ARTICLE: Biophysical and biomolecular determination of cellular age in humans

AUTHORS: Jude M. Phillip, Pei-Hsun Wu, Daniele M. Gilkes, Wadsworth Williams, Shaun McGovern, Jena Daya, Jonathan Chen, Ivie Aifuwa, Jerry S. H. Lee, Rong Fan, Jeremy Walston, Denis Wirtz

JOURNAL: Nature Biomedical Engineering. 2017 Jul 11; 10.1038


Ageing research has focused either on assessing organ- and tissue-based changes, such as lung capacity and cardiac function, or on changes at the molecular scale such as gene expression, epigenetic modifications and metabolism. Here, by using a cohort of 32 samples of primary dermal fibroblasts collected from individuals between 2 and 96 years of age, we show that the degradation of functional cellular biophysical features—including cell mechanics, traction strength, morphology and migratory potential—and associated descriptors of cellular heterogeneity predict cellular age with higher accuracy than conventional biomolecular markers. We also demonstrate the use of high-throughput single-cell technologies, together with a deterministic model based on cellular features, to compute the cellular age of apparently healthy males and females, and to explore these relationships in cells from individuals with Werner syndrome and Hutchinson–Gilford progeria syndrome, two rare genetic conditions that result in phenotypes that show aspects of premature ageing. Our findings suggest that the quantification of cellular age may be used to stratify individuals on the basis of cellular phenotypes and serve as a biological proxy of healthspan.

Ageing is a multifaceted, temporal process of functional deterioration and progressive decline across multiple organs and tissues1,2. These changes arise in part from the progressive accumulation of cellular damage and tissue dysfunction1, which results in pathophysiological phenotypic transformations. In humans, biological age is an important risk factor for numerous pathologies and chronic disease states, many of which negatively impact human healthspan and survival2,3. Moreover, many diseases that were considered disparate in the fundamental mechanisms of their progression have more recently been understood to be connected through ageing1,4. Recent developments in geroscience—the study of how biological ageing relates to chronic disease manifestation and healthspan—have prompted efforts to develop methods to determine the biological age of individuals, with the hope that resulting correlates will help facilitate interventions that could delay the onset of chronic age-related diseases24,5,6,7. Here biological age is defined as the ongoing longitudinal changes that determine the functional healthspan and survival of individuals, typically measured at the clinical level.

For decades, ageing research has been primarily focused on the progressive changes that occur at either the molecular scale, such as changes in genetic, epigenetic and metabolic states, or at larger tissue-level scales, such as changes in muscle physiology and cardiac function. Paradoxically, changes at the intermediate length scales of cells themselves, which we term here as biophysical properties, have been understudied. Importantly, age-related biophysical changes may well drive many observed progressive dysfunctional tissue changes8. Multivariate determination of biological age at the clinical level (patient scale) via measures such as total cholesterol, mean arterial pressure, lung capacity and grip strength, provide a robust solution to assess the biological age in humans2. However, these changes tend to be secondary to changes in the cells themselves, thus advocating the value of cell-based technologies to assess biological age9,10.

Dysfunctions that resonate at the cellular level often have profound effects on the functional decline of organisms, and furthermore enhance their susceptibility to various pathologies, including cancer, cardiovascular disease and frailty11,12,13. Hence, the integrative nature of cells and tissues captured in biophysical cellular measurements, cell mechanics, cell migration, cell morphology and so on, may better capture a variety of perturbations in underlying molecular networks that foster ensemble effects in gross cellular behaviour and properties. Indeed, large differences in gene expression or epigenetic profiles of isogenic individual cells can lead to similar properties14 (that is, similar cell motility or morphology), while highly similar proteomic profiles can lead to significantly different overall cell properties due, for instance, to dynamic, stochastic differences in protein location within the cells (non-measurable) or subtle differences in phosphorylation status. Hence instead of only profiling the molecular changes of cells, either in bulk or at the single-cell level, here we comprehensively assess both the molecular and cellular functions themselves, by way of cellular biophysical characteristics, considered here as ‘integrators’ of these molecular differences.

We hypothesize that specific biophysical features encoded in cells can determine the ‘cellular biological age’, ultimately shedding light on the ageing process, and its role in the overall functional decline, and the development of chronic disease states in older adults. Furthermore, because cellular biophysics represents the ensemble orchestration of many molecular inputs, biophysical features may predict the cellular biological age with more accuracy relative to biomolecular features. To preserve information about cell-to-cell variation and its potential role in ageing, and to provide an unbiased comparison, both biophysical and conventional biomolecular characteristics of hundreds of cells were assessed (most at the single-cell level), and the contribution of heterogeneity to the cellular ageing of apparently healthy individuals and those with ‘accelerated/premature ageing’ disorders was determined. 

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