Sharma, S. D. | 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↗

bioRxiv2017

Hijacking of Multiple Phospholipid Biosynthetic Pathways and Induction of Membrane Biogenesis by a Picornaviral 3CD Protein

RNA viruses induce specialized membranous structures for use in genome replication. These structures are often referred to as replication organelles (ROs). ROs exhibit distinct lipid composition relative to other cellular membranes. In many picornaviruses, phosphatidylinositol-4-phosphate (PI4P) is a marker of the RO. Studies to date indicate that the viral 3A protein hijacks a PI4 kinase to induce PI4P by a mechanism unrelated to the cellular pathway, which requires Golgi-specific brefeldin A-resistance guanine nucleotide exchange factor 1, GBF1, and ADP ribosylation factor 1, Arf1. Here we show that a picornaviral 3CD protein is sufficient to induce synthesis of not only PI4P but also phosphatidylinositol-4,5-bisphosphate (PIP2) and phosphatidylcholine (PC). Synthesis of PI4P requires GBF1 and Arf1. We identified 3CD derivatives: 3CDm and 3CmD, that we used to show that distinct domains of 3CD function upstream of GBF1 and downstream of Arf1 activation. These same 3CD derivatives still supported induction of PIP2 and PC, suggesting that pathways and corresponding mechanisms used to induce these phospholipids are distinct. Phospholipid induction by 3CD is localized to the perinuclear membrane, the outcome of which is the proliferation of membranes in this area of the cell. We conclude that a single viral protein can serve as a master regulator of cellular phospholipid and membrane biogenesis, likely by commandeering normal cellular pathways.\n\nAUTHOR SUMMARYPicornaviruses replicate their genomes in association with host membranes. Early during infection, existing membranes are used but remodeled to contain a repertoire of lipids best suited for virus multiplication. Later, new membrane synthesis occurs, which requires biosynthesis of phosphatidylcholine in addition to the other more specialized lipids. We have learned that a single picornaviral protein is able to induce membrane biogenesis and decorate these membranes with some of the specialized lipids induced by the virus. A detailed mechanism of induction has been elucidated for one of these lipids. The ability of a single viral protein to commandeer host pathways that lead to membrane biogenesis was unexpected. This discovery reveals a new target for antiviral therapy with the potential to completely derail all aspects of the viral lifecycle requiring membrane biogenesis.

biochemistry↗