Wang Hongjie, Devadoss Dinesh, Nair Madhavan, Chand Hitendra S, Lakshmana Madepalli K
Institute for Human Health and Disease Intervention (I-HEALTH), Department of Chemistry and Biochemistry, Center for Molecular Biology and Biotechnology, Florida Atlantic University, Jupiter, FL, United States.
Department of Immunology and Nano-Medicine, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, United States.
Front Cell Neurosci. 2022 Jul 19;16:954071. doi: 10.3389/fncel.2022.954071. eCollection 2022.
Alzheimer's disease (AD) is complex and highly heterogeneous. Less than 10% of AD cases are early-onset (EOAD) caused by autosomal dominantly inherited mutations in amyloid precursor protein (APP), presenilin 1 (PS1), or presenilin 2 (PS2), each of which can increase Aβ generation and, thus, amyloid plaques. The remaining 90% of cases of AD are late-onset (LOAD) or sporadic. Intense research efforts have led to identification of many genes that increase the risk of AD. An IQ motif containing protein K (IQCK) was recently identified by several investigators as an Alzheimer's disease risk gene. However, how IQCK increases AD risk is completely unknown. Since IQCK is a novel gene, there is limited information on its physiological characterization. To understand its role in AD, it is first important to determine its subcellular localization, whether and where it is expressed in the brain, and what type of brain cells express the IQCK protein. Therefore, in this study, we show by immunocytochemical (ICC) staining that IQCK is expressed in both the nucleus and the cytoplasm of SH-SY5Y neuroblastoma cells as well as HeLa cells but not in either HMC3 microglial or CHO cells. By immunohistochemistry (IHC), we also show that IQCK is expressed in both mouse and human neurons, including neuronal processes in the mouse brain. IHC data also show that the IQCK protein is widely expressed throughout the mouse brain, although regional differences were noted. IQCK expression was highest in the brainstem (BS), followed by the cerebellum (CB) and the cortex (CX), and it was lowest in the hippocampus (HP). This finding was consistent with data from an immunoblot analysis of brain tissue homogenates. Interestingly, we found IQCK expression in neurons, astrocytes, and oligodendrocytes using cell-specific antibodies, but IQCK was not detected in microglial cells, consistent with negative results in HMC3 cells. Most importantly, we found that actin-normalized IQCK protein levels were increased by 2 folds in AD brains relative to normal control (NC) brains. Furthermore, the IQCK protein was found in amyloid plaques, suggesting that IQCK may play a pathogenic role in either Aβ generation or amyloid plaque deposition in AD.
阿尔茨海默病（AD）复杂且高度异质性。不到10%的AD病例为早发型（EOAD），由淀粉样前体蛋白（APP）、早老素1（PS1）或早老素2（PS2）的常染色体显性遗传突变引起，其中每一种突变均可增加Aβ生成，进而增加淀粉样斑块。其余90%的AD病例为晚发型（LOAD）或散发性。大量研究工作已导致鉴定出许多增加AD风险的基因。近期，几位研究人员鉴定出一种含IQ模体的蛋白K（IQCK）为阿尔茨海默病风险基因。然而，IQCK如何增加AD风险完全未知。由于IQCK是一个新基因，关于其生理学特性的信息有限。为了解其在AD中的作用，首先重要的是确定其亚细胞定位、在脑中是否表达及何处表达，以及何种类型的脑细胞表达IQCK蛋白。因此，在本研究中，我们通过免疫细胞化学（ICC）染色显示，IQCK在SH-SY5Y神经母细胞瘤细胞以及HeLa细胞的细胞核和细胞质中均有表达，但在HMC3小胶质细胞或CHO细胞中均未表达。通过免疫组织化学（IHC），我们还显示IQCK在小鼠和人类神经元中均有表达，包括小鼠脑中的神经突。IHC数据还显示IQCK蛋白在整个小鼠脑中广泛表达，尽管存在区域差异。IQCK表达在脑干（BS）最高，并依次为小脑（CB）和皮质（CX），在海马体（HP）中最低。这一发现与脑组织匀浆免疫印迹分析的数据一致。有趣的是，我们使用细胞特异性抗体在神经元、星形胶质细胞和少突胶质细胞中发现了IQCK表达，但在小胶质细胞中未检测到IQCK，这与在HMC3细胞中的阴性结果一致。最重要的是，我们发现相对于正常对照（NC）脑，AD脑中肌动蛋白标准化的IQCK蛋白水平增加了2倍。此外，在淀粉样斑块中发现了IQCK蛋白，提示IQCK可能在AD的Aβ生成或淀粉样斑块沉积中发挥致病作用。
