Tau Internalization is Regulated by 6-O Sulfation on Heparan Sulfate Proteoglycans (HSPGs)

Abstract

The misfolding and accumulation of tau protein into intracellular aggregates known as neurofibrillary tangles is a pathological hallmark of neurodegenerative diseases such as Alzheimer’s disease. However, while tau propagation is a known marker for disease progression, exactly how tau propagates from one cell to another and what mechanisms govern this spread are still unclear. Here, we report that cellular internalization of tau is regulated by quaternary structure and have developed a cellular assay to screen for genetic modulators of tau uptake. Using CRISPRi technology we have tested 3200 genes for their ability to regulate tau entry and identified enzymes in the heparan sulfate proteoglycan biosynthetic pathway as key regulators. We show that 6-O-sulfation is critical for tau-heparan sulfate interactions and that this modification regulates uptake in human central nervous system cell lines, iPS-derived neurons, and mouse brain slice culture. Together, these results suggest novel strategies to halt tau transmission.

Salt-free fractionation of complex isomeric mixtures of glycosaminoglycan oligosaccharides compatible with ESI-MS and microarray analysis

“…This structural diversity mediates a wide range of protein-GAG interactions of varying specificity and affinity. Hp/HS has been involved in a wide and growing array of physiological and pathophysiological processes, usually mediated through interactions between proteins and a subset of Hp/HS structures 4-6 . While the importance of oligosaccharide structure has been established in many functions of Hp/HS, understanding the structures that underlie any of the various functions is highly challenging.…”

Minimalistic in vitro systems for investigating tau pathology

“…This process was dependent on heparan sulfate proteoglycans (HSPGs). HSPGs have recently been shown again to play a role in tau internalisation, as the knockdown of Hs6st1 (a gene involved in HSPG synthesis) by CRISPR in H4 human neuroglioma cells and iPSCs resulted in a decreased tau uptake in vitro 110 . This study also demonstrated a similar decrease in tau uptake upon knockdown of dynamin 110,111 , a large GTPase involved in endocytosis 112 .…”

“…HSPGs have recently been shown again to play a role in tau internalisation, as the knockdown of Hs6st1 (a gene involved in HSPG synthesis) by CRISPR in H4 human neuroglioma cells and iPSCs resulted in a decreased tau uptake in vitro 110 . This study also demonstrated a similar decrease in tau uptake upon knockdown of dynamin 110,111 , a large GTPase involved in endocytosis 112 . Tau aggregates were further shown to colocalise with the fluid-phase uptake marker dextran in C17 cells, suggesting that aggregates also enter these cells through engulfment by the membrane in an endocytic pathway 57 .…”

Transcellular Spreading of Tau in Tauopathies

“…Upon measurement of recombinant and AD‐derived tau aggregates based on tau repeat domain (RD; amino acids 243–375) and in cultured HEK293cells and primary cultured neurons, the minimum tau assembly has been shown to be a minimum of three units (trimers) . In a more recent study on a variety of cell models, including human CNS‐derived cell lines and iPS‐derived neurons, full‐length human tau (2N4R) is also internalised efficiently, however, for both monomeric and oligomeric tau . In another study, it was shown that tau fibrils could not be taken up, which suggests that there is a range of lengths of the tau species that are taken up by cells; however, additional experiments are needed to elucidate the conflicting results regarding the uptake or not of tau monomers.…”

“…In a more recent study on a variety of cell models, including human CNS‐derived cell lines and iPS‐derived neurons, full‐length human tau (2N4R) is also internalised efficiently, however, for both monomeric and oligomeric tau . In another study, it was shown that tau fibrils could not be taken up, which suggests that there is a range of lengths of the tau species that are taken up by cells; however, additional experiments are needed to elucidate the conflicting results regarding the uptake or not of tau monomers.…”