The arrhythmogenic N53I variant subtly changes the structure and dynamics in the calmodulin N-terminal domain, altering its interaction with the cardiac ryanodine receptor

Mutations in the genes encoding the highly conserved Ca²⁺-sensing protein calmodulin (CaM) cause severe cardiac arrhythmias, including catecholaminergic polymorphic ventricular tachycardia or long QT syndrome and sudden cardiac death. Most of the identified arrhythmogenic mutations reside in the C-terminal domain of CaM and mostly affect Ca²⁺-coordinating residues. One exception is the catecholaminergic polymorphic ventricular tachycardia-causing N53I substitution, which resides in the N-terminal domain (N-domain). It does not affect Ca²⁺ coordination and has only a minor impact on binding affinity toward Ca²⁺ and on other biophysical properties. Nevertheless, the N53I substitution dramatically affects CaM's ability to reduce the open probability of the cardiac ryanodine receptor (RyR2) while having no effect on the regulation of the plasmalemmal voltage-gated Ca²⁺ channel, Ca_v1.2. To gain more insight into the molecular disease mechanism of this mutant, we used NMR to investigate the structures and dynamics of both apo- and Ca²⁺-bound CaM-N53I in solution. We also solved the crystal structures of WT and N53I CaM in complex with the primary calmodulin-binding domain (CaMBD2) from RyR2 at 1.84-2.13 Å resolutions. We found that all structures of the arrhythmogenic CaM-N53I variant are highly similar to those of WT CaM. However, we noted that the N53I substitution exposes an additional hydrophobic surface and that the intramolecular dynamics of the protein are significantly altered such that they destabilize the CaM N-domain. We conclude that the N53I-induced changes alter the interaction of the CaM N-domain with RyR2 and thereby likely cause the arrhythmogenic phenotype of this mutation.

P5296A healthier lifestyle increases circulating pro-atrial natriuretic peptide concentrations in overweight children

Background

Higher concentrations of atrial natriuretic peptides (ANP) are associated with a poor prognosis among patients with cardiovascular disease (CVD). Counter-intuitively, higher ANP concentrations in healthy populations are associated with an ideal American Heart Association Cardiovascular Health score, which includes high level of physical activity, normal body mass index (BMI), optimal levels of lipids, blood pressure (BP) and glucose. Along this line, overweight individuals have lower than expected ANP concentrations, and it has been proposed that this natriuretic handicap could play a role in overweight related disorders. The mechanism behind the natriuretic handicap is still not clear, but presence of insulin resistance with hyperinsulinemia has been implicated.

Purpose

We investigated whether an intensive lifestyle intervention with an intended weight loss, including an increased level of physical activity and a healthy diet, could increase plasma concentrations of mid-regional pro-ANP (MR-proANP), a stable marker of ANP secretion, in overweight children. In a mechanistic perspective, we investigated metabolic changes associated with increases in MR-proANP concentrations.

Methods

This study is an extension of the Odense Overweight Intervention Study (OOIS) which included 99 overweight children (11–13 years, 55% girls). The children were randomised to a Day Camp Intervention Arm (DCIA) and a Standard Intervention Arm (SIA) for 6 weeks. DCIA included 3 hours physical activity per day and a healthy diet according to Danish recommendations. SIA included 1 weekly fun-based physical activity session and 1 lifestyle education session. OOIS included measurements of anthropometry, body composition, lipids, BP, glucose and insulin. Linear regression analyses, expressed as unstandardized regression coefficients, were used to examine between-group differences in MR-proANP concentrations and to examine the associations between changes in MR-proANP and variables of interest. As we wanted to study physiological relationships, we pooled both arms to one group to increase power in the latter.

Results

At week 6, children in DCIA had lower BMI (−2.4kg/m2) and lower total body fat (−6.5%) but higher level of fitness (4.1 ml/O2/min/kg) compared to children in SIA. From baseline to week 6 DCIA increased MR-proANP concentrations (B (95% CI): 5.7 (1.2 to 10.2) pmol/l, P=0.014) more than SIA. Of the variables studied, we found an inverse association between fall in insulin and increase in MR-proANP concentrations (B (95% CI): −0.52 (−1.02 to −0.02) pmol/l/mIU/ml, P=0.041). None of the other associations between changes in variables reached statistical significance.

Conclusion

A healthier lifestyle, based on a healthy diet and a higher level of physical activity, increases MR-proANP among overweight children. In a mechanistic perspective, improved insulin sensitivity with lower insulin appears to be a factor that leads to higher MR-proANP.

Acknowledgement/Funding

Trygfonden (Grant number: 7-11-0700)

The Arrhythmogenic Calmodulin p.Phe142Leu Mutation Impairs C-domain Ca2+ Binding but Not Calmodulin-dependent Inhibition of the Cardiac Ryanodine Receptor

A number of point mutations in the intracellular Ca²⁺-sensing protein calmodulin (CaM) are arrhythmogenic, yet their underlying mechanisms are not clear. These mutations generally decrease Ca²⁺ binding to CaM and impair inhibition of CaM-regulated Ca²⁺ channels like the cardiac Ca²⁺ release channel (ryanodine receptor, RyR2), and it appears that attenuated CaM Ca²⁺ binding correlates with impaired CaM-dependent RyR2 inhibition. Here, we investigated the RyR2 inhibitory action of the CaM p.Phe142Leu mutation (F142L; numbered including the start-Met), which markedly reduces CaM Ca²⁺ binding. Surprisingly, CaM-F142L had little to no aberrant effect on RyR2-mediated store overload-induced Ca²⁺ release in HEK293 cells compared with CaM-WT. Furthermore, CaM-F142L enhanced CaM-dependent RyR2 inhibition at the single channel level compared with CaM-WT. This is in stark contrast to the actions of arrhythmogenic CaM mutations N54I, D96V, N98S, and D130G, which all diminish CaM-dependent RyR2 inhibition. Thermodynamic analysis showed that apoCaM-F142L converts an endothermal interaction between CaM and the CaM-binding domain (CaMBD) of RyR2 into an exothermal one. Moreover, NMR spectra revealed that the CaM-F142L-CaMBD interaction is structurally different from that of CaM-WT at low Ca²⁺. These data indicate a distinct interaction between CaM-F142L and the RyR2 CaMBD, which may explain the stronger CaM-dependent RyR2 inhibition by CaM-F142L, despite its reduced Ca²⁺ binding. Collectively, these results add to our understanding of CaM-dependent regulation of RyR2 as well as the mechanistic effects of arrhythmogenic CaM mutations. The unique properties of the CaM-F142L mutation may provide novel clues on how to suppress excessive RyR2 Ca²⁺ release by manipulating the CaM-RyR2 interaction.

The effects of physical activity and exercise on brain-derived neurotrophic factor in healthy humans: A review

The purpose of this study was to summarize the effects of physical activity and exercise on peripheral brain-derived neurotrophic factor (BDNF) in healthy humans. Experimental and observational studies were identified from PubMed, Web of Knowledge, Scopus, and SPORT Discus. A total of 32 articles met the inclusion criteria. Evidence from experimental studies suggested that peripheral BDNF concentrations were elevated by acute and chronic aerobic exercise. The majority of the studies suggested that strength training had no influence on peripheral BDNF. The results from most observational studies suggested an inverse relationship between the peripheral BDNF level and habitual physical activity or cardiorespiratory fitness. More research is needed to confirm the findings from the observational studies.

[Moyamoya disease. A rare case of stroke in children?]

Moyamoya disease is a rare cerebrovascular disease with a wide variety of clinical outcomes. The main signs of the disease are progressive occlusion of the main intracerebral arteries and development of a special network of collateral vessels, Symptomatology can be intermittent, with light neurologic symptoms, or the disease can progress step-wise, with eventual physical and mental deterioration. Several operative methods have been evolved to improve cerebral bloodflow in this disease. We describe three children with Moyamoya disease. Two of them were the first patients offered operation for their disease in Norway. The article describes diagnostic measures, possible pathogenic mechanisms, and treatment.

High yield criteria and emergency department skull radiography: two community hospitals' experience

A retrospective analysis of 75 patients admitted with the diagnosis of skull fracture to two community hospitals revealed that 48% of these patients would not have been diagnosed if the high yield criteria recently proposed by the Food and Drug Administration had been adhered to in selecting patients for skull radiography. This included four patients with depressed skull fractures and 32 with linear fractures. The remaining 39 patients had at least one high yielded criterion, the most common being loss of consciousness (21.3%).

Physician extenders in walk-in clinics: a prospective evaluation of the AMOSIST program

The Automated Military Outpatient System (AMOS) Project was developed to improve the ambulatory care of patients with episodic and chronic illnesses. During the development of its episodic care component, the relative frequency of problems treated by the walk-in clinic staff was analyzed and showed a high volume of acute minor illnesses. A simple, conservative triage system run by non-professionals was developed to screen patients to a clinic for benign, self-limited illnesses run by physician-extenders. This group, the equivalent of civilian licensed practical nurses and nurses' aides, was trained in a task-oriented fashion to treat 44 common minor illnesses. Clinical algorithms for these illnesses were developed and used as training tools, memory aids, and auditing instruments. This program is now operating in 26 US Army hospitals and caring for some 44,000 patients a month in the continetal United States. We report the results of a prospective audit of the corpsmen and a study of the patient attitude and acceptance of the program.