Parthanatos Drives Cognitive Decline in Repeated Brain Trauma: MSC-Derived Exosomes as a Novel Therapeutic Strategy

Heba Selim¹Amira A El-Gazar²Dalaal Abdallah³Hagar Abo-Zalam²Ghada Ragab⁴Ahmed Abdallah⁵Rabab El-Gazar²Sultan AlShehri⁶Einas Yousef⁷Rayan Ballal¹Sahar N Aljarallah¹Asmaa Saleh⁸Nada Abou Chahin¹Naheda Alsammak¹Rasha Mandil¹Hanan Salah El-Abhar^3*

• ¹College of Pharmacy, AlMaarefa University, Riyadh, Saudi Arabia
• ²Faculty of Pharmacy, October 6 University, Giza, Egypt
• ³Faculty of Pharmacy, Cairo University, Cairo, Egypt, Cairo, Egypt
• ⁴Faculty of Pharmacy, Misr University for Science and Technology,, Giza, Egypt
• ⁵Medical Research and clinical studies institute, National Research Centre, Cairo, Egypt
• ⁶College of Pharmacy, King Saud University, Riyadh, Saudi Arabia
• ⁷College of Medicine, Alfaisal University, Riyadh, Saudi Arabia
• ⁸College of Pharmacy, Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia

Introduction: Repeated traumatic brain injury (RTBI) represents a cumulative neurological insult associated with progressive neurodegeneration and limited therapeutic options. In this study, we uniquely evaluate the neuroprotective potential of mesenchymal stem cell (MSC)-derived exosomes in a rat model of RTBI, an area scarcely explored.Methods: RTBI was induced via a controlled mechanical impact to the skull once every day for five days. MSC-derived exosomes were administered 24 hours after the final insult in two paradigms: a single dose (MSC-Ex1) with two weeks of follow-up, and a dual dose (MSC-Ex2)given one week apart, with euthanasia one week later. Rats were assigned to four groups: control, RTBI, RTBI + MSC-Ex1, and RTBI + MSC-Ex2.Results: MSC-derived exosome regimens comparably restored cognitive performance in the Novel Object Recognition and Y-maze tests. While both treatment paradigms preserved cortical histoarchitecture, the double-dose regimen led to a more pronounced restoration compared to the moderate tissue recovery observed in the single-dose group. Crucially, this work identifies parthanatos inhibition as a novel mechanistic axis for MSC-derived exosomes-mediated neuroprotection. MSC-derived exosomes attenuated excitotoxicity and oxidative stress, quelling the parthanatos cascade by suppressing PARP1, PAR polymers, nuclear AIF and MIF, as well as calpain, key executors of this caspase-independent cell death pathway. Additionally, MSCderived exosomes normalized cyclophilin B and Hsp70 levels, suggesting their compensatory role in modulating the endogenous stress response.Conclusion: Overall, these findings demonstrate that MSC-derived exosomes counteract RTBIinduced neurodegeneration through multifaceted mechanisms, with parthanatos suppression at the core. Importantly, the dual-dosing regimen conferred no significant benefit over the single dose, highlighting the therapeutic promise of early intervention. This study positions MSCderived exosomes as a novel, cell-free therapy capable of intercepting RTBI-induced neuropathology by targeting an under recognized form of programmed cell death.