Retrograde nerve growth factor signaling abnormalities in familial dysautonomia
Lin Li, … , Katherine Gruner, Warren G. Tourtellotte
Lin Li, … , Katherine Gruner, Warren G. Tourtellotte
Published April 13, 2020
Citation Information: J Clin Invest. 2020;130(5):2478-2487. https://doi.org/10.1172/JCI130401.
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Research Article Cell biology Neuroscience

Retrograde nerve growth factor signaling abnormalities in familial dysautonomia

Abstract

Familial dysautonomia (FD) is the most prevalent form of hereditary sensory and autonomic neuropathy (HSAN). In FD, a germline mutation in the Elp1 gene leads to Elp1 protein decrease that causes sympathetic neuron death and sympathetic nervous system dysfunction (dysautonomia). Elp1 is best known as a scaffolding protein within the nuclear hetero-hexameric transcriptional Elongator protein complex, but how it functions in sympathetic neuron survival is very poorly understood. Here, we identified a cytoplasmic function for Elp1 in sympathetic neurons that was essential for retrograde nerve growth factor (NGF) signaling and neuron target tissue innervation and survival. Elp1 was found to bind to internalized TrkA receptors in an NGF-dependent manner, where it was essential for maintaining TrkA receptor phosphorylation (activation) by regulating PTPN6 (Shp1) phosphatase activity within the signaling complex. In the absence of Elp1, Shp1 was hyperactivated, leading to premature TrkA receptor dephosphorylation, which resulted in retrograde signaling failure and neuron death. Inhibiting Shp1 phosphatase activity in the absence of Elp1 rescued NGF-dependent retrograde signaling, and in an animal model of FD it rescued abnormal sympathetic target tissue innervation. These results suggest that regulation of retrograde NGF signaling in sympathetic neurons by Elp1 may explain sympathetic neuron loss and physiologic dysautonomia in patients with FD.

Authors

Lin Li, Katherine Gruner, Warren G. Tourtellotte

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Figure 6

The phosphatase inhibitor NSC87877 rescues retrograde TrkA phosphorylation and neuron survival.

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The phosphatase inhibitor NSC87877 rescues retrograde TrkA phosphorylati...
(A) Pharmacologic inhibition of Shp1 using the phosphatase inhibitor NSC87877 (NSC) rescued retrograde TrkA Y490 and Y674/5 phosphorylation (pTrkA) in sympathetic neurons grown in partitioned cultures when challenged with NGF at their terminals (results representative of n = 3 replicates). (B) NSC slightly enhanced retrograde neuron survival of TCtl neurons as previously reported for Shp1-inhibition (34) (Student’s t test; *P < 0.001, n = 30–37 images from 3 experimental replicates) and it completely rescued retrograde NGF-dependent neuron survival in TcKO neurons (Student’s t test; **P < 0.000001, n = 3–37 images from 3 experimental replicates). pTrkA was also rescued in vivo by NSC treatment. Compared with (C) PBS-treated (-NSC) Elp1-Ctl mice, (D) PBS-treated Elp1-cKO mice showed markedly diminished pTrkA in SCG sympathetic neurons (Student’s t test; *P < 0.000001, n = 18 images from 3 animals; image gain shown in D magnified 5 times to visualize low signal). (E) Treatment with NSC significantly rescued pTrkA in Elp1-cKO mice compared with PBS-treated Elp1-cKO mice (Student’s t test; **P < 0.000001, n = 36 images from 3 animals). Scale bars in C–E: 50 μm. For B, the results were considered significant if the Bonferroni’s corrected P value was less than 0.012 and for C if it was less than 0.017.