The expression and regulation of HSPB1 (Hsp27) in the rat myometrium during pregnancy and labour

White, Bryan Glover (2012) The expression and regulation of HSPB1 (Hsp27) in the rat myometrium during pregnancy and labour. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (29MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

One avenue available to combat the significant problem of pre-term labour is through a better understanding of regulation of uterine smooth muscle function and contraction. Although there is minimal research into the role of HSPB1 (Hsp27) in uterine smooth muscle, it has been proposed to play an important role in cytoskeletal arrangement and contraction in colonic smooth muscle. It was hypothesized that HspB1 would be highly expressed in the rat myometrium during pregnancy and regulated by the endocrinological environment as well as uterine stretch. Utilizing northern blot, immunoblot, and immunofluorescence analysis, the expression and regulation of HSPB1 mRNA and HSPB1 protein in rat uterine smooth muscle (myometrium) was assessed. Through gestation, HSPB1 mRNA increased to a maximun at day 19 and decreased afterwards, while total HSPB1 phosphorylated on serine-15 (pSer15 HSPB1) increased from d19 to a maximum at labour, falling thereafter. Labour also signalled a switch from peri-nuclear /membrane-associated HSPB1 localization in myometrial cells earlier in pregnancy to cytoplasmic localization in situ. To analyze regulation of HSPB1 by ovarian steroids, experimental models including administration of progesterone or progesterone receptor antagonist (RU486) to pregnant rats were utilized as well as 17β-estradiol administration to non-pregnant rats. Progesterone increased HSPB1 expression, prevented the late-pregnancy increase in HSPB1, and forestalled the normal labour-associated localization shift in situ, while RU486 had the opposite effect, 17β-estradiol stimulated a very rapid (<1hr) increase in pSer15 HSPB1 expression, with an increase in total HSPB1 after 12-24hrs. To analyse the role of myometrial stretch on HSPB1 expression, unilaterally pregnant and non-pregnant ovariectomizcd rat models were utilized. Regardless of the endocrine environment, myometrial stretch facilitated an increase in both HSPB1 and pSerl5 HSPB1 expression. However, total HSPB1 only increased when the hormone environment was intact, which also directed its sub-cellular localization in situ. In total these data validate our hypothesis and specifically show that hormonal and stretch-facilitated signalling pathways, perhaps in concert, regulate HSPB1 gene expression. These data also support an ongoing hypothesis in the lab that prior to labour HSPB1 may facilitate proper structural organization of the actin cytoskeleton and incorporation into focal adhesions on the cell membrane while at labour HSPB1 may facilitate association of myosin with actin in the cytoplasm, to allow for the high amplitude contractions necessary for parturition.

Actions (login required)

View Item