We recently reported that concentrated
conditioned medium (CdM) from human CD133-derived bone marrow progenitor cells (CD133 CdM) was neuroprotective after
stroke. Here we identify stromal-derived factor 1 alpha (SDF-1) as a potential neuroprotective candidate in CD133 CdM by interrogating the transcriptional responses of CD133-derived multipotent stromal cells (CD133dMSCs) after cell injection into the ischemic brain. Human SDF-1
mRNA was upregulated 79-fold by CD133dMSCs when injected into the
stroke peri-
infarct area compared with cells injected into the uninjured parenchyma of
sham-operated animals. In cell protection assays, we replaced the typical growth medium in mouse neural progenitor cell (
mNPC) cultures with serum-free CD133 CdM immediately before exposure to
hypoxia (1%
oxygen) for 48 h. CD133 CdM significantly increased the survival of mNPCs during
hypoxia exposure and
growth factor withdrawal. To determine whether MSC-secreted SDF-1 influenced
mNPC survival, we used lentiviral
short hairpin RNA against SDF1 (shSDF-1) to knockdown SDF-1 expression in CD133dMSCs. The CdM generated from shSDF-1-treated cells had a 94% decrease in secreted SDF-1 and was significantly less protective for mNPCs when compared with control CdM from CD133dMSCs transduced with scrambled
short hairpin RNA. Pharmacological inhibition of the 2 known SDF-1
receptors, CXCR4 and CXCR7, revealed that only CXCR7 activity was functionally linked to survival signaling in mNPCs during
hypoxia exposure. Treatment of mNPCs with CD133 CdM and CXCR7 inhibitor decreased
mNPC viability by 36.5% ± 12.8% and decreased cell number by 21% ± 6.7% compared with
dimethyl sulfoxide treated controls. These data indicate that SDF-1 is a key neuroprotective
cytokine secreted by CD133dMSCs that protects mNPCs through CXCR7.