A familiar cell-cycle protein may be helping aging cells broadcast inflammatory signals throughout the body, according to a new study published in Nature Aging. Researchers report that cyclin D1, or CCND1, and its partner enzyme CDK6 remain unusually active in senescent cells even after those cells have permanently stopped dividing. Rather than being a harmless remnant of cell-cycle activity, the CCND1–CDK6 pair appears to intensify DNA damage and trigger molecular pathways linked to chronic inflammation. Blocking this activity reduced inflammatory gene expression in aged mouse livers and improved physical performance in old animals, raising the possibility that an existing cancer drug could be repurposed to target part of the biology of aging.
Cellular senescence is a protective state that prevents damaged or stressed cells from continuing to proliferate. Senescent cells withdraw from the cell cycle, but they do not become biologically inactive. Many release a complex mixture of signaling molecules known as the senescence-associated secretory phenotype, or SASP. This secretome can include inflammatory cytokines, chemokines, growth factors and interferon-stimulated genes, commonly called ISGs. In the short term, these signals can help coordinate tissue repair or alert the immune system. When senescent cells accumulate with age, however, persistent SASP activity may contribute to tissue dysfunction, chronic inflammation and age-related disease.
The new work focuses on a molecular contradiction at the center of senescence biology. CCND1 is best known for helping cells progress through the early stages of the cell cycle. It binds to cyclin-dependent kinases, particularly CDK4 and CDK6, to promote phosphorylation of retinoblastoma-associated cell-cycle regulators and enable progression toward DNA replication. Senescent cells are not supposed to advance through this process, yet the researchers found that CCND1 is consistently increased across multiple models of nonproliferating senescent cells. The study extends earlier observations by showing that this elevation is not merely a marker of senescence. Instead, CCND1 and CDK6 actively contribute to the inflammatory state.
According to the findings, the CCND1–CDK6 complex promotes the accumulation of DNA damage in senescent cells. DNA damage can arise from replication stress, oxidative injury, defective repair or abnormal activity at fragile regions of the genome. In cells that have exited the cell cycle, damaged DNA may persist because repair processes and chromatin organization are altered. The researchers link increased CCND1–CDK6 activity to a greater burden of DNA damage, creating a chain reaction that connects cell-cycle regulators with innate immune signaling. This connection helps explain how a protein traditionally associated with proliferation can influence the behavior of cells that are no longer dividing.
One consequence of this damage is the production of cytoplasmic chromatin fragments. These are pieces of nuclear DNA or chromatin that become displaced into the cytoplasm, where they can be interpreted as danger signals. The immune sensor cyclic GMP–AMP synthase, or cGAS, recognizes abnormal double-stranded DNA in the cytoplasm and generates the second messenger cyclic GMP–AMP. That molecule activates the adaptor protein STING, which in turn stimulates downstream kinases and transcription factors, including pathways controlled by TBK1 and interferon regulatory factors. The result is the expression of interferon-stimulated genes and other inflammatory programs. By placing CCND1–CDK6 upstream of DNA damage, cytoplasmic chromatin fragments and cGAS–STING signaling, the study outlines a mechanistic route from senescence to inflammation.
The investigators examined this relationship in cellular systems designed to model senescence and found that reducing CCND1 or inhibiting CDK6 weakened the inflammatory output. The findings indicate that the pathway is not simply associated with the presence of senescent cells but helps determine how strongly those cells activate SASP and ISG programs. This distinction is important because senescence is not a single uniform state. Different triggers, including oncogene activation, DNA damage, oxidative stress and replicative exhaustion, can produce cells with overlapping but distinct secretory profiles. A pathway that regulates inflammatory signaling across several models could therefore offer a broader intervention point than therapies aimed at eliminating only one type of senescent cell.
The study also examined aging in living animals, focusing on the liver. Hepatocytes, the liver’s principal functional cells, can acquire senescence-like features as organisms grow older. In aged mouse livers, the researchers observed increased expression of Ccnd1 in senescent hepatocytes, together with signatures of DNA damage and interferon-related activity. To test whether CCND1 was functionally involved, they used a hepatocyte-specific Ccnd1 knockout model. Removing the gene from these liver cells reduced DNA damage and lowered expression of ISGs in aged animals. The results support the idea that elevated CCND1 is not only a consequence of aging-associated cellular stress but also a driver of inflammatory signaling within the aging liver.
The researchers then tested palbociclib, a clinical-grade inhibitor of CDK4 and CDK6. Palbociclib is already used in oncology, particularly for hormone receptor-positive breast cancer, where it restrains tumor-cell proliferation by interrupting cyclin-dependent kinase signaling. In the aged mice, treatment with the drug reduced DNA damage and interferon-stimulated gene expression in the liver, mirroring key effects seen after hepatocyte-specific Ccnd1 deletion. The study further reports that palbociclib-treated aged mice showed less frailty and improved physical performance. These outcomes suggest that dampening CCND1–CDK6 signaling may influence not only molecular markers of inflammation but also whole-animal measures of functional decline.
The findings are particularly notable because they point toward therapeutic repurposing rather than the immediate development of an entirely new drug class. Senolytic drugs are designed to selectively eliminate senescent cells, while senomorphic or senostatic approaches attempt to suppress harmful features such as SASP without necessarily removing the cells. Inhibiting CDK4/6 may fit within the second category by reducing the DNA-damage and inflammatory circuitry of senescent cells. However, the pathway also has essential roles in normal tissues, and CDK4/6 inhibitors can produce clinically important effects, including changes in blood-cell production and other treatment-related toxicities. The study used aged mice, not human patients, so its results do not establish that palbociclib will prevent frailty or extend healthy lifespan in people.
The work nevertheless provides a new framework for understanding why senescent cells can remain inflammatory long after they stop dividing. CCND1 appears to have a second life in senescence: instead of simply pushing cells through the cell cycle, its partnership with CDK6 may help sustain genomic damage and activate the cGAS–STING system. By reducing this activity, genetic deletion and pharmacological inhibition lowered inflammatory gene expression in aged liver and were associated with better physical function in mice. Future studies will need to determine how broadly the mechanism operates across organs, whether treatment windows can be identified that preserve beneficial senescence responses, and whether the benefits observed in animals can be translated safely to older people. For now, the findings place the CCND1–CDK6 axis among the emerging molecular targets connecting cellular aging, DNA damage and chronic inflammation.
Subject of Research: The role of cyclin D1–CDK6 signaling in senescence-associated inflammation, DNA damage, cGAS–STING activation and age-related functional decline.
Article Title: Inhibiting cyclin D1–CDK6 suppresses senescence-associated inflammatory gene expression and age-related functional decline
Article References: Rajesh, A., Havas, A.P., Arnold, R. et al. “Inhibiting cyclin D1–CDK6 suppresses senescence-associated inflammatory gene expression and age-related functional decline.” Nature Aging (2026). https://doi.org/10.1038/s43587-026-01196-x
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s43587-026-01196-x
Keywords: Cellular senescence, cyclin D1, CCND1, CDK6, SASP, interferon-stimulated genes, DNA damage, cGAS–STING, palbociclib, aging, frailty, liver inflammation.
Tags: aging and immune system signalingaging-related functional declineCellular senescencechronic inflammation in agingcyclin D1 and CDK6 in agingimpact of senescent cells on tissue healthinflammation and agingmolecular pathways of cellular senescencerepurposing cancer drugs for age-related diseasesrole of CCND1–CDK6 in DNA damagesenescence-associated secretory phenotypetargeting cell cycle proteins for aging therapy
