Gallo Christina M, Kistler Sabrina A, Natrakul Anna, Labadorf Adam T, Beffert Uwe, Ho Angela
Department of Biology, Boston University, Boston, Massachusetts, United States of America.
Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian & Avedisian School of Medicine, Boston, Massachusetts, United States of America.
PLoS Genet. 2024 Jul 22;20(7):e1011348. doi: 10.1371/journal.pgen.1011348. eCollection 2024 Jul.
Disrupted alternative splicing plays a determinative role in neurological diseases, either as a direct cause or as a driver in disease susceptibility. Transcriptomic profiling of aged human postmortem brain samples has uncovered hundreds of aberrant mRNA splicing events in Alzheimer's disease (AD) brains, associating dysregulated RNA splicing with disease. We previously identified a complex array of alternative splicing combinations across apolipoprotein E receptor 2 (APOER2), a transmembrane receptor that interacts with both the neuroprotective ligand Reelin and the AD-associated risk factor, APOE. Many of the human APOER2 isoforms, predominantly featuring cassette splicing events within functionally important domains, are critical for the receptor's function and ligand interaction. However, a comprehensive repertoire and the functional implications of APOER2 isoforms under both physiological and AD conditions are not fully understood. Here, we present an in-depth analysis of the splicing landscape of human APOER2 isoforms in normal and AD states. Using single-molecule, long-read sequencing, we profiled the entire APOER2 transcript from the parietal cortex and hippocampus of Braak stage IV AD brain tissues along with age-matched controls and investigated several functional properties of APOER2 isoforms. Our findings reveal diverse patterns of cassette exon skipping for APOER2 isoforms, with some showing region-specific expression and others unique to AD-affected brains. Notably, exon 15 of APOER2, which encodes the glycosylation domain, showed less inclusion in AD compared to control in the parietal cortex of females with an APOE ɛ3/ɛ3 genotype. Also, some of these APOER2 isoforms demonstrated changes in cell surface expression, APOE-mediated receptor processing, and synaptic number. These variations are likely critical in inducing synaptic alterations and may contribute to the neuronal dysfunction underlying AD pathogenesis.
异常的可变剪接在神经疾病中起着决定性作用，无论是作为直接病因还是疾病易感性的驱动因素。对老年人类尸检脑样本的转录组分析揭示了阿尔茨海默病（AD）大脑中数百种异常的mRNA剪接事件，将失调的RNA剪接与疾病联系起来。我们之前在载脂蛋白E受体2（APOER2）中鉴定出一系列复杂的可变剪接组合，APOER2是一种跨膜受体，它与神经保护配体Reelin以及AD相关风险因子APOE相互作用。许多人类APOER2异构体主要在功能重要结构域内发生外显子跳跃剪接事件，对受体功能和配体相互作用至关重要。然而，在生理和AD条件下APOER2异构体的完整组成及功能意义尚未完全明确。在此，我们对正常和AD状态下人类APOER2异构体的剪接情况进行了深入分析。利用单分子长读长测序技术，我们对Braak IV期AD脑组织顶叶皮质和海马以及年龄匹配对照的整个APOER2转录本进行了分析，并研究了APOER2异构体的几种功能特性。我们的研究结果揭示了APOER2异构体不同的外显子跳跃模式，一些表现出区域特异性表达，另一些则是AD受累大脑所特有的。值得注意的是，编码糖基化结构域的APOER2外显子15在APOE ε3/ε3基因型女性的顶叶皮质中，与对照相比，在AD中包含率较低。此外，其中一些APOER2异构体在细胞表面表达、APOE介导的受体加工和突触数量方面表现出变化。这些变化可能对诱导突触改变至关重要，并可能导致AD发病机制中的神经元功能障碍。
