Hearing, the ability to sense sounds, and the processing of auditory information are important for perception of the world. Mice lacking expression of neuroplastin (Np), a type-1 transmembrane glycoprotein, display deafness, multiple cognitive deficiencies, and reduced expression of plasma membrane calcium (Ca) ATPases (PMCAs) in cochlear hair cells and brain neurons. In this study, we transferred the deafness causing missense mutations (C315S) and (I122N) into human Np (hNp) constructs and investigated their effects at the molecular and cellular levels. Computational molecular dynamics show that loss of the disulfide bridge in hNp causes structural destabilization of immunoglobulin-like domain (Ig) III and that the novel asparagine in hNp results in steric constraints and an additional N-glycosylation site in IgII. Additional N-glycosylation of hNp was confirmed by PNGaseF treatment. In comparison to hNp, transfection of hNp and hNp into HEK293T cells resulted in normal mRNA levels but reduced the Np protein levels and their cell surface expression due to proteasomal/lysosomal degradation. Furthermore, hNp and hNp failed to promote exogenous PMCA levels in HEK293T cells. In hippocampal neurons, expression of additional hNp or hNp was less efficient than hNp to elevate endogenous PMCA levels and to accelerate the restoration of basal Ca levels after electrically evoked Ca transients. We propose that mutations leading to pathological Np variants, as exemplified here by the deafness causing Np mutants, can affect Np-dependent Ca regulatory mechanisms and may potentially cause intellectual and cognitive deficits in humans.

中文翻译：

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导致神经塑蛋白错义变异的耳聋无法促进质膜 Ca2+-ATP 酶水平和脑神经元 Ca2+ 瞬时调节


听力、感知声音的能力以及听觉信息的处理对于感知世界很重要。缺乏 1 型跨膜糖蛋白神经塑蛋白 (Np) 表达的小鼠会出现耳聋、多种认知缺陷，以及耳蜗毛细胞和脑神经元中质膜钙 (Ca) ATP 酶 (PMCA) 表达减少。在这项研究中，我们将导致耳聋的错义突变 (C315S) 和 (I122N) 转移到人类 Np (hNp) 构建体中，并在分子和细胞水平上研究了它们的影响。计算分子动力学表明，hNp 中二硫键的缺失会导致免疫球蛋白样结构域 (Ig) III 的结构不稳定，而 hNp 中的新型天冬酰胺会导致空间限制，并在 IgII 中产生额外的 N-糖基化位点。 PNGaseF 处理证实了 hNp 的额外 N-糖基化。与hNp相比，将hNp和hNp转染至HEK293T细胞中导致mRNA水平正常，但由于蛋白酶体/溶酶体降解而降低了Np蛋白水平及其细胞表面表达。此外，hNp和hNp未能促进HEK293T细胞中的外源PMCA水平。在海马神经元中，额外的 hNp 或 hNp 的表达在提高内源性 PMCA 水平和加速电诱发 Ca 瞬变后基础 Ca 水平恢复方面的效率低于 hNp。我们认为，导致病理性 Np 变异的突变（如导致耳聋的 Np 突变体为例）可以影响 Np 依赖性 Ca 调节机制，并可能导致人类智力和认知缺陷。