Characterisation of glycan ligands recognised by collectin-11 in ischaemic kidney and development of a specific antagonistic probe

The cells making up our tissues and organs are covered with sugar molecules. This coating normally is important in organ development and maintenance but can be a target for our immune system, causing tissue damage. We have found that blood flow disturbance to the kidney can lead to an abnormal pattern of sugars on the cell surface and this triggers inflammation through a molecule called collectin-11. Collectin-11 is a normal tissue product that acts in self defence. However, in abnormal circumstances such as when the organ is donated for transplantation, the sugar pattern can change and this can provoke inflammation and loss of function of the organ. Our aim is to identify the biochemical composition of the abnormal sugar pattern, because this will provide the key to improved treatment and diagnosis. Very simply, if we can work out how collectin-11 recognises the abnormal pattern, we can potentially mask it from collectin-11.

The first steps of our research involve extracting a representative sample of the hundreds and possibly thousands of sugars (glycans) found in human kidneys after the organs have been removed from the donor. We can then screen the array of glycans to determine which ones bind strongly to collectin-11. To help us manage the complexity and scale of this procedure, we will make use of robotics to display the glycans and mix them with collectin-11. We can then examine the composition of the most interesting sugars which have strong affinity for collectin-11 and find out where and when they are expressed in kidney biopsies from patients. These studies of human tissue will not only reassure us we are on the right track, but they will help identify which patients could potentially benefit from the treatment to block the abnormal sugar pattern and prevent inflammation. A blocking agent that we are developing for this purpose will need further modification to ensure it fits like a glove over the abnormal sugar. That way the treatment will be more selective and have fewer side effects.

Pattern recognition of carbohydrate changes on injured tissue is of medical importance, since it may trigger inflammation and cell death. We have partially characterised the features of carbohydrate structures on hypoxic renal tissue that are bound by the pattern recognition molecule collectin-11 (CL-11) and which trigger complement activation and acute kidney injury. We have established that the major glycans in the kidney detected by CL-11 are fucosylated and furthermore have identified subsets of fucosylated ligands that bind CL-11, including blood group related sequences of the ABH system. These observations suggest a blood group related structure or structures containing alpha1-2 linked fucose are likely to be major ligands for CL-11 and imply there may be multiple fucosylated CL-11 ligands on stressed cells. To test this hypothesis, we propose to identify the main glycan structures recognised by CL-11 in ischaemic renal tissue and determine the range and type of proteins that function as carrier molecules in cells. We will make use of a tissue-derived glycan array to screen for CL-11 binding ability and elucidate the structures of strong binding ligands by micro-sequencing. We will validate their biomedical relevance by determining their presence in human biopsy tissue. We will design of a novel CL-11 analogue that has potential application as a probe to detect and block the recognition of these damage-associated carbohydrate ligands. Our objective is to clarify the biochemical and structural changes caused by hypoxia and explain how they lead to lectin pathway engagement and inflammation, and develop tools that could subsequently be adapted for clinical exploitation as imaging or therapeutic agents. The work has implications for acute ischaemic kidney injury and transplantation in the first instance.

Benefits to the scientific community

The research will help basic and clinician scientists to understand how abnormal sugar patterns on cells can trigger kidney inflammation and tissue injury:

- It will identify the composition and type of sugars (glycans) induced in the kidney following low blood flow/low oxygen

- It will explain how lectin molecules (collectin-11), which normally defend against infection, can direct inflammation against the abnormal pattern on our cells

- Knowledge of the glycan structures detected will help with the design of new diagnostic and treatment approaches to recognise and mask the offending structures

- Clinician scientists will be encouraged by the research findings to support early clinical evaluation and help influence the study design

- The interdisciplinary nature and different skills involved in the research will promote research excellence and rapid translation for patient benefit.


Benefit to patients

Improved quality of life, higher graft and patient survival rates, fewer interventions including less drug and dialysis treatment, based on innovation out of the research:

- Reduced delayed graft function and graft loss, through treatments to lower the impact of ischaemia-reperfusion injury on tissue injury

- Less exposure to the lethal side effects of conventional drugs, by having to take less medication against rejection and treating the organ rather than the recipient

- Shorter waiting times for a kidney transplant, as more organs would be usable through effective prevention of ischaemia-reperfusion damage

- Fewer patients with failed transplants returning to the waiting list by preventing early and late consequences of ischaemia-reperfusion insult


Benefits to the NHS

Cost/resource/efficiency savings through lower treatment (drug and dialysis) costs and improved patient and graft outcomes using collectin-based therapy:

- Lower dialysis costs by enabling more transplants and fewer patients returning to dialysis after transplantation

- Lower cost of dialysis in the early post-transplant period due to more rapid recovery of treated patients

- Lower drug maintenance costs by keeping patients on fewer drugs where graft acceptance is improved

- Increased patient and graft survival rates with wider application of these treatment technologies, within 10 years


Benefits to the Economy

- Healthcare savings, since maintenance on a transplant is more cost-effective than dialysis (costs over a five-year period £45K, versus £125K for haemodialysis)

- Commercialisation of novel diagnostics and therapeutics out of this research


Benefits to Wider Society

Engagement/participation, leading to:

- Public confidence in organ donation, building on our ability to engage with the public and influence policy on matters that include research in transplantation

- Influence willingness to participate in organ donation schemes by appreciating the scientific commitment through research

- Gaining public and political support for complement research in other conditions made worse by lectin complement pathway activity

- Public involvement in ethical issues that affect moving the boundaries of research to the organ donor, to allow earlier application of preventative therapies