The Role of Adipolin in Cutaneous Fibroproliferative Disease

Scars are common and can cause considerable distress and suffering. Keloid disease is a form of excessive skin scarring that is extremely difficult to treat. No approved treatment exists that directly targets the molecular mechanism behind its development. A genetic component is known to be involved as it is heritable within families and is more common in certain ethnic backgrounds. Knowing the gene(s) that contribute to this disease is important in providing relevant direction to future treatment strategies. To date however, no single gene abnormality that directly causes keloids has been identified in any familial keloid disease study.

Excitingly, using a genetic sequencing method, we recently discovered a mutation in adipolin, in a family with a unique form of inherited keloid disease. We have also demonstrated that the skin cells derived from one of the affected individuals in this family carrying this genetic mutation have lost their expression of adipolin. Adipolin is a bioactive compound that maintains glucose balance and inflammatory responses in the body. Its role in scarring has never been researched. We hypothesise that adipolin is protective against scarring and aim to explore the mechanisms by which it acts.

To investigate how loss of adipolin might be implicated in scarring and whether adipolin can reduce the scarring process, we will look at pathways known to be altered in scarring states in cells without adipolin and compare them against normal healthy cells. We will also compare them against cells from other keloid patients that are not known to carry this mutation, to see if there are any similar alterations. As obesity and insulin resistance, conditions that have been associated with adipolin, are linked to abnormal glucose metabolism, we will measure glucose consumption pathways in cells prone to scarring to determine if they are altered. These experiments will enable us to improve the understanding of how scars form and ultimately identify new approaches for treatment.

Background: Keloids are benign fibroproliferative tumours resulting from skin injury. They cause considerable morbidity and treatment is suboptimal. We have identified a novel homozygous loss-of-function mutation in the C1QTNF12 gene encoding adipolin, in an autosomal recessive family with striking keloids and hypothesise that this single genetic aberration has contributed to the fibroproliferative process. Adipolin is an adipokine that regulates glucose homeostasis and inflammatory responses.

Aim: To perform a functional study of adipolin and characterize the state of glucose metabolism in the context of fibroproliferative disease.

Objectives: 1. Determine the function of adipolin in dermal fibroblasts 2. Determine the alterations to glucose metabolism in pro-fibrotic fibroblasts 3. Identify and validate targets to revert the fibrotic/fibroproliferative phenotype

Methods: Adipolin-knockdown fibroblasts will be treated with and without recombinant adipolin and assayed for insulin signalling, proliferation, extracellular matrix production and signalling pathways associated with fibrosis using both candidate and exploratory approaches. Alterations to glucose metabolism in these cells will be determined by assaying glucose uptake and glycolysis. Comparisons will be made against wild-type keloid fibroblasts as prototypic pro-fibrotic cells. Targets will be identified for therapeutic manipulation from the aforementioned objectives and small molecule inhibitors/activators will be employed to reverse the fibroproliferative phenotype.

Scientific and medical opportunities: Understanding the functional consequences of adipolin loss-of-function on the fibroblast and its metabolism will offer new insight and may lead to the discovery of novel approaches to managing disorders of fibroproliferation including and beyond cutaneous scarring.

Impact on science: The proposed research aims to investigate the functional consequences of a novel genetic mutation in a unique pedigree with autosomal recessive keloid disease. Mendelian modes of inheritance of keloid are noted in the literature; however, a specific autosomal recessive genetic mutation has never previously been implicated. The discovery of a Mendelian "extreme" variant in what is commonly a complex disease offers a compelling opportunity to study unequivocal pathologic alterations in the context of a rare condition that may be more broadly applicable to its common counterpart.

The pathogenesis of keloid disease remains incompletely understood. Our keloid pedigree has provided a clue to suggest that dysregulation in glucose metabolism is an important pathogenic factor. The link between metabolism and keloid disease is unexplored even though there is increasing interest concerning metabolic changes in fibrotic processes affecting a range of other organ systems - hepatic, myocardial, renal fibrosis, as well as cancer. Studying keloid metabolism would shed light on mechanisms enabling its hyper-proliferative state, intracellular signalling alterations that accompany a dysregulated metabolic state and metabolite interactions with the extracellular matrix - knowledge that is applicable to academics beyond the field of cutaneous fibrosis.

Impact on patients/clinicians: Keloid disease, although benign is often a debilitating disorder with ineffective management. Although several treatment options exist, they offer limited therapeutic benefit and are complicated by frequent recurrences. There are currently no approved treatments that target the pathogenic process in this condition, reflecting the underlying problem with this disease: its molecular mechanisms are still poorly defined. Insight into signalling/metabolic pathways is critical to understanding disease processes. The proposed study aims to identify and validate key target signalling/metabolic changes in this disorder that could provide important new knowledge on biomarkers that reflect responses to current available treatments and enrich efforts in pharmaceutical discovery and development. Any therapeutic targets identified would be candidates for a clinical trial, to hopefully benefit the 5 to 15% of individuals who are susceptible to this debilitating scarring condition. Furthermore, if our hypothesis that metabolic derangements on a cellular level exist in keloid disease is true, this may spark consideration of and future studies into similar derangements on a systemic level, and be of interest to patients and clinicians alike.