Regulation of Mesenchymal Stem Cell Secretome for Treatment of Microglia Damage in Traumatic Brain Injury

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ABSTRACT The World Health Organization predicts that traumatic brain injury (TBI) will surpass many diseases, including infectious diseases, as a significant cause of death and disabilities, including significant cognitive dysfunction and visual impairment. Mesenchymal stem/stromal cell (MSC) therapies have gained considerable attention as a strategy for protecting against neurodegenerative diseases. However, a poor understanding of the mechanisms of therapeutic action has hampered their regulatory approval for clinical use. We have pioneered the therapeutic application of adipose MSC-derived concentrated conditioned media (ASC-CCM), a "secretome" containing soluble proteins and exosomes, for neurovascular pathologies across a range of preclinical models. Guided by promising in vivo efficacy data and identification of TNF-Stimulated Gene-6 protein (TSG-6) as an exosome-cargo protein that suppresses microglial activation, we now propose studies to determine if non- invasive delivery of ASC-CCM protects against TBI-induced damage. We will test the central hypothesis that TSG-6 enriched ASC-CCM ameliorates the generation of TBI-induced disease-associated microglia (DAM), thereby modulating phagocytosis and inflammation to restore the microglial homeostatic state to protect visual and cognitive function. In Aim 1, using a validated controlled cortical impact model of TBI (CCI-TBI) with and without intranasal ASC-CCM treatment, we will a) establish the DAM phenotypic correlates of TBI-induced loss of cognitive and visual functions and b) establish the efficacy of ASC-CCM treatment in TBI. In Aim 2, using microglia in culture, we will determine if activation of the DAM signature through TYROBP-APOE4-axis signaling leads to phagocytosis and inflammation and determine how exosomal TSG-6 modulates TYROBP-APOE4- mediated DAM activation. In Aim 3, we will investigate the hypothesis that exosomes carrying TSG-6 protein are sufficient to modulate the activation of DAM signature and thus impart the therapeutic benefit in TBI. We will also study the distribution of exosomes in the tissues and study potential safety and toxicity. The proposed research is significant and innovative because our expected results would provide the rationale for developing mechanistically defined regenerative therapies tailored to modulating microglial phenotypes and signaling pathways involved in neurodegeneration. The PI's laboratories have been engaged for nearly a decade in developing regenerative and pharmacological therapies for neurotrauma and are well suited to conduct studies proposed in this application. Our environment at the University of Tennessee Health Science Center and Diadem Biotherapeutics, Inc makes us uniquely qualified to pursue this objective, given the extensive collective experience in molecular and stem cell biology, exosome engineering, proinflammatory signaling networks, and neurotrauma models.