Bioorganic Chemistry Laboratory, Department of Physics, University of Trento, 38123, Povo, Trento, Italy.
Climate and Ecology Unit, Research and Museum Collections Office, MUSE-Museo delle Scienze, Trento, Italy.
Cryobiology. 2022 Jun;106:84-90. doi: 10.1016/j.cryobiol.2022.03.004. Epub 2022 Mar 19.
Cell-membrane fluidity is a fundamental parameter in cold resistance. It is regulated by a fine tuning of lipid composition, usually involving a great chemical diversity among head-groups, chain lengths, and degree of unsaturation. To give new insights on Alpine chironomid cold adaptation, we analysed the lipid membrane composition of Diamesa tonsa and Pseudodiamesa branickii, two species known to have different cold-tolerance, stronger in the former. Membrane lipid composition was analysed by NMR and HPLC-MS in larvae under natural (4 °C) and laboratory conditions (30 min at - 4 °C). In both species the major class of membrane lipids were phosphatidylethanolamine (PE), reaching 93% in D. tonsa and 80% in P. branickii, followed by a minor relative amount of phosphatidylcholine (PC). Phospholipids (PL) acyl chains were highly unsaturated given the presence of a relevant amount of polyunsaturated fatty acid (PUFA), among which a high proportion of ω-3 chains. This study demonstrated that these species have a similar lipidome (e.g. relevant amount of PUFA and predominance of PE), but with relevant differences on which to base different membrane fluidity: (i) a higher unsaturation index and chain length of both PE and PC and a higher ratio PE/PC ratio in D. tonsa than in P. branickii; (ii) the absence of modifications in the lipid composition in D. tonsa under sub-zero temperature. These differences might support the different cold-tolerance of the two species. In fact, we suggest that the high PE/PC ratio and the low sterols content (as in D. tonsa) could be involved in the formation of highly deformable membranes increasing their capacity to survive freezing. Interestingly, LC-MS analysis of D. tonsa lipidome revealed a new class of lipids that we named 'PpC', absent in P. branickii, that is worth investigating.
细胞膜流动性是抗寒性的一个基本参数。它通过脂质组成的精细调节来控制，通常涉及到头部基团、链长和不饱和程度的巨大化学多样性。为了深入了解高山摇蚊的耐寒适应，我们分析了两种具有不同耐寒性的物种 Diamesa tonsa 和 Pseudodiamesa branickii 的脂质膜组成，前者的耐寒性更强。在自然条件（4°C）和实验室条件（-4°C 下 30 分钟）下，通过 NMR 和 HPLC-MS 分析幼虫的膜脂组成。在这两个物种中，膜脂的主要类别是磷脂酰乙醇胺（PE），D. tonsa 中达到 93%，P. branickii 中达到 80%，其次是相对少量的磷脂酰胆碱（PC）。由于存在大量多不饱和脂肪酸（PUFA），包括相当数量的ω-3 链，因此磷脂（PL）酰基链高度不饱和。这项研究表明，这些物种具有相似的脂质组（例如，PUFA 的含量相当，PE 占优势），但在不同的膜流动性方面存在显著差异：（i）D. tonsa 中 PE 和 PC 的不饱和指数和链长更高，PE/PC 比值也更高，而 P. branickii 则较低；（ii）D. tonsa 在下冰点温度下的脂质组成没有变化。这些差异可能支持这两个物种的不同耐寒性。事实上，我们认为高的 PE/PC 比值和低的固醇含量（如 D. tonsa 中）可能参与形成高度可变形的膜，从而提高其抗冻能力。有趣的是，D. tonsa 脂质组的 LC-MS 分析揭示了一类我们命名为“PpC”的新脂质，在 P. branickii 中不存在，值得进一步研究。
