Nicotine Hijacks Rare Lung Cells to Damage the Brain, Raise Dementia Risk

The lung has always seemed like the obvious casualty in the smoking story. Blackened alveoli, scarred airways, the slow choking of capacity over decades. What nobody suspected, or at least couldn’t demonstrate until now, was that the lung was also talking. Sending signals. Dispatching molecular parcels north through the body toward the brain, parcels packed with a protein that throws neuronal iron regulation into disarray. A study published today in Science Advances by researchers at the University of Chicago has mapped, for the first time, a direct chemical communication route between the lungs and the brain, one that nicotine appears to hijack with every exposure. The finding may help explain something that has puzzled researchers for years: why heavy smokers in midlife face roughly double the risk of dementia two or three decades later.

The connection between smoking and cognitive decline is well-established in the epidemiological record. What’s been missing is mechanism, the molecular plumbing that links tobacco smoke inhaled in your forties to a diagnosis of Alzheimer’s or vascular dementia in your seventies.

The leading theories have always centered on the vascular system. Tobacco damages blood vessels, reduces oxygen delivery, accelerates arterial stiffening, and over time, this taxes the brain. That picture isn’t wrong, exactly, but it’s probably incomplete. The new work points to something rather different: a population of cells deep in the airway epithelium, cells so rare they make up less than one per cent of all lung cells, that appear to function as sentinels for the entire body’s iron supply. When nicotine arrives, these cells respond by flooding the system with messages the brain was never supposed to receive.

The cells in question are pulmonary neuroendocrine cells, or PNECs. They’re odd things. Part neuron, part hormone-secreting gland, they cluster at the branching points of the airways where they can sample whatever’s passing through. For researchers, they’ve been almost impossible to work with: too rare to isolate in useful quantities, too finicky to grow in culture. Joyce Chen’s lab at the University of Chicago got around this by generating what they call induced PNECs, deriving the cells from human pluripotent stem cells in sufficient numbers to actually run experiments.

What they found when they exposed those iPNECs to nicotine was, to put it mildly, striking. The cells began releasing exosomes, the tiny vesicles that cells use to ship biological cargo around the body, at nearly three times the normal rate. And those exosomes were stuffed with a protein called serotransferrin, which the body uses to regulate how iron moves through the bloodstream. “The primary challenge was the extreme rarity of PNECs, which make up less than 1% of lung cells, making them nearly impossible to isolate and study in depth,” said postdoctoral researcher Kui Zhang, co-first author of the study. The stem-cell approach, he noted, was what made the work tractable at all.

“This nicotine will have an impact on the PNEC, and this PNEC will release a massive amount of exosomes, and that causes perturbation in terms of iron homeostasis,” said co-first author Abhimanyu Thakur, now at Harvard Medical School’s Department of Neurosurgery. The serotransferrin-laden exosomes, once released, don’t stay in the lung.

The vagus nerve is the body’s great wanderer, snaking from the brainstem down through the chest and abdomen, touching the heart, the gut, the lungs. PNEC clusters sit in close proximity to vagal sensory neurons, and the team found that nicotine-triggered exosomes were taken up by those neurons in the lung tissue. From there, the signal propagates. Neurons exposed to nicotine-loaded PNEC exosomes showed elevated levels of multiple iron transporter proteins, ferritin accumulation, depleted ATP, and a measurable spike in oxidative stress. Alpha-synuclein, a protein implicated in Parkinson’s disease and other neurodegenerative conditions, went up too. “We are finding neurodegeneration-related markers, which are going up, and which can be linked with many cognitive and dementia-related diseases,” Thakur said. In mice given nicotine, cognitive tests showed impaired recognition memory and reduced locomotor performance. When the team injected mice directly with exosomes harvested from nicotine-exposed iPNECs, similar neuroinflammatory signatures appeared in brain tissue.

The iron angle is particularly interesting given what the field already knows. Iron dysregulation in neurons precedes the formation of the amyloid plaques and neurofibrillary tangles that define Alzheimer’s pathology, and ferroptosis, a form of programmed cell death that depends on iron levels, has been linked to both Alzheimer’s and Parkinson’s. “This iron dyshomeostasis drives oxidative stress, mitochondrial dysfunction, and increased α-synuclein expression,” said Chen, “hallmarks of neurodegenerative disease.” The team found they could partially reverse the damage in cell culture by blocking TFR1, the neuronal receptor through which serotransferrin delivers its iron-disrupting payload, which at least suggests the pathway is real and targetable, not just an artifact of the experimental setup.

It’s worth being clear about what this research does and doesn’t show. The causal chain from nicotine exposure to PNEC activation to exosome release to neuronal iron disruption to dementia has been established in cell culture and mouse models; direct evidence in living humans isn’t there yet, and may be years away. The team validated several of their findings using single-cell RNA sequencing data from human smokers and non-smokers, finding consistent patterns in gene expression related to iron handling and exosome production. But associative data from real people is not the same as a demonstrated mechanism in real people.

What the work does do is reframe how we think about the lung. “It reveals that the lung is not just a passive target of smoke exposure, but an active signalling organ influencing brain pathology,” said Chen. That’s a genuinely different framing, and it has implications beyond dementia. The vagus-mediated lung-brain axis that this study maps is probably involved in a lot of things scientists haven’t looked at yet. Chronic lung disease, respiratory infection, air pollution, vaping. If PNECs can be activated to fire off iron-perturbing signals by nicotine, the question of what else activates them is now very much open.

Chen’s team is already working on whether blocking exosome release from PNECs could have therapeutic applications. That’s a longer road than the paper makes it sound, involving years of preclinical work before anything reaches a clinic. But the iron transporter angle is at least a target. “Understanding these cross-organ communication pathways is critical for developing better prevention and intervention strategies for neurodegenerative diseases,” Chen said. The lung, it turns out, has been sending the brain messages all along. Scientists are only now learning to read them.

Source: Thakur et al., “Pulmonary neuroendocrine cell-derived exosomes regulate iron homeostasis and oxidative stress in lung neurons,” Science Advances, April 8, 2026. DOI: 10.1126/sciadv.ady2696