Sulfakinins (SKs) are pleiotropic neuropeptides commonly found in insects, structurally and functionally homologous to the mammalian gastrin/cholecystokinin (CCK) neuropeptides. SKs together with sulfakinin receptors (SKRs) are involved in sulfakinin signaling responsible for variety of biological functions, including food intake or fatty acid metabolism. In the present study, we determined the distribution of SKRs in Tenebrio molitor larvae and characterized the impact of nonsulfated and sulfated SKs on carbohydrates and insulin-like peptides (ILPs) level in beetle hemolymph. Our results indicate the presence of both sulfakinin receptors, SKR1 and SKR2, in the nervous system of T. molitor. The distribution of SKR2 in peripheral tissues was more widespread than SKR1, and their transcripts have been found in fat body, gut and hemolymph. This is also the first evidence for SKRs presence in insect hemocytes indicating immunotropic activity of SKs. Moreover, in the present study, we have demonstrated that SKs regulate ILPs and carbohydrates level in insect hemolymph, and that sulfation is not crucial for peptides activity. Our study confirms the role of SKs in maintaining energy homeostasis in beetles.

中文翻译：

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黄粉虫磺胺激肽受体 (SKR) 的鉴定及磺胺激肽对碳水化合物代谢的影响

Sulfakinins (SKs) 是昆虫中常见的多效性神经肽，在结构和功能上与哺乳动物胃泌素/胆囊收缩素 (CCK) 神经肽同源。SK 与磺胺激肽受体 (SKR) 一起参与磺胺激肽信号传导，负责多种生物功能，包括食物摄入或脂肪酸代谢。在本研究中，我们确定了黄粉虫幼虫中 SKR 的分布，并描述了非硫酸化和硫酸化 SK 对甲虫血淋巴中碳水化合物和胰岛素样肽 (ILP) 水平的影响。我们的研究结果表明，在 T. molitor 的神经系统中同时存在磺胺激肽受体 SKR1 和 SKR2。SKR2在外周组织中的分布比SKR1更广泛，其转录本已在脂肪体、肠道和血淋巴中发现。这也是 SKRs 存在于昆虫血细胞中的第一个证据，表明 SKs 具有免疫活性。此外，在本研究中，我们已经证明 SKs 调节昆虫血淋巴中的 ILPs 和碳水化合物水平，并且硫酸化对肽活性并不重要。我们的研究证实了 SK 在维持甲虫能量稳态中的作用。