weakness include cross-sectional fiber atrophy and contractile protein dysfunction, but whether additional mechanisms are at play is unknown. To test the hypothesis that mechanical ventilation with positive end-expiratory pressure (PEEP) induces longitudinal atrophy by displacing the diaphragm in the caudal direction and reducing the length of fibers. We studied structure and function of diaphragm fibers of mechanically ventilated critically ill patients and mechanically ventilated rats with normal and increased titin compliance. PEEP causes a caudal movement of the diaphragm, both in critically ill patients and in rats, and this caudal movement reduces fiber length. Diaphragm fibers of 18-hour mechanically ventilated rats (PEEP of 2.5 cm H2O) adapt to the reduced length by absorbing serially linked sarcomeres, the smallest contractile units in muscle (i.e., longitudinal atrophy). Increasing the compliance of titin molecules reduces longitudinal atrophy. Mechanical ventilation with PEEP results in longitudinal atrophy of diaphragm fibers, a response that is modulated by the elasticity of the giant sarcomeric protein titin. We postulate that longitudinal atrophy, in concert with the aforementioned cross-sectional atrophy, hampers spontaneous breathing trials in critically ill patients: during these efforts, end-expiratory lung volume is reduced, and the shortened diaphragm fibers are stretched to excessive sarcomere lengths. At these lengths, muscle fibers generate less force, and diaphragm weakness ensues.

Whole-exome sequencing reveals doubly novel heterozygous Myosin Binding Protein C and Titin mutations in a Chinese patient with severe dilated cardiomyopathy.

Dilated Cardiomyopathy is a serious heart disorder that may induce sudden cardiac death and heart failure. Significant progress has been made in understanding the molecular basis of dilated cardiomyopathy. In previous studies, mutations in more than fifty genes have been identified in dilated cardiomyopathy patients. The purpose of this study was to detect the genetic lesion in a family from the central south of China affected by severe dilated cardiomyopathy. Whole-exome sequencing combined with cardiomyopathy-related genes list were used to analyse the mutations of the proband. Co-segregation analysis was performed by Sanger sequencing.Results and conclusionsTwo novel heterozygous mutations - Myosin Binding Protein C: p.L1014RfsX6 and Titin: p.R9793X - were identified in the proband. The deletion mutation c.3041delT/p.L1014RfsX6 caused a premature stop codon at position 1020 in exon 28 of the Myosin Binding Protein C. The nonsense mutation, c.29377 C>T/ p. R9793X, of Titin was located in the highly evolutionarily conserved domain, resulting in truncation of the Titin protein as well. Co-segregation analysis further revealed that the Myosin Binding Protein C mutation came from his mother and the Titin mutation came from his father. Both mutations are reported in dilated cardiomyopathy patients for the first time. Our study not only provides a unique example of the genes and molecular mechanisms involved in dilated cardiomyopathy but also expands the spectrum of Myosin Binding Protein C and Titin mutations and contributes to the genetic diagnosis and counselling of dilated cardiomyopathy patients.

Abstract 231: Identification of a Titin Enhancer using hiPSC-Derived Cardiomyocytes and CRISPR/Cas9 Genome Editing

Dilated cardiomyopathy (DCM), a disorder that occurs in 1:250 individuals, is associated with rates of mortality of 20% within 5 years of diagnosis and is a leading cause for heart failure and cardiac transplantation. Mutations in the massive sarcomere protein titin (encoded by TTN ) are the most common genetic cause of DCM, occurring in 10-20% of cases. As dominant DCM mutations truncate titin (TTNtv) and result in haploinsufficiency, we predict that strategies to increase the expression of the wild type (WT) TTN allele might attenuate the damaging effects of TTNtv. We used bioinformatic analyses to identify a putative TTN enhancer within intron 1. To confirm its function, we deleted 658 bp from intron 1 that encompasses the putative TTN enhancer in human induced pluripotent stem cells (hiPSCs) using CRISPR/Cas9 genome editing. We used qPCR and RNA sequencing of RNA harvested from hiPSC-derived cardiomyocytes (hiPSC-CMs) and demonstrated that a homozygous deletion in this region leads to decreased TTN gene expression compared to the WT control (0.344 fold change, p < 0.001), and also to decreased expression of other sarcomeric genes such as TNNT2 (0.074 fold change, p < 0.001), MYH6 (0.18 fold change, p < 0.001), MYH7 (0.008 fold change, p < 0.001), and ACTN2 (0.118 fold change, p < 0.001). The expression of transcription factors (TF) that have binding sites in this region is also affected, such as MEIS2 (0.4 fold change, p < 0.001) and KLF6 (0.33 fold change, p < 0.001), both of which are known to be involved in cardiogenesis. These TF may act as a link between the deletion in TTN Intron 1 and a decreased transcription of other cardiac-relevant genes. We also utilized Assay for Transposase-Accessible Chromatin Sequencing (ATAC-Seq) on WT hiPSC-CMs to identify open regions of chromatin that are accessible for TF binding. This provided additional evidence that this 658 bp region in TTN intron 1 has enhancer activity. Ongoing studies are aiming to refine the TTN Intron 1 enhancer by further studies using CRISPR/Cas9, CRISPR droplet sequencing (CROP-Seq), and luciferase-based enhancer activity assays. If confirmed, we expect that increasing the activity of this 658 bp region with small molecules may provide a novel therapeutic target for DCM caused by TTNtv.

Abstract 532: Titin’s N2B Element is Critical to Cardiac Mechanotransduction during Volume Overload, but not Pressure Overload

The heart senses and responds to changes in mechanical loading conditions by initiating signaling events to produce structural and functional remodeling through a process known as mechanotransduction. Within cardiac myocytes, the giant protein titin has been implicated as a key player in the conversion of mechanical stimuli into downstream signaling events as part of the adaptive responses of mechanotransduction. The N2B element within the extensible I-band of titin has been proposed to be a stretch sensor and signaling hot spot important to titin’s role as a mechanosensor. To investigate the role of the N2B element in mechanotransduction, N2B knockout (N2BKO) mice were subjected to cardiac pressure overload by transverse aortic constriction (TAC) or volume overload by aortocaval fistula (ACF). Following 4 weeks TAC, WT mice respond with 37% LV hypertrophy (4.0 ± 0.1 mg/gBW for TAC vs 2.9 ± 0.1 mg/gBW for sham) compared to 51% (3.8 ± 0.1 mg/gBW for TAC vs 2.5 ± 0.1 mg/gBW for sham) in N2BKO. In contrast, N2BKO mice demonstrated a severe lack of a hypertrophic response following 1-week ACF with 26% (4.0 ± 0.1 mg/gBW for ACF vs 3.1 ± 0.1 mg/gBW for sham) LV hypertrophy in WT compared to -2% (2.8 ± 0.1 mg/gBW for ACF vs 2.8 ± 0.1 mg/gBW for sham) in N2BKO. Additionally, while there was no incidence of mortality in WT mice subjected to ACF, approximately 36% (5 of 14) of N2BKO mice died within 1 week following ACF. Western blot analysis of canonical hypertrophy signaling kinases revealed no differences between WT and N2BKO mice at baseline or 1 week post-ACF. Four-and-a half LIM domains 1 and 2 (FHL1 and FHL2) have previously been shown to localize to the N2B element and FHL1 has been linked to mechanotransduction in TAC. In N2BKO, FHL1 protein is expressed at levels comparable to WT in both TAC and ACF; however, FHL2 protein levels are reduced by ~98% compared to WT (1.00 ± 0.26 for WT vs 0.02 ± 0.01% for N2BKO). These data indicate that while the N2B element is not required for mechanotransduction in pressure overload of the LV, it is critical for mechanosensing and the adaptive hypertrophy response during volume overload. FHL2 is an attractive candidate as a link between titin’s N2B element and the hypertrophy response following ACF and further work will critical examine its involvement.

Segmentation and the Entropic Elasticity of Modular Proteins.

Single-molecule force spectroscopy utilizes polyproteins, which are composed of tandem modular domains, to study their mechanical and structural properties. Under the application of external load, the polyproteins respond by unfolding and refolding domains to acquire the most favored extensibility. However, unlike single-domain proteins, the sequential unfolding of the each domain modifies the free energy landscape (FEL) of the polyprotein nonlinearly. Here we use force-clamp (FC) spectroscopy to measure unfolding and collapse-refolding dynamics of polyubiquitin and poly(I91). Their reconstructed unfolding FEL involves hundreds of kB T in accumulating work performed against conformational entropy, which dwarfs the ∼30 kB T that is typically required to overcome the free energy difference of unfolding. We speculate that the additional entropic energy caused by segmentation of the polyprotein to individual proteins plays a crucial role in defining the "shock absorber" properties of elastic proteins such as the giant muscle protein titin.

Evolution of metal nitriding and hydriding reactions during ammonia plasma-assisted ball milling

Nanocrystalline metal nitride and hydride powders were prepared using plasma-assisted ball milling in ammonia gas (NH3-P-milling) via an in situ synthesis reaction. The gas–solid reactions were triggered by a short duration of plasma milling of Mg and Ti under a constant pressure of ammonia gas, and the products in the two systems were nanocrystalline Mg3N2 and TiN, TiH2 after 10 h, respectively. During the NH3-P-milling of Ti powder, TiH2 and TiN were formed during the initial stages of milling, and then, the TiH2 decomposed during further milling upon reaction with N radicals, transforming into the TiN phase. In contrast, no chemical reaction occurred between NH3 and Mg/Ti after 10 h of C-milling. The discharge plasma activated and decomposed the ammonia gas and activated the surface of the powders, which, together with the mechanical effect of high-energy ball milling, accelerated the gas–solid reactions.

Efficient Quantum Algorithm for Similarity Measures for Molecules

The similarity measures for molecules play an important role for research in chemistry, biology and drug design. In order to obtain similarity measures for giant molecules such as muscle protein titin, the existing classical algorithms possess high computational complexity and many other disadvantages. An effective quantum algorithm, Quantum Method for Similarity Measures for Molecules (QMSM), is introduced to obtain similarity measure for molecules based on the quantum phase estimation algorithm. Moreover, we discuss the feasibility of simulating the quantum algorithm QMSM with quantum circuits. Finally, the performance evaluation and comparison of the QMSM algorithm are presented, where the QMSM can obtain exponential speedups compared to its classical counterparts.

A Spatially Explicit Model Shows How Titin Stiffness Modulates Muscle Mechanics and Energetics.

In striated muscle, the giant protein titin spans the entire length of a half-sarcomere and extends from the backbone of the thick filament, reversibly attaches to the thin filaments, and anchors to the dense protein network of the z-disk capping the end of the half-sarcomere. However, little is known about the relationship between the basic mechanical properties of titin and muscle contractility. Here, we build upon our previous multi-filament, spatially explicit computational model of the half-sarcomere by incorporating the nonlinear mechanics of titin filaments in the I-band. We vary parameters of the nonlinearity to understand the effects of titin stiffness on contraction dynamics and efficiency. We do so by simulating isometric contraction for a range of sarcomere lengths (SLs; 1.6-3.25 µm). Intermediate values of titin stiffness accurately reproduce the passive force-SL relation for skeletal muscle. The maximum force-SL relation is not affected by titin for SL≤2.5 µm. However, as titin stiffness increases, maximum force for the four thick filament system at SL = 3.0 µm significantly decreases from 103.2 ± 2 to 58.8 ± 1 pN. Additionally, by monitoring ATP consumption, we measure contraction efficiency as a function of titin stiffness. We find that at SL = 3.0 µm, efficiency significantly decreases from 13.9 ± 0.4 to 7.0 ± 0.3 pN/ATP when increasing titin stiffness, with little or no effect below 2.5 µm. Taken together, our results suggest that, despite an increase in the fraction of motors bound to actin along the descending limb when titin is stiffer, the force-generating capacity of the motors is reduced. These results suggest that titin stiffness has the potential to affect contractile efficiency.

Phosphorylation of the RSRSP stretch is critical for splicing regulation by RNA-Binding Motif Protein 20 (RBM20) through nuclear localization

RBM20 is a major regulator of heart-specific alternative pre-mRNA splicing of TTN encoding a giant sarcomeric protein titin. Mutation in RBM20 is linked to autosomal-dominant familial dilated cardiomyopathy (DCM), yet most of the RBM20 missense mutations in familial and sporadic cases were mapped to an RSRSP stretch in an arginine/serine-rich region of which function remains unknown. In the present study, we identified an R634W missense mutation within the stretch and a G1031X nonsense mutation in cohorts of DCM patients. We demonstrate that the two serine residues in the RSRSP stretch are constitutively phosphorylated and mutations in the stretch disturb nuclear localization of RBM20. Rbm20S637A knock-in mouse mimicking an S635A mutation reported in a familial case showed a remarkable effect on titin isoform expression like in a patient carrying the mutation. These results revealed the function of the RSRSP stretch as a critical part of a nuclear localization signal and offer the Rbm20S637A mouse as a good model for in vivo study.

Drug discovery with an RBM20 dependent titin splice reporter identifies cardenolides as lead structures to improve cardiac filling.

Diastolic dysfunction is increasingly prevalent in our ageing society and an important contributor to heart failure. The giant protein titin could serve as a therapeutic target, as its elastic properties are a main determinant of cardiac filling in diastole. This study aimed to develop a high throughput pharmacological screen to identify small molecules that affect titin isoform expression through differential inclusion of exons encoding the elastic PEVK domains. We used a dual luciferase splice reporter assay that builds on the titin splice factor RBM20 to screen ~34,000 small molecules and identified several compounds that inhibit the exclusion of PEVK exons. These compounds belong to the class of cardenolides and affect RBM20 dependent titin exon exclusion but did not affect RBFOX1 mediated splicing of FMNL3. We provide evidence that cardenolides do not bind to the RNA interacting domain of RBM20, but reduce RBM20 protein levels and alter transcription of select splicing factors that interact with RBM20.Cardenolides affect titin isoform expression. Understanding their mode of action and harnessing the splice effects through chemical modifications that suppress the effects on ion homeostasis and more selectively affect cardiac splicing has the potential to improve cardiac filling and thus help patients with diastolic heart failure, for which currently no targeted therapy exists.

Congenital Titinopathy: Comprehensive characterization and pathogenic insights

ObjectiveComprehensive clinical characterization of congenital titinopathy to facilitate diagnosis and management of this important emerging disorder.MethodsUsing massively parallel sequencing we identified 30 patients from 27 families with 2 pathogenic nonsense, frameshift and/or splice site TTN mutations in trans. We then undertook a detailed analysis of the clinical, histopathological and imaging features of these patients.ResultsAll patients had prenatal or early onset hypotonia and/or congenital contractures. None had ophthalmoplegia. Scoliosis and respiratory insufficiency typically developed early and progressed rapidly, whereas limb weakness was often slowly progressive, and usually did not prevent independent walking. Cardiac involvement was present in 46% of patients. Relatives of 2 patients had dilated cardiomyopathy. Creatine kinase levels were normal to moderately elevated. Increased fiber size variation, internalized nuclei and cores were common histopathological abnormalities. Cap‐like regions, whorled or ring fibers, and mitochondrial accumulations were also observed. Muscle magnetic resonance imaging showed gluteal, hamstring and calf muscle involvement. Western blot analysis showed a near‐normal sized titin protein in all samples. The presence of 2 mutations predicted to impact both N2BA and N2B cardiac isoforms appeared to be associated with greatest risk of cardiac involvement. One‐third of patients had 1 mutation predicted to impact exons present in fetal skeletal muscle, but not included within the mature skeletal muscle isoform transcript. This strongly suggests developmental isoforms are involved in the pathogenesis of this congenital/early onset disorder.InterpretationThis detailed clinical reference dataset will greatly facilitate diagnostic confirmation and management of patients, and has provided important insights into disease pathogenesis. Ann Neurol 2018;83:1105–1124

Clinical differences between early-and late-onset myasthenia

Objective To explore the clinical differences between patients with early-onset myasthenia gravis(EOMG)and those with late-onset myasthenia gravis(LOMG). Methods This was a retrospective study enrolling 157 MG patients.Based on the age of onset, patients were divided into the EOMG group(n=85)and the LOMG group(n=72). The groups were compared on clinical characteristics, including clinical manifestations, MG classification, electrophysiological findings on repetitive nerve stimulation(RNS), single fiber electromyography(SFEMG), levels of antibody against acetylcholine receptors(Ach-R Ab), antibody to muscle-specific kinase(MuSK Ab), titin antibody(Titin Ab), ryanodine receptor antibody(RyR Ab), thyroid function, thymectomy, thymus pathology and responses to treatment. Results The mean ages of onset were markedly different〔(40.9±9.7)years vs.(62.0±12.2)years, P 0.05). Moreover, patients in the EOMG group were more likely to have abnormal thyroid function and higher percentages of receiving steroids, tacrolimus, plasma exchange therapy, and thymectomy(P<0.05). Conclusions The clinical profiles of LOMG are different from those of EOMG in clinical manifestations, thyroid function, thymectomy frequency, striational antibody levels and disease-modifying drug options. Key words: Myasthenia gravis; Recepors, cholinergic

Acute stimulation of the soluble guanylate cyclase does not impact on left ventricular capacitance in normal and hypertrophied porcine hearts in vivo.

Experimental data indicate that stimulation of the nitric oxide-soluble guanylate cyclase(sGC)-cGMP-PKG pathway can increase left ventricular (LV) capacitance via phosphorylation of the myofilamental protein titin. We aimed to test whether acute pharmacological sGC stimulation with BAY 41-8543 would increase LV capacitance via titin phosphorylation in healthy and deoxycorticosteroneacetate (DOCA)-induced hypertensive pigs. Nine healthy Landrace pigs and 7 pigs with DOCA-induced hypertension and LV concentric hypertrophy were acutely instrumented to measure LV end-diastolic pressure-volume relationships (EDPVRs) at baseline and during intravenous infusion of BAY 41-8543 (1 and 3 μg·kg-1·min-1 for 30 min, respectively). Separately, in seven healthy and six DOCA pigs, transmural LV biopsies were harvested from the beating heart to measure titin phosphorylation during BAY 41-8543 infusion. LV EDPVRs before and during BAY 41-8543 infusion were superimposable in both healthy and DOCA-treated pigs, whereas mean aortic pressure decreased by 20-30 mmHg in both groups. Myocardial titin phosphorylation was unchanged in healthy pigs, but total and site-specific (Pro-Glu-Val-Lys and N2-Bus domains) titin phosphorylation was increased in DOCA-treated pigs. Bicoronary nitroglycerin infusion in healthy pigs ( n = 5) induced a rightward shift of the LV EDPVR, demonstrating the responsiveness of the pathway in this model. Acute systemic sGC stimulation with the sGC stimulator BAY 41-8543 did not recruit an LV preload reserve in both healthy and hypertrophied LV porcine myocardium, although it increased titin phosphorylation in the latter group. Thus, increased titin phosphorylation is not indicative of increased in vivo LV capacitance. NEW & NOTEWORTHY We demonstrate that acute pharmacological stimulation of soluble guanylate cyclase does not increase left ventricular compliance in normal and hypertrophied porcine hearts. Effects of long-term soluble guanylate cyclase stimulation with oral compounds in disease conditions associated with lowered myocardial cGMP levels, i.e., heart failure with preserved ejection fraction, remain to be investigated.

Case Study: A Bio-Inspired Control Algorithm for a Robotic Foot-Ankle Prosthesis Provides Adaptive Control of Level Walking and Stair Ascent.

Powered ankle-foot prostheses assist users through plantarflexion during stance and dorsiflexion during swing. Provision of motor power permits faster preferred walking speeds than passive devices, but use of active motor power raises the issue of control. While several commercially available algorithms provide torque control for many intended activities and variations of terrain, control approaches typically exhibit no inherent adaptation. In contrast, muscles adapt instantaneously to changes in load without sensory feedback due to the intrinsic property that their stiffness changes with length and velocity. We previously developed a “winding filament” hypothesis (WFH) for muscle contraction that accounts for intrinsic muscle properties by incorporating the giant titin protein. The goals of this study were to develop a WFH-based control algorithm for a powered prosthesis and to test its robustness during level walking and stair ascent in a case study of two subjects with 4–5 years of experience using a powered prosthesis. In the WFH algorithm, ankle moments produced by virtual muscles are calculated based on muscle length and activation. Net ankle moment determines the current applied to the motor. Using this algorithm implemented in a BiOM T2 prosthesis, we tested subjects during level walking and stair ascent. During level walking at variable speeds, the WFH algorithm produced plantarflexion angles (range = −8 to −19°) and ankle moments (range = 1 to 1.5 Nm/kg) similar to those produced by the BiOM T2 stock controller and to people with no amputation. During stair ascent, the WFH algorithm produced plantarflexion angles (range −15 to −19°) that were similar to persons with no amputation and were ~5 times larger on average at 80 steps/min than those produced by the stock controller. This case study provides proof-of-concept that, by emulating muscle properties, the WFH algorithm provides robust, adaptive control of level walking at variable speed and stair ascent with minimal sensing and no change in parameters.