Can a tissue sample help us understand a major genetic cause of stroke & vascular dementia?

Transcription

1 stroke.org.uk Final report summary: Can a tissue sample help us understand a major genetic cause of stroke & vascular dementia? Characterising the vascular pathophysiology in CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy) by analysis of gluteal biopsy vessels. PROJECT CODE: TSA PRINCIPAL INVESTIGATOR: PROFESSOR KEITH MUIR INSTITUTION: UNIVERSITY OF GLASGOW

2 Why did we fund this research? One of the main causes of stroke is disease of the small blood vessels of the brain, which can occur with high blood pressure or diabetes, but whose development is poorly understood 1. Problems with the small blood vessels of the brain also occur in people with a genetic disease called CADASIL, which is the most common inherited cause of stroke due to a fault in a single gene. It affects at least 1 in 10,000 people in Scotland alone, and there are currently no specific treatments available 2,3. People with CADASIL are at risk of suffering repeated strokes, mood problems and eventually dementia. An inherited disease, 50% of the children of an affected parent will inherit the faulty gene that causes CADASIL and likely go on to develop the disease 4. This means that families with CADASIL are burdened with a disease that is unpredictable, and people with CADASIL will often have to care for disabled relatives whilst knowing they too have the disease. The genetic fault (mutation) is in a gene called NOTCH3. We do not have a complete understanding of what the protein produced by this gene does, but it is found in the cells that line small blood vessels in the body, called vascular smooth muscle cells (VSMCs). The abnormal NOTCH3 protein prevents these cells from functioning normally and they die. This leads to reduced and poorly controlled blood flow to the brain. Strokes can then occur, as well as damage to the networks of cells that make up the wiring of the brain called the white matter. Despite only the brain being obviously affected by CADASIL, blood vessels that use the NOTCH3 gene are found throughout the body. This project aimed to study these blood vessels directly, hoping to answer three key questions: Do small arteries from CADASIL patients change shape as a result of the disease and exhibit abnormal function? Does the abnormal protein produced by the NOTCH3 gene in CADASIL patients alter the function of vascular smooth muscle cells taken from these patients, when cultured and analysed in the lab? Is there a relationship between the vascular functioning of small arteries from CADASIL patients and the clinical status of these patients? Answering these questions will provide us with a better understanding of the disease, could help lead to the developments of treatments of the disease, and could also shed light on other more common forms of small vessel disease (SVD) of the brain such as those associated with high blood pressure. What did the researchers do? Twenty participants with CADASIL were recruited. Information on each participant s medical history, medication, stroke risk factors and details of symptoms relevant to CADASIL including stroke, migraine and memory problems were documented. The severity of each participant s CADASIL symptoms was assessed by a neurological examination and by reviewing their day-to-day functioning using standard outcome scales. 2 Can a tissue sample help us understand a major genetic cause of stroke & vascular dementia?

3 Each participant had a small sample of muscle tissue, called a biopsy, taken from their buttock. A small cut was made in the skin and a sample of muscle and skin was removed (about the size of a sugar cube), with the cut then stitched up. Placing each biopsy under a microscope, small arteries were removed, the shape and function of which were then studied. Individual vascular smooth muscle cells from these small artery samples were then further extracted, cultured and grown in the laboratory and studied. Skin cells were also cultured and later used to create stem cells that were investigated to see how they developed into blood vessels. Tests of how the small arteries and vascular cells were behaving were performed and compared to the clinical status of the participants. What did the research find? Do small arteries from CADASIL patients function abnormally? Yes. The blood vessels in CADASIL patients were shaped differently and behaved differently compared to those from healthy people, or from people with high blood pressure. The blood vessels failed to get larger or smaller in response to a range of different chemicals involved in regulating blood flow. However, adding a chemical that helps get rid of molecules known as free radicals improved how the blood vessels responded. Free radicals are highly reactive and created when oxygen interacts with certain other chemicals. It causes damage to living tissue known as oxidative stress. The chemicals which can reduce the effect of free radicals are called antioxidants. Does abnormal NOTCH3 protein alter smooth muscle cell function? Yes, in many ways. There were a number of changes in levels of proteins and chemicals inside the vascular smooth muscle cells affected by the abnormal NOTCH3 protein in CADASIL patients some higher and some lower compared with healthy people and with people who had high blood pressure. Biopsy from the buttock of a CADASIL patient The samples collected from CADASIL participants were compared to samples collected in a previous study from participants with: high blood pressure (hypertension) healthy people without high blood pressure or CADASIL (the control group). Other genes affected by the NOTCH3 gene were produced in different proportions in people with CADASIL. These included genes which were produced in higher amounts in people with CADASIL, and which help get rid of abnormally folded proteins inside the vascular smooth muscle cells. Is there a link between the functioning of the small arteries of patients and their clinical status? This is not yet clear. When the functioning of these blood vessels in CADASIL patients was compared to clinical information about them, including their memory and thinking (cognitive) performance and findings on their brains scans, no significant links were discovered. However, full analyses were only available for eight out of the 20 patients who had undergone very detailed scanning as part of another study. stroke.org.uk 3

4 Overall This study confirmed that blood vessels in CADASIL patients are highly abnormal. Oxidative stress from free radicals appears to play a role in vessel damage, and the functioning of the NOTCH3 gene in vessels was also altered. Both these observations offer pathways to investigate treatments to correct some of the abnormalities found in CADASIL patients, to see if their blood vessel function can be improved. For example, drugs could potentially make the vessels behave more normally, and several are worth further investigation. Next steps Next steps for this research include performing more in-depth comparisons between the blood vessels from CADASIL patients and those from healthy people and people with high blood pressure. The success of this project has led to the planning of further patients taking part in the future, which is part of ongoing research at the BHF Centre of Excellence in Vascular Science and Medicine at the University of Glasgow. References 1. Tournier-Lasserve E, Joutel A, Melki J, Weissenbach J, Lathrop GM, Chabriat H, et al. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy maps to chromosome 19q12. Nat Genet 1993 Mar;3(3): Razvi SSM, Davidson R, Bone I, Muir KW. The prevalence of cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) in the west of Scotland. Journal of Neurology, Neurosurgery & Psychiatry 2005 May 1;76(5): Dichgans M, Mayer M, Uttner I, Brüning R, Müller-Höcker J, Rungger G, et al. The phenotypic spectrum of CADASIL: Clinical findings in 102 cases. Ann Neurol 1998;44(5): Moreton FC, Razvi SSM, Davidson R, Muir KW. Increasing prevalence of CADASIL and delay to first vascular event. International Journal of Stroke 7[Supplement 2], What does this mean for stroke survivors? This study has provided important new information about the abnormal behaviour of blood vessels in people affected by CADASIL. This knowledge is a step toward targeted research into potential treatments for the damage that leads to CADASIL and possibly other forms of small vessel disease (SVD). 4 Can a tissue sample help us understand a major genetic cause of stroke & vascular dementia?

5 We are the Stroke Association The Stroke Association is the leading stroke charity in the UK. We believe in the power of research to save lives, prevent stroke and ensure that people make the best recovery they can after a stroke. We re here for you. If you d like to know more, please get in touch. Stroke Helpline: Website: stroke.org.uk info@stroke.org.uk From a textphone: Our research programme relies on voluntary donations. Please help us to fund more vital research. Call our Donations line on , or visit stroke.org.uk Together we can conquer stroke Stroke Association, March 2018 Stroke Association is a Company Limited by Guarantee, registered in England and Wales (No 61274). Registered office: Stroke Association House, 240 City Road, London EC1V 2PR. Registered as a Charity in England and Wales (No ) and in Scotland (SC037789). Also registered in Northern Ireland (XT33805) Isle of Man (No 945) and Jersey (NPO 369).