Weissleder, Christin

ABSTRACT The C9orf72 hexanucleotide repeat expansion mutation is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia, but its cell type‐specific effects on energy metabolism and immune pathways remain poorly understood. Using induced pluripotent stem cell (iPSC)‐derived motor neurons, astrocytes, and microglia from C9orf72 patients and their isogenic controls, we investigated metabolic changes at the single‐cell level under basal and inflammatory conditions. Our results showed that microglia are particularly susceptible to metabolic disturbances. While C9orf72 motor neurons exhibited impaired mitochondrial respiration and reduced ATP production, C9orf72 microglia presented pronounced increases in glycolytic activity and oxidative stress, accompanied by the upregulation of the expression of key metabolic enzymes. These metabolic changes in microglia were exacerbated by inflammatory stimuli. To investigate how these changes affect the broader cellular environment, we developed a human iPSC‐derived triculture system comprising motor neurons, astrocytes, and microglia. This model revealed increased metabolic activity in all cell types and highlighted that microglia‐driven metabolic reprogramming in astrocytes contributes to the vulnerability of motor neurons under inflammatory conditions. Our findings highlight the central role of microglia in driving metabolic dysregulation and intercellular crosstalk in ALS pathogenesis and suggest that targeting metabolic pathways in immune cells may provide new therapeutic avenues.

AbstractNeurogenesis in the subependymal zone (SEZ) declines across the human lifespan, and reduced local neurotrophic support is speculated to be a contributing factor. While tyrosine receptor kinase B (TrkB) signalling is critical for neuronal differentiation, maturation and survival, little is known about subependymal TrkB expression changes during postnatal human life. In this study, we used quantitative PCR and in situ hybridisation to determine expression of the cell proliferation marker Ki67, the immature neuron marker doublecortin (DCX) and both full‐length (TrkB‐TK+) and truncated TrkB receptors (TrkB‐TK‐) in the human SEZ from infancy to middle age (n = 26–35, 41 days to 43 years). We further measured TrkB‐TK+ and TrkB‐TK‐ mRNAs in the SEZ from young adulthood into ageing (n = 50, 21–103 years), and related their transcript levels to neurogenic and glial cell markers. Ki67, DCX and both TrkB splice variant mRNAs significantly decreased in the SEZ from infancy to middle age. In contrast, TrkB‐TK‐ mRNA increased in the SEZ from young adulthood into ageing, whereas TrkB‐TK+ mRNA remained stable. TrkB‐TK‐ mRNA positively correlated with expression of neural precursor (glial fibrillary acidic protein delta and achaete‐scute homolog 1) and glial cell markers (vimentin and pan glial fibrillary acidic protein). TrkB‐TK+ mRNA positively correlated with expression of neuronal cell markers (DCX and tubulin beta 3 class III). Our results indicate that cells residing in the human SEZ maintain their responsiveness to neurotrophins; however, this capability may change across postnatal life. We suggest that TrkB splice variants may differentially influence neuronal and glial differentiation in the human SEZ.