Astrocytic Heparan Sulfate 6-O-Sulfation in Brain Function

This study examines the role of Hs6st2, an enzyme that catalyzes heparan sulfate (HS) 6-O-sulfation, in brain structure, molecular signaling, and behavior by characterizing Hs6st2 knockout mice. HS is a linear polysaccharide with crucial roles in cellular signaling, and its functional modulation by 6-O-sulfation is mediated by HS6ST family enzymes. HS6ST2 is primarily expressed in the brain and has been genetically linked to neurodevelopmental and cognitive disorders, yet the mechanisms by which HS6ST2 influences brain function have remained unclear.

To address this, the investigators generated Hs6st2 knockout mice and performed biochemical, morphological, transcriptomic, metabolic, and behavioral assessments. Biochemically, strong anion exchange–high performance liquid chromatography revealed that loss of Hs6st2 produces a moderate decrease in HS 6-O-sulfation levels in the brain, demonstrating a measurable but partial contribution of Hs6st2 to overall 6-O-sulfation. Phenotypically, Hs6st2 knockout animals exhibited increased body weight, and analyses indicated associations with altered metabolic pathways, suggesting that HS 6-O-sulfation via Hs6st2 may influence systemic metabolism or energy balance in addition to neural processes.

Behaviorally, the knockout mice displayed memory deficits that mirror clinical features observed in patients carrying HS6ST2 mutations, establishing a link between Hs6st2 function and cognitive performance. To probe molecular underpinnings, RNA sequencing was performed on two memory-related brain regions, the hippocampus and the cerebral cortex. The transcriptomic analyses revealed that Hs6st2 loss leads to pronounced transcriptome changes in the hippocampus but only mild alterations in the cerebral cortex. The hippocampal transcriptome disruptions were enriched for genes and pathways related to dendritic and synaptic structure and function, pointing to synaptic biology as a key affected domain. Complementing transcriptomic findings, direct biochemical and anatomical measures showed decreased overall HS levels and structural impairments of dendritic spines in hippocampal CA1 pyramidal neurons of Hs6st2 knockout mice. These dendritic spine deficits provide a cellular substrate that plausibly explains the observed hippocampal-dependent memory impairments.

Together, the multidisciplinary evidence from this work—linking reduced 6-O-sulfation, altered hippocampal gene expression networks, dendritic spine pathology, metabolic perturbation, and memory deficits—offers novel molecular and behavioral insights into how Hs6st2 contributes to brain function. The findings advance understanding of HS6ST2’s role in the central nervous system and provide a mechanistic framework for interpreting how HS6ST2 mutations may give rise to HS-linked brain disorders characterized by cognitive impairment and synaptic dysfunction.