Ependymal polarity defects coupled with disorganized ciliary beating drive abnormal cerebrospinal fluid flow and spine curvature in zebrafish

Abstract

Idiopathic scoliosis (IS) is the most common spinal deformity diagnosed in childhood or early adolescence, while the underlying pathogenesis of this serious condition remains largely unknown. Here, we report zebrafish ccdc57 mutants exhibiting scoliosis during late development, similar to that observed in human adolescent idiopathic scoliosis (AIS). Zebrafish ccdc57 mutants developed hydrocephalus due to cerebrospinal fluid (CSF) flow defects caused by uncoordinated cilia beating in ependymal cells. Mechanistically, Ccdc57 localizes to ciliary basal bodies and controls the planar polarity of ependymal cells through regulating the organization of microtubule networks and proper positioning of basal bodies. Interestingly, ependymal cell polarity defects were first observed in ccdc57 mutants at approximately 17 days postfertilization, the same time when scoliosis became apparent and prior to multiciliated ependymal cell maturation. We further showed that mutant spinal cord exhibited altered expression pattern of the Urotensin neuropeptides, in consistent with the curvature of the spine. Strikingly, human IS patients also displayed abnormal Urotensin signaling in paraspinal muscles. Altogether, our data suggest that ependymal polarity defects are one of the earliest sign of scoliosis in zebrafish and disclose the essential and conserved roles of Urotensin signaling during scoliosis progression.

Loss of CSF-contacting neuron sensory function is associated with a hyper-kyphosis of the spine reminiscent of Scheuermann’s disease

“…Mutations in COL2A1 and COL9A3 encoding for collagens enriched in intervertebral disks 58 were recently reported in patients with Scheuermann’s kyphosis and associated with a defective growth of the cartilage endplates at the vertebrae margins 59 , 60 . Interestingly, recent findings report that murine intervertebral disks are enriched with UTS2R 61 , a receptor for Urp1/2 peptides expressed by CSF-cNs, which is asymmetrically expressed in the paravertebral muscles of AIS patients 62 . This raises the question of whether CSF-cNs could influence the development of intervertebral discs or muscles surrounding the vertebrae during growth.…”

The role of cilia during organogenesis in zebrafish

“…Motile cilia in the ventricles and central canal promote the flow of cerebrospinal fluid, which contains signalling molecules necessary for organism growth and development. Therefore, defects in ciliary beating in these areas can cause abnormal cerebrospinal fluid circulation, resulting in hydrocephalus [40][41][42]. The rhythmic beating of cilia in the node of the mouse and KV of zebrafish creates a polarized distribution of signalling molecules and ensures the proper distribution of organs [35,43].…”

“…However, in recent years, with advancements in gene editing technology and genomics, the mechanisms underlying scoliosis have started to be unraveled in zebrafish. Of particular interest is the association between abnormal cilia function and scoliosis [42,138,[144][145][146].…”

“…Motile cilia in the KV and early otic placode exhibit a circular beating pattern [ 80 ]. In the pronephric/kidney duct, motile cilia show a rhythmic sinusoidal wave pattern, while in the central canal and ventricles, the beating pattern is back and forth [ 42 , 73 ].

Figure 2 Cilia in zebrafish larvae.

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Astrogliosis and Neuroinflammation Underlie Scoliosis Upon Cilia Dysfunction

“…Moreover, two scoliotic models develop axial curvature while maintaining a RF showing that their curvature onset occurs independently of RF loss (17,18). Finally, neuro-inflammation has been described in a small subset of zebrafish IS models for which anti-inflammatory/anti-oxidant treatments (with NAC or NACET) partially rescue scoliosis penetrance and severity (5,19).…”