Abstract
Chronic hemodynamic overload results in left ventricular hypertrophy, fibroblast proliferation, and interstitial fibrosis. The small heat shock protein hsp27 has been shown to be cardioprotective and this requires a phosphorylatable form of this protein. To further understand the regulation of hsp27 in heart in response to stress, we investigated the ability of elevated aortic pressure to activate hsp27-kinase activities. Isolated hearts were subjected to retrograde perfusion and then snap frozen. Hsp27-kinase activity was measured in vitro as hsp27 phosphorylation. Immune complex assays revealed that MK2 activity was low in non-perfused hearts and increased following crystalline perfusion at 60 or 120 mmHg. Hsp27-kinase activities were further studied following ion-exchange chromatography. Anion exchange chromatography on Mono Q revealed 2 peaks (b and c) of hsp27-kinase activity. A third peak a was detected upon chromatography of the Mono Q flow-through fractions on the cation exchange resin, Mono S. The hsp27-kinase activity underlying peaks a and c increased as perfusion pressure was increased from 40 to 120 mmHg. In contrast, peak b increased over pressures 60-100 mmHg but was decreased at 120 mmHg. Peaks a, b, and c contained MK2 immunoreactivity, whereas MK3 and MK5 immunoreactivity was detected in peak a. p38 MAPK and phospho-p38 MAPK were also detected in peaks b and c but absent from peak a. Hsp27-kinase activity in peaks b and c (120 mmHg) eluted from a Superose 12 gel filtration column with an apparent molecular mass of 50 kDa. Hence, peaks b and c were not a result of MK2 forming complexes. In-gel hsp27-kinase assays revealed a single 49-kDa renaturable hsp27-kinase activity in peaks b and c at 60 mmHg, whereas several hsp27-kinases (p43, p49, p54, p66) were detected in peaks b and c from hearts perfused at 120 mmHg. Thus, multiple hsp27-kinases were activated in response to elevated aortic pressure in isolated, perfused rat hearts and hence may be implicated in regulating the cardioprotective effects of hsp27 and thus may represent targets for cardioprotective therapy.