Summary: When a motor neuron-specific pool of heat shock protein 90 (Hps90) was inhibited, motor neuron apoptosis was triggered.
Source: Oregon State University
Researchers at Oregon State University have made an important advance toward understanding why certain cells in the nervous system are prone to breaking down and dying, which is what happens in patients with ALS and other neurodegenerative disorders.
The study into the role a protein known as heat shock protein 90 plays in intracellular signaling is a key step on the way to figuring out the reason some motor neurons in the spinal cord die and some do not.
Findings, which could eventually lead to therapies to counter motor neuron death, were published in Experimental Biology and Medicine.
Neurons are cells in the nervous system that carry information to muscles, glands and other nerves. Motor neurons are large neurons in the spine and brain stem, with long axons extending outside the nervous system to contact muscles and control their movements via contraction.
Researchers led by Alvaro Estevez and Maria Clara Franco of the OSU College of Science have shown that a ubiquitous “protein chaperone,” heat shock protein 90, is particularly sensitive to inhibition in motor neurons that depend for survival on “trophic factors” – small proteins that serve as helper molecules.
Trophic factors attach to docking sites on the surface of nerve cells, setting in motion processes that help keep a cell alive. Research in animal models has shown trophic factors may have the ability to salvage dying neurons.
“It is well known that there are some motor neuron subpopulations resistant to degeneration in ALS, and other subpopulations that are highly susceptible to degeneration,” said Estevez, associate professor of biochemistry and biophysics and the corresponding author on this research. “Understanding the mechanisms involved in these different predispositions could provide new insight into how ALS progresses and open new alternatives for the development of novel treatments for the disease.”
In this study, a motor-neuron-specific pool of heat shock protein 90, also known as Hsp90, repressed activation of a key cellular receptor and thus was shown to be critical to neuron survival; when Hsp90 was inhibited, motor neuron death was triggered.
The Hsp90 inhibitor used in this research was geldanamycin, an antitumor antibiotic used in chemotherapy. Findings suggest the drug may have the unintended consequence of decreasing motor neurons’ trophic pathways and thus putting those nerve cells at risk.
“The inhibition of Hsp90 as a therapeutic approach may require the development of inhibitors that are more selective so the cancer cells are targeted and healthy motor neurons are not,” said Franco, assistant professor of biochemistry and biophysics.
ALS, short for amyotrophic lateral sclerosis and also known as Lou Gehrig’s disease, is caused by the deterioration and death of motor neurons in the spinal cord. It is progressive, debilitating and fatal.
ALS was first identified in the late 1800s and gained international recognition in 1939 when it was diagnosed in a mysteriously declining Gehrig, ending the Hall of Fame baseball career of the New York Yankees first baseman. Known as the Iron Horse for his durability – he hadn’t missed a game in 15 seasons – Gehrig died two years later at age 37.
Funding: The National Institutes of Health and the ALS Association supported this research.
Joe Beckman, a distinguished professor of biochemistry and biophysics at OSU who has a long history as a leading ALS researcher, collaborated on this study, as did scientists from Cornell Medical College, the University of Central Florida, and the University of Alabama-Birmingham.
Oregon State University
Alvaro Estevez – Oregon State University
The image is in the public domain.
Original Research: Open access
“Highlight article: Ligand-independent activation of the P2X7 receptor by Hsp90 inhibition stimulates motor neuron apoptosis”. Alvaro Estevez et al.
Experimental Biology and Medicine doi:10.1177/1535370219853798
Highlight article: Ligand-independent activation of the P2X7 receptor by Hsp90 inhibition stimulates motor neuron apoptosis
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.