Modeling Hereditary Diffuse Leukoencephalopathy with Axonal Spheroids using microglia-sufficient brain organoids

Hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) is a rare, fatal, adult-onset neurodegenerative disease that is most often caused by mutations affecting the Colony Stimulating factor-1 Receptor (CSF-1R). To understand how CSF-1R-mutation affects human microglia – the specialized brain-resident macrophages of the central nervous system – and the downstream consequences for neuronal cells, we used a macrophage and forebrain organoid co-culture system based on induced pluripotent stem cells generated from two patients with HDLS, with CSF-1R gene-corrected isogenic organoids as controls. Macrophages derived from iPSC (iMacs) of patients exhibited a metabolic shift towards the glycolytic pathway and reduced CSF-1 sensitivity, which was associated with higher levels of IL-1ß production and an activated inflammatory phenotype. Single-cell RNA sequencing revealed that iMacs adopt a reactive state that leads to impaired regulation of neuronal cell populations in organoid cultures, thereby identifying microglial dysregulation and specifically IL-1ß production as key contributors to the degenerative neuro-environment in HDLS. Overall design: To better understand how diseased or non-diseased macrophages affect the developing brain, we co-cultured iMacs and forebrain organoids generated from donor-derived iPSCs (HD1 and HD2). Isogenic control counterparts were also derived. We then performed gene expression profiling analysis using data obtained from the bulk RNA-seq of iMacs before and after co-culture, as well as neurons and NPCs populations from forebrain organoid.