Neuroinflammation in endometriosis: macrophages behaving badly?

Endometriosis is an inflammatory condition, defined by the presence of womb lining (endometrium) outside the womb, most commonly on the lining of the wall of the pelvic cavity ('endometriosis lesions'). This is thought to occur via a phenomenon known as 'retrograde menstruation', where the endometrium that is shed during menstruation is refluxed backwards through the Fallopian tubes into the pelvic cavity. Endometriosis affects approx.1.5 million women in the UK and a large majority of women with endometriosis also have debilitating pelvic pain. Costs incurred by treating women with endometriosis and associated loss of productivity are estimated at £11.7 billion per year. Endometriosis is treated surgically or with drugs that suppress hormones, but symptoms usually recur after surgery and the available medical treatments have undesirable side effects. Women want new treatments to ease their suffering.
Why endometriosis causes pain is poorly understood but I believe that it is due to the growth of new nerves into the lesions and their stimulation by molecules involved in inflammation (neuroinflammation). Notably, endometriosis can also be found associated with a general increased sensitivity to pain. Immune cells, such as macrophages are critical in the inflammatory process. Each tissue has its own 'type' of macrophage and they have been identified as important cells in the disease progression of endometriosis. We do not know how macrophages affect nerve growth in endometriosis or contribute to pain in the condition. However, I have recently shown that macrophages manipulated in the laboratory to mimic macrophages found in endometriosis lesions increase nerve growth and inflammation. I have developed a novel experimental mouse model of endometriosis that mirrors the human condition. The lesions form in a similar way to the human, and the mice also exhibit endometriosis-associated pain. Using this model I have shown that macrophages from the pelvic cavity migrate into lesions. Notably, for the first time I have also shown that macrophages present in the shed endometrium at the time of menstruation also survive in the lesions. This model will allow me to determine how macrophages contribute to neuroinflammation, endometriosis-associated pain and subsequent increases in sensitivity to pain.
My specific aims are fourfold; firstly I will investigate how macrophages, that are present in the shed endometrium at the time menstruation, influence the formation of endometriosis lesions using a laboratory mouse model of 'menstruation' and endometriosis. Secondly, I will determine how macrophages influence nerve growth and neuroinflammation in endometriosis lesions. Thirdly, I will determine how factors produced by macrophages that have been identified in the previous objective, interact with nerves by using pain-sensing nerves grown in the laboratory. Finally, I will determine if macrophages play a role in endometriosis-associated pain and general increased sensitivity to pain, and to discover whether inhibition of factors produced by macrophages can reduce this pain.
I have developed innovative new models and produced exciting and informative novel preliminary data and I am confident that I can deliver the specified aims. I believe that information generated during this fellowship will lead to quality high impact publications, new understanding of how endometriosis causes pain and will inform new ways to treat endometriosis-associated pain.

Endometriosis is a common chronic inflammatory disorder characterised by debilitating pelvic pain and hypersensitivity. Treatments are limited to hormonal suppression or surgical excision of lesions and symptoms commonly recur. There is an un-met clinical need for new strategies to treat endometriosis-associated pain. I believe that the pain is a consequence of neuroinflammation; the growth of new nerves and their activation by inflammatory mediators within the lesion. Endometriosis-associated macrophages are critical players in the pathophysiology of endometriosis. I have generated evidence indicating that isolated human M2 or 'regenerative' macrophages exposed to oestrogen to mimic the microenvironment of human endometriosis lesions both enhance neurogenesis and increase the expression of inflammatory cytokines. However, it is unknown how endometriosis-associated macrophages contribute to neurogenesis, neuroinflammation and pain in vivo. The objectives of this project are:
1. To use the macrophage depletion mouse, Cd11b-DTR to determine how macrophages present in the shed endometrium contribute to the establishment of lesions using a mouse model of 'menstruation' and a novel mouse model of endometriosis
2. To use the Cd11b-DTR mouse to determine how macrophages influence neurogenesis and neuroinflammation in established lesions in a mouse model of endometriosis.
3. To interrogate the effect of macrophage-derived factors identified in (2) on nerve function using in vitro models of sensory neurons.
4. To determine the role of macrophages in endometriosis-associated pain and hypersensitivity using behavioural monitoring in mice and to explore how inhibition of macrophage-derived factors ameliorate endometriosis-associated pain.
I am confident the work will generate novel data leading to high impact publications, significant advances in the field and the identification of novel targets with translational value for the treatment of endometriosis-associated pain.

Benefit to patients and to the NHS:
Endometriosis UK (http://www.endometriosis-uk.org/) estimates that 1.5 million women in the UK suffer from endometriosis and associated debilitating pelvic pain. Endometriosis has a huge impact on their quality of life, ability to work and care for their families. The development of novel therapeutics that avoid the side-effects of current therapy options will greatly improve the health, quality of life and productivity of endometriosis patients. The costs associated with supporting patients places a significant economic burden on healthcare providers. The work described in this proposal represents an opportunity to advance understanding of the mechanisms of endometriosis-associated pain and a platform for development of a therapy that avoids surgery or contraceptive/menopausal side effects. We have established a network within Scotland (Scottish Endometriosis Network) who meet regularly to debate way(s) in which we can improve patient care and who will provide ongoing input into my research project. We have a close dialogue with patient organizations including Endometriosis UK (letter of support) to ensure the impact on patient care of any findings is maximized.
Benefit to commercial organisations:
Data generated will be of particular interest to commercial organizations because it will lead to an understanding of macrophage-derived factors involved in pain and hypersensitivity, identify novel targets and lead to the development of therapies that have an effect on the pain-regulatory cascade that accompanies this disorder. I have already built in a platform for commercialisation of the results obtained by working closely with the University of Edinburgh's BioQuarter Team, a realistic time-frame for this to be realised is 5-10 years.
Benefit to charities:
We work in close association with the charity Endometriosis UK. I am part of a team involved in disseminating information to patients at a recent patient information day hosted by the charity (April 2014). I will continue to work with Endometriosis UK to help healthcare providers and communicate my research to patients and their families. My co-sponsor Dr Andrew Horne also recently organised an event for endometriosis awareness at the Scottish Parliament with Endometriosis UK, and we received a statement from the Health Minister stating that funding should be allocated in this area.
Benefit to policy-makers:
Mounting evidence suggests endometriosis causes general hypersensitivity to pain due to changes that occur in the CNS of women with chronic pain. The proposed work will generate new knowledge on this and benefit policy makers, because it should inform alterations in the way patients are received in the clinic with more emphasis on input from pain psychologists, and pain experts. Dr Andrew Horne's Pelvic Pain Team is multidisciplinary, however this is not the case throughout the whole of the UK.
Benefit to wider public:
New treatments that arise as a result of the proposed programme of work will benefit members of the general public including the families, partners and employers of women with endometriosis.
Benefit to researchers and clinicians working in the field of pain and endometriosis:
Endometriosis remains an enigmatic disorder and its aetiology is poorly understood. I will publish my findings in high impact academic journals, share them via our website and communicate them at local and international meetings that attract experts in the field.
Benefit to capacity building:
The proposed work will allow me to launch my independent career and the work will involve training in new techniques. It will allow me to develop my own supervision and mentoring roles and offer the opportunity for both MSc and undergraduate medical students to undertake projects within the vibrant environment of the Institute. The research will generate a 4 year post for a UoE grade 6 technician providing job security and training.