Neuronal NLRC5 regulates MHC class I expression in Neuro‐2a cells and also during hippocampal development

Abstract

Major histocompatibility Complex class I (MHC I) molecules are ubiquitously expressed, being found in most nucleated cells, where they are central mediators of both the adaptive and innate immune responses. Recent studies have shown that MHC I are also expressed in the developing brain where they participate in synapse elimination and plasticity. Up‐regulation of MHC I within the developing brain has been reported, however, the mechanism(s) regulating this developmental up‐regulation of neuronal MHC I remains unknown. Here, we show NLR family CARD domain containing 5 (NLRC5), a newly identified member of the NLR family, is widely expressed in hippocampal neurons, and the expression pattern of NLRC5 coincides with increased MHC I mRNA in the developing hippocampus. Using a luciferase assay in Neuro‐2a cells we demonstrate that NLRC5 can induce the activation of MHC I and this induction requires the W/S‐X‐Y motif. Further studies show that transcription factors regulatory factor X (RFX) and CREB1, which bind to X1 and X2 box, are crucial for NLRC5‐mediated induction. Moreover immunoprecipitation experiments reveal that NLRC5 interacts with RFX subunits RFX5 and RFXANK. Knockout of Nlrc5 dramatically impairs basal expression of MHC I in mouse hippocampus. Taken together, our findings identify NLRC5 as a key regulator of MHC I up‐regulation in the developing hippocampus and suggest an important role for NLRC5 in neurons. Cover Image for this issue: doi: .

MiR34a Regulates Neuronal MHC Class I Molecules and Promotes Primary Hippocampal Neuron Dendritic Growth and Branching

“…signaling cascade relied on activation of the MAPK pathway (Lv et al, 2015). We also confirmed that NLRC5, but not CIITA, was broadly expressed in the mouse brain and promoted MHC-I expression in hippocampal neurons (Li et al, 2020). In this study, we analyze the regulation of MHC-I expression from a new perspective: regulation by miRNAs in hippocampal neurons, adding new information regarding the tight and complex regulatory system that controls classical MHC-I molecule levels during the development of the hippocampus.…”

“…After completing their functions, protein abundance becomes significantly reduced with age until neuronal MHC-I proteins can no longer be detected after P60. In contrast, mRNA expression is gradually increased from P0 to P60 after which it remains relatively stable (Liu et al, 2013;Li et al, 2020). A similar expression pattern of MHC-I proteins is observed during human CNS development (Zhang et al, 2013a,b).…”

“…We previously reported on the expression of H-2K b and H-2D b mRNA and protein from P0 to P60 in the hippocampus of C57BL/6 mice (Li et al, 2020). There was an increase of H-2K b and H-2D b proteins from P0 to P15 before it decreased to a relatively low level, despite a sustained increased H-2K b and H-2D b mRNA from P0 to P60, suggesting post-transcriptional regulation mechanisms such as miRNAs might be involved after P15.…”

“…To further verify the regulation of MHC-I by miR34a, we investigated its effect on Neuro-2a cell lines using miR34a mimics and inhibitors. Neuro-2a cells were previously reported to express H-2D b but not H-2K b (Li et al, 2020), so only the expression of H-2D b was investigated here. In contrast to miRNA mimics, the miRNA inhibitors could effectively inhibit mature miRNA function without degrading it (the endogenous miRNA levels remained unchanged).…”

“…We recently found that NLRC5 is a critical transcriptional factor of MHC-I during development from P0 to P15 in hippocampal neurons (Li et al, 2020). All previous studies on the post-transcriptional regulation of MHC-I expression have only detailed regulation in the immune system.…”