PKA phosphorylation activates the calcium release channel (ryanodine receptor) in skeletal muscle: defective regulation in heart failure

The type 1 ryanodine receptor (RyR1) on the sarcoplasmic reticulum (SR) is the major calcium (Ca2+) release channel required for skeletal muscle excitation-contraction (EC) coupling. RyR1 function is modulated by proteins that bind to its large cytoplasmic scaffold domain, including the FK506 binding protein (FKBP12) and PKA. PKA is activated during sympathetic nervous system (SNS) stimulation. We show that PKA phosphorylation of RyR1 at Ser2843 activates the channel by releasing FKBP12. When FKB12 is bound to RyR1, it inhibits the channel by stabilizing its closed state. RyR1 in skeletal muscle from animals with heart failure (HF), a chronic hyperadrenergic state, were PKA hyperphosphorylated, depleted of FKBP12, and exhibited increased activity, suggesting that the channels are "leaky." RyR1 PKA hyperphosphorylation correlated with impaired SR Ca2+ release and early fatigue in HF skeletal muscle. These findings identify a novel mechanism that regulates RyR1 function via PKA phosphorylation in response to SNS stimulation. PKA hyperphosphorylation of RyR1 may contribute to impaired skeletal muscle function in HF, suggesting that a generalized EC coupling myopathy may play a role in HF.     

The polymorphism of the genes/enzymes involved in the last two reductive steps of monolignol synthesis: what is the functional significance?

The polymorphism of genes and enzymes involved in the last two steps of monolignol synthesis is examined in the light of recent data coming from genomic studies and mutant/transformant analyses. The two catalytic activities considered--cinnamoyl-CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD)--are encoded by small multigene families. While some degree of diversification can be noted at the sequence level, it is often difficult to use this information to assign substrate specificities to each member of a gene family. Expression profiles, however, suggest for both CAD and CCR the existence of two sub-families: one devoted to developmental lignification, and the other involved in the synthesis of defence-related compounds.     

Seeing a Ghost? Vigilance and Its Drivers in a Predator‐free World

Vigilance is a key to the early detection of predators, but may be costly if it impairs foraging efficiency. Hence, we would expect vigilance to be suppressed and/or counter‐selected in predator‐free environments, although this might depend on the environmental drivers influencing perceived predation risk. We studied vigilance in two populations of Sitka black‐tailed deer (Odocoileus hemionus sitkensis) on Haida Gwaii (Canada) which have not been exposed to predators since they colonized the study islands approx. 60 yr ago. In this context, anti‐predator behavior should not have any obvious current benefit. Moreover, its maintenance should be particularly costly in our study populations because these deer have depleted their food resources and, thus, anti‐predator behaviors should interfere with time spent searching for scarce resources. We used bait stations equipped with camera traps to assess vigilance under standardized feeding conditions. We expected to observe lower vigilance levels than those observed elsewhere in locations with predators. We investigated how vigilance varied in relation to the amount of bait, the level of visibility, and between day and night. During the day, deer spent, on average, 14% of their time in overt vigilance during foraging bouts, a level similar to, although in the lower range of, values reported at sites where predators are present. Levels of vigilance were lower at night, and decreased with increasing visibility, but not during the day. Deer were less vigilant when bait availability was high, but only when visibility was also high. We discuss why the maintenance of vigilance is here best explained by the ghosts of predators past, and how, at the temporal scale of a few generations, the ecological factors driving vigilance levels might override the absence of significant risk from large predators.     

A receptor-like kinase mediates the response of Arabidopsis cells to the inhibition of cellulose synthesis

BACKGROUND: A major challenge is to understand how the walls of expanding plant cells are correctly assembled and remodeled, often in the presence of wall-degrading micro-organisms. Plant cells, like yeast, react to cell-wall perturbations as shown by changes in gene expression, accumulation of ectopic lignin, and growth arrest caused by the inhibition of cellulose synthesis. RESULTS: We have identified a plasma-membrane-bound receptor-like kinase (THESEUS1), which is present in elongating cells. Mutations in THE1 and overexpression of a functional THE1-GFP fusion protein did not affect wild-type (WT) plants but respectively attenuated and enhanced growth inhibition and ectopic lignification in seedlings mutated in cellulose synthase CESA6 without influencing the cellulose deficiency. A T-DNA insertion mutant for THE1 also attenuated the growth defect and ectopic-lignin production in other but not all cellulose-deficient mutants. The deregulation of a small number of genes in cesA6 mutants depended on the presence of THE1. Some of these genes are involved in pathogen defense, in wall crosslinking, or in protecting the cell against reactive oxygen species. CONCLUSIONS: The results show that THE1 mediates the response of growing plant cells to the perturbation of cellulose synthesis and may act as a cell-wall-integrity sensor.     

“Ryanopathies” and RyR2 dysfunctions: can we further decipher them using in vitro human disease models?

The regulation of intracellular calcium (Ca²⁺) homeostasis is fundamental to maintain normal functions in many cell types. The ryanodine receptor (RyR), the largest intracellular calcium release channel located on the sarco/endoplasmic reticulum (SR/ER), plays a key role in the intracellular Ca²⁺ handling. Abnormal type 2 ryanodine receptor (RyR2) function, associated to mutations (ryanopathies) or pathological remodeling, has been reported, not only in cardiac diseases, but also in neuronal and pancreatic disorders. While animal models and in vitro studies provided valuable contributions to our knowledge on RyR2 dysfunctions, the human cell models derived from patients’ cells offer new hope for improving our understanding of human clinical diseases and enrich the development of great medical advances. We here discuss the current knowledge on RyR2 dysfunctions associated with mutations and post-translational remodeling. We then reviewed the novel human cellular technologies allowing the correlation of patient’s genome with their cellular environment and providing approaches for personalized RyR-targeted therapeutics.Subject terms: Ventricular tachycardia, Ventricular tachycardia     

Versatility of non-native forms of human cytochrome c: pH and micellar concentration dependence

In addition to its electron transfer activity, cytochrome c is now known to trigger apoptosis via peroxidase activity. This new function is related to a structural modification of the cytochrome upon association with anionic lipids, particularly cardiolipin present in the mitochondrial membrane. However, the exact nature of the non-native state induced by this interaction remains an active subject of debate. In this work, using human cytochromes c (native and two single-histidine mutants and the corresponding double mutant) and micelles as a hydrophobic medium, we succeeded, through UV–visible spectroscopy, circular dichroism spectroscopy and NMR spectroscopy, in fully characterizing the nature of the sixth ligand replacing the native methionine. Furthermore, careful pH titrations permitted the identification of the amino acids involved in the iron binding over a range of pH values. Replacement of the methionine by lysine was only observed at pH above 8.5, whereas histidine binding is dependent on both pH and micelle concentration. The pH variation range for histidine protonation is relatively narrow and is consistent with the mitochondrial intermembrane pH changes occurring during apoptosis. These results allow us to rule out lysine as the sixth ligand at pH values close to neutrality and reinforce the role of histidines (preferentially His33 vs. His26) as the main candidate to replace methionine in the non-native cytochrome c. Finally, on the basis of these results and molecular dynamics simulations, we propose a 3D model for non-native cytochrome c in a micellar environment.     

Ryanodine receptor oxidation causes intracellular calcium leak and muscle weakness in aging

Age-related loss of muscle mass and force (sarcopenia) contributes to disability and increased mortality. Ryanodine receptor 1 (RyR1) is the skeletal muscle sarcoplasmic reticulum calcium release channel required for muscle contraction. RyR1 from aged (24?months) rodents was oxidized, cysteine-nitrosylated, and depleted of the channel-stabilizing subunit calstabin1, compared to RyR1 from younger (3-6?months) adults. This RyR1 channel complex remodeling resulted in "leaky" channels with increased open probability, leading to intracellular calcium leak in skeletal muscle. Similarly, 6-month-old mice harboring leaky RyR1-S2844D mutant channels exhibited skeletal muscle defects comparable to 24-month-old wild-type mice. Treating aged mice with S107 stabilized binding of calstabin1 to RyR1, reduced intracellular calcium leak, decreased reactive oxygen species (ROS), and enhanced tetanic Ca(2+) release, muscle-specific force, and exercise capacity. Taken together, these data indicate that leaky RyR1 contributes to age-related loss of muscle function.