There is much evidence to suggest that brain-derived neurotrophic factor (BDNF) is a prominent candidate in promoting neuroprotection, axonal regeneration, and synaptic plasticity following spinal cord injury (SCI). Although some evidence indicates that BDNF has potent anti-oxidative effects and may be involved in the regulation of the immune response, the effects of BDNF in the inflammatory response during the course of secondary damage after SCI is still unclear. The present study was designed to investigate the effects of BDNF with a special focus on their effect on macrophage polarization after SCI. Adult C57 mice underwent T10 spinal cord clip compression injury and received lenti-BDNF vector injections at the epicenter of the lesion site. Four days later, total BDNF levels were greatly increased in animals that received lenti-BDNF injections. Confocal imaging showed that more than 80 % of the lenti-virus infected cells were CD11b-positive macrophages. In addition, the expression of arginase-1 and CD206 (associated with M2 macrophage phenotype) significantly increased in the animals that received lenti-BDNF injections compared with those that received lenti-EGFP injections. On the contrary, the expression of CD16/32 and inducible nitric oxide synthase (M1 phenotype marker) was down-regulated as demonstrated using flow cytometry and immunohistochemistry. Furthermore, the production of interleukin 1β and tumor necrosis factor alpha was significantly reduced whereas the levels of interleukin 10 and interleukin 13 were elevated in subjects that received lenti-BDNF vector injections. The time course of functional recovery revealed that gradual recovery was observed in the subacute phase in lenti-BDNF group, little improvement was observed in lenti-EGFP group. At the axonal level, significant retraction of the CST axons were observed in lenti-EGFP injected animals relative to lenti-BDNF group by biotinylated dextran amine tracing. In addition, compared to lenti-BDNF group markedly demyelination was observed in the lenti-EGFP group using luxol fast blue staining. In conclusion, we found that BDNF could promote the shift of M1 to M2 phenotype and ameliorate the inflammatory microenvironment. Furthermore, the roles of BDNF in immunity modulation may enhance neuroprotective effects and partially contribute to the locomotor functional recovery after SCI.

Along with the development of stem cell-based therapies for central nervous system (CNS) disease, the safety of stem cell grafts in the CNS, such as induced pluripotent stem cells (iPSCs) and induced neural stem cells (iNSCs), should be of primary concern. To provide scientific basis for evaluating the safety of these stem cells, we determined their tumourigenicity and immunogenicity in syngeneic mouse brain. Both iPSCs and embryonic stem cells (ESCs) were able to form tumours in the mouse brain, leading to tissue destruction along with immune cell infiltration. In contrast, no evidence of tumour formation, brain injury or immune rejection was observed with iNSCs, neural stem cells (NSCs) or mesenchymal stem cells (MSCs). With the help of gene ontology (GO) enrichment analysis, we detected significantly elevated levels of chemokines in the brain tissue and serum of mice that developed tumours after ESC or iPSC transplantation. Moreover, we also investigated the interactions between chemokines and NF-κB signalling and found that NF-κB activation was positively correlated with the constantly rising levels of chemokines, and vice versa. In short, iNSC grafts, which lacked any resulting tumourigenicity or immunogenicity, are safer than iPSC grafts.

The complement system is a crucial component of immunity, and its activation has critical roles in neuroinflammatory response and cellular damage following closed head injury (CHI). We previously demonstrated that systemically injected induced neural stem cells (iNSCs) could modulate complement activation to ameliorate neuronal apoptosis in mouse CHI models. However, it remains unknown whether iNSC derivatives can regulate complement activation. In the present study, after CHI mouse serum treatment, we found dramatic decreases in the cellular viabilities of differentiated iNSCs. Interestingly, following CHI mouse serum treatment, the death of astrocytes derived from iNSCs which were pre-treated with CHI mouse serum was significantly decreased. Meanwhile, the deposition of C3 (C3d) and C5b-9 in these astrocytes was substantially reduced. Remarkably, we detected increased expression of complement receptor type 1-related protein y (Crry) in these astrocytes. Moreover, these astrocytes could reduce the numbers of apoptotic neurons via Crry expression post-CHI mouse serum treatment. Additionally, intracerebral-transplanted iNSCs, pre-treated with CHI mouse serum, significantly increased the levels of Crry expression in astrocytes to reduce the accumulation of C3d and C9 and the death of neurons in the brains of CHI mice. In summary, iNSCs receiving CHI mouse serum pre-treatment could enhance the expression of Crry in iNSC-derived astrocytes to modulate complement activation and mediate neuroprotection following CHI.

Induced neural stem cells (iNSCs) can be directly transdifferentiated from somatic cells. One potential clinical application of the iNSCs is for nerve regeneration. However, it is unknown whether iNSCs function in disease models. We produced transdifferentiated iNSCs by conditional overexpressing Oct4, Sox2, Klf4, c-Mycin mouse embryonic fibroblasts. They expanded readily in vitro and expressed NSC mRNA profile and protein markers. These iNSCs differentiated into mature astrocytes, neurons and oligodendrocytes in vitro. Importantly, they reduced lesion size, promoted the recovery of motor and sensory function as well as metabolism status in middle cerebral artery stroke rats. These iNSCs secreted nerve growth factors, which was associated with observed protection of neurons from apoptosis. Furthermore, iNSCs migrated to and passed through the lesion in the cerebral cortex, where Tuj1+ neurons were detected. These findings have revealed the function of transdifferentiated iNSCs in vivo, and thus provide experimental evidence to support the development of personalized regenerative therapy for CNS diseases by using genetically engineered autologous somatic cells.