The Sweet Science: Unlocking the Hidden Role of Glycans

It’s early 2020. The world is in the grip of a new and previously unknown virus: COVID-19. As more countries enter lockdown and infection rates rise, researchers scramble to understand what makes it so infectious. An under-studied life sciences field, Glycobiology, uncovers a crucial clue: sugars on the spike protein of the virus play a key role in its ability to infect cells^1,2. These insights ultimately contribute to vaccine development and a deeper understanding of viral transmission.

But what exactly is Glycobiology? It is the study of the structure, function, and biology of carbohydrates (glycans), which play fundamental roles in cellular communication, immunity, and disease. Despite its significance, the field has long been overlooked. Glycans are often invisible in traditional biological analyses, and their link to functional biology has been underappreciated.

That perception is slowly changing. Glycobiology is increasingly being recognized as the “dark matter” of biology, with new research revealing that incorporating glycans into our understanding is redefining fundamental biological processes³.

Within glycobiology, there are different families of glycans that perform different biological processes. One of the most common class of glycans are called glycosaminoglycans (GAGs)⁴. GAGs are attached to core proteins, together forming proteoglycans, on the cell surface and within the extracellular matrix. As part of the cell surface proteoglycans act as key receptors for cell entry of many viruses, for example SARS-CoV-2¹.

Not only are glycans important in viral biology, but a number of studies have also demonstrated their function in cancer cell proliferation, survival, metastasis and ultimately pathology⁵. Whilst complex and multi-faceted, one specific example of glycan function on tumors is GAG-mediated integration of external signals, e.g. morphogens such as FGF, to promote cell survival⁶. This pro-survival function is key for subsequent tumor cell migration (metastasis) and subsequent pathology. This glycan function is likely a hijacking of their role in normal biology of forming a cell shield and integrating signals from the cellular environment. By understanding the role of glycans in cancer biology we are likely to generate new targets for therapeutic intervention to manipulate glycobiology for patient benefit during different forms of cancer.

As well as the classes, studies have also demonstrated the importance of other glycan types (e.g. mucins) to regulating the gut barrier⁷ and in forming the blood brain barrier that is crucial to all functions of the brain⁸.

These are just a few examples underlying how it is crucial to properly incorporate the function of glycans into our research to better understand an array of biological processes from development to cancer biology to ultimately produce better drugs for therapeutic benefit.

One of the reasons for the lack of progress behind our understanding of glycans in biology has been the limited availability of tools to quantify and localize glycans in complex biological scenarios. Several labs have made progress in applying existing technologies to these studies and also developing new approaches for glycan analysis^9,10.

It is crucial moving forward to embrace these technologies, the inherent complexity of glycans and understand that there are distinct classes of glycans that have very different structure and function in biology.

Going back to glycosaminoglycans, GAGs are a specific class of glycan that represent much of these historical challenges that are beginning to be broken down. GAGs are unbranched linear polysaccharides formed of repeating disaccharide units that are attached to protein cores to form proteoglycans that can be found on the cell surface as part of the glycocalyx or can be secreted into the extracellular matrix (ECM)¹¹.

There are different types of GAG based on their sequence, heparan sulfate (HS) is made up of glucuronic acid (GlcA) (epimerised to iduronic acid (IdoA)) and N-acetylglucosamine (GlcNAc) repeating units. Chondroitin sulfate (CS) is composed of glucuronic acid and N-acetylgalactosamine (GalNAc) repeating sequences. Dermatan sulfate (DS) is similar to CS but has glucuronic acid residues epimerised to iduronic acid. Crucially GAG chains are chemically modified during their synthesis, and also subsequently, through sulfation at specific sites¹².

These modifications confer these chains with a capacity to have extreme specificity and contain huge amounts of information¹². Whilst we know these chemical modifications can produce specific interaction with proteins (e.g. anti-thrombin¹³) and also refine interactions with key immune components (e.g. chemokines^14,15) to determine GAG function in regulating processes all the way from development to immunology and cancer metastasis.

It is crucial to understand that glycans contain a huge diversity of structures and classes and rules for analysing one type, e.g. GAGs, do not necessarily apply for analyzing others, e.g. n-glycans.

Until recently, localizing HS proteoglycans on immune cells was challenging, but new tools now allow researchers to gain a greater understanding. For example development of GAG sequencing technologies¹⁰ and algorithms to analyse sequencing data from a glycan focused perspective⁹ is producing breakthroughs in our understanding of their cellular location and function.

Following recent developments, it is now possibly to utilize Ambsio reagents to specifically detect different GAGs across different biological scenarios (e.g. ELISA kits). This has included localizing HS proteoglycans onto immune cells for the first time¹⁶, as well as imaging to localize different GAG components of the glycocalyx¹⁷.

Additionally other products are available to remove GAGs from cell surfaces to determine their function (GAG lyases) and also analyze biological shedding of GAGS in different contexts (heparanse and hyaluronidase kits).

In short, we are now at a key juncture in revolutionizing our understanding of the crucial role that glycans play in biology and leveraging existing tools and developing new technologies will be crucial in the future. A key question will be to determine the cell specific structure and function of specific glycans in complex biological scenarios from development, immunology and cancer biology perspectives.

Dr. Douglas Dyer is a Sir Henry Dale Fellow in the Division of Immunology, Immunity to Infection, and Respiratory Medicine at The University of Manchester. His research focuses on the role of chemokines and the endothelial glycocalyx in leukocyte migration and inflammatory diseases, aiming to uncover novel therapeutic targets for conditions ranging from inflammatory pathologies to cancer. Dr. Dyer leads the glyco-immunology lab within the Wellcome Centre for Cell-Matrix Research and the Lydia Becker Institute of Immunology and Inflammation, employing multidisciplinary approaches to advance understanding of immune system functions and train the next generation of scientists.

If you would like to connect with Dr Dyer, you can find his profiles on:

• LinkedIn
• University of Manchester: which includes a list of his research interests, collaborations and publications
• BlueSky

AMSBIO would like to thank Douglas Dyer for his time and expertise.

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11. Sutherland, T. E., Dyer, D. P. & Allen, J. E. The extracellular matrix and the immune system: A mutually dependent relationship. Science 379, (2023).

12. Xu, D. & Esko, J. D. Demystifying heparan sulfate-protein interactions. Annual Review of Biochemistry 83, 129–157 (2014).

13. Karlsson, R. et al. Dissecting structure-function of 3-O-sulfated heparin and engineered heparan sulfates. Science Advances 7, eabl6026 (2021).

14. Gray, A. L. et al. Chemokine CXCL4 interactions with extracellular matrix proteoglycans mediate widespread immune cell recruitment independent of chemokine receptors. Cell Reports 42, 111930 (2023).

15. Ridley, A. J. L. et al. Chemokines form complex signals during inflammation and disease that can be decoded by extracellular matrix proteoglycans. Science Signaling 16, eadf2537 (2023).

16. Priestley, M. J. et al. Leukocytes have a heparan sulfate glycocalyx that regulates recruitment during inflammation. bioRxiv 2024.05.21.595098 (2024) doi:10.1101/2024.05.21.595098.

17. Gray, A. L., Schiessl, I. & Dyer, D. P. Chronic cranial window implantation for high-resolution intravital imaging of the endothelial glycocalyx in mouse cortex. STAR Protocols 4, 102712 (2023).