Mesenchymal stem cell secretome attenuates disease-associated microglial activation and cognitive decline in...

Therapeutic options for traumatic brain injury (TBI) remain limited, in part due to injury-induced activation of microglia toward disease-associated microglia (DAM) phenotypes that contribute to persistent neuroinflammation and cognitive decline. We evaluated whether non-invasive intranasal delivery of mesenchymal stem cell secretome can enhance recovery after TBI by modulating microglial DAM signaling. Adult C57BL/6 mice underwent moderate controlled cortical impact (CCI) TBI. Adipose Stem Cell-derived Concentrated Conditioned Media (ASC-CCM) (∼20 ng protein/day, four doses) was administered intranasally, while sham and TBI controls received saline. Cognitive and memory functions assessed at 7 and 30 days post-injury showed TBI mice with impairments in learning, working, and long-term memory, while ASC-CCM-treated TBI mice performed similar to sham. These functional deficits correlated with increased astrogliosis (GFAP) and apoptosis (TUNEL), both of which were attenuated by ASC-CCM. TBI induced a time-dependent increase in astrocyte-associated APOE in the ipsilateral peri-lesion area and TYROBP in activated microglia near the impact site; ASC-CCM treatment significantly reduced both markers. Transcriptomic analysis of peri-lesion tissue at days 7 and 30 confirmed robust upregulation of DAM-associated genes (APOE, TYROBP, TREM2) after TBI, which was mitigated by intranasal ASC-CCM. Consistent with these findings, TREM2 expression in ipsilateral CD11b ⁺ CD45^high cells was markedly reduced following treatment. These data show that microglial DAM signaling is a modifiable neurochemical pathway after TBI, and that intranasal delivery of ASC-CCM reduces microglial activation and improves cognitive outcomes. This strategy potentially offers a translational path to a non-invasive therapeutic for acute and chronic TBI.