Summary: Kinase enzymes are required for neurons to carry out autophagy. Deleting the genes that encode kinases NDR1 and NDR2 disrupts neuron function and triggers neurodegeneration in both young and adult mice.
Source: Francis Crick Institute
Researchers at the Francis Crick Institute report that removing two genes that encode the conserved kinases NDR1 and NDR2 impairs neuronal health and leads to progressive neurodegeneration in mice.
Their work, published in Life Science Alliance, highlights the critical role of NDR1 and NDR2 in maintaining neuronal protein homeostasis and proper membrane trafficking. These findings deepen our understanding of mechanisms that protect the brain and could point to new therapeutic strategies for neurodegenerative diseases such as Parkinson’s disease and amyotrophic lateral sclerosis (ALS).
The team used mouse models with targeted deletions of Ndr1 and Ndr2 in neurons. Deleting either kinase alone produced no obvious defects, but simultaneous loss of both NDR1 and NDR2 caused clear neurodegeneration. This degeneration occurred whether the kinases were deleted during embryonic development or after the animals reached adulthood, indicating that NDR1/2 activity is required throughout life to preserve neuronal integrity.
Detailed examination of brain tissue from double knockout mice revealed accumulation of protein aggregates that are normally tagged for degradation—an established hallmark of many neurodegenerative disorders. These aggregates included increased levels of ubiquitinated proteins and p62, indicating a breakdown in the cellular systems that clear damaged or excess proteins. The researchers conclude that NDR1 and NDR2 are essential for neuronal autophagy, the process that removes and recycles damaged cellular components.
“A neuron’s ability to clear toxic and misfolded proteins is a fundamental defense against neurodegeneration,” says Sila Utanir, head of the Crick’s Kinases and Brain Development Laboratory. “Understanding that NDR1 and NDR2 support autophagy suggests they could be therapeutic targets. If future drugs can enhance their activity, it may be possible to reduce the harmful protein accumulation seen in many brain diseases.”
To uncover how loss of NDR1/2 leads to impaired autophagy, the scientists performed proteomic and phosphoproteomic analyses of knockout and control brains. These studies revealed novel substrates of NDR kinases and implicated defects in endocytosis and membrane recycling as central problems when NDR1/2 are absent.
One key discovery concerned ATG9A, a transmembrane protein involved in autophagy and lipid recycling. In neurons lacking NDR1/2, ATG9A showed abnormal localization, accumulating at the neuronal periphery and failing to traffic properly along axons. This mislocalization correlated with fewer LC3-positive autophagosomes and increased ATG9A at the cell surface, consistent with compromised autophagy and impaired membrane trafficking.
The team also identified the endocytic protein Raph1 (also known as Lpd1) as a novel substrate of NDR1/2. Functional studies showed that both NDR kinases and Raph1 are essential for efficient endocytosis and membrane recycling in neurons. Loss of these activities likely contributes to the buildup of transferrin receptor, ubiquitinated proteins, and p62 observed in the knockout brains.
“Neuronal communication depends on tightly regulated protein and membrane trafficking,” explains Flavia Roșianu, first author of the paper. “Disrupting key signaling nodes like NDR1/2 changes how membranes and cargos are handled inside neurons, which can cascade into fatal defects in protein clearance and eventually cell loss.”
Overall, the study provides new mechanistic insight into how conserved kinases support neuronal health: NDR1 and NDR2 maintain endomembrane trafficking and autophagy, preventing the harmful protein accumulation that drives neurodegeneration. These findings expand our understanding of the molecular pathways that preserve neuronal homeostasis and identify NDR kinases and their substrates as potential targets for therapeutic development.
About this genetics and neuroscience research news
Author: Press Office
Source: Francis Crick Institute
Contact: Press Office – Francis Crick Institute
Image: The image is in the public domain
Original Research: Open access. “Loss of NDR1/2 kinases impairs endomembrane trafficking and autophagy leading to neurodegeneration” by Flavia Roşianu et al., Life Science Alliance
Abstract
Loss of NDR1/2 kinases impairs endomembrane trafficking and autophagy leading to neurodegeneration
Autophagy is essential for neuronal development and its dysregulation contributes to neurodegenerative disease. NDR1 and NDR2 are evolutionarily conserved kinases implicated in neuronal development, mitochondrial health, and autophagy, but their roles in the mammalian brain in vivo were not fully understood.
Using single and double Ndr1/2 knockout mouse models, the study shows that only combined loss of Ndr1 and Ndr2 in neurons produces neurodegeneration. This phenotype appears when NDR kinases are deleted during embryonic development and when deleted in adult animals, highlighting an ongoing requirement for these kinases in neuronal maintenance.
Comparative proteomic and phosphoproteomic analyses between knockout and control brains revealed novel kinase substrates and pointed to substantial disruption of endocytosis in the absence of NDR1/2. The researchers validated Raph1/Lpd1 as a new NDR1/2 substrate and demonstrated that both NDR kinases and Raph1 are necessary for efficient endocytosis and membrane recycling.
In NDR1/2-deficient brains, there was a notable accumulation of transferrin receptor, p62, and ubiquitinated proteins, indicating severe impairment of protein homeostasis. Knockout neurons also had reduced numbers of LC3-positive autophagosomes, suggesting lower autophagy efficiency that likely contributes to p62 accumulation and neuronal toxicity.
Mechanistically, pronounced mislocalization of the transmembrane autophagy protein ATG9A to neuronal peripheries, disrupted axonal ATG9A trafficking, and elevated ATG9A at the cell surface underscore defects in membrane trafficking that likely underlie impaired autophagy.
These results provide new insight into how NDR1 and NDR2 kinases preserve neuronal health by regulating endomembrane trafficking and autophagy, and they identify molecular targets for future research into neuroprotection and disease intervention.