Two simple assays for assessing the seeding activity of proteopathic tau

Fei Liu; Ruozhen Wu; Nana Jin; Dandan Chu; Jianlan Gu; Yunn Chyn Tung; Zhihao Hu; Cheng-Xin Gong; Khalid Iqbal

doi:10.3389/fnagi.2023.1073774

Two simple assays for assessing the seeding activity of proteopathic tau

Front Aging Neurosci. 2023 Apr 6:15:1073774. doi: 10.3389/fnagi.2023.1073774. eCollection 2023.

Authors

Fei Liu¹, Ruozhen Wu^{1

2}, Nana Jin^{1

2}, Dandan Chu^{1

2}, Jianlan Gu^{1

2}, Yunn Chyn Tung¹, Zhihao Hu¹, Cheng-Xin Gong¹, Khalid Iqbal¹

Affiliations

¹ Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, New York, NY, United States.
² Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education of China, Nantong University, Nantong, Jiangsu, China.

Abstract

The regional distribution of neurofibrillary tangles of hyperphosphorylated tau aggregates is associated with the progression of Alzheimer's disease (AD). Misfolded proteopathic tau recruits naïve tau and templates its misfolding and aggregation in a prion-like fashion, which is believed to be the molecular basis of propagation of tau pathology. A practical way to assess tau seeding activity is to measure its ability to recruit/bind other tau molecules and to induce tau aggregation. Based on the properties of proteopathic tau, here we report the development of two simple assays to assess tau seeding activity ----- capture assay in vitro and seeded-tau aggregation assay in cultured cells. In the capture assay, proteopathic tau was applied onto a nitrocellulose membrane and the membrane was incubated with cell lysate containing HA-tagged tau_151-391 (HA-tau_151-391). The captured tau on the membrane was determined by immuno-blots developed with anti-HA. For the seeded-tau aggregation assay, HEK-293FT cells transiently expressing HA-tau_151-391 were treated with proteopathic tau in the presence of Lipofectamine 2000 and then lysed with RIPA buffer. RIPA-insoluble fraction containing aggregated tau was obtained by ultracentrifugation and analyzed by immuno-blot developed with anti-HA. To validate these two assays, we assessed the seeding activity of tau in the middle frontal gyrus, middle temporal gyrus and basal forebrain of AD and control brains and found that AD, but not control, brain extracts effectively captured and seeded tau_151-391 aggregation. Basal forebrain contained less phospho-tau and tau seeding activity. The levels of captured tau or seeded-tau aggregates were positively correlated to the levels of phospho-tau, Braak stages and tangle sores. These two assays are specific and sensitive and can be carried out in a regular biomedical laboratory setting by using routine biochemical techniques.

Keywords: Alzheimer’s disease; seeding activity; tau; tau pathology; tau propagation.