Fleng Steffensen, J. | bioRxiv Science

bioRxiv2025

Resilience to cardiac aging in Greenland shark Somniosus microcephalus

The Greenland shark (Somniosus microcephalus), with a lifespan exceeding 400 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 abundance of damaged mitochondria and the presence of strikingly enlarged lysosomes filled with electrondense 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 damage, 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 hallmarks, supporting sustained cardiac function over centuries and offering new insights into the mechanisms of extreme vertebrate longevity.

cell biology↗

bioRxiv2025

The visual system of the longest-living vertebrate, the Greenland shark

The Greenland shark (Somniosus microcephalus) is the longest-living vertebrate and inhabits the extremely dim and cold waters of the Arctic deep sea. This has led to speculations that it may have lost functional vision. Here, we present genomic, transcriptomic, histological and functional evidence that the Greenland shark retains an intact visual system well-adapted for life in dim light. Histology and in vitro opsin expression revealed visual adaptations typical of deep-sea species, including densely packed, elongated rods and a short-wavelength shift in rod visual pigment sensitivity. RNAscope confirmed the presence of essential visual cell types, such as rods, Muller glia, and bipolar, amacrine, and ganglion cells. Moreover, despite being centuries old, the examined specimens showed no signs of retinal degeneration. Using whole genome and retinal RNA-sequencing, we further show that dim-light (rod-based) vision genes are intact and robustly expressed, while many bright-light (cone-based) vision genes have become pseudogenized and/or are no longer expressed. Finally, our data suggest that efficient DNA repair mechanisms may contribute to the long-term preservation of retinal function over centuries in the Greenland shark.

evolutionary biology↗