X-linked adrenoleukodystrophy (ALD) is a devastating neurologic disorder caused by mutations in the ABCD1 gene characterized by the accumulation of very long-chain fatty acids that affects 1:17,000 individuals in the U.S. Approximately 60% of male patients with ALD will convert to a devastating rapidly progressive form of inflammatory demyelination that leads to incapacitation or death within 2-3 years (cerebral ALD). Age of onset and phenotype varies even among individuals with the same mutation but a constant initial event in cerebral ALD is blood brain barrier (BBB) disruption with migration of leukocytes to the brain. The precise molecular and cellular mechanisms controlling BBB function during the course of ALD disease progress remain poorly understood given lack of cellular or animal models that faithfully recapitulate cerebral ALD. To address this critical knowledge gap, Dr. Musolino?s laboratory recently developed an ALD ex-vivo model system using gene-editing strategies and human brain microvascular endothelial cells. Dr. Musolino?s initial studies provide evidence that loss of ABCD1 directly impairs brain endothelial barrier integrity by increasing TGF?1 levels in a manner correlated with severe transcriptional downregulation of Claudin 5 and increased permeability to small molecules. These alterations precede the accumulation of very-long chain fatty acids suggesting that the BBB dysfunction is not a direct consequence of their accumulation. As with patients, in addition to ABCD1 deficiency in this model, a second event, endothelial activation by inflammatory cytokines or flow sheer stress, is necessary to increase the permeability to leukocytes. Building upon these strong preliminary data Dr. Musolino?s hypothesizes that levels of ABCD1 expression in brain microvascular endothelium controls transcriptional regulation of tight junction proteins via TGF?1-regulated pathways and determines the permeability to leukocytes during endothelial activation in a dose-dependent manner. To test this hypothesis Dr. Musolino will probe the effect of ABCD1 deficiency upon the BBB by (1) Identifying the molecular mechanisms governing tight junction disruption and increased permeability of ABCD1- deficient brain endothelium (Aim 1), (2) Determining functional consequences of downregulation of tight junction proteins and main regulatory pathways (Aim 2), and (3) Quantifying ABCD1 gene-dose effect on endothelial barrier function (Aim 3). Upon successful completion of these studies Dr. Musolino will have leverage the ability to model the impact of a single-gene mutation to unravel the mechanisms governing the traffic of cells across the BBB in ALD setting forth a strategy to identify the molecular and cell biological mechanisms underlying the conversion to cerebral disease, develop functional assays to test novel therapeutic approaches, and inform the field of neuroinflammation.

Public Health Relevance

Cerebral Adrenoleukodystrophy is an inherited devastating disease where inflammatory cells infiltrate the brain and cause progressive degeneration that leads to vegetative state or death in months to years. Unfortunately, current therapies either fail to prevent cerebral disease or carry high toxicity and mortality. In this project we will study how the gene defect changes the brain vessel permeability to allow access of inflammatory cells to the brain using laboratory tools at the bench. If validated by this study, our approach sets forth a successful strategy for identifying factors that contribute to develop cerebral degeneration and a laboratory tool urgently needed to screen for new less toxic and targeted therapies.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Cellular and Molecular Biology of Glia Study Section (CMBG)
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Morris, Jill A
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Massachusetts General Hospital
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