Greenland sharks can live for at least a few centuries, and are thus of interest in the study of the comparative biology of aging. Here, researchers take a first step in examining the cellular biochemistry of aging in this species. As a rule, aquatic species are less well investigated in this regard than is the case for land animals, and most land animals are less well investigated than mammals. One never knows what might be discovered, of course, though it remains the case that efforts to bring beneficial mechanisms from a long-lived species into a short-lived species are in their infancy. Developing therapies based on the biochemistry of a long-lived species has yet to happen, so it is hard to predict just how great a utility this research will provide over time.
The Greenland shark (Somniosus microcephalus), with a lifespan estimated around 300 years, represents a unique model for studying vertebrate longevity. Here, we characterize its cardiac aging profile and compare it with two other species: the deep-sea shark Etmopterus spinax and the short-lived teleost Nothobranchius furzeri.
Histological analysis revealed extensive interstitial and perivascular fibrosis throughout the ventricular myocardium of S. microcephalus, affecting both compact and spongy layers of both sexes. This fibrotic pattern was absent in E. spinax and N. furzeri, suggesting it is a specific feature of S. microcephalus. We also observed extreme lipofuscin accumulation within cardiomyocytes of S. microcephalus, which correlates at the ultrastructural level with the abundance of damaged mitochondria and the presence of strikingly enlarged lysosomes filled with electron-dense material of likely mitochondrial origin. Additionally, in the myocardium of S. microcephalus we found abundant deposition of the oxidative stress marker 3-nitrotyrosine.
Remarkably, despite showing multiple canonical markers of aging such as fibrosis, lipofuscin accumulation, and oxidative stress, S. microcephalus individuals appeared healthy and physiologically uncompromised at the time of capture. These findings suggest that S. microcephalus has evolved resilience to molecular and tissue-level aging signs and hallmarks, supporting sustained cardiac function over centuries and offering new insights into the mechanisms of extreme vertebrate longevity.
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