Cellular and molecular phenotypes ofC9orf72ALS/FTD patient derived iPSC-microglia mono-cultures

Abstract

Background: A mutation in the C9orf72 gene is the most common genetic mutation of familial and sporadic ALS, as well as familial FTD. While prior studies have focused on elucidating the mechanisms of neuronal dysfunction and neurodegeneration associated with this genetic mutation, the contribution of microglia to disease pathogenesis in the ALS/FTD disease spectrum remains poorly understood. Methods: Here, we generated a new disease model consisting of cultured C9orf72 ALS/FTD patient-derived induced pluripotent stem cells differentiated into microglia (iPSC-MG). We used this model to study the intrinsic cellular and molecular phenotypes of microglia triggered by the C9orf72 gene mutation. Results: We show that C9orf72 ALS/FTD iPSC-MG have a similar transcriptional profile compared to control iPSC-MG, despite the presence of C9orf72-associated phenotypes including reduced C9orf72 protein levels and dipeptide-repeat protein translation. Interestingly, C9orf72 ALS/FTD iPSC-MG exhibit intrinsic dysfunction of phagocytic activity upon exposure to Aβ or brain synaptoneurosomes and display a heightened inflammatory response. Detailed analysis of the endosomal and lysosomal pathways revealed altered expression of endosomal marker early endosome antigen 1 and lysosomal associated membrane protein 1 in C9orf72 ALS/FTD iPSC-MG, which was confirmed in patient postmortem tissues. Conclusions: These findings demonstrate that unstimulated C9orf72 iPSC-MG mono-cultures share a largely similar transcriptome profile with control microglia, despite the presence of C9orf72 disease phenotypes. The dysfunction of the endosomal-lysosomal pathway as demonstrated by aberrant microglia phagocytosis and engulfment of cellular debris and brain pathogens suggests that disease-related microglia phenotypes are not intrinsic but instead require microglia to be activated. In summary, the C9orf72 iPSC-MG culture system provides a novel human disease model to study the role of microglia in C9orf72 ALS/FTD disease pathogenesis.

Glial Metabolic Reprogramming in Amyotrophic Lateral Sclerosis

“…In addition, loss of C9orf72 led to metabolic modifications and lysosomal accumulation in microglia, with agerelated neuroinflammation similar to C9orf72 ALS but not SALS patient tissue [68,69], further indicating that metabolic alterations in microglia contribute to neuroinflammation. Remarkably, AbGC are also characterized by an increased proliferation rate and reduced mitochondrial bioenergetics [70], associated with abundance of lipid droplets, as well as ER cistern dilatation when analyzed by electron microscopy [38].…”

Recent insights from human induced pluripotent stem cell models into the role of microglia in amyotrophic lateral sclerosis

“…[5][6][7] Interestingly, neither our study [5] nor Lorenzini et al [7] found substantial differences in unstimulated C9orf72 mutant microglia compared to controls by RNA sequencing, and baseline key inflammatory marker expression, such as IL1B or IL6, was unchanged. [5][6][7] These findings suggest that the mere presence of the C9orf72 HRE does not inherently skew microglia towards a pro-inflammatory phenotype compared to control cells.…”

The versatile applications of human pluripotent stem cell-derived microglia and microglia-containing brain organoids

“…Although the role of neurochemical pathways in microglia has been extensively studied, the mechanoreceptors that regulate microglial function remain largely unexplored. A very recent study used hPSC-derived MGLs to study PIEZO1, a mechanotransduction ion channel [120] . They found that PIEZO1 orchestrated the clearance of Aβ by improving phagocytosis, survival, and lysosomal activity.…”