Retrograde nerve growth factor signaling abnormalities in familial dysautonomia
Lin Li, Katherine Gruner, Warren G. Tourtellotte
Lin Li, Katherine Gruner, Warren G. Tourtellotte
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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 5

Elp1 maintains TrkA phosphorylation by negatively regulating Shp1 phosphatase activity.

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Elp1 maintains TrkA phosphorylation by negatively regulating Shp1 phosph...
(A) Shp1 and Elp1 recruitment to a protein complex containing TrkA in TCtl neurons is NGF-dependent and binding of Shp1 to TrkA is independent of Elp1 (results representative of n = 3 replicates). (B) Although no detectable differences in total phosphatase activity were identified between TCtl and TcKO neurons, immunoprecipitation of Shp1 showed it was significantly hyperactivated in the absence of Elp1 in TcKO neurons compared with TCtl neurons (Student’s t test; *P < 0.00001, n = 4). (C) Adenovirus-mediated expression of a short hairpin RNA (shShp1) reduced the level of Shp1 protein more than 80% relative to expression of a scrambled (shScr) shRNA in TCtl neurons. (D) Whereas TcKO neurons expressing shScr showed significant retrograde NGF-dependent survival abnormalities (Student’s t test; *P < 0.001, n = 3–6), expression of shShp1 significantly and completely rescued retrograde NGF-dependent survival (Student’s t test; **P < 0.000001, n = 4). (E) Accordingly, the level of retrograde pTrkA in cell bodies was highly decreased in TcKO neurons compared with TCtl neurons infected with adenovirus expressing shScr (Student’s t test; *P < 0.000005, n = 28) and it was completely rescued by infection with shShp1-expressing adenovirus (Student’s t test; **P < 0.0001, n = 11; arrowheads, results represent pTrkA fluorescence). Scale bars: 25 μM. For D and E, the results were considered significant if the Bonferroni’s corrected P value was less than 0.017.