Ciliary Dysfunction Leads to Scoliosis Through Astrogliosis and Neuroinflammation in Zebrafish

Core Concepts

Ciliary dysfunction in zebrafish rpgrip1l and cep290 mutants leads to scoliosis through a pathogenic mechanism involving astrogliosis and neuroinflammation, which can be partially rescued by anti-inflammatory treatment.

Abstract

The study investigates the mechanisms underlying scoliosis development in zebrafish mutants for the ciliary transition zone genes rpgrip1l and cep290.
Key findings:

rpgrip1l mutant fish develop scoliosis during juvenile stages with near-total penetrance, providing a valuable model for studying the etiology of idiopathic scoliosis.
Scoliosis onset in rpgrip1l mutants is preceded by brain ventricle dilations and perturbation of Reissner fiber polymerization, as well as loss of multicilia tufts around the subcommissural organ (SCO).
Transcriptomic and proteomic analyses of rpgrip1l mutants reveal upregulation of genes and proteins involved in ciliary motility, inflammation, and astrogliosis.
Astrogliosis, characterized by increased GFAP and Annexin2 expression, arises in glial cells surrounding the diencephalic and rhombencephalic ventricles just before scoliosis onset and increases in severity over time.
Increased macrophage/microglia recruitment around the SCO also precedes scoliosis onset.
Anti-inflammatory drug treatment (NACET) reduces scoliosis penetrance and severity in rpgrip1l mutants, correlating with reduced astrogliosis and macrophage/microglia enrichment around the diencephalic ventricle.
Astrogliosis is also observed in the scoliotic zebrafish cep290 mutant, suggesting a conserved pathogenic mechanism in ciliary transition zone mutants.

In summary, the study uncovers a novel pathogenic mechanism of scoliosis in zebrafish ciliary mutants, involving a feed-forward loop between astrogliosis, induced by perturbed ventricular homeostasis, and immune cell recruitment, which can be partially rescued by anti-inflammatory treatment.

Stats

"Scoliosis appeared asynchronously in rpgrip1l-/- juveniles from 4 to 11 weeks post-fertilization, with 90% penetrance in adults."
"Micro-computed tomography confirmed that spine curvature in rpgrip1l-/- fish was three-dimensional, with no evidence of vertebral fusion, malformation or fracture."
"Reintroducing RPGRIP1L in foxj1a-expressing cells, but not in col2a1a-expressing cells, was sufficient to fully rescue scoliosis in rpgrip1l-/- fish."
"Transcriptomic and proteomic analyses revealed upregulation of genes and proteins involved in ciliary motility, inflammation, and astrogliosis in rpgrip1l-/- fish."
"Anti-inflammatory drug treatment (NACET) reduced scoliosis penetrance from 92% to 58% and decreased severity in rpgrip1l-/- fish."

Quotes

"Ciliary beating is an essential actor of CSF flow and of ventricular development in zebrafish larvae."
"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."
"Astrogliosis is conserved in another zebrafish ciliary TZ mutant, cep290, identifying a novel mechanism associated with scoliosis upon ciliary dysfunction."

Key Insights Distilled From

Astrogliosis and Neuroinflammation Underlie Scoliosis Upon Cilia Dysfunction

by Djebar,M., A... at www.biorxiv.org 02-25-2024

https://www.biorxiv.org/content/10.1101/2024.02.22.581530v1

Deeper Inquiries

What other cellular and molecular pathways, beyond astrogliosis and neuroinflammation, might contribute to scoliosis development in ciliary transition zone mutants

In addition to astrogliosis and neuroinflammation, several other cellular and molecular pathways may contribute to scoliosis development in ciliary transition zone mutants. One potential pathway is the dysregulation of cilia-driven cerebrospinal fluid (CSF) flow. Cilia defects in the CNS can disrupt the flow of CSF, leading to altered signaling and nutrient transport, which could impact spine development and maintenance. Another pathway could involve the disruption of signaling molecules or pathways that are crucial for spine development, such as the Wnt signaling pathway. Ciliary dysfunction may interfere with the proper transmission of signals that regulate spinal growth and alignment. Additionally, abnormalities in the extracellular matrix composition or organization due to ciliary defects could also contribute to scoliosis by affecting the structural integrity of the spine.

How do the specific ciliary defects in rpgrip1l and cep290 mutants lead to the observed perturbations in ventricular homeostasis and Reissner fiber maintenance

The specific ciliary defects in rpgrip1l and cep290 mutants can lead to the observed perturbations in ventricular homeostasis and Reissner fiber maintenance through several mechanisms. In rpgrip1l mutants, the loss of multiciliated tufts around the subcommissural organ (SCO) and the subsequent disruption of cerebrospinal fluid (CSF) flow can result in ventricular dilations. This altered CSF flow can impact the maintenance of the Reissner fiber, a structure crucial for spinal cord development and straightness. Similarly, in cep290 mutants, ciliary dysfunction can lead to abnormal cilia structure and function, affecting CSF dynamics and Reissner fiber integrity. The perturbations in ventricular homeostasis and Reissner fiber maintenance in both mutants likely stem from the primary ciliary defects that impact cilia-driven processes in the CNS.

Could the insights from this zebrafish study be leveraged to develop new therapeutic strategies for treating idiopathic scoliosis in humans

The insights from this zebrafish study could be leveraged to develop new therapeutic strategies for treating idiopathic scoliosis in humans. Understanding the molecular pathways and cellular processes involved in scoliosis development in ciliary transition zone mutants can provide valuable targets for therapeutic intervention. For example, targeting the pathways related to cilia function, CSF flow regulation, and Reissner fiber maintenance could offer potential avenues for developing novel treatments. Additionally, the identification of astrogliosis and neuroinflammation as contributing factors to scoliosis suggests that anti-inflammatory and antioxidant therapies, similar to the NACET treatment used in the study, could be explored for managing scoliosis in humans. By translating these findings into clinical research, researchers may uncover new approaches to prevent or mitigate the progression of idiopathic scoliosis in patients.