Rodrigo Moraga-Amaro ¹ Oscar Moreno ² Jordi Llop ² Marion Bankstahl ^3,4 Jens P Bankstahl ^3*

• ¹ Department of Nuclear Meedicine, Hannover Medical School, Hanover, Germany
• ² Basque Research and Technology Alliance (BRTA), CIC biomaGUNE, San Sebastian, Spain
• ³ Institute for Laboratory Animal Science, Hannover Medical School, Hanover, Germany
• ⁴ Department of Biological Sciences and Pathobiology, Institute of Pharmacology, University of Veterinary Medicine Vienna, Vienna, Vienna, Austria

Introduction. Chronic traumatic encephalopathy (CTE) is a progressive neurodegenerative disease resulting from repeated mild traumatic brain injuries (rmTBI). Because diagnosis of CTE can so far only be confirmed post-mortem, new approaches to early diagnose this disease are needed to facilitate translation of novel treatment strategies to the clinic. Several studies have found suitable candidate biomarkers, but results are not straight forward. As biological sex is suggested to be a major confounding factor, we explored how sex influences behavioural and candidate blood biomarkers during CTE-like progression following experimental rmTBI.Methods. For induction of CTE-like development, male and female rats were subjected to three mTBIs with an interval of 5 days, and differences in neurological, behavioural, and physiological parameters were monitored and analyzed up to 12 weeks after, both by sex and grouped, and underwent further analysis by generalized estimated equation (GEE). To determine long-term changes in tau aggregation as a hallmark of CTE, we used [18F]-florzolotau (florzolotau) autoradiography in brain slices.Results. Both short-term weight gain and time-to-right after rmTBI were increased in grouped animals, with male rats showing more prominent changes. Neurological state was impaired after each mTBI and still 12 weeks later, independent of the sex. A protracted anhedonic-like behaviour due to rmTBI was found at group level only at week 2, but remained continuously present in male rats. While spatial memory was not impaired, male rats showed increased anxiety-like behaviour. Moreover, neuron specific enolase (NSE) was elevated in the blood 1 day after rmTBI, but only in females. On the other hand, blood p-tau was increased 3-days after rmTBI only in males. In addition, male rats showed significantly increased florzolotau binding in the brain after 12-weeks, suggesting brain contusion causes increased tau aggregation. Interestingly, brain neurofibrillary tangles (NFTs) at 12-weeks after rmTBI showed a strong correlation with the neurological state at 1-day after rmTBI.Discussion. Taken together, male rats may be more susceptible to short-and long-term consequences of rmTBI in the applied model. These sex differences should be considered when translating preclinical biomarker candidates to the clinic in order to guide diagnosis and treatment of CTE in a personalized manner.