AMPA receptor activation, but not the accumulation of endogenous extracellular glutamate, induces paralysis and motor neuron death in rat spinal cord in vivo

Activation of the extracellular ATP ionotropic receptor P2X7 stimulates motor neuron apoptosis, whereas its inhibition in cell and animal models of amyotrophic lateral sclerosis can be protective. These observations suggest that P2X7 receptor activation is relevant to motor neuron disease and that it could be targeted for therapeutic development. Heat shock protein 90 (Hsp90) is an integral regulatory component of the P2X7 receptor complex, antagonizing ligand-induced receptor activation. Here, we show that the repressive activity of Hsp90 on P2X7 receptor activation in primary motor neurons is highly sensitive to inhibition. Primary motor neurons in culture are 100-fold more sensitive to Hsp90 inhibition by geldanamycin than other neuronal populations. Pharmacological inhibition and down-regulation of the P2X7 receptor prevented motor neuron apoptosis triggered by Hsp90 inhibition, which occurred in the absence of extracellular ATP. These observations suggest that inhibition of a seemingly motor neuron specific pool of Hsp90 leads to ligand independent activation of P2X7 receptor and motor neuron death. Downstream of Hsp90 inhibition, P2X7 receptor activated the phosphatase and tensin homolog (TPEN), which in turn suppressed the pro-survival phosphatidyl inositol 3 kinase (PI3K)/Akt pathway, leading to Fas-dependent motor neuron apoptosis. Conditions altering the interaction between P2X7 receptor and Hsp90, such as recruitment of Hsp90 to other subcellular compartments under stress conditions, or nitration following oxidative stress can induce motor neuron death. These findings may have broad implications in neurodegenerative disorders, including amyotrophic lateral sclerosis, in which activation of P2X7 receptor may be involved in both autonomous and non-autonomous motor neurons death. Impact statement Here we show that a motor neuron specific pool of Hsp90 that is highly sensitive to geldanamycin inhibition represses ligand-independent activation of P2X7 receptor and is critical to motor neuron survival. Activation of P2X7 receptor by Hsp90 inhibition triggers motor neuron apoptosis through the activation of PTEN, which in turn inhibits the PI3 kinase/Akt survival pathway. Thus, inhibition of Hsp90 for therapeutic applications may have the unexpected negative consequence of decreasing the activity of trophic pathways in motor neurons. The inhibition of Hsp90 as a therapeutic approach may require the identification of the Hsp90 complexes involved in pathogenic processes and the development of inhibitors selective for these complexes.

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ONO-5046 attenuation of delayed motor neuron death and effect on the induction of brain-derived neurotrophic factor, phosphorylated extracellular signal–regulated kinase, and caspase3 after spinal cord ischemia in rabbits

Journal of Thoracic and Cardiovascular Surgery ◽

10.1016/j.jtcvs.2005.06.041 ◽

2006 ◽

Vol 131 (3) ◽

pp. 644-650 ◽

Cited By ~ 4

Author(s):

Takashi Yamauchi ◽

Yoshiki Sawa ◽

Masahiro Sakurai ◽

Takano Hiroshi ◽

Goro Matsumiya ◽

...

Keyword(s):

Spinal Cord ◽

Motor Neuron ◽

Neurotrophic Factor ◽

Spinal Cord Ischemia ◽

Brain Derived Neurotrophic Factor ◽

Neuron Death ◽

Extracellular Signal Regulated Kinase ◽

Extracellular Signal ◽

Motor Neuron Death

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Divergent receptor utilization is necessary for phrenic long-term facilitation over the course of motor neuron loss following CTB-SAP intrapleural injections

Journal of Neurophysiology ◽

10.1152/jn.00236.2021 ◽

2021 ◽

Author(s):

Lauren F. Borkowski ◽

Catherine L. Smith ◽

Amy N. Keilholz ◽

Nicole L. Nichols

Keyword(s):

Motor Neuron ◽

Receptor Antagonist ◽

Receptor Activation ◽

Receptor Expression ◽

Male Rats ◽

Neuron Death ◽

Receptor Inhibition ◽

Motor Neuron Death ◽

Long Term Facilitation

Intrapleural injection of cholera toxin B conjugated to saporin (CTB-SAP) mimics respiratory motor neuron death and respiratory deficits observed in rat models of neuromuscular diseases. 7d CTB-SAP rats elicit enhanced phrenic long-term facilitation (pLTF) primarily through TrkB and PI3K/Akt-dependent mechanisms (i.e., Gs-pathway, which can be initiated by adenosine 2A (A2A) receptors in naïve rats), while 28d CTB-SAP rats elicit moderate pLTF though BDNF and MEK/ERK-dependent mechanisms (i.e., Gq-pathway, which is typically initiated by serotonin (5-HT) receptors in naïve rats). Here, we tested the hypothesis that pLTF following CTB-SAP is: 1) A2A receptor-dependent at 7d; and 2) 5-HT receptor-dependent at 28d. Adult Sprague Dawley male rats were anesthetized, paralyzed, ventilated, and were exposed to acute intermittent hypoxia (AIH; 3, 5 min bouts of 10.5% O2) following bilateral, intrapleural injections at 7d and 28d of: 1) CTB-SAP (25 μg), or 2) un-conjugated CTB and SAP (control). Intrathecal C4 delivery included either the: 1) A2A receptor antagonist (MSX-3; 10 μM; 12 μl); or 2) 5-HT receptor antagonist (methysergide; 20 mM; 15 μl). pLTF was abolished with A2A receptor inhibition in 7d, not 28d, CTB-SAP rats vs. controls (p<0.05), while pLTF was abolished following 5-HT receptor inhibition in 28d, not 7d, CTB-SAP rats vs. controls (p<0.05). Additionally, 5-HT2A receptor expression was unchanged in CTB-SAP rats vs. controls, while 5-HT2B receptor expression was decreased in CTB-SAP rats vs. controls (p<0.05). This study furthers our understanding of the contribution of differential receptor activation to pLTF and its implications for breathing following respiratory motor neuron death.

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