Decoding the Mysteries of Aging: A Marine Organism Alters Scientific Understanding

Scientists have established a connection between the processes of healing and aging by examining the unique regenerative abilities of a marine organism known as Hydractinia symbiolongicarpus. This organism has the remarkable capability to grow an entirely new body originating from just its oral region, providing novel insights that suggest the process of senescence—commonly linked to aging—may be integral to its unparalleled regenerative faculties.

Researchers affiliated with the National Institutes of Health, in collaboration with other institutions, have made groundbreaking discoveries about the relationship between aging and healing. They focused their investigation on Hydractinia symbiolongicarpus, a diminutive, tube-shaped marine entity that resides within hermit crab shells. Through RNA sequencing, the creature’s molecular structure was thoroughly examined.

As the Hydractinia began to regenerate new bodies, the researchers identified a molecular signature connected with senescence, the biological aspect of aging. According to the research published in the journal Cell Reports, the Hydractinia has shown that the foundational biological mechanisms governing both aging and healing are intricately linked. This offers a revolutionary viewpoint on the evolutionary origins of aging.

Charles Rotimi, Ph.D., the director of the Intramural Research Program at the National Human Genome Research Institute, a subdivision of NIH, noted, “Inquiries such as this that delve into the biology of atypical organisms illuminate not only the universality of numerous biological operations but also the substantial gaps in our understanding of their functionalities, interconnections, and evolutionary development. These revelations carry considerable promise for advancing our comprehension of human biology.”

The stem cells that drive Hydractinia’s regenerative abilities are stored in the lower section of the creature’s anatomy, away from the oral region.

Understanding the evolutionary roots of fundamental biological functions like healing and aging is crucial for insights into human health and pathology. While humans have some regenerative capabilities, like mending broken bones or even redeveloping damaged liver tissue, animals with simpler anatomical structures, such as Hydractinia, often exhibit more extraordinary regenerative powers, including the growth of an entirely new body from a fragment of tissue.

Contrary to findings in human cellular studies, where senescence is often linked to chronic inflammation and various age-related diseases, Hydractinia offers a different narrative. Andy Baxevanis, Ph.D., a senior scientist at NHGRI and one of the authors of the study, mentioned, “Generally in humans, senescent cells remain senescent and provoke chronic inflammation while influencing aging in adjacent cells. From organisms like Hydractinia, we gain novel insights into the potential benefits of senescence, broadening our understanding of aging and healing mechanisms.”

Previous research had identified a specialized cluster of stem cells in Hydractinia responsible for its regenerative capabilities. Unlike humans, where stem cells primarily function during development, Hydractinia employs stem cells throughout its life cycle. These are stored in the lower portion of its anatomical structure.

Interestingly, when the researchers excised the oral region—a location far removed from the stem cells—the mouth regenerated an entirely new body. Unlike human cells, which are fixed in their roles, the cells in highly regenerative species like Hydractinia can revert to stem cells when injured, although this process remains poorly understood. Researchers hypothesized that Hydractinia must be generating new stem cells and sought molecular cues directing this activity.

Upon discovering a link to senescence via RNA sequencing, the scientists scrutinized Hydractinia’s genome for sequences resembling human senescence-related genes. Of the three genes they discovered, one was activated near the site of the incision. When this gene was deactivated, the creature lost its ability to develop senescent cells, and consequently, could not regenerate.

Remarkably, researchers found that Hydractinia expels senescent cells through its mouth, thus avoiding the detrimental effects of senescence often observed in humans. This led to further inquiries about how the evolutionary role of senescence-related genes in Hydractinia could provide insights into the evolutionary history of aging itself.

Hydractinia, along with its close relatives jellyfish and corals, diverged from a common ancestor with humans over 600 million years ago. These creatures do not age, thereby making them invaluable models for studying the origins of senescence. Researchers speculate that in the earliest animals, the primary function of senescence might have been for regenerative purposes.

Dr. Baxevanis concluded, “The mechanisms by which senescent cells stimulate regeneration remain a subject of ongoing research. The examination of our most distant animal relatives offers a promising avenue for unearthing fundamental secrets of aging and regeneration. These discoveries have the potential to significantly influence regenerative medicine and the study of age-related diseases.”

Reference: “Senescence-induced cellular reprogramming drives cnidarian whole-body regeneration” by Miguel Salinas-Saavedra, Gabriel Febrimarsa, Helen R. Krasovec, Andreas D. Horkan, and Uri Baxevanis, published on June 30, 2023, in Cell Reports.
DOI: 10.1016/j.celrep.2023.112687

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More about Regenerative capabilities and aging

• Cell Reports Journal where the Study was Published
• National Institutes of Health
• National Human Genome Research Institute
• Overview of Senescence in Humans
• Introduction to Regenerative Medicine
• Understanding Stem Cells and Their Role in Regeneration
• Marine Organism Regenerative Capabilities
• Evolutionary Origins of Aging
• Biological Processes: Healing vs Aging