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Mild Traumatic Brain Injury/Concussion Initiates an Atypical Astrocyte Response Caused by Blood-Brain Barrier
Kijana K George1,2, Benjamin P Heithoff1,3, Oleksii Shandra1,4
1Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia, USA.
Abstract:
Mild traumatic brain injury/concussion (mTBI) accounts for 70-90% of all reported TBI cases and causes long-lasting neurological consequences in 10-40% of patients. Recent clinical studies revealed increased blood-brain barrier (BBB) permeability in mTBI patients, which correlated with secondary damage after mTBI. However, the cascade of cellular events initiated by exposure to blood-borne factors resulting in sustained damage is not fully understood. We previously reported that astrocytes respond atypically to mTBI, rapidly losing many proteins essential to their homeostatic function, while classic scar formation does not occur. Here, we tested the hypothesis that mTBI-induced BBB damage causes atypical astrocytes through exposure to blood-borne factors. Using an mTBI mouse model, two-photon imaging, an endothelial cell-specific genetic ablation approach, and serum-free primary astrocyte cultures, we demonstrated that areas with atypical astrocytes coincide with BBB damage and that exposure of astrocytes to plasma proteins is sufficient to initiate loss of astrocyte homeostatic proteins. Although mTBI resulted in frequent impairment of both physical and metabolic BBB properties and leakage of small-sized blood-borne factors, deposition of the coagulation factor fibrinogen or vessel rupture were rare. Surprisingly, even months after mTBI, BBB repair did not occur in areas with atypical astrocytes. Together, these findings implicate that even relatively small BBB disturbances are sustained long term, and render nearby astrocytes dysfunctional, likely at the cost of neuronal health and function.
Insights
Mild traumatic brain injury (mTBI) causes long-lasting neurological issues. This study shows that even minor blood-brain barrier damage from mTBI leads to persistent astrocyte dysfunction, impacting brain health.
Area of Science:
- Neuroscience
- Traumatic Brain Injury Research
- Astrocyte Biology
Background:
- Mild traumatic brain injury (mTBI) constitutes the majority of TBI cases, often leading to prolonged neurological deficits.
- Increased blood-brain barrier (BBB) permeability post-mTBI is linked to secondary brain damage, but the underlying cellular mechanisms remain unclear.
- Astrocytes exhibit atypical responses to mTBI, losing essential proteins without forming classic scars.
Purpose of the Study:
- To investigate if mTBI-induced BBB damage triggers atypical astrocyte responses via exposure to blood-borne factors.
- To understand the long-term consequences of BBB disturbances on astrocyte function after mTBI.
Main Methods:
- Utilized an mTBI mouse model and two-photon imaging.
- Employed endothelial cell-specific genetic ablation and serum-free primary astrocyte cultures.
- Assessed BBB properties, astrocyte protein expression, and fibrinogen deposition.
Main Results:
- Atypical astrocyte locations directly correlated with areas of BBB damage.
- Exposure of astrocytes to plasma proteins was sufficient to induce loss of homeostatic proteins.
- mTBI frequently impaired BBB physical and metabolic functions, allowing small factor leakage.
- BBB repair was notably absent even months after mTBI in regions with atypical astrocytes.
- Vessel rupture and fibrinogen deposition were infrequent.
Conclusions:
- Even minor BBB disturbances following mTBI can lead to sustained, long-term astrocyte dysfunction.
- This persistent astrocyte dysfunction likely compromises neuronal health and function.
- The findings highlight a critical mechanism linking BBB integrity to chronic neurological consequences after mTBI.
