Findings from a recent study published in Proceedings of the National Academy of Sciences show that cigarette smoke causes epigenetic changes in retinal pigment epithelial (RPE) cells in mice, producing a pattern of cellular degeneration that closely resembles what happens with normal aging.
The results point to a specific mechanism by which smoking may set the stage for age-related macular degeneration (AMD).
Give me some background first.
Some context: AMD is a leading cause of irreversible vision loss among people over 50 worldwide. Smokers face up to four times the risk of developing the disease compared to nonsmokers.
But here’s the gap: While the link between smoking and AMD risk is well established, the biological mechanism has remained unclear.
- The conventional assumption: That smoking drives damage primarily through oxidative stress, with free radicals directly injuring retinal tissue.
And with this new research?
This study tested a different angle: whether smoking also causes epigenetic changes to RPE cells that alter which genes get turned on or off, without changing the DNA sequence itself.
Now, talk about the study.
A team at Johns Hopkins’ Wilmer Eye Institute used single nuclear ATAC sequencing (snATAC-seq) and single nuclear RNA sequencing (snRNA-seq) to examine how RPE cells respond to cigarette smoke exposure at the epigenetic level.
The approach: snATAC-seq measures chromatin accessibility, meaning how physically open or closed a cell’s DNA packaging is. When chromatin is accessible, genes can be read and expressed. When it’s closed off, those genes go silent.
- Paired with snRNA-seq, the researchers could track both the structural changes and the resulting shifts in gene expression at single-cell resolution.
Who was included in the study?
Investigators injected cigarette smoke condensate (CSC) intravitreally into 3-month-old and 12-month-old mice, corresponding roughly to young adulthood and late middle age in humans.
- RPE/choroid tissue was collected at 3, 6, and 10 days post-injection.
A separate cohort of mice was exposed to cigarette smoke daily for 4 months to assess chronic exposure effects.
Human tissue was also examined: RPE cells from 4 donors were analyzed. Two had no AMD and did not smoke, one had no AMD but did smoke, and one had early AMD.
Findings?
In both young and aged mice, acute CSC exposure caused the formation of a distinct cluster of dysfunctional, dedifferentiated RPE cells.
- These cells showed globally decreased chromatin accessibility and reduced expression of core RPE function genes.
Any key patterns?
Genes linked to “hallmarks of aging” were downregulated across these dedifferentiated cells—including genes tied to genomic instability, telomere maintenance, and mitochondrial function, among others.
Worth noting: The chromatin-level changes in young CSC-treated RPE were similar to what the researchers saw in aged vehicle-treated RPE.
- Smoke exposure in young mice was producing a cellular profile that resembled natural aging.
Tell me more.
Here’s where the age difference mattered.
Young de-differentiated RPE cells mounted a compensatory response: they upregulated a separate subset of hallmark aging genes specifically involved in mitochondrial function, proteostasis, autophagy, inflammation, and metabolism.
Aged dedifferentiated RPE cells did not activate this compensatory pathway.
And what was the functional consequence?
Using TUNEL labeling (a method for identifying dead cells), the researchers confirmed that aging gene activation protected young CSC-treated RPE from cell death.
- Their aged counterparts, lacking that compensatory expression, died.
Mice exposed to chronic cigarette smoke for 4 months showed the same pattern of dedifferentiated and healthy RPE clusters, confirming that the acute findings held under sustained exposure.
Any limitations to note?
As this was a mouse model study, the degree to which these epigenetic patterns translate directly to human AMD progression could not be confirmed.
Plus, the human donor sample was small (only four donors).
- While the findings were consistent with the mouse data, larger human tissue studies will be needed to validate the conclusions.
The study also does not yet distinguish which epigenetic changes are reversible and which are permanent, a question the investigators flagged as a priority for future work.
Anything else?
The human tissue findings: When the researchers examined macular RPE from their four donors, they identified 1,698 genes with altered expression that were shared between dysfunctional human and mouse RPE cells.
The dedifferentiated and healthy RPE clusters observed in mice were present in the smoker donor and the early AMD donor, but not in the two nonsmoker donors without AMD.
So what did the study authors have to say about all of this?
They argued that the results reframe how clinicians should think about smoking’s role in AMD.
Their reasoning: Smoking reprograms RPE cells epigenetically, shutting down the genes they need to handle stress and survive. The oxidative injury from free radicals is only part of the picture.
Interesting … and what are the next steps?
The researchers plan to characterize how age and continuous smoke exposure contribute to eye damage and comorbidities seen in patients with late-stage AMD. A central question going forward is sorting out which of these epigenetic changes are temporary and which are locked in.
Take home.
Smoking rewires retinal cell gene expression at the epigenetic level, producing a degeneration pattern that mirrors aging itself. Young cells can mount a compensatory response; older cells cannot.
For clinicians counseling patients on AMD risk, this adds a concrete mechanistic argument to the case for smoking cessation.