A single inflammatory molecule can fundamentally alter the destiny of stem cells in the human hippocampus, the brain region essential for learning, memory, and mood. New research from King’s College London reveals that the cytokine tumor necrosis factor-alpha (TNF-α) does not merely impair the birth of new neurons—it actively reprograms hippocampal stem cells into an immune-alert state, amplifying inflammation and stalling the brain’s regenerative capacity. The findings, published in Nature Communications, offer a mechanistic explanation for the cognitive decline seen in disorders marked by chronic neuroinflammation, such as Alzheimer’s disease, long-term depression, and the lingering neurological consequences of viral infections.
Adult hippocampal neurogenesis is a rare process in the human brain. In the dentate gyrus, a subregion of the hippocampus, neural stem cells continuously give rise to newborn neurons that integrate into existing circuits underlying memory formation and emotional regulation. Disruption of this process is a hallmark of ageing and neurodegenerative disease, yet the precise molecular triggers that derail it have remained elusive. The team at King’s set out to determine how inflammatory cytokines—chemical messengers released during immune threats like viral infections—impact this delicate cellular niche.
When the researchers exposed human hippocampal stem cells to low concentrations of TNF-α, a mere 1 nanogram per milliliter, the cells abruptly ceased their developmental trajectory toward mature neurons. Instead, they adopted a phenotype reminiscent of an immune-sensing cell. The stem cells began secreting chemokines, notably those that act as chemoattractants for T cells, the adaptive immune system’s foot soldiers. This effectively converts a neurogenic microenvironment into a pro-inflammatory hub, where local immune activity is reinforced at the expense of new neuron production. Immunofluorescence staining confirmed the stark reduction in markers of neuronal maturation—MAP2 and DCX—while the cells themselves remained viable, now dedicated to a different functional role.
“What surprised us most was that the stem cells were not simply impaired by inflammation, they actively adopted behaviours that could potentially sustain immune responses in the brain,” said Dr. Tinne A. D. Nissen, who led the experimental work during her PhD. Professor Sandrine Thuret, the study’s co-corresponding author and a professor of neuroscience at King’s, added, “Inflammatory signals can effectively redirect hippocampal stem cells away from their normal role of producing neurons and toward supporting immune activity instead.”
Digging deeper into the molecular machinery, the team identified an unexpected signaling pathway mediating this switch. The stem cells responded to TNF-α by upregulating type I interferon signaling, a cascade classically associated with antiviral defence. Typically, interferons are released by infected cells to alert neighboring cells and prime innate immune mechanisms. In this context, however, the interferon pathway acted as a master regulator of the stem cell fate change. By applying an existing therapeutic antibody that blocks the type I interferon receptor, the researchers were able to partially reverse the inflammatory effect: neuronal differentiation resumed, and the release of T-cell–attracting factors was diminished.
“Our work uncovers a new mechanism that may help explain why ongoing inflammation is so damaging to brain health,” said Professor Linda S. Klavinskis, professor of viral immunology and the study’s other co-corresponding author. “Importantly, it also points to possible treatments to protect or restore the brain’s regenerative capacity.” The dual finding—that TNF-α both suppresses neurogenesis and promotes immune cell recruitment via an interferon-dependent route—adds a fresh layer of complexity to neuroimmune crosstalk.
The implications extend far beyond the petri dish. Chronic elevation of TNF-α is a feature of many systemic and central nervous system conditions, including rheumatoid arthritis, multiple sclerosis, and the persistent inflammatory state observed in some patients after COVID-19. If hippocampal stem cells respond similarly in the living brain, the findings could illuminate why such conditions often come with cognitive fog, memory lapses, and mood disturbances. The study also reinforces the concept that the brain’s resident stem cells are not passive victims of inflammation but active participants in immune surveillance.
This research, a collaboration between the Department of Infectious Diseases and the Department of Basic and Clinical Neuroscience at King’s College London, was supported by the Wellcome Trust, the Medical Research Council UK, and the National Institute for Health Research Biomedical Research Centre. The use of primary human hippocampal stem cells strengthens the translational relevance of the results, although further work in animal models and human tissue will be needed to confirm the in vivo dynamics. The identification of type I interferon signaling as a druggable node opens avenues for repurposing existing interferon-blocking therapies—already in use for autoimmune diseases—to preserve cognitive function in patients with chronic neuroinflammation. As the global burden of dementia and post-viral neurological syndromes grows, such strategies may become critical in shielding the brain’s delicate capacity for self-renewal.
Subject of Research: Role of TNF-α and type I interferon signaling in redirecting human hippocampal stem cell fate from neurogenesis to immune-alert state
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References: Nature Communications
Image Credits: King’s College London
