Spolaor Simone, Rovetta Mattia, Nobile Marco S, Cazzaniga Paolo, Tisi Renata, Besozzi Daniela
Department of Informatics, Systems and Communication, University of Milano-Bicocca, Milan, Italy.
Department of Environmental Sciences, Informatics and Statistics, Ca' Foscari University of Venice, Venice, Italy.
Front Mol Biosci. 2022 May 18;9:856030. doi: 10.3389/fmolb.2022.856030. eCollection 2022.
Calcium homeostasis and signaling processes in , as well as in any eukaryotic organism, depend on various transporters and channels located on both the plasma and intracellular membranes. The activity of these proteins is regulated by a number of feedback mechanisms that act through the calmodulin-calcineurin pathway. When exposed to hypotonic shock (HTS), yeast cells respond with an increased cytosolic calcium transient, which seems to be conditioned by the opening of stretch-activated channels. To better understand the role of each channel and transporter involved in the generation and recovery of the calcium transient-and of their feedback regulations-we defined and analyzed a mathematical model of the calcium signaling response to HTS in yeast cells. The model was validated by comparing the simulation outcomes with calcium concentration variations before and during the HTS response, which were observed experimentally in both wild-type and mutant strains. Our results show that calcium normally enters the cell through the High Affinity Calcium influx System and mechanosensitive channels. The increase of the plasma membrane tension, caused by HTS, boosts the opening probability of mechanosensitive channels. This event causes a sudden calcium pulse that is rapidly dissipated by the activity of the vacuolar transporter Pmc1. According to model simulations, the role of another vacuolar transporter, Vcx1, is instead marginal, unless calcineurin is inhibited or removed. Our results also suggest that the mechanosensitive channels are subject to a calcium-dependent feedback inhibition, possibly involving calmodulin. Noteworthy, the model predictions are in accordance with literature results concerning some aspects of calcium homeostasis and signaling that were not specifically addressed within the model itself, suggesting that it actually depicts all the main cellular components and interactions that constitute the HTS calcium pathway, and thus can correctly reproduce the shaping of the calcium signature by calmodulin- and calcineurin-dependent complex regulations. The model predictions also allowed to provide an interpretation of different regulatory schemes involved in calcium handling in both wild-type and mutants yeast strains. The model could be easily extended to represent different calcium signals in other eukaryotic cells.
在酵母以及任何真核生物中，钙稳态和信号传导过程都依赖于位于质膜和内膜上的各种转运蛋白和通道。这些蛋白质的活性受多种通过钙调蛋白 - 钙神经磷酸酶途径起作用的反馈机制调节。当暴露于低渗休克（HTS）时，酵母细胞会以增加的胞质钙瞬变做出反应，这似乎是由拉伸激活通道的开放所决定的。为了更好地理解参与钙瞬变产生和恢复的每个通道和转运蛋白的作用以及它们的反馈调节，我们定义并分析了酵母细胞中对HTS的钙信号响应的数学模型。通过将模拟结果与在野生型和突变株中实验观察到的HTS响应之前和期间的钙浓度变化进行比较，对该模型进行了验证。我们的结果表明，钙通常通过高亲和力钙流入系统和机械敏感通道进入细胞。由HTS引起的质膜张力增加会提高机械敏感通道的开放概率。这一事件会导致突然的钙脉冲，该脉冲会被液泡转运蛋白Pmc1的活性迅速消散。根据模型模拟，另一种液泡转运蛋白Vcx1的作用则很小，除非钙神经磷酸酶被抑制或去除。我们的结果还表明，机械敏感通道受到钙依赖性反馈抑制，可能涉及钙调蛋白。值得注意的是，模型预测与关于钙稳态和信号传导某些方面的文献结果一致，而这些方面在模型本身中并未具体涉及，这表明它实际上描绘了构成HTS钙途径的所有主要细胞成分和相互作用，因此可以通过钙调蛋白和钙神经磷酸酶依赖性复杂调节正确再现钙信号特征的形成。模型预测还能够对野生型和突变酵母菌株中钙处理所涉及的不同调节方案进行解释。该模型可以很容易地扩展以代表其他真核细胞中的不同钙信号。
