Specific glycosaminoglycan chain length and sulfation patterns are required for cell uptake of tau versus α-synuclein and β-amyloid aggregates

Abstract

Transcellular propagation of protein aggregate "seeds" has been proposed to mediate the progression of neurodegenerative diseases in tauopathies and α-synucleinopathies. We previously reported that tau and α-synuclein aggregates bind heparan sulfate proteoglycans (HSPGs) on the cell surface, promoting cellular uptake and intracellular seeding. However, the specificity and binding mode of these protein aggregates to HSPGs remain unknown. Here, we measured direct interaction with modified heparins to determine the size and sulfation requirements for tau, α-synuclein, and β-amyloid (Aβ) aggregate binding to glycosaminoglycans (GAGs). Varying the GAG length and sulfation patterns, we next conducted competition studies with heparin derivatives in cell-based assays. Tau aggregates required a precise GAG architecture with defined sulfate moieties in the - and 6--positions, whereas the binding of α-synuclein and Aβ aggregates was less stringent. To determine the genes required for aggregate uptake, we used CRISPR/Cas9 to individually knock out the major genes of the HSPG synthesis pathway in HEK293T cells. Knockouts of the extension enzymes exostosin 1 (), exostosin 2 (), and exostosin-like 3 (), as well as -sulfotransferase () or 6--sulfotransferase () significantly reduced tau uptake, consistent with our biochemical findings, and knockouts of , or but not reduced α-synuclein uptake. In summary, tau aggregates display specific interactions with HSPGs that depend on GAG length and sulfate moiety position, whereas α-synuclein and Aβ aggregates exhibit more flexible interactions with HSPGs. These principles may inform the development of mechanism-based therapies to block transcellular propagation of amyloid protein-based pathologies.

The biomarker potential of cell‐free microRNA from cerebrospinal fluid in Parkinsonian Syndromes

“…Proteoglycans, a membrane-bound surface protein, has been reported to bind to α-syn and promote cellular uptake. 23,24 The hippo signaling pathway, involved in cell proliferation and apoptosis, 25 has, to our knowledge, not been reported to be associated with parkinsonism, and the relevance can only be speculated on.…”

3‐O‐Sulfation of Heparan Sulfate Enhances Tau Interaction and Cellular Uptake

“…HS, [14] tau requires more specific sulfate moieties. [13,29,14] In previous work, we were the first to report that 6-O-S,but not 2-O-S,i sr equired for tau binding,u sing structurally heterogeneous polysaccharides.…”

“…Akey step in tau transcellular movement is tau binding to heparan sulfate proteoglycans (HSPGs) [11][12][13][14] on the cell surface ( Figure 1B), followed by the endocytosis of tau. HSPGs are HS glycosaminoglycan (GAG) chains covalently linked to ap rotein core.H Si salinear, polyanionic GAG composed of disaccharide repeats of uronic acid (glucuronic acid or iduronic) and glucosamine with sulfation substitution on the 3-OH, 6-OH and -NH of the glucosamine residue,and the 2-OH of the uronic acid residue ( Figure 1C).…”

Sulfation Patterns of Saccharides and Heavy Metal Ion Binding

“…[1] However, understanding the specific interactions of each component of the ECM constitutesamajor challenge. [4][5][6] Given that sulfated saccharides exist in metal-ion-rich environments, they interact with, absorb, and store av ariety of metal ions. Sulfated saccharides such as glycosaminoglycans (GAG) and carrageenans are major components of the ECM of organismsf rom animals to algae.…”

“…[2,3] These molecules have a large variety of sulfationp atterns that affect their structural properties and biologicala ctivities. [4][5][6] Given that sulfated saccharides exist in metal-ion-rich environments, they interact with, absorb, and store av ariety of metal ions. [7][8][9] Metal ion binding to saccharides can result in changes of the physical properties and the biological interactions of these saccharides and can lead to the accumulation of both essential and toxic heavym etal ions.…”