Pre-Eclampsia
Question Received:
Response:
Is there any relation between heat shock proteins and physiopathology of pre-eclampsia in women?
21st March 1999
There is indeed evidence that heat-shock proteins are produced by the placenta and decidual tissues and that they have a physiological role, but it is not yet clear what contribution they make (if any) to pre-eclampsia.
Pre-eclampsia is a leading cause of premature delivery and fetal growth retardation. It is characterized by raised blood pressure in the mother, reduced blood flow through the placenta, the excretion of protein in the urine, and oedema.
Heat-shock proteins have been found in all organisms so far studied - they have been conserved throughout evolution - and have a wide variety of important functions. There are 5 families of heat-shock proteins, categorised according to their molecular weight: Hsp 100, Hsp 90, Hsp 70, Hsp60, and sHsp (small heat-shock proteins). They appear in greater quantities in cells exposed to higher-than-normal levels of heat and also in response to other stressors such as oxygen starvation, free-radical damage, and in some chronic degenerative diseases (Cossins, 1998). They are thought to protect other proteins vital to the stressed cell and to help in the repair of damaged proteins. In normal, unstressed cells the heat-shock proteins are present at lower concentrations, and chaperone the folding of new proteins and assist their passage through membranes within the cell.
As metabolically active tissues vital to the maintenance of pregnancy, it is probable that placental tissues experience stress and this may be why they boost the production of heat-shock proteins. How this might influence the mother’s cardiovascular system is not yet clear, but the small signalling molecule nitric oxide may provide a link between heat-shock proteins and maternal cardiovascular dynamics. Nitric oxide has a powerful effect on maternal blood vessels, and its release is partly regulated by the heat-shock protein Hsp90 (Garcia-Cardena et al, 1998). The production of Hsp90 in decidual and placental tissues is influenced by a variety of different stimuli, including vascular endothelial growth factor, histamine, and the dynamics of placental blood flow through the placenta. However, the initial indications are that changes in nitric oxide production are not necessarily a cause of hypertension in preeclampsia (Grunewald et al, 1998).
However, there is a growing consensus that heat-shock proteins, or ‘stress proteins’, may be of physiological significance in reproductive events (Ron and Birkenfeld, 1987). Heat-shock proteins form associations with steroid receptors, including estrogen receptors and progesterone receptors, so since progesterone and estrogen regulate myometrial contractility throughout pregnancy and during parturition, changes in Hsp90 and Hsp70 abundance may modulate uterine function (Wu et al, 1996).
There are several other hypotheses about the causes of pre-eclampsia that may not require direct involvement of heat-shock proteins (Dekker and Sibai, 1998):
Placental ischemia may cause dysfunction in endothelial cells lining the maternal vascular system
Lipid deposition in decidual spiral arteries (acute atherosis) may cause maternal endothelial dysfunction in preeclampsia (Staff et al, 1999).
Very low-density lipoproteins being carried in the maternal blood to meet the increased energy demand during pregnancy might produce toxicity
Immune maladaptation may cause shallow invasion of spiral arteries by cytotrophoblast cells and produce endothelial cell dysfunction mediated by an increased decidual release of cytokines, proteolytic enzymes, and free radicals
A change in genetic imprinting may cause a single recessive gene or a dominant gene with incomplete penetrance to become activated during pregnancy
Endothelial dysfunction stems from a more generalized intravascular inflammatory reaction involving leukocytes, clotting factors, and the complement system (Redman, Sacks and Sargent, 1999)
Increased lipid peroxidation in the maternal circulation and in the mitochondria of the placenta produces oxidative stress predisposing to pre-eclampsia (Wang and Walsh, 1998)
Page et al (2000) have demonstrated recently that a likely candidate for the initiation of pre-eclampsia is over-production by the placenta of a signalling molecule identical to neurokinin B. Neurokinin B is known to have hypertensive actions through its effects on blood vessels and the heart. The identification of this link between neurokinin B and pre-eclampsia may enable the development of a test to allow early detection of pre-eclampsia and treatment with neurokinin receptor antagonists.
References
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Cossins, A. (1998) Cryptic clues revealed. Nature, 396, 309-310.
Dekker, G.A., and Sibai, B.M. (1998) Etiology and pathogenesis of preeclampsia: current concepts. American Journal of Obstetrics and Gynecology, 179(5), 1359-1375 (Nov).
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Grunewald, C., Carlstrom, K., Kumlien, G., Ringqvist, A., and Lundberg, J. (1998) Exhaled oral and nasal nitric oxide during L-arginine infusion in preeclampsia. Gynecological and Obstetrical Investigations, 46(4), 232-237.
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Page, N.M., Woods, R.J., Gardiner, S.M., Lomthaisong, K., Gladwell, R.T., Butlin, D.J., Manyonda, I.T., and Lowry, P.J. (2000) Excessive placental secretion of neurokinin B during the third trimester causes pre-eclampsia. Nature, 405, 797-800 (Jun 15).
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Wu, W.X., Derks, J.B., Zhang, Q., and Nathanielsz, P.W. (1996) Changes in heat shock protein-90 and -70 messenger ribonucleic acid in uterine tissues of the ewe in relation to parturition and regulation by estradiol and progesterone. Endocrinology, 137(12), 5685-5693 (Dec).