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Heat Shock Proteins
In mammalian species, the subfamily of small
heat shock proteins (sHsps, 15–30 kDa) consists of ten known members
(Kappe et al. 2003), namely Hsp27 (Hsp25 of rodents, HspB1), myotonic
dystrophy protein kinase binding protein (MKBP, HspB2), HspB3, aA-crystallin
(HspB4), aB-crystallin (HspB5), Hsp20 (P20, HspB6), cvHsp (HspB7), Hsp22
(H11, HspB8), HspB9, and HspB10. According to their different patterns
of gene expression and sub-cellular localization, Taylor et al. (2005,
J. Mol. Cell Cardiol.) classified these sHsps into two major categories:
Class I and Class II. Class I sHsps (HspB1, HspB5, HspB6 and HspB8) are
ubiquitously expressed, whereas Class II members (HspB2, HspB3, HspB4,
HspB7, HspB9 and HspB10) display tissue-restricted patterns of expression.
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Hsp20,
also referred to as P20/HspB6, was originally co-purified with the
small heat-shock protein Hsp27/Hsp28 from rat and human skeletal
muscles (Kato et al.1994, J. Biol. Chem.). Of particular interest,
our recent work (Chu et al. 2004, Cir. Res.) identified a cardiac
isoform of Hsp20 in mouse heart, which was induced by isoproterenol
(ISO) stimulation. In cultured adult rat cardiomyocytes, the expression
levels of Hsp20 and its phosphorylation are transiently increased
after exposure to ISO (Fig. 1), suggesting that Hsp20 may provide
cardioprotection against ISO-induced cardiac apoptosis. |
Actually, we found that overexpression
of Hsp20 inhibits ISO-mediated apoptosis in cardiomycytes (Fig.2) (Fan
et al, 2004, Cir. Res.).
Furthermore, using transgenesis, we found
that increased Hsp20 expression in the heart protects against ischemia/reperfusion-induced
injury, resulting in improved recovery of cardiac function and reduced
infarction (Fig. 3) (Fan et al, 2005, Circulation).
Fig.
3: Decreased infarction size in Hsp20-TG hearts in vivo .
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