Whole genome CRISPR screens identify a LRRK2-regulated pathway for extracellular tau uptake by human neurons

Abstract

Pathological protein aggregation in Alzheimer's disease and other dementias is proposed to spread through the nervous system by a process of intercellular transfer of pathogenic forms of tau protein. Defining the cellular mechanisms of tau entry to human neurons is essential for understanding dementia pathogenesis and the rational design of disease-modifying therapeutics. Using whole genome CRISPR knockout screens in human iPSC-derived excitatory neurons, the primary cell type affected in these diseases, we identified genes and pathways required specifically for uptake of monomeric and aggregated tau. Monomeric and aggregated tau are both taken up by human neurons by receptor-mediated endocytosis, with the low-density lipoprotein LRP1 a significant surface receptor for both forms of tau. Perturbations of the endolysosome and autophagy systems at many levels, and specifically endosome sorting and receptor recycling, greatly reduced tau uptake. Of particular therapeutic interest is that loss of function of the endocytosis and autophagy regulator LRRK2, as well as acute inhibition of its kinase activity, reduced neuronal uptake of monomeric and aggregated tau. Kinase-activating mutations in LRRK2 are a cause of Parkinson's disease accompanied by neuronal tau aggregation, suggesting that LRRK2 mediates tau spreading in vivo and that LRRK2 inhibition has the potential to inhibit interneuronal spread of tau pathology, slowing disease progression. Overall, pathways for tau entry share significant similarity with those required for virus entry by receptor-mediated endocytosis, suggesting that tau spreading is a quasi-infectious process.

Exosomal and vesicle‐free tau seeds—propagation and convergence in endolysosomal permeabilization

“…This article is protected by copyright. All rights reserved has in the uptake of vesicle-free tau, and also in receptor recycling that when disrupted could likely have considerable impact on surface receptor numbers and composition at the plasma membrane [66].…”

Tau Seeding Mouse Models with Patient Brain-Derived Aggregates

“…Once in the extracellular space, pathological tau proteins need to be internalized into a neighboring recipient cell. This can also occur in several ways, including dynamin-dependent bulk endocytosis [ 67 ], macropinocytosis following heparan sulphate proteoglycan binding on the plasma membrane [ 68 , 69 ], and/or through the interaction with several specific receptors located at the cell surface, such as low-density lipoprotein receptor-related protein 1 (LRP1) [ 70 , 71 , 72 , 73 ]. Tau aggregates then leak into the cytosol by rupturing the endosomal membrane, where they can interact with physiological tau [ 74 , 75 ].…”

“…Neuronal tau uptake can occur through receptor-mediated endocytosis, for instance via heparan sulfate proteoglycans in conjunction with specific receptors like LRP1 [ 68 , 73 ]. Loss of function of the endocytosis regulator leucine-rich repeat kinase 2 ( LRRK2 ) is known to impede tau internalization by neuronal cells [ 70 ]. A recent study identified LRRK2-regulated receptor-mediated endocytosis as the main uptake mechanism for monomeric and aggregated tau species upon application of whole-genome clustered regularly interspaced short palindromic repeats (CRISPR) knockout screens in human induced pluripotent stem cell (iPSC)-derived excitatory neurons [ 70 ].…”

“…Loss of function of the endocytosis regulator leucine-rich repeat kinase 2 ( LRRK2 ) is known to impede tau internalization by neuronal cells [ 70 ]. A recent study identified LRRK2-regulated receptor-mediated endocytosis as the main uptake mechanism for monomeric and aggregated tau species upon application of whole-genome clustered regularly interspaced short palindromic repeats (CRISPR) knockout screens in human induced pluripotent stem cell (iPSC)-derived excitatory neurons [ 70 ]. Further, inhibition of LRRK2 kinase activity prevented tau uptake, confirming its pivotal role in tau internalization, but not tau pathology induction [ 156 ].…”

Tau assemblies enter the cytosol in a cholesterol sensitive process essential to seeded aggregation

“…We next tested whether entry could be inhibited by reducing uptake to the cell. Previous studies have shown that tau uptake occurs via endocytosis and relies on the vesicle coat protein clathrin, as well as the GTPase dynamin (Calafate et al, 2016;Evans et al, 2018Evans et al, , 2020Shrivastava et al, 2019). We pre-treated cells with the clathrin inhibitor PitStop 2 or the dynamin inhibitor Dyngo 4a.…”