HIF1A and brain ischemia: For the peak of HIF-1 expression after ischemia, there are various scenarios appearing among different literature, for the delayed peak of HIF-1α expression after simple cerebral ischemia; this phenomenon has not been clearly explained in the literature, which may be related to a combination of factors such as induction of HIF-1 by rehypoxia after ischemic tolerance and induction of HIF-1α expression by inflammatory factors in response to tissue inflammation after ischemia [37].