Proceedings of The Physiological Society
University of Edinburgh (2011) Proc Physiol Soc 25, PC40
Lipid droplets in gravid myometrium from normal and obese BMI women
E. M. Sweeney1, D. J. Crankshaw2, P. Dockery1, J. J. Morrison3
1. Anatomy, National University of Ireland, Galway, Galway, Ireland. 2. Obstetrics & Gynecology, McMaster University, Hamilton, Ontario, Canada. 3. Obstetrics & Gynaecology, National University of Ireland, Galway, Galway, Ireland.
Pregnancy in the presence of maternal obesity is associated with several undesirable outcomes including a reduction in the incidence of spontaneous term labour, and increases in the need for labour induction and caesarean sections (1). This implies maternal obesity may have an inhibitory effect on myometrial function. In obesity there is an excess of lipid droplets (LDs) (2). LDs are intracellular accumulations of lipid surrounded by a phospholipid bilayer (3). In non-adipocyte cells, LDs function in intracellular lipid homeostasis and other diverse cellular functions. Our hypothesis states that increased BMI may be associated with an increase in LDs in the myometrium and this may adversely affect contractility of these cells. Nile Red was used to stain LDs; this is a fluorescent dye with an emission wavelength that depends on the nature of the environment. In neutral lipids (eg triglycerides found in LDs) it fluoresces yellow-gold, in polar lipids (eg phospholipids) it fluoresces red, and in aqueous media it is quenched. Biopsies of human myometrium were obtained at elective caesarean section performed in the third trimester in obese (BMI 30.6-38.3, n=14) and normal (20.3-24.7, n=15) women. All biopsies were performed with local ethical committee approval. Biopsies were fixed, cryoprotected, frozen and sectioned. Sections were stained with 20µg/ml Nile red solution. Z-stacks were collected with an Olympus Fluoview confocal microscope. 2 slides were stained per biopsy and 2 z-stacks were imaged for each slide. Volocity Improvision Software was used to estimate volumes of LDs and total tissue from which volume fractions were calculated. Statistical analysis was carried out with Minitab Software using log transformed data which was normally distributed and had equal variance. The mean volume fraction ± SEM of LDs in tissue was (0.00041 ±0.000073) for normal and (0.00073 ±0.000165) for obese groups. A 2-sample T-test was performed, no significant difference was found between obese (BMI >30, n= 14) and normal (BMI < 25, n=15) groups (p -value 0.082). There was also no significant difference observed when a morbidly obese subgroup (BMI >35, n=4) was compared to the normal group (p-value 0.079). The distribution of LD volumes was also considered. The droplets were assumed to be spherical and volumes were calculated from the x and y dimensions. Volumes of individual droplets were distributed into 19 size categories and the number of droplets in each bin was considered. A Chi square test was performed which showed no significant difference in the distribution of LD volumes between normal and obese groups (p-value 0.995). Despite the apparently different functional characteristics of human myometrium in obese BMI women, in comparison to normal BMI women, the volume and size distribution of LDs does not vary in the myometrium from both of these groups.
Where applicable, experiments conform with Society ethical requirements