Decoding Glycosylation Changes in the Prader-Willi Syndrome Mouse Brain

Prader-Willi syndrome (PWS) is a developmental neurogenetic disorder caused by the deletion or inactivation of imprinted genes within the PWS locus on the paternally inherited human chromosome 15. This locus contains two tandemly repeated non-protein-coding RNA (snoRNA) gene clusters, SNORD116 and SNORD115. Deletion of the SNORD116 region is associated with PWS in humans and results in growth retardation with 15% postnatal lethality in mice (PWS-like model). PWS is a multisystem disorder characterized by endocrine, neurological, and behavioral/psychiatric abnormalities. Glycosylation plays a crucial role in numerous cellular functions, and disruptions in glycosylation processes could significantly contribute to the pathophysiology of PWS. Previous studies have shown that glycoprotein-related dysfunctions may be involved in the development of the biological phenotype of PWS. For instance, attempts to analyze protein glycosylation in the blood serum of children with PWS have indicated hyposialylation, reflecting abnormalities in O-linked protein glycosylation pathways. However, comprehensive analyses of the glycoproteome in PWS-affected tissues, including the brain, have not been performed until now. For the first time, we have constructed a quantitative map of the O-GalNAc type glycoproteome in the pituitary gland, hypothalamus, thalamus, hippocampus, and olfactory bulb brain areas of a postnatal day 28 PWS-mouse model compared to wild-type siblings. To ensure deep mapping of protein glycosylation, we performed label free quantitative glycoproteomics with the GlycoDIA method. Our analysis revealed, on average, 7628±1461 unique glycopeptide precursors as well as 3799±300 distinct proteins per compartment, with the most significant differences in glycosylation patterns observed in the hypothalamus and pituitary gland.

Altered glycosylation patterns in these brain areas may affect functional brain pathways by altering protein interactions, cell adhesion, and signaling. These changes can affect neuronal development, synaptic plasticity, and network formation that are critical for cognitive function and behavior. In the context of PWS, such dysregulation may contribute to the characteristic cognitive deficits, behavioral problems, developmental delay, and growth retardation. Understanding the underlying molecular mechanisms may provide insight into potential therapeutic targets to mitigate these symptoms. This study represents a significant step forward in understanding the role of glycosylation in PWS and underscores the importance of investigating glycosylation patterns to unravel the complexities of this disorder.