Sonic Hedgehog repression underlies gigaxonin mutation–induced motor deficits in giant axonal neuropathy
Yoan Arribat, … , Mireille Rossel, Pascale Bomont
Yoan Arribat, … , Mireille Rossel, Pascale Bomont
Published September 10, 2019
Citation Information: J Clin Invest. 2019;129(12):5312-5326. https://doi.org/10.1172/JCI129788.
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Research Article Neuroscience

Sonic Hedgehog repression underlies gigaxonin mutation–induced motor deficits in giant axonal neuropathy

Abstract

Growing evidence shows that alterations occurring at early developmental stages contribute to symptoms manifested in adulthood in the setting of neurodegenerative diseases. Here, we studied the molecular mechanisms causing giant axonal neuropathy (GAN), a severe neurodegenerative disease due to loss-of-function of the gigaxonin–E3 ligase. We showed that gigaxonin governs Sonic Hedgehog (Shh) induction, the developmental pathway patterning the dorso-ventral axis of the neural tube and muscles, by controlling the degradation of the Shh-bound Patched receptor. Similar to Shh inhibition, repression of gigaxonin in zebrafish impaired motor neuron specification and somitogenesis and abolished neuromuscular junction formation and locomotion. Shh signaling was impaired in gigaxonin-null zebrafish and was corrected by both pharmacological activation of the Shh pathway and human gigaxonin, pointing to an evolutionary-conserved mechanism regulating Shh signaling. Gigaxonin-dependent inhibition of Shh activation was also demonstrated in primary fibroblasts from patients with GAN and in a Shh activity reporter line depleted in gigaxonin. Our findings establish gigaxonin as a key E3 ligase that positively controls the initiation of Shh transduction, and reveal the causal role of Shh dysfunction in motor deficits, thus highlighting the developmental origin of GAN.

Authors

Yoan Arribat, Karolina S. Mysiak, Léa Lescouzères, Alexia Boizot, Maxime Ruiz, Mireille Rossel, Pascale Bomont

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Figure 2

Impaired MN specification, altered axonogenesis, and neuromuscular junctions in gan morphants.

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Impaired MN specification, altered axonogenesis, and neuromuscular junct...
(A) Gigaxonin repression impairs late specification of motor neuron progenitors and differentiation of sMNs. Progenitors and motor neurons were visualized with Nkx6.1 and Islet immunostaining, respectively, in a lateral view of spinal cord in WT and Mis-, and MO-injected embryos at 36 hpf. Ventral Islet-positive cells correspond to motor neurons (arrow), dorsal Islet-positive cells correspond to the sensory Rohon-Beard neurons (arrowhead). In the absence of gigaxonin, a large reduction in both Nkx6.1-positive MN progenitors and Islet-positive sMN is observed at 36 hpf. (B–E) Gigaxonin depletion leads to abnormal architecture of MN axons. (B) Gigaxonin depletion leads to the absence of sMN cell bodies (Islet) and axons (Zn8) at 56 hpf. (C) pMN axonal projections (Znp1) show abnormal arborization in morphants at 56 hpf, with some CaP pMN axons exhibiting reduced length (white asterisk). (D, left) Three-dimensional examination of the spinal cord of gigaxonin-depleted embryos at 48 hpf, using LightSheet microscopy. Gigaxonin depletion leads to additional abnormalities in the spinal cord architecture, such as protruding axons (arrow) and absence of MiP and RoP motor axons (transverse view) (see Supplemental Videos 2 and 3). (D, middle and right) Neuromuscular junctions (α-bungarotoxin) and subsequent innervation of trunk muscles are abolished in gan morphants. Note that CaP axons are occasionally absent (white asterisk). (E) Quantification of the mean length of pMN CaP axons (left) and mean length relative to the body thickness of the embryos, as defined by phase contrast pictures (right), showing significant neurite abnormalities. Statistics: with normality of the distribution of the data, a 1-way ANOVA test (Bonferroni’s post hoc test) was used. Data represent mean ± SD; individual values are represented; n = 8 (WT), n = 9 (Mis), n = 11 (MO); NS, not statistically significant; ****P < 0.0001. Scale bars: 25 μm (A); 100 μm (B–D).