Characteristics of lipid droplets and the expression of proteins involved in lipolysis in the murine cervix during mid-pregnancy

Lipid droplets (LDs) are reservoirs of arachidonoyl lipids for prostaglandin (PG) E2 synthesis, and progesterone can stimulate PGE2 synthesis; however, the relationship between progesterone and LD metabolism in the murine cervix remains unclear. In the present study we examined LD distribution and changes in the expression of proteins involved in lipolysis and autophagy in the murine cervix during pregnancy, and compared the findings with those in dioestrous mice. During mid-pregnancy, LDs were predominantly distributed in the cervical epithelium. Electron microscopy revealed the transfer of numerous LDs from the basal to apical region in the luminal epithelium, marked catabolism of LDs, an elevated number of LDs and autophagosomes and a higher LD : mitochondrion size ratio in murine cervical epithelial cells (P < 0.05). In addition, immunohistochemical and western blotting analyses showed significantly higher cAMP-dependent protein kinase, adipose triglyceride lipase and hormone-sensitive lipase expression, and a higher light chain 3 (LC3) II : LC3I ratio in the stroma and smooth muscles and, particularly, in murine cervical epithelial cells, during mid-pregnancy than late dioestrus. In conclusion, these results suggest that the enhanced lipolysis of LDs and autophagy in murine cervical tissues were closely related to pregnancy and were possibly controlled by progesterone because LD catabolism may be necessary for energy provision and PGE2 synthesis to maintain a closed pregnant cervix.