Astrogliosis and Neuroinflammation Underlie Scoliosis Upon Cilia Dysfunction

Abstract

Cilia defects lead to scoliosis in zebrafish, but the underlying pathogenic mechanisms are poorly understood and may diverge depending on the mutated gene. We dissected the mechanisms of scoliosis onset in a zebrafish mutant for therpgrip1lgene encoding a ciliary transition zone protein.rpgrip1lmutant fish developed scoliosis with near-total penetrance but asynchronous onset in juveniles. Taking advantage of this asynchrony, we found that curvature onset was preceded by brain ventricle dilations and concomitant to the perturbation of Reissner fiber polymerization and to the loss of multicilia tufts around the subcommissural organ. Rescue experiments showed that Rpgrip1l was exclusively required infoxj1a-expressing cells to prevent axis curvature. Transcriptomic and proteomic studies identified neuroinflammation associated with increased Annexin levels as a potential mechanism of scoliosis development inrpgrip1ljuveniles. Investigating the cell types associated withannexin2over-expression, we uncovered astrogliosis, arising in glial cells surrounding the diencephalic and rhombencephalic ventricles just before scoliosis onset and increasing with time in severity. Anti-inflammatory drug treatment reduced scoliosis penetrance and severity and this correlated with both reduced astrogliosis and macrophage/microglia enrichment around the diencephalic ventricle. Mutation of thecep290gene encoding another transition zone protein also associated astrogliosis with scoliosis. Thus, we propose that the onset of a feed-forward loop between astrogliosis, induced by perturbed ventricular homeostasis, and immune cells recruitment as a novel pathogenic mechanism of zebrafish scoliosis in ciliary transition zone mutants.

Ciliogenesis defects after neurulation impact brain development and neuronal activity in larval zebrafish

“…In fact, most genes associated with motile cilia function, e.g., the master regulator of motile ciliogenesis foxj1a and some of its target genes, 30 , 73 were upregulated ( Figure 4C2 , red highlight), suggesting a potential genetic compensation mechanism as observed in the ccdc103 (also known as smh ) and rpgrip1l mutants. 51 , 74 Among genes associated with the GO terms “neurological system process” and “neuron part”, we identified that genes encoding for the grow factor brain-derived neurotrophic factor ( bdnf ), 75 various synaptic proteins ( synaptotagmin , synaptic vesicle glycoprotein 2b , synaptophysin b ) and enzymes involved in serotonin and catecholamine production ( tyrosin and tryptophan hydroxylase ) were downregulated ( Figure 4C3 , red highlights). Finally, genes involved in common cilia-related signaling pathways especially the sonic hedgehog pathway were differentially regulated suggesting a dampened sonic hedgehog pathway 15 , 17 ( Figure 4C4 ).…”