Investigating the role of oxidative metabolites in joint destruction in osteoarthritis

Description

We are seeking a motivated researcher to work on a pioneering project investigating the role of oxidative stress in alkaptonuria (AKU) and associated conditions.
AKU is a rare disorder of metabolism caused by congenital deficiency in the enzyme homogentisate 1,2-dioxygenase (HGD), resulting in increased circulating concentrations of homogentisic acid (HGA). Over many years HGA is deposited in connective tissues throughout the body as a dark pigment, which is central to the devastating multiple organ pathology observed in AKU including severe early-onset osteoarthropathy and cardiac disease.

There is growing evidence that oxidative stress is a major part of AKU disease pathophysiology. The Liverpool AKU Research Group has shown that HGA is redox-active, that pigment derived from HGA is a direct source of free-radicals and that anti-oxidant pathways are markedly altered in AKU biofluids and tissues1,2. Oxidative stress associated with lifelong exposure to HGA is thought to account for a number of co-morbidities in AKU, including common diseases such as osteoarthritis (OA), Parkinson’s disease and cataracts; these diseases have markedly increased prevalence in AKU compared with the general population.

This project will explore the potential role of NRF2, a major antioxidant regulator, in AKU and associated conditions. NRF2 is shown to be a key mediator of oxidative stress in common osteoarthritis and is identified as a treatment target in numerous common diseases. Mouse models of AKU have been developed in which the gene for HGD is deleted and is able to reproduce most of the AKU phenotypes, including elevated plasma HGA and joint pigmentation, but not the major degenerative changes to multiple organ systems observed in human AKU3.

You will help generate and characterize a novel mouse model through genetic deletion of HGD and NRF2; two key genes related to AKU and antioxidant pathways. This innovative model presents new opportunities to uncover disease mechanisms and therapeutic targets. The study of lifelong exposure to specific oxidative metabolites in this model has potential to uncover the involvement of these molecules in the pathology of more common degenerative diseases including OA and Parkinson’s disease.

OBJECTIVES:

Objective 1: To measure severity of AKU phenotypes in the new AKU model with HGD/NRF2 double KO (DKO) compared to HGD KO mice. Phenotypes include joint and connective tissue pathology, HGA/HGA-derived pigment accumulation and the metabolome.

Objective 2: To assess the effects of applied mechanical joint loading in vivo on OA development in HGD/NRF2 DKO. This will test whether the combination of the DKO and joint trauma can better reproduce AKU joint phenotypes.

Objective 3: To test the efficacy of nitisinone treatment on disease severity in this new model of AKU.

NOVELTY:

Your research will provide the first systematic exploration of oxidative stress in AKU experimental models. You will break new ground by being the first to:

• Perform joint loading experiments in the new mouse model to understand the connective tissue phenotype and severe osteoarthritis development4.
• Assess extracellular and cellular mechanisms as potential novel treatment approaches.

EXPERIMENTAL APPROACH:

Generation and characterisation of a new DKO mouse model of AKU, in which two current mouse lines will be crossed (underway). The main focus for this proposal is characterisation of the joints and connective tissue compared to the AKU phenotype. You will gain experience with a range of widely-applicable investigative techniques: in vivo experimentation, tissue collection, mass spectrometry, micro-CT and histological analysis of tissue phenotypes, immunohistochemistry for specific proteins and signalling pathways, and metabolomics2.

POTENTIAL IMPACT:

• Inform new treatments in multiple diseases including OA as a common chronic ageing-related disease, which is currently not treatable (except for pain and end-stage joint replacement).
• Securing of further funds – broadened appeal through relevance to common chronic diseases, partnership with Royal Liverpool University Hospital will maximise clinical potential of research.