Expression and regulation of HSPB5 in the myometrium throughout pregnancy

Abstract

The uterine smooth muscle or myometrium goes through phases of differentiation during pregnancy to become a powerful contractile tissue at term. Small Heat Shock proteins (sHSPs) are a family of ten small molecular weight proteins in mammals that are induced by many physiological stressors such as uterine stretch. Some sHSPs act as chaperones, but also others assist in cell death regulation, cytoskeleton rearrangements, and immune system activation. We examined the spatio-temporal expression of HSPB5 protein throughout gestation via immunoblot and immunofluorescence analysis, as well as the effect of uterine distension on myometrial HSPB5 protein expression using unilaterally pregnant rat models. HSPB5 protein expression significantly increased on day (d) 17 (p<0.05; vs all other timepoints) and levels steadily decreased thereafter through to postpartum (PP). In contrast, serine-59 phosphorylated (pSer59) HSPB5 protein detection was significantly increased from d19 through to PP (p<0.05). Both HSPB5 and pSer59-HSPB5 were detected in the cytoplasm of myocytes within both uterine muscle layers mid- to late-pregnancy. In unilaterally pregnant rats, HSPB5 protein and pSer59-HSPB5 protein expression were significantly elevated in gravid uterine horns at both d19 of gestation and d23 (labour) compared to non-gravid horns. The spatial expression of total and pSer59-HSPB5 protein in a human myometrial cell line was examined by immunofluorescence analysis. Total HSPB5 co-localized with α-smooth muscle actin and pSer59-HSPB5 was co-localized with the focal adhesion protein kindlin-2 (KIN-2) and the exosomal marker CD63. Therefore, HSPB5 is highly expressed during mid- to late-pregnancy and expression appears to be regulated by uterine distension. HSPB5 may be involved in regulating actin filament dynamics and could be secreted by exosomes.