SPP1 and Stroke: Regarding NSC, thus far non-conclusive effects of OPN on proliferation have been reported: while some reports failed to detect any effect of OPN on NSC proliferation in vitro [41] or in vivo after experimental stroke [49], others showed that NSC proliferation was reduced in the absence of OPN in a mouse model of hypoxic brain injury [50], or that OPN directly induced proliferation of NSC grown as neurosphere cultures [39].