Heparan sulfate 3‐O‐sulfation and Tgfb1 involvement in Alzheimer’s disease related tau aggregation

Abstract

AbstractBackgroundAging is the main risk factor for Alzheimer’s disease (AD) characterized by a cognitive decline related to a synaptic disfunction (Chen et al., 2019). In AD brains, tau abnormal phosphorylation coexists with heparan sulfates (HS), suggesting that HS could lead to the formation of neurofibrillary tangles (NFT) (Goedert et al., 1996). In vitro, the aggregation of tau is not possible in the absence of heparin, a highly sulfated HS carrying 3‐O‐sulfation (3S‐HS). 3S‐HS are the product of HS 3‐O Sulfotransferase (HS3ST) enzymes (Sepulveda‐Diaz et al., 2015). In AD, Heparan Sulfate‐Glucosamine 3‐Sulfotransferase 2 (HS3ST2) expression is higher in tauopathy vulnerable brain regions, such as the hippocampus and cortex (Huynh et al., 2019). Previously, we showed in a cellular model that HS3ST2 induces cell autonomous aggregation of tau (Huynh et al., 2022). However, the mechanism leading to an increased expression of HS3ST2, and therefore increase in 3S‐HS synthesis are unknown. Additionally, it is not known the effect of reducing the levels of HS3ST2 in tau oligomerization and aggregation in neurons.MethodPrimary hippocampal neurons (PHN) from the rTg4510 mice model were dissected and maintained in vitro for 20 days (DIV20). All treatments (ALK5inh, Tgfb1) and lentiviral transduction (Lv‐NonTarget, Lv‐shHs3st2) were done at day in vitro 15 (DIV15).ResultIn brain of aged individuals, transforming growth factor TGFB1 is upregulated, modulating gene expression (Doyle et al., 2010). SMAD4 transcription factor is activated upon the dimerization of TGFB receptor targeting specific genes (Martin‐Malpartida et al., 2017). SMAD4 contains genome wide recognition motifs that are present in the Hs3st2 promoter, suggesting a possible regulation. We showed that Hs3st2 is under regulation of Tgfb1 and blocking pSmad2/3 reduces its levels. Contrarily, Hs3st2 levels were increased by increasing pSmad2/3. The importance of Tgfb1 coregulation with Hs3st2 was assessed by blocking the expression of Hs3st2, leading to a decrease in tau oligomerization and aggregation. Finally, we found that the reduction of 3S‐HS enhances synaptic size, and presynaptic/postsynaptic connectivity.ConclusionOverall, we depicted the regulation of Hs3st2, and demonstrate its involvement in synaptic connectivity and tau aggregation, confirming the importance of 3S‐HS in the physiopathology of AD.