https://faseb.onlinelibrary.wiley.com/doi/epdf/10.1096/fj.202504570RR
I don’t personally think the liver is the best organ to look at as it tends to be exceptional. Also it often has a high expression of SLC13A5 (in drosophila INDY) which gives it high levels of exogenous citrate.
chatGPT:
Summary
This is a narrative review on liver aging that frames age-related hepatic decline as partly a problem of regulatory information loss, rather than simply accumulated molecular damage. Its central claim is that liver aging involves two interacting processes: epigenetic information loss and chronosenescence, meaning deterioration of circadian clock robustness and synchrony. The authors argue that these are linked through the NAD⁺/SIRT1 axis, which connects metabolism, chromatin regulation, mitochondrial function, inflammation, and circadian timing.
The paper begins by placing liver aging in the context of MASLD/MASH, fibrosis, and hepatocellular carcinoma risk. It argues that aging increases vulnerability to metabolic liver disease, and that the liver is especially sensitive to obesity-driven epigenetic aging. A cited point is that a 10-unit BMI increase has been associated with roughly 3.3 years of additional liver epigenetic aging, a relationship the authors present as liver-specific.
The review then develops the idea of epigenetic drift in liver aging. DNA methylation clocks, methylation changes in metabolic genes, altered histone acetylation/methylation, and miRNA dysregulation are presented as mechanisms by which hepatocytes lose precise metabolic identity. The authors give particular weight to studies suggesting that liver-specific methylation patterns regress toward pan-tissue averages during aging and MASLD, which they describe as hepatocytes “forgetting” their liver identity.
A major theme is the interaction between circadian biology and epigenetics. The paper describes how CLOCK/BMAL1, PER/CRY, REV-ERB/ROR loops regulate hepatic metabolism, while histone acetylation and SIRT1-dependent deacetylation act as “epigenetic gears” of the clock. With aging, the amplitude and coordination of liver clock outputs decline, causing metabolic genes to lose proper daily timing.
The authors identify NAD⁺ decline as a key convergence point. Reduced NAD⁺ lowers SIRT1 activity, weakens circadian feedback, worsens mitochondrial dysfunction, and may be amplified by PARP1 and CD38 activity during DNA damage and inflammaging. Figure 1 summarises this as a vicious cycle of NAD⁺ depletion linking epigenetic information loss, chronosenescence, inflammation, mitochondrial dysfunction, and spatial heterogeneity in the liver.
The review also highlights newer technologies: single-cell multiomics, spatial transcriptomics, and CRISPR-dCas9 epigenetic editing. Spatial profiling is used to argue that liver aging is not uniform: periportal zones show more mitochondrial/OxPhos dysfunction, while pericentral zones are more prone to lipid accumulation and steatosis. Figure 2 illustrates aged liver lobules with steatosis, ROS, fibrosis, and altered liver sinusoidal endothelial cell–stellate cell communication.
Therapeutic sections cover lifestyle interventions, calorie restriction/intermittent fasting, ketogenic diets, methylation diets, NAD⁺ precursors, SIRT1 activators, HDAC inhibitors, chronotherapy, partial reprogramming, chemical reprogramming, CRISPR epigenetic editing, and extracellular vesicle approaches such as eNAMPT-EVs. The authors are cautious: exercise, weight loss, and circadian-aligned behavioural interventions have the strongest human support, whereas partial reprogramming, CRISPR editing, engineered EVs, and zonation-targeted therapies remain mostly preclinical or conceptual.
Novelty
The main novelty is not a new experiment, because this is a review with no new original data, but rather a proposed synthesis.
The strongest novel framing is the explicit combination of epigenetic information loss with chronosenescence as a unified model of liver aging. Many reviews discuss liver epigenetics, circadian decline, NAD⁺, or MASLD separately; this paper tries to treat them as one interacting regulatory system.
A second novel feature is the emphasis on liver aging as spatially heterogeneous. The review links modern spatial transcriptomics to the idea that different liver zones age differently: periportal mitochondrial decline versus pericentral lipid accumulation. That is useful because it moves beyond “the aged liver” as a single average tissue state.
A third useful contribution is the paper’s translational caution. It discusses fashionable rejuvenation approaches such as OSKM partial reprogramming, chemical reprogramming, CRISPR epigenetic editing, and EV-based NAD⁺ delivery, but repeatedly states that these are not ready for clinical liver-aging use. That restraint improves the review.
A fourth novel element is its framing of NAD⁺/SIRT1 as a temporal-epigenetic hub, rather than merely a metabolic or longevity pathway. The review’s logic is that NAD⁺ decline disrupts not only energy metabolism but also clock amplitude, histone acetylation dynamics, mitochondrial rhythmicity, and inflammatory feedback.
Critique
The review is conceptually strong, but it sometimes risks over-unification. Epigenetic information loss, circadian decline, NAD⁺ depletion, inflammaging, mitochondrial dysfunction, fibrosis, and MASLD are all linked, but the paper sometimes presents them as if they form a single coherent causal loop. In reality, the directionality is often uncertain: epigenetic change may cause dysfunction, reflect altered cell composition, or arise as an adaptive response to metabolic stress.
The term “chronosenescence” is useful but may be somewhat rhetorical. It names an important phenomenon—age-related weakening of circadian robustness—but the paper does not fully distinguish whether chronosenescence is a primary driver, a mediator, or a secondary consequence of systemic aging, altered feeding, inflammation, sleep disruption, and metabolic disease.
The human evidence is limited. The paper acknowledges this, but much of the mechanistic confidence still comes from mouse models, cell systems, omics correlations, and preclinical interventions. Translation to older humans with obesity, diabetes, polypharmacy, CKD, alcohol exposure, variable sleep patterns, and established fibrosis will be much harder.
The review also leans heavily on epigenetic clocks and methylation signatures, but these are not straightforward mechanistic readouts. A lower or higher epigenetic age score does not necessarily prove functional rejuvenation or causal repair. For liver disease, clinically meaningful endpoints still include steatosis, inflammation, fibrosis regression, liver stiffness, portal hypertension, HCC risk, and mortality.
The therapeutic discussion is broad, but this breadth comes at the cost of depth. Exercise, weight loss, NAD⁺ precursors, HDAC inhibitors, partial reprogramming, CRISPR editing, EVs, and chronotherapy are very different intervention classes with different evidence levels. The paper correctly distinguishes clinical maturity, but the review could have benefited from a clearer graded evidence table.
There is also a potential issue with NAD⁺ centrality. NAD⁺ decline is important, but making it the central hub may underplay other drivers: insulin resistance, bile acid signalling, immune cell infiltration, senescent stellate cells, vascular ageing, mitochondrial DNA damage, ER stress, gut-liver axis changes, and clonal hepatocyte expansion. NAD⁺ restoration may help some regulatory loops without necessarily reversing advanced fibrosis or architectural damage.
The CRISPR epigenetic editing section is useful as a causality-testing framework, but its therapeutic implications remain remote. The authors do state this, but the illustrative logic—demethylate a promoter, restore PPARA, reduce lipid—may be too clean compared with real polygenic, zonated, inflammatory liver disease.
Overall assessment
This is a good, ambitious review. Its main value is the integrated framework: liver aging as a loss of epigenetic identity, circadian coordination, and NAD⁺/SIRT1-mediated regulatory resilience. The paper is strongest when it discusses mechanisms and technological approaches for resolving liver aging heterogeneity.
Its weakness is that the model may be more coherent than the evidence currently permits. The most clinically grounded interventions remain ordinary but powerful: weight loss, exercise, improved metabolic control, and circadian-aligned behaviour. The more exciting rejuvenation strategies are scientifically important but still far from proven human liver-aging therapies.