Background <p>Neurological disorders, such as stroke and traumatic brain injury are the most significant global health challenges, leading to long-term physical and cognitive impairments. Cell transplantation therapy holds substantial promise for facilitating recovery, with numerous clinical trials currently underway. Intracerebral stem cell infusion offers the advantage of directly delivering a sufficient number of stem cells to the targeted area. Both our team and other researchers have observed a notable phenomenon following intracerebral stem cell therapy in clinical trials, wherein transient edema, as detected by Fluid Attenuated Inversion Recovery (FLAIR) magnetic resonance (MR) imaging, can be monitored between one and two weeks post-transplantation, with a subsequent resolution occurring approximately one month later. Notably, patient recovery appears to accelerate during the period of elevated FLAIR signals. However, the precise mechanisms underlying this distinctive phenomenon remain poorly understood. Therefore, this reverse translational research employs proteomics and histological analysis to investigate the mechanisms driving this phenomenon, thereby enhancing our understanding of stem cell therapy.</p> Methods <p>Bone marrow-derived mesenchymal stem cells (BMSCs) were isolated from Sprague-Dawley (SD) rats, with passage 3 cells utilized for subsequent experiments. A total of one million cells, suspended in 10 µL of phosphate-buffered saline, were intracerebrally transplanted into the striatum of SD rats. Serial magnetic resonance imaging (FLAIR) scans were performed up to three weeks post-transplantation. Brain tissues were collected from the pre-signal (1 week post-transplantation), signal (2 weeks post-transplantation), and post-signal (3 weeks post-transplantation) groups for proteomic analysis, network analysis, and immunofluorescence imaging.</p> Results <p>Consistent with clinical trials, transient FLAIR hyperintense signals were not detected until approximately two weeks post-intracranial stem cell therapy. These signals emerged around week two and diminished by week three. Proteomic analysis of brain specimens from the pre-signal and signal groups identified 231 differentially expressed proteins, which were primarily involved in vesicle-mediated transport, synaptic remodeling, and cellular communication. Glial fibrillary acidic protein (GFAP), Aquaporin-4 (AQP4), and Apolipoprotein E (APOE) were identified as key hub proteins. Immunofluorescence studies further confirmed that expression levels of GFAP, AQP4, and APOE increased around two weeks post-transplantation and significantly decreased by week three, coinciding with the resolution of the FLAIR signal.</p> Conclusions <p>Our findings suggest that the transient FLAIR hyperintensity observed following intracerebral stem cell therapy is primarily attributed to transient glial cell activation, resulting in increased AQP4 expression and transient brain water influx. Additional mechanisms, including vesicle-mediated transport, secretion, synaptic activity, and lipid signaling, also contribute to the transient FLAIR hyperintensity signals and may play a role in the manifestation of clinical symptoms.</p>