The role of heat shock protein 20 and paraoxonase 2 in the human placenta: influence of obesity and labour

The mechanisms that control uterine contractions during parturition are better understood, however significant gaps in our knowledge still remain. Until it is fully understood, it will be difficult to understand the causes of idiopathic pre-term labour. The placenta plays an essential role during labour, which involves inflammatory pathways, mechanical stretching, hormonal, and the neurological process. Placental oxidative stress is a feature of human labour and maternal obesity. Heat-shock proteins (HSPs) can protect cells during stress. The small heat-shock protein 20 (HSP20), which belongs to the sHSP family, acts as a chaperone as well as regulating acting cytoskeleton dynamics, and may also regulate contractile protein activation. HSP20 is also known as HSPB6, and has been shown to protect against a number of pathophysiological processes, including apoptosis and oxidative stress. The hypothesis of this work is that placental expression of HSP20 would be changed during labour and obesity. In addition, expression may alter in different zones of the placenta. We recruited 6 women in labour who delivered vaginally (uncomplicated labour), and 6 women who were delivered by Caesarean section (not in labour). Furthermore, women who had normal pregnancies with different body mass indices (BMI)s were also recruited. Four BMI groups were studied: 1) BMI <30 (n=6), 2) BMI 30- 35 (n=6), 3) BMI 35-40 (n=6) and 4) BMI<40 (n=6). These women delivered by Caesarean section and were not in labour. Sampling of 4 equally spaced pieces performed for 3 placental zones (inner, middle and outer) of each placenta (total 12 samples per placenta). Western blot analysis and RT-PCR were used to investigate expression of HSP20. The results demonstrated that there was a significant decrease in HSPB6mRNA expression at the middle area in the labour group when compared to the nonlabour group (p=0.01). No significant difference was found at the inner and outer areas (p=0.3) for both. For BMI groups no differences were found in HSP20 expression at protein and molecular levels. Oxidative stress and inflammation are significant features of maternal obesity, and Paroxonase 2 (PON2) has a clear role in oxidative stress and inflammation. It protects cells against oxidative damage and lipid peroxidation, modulation of endoplasmic reticulum stress, and regulation of apoptosis. As a result, the hypothesis was that expression of placental PON2 would change during obesity. PON2 was examined in placentas obtained from women who had normal pregnancies with different BMIs. Four BMI groups were studied as per the HSP20 study. Western blotting and real time PCR were performed to investigate the expression of placental PON2, which has 2 isoforms: one at 62kDa, and another at 43kDa, in all samples. The results showed no spatial differences in PON2 protein or mRNA expression of either isoform at the three sites (inner, middle, and outer) between all BMI groups. Conclusion: This is the first study to investigate the expression of HSP20 in labour and during maternal obesity. Whether differences in phosphorylation of the protein occur requires future investigation. Similarly, this work is the first to investigate the expression of PON2 in different BMI groups in the human placenta at the three sites (inner, middle, and outer). However, knowledge concerning its role in the reproductive system is still under investigation, and more studies need to be conducted to explain its precise roles. It would be of interest in future work to determine how other PONs 1 and 2 are altered.