Summary: Kinase enzymes are essential for neurons to perform autophagy. Researchers found deleting genes that encode kinase NDR1 and NDR2 impairs neuron health and spurs neurodegeneration in both young and old mice.
Source: Francis Crick Institute
Scientists at the Francis Crick Institute have found that deleting two genes that encode key enzyme proteins (kinases NDR1 and NDR2), impairs the health of neurons and leads to neurodegeneration in young mice as well as in adults.
Their study of mouse neurons highlights the essential role of these proteins in maintaining brain health and preventing disease, a finding that could help with the discovery of future treatments for neurodegenerative diseases like Parkinson’s and Amyotrophic lateral sclerosis (ALS).
As part of their work published in Life Science Alliance on November 29, the researchers set out to understand the role of kinase enzymes in the development of the nervous system and maintaining healthy neurons. For the first time in mice, they deleted genes that encode for both kinases NDR1 and NDR2 in neurons.
They found that deleting of either of the enzymes alone had no effect on neuronal health, but when both were eliminated simultaneously, the loss caused neurodegeneration.
In order to understand why neurodegeneration occurs in the absence of these enzymes, the team further analyzed the brain tissue and found accumulation of protein clusters tagged for removal, a key characteristic of many neurodegenerative diseases. This suggests that the kinase enzymes are essential for the neurons to perform autophagy, the process of removing old or damaged components.
“The neuron’s ability to remove toxic proteins is an essential defense against neurodegeneration,” says Sila Utanir, head of the Crick’s Kinases and Brain Development Laboratory.
“Understanding that kinases NDR1 and NDR2 are vital to autophagy is important because if there was a way to boost their activity with future medicines, it could help clear the protein accumulation associated with disease.”
The team also looked in even more detail at the mechanisms at play when these key enzymes are lost. They found that ATG9A, a protein found in some cellular membranes, which is associated with autophagy and lipid recycling, was incorrectly positioned and as such, couldn’t function properly.
Flavia Roșianu, first author of the paper, said, “The complex signals sent between cells in our brain are all part of a bigger picture of neuronal health.
“In order to understand how our brain develops and why disease occurs, we need to piece together these connections and identify the most significant proteins and signals.”
About this genetics and neuroscience research news
Autophagy is essential for neuronal development and its deregulation contributes to neurodegenerative diseases. NDR1 and NDR2 are highly conserved kinases, implicated in neuronal development, mitochondrial health and autophagy, but how they affect mammalian brain development in vivo is not known.
Using single and double Ndr1/2 knockout mouse models, we show that only dual loss of Ndr1/2 in neurons causes neurodegeneration. This phenotype was present when NDR kinases were deleted both during embryonic development, as well as in adult mice.
Proteomic and phosphoproteomic comparisons between Ndr1/2 knockout and control brains revealed novel kinase substrates and indicated that endocytosis is significantly affected in the absence of NDR1/2.
We validated the endocytic protein Raph1/Lpd1, as a novel NDR1/2 substrate, and showed that both NDR1/2 and Raph1 are critical for endocytosis and membrane recycling. In NDR1/2 knockout brains, we observed prominent accumulation of transferrin receptor, p62 and ubiquitinated proteins, indicative of a major impairment of protein homeostasis.
Furthermore, the levels of LC3-positive autophagosomes were reduced in knockout neurons, implying that reduced autophagy efficiency mediates p62 accumulation and neurotoxicity.
Mechanistically, pronounced mislocalisation of the transmembrane autophagy protein ATG9A at the neuronal periphery, impaired axonal ATG9A trafficking and increased ATG9A surface levels further confirm defects in membrane trafficking, and could underlie the impairment in autophagy.
We provide novel insight into the roles of NDR1/2 kinases in maintaining neuronal health.