For decades, the mechanism by which Alzheimer’s disease kills neurons has been frustratingly incomplete. Known cell-death pathways, apoptosis, necroptosis, ferroptosis, can account for some neuronal loss, but not all. A significant fraction of brain cells simply seem to vanish, leaving no clear molecular signature of how they died.
Researchers at King’s College London have now identified a previously unknown cell-death mechanism they call “karyoptosis,” which they estimate accounts for approximately 18 to 20 percent of neuronal degeneration in Alzheimer’s disease beyond what is seen in normal aging. The finding, published in Nature Communications, closes a gap that has puzzled neuropathologists for years and identifies a potentially druggable pathway for slowing neurodegeneration.
Nuclear Shrinkage
Karyoptosis, from the Greek karyon (nucleus) and ptosis (falling), describes a form of cell death characterized by the progressive shrinkage and disintegration of the cell nucleus. The team, led by senior author Manolis Fanto at the UK Dementia Research Institute at King’s College London, analyzed approximately 3,000 brain cells from 28 patients, including Alzheimer’s disease cases, frontotemporal dementia (FTD) cases, and healthy aged controls.
In Alzheimer’s and FTD patients, roughly 35 percent of frontal cortex cells showed signs of karyoptosis. In healthy older adult controls, the figure was about 15 percent, suggesting that this pathway is active at low levels in normal aging but dramatically amplified in neurodegenerative disease.
The dying cells showed shriveled nuclei, structural proteins leaking into the cytoplasm, and the release of nuclear material into large extracellular vesicles. Critically, they did not show caspase-3 activation (apoptosis marker), PARP-1 cleavage (necroptosis marker), or plasma membrane rupture (necrosis marker). This was a distinct cell-death program.
The Molecular Mechanism
The team traced the pathway to the p38 MAP kinase, a stress-responsive enzyme already known to be activated by proteotoxic stress. In Alzheimer’s and FTD, the accumulation of toxic protein aggregates (such as amyloid-beta and tau) activates p38 MAPK. The activated kinase then directly phosphorylates a nuclear structural protein called LaminB1 at a specific site, serine 391.
LaminB1 is a component of the nuclear lamina, the meshwork of proteins that gives the nucleus its shape and structural integrity. Phosphorylation at Ser391 destabilizes this lamina, causing the nucleus to shrivel and eventually disintegrate. The cell dies not by activating a programmed suicide cascade, but by losing the physical integrity of its control center.
“We were able to block this process,” said first author Rebecca Casterton, also at the King’s Dementia Research Institute. In rat neurons and Drosophila models, treatment with the p38 MAPK inhibitor SB203580, or expression of a non-phosphorylatable mutant of LaminB1 (S391A/T413A), prevented nuclear shrinkage and reduced karyoptosis markers.
Why It Matters
The discovery of karyoptosis is significant for several reasons. First, it fills a mechanistic gap: the approximately 20 percent of neuronal loss unexplained by apoptosis and other known pathways now has a candidate mechanism. Second, it explains why anti-apoptotic drugs have not been more effective in Alzheimer’s trials, the dominant cell-death mechanism may not be apoptosis.
Third, and most practically, the pathway is druggable. p38 MAPK inhibitors have been developed for inflammatory conditions and are in clinical trials for other indications. While these drugs were not designed to cross the blood-brain barrier at therapeutic concentrations, the structural data on the p38-LaminB1 interaction, including the specific phosphorylation site, provides a molecular target for designing brain-penetrant inhibitors.
The study also found karyoptosis in Drosophila models, suggesting the pathway is evolutionarily conserved. This means findings in the fly model are likely to translate to human biology, and it opens the door to using Drosophila for high-throughput drug screening against karyoptosis.
Caveats
The human data is cross-sectional and correlational, the study identifies karyoptosis in post-mortem brain tissue but does not prove it is the primary driver of neuronal loss. Mouse model experiments showing that blocking karyoptosis rescues cognitive function would significantly strengthen the case. The p38 MAPK-LaminB1 axis has been demonstrated in cell and Drosophila models, but whether the same mechanism operates in human neurons in vivo remains to be confirmed with clinical-stage inhibitors.
For now, karyoptosis joins the growing list of regulated cell-death pathways, distinguished by its signature of nuclear disintegration without caspase activation. Its role in Alzheimer’s makes it a target worth pursuing.
Disclosure: Based on a peer-reviewed paper in Nature Communications, 2026. DOI: 10.1038/s41467-026-73802-w. Open access. First author Rebecca Casterton, senior author Manolis Fanto, UK Dementia Research Institute at King’s College London.