Paza, E. | Search bioRxiv

bioRxiv2024

Human induced pluripotent stem cell-derived microglia contribute to thepathophysiology of Fragile X syndrome via increased RAC1 signaling

Fragile X syndrome (FXS) is one of the most common monogenic causes of neurodevelopmental disorders characterized by intellectual disability, autism and epilepsy. Emerging evidence suggests a role for immune dysfunction in autism. Using induced pluripotent stem cell (iPSC)-derived microglial cells from FXS patients (mFXS-MG) and FMR1-deficient microglia from FMR1-knock out human embryonic stem cells (FMR1 KO-MG), we show that loss-of-function of Fragile X Messenger Ribonucleoprotein (FMRP) leads to cell autonomous phagocytic deficits and a proinflammatory state in microglia when compared to gene-corrected controls. Moreover, increased RAC1 signaling in mFXS-MG and FMR1 KO-MG results in increased actin polymerization and enhanced activation of NF-{kappa}B signaling. Exposure of control iPSC-derived cortical neuron cultures to conditioned medium from proinflammatory mFXS-MG results in hyperexcitability. Importantly, pharmacological inhibition of RAC1 signaling in mFXS-MG attenuates their proinflammatory profile and corrects the neuronal hyperexcitability caused by the conditioned medium. Our results suggest that microglia impair neuronal function in FXS, which can be prevented by targeting of RAC1 signaling. Significance statementFXS is one of the most common monogenic causes of neurodevelopmental disorders characterized by intellectual disability, autism, epilepsy and has been associated with immune dysfunction. We therefore generated brain macrophages (microglia) from patient-derived induced pluripotent stem cells (mFXS-MG) and an embryonic stem cell line deficient in the Fragile X messenger ribonucleoprotein 1 (FMR1 KO-MG). We find enhanced activation of RAC1 signaling resulting in phagocytic deficits and immune activation of mFXS-MG and FMR1 KO-MG. Exposure of control iPSC-derived cortical neurons to conditioned medium from proinflammatory mFXS-MG results in neuronal hyperexcitability, which can be prevented by pharmacological RAC1 inhibition in mFXS-MG. We conclude that RAC1 signaling in microglia could be a potential therapeutic target in FXS.

neuroscience↗

bioRxiv2022

Cell-autonomous immune dysfunction driven by disrupted autophagy in C9orf72-ALS iPSC-derived microglia contributes to neurodegeneration

The most common genetic mutation found in familial and sporadic amyotrophic lateral sclerosis (ALS), as well as fronto-temporal dementia (FTD), is a repeat expansion in the C9orf72 gene. C9orf72 is highly expressed in human myeloid cells, and although neuroinflammation and microglial pathology are widely found in ALS/FTD, the underlying mechanisms are poorly understood. Here, using human induced pluripotent stem cell-derived microglia-like cells (hiPSC-MG) harbouring C9orf72 mutation (mC9-MG) together with gene-corrected isogenic controls (isoC9-MG) and C9ORF72 knock-out hiPSC-MG (C9KO-MG), we show that reduced C9ORF72 protein is associated with impaired phagocytosis and an exaggerated inflammatory response upon stimulation with lipopolysaccharide, driven by sustained activation of NLRP3 inflammasome and NF-{kappa}B signalling. Analysis of the hiPSC-MG C9ORF72 interactome revealed an association of C9ORF72 with key regulators of autophagy, a process involved in the homeostatic regulation of the innate immune response. We found impaired initiation of autophagy in C9KO-MG and mC9-MG. Furthermore, through motor neuron-microglial (MN-MG) co-culture studies, we identified that autophagy deficit in mC9-MG led to increased vulnerability of C9 MNs to excitotoxic stimulus. Pharmacological activation of autophagy ameliorated the sustained activation of NLRP3 inflammasome and NF-{kappa}B signalling, reversed the phagocytic deficit found in mC9-MG and also reduced MN death in MN-MG co-cultures. We validated these findings in blood-derived macrophages from people with C9orf72 mutation. Our results reveal an important role for C9ORF72 in regulating microglial immune homeostasis and identify dysregulation in human myeloid cells as a contributor to neurodegeneration in ALS/FTD. TeaserDisrupted autophagy led immune activation in microglia results in enhanced motor neuronal death in C9orf72-ALS.

neuroscience↗