Alzheimer’s Biology May Worsen Long-Term Damage After Traumatic Brain Injury
Miller School researchers found that Alzheimer’s-related biological changes were associated with persistent inflammation, greater tissue loss and elevated markers of neurodegeneration following traumatic brain injury.
Key Takeaways
- Alzheimer’s-related biological changes were associated with more persistent inflammation after traumatic brain injury.
- The Miami Project to Cure Paralysis researchers observed greater tissue loss and higher levels of markers linked to neurodegeneration when Alzheimer’s-related pathology accompanied brain injury.
- The findings point to inflammasome signaling and extracellular vesicles as priorities for further research, not yet established clinical tools.
A traumatic brain injury can change a life in an instant. For some patients, the effects linger for years, contributing to memory problems, impaired thinking and an increased risk of neurodegenerative disease.
New research from the University of Miami Miller School of Medicine sheds light on why that may happen, showing that Alzheimer’s disease-related biology amplifies chronic inflammation and brain damage following traumatic brain injury (TBI).
The study, led by investigators at The Miami Project to Cure Paralysis and collaborating Miller School departments, found that Alzheimer’s-associated biological changes were linked to more severe chronic inflammation, greater brain tissue loss and higher levels of markers associated with neurodegeneration after traumatic brain injury.
The findings provide new insight into the molecular pathways that may connect brain injury and Alzheimer’s disease.
“The most interesting finding is that, if someone has a traumatic brain injury but no Alzheimer’s disease, the inflammatory response is elevated acutely and then settles down in the chronic stage,” said Juan Pablo de Rivero Vaccari, Ph.D., associate professor of neurological surgery at the Miller School. “If the same trauma happens to someone with Alzheimer’s disease, that inflammatory response is going to persist chronically instead of settling down.”
The Miller School and Miami Project researchers contributing to the study include:
- W. Dalton Dietrich, Ph.D., professor of neurological surgery at the Miller School and Miami Project scientific director
- Helen Bramlett, Ph.D., professor of neurological surgery at the Miller School
- Robert Keane, Ph.D., professor of physiology and biophysics, neurological surgery and microbiology and immunology at the Miller School
- Dr. de Rivero Vaccari
- Nadine Kerr, Ph.D., assistant professor of neurological surgery at the Miller School
- Andrew Sawaya, Ph.D, assistant professor in the Dr. Phillip Frost Department of Dermatology and Cutaneous Surgery
- Erika Cabrera Ranaldi, a researcher for The Miami Project pursuing her Ph.D. in the Neuroscience Graduate Program at the Miller School
- Jhianyn Herrera, a student researcher at The Miami Project to Cure Paralysis
Investigating a Long-Recognized Link
Researchers have long known that traumatic brain injury increases the risk of developing Alzheimer’s disease later in life. Both conditions are associated with persistent inflammation in the brain, particularly through activation of molecular complexes known as inflammasomes. While inflammasomes help coordinate immune responses, excessive or prolonged activation can contribute to ongoing tissue damage.
“A predisposition to Alzheimer’s disease worsens the loss of the hippoccampus and the cortex, more than when a brain injury occurs on its own,” said Cabrera Ranaldi, who is working under the mentorship of Dr. Dietrich and Dr. de Rivero Vaccari. “This amplified brain atrophy informs of the changes occurring at the cellular level that can affect cognition and function when both Alzheimer’s disease and traumatic brain injury intersect.”
Previous studies by the team found that Alzheimer’s-related pathology intensifies inflammatory responses shortly after a traumatic brain injury. In the new study, investigators examined how those responses evolve over longer periods and whether biological sex influences disease-related signaling pathways.
Tracking Inflammation and Neurodegeneration
The researchers analyzed a broad range of inflammatory and neurodegenerative markers, including proteins involved in inflammasome signaling, inflammatory cytokines, brain tissue volume changes and biomarkers of nerve cell injury. They also examined extracellular vesicles, tiny particles released by cells that transport proteins and other biological signals throughout the body.
“Extracellular vesicles are very promising for biomarker use because they’re released from all cells,” said Cabrera Ranaldi. “This means we can gain a detailed understanding of what cells in organ systems are doing in a much more accessible, less invasive manner.”
The analysis revealed persistently elevated levels of several inflammation-related proteins associated with injury, including NLRP3, ASC, IL-1β, caspase-1, and caspase-8. The findings suggest that Alzheimer’s-related biological processes may help sustain inflammatory activity long after the initial injury occurs through non-canonical inflammasomes (caspase-8).
Investigators also observed greater loss of tissue volume when Alzheimer’s disease pathology was accompanied by traumatic brain injury in brain regions responsible for memory and cognition, including the cortex and hippocampus. In addition, they detected higher levels of glial fibrillary acidic protein (GFAP), a marker associated with astrocyte activation and chronic neuroinflammation, as well as elevated neurofilament light (NfL), a marker of axonal damage and neurodegeneration.
Important Differences Between Males and Females
One of the study’s most notable findings involved biological differences between males and females. Analysis of extracellular vesicles revealed distinct signaling profiles, with females showing greater activation of several Alzheimer’s disease-related pathways and males demonstrating stronger activation of pathways associated with immune-cell recruitment and inflammatory responses.
“Alzheimer’s affects females more than males,” said Dr. de Rivero Vaccari. “Understanding how the disease behaves in different sexes is critical to developing more effective personalized therapies.”
Researchers also identified differences in the expression of inflammatory cytokines, including TNF-α and KC/GRO, suggesting that the inflammatory response following brain injury in the context of Alzheimer’s disease may vary based on biological sex. These findings reinforce the importance of considering sex as a factor in neurological research and future treatment strategies.
Potential Implications for Patients
Although additional research is needed to determine how these findings translate to clinical care, the study advances understanding of why some individuals may experience more severe or prolonged neurological consequences after a traumatic brain injury. The results suggest that Alzheimer’s-related biological processes may accelerate chronic inflammation, tissue loss and neurodegeneration following injury.
The findings also highlight inflammasome-related proteins and extracellular vesicles as potentially viable targets for future diagnostics and therapies. Researchers hope that a deeper understanding of these pathways could eventually lead to improved methods for identifying patients at risk for long-term complications and developing interventions that limit ongoing brain damage after injury.
“We need to continue understanding the effects of TBI in those that have genetic predispositions towards Alzheimer’s disease and expand on the vascular aspects related to the disease since it is likely that vascular changes are critical contributors to Alzheimer’s disease development,” said Dr. de Rivero Vaccari.
Ultimately, the study strengthens growing evidence that traumatic brain injury and Alzheimer’s disease are closely interconnected and underscores the importance of understanding how inflammation drives that relationship.
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Tags: Alzheimer's disease, cognitive decline, Dr. Pablo de Rivero Vaccari, Dr. W. Dalton Dietrich III, inflammasomes, inflammation, TBI, The Miami Project to Cure Paralysis, traumatic brain injury