Circadian Clock Gene BMAL1 Drives Thyroid Aging by Triggering Cellular Senescence
Single-cell sequencing reveals how declining BMAL1 silences a key inflammation brake, accelerating thyroid cell senescence and hormone loss.
Summary
Researchers used single-cell RNA sequencing of 134,360 human thyroid cells across young, middle-aged, and elderly donors to map aging-related gene changes. They found that aging progressively amplifies cellular senescence—especially in a distinct epithelial subpopulation called CDKN1A_EPI—and that the core circadian clock gene BMAL1 drops significantly with age. Using thyroid-specific Bmal1 knockout mice and cell line experiments, the team showed that loss of BMAL1 suppresses the NF-κB inhibitor NFKBIA, unleashing inflammatory signaling that accelerates senescence and impairs thyroid hormone synthesis. The findings position the BMAL1–NFKBIA axis as a central driver of age-related thyroid dysfunction.
Detailed Summary
**Why it matters:** Hypothyroidism becomes increasingly common with age, and TSH levels rise even in otherwise healthy elderly people, yet the cellular and molecular drivers of thyroid aging remain poorly understood. This study provides the first comprehensive single-cell atlas of human thyroid aging and links circadian rhythm disruption directly to cellular senescence and hormone production failure.
**What was studied:** The team performed scRNA-seq on 25 human thyroid samples grouped as young (18–35 yrs), middle-aged (35–65 yrs), and old (>65 yrs), profiling 134,360 cells after quality filtering. Eight major cell types and 22 subtypes were identified. Differentially expressed genes (DEGs) were compared across age groups, and functional enrichment analyses were carried out. Findings were validated using thyroid-specific Bmal1 conditional knockout mice and in vitro BMAL1-knockout thyroid cell lines with transcriptome sequencing.
**Key results:** Thousands of DEGs were identified across cell types, with epithelial cells (EPI) showing the greatest transcriptional noise and vulnerability to aging stress. Crucially, many old-group DEGs were already present in middle-aged individuals, revealing early onset of thyroid aging. As aging advanced, TH synthesis genes (TG, TPO, TSHR) were upregulated—interpreted as an adaptive response to rising TSH—while senescence-associated secretory phenotype (SASP) markers increased progressively in EPI. A senescence-enriched epithelial subpopulation, CDKN1A_EPI, was characterized by high p21 expression, reduced function, and elevated SASP. The circadian gene BMAL1 (ARNTL) was consistently downregulated with aging. Thyroid-specific Bmal1 knockout mice showed accelerated cellular senescence (elevated p21, p16, SA-β-gal), reduced NFKBIA (IκBα) expression, activated NF-κB signaling, enhanced SASP, and impaired hormone synthesis. Cell line knockouts and transcriptome sequencing confirmed the BMAL1→NFKBIA→NF-κB pathway as the mechanistic link.
**Implications:** The study establishes that circadian rhythm disruption—via BMAL1 loss—removes a critical brake on NF-κB-driven inflammation in thyroid follicular cells, accelerating senescence and functional decline. This BMAL1–NFKBIA axis represents a novel, actionable target for interventions aimed at preserving thyroid health in aging populations, and potentially for addressing age-related hypothyroidism more broadly.
**Caveats:** The scRNA-seq data are cross-sectional and cannot establish causality in humans. Sample sizes per age group were limited. Mouse knockout models do not fully recapitulate the gradual, multifactorial nature of human thyroid aging, and cell line experiments lack the tissue microenvironment context.
Key Findings
- Middle-aged thyroid transcriptomes cluster closer to old than young, indicating aging begins earlier than expected.
- A senescence-enriched epithelial subpopulation (CDKN1A_EPI) shows high p21, low function, and amplified SASP with aging.
- BMAL1 expression declines progressively in aging thyroid epithelial cells across all three age groups.
- Thyroid-specific Bmal1 knockout mice display accelerated senescence, elevated NF-κB activity, and impaired hormone synthesis.
- BMAL1 loss suppresses NFKBIA (IκBα), unleashing NF-κB inflammatory signaling as the key senescence mechanism.
Methodology
Cross-sectional scRNA-seq of 134,360 human thyroid cells from 25 donors (young/middle-aged/old), with Harmony batch correction and UMAP visualization. Findings were validated in thyroid-specific Bmal1 conditional knockout mice and BMAL1-knockout thyroid cell lines with bulk transcriptome sequencing.
Study Limitations
The human data are cross-sectional, preventing longitudinal causal inference. Mouse conditional knockouts represent an acute genetic loss rather than the gradual BMAL1 decline seen in human aging. Cell line experiments lack the complexity of intact thyroid tissue microenvironment.
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