An Exploratory Study of Heat Shock Protein Changes in Women with Unexplained Infertility

Unexplained infertility affects up to 30% of couples and has been associated with heat shock proteins (HSP) and endometrial stress. HSPs and their co-chaperones are part of a complex network of proteins responsible for maintaining protein homeostasis and cell survival. This exploratory hypothesis-generating study investigated the possible relationship between HSPs and unexplained infertility. Twenty-five women were recruited from an IVF clinic. Eleven were confirmed for unexplained infertility (UI), while fourteen were age- and body mass index (BMI)-matched couples with confirmed male factor infertility (MFI), acting as controls. Blood samples were obtained at day 21 of the luteal phase, and plasma measurement of 19 HSPs and co-chaperones undertaken using the slow off-rate modified aptamer (SomaScan) platform. Welch's t-test and a permutation test were used to compare group means, and Pearson's correlations to examine relationships with HSPs. Of the 19 proteins measured, plasma HSP70 was decreased (permutation p = 0.002) in cases with unexplained infertility, while HSC70 and STIP1 were increased (permutation p = 0.017 and p = 0.001, respectively) when compared to MFI control. HSP70 was negatively correlated to both HSC70 and STIP 1 in UI (r = -0.77, permutation p = 0.017; -0.80, permutation p = 0.003, respectively), but not in MFI, whilst HSC70 and STIP1 were positively correlated in both UI and MFI (r = 0.93, permutation p = 0.001; r = 0.65, permutation p = 0.035, respectively). The HSP70-HSC70-STIP1 axis showed HSC70-STIP1 coupling with an inverse relationship with inducible HSP70, findings that may suggest dysregulation of constitutive and stress-inducible chaperone systems in UI.