Mechanosensing in myosin filament solves a 60 years old conflict in skeletal muscle modeling between high power output and slow rise in tension

Almost 60 years ago Andrew Huxley with his seminal paper \cite{Huxley1957} laid the foundation of modern muscle modeling, linking chemical events to mechanical performance. He described mechanics and energetics of muscle contraction through the cyclical attachment and detachment of myosin motors to the actin filament with ad hoc assumptions on the dependence of the rate constants on the strain of the myosin motors. That relatively simple hypothesis is still present in recent models, even though with several modifications to adapt the model to the different experimental constraints which became subsequently available. However, already in that paper, one controversial aspect of the model became clear. Relatively high attachment and detachment rates of myosin to the actin filament were needed to simulate the high power output at intermediate velocity of contraction. However, these rates were incompatible with the relatively slow rise in tension after activation, despite the rise should be generated by the same rate functions. This discrepancy has not been fully solved till today, despite several hypotheses have been forwarded to reconcile the two aspects. Here, using a conventional muscle model, we show that the recently revealed mechanosensing mechanism of recruitment of myosin motors \cite{Linarietal2015} can solve this long standing problem without any further ad-hoc hypotheses

Activation of skeletal muscle is controlled by a dual-filament mechano-sensing mechanism

Contraction of skeletal muscle is triggered by a transient rise in intracellular calcium concentration leading to a structural change in the actin-containing thin filaments that allows binding of myosin motors from the thick filaments. Most myosin motors are unavailable for actin binding in resting muscle because they are folded back against the thick filament backbone. Release of the folded motors is triggered by thick filament stress, implying a positive feedback loop in the thick filaments. However, it was unclear how thin and thick filament activation mechanisms are coordinated, partly because most previous studies of the thin filament regulation were conducted at low temperatures where the thick filament mechanisms are inhibited. Here, we use probes on both troponin in the thin filaments and myosin in the thick filaments to monitor the activation states of both filaments in near-physiological conditions. We characterize those activation states both in the steady state, using conventional titrations with calcium buffers, and during activation on the physiological timescale, using calcium jumps produced by photolysis of caged calcium. The results reveal three activation states of the thin filament in the intact filament lattice of a muscle cell that are analogous to those proposed previously from studies on isolated proteins. We characterize the rates of the transitions between these states in relation to thick filament mechano-sensing and show how thin- and thick-filament-based mechanisms are coupled by two positive feedback loops that switch on both filaments to achieve rapid cooperative activation of skeletal muscle

SOLAR ENERGETIC PARTICLE MODULATIONS ASSOCIATED WITH COHERENT MAGNETIC STRUCTURES

In situ observations of solar energetic particles (SEPs) often show rapid variations of their intensity profile, affecting all energies simultaneously, without time dispersion. A previously proposed interpretation suggests that these modulations are directly related to the presence of magnetic structures with a different magnetic topology. However, no compelling evidence of local changes in magnetic field or in plasma parameters during SEP modulations has been reported. In this paper, we performed a detailed analysis of SEP events and we found several signatures in the local magnetic field and/or plasma parameters associated with SEP modulations. The study of magnetic helicity allowed us to identify magnetic boundaries, associated with variations of plasma parameters, which are thought to represent the borders between adjacent magnetic flux tubes. It is found that SEP dispersionless modulations are generally associated with such magnetic boundaries. Consequently, we support the idea that SEP modulations are observed when the spacecraft passes through magnetic flux tubes, filled or devoid of SEPs, which are alternatively connected and not connected with the flare site. In other cases, we found SEP dropouts associated with large-scale magnetic holes. A possible generation mechanism suggests that these holes are formed in the high solar corona as a consequence of magnetic reconnection. This reconnection process modifies the magnetic field topology, and therefore, these holes can be magnetically isolated from the surrounding plasma and could also explain their association with SEP dropouts

Non-pegylated liposomal doxorubicin in older adjuvant early breast cancer patients: cardiac safety analysis and final results of the COLTONE study

Aims: To explore the cardiac safety of adjuvant Non-Pegylated Liposomal Doxorubicin (NPL-DOX) plus Cyclophosphamide (CTX) followed by weekly Paclitaxel, in elderly women (≥ 65 years) with high-risk breast cancer. Previously, we described no symptomatic cardiac events within the first 12 months from starting treatment. We now reported the updated results after a median follow-up 76 months. Methods: The cardiac activity was evaluated with left ventricular ejection fraction (LVEF) echocardiograms assessments, before starting chemotherapy and every 6 months, until 30 months from baseline, then yearly for at least 5 years. Results: Forty-seven women were recruited by two Units of Medical Oncology (Ethics Committee authorization CESM-AOUP, 3203/2011; EudraCT identification number: 2010-024067-41, for Pisa and Pontedera Hospitals). An episode of grade 3 CHF (NCI-CTCAE, version 3.0) occurred after 18 months the beginning of chemotherapy. The echocardiograms assessments were performed comparing the LVEF values of each patient evaluated at fixed period of time, compared to baseline. We observed a slight changed in terms of mean values at 48, 60, 72 and 84 months. At these time points, a statistically significant reduction of - 3.2%, - 4.6%, - 6.4% and - 7.1%, respectively, was observed. However, LVEF remained above 50% without translation in any relevant clinical signs. No other cardiac significant episodes were reported. To this analysis, in 13 patients (28%) occurred disease relapse and,  of them, 11 (23%) died due to metastatic disease. Eight patients died of cancer-unrelated causes. Conclusions: The combination including NPL-DOX in elderly patients revealed low rate of cardiac toxic effects. Comparative trials are encouraged

Contribution to the floristic knowledge of eastern Irpinia and Vulture-Melfese area (Campania and Basilicata, southern Italy)

In order to improve the floristic knowledge of the Italian territory, we report the inventory of the taxa collected during the annual field trip of the working group for Floristics, Systematics and Evolution of the Italian Botanical Society held in 2015 in eastern Irpinia and Vulture-Melfese area (South Italy). The investigated territories are located in southern Apennines, along the border between the Campania and Basilicata administrative regions. These areas are scarcely known in terms of vascular flora. The floristic samplings were performed in 19 sites selected as representative of the local environmental diversity as regards to climate, litho-morphology and land-use. The research led to the identification of 4,137 specimens of vascular plants, belonging to 815 species and subspecies, 399 genera, and 85 families. Among these taxa, 42 were endemic to Italy, 38 were included in the IUCN Red List of the Italian Flora, 28 were alien and 5 were cryptogenic in Campania and/ or Basilicata administrative regions. Two taxa, Aquilegia coerulea (casual alien, native to North America) and Lolium ×boucheanum (native), were found to be new for Italy. On the basis of the available floristic literature the first one is also to be considered new for the European flora. At regional scale, we have found 18 taxa new for the Campania and 15 new for the Basilicata region. Finally, 10 taxa were confirmed for Campania. Data obtained during this study, confirmed the important role of a collaborative approach among botanists and the great relevance of these territories for plant diversity

Refinement of the diagnostic approach for the identification of children and adolescents affected by familial hypercholesterolemia: Evidence from the LIPIGEN study

Background and aims: We aimed to describe the limitations of familiar hypercholesterolemia (FH) diagnosis in childhood based on the presence of the typical features of FH, such as physical sings of cholesterol accumulation and personal or family history of premature cardiovascular disease or hypercholesterolemia, comparing their prevalence in the adult and paediatric FH population, and to illustrate how additional information can lead to a more effective diagnosis of FH at a younger age.Methods: From the Italian LIPIGEN cohort, we selected 1188 (>= 18 years) and 708 (<18 years) genetically-confirmed heterozygous FH, with no missing personal FH features. The prevalence of personal and familial FH features was compared between the two groups. For a sub-group of the paediatric cohort (N = 374), data about premature coronary heart disease (CHD) in second-degree family members were also included in the evaluation.Results: The lower prevalence of typical FH features in children/adolescents vs adults was confirmed: the prevalence of tendon xanthoma was 2.1% vs 13.1%, and arcus cornealis was present in 1.6% vs 11.2% of the cohorts, respectively. No children presented clinical history of premature CHD or cerebral/peripheral vascular disease compared to 8.8% and 5.6% of adults, respectively. The prevalence of premature CHD in first-degree relatives was significantly higher in adults compared to children/adolescents (38.9% vs 19.7%). In the sub-cohort analysis, a premature CHD event in parents was reported in 63 out of 374 subjects (16.8%), but the percentage increased to 54.0% extending the evaluation also to second-degree relatives.Conclusions: In children, the typical FH features are clearly less informative than in adults. A more thorough data collection, adding information about second-degree relatives, could improve the diagnosis of FH at younger age

Refinement of the diagnostic approach for the identification of children and adolescents affected by familial hypercholesterolemia: Evidence from the LIPIGEN study

Background and aims: We aimed to describe the limitations of familiar hypercholesterolemia (FH) diagnosis in childhood based on the presence of the typical features of FH, such as physical sings of cholesterol accumulation and personal or family history of premature cardiovascular disease or hypercholesterolemia, comparing their prevalence in the adult and paediatric FH population, and to illustrate how additional information can lead to a more effective diagnosis of FH at a younger age. Methods: From the Italian LIPIGEN cohort, we selected 1188 (≥18 years) and 708 (<18 years) genetically-confirmed heterozygous FH, with no missing personal FH features. The prevalence of personal and familial FH features was compared between the two groups. For a sub-group of the paediatric cohort (N = 374), data about premature coronary heart disease (CHD) in second-degree family members were also included in the evaluation. Results: The lower prevalence of typical FH features in children/adolescents vs adults was confirmed: the prevalence of tendon xanthoma was 2.1% vs 13.1%, and arcus cornealis was present in 1.6% vs 11.2% of the cohorts, respectively. No children presented clinical history of premature CHD or cerebral/peripheral vascular disease compared to 8.8% and 5.6% of adults, respectively. The prevalence of premature CHD in first-degree relatives was significantly higher in adults compared to children/adolescents (38.9% vs 19.7%). In the sub-cohort analysis, a premature CHD event in parents was reported in 63 out of 374 subjects (16.8%), but the percentage increased to 54.0% extending the evaluation also to second-degree relatives. Conclusions: In children, the typical FH features are clearly less informative than in adults. A more thorough data collection, adding information about second-degree relatives, could improve the diagnosis of FH at younger age

Spectrum of mutations in Italian patients with familial hypercholesterolemia: New results from the LIPIGEN study

Background Familial hypercholesterolemia (FH) is an autosomal dominant disease characterized by elevated plasma levels of LDL-cholesterol that confers an increased risk of premature atherosclerotic cardiovascular disease. Early identification and treatment of FH patients can improve prognosis and reduce the burden of cardiovascular mortality. Aim of this study was to perform the mutational analysis of FH patients identified through a collaboration of 20 Lipid Clinics in Italy (LIPIGEN Study). Methods We recruited 1592 individuals with a clinical diagnosis of definite or probable FH according to the Dutch Lipid Clinic Network criteria. We performed a parallel sequencing of the major candidate genes for monogenic hypercholesterolemia (LDLR, APOB, PCSK9, APOE, LDLRAP1, STAP1). Results A total of 213 variants were detected in 1076 subjects. About 90% of them had a pathogenic or likely pathogenic variants. More than 94% of patients carried pathogenic variants in LDLR gene, 27 of which were novel. Pathogenic variants in APOB and PCSK9 were exceedingly rare. We found 4 true homozygotes and 5 putative compound heterozygotes for pathogenic variants in LDLR gene, as well as 5 double heterozygotes for LDLR/APOB pathogenic variants. Two patients were homozygous for pathogenic variants in LDLRAP1 gene resulting in autosomal recessive hypercholesterolemia. One patient was found to be heterozygous for the ApoE variant p.(Leu167del), known to confer an FH phenotype. Conclusions This study shows the molecular characteristics of the FH patients identified in Italy over the last two years. Full phenotypic characterization of these patients and cascade screening of family members is now in progress

Twelve Variants Polygenic Score for Low-Density Lipoprotein Cholesterol Distribution in a Large Cohort of Patients With Clinically Diagnosed Familial Hypercholesterolemia With or Without Causative Mutations

: Background A significant proportion of individuals clinically diagnosed with familial hypercholesterolemia (FH), but without any disease-causing mutation, are likely to have polygenic hypercholesterolemia. We evaluated the distribution of a polygenic risk score, consisting of 12 low-density lipoprotein cholesterol (LDL-C)-raising variants (polygenic LDL-C risk score), in subjects with a clinical diagnosis of FH. Methods and Results Within the Lipid Transport Disorders Italian Genetic Network (LIPIGEN) study, 875 patients who were FH-mutation positive (women, 54.75%; mean age, 42.47±15.00 years) and 644 patients who were FH-mutation negative (women, 54.21%; mean age, 49.73±13.54 years) were evaluated. Patients who were FH-mutation negative had lower mean levels of pretreatment LDL-C than patients who were FH-mutation positive (217.14±55.49 versus 270.52±68.59 mg/dL, P<0.0001). The mean value (±SD) of the polygenic LDL-C risk score was 1.00 (±0.18) in patients who were FH-mutation negative and 0.94 (±0.20) in patients who were FH-mutation positive (P<0.0001). In the receiver operating characteristic analysis, the area under the curve for recognizing subjects characterized by polygenic hypercholesterolemia was 0.59 (95% CI, 0.56-0.62), with sensitivity and specificity being 78% and 36%, respectively, at 0.905 as a cutoff value. Higher mean polygenic LDL-C risk score levels were observed among patients who were FH-mutation negative having pretreatment LDL-C levels in the range of 150 to 350 mg/dL (150-249 mg/dL: 1.01 versus 0.91, P<0.0001; 250-349 mg/dL: 1.02 versus 0.95, P=0.0001). A positive correlation between polygenic LDL-C risk score and pretreatment LDL-C levels was observed among patients with FH independently of the presence of causative mutations. Conclusions This analysis confirms the role of polymorphisms in modulating LDL-C levels, even in patients with genetically confirmed FH. More data are needed to support the use of the polygenic score in routine clinical practice