Use of IPSC to define role of astrocytes in specifying risk for onset of cerebral adrenoleukodystrophy

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PROJECT SUMMARY/ABSTRACT The mechanism of onset of neuroinflammation in fatal phenotypes in males with inherited X-linked adrenoleukodystrophy (X-ALD) disease remains unknown. 60% of male X-ALD patients develop fatal cerebral neuroinflammation (cALD) while remaining develop milder adrenomyeloneuropathy (AMN) characterized by axonopathy without neuroinflammation. The primary genetic defect in X-ALD (mutation/deletion in ABCD1 gene) and the biochemical defect (accumulation of very long chain fatty acid; C>22:0 in plasma and tissues) cannot predict the onset of AMN or cALD. Our long-term goal is to dissect the molecular mechanism underlying differential phenotype development in X-ALD. The objective of this application is to identify metabolic pathways that underlie the differential neuroinflammatory response in AMN and cALD human astrocytes. These astrocytes were differentiated from induced pluripotent stem cells (iPSCs), which in turn were generated by reprogramming of human control, AMN and cALD patient-derived fibroblasts. Metabolic reprogramming is emerging as a novel regulator of inflammatory response. Astrocytes rely on mitochondrial respiration (OXPHOS) for their metabolic needs but switch to glycolysis under neuroinflammatory environment to boost biosynthetic pathways to produce inflammatory mediators. Our preliminary proof-of-concept data, with untargeted metabolomics, identified metabolites altered between healthy-control and cALD phenotype postmortem brain. Within the cALD brain white matter, unique metabolite changes were recorded between distant normal looking areas and areas adjacent to the plaque suggesting an association with disease progression. We found both OXPHOS and glycolysis decreased (low metabolic state) in human cALD astrocytes despite higher inflammatory response. This low metabolic state suggests role of novel alternative source(s) of fuel driving the neuroinflammatory response in cALD astrocytes. Our central hypothesis is that metabolic reprogramming in cALD astrocytes drives their proinflammatory shift that underlies the neuroinflammatory disease progression in cALD. To test our hypothesis we propose two specific aims: 1) To elucidate the metabolic reprogramming responsible for inflammatory response in cALD astrocytes. 2) To determine if dysfunctional mitochondria play a role in inflammatory nature of cALD astrocytes? We will take advantage of control, AMN and cALD astrocytes generated from iPSC’s in our laboratory for these studies. This proposal is innovative, because it departs from the status quo by identifying for the first time, metabolic pathways differentially regulating inflammatory response in human AMN and cALD astrocytes. The proposed research is significant because the cellular mechanism(s) that lead to less severe AMN or fatal cALD phenotype in response to same ABCD1 mutation remain unknown even four decades after the identification of gene defect in X-ALD. Impact: With the rising rate of newly diagnosed cases after X-ALD was added to the federal newborn screening list in 2016, there is urgent need to identify novel targets to develop effective therapies for AMN and cALD for which no satisfactory therapy exists.