Qki is an essential regulator of microglial phagocytosis in demyelination

Abstract

The mechanism underpinning the regulation of microglial phagocytosis in demyelinating diseases is unclear. Here, we showed that the Quaking protein (Qki) in microglia was greatly induced by demyelination in the brains of both mice and humans. Deletion of the Quaking gene (Qk) in microglia severely impaired the clearance of myelin debris. Transcriptomic profiling indicated that depletion of Qki impaired total RNA levels and splicing of the genes involved in phagosome formation and maturation. RNA immunoprecipitation (RIP) confirmed the physical interactions between the Qki protein and the mRNAs of Qki targets that are involved in phagocytosis, indicating that Qki regulates their RNA stability. Both Qki depletion and inhibition of Qki target Cd36 greatly reduced the phagocytic activity of microglia and macrophages. The defective uptake and degradation of myelin debris caused by Qki depletion in microglia resulted in unresolved myelin debris that impaired axon integrity, oligodendrocyte maturation, and subsequent remyelination. Thus, our results demonstrate that Qki is an essential regulator of microglia’s phagocytic activity under demyelinating conditions.

Loss of Quaking RNA binding protein disrupts the expression of genes associated with astrocyte maturation in mouse brain

“…As these gangliosides are prevalent on neuronal membrane, the upregulation of this key lysosomal regulator during a period of astrocyte maturation that covers synaptic pruning, suggests QKI might dynamically regulate aspects of local lysosomal function related to synaptic pruning by astrocytes and the subsequent clearance of this breakdown product. Indeed, a very recent report defined a similar role for QKI in microglia in clearance of myelin debris after experimentally induced demyelination 52 .…”

The roles of microglia and astrocytes in phagocytosis and myelination: Insights from the cuprizone model of multiple sclerosis

“…Step 4: One of the prerequisites of effective remyelination is the phagocytosis of myelin debris (Step 1). Recent evidence shows that this process is facilitated by the upregulation of various transcripts such as Qki, Trem2 and Mertk, expressed by microglia and astrocytes (Cignarella et al, 2020; Ren et al, 2021; Shen et al, 2021). In addition, increased expression of other microglial genes (e.g., Lrp and Calr) facilitates phagocytosis and the removal of myelin debris (Olah et al, 2012).…”

“…Quaking is an RNA‐binding signaling protein that controls alternative splicing in vascular cell differentiation (Caines et al, 2019). The study by Ren et al (2021) rigorously analyzed the involvement of Qki in myelin debris clearance using multiple experimental approaches, including immunohistochemistry, Western blotting, transcriptomics, and transmission electron microscopy, demonstrating that deletion of the Qki gene (using an inducible conditional knockout; iCKO) preferentially impaired microglia‐mediated myelin debris clearance by affecting their phagocytic activity. Using the CPZ model, Ren et al (2021) first observed the activation of microglia by immunofluorescence staining of enhanced yellow fluorescent protein (Eyfp) expression in mice bearing Cx3cr1 CreER‐Eyfp allele (Eyfp labeled all Iba1 + microglia) in the corpus callosum.…”

“…Whether this microglial activation up‐regulated phagocytic activity in the CPZ‐fed mice was then investigated. It was found that microglial cells showed a ~6‐fold increase of Qki protein after 4 weeks of CPZ‐feeding compared to Qki expression in microglia of naïve mice (Ren et al, 2021). Importantly, there was a greater than 10‐fold increase of phago‐lysosomal components (e.g., lysosomal‐associated membrane protein‐1 and 2; assessed by Western blotting) from isolated microglia of CPZ‐fed (using Qki inducible conditional knockout mice, Qki‐iCKO) compared to control mice.…”

Microexon alternative splicing of small GTPase regulators: Implication in central nervous system diseases

“…This binding site, termed the QKI response element (QRE), is frequently located in introns, as observed by various CLIP strategies (Hafner et al, 2010;Van Nostrand et al, 2020). QKI has been extensively studied in the context of oligodendrocyte maturation, cancer progression, immune cell function, and muscle cell differentiation as regulating pre-mRNA splicing, mRNA export, mRNA stability, miRNA maturation and circular RNA biogenesis (Conn et al, 2015;Darbelli & Richard, 2016;De Bruin et al, 2016;De Bruin et al, 2020;Fagg et al, 2020;Ren et al, 2021).…”