Tuning the brain glycan symphony using engineered biomaterials towards brain repair in ischemic stroke

Introduction:: Glycosylation is critically implicated in multiple physiological and pathological processes including central nervous system (CNS) disorders. Most (~80%) congenital glycosylation diseases result in neuropathological symptoms¹ and most biological functions in the CNS occur through glycosylated proteins and lipids. Although previous studies have implied the significance of glycan changes in neuroinflammation^2,3, changes in tissue glycosylation patterns during ischemic stroke or after stroke treatment have not been investigated. Ischemic stroke is a sudden blood flow blockage in the brain, which induces neuroinflammation and leads to permanent tissue damage and long-term physical disability. We hypothesize that investigation of brain glycosignature in ischemic stroke and post-therapeutic biomaterial treatment will lead to the identification of glycosylation patterns associated with brain regeneration, directing the design of glycan-functionalized biomaterials with greater therapeutic impact. The current study investigates the change in brain glycosignature following a therapeutic biomaterial treatment in ischemic stroke to identify the glycosylation cues involved in tissue repair.


Materials and Methods:: To study the spatial modulation of brain glycosignature from the in-vivo temporal analysis of ischemic stroke progression in a rodent photothrombotic stroke model and following therapeutic biomaterial treatment⁴, we developed and used an elaborate multi-modal glycoanalytical platform. Therapeutic biomaterial synthesis and characterization were performed as described previously⁴. The modulation of gene expression for the glycosylation enzymes over a period of four months was investigated using real-time polymerase chain reaction (RT-PCR). Tissue-level modulation of overall glycosylation was investigated using lectin histochemistry. Corresponding quantification and spatial resolution of glycan modulation in the tissue were performed using matrix-assisted laser desorption electrospray ionization mass spectrometric imaging (IR-MALDESI MSI). An Orbitrap Exploris 240 mass spectrometer was used for data collection for MSI in negative ionization mode within a range of 500 to 2000 m/z.


Results, Conclusions, and Discussions:: Using IR-MALDESI analysis of stroke brains, we report a novel stroke-specific glycan marker that shows minimal detection in healthy brains. The results from the temporal analysis of glycosylation enzymes and tissue-level glycan expression showed an overall reduction in sialylation and complex glycosylation and an increase in fucosylation and mannosylation. A concomitant change in tissue glycosylation was observed using lectin histochemistry. These trends of ‘injury-specific’ tissue glycosylation in ischemic stroke are remarkably reversed by the application of a previously developed pro-regenerative therapeutic biomaterial⁴ as represented in Figure 1. The results show the involvement of glycan-mediated pathways in brain repair observed as a result of the application of engineered materials.
To summarize, this study presents a detailed comparative temporal analysis of glycans in rodent brains and their modulation in ischemic stroke after biomaterial treatment, thus enabling the identification of glycan cues for targeting using engineered materials. This study is foundational for the development of future biomaterial-based glycan-targeted therapies to enhance extracellular matrix-inspired brain regeneration following ischemic stroke.


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References (Optional): : 1 Chang, I. J., He, M. & Lam, C. T. Congenital disorders of glycosylation. Ann Transl Med 6, 477-477 (2018). https://doi.org:10.21037/atm.2018.10.45

2 Puigdellívol, M., Allendorf, D. H. & Brown, G. C. Sialylation and Galectin-3 in Microglia-Mediated Neuroinflammation and Neurodegeneration. Front Cell Neurosci 14, 162-162 (2020). https://doi.org:10.3389/fncel.2020.00162

3 Li, J. et al. Inhibition of fucosylation reshapes inflammatory macrophages and suppresses type II collagen-induced arthritis. Arthritis Rheumatol 66, 2368-2379 (2014). https://doi.org:10.1002/art.38711

4 Nih, L. R., Gojgini, S., Carmichael, S. T. & Segura, T. Dual-function injectable angiogenic biomaterial for the repair of brain tissue following stroke. Nat Mater 17, 642-651 (2018). https://doi.org:10.1038/s41563-018-0083-8