Repeated intrathecal injections of peripheral nerve-derived stem cell spheroids improve outcomes in a rat model of traumatic brain injury.

Background: Traumatic brain injury (TBI) is a major cause of disability and mortality worldwide. However, existing treatments still face numerous clinical challenges. Building on our prior research showing peripheral nerve-derived stem cell (PNSC) spheroids with Schwann cell-like phenotypes can secrete neurotrophic factors to aid in neural tissue regeneration, we hypothesized that repeated intrathecal injections of PNSC spheroids would improve the delivery of neurotrophic factors, thereby facilitating the restoration of neurological function and brain tissue repair post-TBI.

Methods: We generated PNSC spheroids from human peripheral nerve tissue using suspension culture techniques. These spheroids were characterized using flow cytometry, immunofluorescence, and reverse-transcription polymerase chain reaction. The conditioned media were evaluated in SH-SY5Y and RAW264.7 cell lines to assess their effects on neurogenesis and inflammation. To simulate TBI, we established a controlled cortical impact (CCI) model in rats. The animals were administered intrathecal injections of PNSC spheroids on three occasions, with each injection spaced at a 3-day interval. Recovery of sensory and motor function was assessed using the modified neurological severity score (mNSS) and rotarod tests, while histological (hematoxylin and eosin, Luxol fast blue staining) and T2-weighted magnetic resonance imaging analyses, alongside immunofluorescence, were conducted to evaluate the recovery of neural structures and pathophysiology.

Results: PNSC spheroids expressed high levels of Schwann cell markers and neurotrophic factors, such as neurotrophin-3 and Ephrin B3. Their conditioned medium was found to promote neurite outgrowth, reduce reactive oxygen species-mediated cell death and inflammation, and influence M1-M2 macrophage polarization. In the CCI rat model, rats receiving repeated triple intrathecal injections of PNSC spheroids showed significant improvements in sensory and motor function, with considerable neural tissue recovery in damaged areas. Notably, this treatment promoted nerve regeneration, axon regrowth, and remyelination. It also reduced glial scar formation and inflammation, while encouraging angiogenesis.

Conclusion: Our findings suggest that repeated intrathecal injections of PNSC spheroids can significantly enhance neural recovery after TBI. This effect is mediated by the diverse neurotrophic factors secreted by PNSC spheroids. Thus, the strategy of combining therapeutic cell delivery with multiple intrathecal injections holds promise as a novel clinical treatment for TBI recovery.