Seitz, A. | bioRxiv Science

bioRxiv2023

S100A1's single cysteine is an indispensable redox-switch for the protection against diastolic calcium leakage in cardiomyocytes

The EF-hand calcium (Ca2+) sensor protein S100A1 combines inotropic with antiarrhythmic potency in cardiomyocytes (CM). Oxidative posttranslational modification (ox-PTM) of S100A1s conserved, single cysteine residue (C85) via reactive nitrogen species (i.e. S-nitrosylation or glutathionylation) was proposed to modulate conformational flexibility of intrinsically disordered sequence fragments and to increase the molecules affinity towards Ca2+. In light of the unknown biological functional consequence, we aimed to determine the impact of the C85 moiety of S100A1 as a potential redox-switch. We first uncovered that S100A1 is endogenously glutathionylated in the adult heart in vivo. To prevent glutathionylation of S100A1, we generated S100A1 variants that were unresponsive to ox-PTMs. Overexpression of wildtype (WT) and C85-deficient S100A1 protein variants in isolated CM demonstrated equal inotropic potency, as shown by equally augmented Ca2+ transient amplitudes under basal conditions and {beta}-adrenergic receptor ({beta}AR) stimulation. However, in contrast ox-PTM defective S100A1 variants failed to protect against arrhythmogenic diastolic sarcoplasmic reticulum (SR) Ca2+ leak and ryanodine receptor (RyR2) hypernitrosylation during {beta}-AR stimulation. Despite diastolic performance failure, C85-deficient S100A1 protein variants exerted similar Ca2+-dependent interaction with the RyR2 than WT-S100A1. Dissecting S100A1s molecular structure-function relationship, our data indicate for the first time that the conserved C85 residue potentially acts as a redox-switch that is indispensable for S100A1s antiarrhythmic but not its inotropic potency in CM. We therefore propose a model where C85s ox-PTM determines S100A1s ability to beneficially control diastolic but not systolic RyR2 activity.

molecular biology↗

bioRxiv2022

Locus coeruleus neuromelanin predicts ease of attaining and maintaining neural states of arousal

The locus coeruleus (LC), a small subcortical structure in the brainstem, is the brains principal source of norepinephrine. It plays a primary role in regulating stress, the sleep-wake cycle, and attention, and its degradation is associated with aging and neurodegenerative diseases associated with cognitive deficits (e.g., Parkinsons, Alzheimers). Yet precisely how norepinephrine drives brain networks to support healthy cognitive function remains poorly understood - partly because LCs small size makes it difficult to study noninvasively in humans. Here, we characterized LCs influence on brain dynamics using a hidden Markov model fitted to functional neuroimaging data from healthy young adults across four attention-related brain networks and LC. We modulated LC activity using a behavioral paradigm and measured individual differences in LC magnetization transfer contrast. The model revealed five hidden states, including a stable state dominated by salience-network activity that occurred when subjects actively engaged with the task. LC magnetization transfer contrast correlated with this states stability across experimental manipulations and with subjects propensity to enter into and remain in this state. These results provide new insight into LCs role in driving spatiotemporal neural patterns associated with attention, and demonstrate that variation in LC integrity can explain individual differences in these patterns even in healthy young adults.

neuroscience↗