Differential Renal Expression of Hsp27 and αB-Crystallin in Rats Following Acute Ischemia † 1837

Abstract

The mammalian small stress proteins αB-crystallin and hsp27 are structurally related; the latter is induced by a variety of insults including heat and ischemia. Both proteins protect cells from these insults, possibly by molecular chaperoning and/or by stabilization of the cytoskeleton. This study shows the amounts and localization of hsp27 and αB-crystallin in the renal cortex (CO), isolated glomeruli (GL), inner (IM), and outer medulla (OM) at 6 h, 24 h, and 5 days following sham-operation (sham) or severe renal ischemia (60 min complete renal artery occlusion). The amount of hsp27 in sham kidneys was approximately 0.1 ng hsp27/μg total protein in CO and OM, 0.3 ng/μg in GL, and 1 ng/μg in the IM, while the amount ofαB-crystallin was 0.2 ng/μg in CO and GL, 1 ng/μg in OM, and 4 ng/μg in IM as determined by Western blotting. Ischemia led to a 200 to 500% increase in the amount of hsp27 in CO and OM at all times. There was a 200% increase in hsp27 in IM at 6 h, no change at 24 h, and a 50% decrease at five days. The amount of hsp27 in GL decreased by 50% at 5 days. No change in the amount of αB-crystallin was detected after ischemia, while hsp70 was induced to a similar extent and with the same distribution as hsp27. In both sham and ischemic kidneys the non-phosphorylated isoform of hsp27 predominated in OM, IM, and GL, while in CO the majority of hsp27 was mono-phosphorylated. Immuno-fluorescence microscopy of sham kidneys revealed that hsp27 was primarily localized in the smooth muscle cells with weak staining of glomeruli and medullary capillary endothelial cells, while αB-crystallin was found throughout the medulla with weak staining of Bowman's capsule. The distribution of hsp27 and aB-crystallin was unchanged after ischemia. We conclude 1) hsp27 and αB-crystallin are differentially expressed in normal rat kidney and undergo differential regulation in response to ischemia, 2) hsp27 induction is part of a general stress response, and 3) hsp27 may play an important role in the pathogenesis of or recovery from ischemia.