Effects study of SCGB2A2 on cell proliferation and milk components biosynthesis in ovine mammary epithelial cells

The Small-Tailed Han (STH) sheep milk has significantly higher fat and protein than DairyMeade (DM) sheep milk. Further study found that the expression of whey protein secretoglobin family 2 A member 2 (SCGB2A2) in STH sheep milk was significantly higher than in DM sheep milk. Thus we surmise that the SCGB2A2 may be involved in the regulation of the mammary biological function. Here, the expression of SCGB2A2 at different lactation periods was detected first. Then the cell proliferation and milk component synthesis effects on ovine mammary epithelial cells (OMECs) were analyzed. And the CUT&Tag analysis was used to identify SCGB2A2 target binding sites at the genome. The transcriptome of SCGB2A2 overexpression and knockdown OMECs was analyzed. Two co-analyses were conducted to further screen out SCGB2A2 potential target genes. Finally, the potential interacting protein was verified by CO-IP and UHLP-MS analysis. Results showed that the SCGB2A2 was expressed highest at the colostrum stage and lowest at the dry milk stage. Immunohistochemical analysis showed that it was mainly expressed in mammary epithelial cells. CCK8 and cell cycle analysis showed that SCGB2A2 promotes the OMECs proliferation. Milk components synthesis detection found that the SCGB2A2 was positively correlated with the CSN2, lactose, and triglyceride (TG). CUT&Tag and transcriptome co-analyses found that 20 genes were consistently detected, including FBP2, IFIT3 and so on. CO-IP analysis demonstrated that mTOR interacted with SCGB2A2. Taken together, we demonstrated that SCGB2A2 plays a positive role in OMECs proliferation and biosynthesis of milk components. Some SCGB2A2 direct regulated genes are involved in the cell proliferation. The regulation of SCGB2A2 for milk components biosynthesis mainly interacts with mTOR. However, the specific regulatory mechanism is needed to further study.