Divergent Biochemical Properties and Disparate Impact of Arrhythmogenic Calmodulin Mutations on Zebrafish Cardiac Function.

Calmodulin (CaM) is a ubiquitous, small cytosolic calcium (Ca2+)-binding sensor that plays a vital role in many cellular processes by binding and regulating the activity of over 300 protein targets. In cardiac muscle, CaM modulates directly or indirectly the activity of several proteins that play a key role in excitation-contraction coupling (ECC), such as ryanodine receptor type 2 (RyR2), l-type Ca2+ (Cav1.2), sodium (NaV1.5) and potassium (KV7.1) channels. Many recent clinical and genetic studies have reported a series of CaM mutations in patients with life-threatening arrhythmogenic syndromes, such as long QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardia (CPVT). We recently showed that four arrhythmogenic CaM mutations (N98I, D132E, D134H, and Q136P) significantly reduce the binding of CaM to RyR2. Herein, we investigate in vivo functional effects of these CaM mutations on the normal zebrafish embryonic heart function by microinjecting complementary RNA corresponding to CaMN98I, CaMD132E, CaMD134H, and CaMQ136P mutants. Expression of CaMD132E and CaMD134H mutants results in significant reduction of the zebrafish heart rate, mimicking a severe form of human bradycardia, whereas expression of CaMQ136P results in an increased heart rate mimicking human ventricular tachycardia. Moreover, analysis of cardiac ventricular rhythm revealed that the CaMD132E and CaMN98I zebrafish groups display an irregular pattern of heart beating and increased amplitude in comparison to the control groups. Furthermore, circular dichroism spectroscopy experiments using recombinant CaM proteins reveals a decreased structural stability of the four mutants compared to the wild-type CaM protein in the presence of Ca2+. Finally, Ca2+-binding studies indicates that all CaM mutations display reduced CaM Ca2+-binding affinities, with CaMD132E exhibiting the most prominent change. Our data suggest that CaM mutations can trigger different arrhythmogenic phenotypes through multiple and complex molecular mechanisms.

Hypertrophic cardiomyopathy-linked variants of cardiac myosin-binding protein C3 display altered molecular properties and actin interaction.

The most common inherited cardiac disorder, hypertrophic cardiomyopathy (HCM), is characterized by thickening of heart muscle, for which genetic mutations in cardiac myosin-binding protein C3 (c-MYBPC3) gene, is the leading cause. Notably, patients with HCM display a heterogeneous clinical presentation, onset and prognosis. Thus, delineating the molecular mechanisms that explain how disparate c-MYBPC3 variants lead to HCM is essential for correlating the impact of specific genotypes on clinical severity. Herein, five c-MYBPC3 missense variants clinically associated with HCM were investigated; namely V1 (R177H), V2 (A216T), V3 (E258K), V4 (E441K) and double mutation V5 (V3 + V4), all located within the C1 and C2 domains of MyBP-C, a region known to interact with sarcomeric protein, actin. Injection of the variant complementary RNAs in zebrafish embryos was observed to recapitulate phenotypic aspects of HCM in patients. Interestingly, V3- and V5-cRNA injection produced the most severe zebrafish cardiac phenotype, exhibiting increased diastolic/systolic myocardial thickness and significantly reduced heart rate compared with control zebrafish. Molecular analysis of recombinant C0-C2 protein fragments revealed that c-MYBPC3 variants alter the C0-C2 domain secondary structure, thermodynamic stability and importantly, result in a reduced binding affinity to cardiac actin. V5 (double mutant), displayed the greatest protein instability with concomitant loss of actin-binding function. Our study provides specific mechanistic insight into how c-MYBPC3 pathogenic variants alter both functional and structural characteristics of C0-C2 domains leading to impaired actin interaction and reduced contractility, which may provide a basis for elucidating the disease mechanism in HCM patients with c-MYBPC3 mutations.

Male infertility-linked point mutation reveals a vital binding role for the C2 domain of sperm PLCζ.

Sperm-specific phospholipase C zeta (PLCζ) is widely considered to be the physiological stimulus that evokes intracellular calcium (Ca2+) oscillations that are essential for the initiation of egg activation during mammalian fertilisation. A recent genetic study reported a male infertility case that was directly associated with a point mutation in the PLCζ C2 domain, where an isoleucine residue had been substituted with a phenylalanine (I489F). Here, we have analysed the effect of this mutation on the in vivo Ca2+ oscillation-inducing activity and the in vitro biochemical properties of human PLCζ. Microinjection of cRNA or recombinant protein corresponding to PLCζI489F mutant at physiological concentrations completely failed to cause Ca2+ oscillations and trigger development. However, this infertile phenotype could be effectively rescued by microinjection of relatively high (non-physiological) amounts of recombinant mutant PLCζI489F protein, leading to Ca2+ oscillations and egg activation. Our in vitro biochemical analysis suggested that the PLCζI489F mutant displayed similar enzymatic properties, but dramatically reduced binding to PI(3)P and PI(5)P-containing liposomes compared with wild-type PLCζ. Our findings highlight the importance of PLCζ at fertilisation and the vital role of the C2 domain in PLCζ function, possibly due to its novel binding characteristics.

Antigen unmasking enhances visualization efficacy of the oocyte activation factor, phospholipase C zeta, in mammalian sperm.

STUDY QUESTION: Is it possible to improve clinical visualization of phospholipase C zeta (PLCζ) as a diagnostic marker of sperm oocyte activation capacity and male fertility? SUMMARY ANSWER: Poor PLCζ visualization efficacy using current protocols may be due to steric or conformational occlusion of native PLCζ, hindering antibody access, and is significantly enhanced using antigen unmasking/retrieval (AUM) protocols. WHAT IS KNOWN ALREADY: Mammalian oocyte activation is mediated via a series of intracellular calcium (Ca2+) oscillations induced by sperm-specific PLCζ. PLCζ represents not only a potential clinical therapeutic in cases of oocyte activation deficiency but also a diagnostic marker of sperm fertility. However, there are significant concerns surrounding PLCζ antibody specificity and detection protocols. STUDY DESIGN, SIZE DURATION: Two PLCζ polyclonal antibodies, with confirmed PLCζ specificity, were employed in mouse, porcine and human sperm. Experiments evaluated PLCζ visualization efficacy, and whether AUM improved this. Antibodies against two sperm-specific proteins [post-acrosomal WW-binding protein (PAWP) and acrosin] were used as controls. PARTICIPANTS/MATERIALS, SETTING, METHODS: Aldehyde- and methanol-fixed sperm were subject to immunofluorescence analysis following HCl exposure (pH = 0.1-0.5), acid Tyrode's solution exposure (pH = 2.5) or heating in 10 mM sodium citrate solution (pH = 6.0). Fluorescence intensity of at least 300 cells was recorded for each treatment, with three independent repeats. MAIN RESULTS AND THE ROLE OF CHANCE: Despite high specificity for native PLCζ following immunoblotting using epitope-specific polyclonal PLCζ antibodies in mouse, porcine and human sperm, immunofluorescent visualization efficacy was poor. In contrast, sperm markers PAWP and acrosin exhibited relatively impressive results. All methods of AUM on aldehyde-fixed sperm enhanced visualization efficacy for PLCζ compared to visualization efficacy before AUM (P < 0.05 for all AUM interventions), but exerted no significant change upon PAWP or acrosin immunofluorescence following AUM. All methods of AUM enhanced PLCζ visualization efficacy in mouse and human methanol-fixed sperm compared to without AUM (P < 0.05 for all AUM interventions), while no significant change was observed in methanol-fixed porcine sperm before and after. In the absence of aldehyde-induced cross-linkages, such results suggest that poor PLCζ visualization efficacy may be due to steric or conformational occlusion of native PLCζ, hindering antibody access. Importantly, examination of sperm from individual donors revealed that AUM differentially affects observable PLCζ fluorescence, and the proportion of sperm exhibiting detectable PLCζ fluorescence in sperm from different males. LIMITATIONS, REASONS FOR CAUTION: Direct correlation of fertility outcomes with the level of PLCζ in the sperm samples studied was not available. Such analyses would be required in future to determine whether the improved methodology for PLCζ visualization we propose would indeed reflect fertility status. WIDER IMPLICATIONS OF THE FINDINGS: We propose that AUM alters conformational interactions to enhance PLCζ epitope availability and visualization efficacy, supporting prospective application of AUM to reduce misinterpretation in clinical diagnosis of PLCζ-linked male infertility. Our current results suggest that it is perhaps prudent that previous studies investigating links between PLCζ and fertility parameters are re-examined in the context of AUM, and may pave the way for future work to answer significant questions such as how PLCζ appears to be kept in an inactive form in the sperm. LARGE SCALE DATA: Not applicable. STUDY FUNDING/COMPETING INTERESTS: J.K. is supported by a Health Fellowship award from the National Institute for Social Care and Health Research (NISCHR). M.N. is supported by a Marie Curie Intra-European Research Fellowship award. This work was also partly funded by a research grant from Cook Medical Technologies LLC. There are no competing financial interests to declare.

Essential Role of the EF-hand Domain in Targeting Sperm Phospholipase Cζ to Membrane Phosphatidylinositol 4,5-Bisphosphate (PIP2).

Sperm-specific phospholipase C-ζ (PLCζ) is widely considered to be the physiological stimulus that triggers intracellular Ca(2+) oscillations and egg activation during mammalian fertilization. Although PLCζ is structurally similar to PLCδ1, it lacks a pleckstrin homology domain, and it remains unclear how PLCζ targets its phosphatidylinositol 4,5-bisphosphate (PIP2) membrane substrate. Recently, the PLCδ1 EF-hand domain was shown to bind to anionic phospholipids through a number of cationic residues, suggesting a potential mechanism for how PLCs might interact with their target membranes. Those critical cationic EF-hand residues in PLCδ1 are notably conserved in PLCζ. We investigated the potential role of these conserved cationic residues in PLCζ by generating a series of mutants that sequentially neutralized three positively charged residues (Lys-49, Lys-53, and Arg-57) within the mouse PLCζ EF-hand domain. Microinjection of the PLCζ EF-hand mutants into mouse eggs enabled their Ca(2+) oscillation inducing activities to be compared with wild-type PLCζ. Furthermore, the mutant proteins were purified, and the in vitro PIP2 hydrolysis and binding properties were monitored. Our analysis suggests that PLCζ binds significantly to PIP2, but not to phosphatidic acid or phosphatidylserine, and that sequential reduction of the net positive charge within the first EF-hand domain of PLCζ significantly alters in vivo Ca(2+) oscillation inducing activity and in vitro interaction with PIP2 without affecting its Ca(2+) sensitivity. Our findings are consistent with theoretical predictions provided by a mathematical model that links oocyte Ca(2+) frequency and the binding ability of different PLCζ mutants to PIP2. Moreover, a PLCζ mutant with mutations in the cationic residues within the first EF-hand domain and the XY linker region dramatically reduces the binding of PLCζ to PIP2, leading to complete abolishment of its Ca(2+) oscillation inducing activity.

Distinctive malfunctions of calmodulin mutations associated with heart RyR2-mediated arrhythmic disease.

Calmodulin (CaM) is a cytoplasmic calcium sensor that interacts with the cardiac ryanodine receptor (RyR2), a large Ca(2+) channel complex that mediates Ca(2+) efflux from the sarcoplasmic reticulum (SR) to activate cardiac muscle contraction. Direct CaM association with RyR2 is an important physiological regulator of cardiac muscle excitation-contraction coupling and defective CaM-RyR2 protein interaction has been reported in cases of heart failure. Recent genetic studies have identified CaM missense mutations in patients with a history of severe cardiac arrhythmogenic disorders that present divergent clinical features, including catecholaminergic polymorphic ventricular tachycardia (CPVT), long QT syndrome (LQTS) and idiopathic ventricular fibrillation (IVF). Herein, we describe how two CPVT- (N54I & N98S) and three LQTS-associated (D96V, D130G & F142L) CaM mutations result in alteration of their biochemical and biophysical properties. Ca(2+)-binding studies indicate that the CPVT-associated CaM mutations, N54I & N98S, exhibit the same or a 3-fold reduced Ca(2+)-binding affinity, respectively, versus wild-type CaM, whereas the LQTS-associated CaM mutants, D96V, D130G & F142L, display more profoundly reduced Ca(2+)-binding affinity. In contrast, all five CaM mutations confer a disparate RyR2 interaction and modulation of [(3)H]ryanodine binding to RyR2, regardless of CPVT or LQTS association. Our findings suggest that the clinical presentation of CPVT or LQTS associated with these five CaM mutations may involve both altered intrinsic Ca(2+)-binding as well as defective interaction with RyR2.

Human PLCζ exhibits superior fertilization potency over mouse PLCζ in triggering the Ca(2+) oscillations required for mammalian oocyte activation.

A sperm-specific phospholipase C-zeta (PLCζ) is believed to play an essential role in oocyte activation during mammalian fertilization. Sperm PLCζ has been shown to trigger a prolonged series of repetitive Ca(2+) transients or oscillations in oocytes that precede activation. This remarkable intracellular Ca(2+) signalling phenomenon is a distinctive characteristic observed during in vitro fertilization by sperm. Previous studies have notably observed an apparent differential ability of PLCζ from disparate mammalian species to trigger Ca(2+) oscillations in mouse oocytes. However, the molecular basis and confirmation of the apparent PLCζ species difference in activity remains to be provided. In the present study, we provide direct evidence for the superior effectiveness of human PLCζ relative to mouse PLCζ in generating Ca(2+) oscillations in mouse oocytes. In addition, we have designed and constructed a series of human/mouse PLCζ chimeras to enable study of the potential role of discrete PLCζ domains in conferring the enhanced Ca(2+) signalling potency of human PLCζ. Functional analysis of these human/mouse PLCζ domain chimeras suggests a novel role of the EF-hand domain in the species-specific differences in PLCζ activity. Our empirical observations are compatible with a basic mathematical model for the Ca(2+) dependence of generating cytoplasmic Ca(2+) oscillations in mammalian oocytes by sperm PLCζ.

Loss of Tuberous Sclerosis Complex 2 confers inflammation via dysregulation of Nuclear factor kappa-light-chain-enhancer of activated B cells.

Background: Aberrant activation of mTORC1 is clearly defined in TSC, causing uncontrolled cell growth. While mTORC1 inhibitors show efficacy to stabilise tumour growth in TSC, they are not fully curative. Disease facets of TSC that are not restored with mTOR inhibitors might involve NF-κB. The study aimed to characterise NF-κB in the context of TSC. Results: Enrichment of NF-κB-regulated genes was observed in TSC patient tumours, SEN/SEGAs, cortical tubers and a TSC tumour-derived cell line (621 - 101). Highlighting an inflammatory component of TSC, TSC cell models showed an elevated level of NF-κB and STAT3 activation. Herein, we report a dysregulated inflammatory phenotype of TSC2-deficient cells where NF-κB promotes autocrine signalling involving IL-6. Of importance, mTORC1 inhibition does not block this inflammatory signal to promote STAT3, while NF-κB inhibition was much more effective. Combined mTORC1 and NF-κB inhibition was potent at preventing anchorage-independent growth of TSC2-deficient cells, and unlike mTORC1 inhibition alone was sufficient to prevent colony regrowth after cessation of treatment. Conclusion: This study reveals autocrine signalling crosstalk between NF-κB and STAT3 in TSC cell models. Furthermore, the data presented indicate that NF-κB pathway inhibitors could be a viable adjunct therapy with the current mTOR inhibitors to treat TSC.

Phospholipase Cζ binding to PtdIns(4,5)P2 requires the XY-linker region.

Phospholipase C-zeta (PLCζ) is a strong candidate for the mammalian sperm-derived factor that triggers the Ca(2+) oscillations required for egg activation at fertilization. PLCζ lacks a PH domain, which targets PLCδ1 to the phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)) substrate in the plasma membrane. Previous studies failed to detect PLCζ in the plasma membrane, hence the means of PLCζ binding to PtdIns(4,5)P(2) is unclear. We find that the PLCζ XY linker, but not the C2 domain, exhibits robust binding to PtdIns(4,5)P(2) or to liposomes containing near-physiological levels of PtdIns(4,5)P(2). The role of positively charged residues within the XY linker was addressed by sequentially substituting alanines for three lysine residues, K374, K375 and K377. Microinjection of these mutants into mouse eggs enabled their Ca(2+) oscillation-inducing activities to be compared with wild-type PLCζ. The XY-linker mutant proteins were purified and the in vitro PtdIns(4,5)P(2) hydrolysis and binding properties were monitored. Successive reduction of net positive charge within the PLCζ XY linker significantly affects both in vivo Ca(2+)-oscillation-inducing activity and in vitro PtdIns(4,5)P(2) interaction of mouse PLCζ. Our data suggest that positively charged residues within the XY linker play an important role in the PLCζ interaction with PtdIns(4,5)P(2), a crucial step in generating the Ca(2+) activation signal that is essential for fertilization in mammals.

Chimeras of sperm PLCζ reveal disparate protein domain functions in the generation of intracellular Ca2+ oscillations in mammalian eggs at fertilization.

Phospholipase C-zeta (PLCζ) is a sperm-specific protein believed to cause Ca(2+) oscillations and egg activation during mammalian fertilization. PLCζ is very similar to the somatic PLCδ1 isoform but is far more potent in mobilizing Ca(2+) in eggs. To investigate how discrete protein domains contribute to Ca(2+) release, we assessed the function of a series of PLCζ/PLCδ1 chimeras. We examined their ability to cause Ca(2+) oscillations in mouse eggs, enzymatic properties using in vitro phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis and their binding to PIP2 and PI(3)P with a liposome interaction assay. Most chimeras hydrolyzed PIP2 with no major differences in Ca(2+) sensitivity and enzyme kinetics. Insertion of a PH domain or replacement of the PLCζ EF hands domain had no deleterious effect on Ca(2+) oscillations. In contrast, replacement of either XY-linker or C2 domain of PLCζ completely abolished Ca(2+) releasing activity. Notably, chimeras containing the PLCζ XY-linker bound to PIP2-containing liposomes, while chimeras containing the PLCζ C2 domain exhibited PI(3)P binding. Our data suggest that the EF hands are not solely responsible for the nanomolar Ca(2+) sensitivity of PLCζ and that membrane PIP2 binding involves the C2 domain and XY-linker of PLCζ. To investigate the relationship between PLC enzymatic properties and Ca(2+) oscillations in eggs, we have developed a mathematical model that incorporates Ca(2+)-dependent InsP3 generation by the PLC chimeras and their levels of intracellular expression. These numerical simulations can for the first time predict the empirical variability in onset and frequency of Ca(2+) oscillatory activity associated with specific PLC variants.

Life-threatening arrhythmogenic CaM mutations disrupt CaM binding to a distinct RyR2 CaM-binding pocket.

Calmodulin (CaM) modulates the activity of several proteins that play a key role in excitation-contraction coupling (ECC). In cardiac muscle, the major binding partner of CaM is the type-2 ryanodine receptor (RyR2) and altered CaM binding contributes to defects in sarcoplasmic reticulum (SR) calcium (Ca2+) release. Many genetic studies have reported a series of CaM missense mutations in patients with a history of severe arrhythmogenic cardiac disorders. In the present study, we generated four missense CaM mutants (CaMN98I, CaMD132E, CaMD134H and CaMQ136P) and we used a CaM-RyR2 co-immunoprecipitation and a [3H]ryanodine binding assay to directly compare the relative RyR2-binding of wild type and mutant CaM proteins and to investigate the functional effects of these CaM mutations on RyR2 activity. Furthermore, isothermal titration calorimetry (ITC) experiments were performed to investigate and compare the interactions of the wild-type and mutant CaM proteins with various synthetic peptides located in the well-established RyR2 CaM-binding region (3584-3602aa), as well as another CaM-binding region (4255-4271aa) of human RyR2. Our data revealed that all four CaM mutants displayed dramatically reduced RyR2 interaction and defective modulation of [3H]ryanodine binding to RyR2, regardless of LQTS or CPVT association. Moreover, our isothermal titration calorimetry ITC data suggest that RyR2 3584-3602aa and 4255-4271aa regions interact with significant affinity with wild-type CaM, in the presence and absence of Ca2+, two regions that might contribute to a putative intra-subunit CaM-binding pocket. In contrast, screening the interaction of the four arrhythmogenic CaM mutants with two synthetic peptides that correspond to these RyR2 regions, revealed disparate binding properties and signifying differential mechanisms that contribute to reduced RyR2 association.

Male infertility-linked point mutation disrupts the Ca2+ oscillation-inducing and PIP(2) hydrolysis activity of sperm PLCζ.

A male infertility-linked human PLCζ (phospholipase Cζ) mutation introduced into mouse PLCζ completely abolishes both in vitro PIP(2) (phosphatidylinositol 4,5-bisphosphate) hydrolysis activity and the ability to trigger in vivo Ca2+ oscillations in mouse eggs. Wild-type PLCζ initiated a normal pattern of Ca2+ oscillations in eggs in the presence of 10-fold higher mutant PLCζ, suggesting that infertility is not mediated by a dominant-negative mechanism.

Drug Inhibition of Redox Factor-1 Restores Hypoxia-Driven Changes in Tuberous Sclerosis Complex 2 Deficient Cells.

Therapies with the mechanistic target of rapamycin complex 1 (mTORC1) inhibitors are not fully curative for tuberous sclerosis complex (TSC) patients. Here, we propose that some mTORC1-independent disease facets of TSC involve signaling through redox factor-1 (Ref-1). Ref-1 possesses a redox signaling activity that stimulates the transcriptional activity of STAT3, NF-kB, and HIF-1α, which are involved in inflammation, proliferation, angiogenesis, and hypoxia, respectively. Here, we demonstrate that redox signaling through Ref-1 contributes to metabolic transformation and tumor growth in TSC cell model systems. In TSC2-deficient cells, the clinically viable Ref-1 inhibitor APX3330 was effective at blocking the hyperactivity of STAT3, NF-kB, and HIF-1α. While Ref-1 inhibitors do not inhibit mTORC1, they potently block cell invasion and vasculature mimicry. Of interest, we show that cell invasion and vasculature mimicry linked to Ref-1 redox signaling are not blocked by mTORC1 inhibitors. Metabolic profiling revealed that Ref-1 inhibitors alter metabolites associated with the glutathione antioxidant pathway as well as metabolites that are heavily dysregulated in TSC2-deficient cells involved in redox homeostasis. Therefore, this work presents Ref-1 and associated redox-regulated transcription factors such as STAT3, NF-kB, and HIF-1α as potential therapeutic targets to treat TSC, where targeting these components would likely have additional benefits compared to using mTORC1 inhibitors alone.

Inflammation and frailty measures in older people.

Inflammation in patients defined as frail by Fried's phenotypic definition may be related to sarcopenia. This study aimed to investigate inflammation in older patients across different frailty criteria. Frailty status was determined in 110 patients aged over 75 years (mean 83.9 years) according to function (dependent, intermediate, independent); Fried (three or more items of exhaustion, weight loss, slow walking speed, low handgrip strength, low physical activity) and Frailty Index (a measure of accumulated deficits). With increasing patient frailty as defined by function and by Fried phenotype, tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and C-reactive protein (CRP) increased significantly. Albumin was lowest in the frailest subjects by each definition. The greatest differences were seen between intermediate and dependent groups and between the pre-frail and frail. Adjustment for multiple covariates (age, sex, BMI category, smoking status, number of co-morbidities and number of prescribed medications) did not account for any of the observed differences in levels of inflammatory markers. The Frailty Index correlated significantly with log-transformed CRP (r= 0.221, P < 0.05), log-transformed IL-6 (r= 0.369, P < 0.01), TNF-alpha (r= 0.379, P < 0.01) and inversely with albumin (r=- 0.545, P < 0.01). This study provides further evidence linking inflammation and frailty in older people, an association that seems consistent across different frailty measures.

Arrhythmogenic calmodulin E105A mutation alters cardiac RyR2 regulation leading to cardiac dysfunction in zebrafish.

Calmodulin (CaM) is a universal calcium (Ca2+ )-binding messenger that regulates many vital cellular events. In cardiac muscle, CaM associates with ryanodine receptor 2 (RyR2) and regulates excitation-contraction coupling. Mutations in human genes CALM1, CALM2, and CALM3 have been associated with life-threatening heart disorders, such as long QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardia. A novel de novo LQTS-associated missense CaM mutation (E105A) was recently identified in a 6-year-old boy, who experienced an aborted first episode of cardiac arrest. Herein, we report the first molecular characterization of the CaM E105A mutation. Expression of the CaM E105A mutant in zebrafish embryos resulted in cardiac arrhythmia and increased heart rate, suggestive of ventricular tachycardia. In vitro biophysical and biochemical analysis revealed that E105A confers a deleterious effect on protein stability and a reduced Ca2+ -binding affinity due to loss of cooperativity. Finally, the CaM E105A mutation resulted in reduced CaM-RyR2 interaction and defective modulation of ryanodine binding. Our findings suggest that the CaM E105A mutation dysregulates normal cardiac function by a complex mechanism involving alterations in both CaM-Ca2+ and CaM-RyR2 interactions.

Plasma esterases and inflammation in ageing and frailty.

OBJECTIVES: Esterases are enzymes of drug metabolism known to be reduced in frail older people and during acute illness. The mechanism for this is unknown. The aim of this study was to examine esterase activity and inflammation in ageing and frailty. METHODS: Thirty frail patients (mean age 84.9 years) dependent on continuing inpatient care, 40 patients of intermediate frailty attending Day Hospital (84.2 years), 40 fit older controls (82.7 years) and 30 young controls (23.3 years) were studied. Frailty indicators, plasma esterase activities and markers of inflammation were measured. RESULTS: With increasing patient frailty, C-reactive protein (CRP), interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-alpha) increased significantly and esterase activity, with the exception of aspirin esterase, fell significantly (p < 0.005). There were significant negative correlations between log-transformed IL-6 and acetylcholinesterase (r = -0.354, p < 0.01), butyrylcholinesterase (r = -0.392, p < 0.01) and benzoylcholinesterase activity (r = -0.241, p < 0.05) and significant negative correlations between TNF-alpha and acetylcholinesterase (r = -0.223, p < 0.01), butyrylcholinesterase (r = -0.279, p < 0.01) and benzoylcholinesterase activity (r = -0.253, p < 0.01). Aspirin esterase activity did not correlate with IL-6 or TNF- alpha. CONCLUSION: Frailty was associated with higher inflammatory markers and lower esterase activity. There was a weak but significant negative correlation between both IL-6 and TNF-alpha and the activity of three of four esterases. The negative correlation between esterase activity and inflammatory markers may have a causal basis, comparable to the inflammatory suppression of cytochrome P-450 enzymes.

Mutations in PLCδ1 associated with hereditary leukonychia display divergent PIP2 hydrolytic function.

Hereditary leukonychia is a rare genetic nail disorder characterized by distinctive whitening of the nail plate of all 20 nails. Hereditary leukonychia may exist as an isolated feature, or in simultaneous occurrence with other cutaneous or systemic pathologies. Associations between hereditary leukonychia and mutations in the gene encoding phospholipase C delta-1 (PLCδ1) have previously been identified. However, the molecular mechanisms underlying PLCδ1 mutations and hereditary leukonychia remain uncharacterized. In the present study, we introduced hereditary leukonychia-linked human PLCδ1 mutations (C209R, A574T and S740R) into equivalent residues of rat PLCδ1 (C188R, A553T and S719R), and investigated their effect on the biophysical and biochemical properties of the PLCδ1 protein. Our data suggest that these PLCδ1 mutations associated with hereditary leukonychia do not uniformly alter the enzymatic ability of this protein leading to loss/gain of function, but result in significantly divergent enzymatic properties. We demonstrate here for the first time the importance of PLC-mediated calcium (Ca2+ ) signalling within the manifestation of hereditary leukonychia. PLCδ1 is almost ubiquitous in mammalian cells, which may explain why hereditary leukonychia manifests in association with other systemic pathologies relating to keratin expression.

Altered RyR2 regulation by the calmodulin F90L mutation associated with idiopathic ventricular fibrillation and early sudden cardiac death.

Calmodulin (CaM) association with the cardiac muscle ryanodine receptor (RyR2) regulates excitation-contraction coupling. Defective CaM-RyR2 interaction is associated with heart failure. A novel CaM mutation (CaM(F90L)) was recently identified in a family with idiopathic ventricular fibrillation (IVF) and early onset sudden cardiac death. We report the first biochemical characterization of CaM(F90L). F90L confers a deleterious effect on protein stability. Ca(2+)-binding studies reveal reduced Ca(2+)-binding affinity and a loss of co-operativity. Moreover, CaM(F90L) displays reduced RyR2 interaction and defective modulation of [(3)H]ryanodine binding. Hence, dysregulation of RyR2-mediated Ca(2+) release via aberrant CaM(F90L)-RyR2 interaction is a potential mechanism that underlies familial IVF.

Nutrition, inflammation, and leptin levels in aging and frailty.

OBJECTIVES: To examine nutritional indices and levels of leptin and inflammatory markers across age and frailty. DESIGN: Observational study. SETTING: Continuing care wards and a day hospital in Cardiff, South Wales, United Kingdom. PARTICIPANTS: Thirty dependent patients (mean age 84.9) needing continuing inpatient care, 40 patients with falls attending a day hospital (mean age 84.2), 40 independent controls (mean age 82.7), and 30 young controls (mean age 23.3). MEASUREMENTS: Functional status, including the five frailty indicators proposed by Fried et al., anthropometry, and serum markers of nutrition and inflammation. RESULTS: The continuing care patients were frail, all having three to five frailty indicators. Day hospital patients were of intermediate frailty (mean Fried score 2.97), and the independent group was fittest (0.83). Body mass index, triceps skinfold thickness (TSF), and mid-arm muscle area were lowest in continuing care patients. With increasing patient frailty, albumin levels fell significantly (P<.005) and C-reactive protein (CRP) levels increased significantly (P<.005). Continuing care patients had significantly lower leptin levels (P<.005) and significantly higher interleukin (IL)-6 levels (P<.005). There was a significant correlation between log transformed leptin and TSF for each patient group. CONCLUSION: The frailest older people displayed features of cachexia. Their leptin levels were appropriately low given their low body fat, and IL-6 and CRP levels were high. The mechanism of their cachexia may therefore be similar to that proposed in heart failure and cancer: disturbed hypothalamic feedback of leptin or effects of proinflammatory cytokines.