Abstract: BACKGROUND: It has been recently discovered that vitamin D receptor is widely distributed in the female reproductive system such as the ovary and uterus, which is closely related to adverse pregnancy outcomes such as spontaneous abortion and gestational diabetes mellitus, but its specific mechanism is still unclear.  
OBJECTIVE: To investigate potential differentially expressed miRNAs and related regulatory networks via a whole transcriptome analysis of the uterine tissue of vitamin D-deficient mice.
METHODS: Eighteen female C57BL/6J mice were randomly divided into two groups: a vitamin D deficiency group and a normal control group. Mice in the vitamin D deficiency group were fed with vitamin D deficiency diet, and mice in the normal control group were fed with vitamin D sufficiency diet. The body mass of the mice was recorded every week. After 8 weeks, the serum levels of 25,(OH)D3 and hormones in the mice were tested. Hematoxylin-eosin staining was used to detect mouse uterine tissue. Uterine tissue samples of two groups were collected for transcriptome sequencing, and bioinformatics analyses of gene ontology and Kyoto encyclopedia of genes and genomes.  
RESULTS AND CONCLUSION: There was no difference in body mass between the two groups. Compared with the normal control group, the levels of 25,(OH)D3 and estradiol in mouse serum were significantly reduced, and the testosterone level was significantly increased in the vitamin D deficiency group. Hematoxylin-eosin staining of uterine tissue showed a reduction in the endometrial folds of mice in the vitamin D deficiency group. Twenty-five differentially expressed miRNAs were screened out by transcriptome sequencing, of which 9 were up-regulated (such as miR-541-5p and miR-205-5p) and 16 were down-regulated (such as miR-378d and miR-708-5p). At the same time, vitamin D deficient mice showed significantly differences in multiple gene ontology enrichment categories, such as developmental process, cell composition, tissue or biogenesis. In addition, the functional enrichment results of Kyoto genes and genomes encyclopedia showed that differentially expressed genes were mostly related to biochemical metabolic pathways and signal transduction pathways. Differentially expressed genes in these enrichment pathways mainly affected PI3K-Akt signaling pathway, MAPK signaling pathway, insulin signaling pathway, gonadotropin releasing hormone signaling pathway, and oocyte meiosis pathway, all of which were closely related to the regulation of the reproductive system. To conclude, vitamin D deficiency can lead to poor uterine implantation conditions in female mice, which is related to multiple signaling pathways, such as insulin regulation, in mouse reproductive system.

Key words: vitamin D deficiency, uterus, transcriptome sequencing, miRNA, reproductive system