Transient induction of heme oxygenase after cortical stab wound injury

Heme oxygenase (HO) exists as two isoenzymes designated heme oxygenase-1 (HO-1) and heme oxygenase-2 (HO-2), HO-1 has been identified as a heat shock or stress protein and is inducible whereas HO-2 is largely refractory to induction. HO-2 is the predominant isoenzyme in normal brain and appears to have a predominantly neuronal distribution in cerebral cortex. Cortical stab wound injury resulted in HO-1 induction as determined by Western blot analysis. Immunohistochemical analysis suggested that induced HO-1 was largely restricted to reactive astrocytes and macrophage-like cells. Enhanced HO-1 immunoreactivity was observed in hypertrophied, GFAP(+) reactive astrocytes near the wound margin as early as 12 h after injury, Very rarely were HO-1(+) neurons observed and then only up to 6 h after stabbing. Maximal numbers of HO-1(+) astrocytes were found 3 days after stabbing, Their numbers declined thereafter. By 5 days after stab injury few HO-1(+) reactive astrocytes were observed although GFAP(+) reactive astrocytes were still prominent near the wound margin, HO-1(+) macrophage-like cells were initially observed between 1 and 3 days after injury and they persisted in the margin of the wound for at least 14 days, The proximity of HO-1(+) cells to the wound margin suggests that factors associated with injury contribute to the regulation of HO-1 in injured cortex.