The motivation behind the work lies in a paradox that has emerged from large-scale plasma proteomics studies. Over the past several years, researchers measuring thousands of proteins in blood samples from tens of thousands of individuals have shown that these molecular fingerprints can estimate chronological age with striking accuracy. Yet a protein that predicts age is not necessarily a protein that drives ageing. Correlation, as the field has repeatedly learned, does not equal causation, and the leap from a predictive biomarker to a druggable target requires layers of evidence that simple statistical associations cannot supply. PEN was designed specifically to make that leap more systematic, transparent, and reproducible.

Architecturally, PEN unfolds in six sequential stages, each of which adds a distinct form of biological reasoning. The pipeline begins with a plasma proteome input, typically a matrix of protein abundance measurements across many individuals. In the second stage, a multilayer perceptron, a classic type of deep neural network, is trained to predict chronological age from the protein measurements. In the demonstration study, the team applied this stage to data from 44,179 UK Biobank participants profiled for approximately 2,920 plasma proteins. The model achieved a test coefficient of determination of 0.8723, a Pearson correlation of 0.934, and a mean absolute error of just 2.30 years, confirming that the proteomic age clock was performing at a level comparable to the best published proteomic predictors.

The third stage is where PEN begins to move beyond prediction. Using a technique called Integrated Gradients, an attribution method originally developed for interpreting deep learning models, the researchers identified which proteins contributed most strongly to the age predictions and characterized the functional modules those proteins participate in. Integrated Gradients works by accumulating the gradients of the model’s output with respect to its inputs as features are gradually shifted from a baseline to the actual value, yielding a per-protein importance score. This step converts the opaque neural network into a ranked list of diagnostic proteins, providing the raw material for the target discovery stages that follow.

Stage four introduces the graph-based core of the framework. The diagnostic proteins are mapped onto a protein-protein interaction network, a vast molecular map in which nodes represent proteins and edges represent known physical or functional interactions. Graph convolutional propagation and diffusion algorithms then spread information across this network, allowing the framework to identify candidate targets that are not merely important on their own but are embedded in neighborhoods of ageing-relevant biology. This network context matters because biological systems rarely act through single molecules; perturbing one node of a densely connected module can ripple through entire pathways. By propagating evidence through the interactome, PEN surfaces candidates that a purely statistical analysis would likely overlook.

The fifth stage applies a discovery-oriented reranking that integrates multiple components of biological evidence, weighing each candidate against additional criteria before a final prioritization is issued. Applied to the UK Biobank plasma proteomics data, this process produced a shortlist of candidate mechanistic target hypotheses that includes FBN1, FBLN5, EDA, RLN3, LHCGR, COL14A1, HLA-E, and TSPAN4. Several of these names will be familiar to students of ageing biology. FBN1 encodes fibrillin-1, a structural component of elastic fibers, and FBLN5 encodes fibulin-5, another extracellular matrix protein essential for elastic fiber assembly, both of which connect plausibly to the vascular stiffening and tissue degeneration characteristic of ageing. HLA-E, an immune regulatory molecule, hints at the inflammatory and immunological dimensions of the ageing process.

The sixth and final stage provides what the authors describe as orthogonal in silico support through virtual perturbation. Here the framework turns to Geneformer, a foundation model of gene regulatory networks trained on large corpora of single-cell transcriptomic data. Geneformer can simulate, computationally, what happens to a cell’s transcriptional state when a particular gene’s activity is reduced or abolished, a process the researchers call virtual perturbation. The team applied this approach to an independent dataset, GSE130973, a publicly available single-cell RNA sequencing dataset of ageing human skin. By asking whether virtual perturbation of each candidate gene shifts cells from an OLD transcriptional state toward a YOUNG one, or vice versa, the framework obtained an independent line of computational evidence that is entirely separate from the plasma proteomics data used to generate the candidates.

The results of this final stage were instructive in both their successes and their limitations. After recalibrating the analysis using an expanded null distribution of 500 random token-valid genes, FBLN5 and HLA-E showed significant positive OLD-to-YOUNG transcriptional state shifts in specific cell populations, strengthening the case that these two proteins merit experimental attention. Other candidates, including several on the original shortlist, displayed weaker or context-dependent effects, a reminder that computational prioritization is a hypothesis-generating exercise rather than a guarantee of biological validity. The authors are explicit on this point: the Geneformer perturbation stage strengthens biological plausibility but does not constitute experimental validation. Laboratory work with cell models, organoids, or animal systems remains essential before any of these candidates can be considered genuine therapeutic targets.

What makes PEN notable is less any single algorithmic component than the discipline of its overall design. Each stage is modular and auditable, and the framework is explicitly intended to be reproducible and generalizable. The authors argue that the same six-stage logic, proteomic input, deep learning prediction, interpretability analysis, graph-based propagation, evidence-weighted reranking, and foundation-model perturbation testing, could be applied to other biomarker-driven target discovery problems far beyond ageing, from cardiometabolic disease to neurodegeneration. The study was conducted using the UK Biobank Resource under Application Number ID200882 and was supported by the Zhangjiang Special Funding Major Project 2024, an initiative titled AI-driven and multi-ancestry evaluated protein therapeutic discovery system, reflecting a broader industrial and academic push to convert population-scale omics data into actionable drug discovery pipelines.

The broader significance of the work lies in its timing. Proteomic age clocks are proliferating, foundation models for biology are maturing rapidly, and the pharmaceutical industry is increasingly willing to pursue ageing itself, or age-related frailty, as a therapeutic domain. What has been missing is a principled way to connect these pieces, to move from a blood test that knows how old you are to a molecule worth targeting in the clinic. PEN offers one template for that connection, complete with built-in humility about what computation can and cannot establish. If candidates such as FBLN5 and HLA-E survive the crucible of experimental validation, the framework that nominated them may well become a standard fixture in the computational geroscience toolkit, and the era in which a blood draw could point directly toward an anti-ageing intervention will have moved one decisive step closer.

Subject of Research: A graph-guided computational framework for prioritizing ageing-associated drug target hypotheses from plasma proteomics data.

Article Title: Protein Expression Net: an integrated graph-guided computational framework and virtual perturbation approach for prioritizing ageing-associated target hypotheses from plasma proteomics

Article References: Wu, W., Jiang, Y., Wei, K., Lin, Z., Gu, R., Wei, S., Wang, Z., Fang, L., Wang, X., Fu, X., Wang, Y., & Pan, L. (2026). Protein Expression Net: an integrated graph-guided computational framework and virtual perturbation approach for prioritizing ageing-associated target hypotheses from plasma proteomics. BMC Bioinformatics. https://doi.org/10.1186/s12859-026-06645-3

Image Credits: AI Generated

DOI: 10.1186/s12859-026-06645-3

Keywords: ageing, plasma proteomics, UK Biobank, deep learning, graph neural network, Integrated Gradients, Geneformer, virtual perturbation, target prioritization, BMC Bioinformatics, protein-protein interaction network, biomarkers