Inflammation is part of our body’s natural defence against infection and is required to successfully heal wounds. However, if inflammation continues unchecked (that is, it becomes chronic) then damage to our tissues occurs; for example, as is seen in the joints of individuals with rheumatoid arthritis. We want to better understand the molecular processes that occur during inflammatory diseases. This includes investigating the role of the innate immune system in a major form of blindness (AMD) and how a protective mechanism, triggered by acute inflammation, may serve to prevent cartilage and bone breakdown.

A major focus for our studies is a type of sugar that is found on all cell surfaces and in the extracellular matrix (ECM) of every tissue. These so called, GAGs, determine the location and functions of protein molecules and therefore play a key role in human biology. For example, we have found recently that a mutation in an immune system protein, which increases the risk of AMD, alters its binding to GAGs found in a particular part of the retina. A reduced amount of this immune regulator at this site is likely to lead to local chronic inflammation and thus directly contribute to the AMD disease process and loss of central vision.

We are also studying the role of GAGs and GAG-binding proteins in mammalian ovulation – a process that has a lot in common with inflammation. Before the egg is released from the ovary a jelly-like ECM forms rapidly round the egg; this elastic matrix protects the egg during ovulation and is also necessary for the attachment of sperm prior to fertilisation. Thus the formation of this matrix is critical for female fertility. A major aim of our work is to characterise the molecular interactions that organise and stabilise this essential ECM and determine whether defects in this process underlie infertility in humans.

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Glycosaminoglycan-protein interactions in inflammatory processes

Our main area of interest is the role of glycosaminoglycan-binding proteins in inflammatory disease (e.g. arthritis and age-related macular degeneration) and inflammation-like processes (e.g. ovulation). Glycosaminoglycans (GAGs) are linear polysaccharides that are key components of extracellular matrix as well as being found ubiquitously on cell surfaces. For example, the interactions of hyaluronan (HA) – a high molecular weight GAG – with specific HA-binding proteins (hyaladherins) are responsible for the mechanical properties of cartilage and blood vessel walls. They also mediate the formation of a viscoelastic “cumulus” matrix around the oocyte required for ovulation/fertilisation as well as mediating immune cell trafficking.

One of the long-standing aims of our research is to determine the structural basis and molecular regulation of HA-protein interactions. We have already made significant progress on this, for example, through X-ray crystallographic and NMR analysis of TSG-6, a secreted protein often associated with inflammation, and CD44, the major cell surface receptor for HA. We are also using biophysical techniques such as AUC, SEC-MALLS and SAXS to help characterise multi-molecular hyaladherin/HA complexes and provide models for non-HA-binding proteins that are implicated in HA matrix organisation, e.g. PTX3. In addition to HA, TSG-6 binds to sulphated GAGs (i.e. chondroitin-4-sulphate, dermatan sulphate (DS), heparan sulphate (HS) and heparin) as well as a growing list of proteins (e.g. inter-α-inhibitor (IαI), PTX3 and RANKL) where these interactions underpin a wide range of different functional activities. For example, TSG-6 catalyses the covalent transfer of heavy chains from IaI onto HA to form HC•HA complexes that are essential for the formation/stability of the cumulus matrix and where this modification of HA can also occur at sites of inflammation. Furthermore, TSG-6 has been shown to be a potent inhibitor of neutrophil migration, protect cartilage in models of inflammatory arthritis and has been implicated in the regulation of bone turnover (e.g. inhibiting osteoclast-mediated bone resorption). Thus TSG-6 is likely an endogenous protector of joint and bone function during inflammation making it an attractive target for the development of novel treatments for arthritis and osteoporosis.

Another key area of interest is the investigation of the role of complement factor H (CFH) in Age-related Macular Degeneration (AMD), which is the predominant cause of blindness in the industrialised world; the Y402H polymorphism in CFH (first described by Tony in 1988) has been implicated as a major risk factor for developing AMD. We have shown that this Tyr to His coding change has a large effect on the binding of CFH to sulphated GAGs, e.g. HS and DS present in the Bruch’s membrane of the human retina, which is the site of AMD pathology. The poorer binding of the disease-associated 402H variant could lead to chronic local inflammation (due to complement dysregulation), contributing directly to the development and/or progression of AMD. Our ongoing work is focused on further investigation of this putative disease mechanism.

Recent discoveries