The Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao, PR China.
Institute of Biochemistry, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada.
Peptides. 2022 Sep;155:170839. doi: 10.1016/j.peptides.2022.170839. Epub 2022 Jul 12.
The functional characteristics of neuropeptides in marine invertebrates have attracted significant attention recently although functional studies of luqin-type neuropeptides are still very limited, especially in deuterostomes. The sea cucumber, Apostichopus japonicus, is a representative species of deuterostomian Holothurian invertebrates. The species has high nutritional and medicinal value in China. In this study, we report the first comprehensive histological, biochemical and pharmacological characterization of luqin-type neuropeptide signaling in the sea cucumber A. japonicus. The A. japonicus luqin-like neuropeptide precursor (AjLQP) contains a single typical deuterostomian luqin-like neuropeptide AjLQ with an xFxRWamide motif. AjLQ was identified as the ligand for a luqin-type neuropeptide receptor AjLQR, that was previously predicted to be a tachykinin-type receptor, and triggers a rapid intracellular mobilization of Ca, followed by receptor internalization and a transient increase in ERK1/2 phosphorylation. In situ hybridization, immunohistochemistry and qRT-PCR analysis revealed extensive expression of AjLQP and AjLQ in A. japonicus tissues, especially in locomotion-related organs. In vitro pharmacological tests revealed that AjLQ caused 12.69% ± 1.99% (p < 0.01) relaxation of longitudinal muscle preparations at 10 M concentration. Furthermore, we observed significantly increased expression of AjLQP (about 17.63 fold, p < 0.01) in intestine of deeply aestivating sea cucumbers, which suggests that AjLQ might be involved in feeding inhibition during aestivation. The present study provides a first insight into the experimental characterization of luqin-type neuropeptide signaling in a sea cucumber. The results will broaden our understanding of the potential function of neuropeptides during important biological processes in marine invertebrates and provide theoretical support for optimizing sea cucumber aquaculture technology.
尽管在后口动物中对 luqin 型神经肽的功能研究仍然非常有限，但海洋无脊椎动物中神经肽的功能特征最近引起了人们的极大关注。海参是后口动物棘皮动物海胆纲的代表性物种。在中国，该物种具有很高的营养价值和药用价值。本研究首次全面描述了海参 A. japonicus 中 luqin 型神经肽信号的组织学、生化和药理学特征。A. japonicus 类 luqin 神经肽前体（AjLQP）包含一个单一的典型后口动物类 luqin 神经肽 AjLQ，其具有 xFxRWamide 基序。AjLQ 被鉴定为先前预测为速激肽型受体的 luqin 型神经肽受体 AjLQR 的配体，它触发 Ca 的快速细胞内动员，随后是受体内化和 ERK1/2 磷酸化的短暂增加。原位杂交、免疫组织化学和 qRT-PCR 分析显示 AjLQP 和 AjLQ 在 A. japonicus 组织中广泛表达，尤其是在与运动相关的器官中。体外药理学试验表明，AjLQ 在 10 M 浓度下引起纵向肌肉制剂 12.69%±1.99%（p<0.01）的松弛。此外，我们观察到在深度休眠的海参中，肠组织中 AjLQP 的表达显著增加（约 17.63 倍，p<0.01），这表明 AjLQ 可能参与休眠期间的摄食抑制。本研究首次深入了解了海参中 luqin 型神经肽信号的实验特征。研究结果将拓宽我们对海洋无脊椎动物重要生物学过程中神经肽潜在功能的理解，并为优化海参养殖技术提供理论支持。
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