Short communication: aquaporin-7 mRNA in adipose depots of primiparous and pluriparous dairy cows: long-term physiological and conjugated linoleic acid-induced changes.

Aquaglyceroporins act as channel proteins and regulate water and glycerol exchange through cell membranes. The aquaglyceroporin aquaporin-7 (AQP7) is abundantly expressed in adipose tissue (AT) and regulates the release of glycerol produced by lipolysis. We aimed to investigate the expression of AQP7 mRNA during lactation in subcutaneous (s.c.) and visceral (v.c.) adipose depots of primiparous and pluriparous dairy cows. In 2 independent experiments, Holstein cows were supplemented with conjugated linoleic acids (CLA) or a control (CON) fat supplement at 100g/d. Pluriparous cows were supplemented starting with the first day in milk (DIM) up to 182 DIM and biopsies from s.c. AT were collected at d -21, 1, 21, 70, 105 182 196, 224, and 252 relative to calving (CLA=11; CON=10). Samples from 3s.c. and v.c. adipose depots were investigated in primiparous cows (n=25) receiving the supplements from 1 DIM until slaughter at 1, 42, or 105 DIM. The AQP7 mRNA abundance decreased from d -21 to 1 in s.c. AT of pluriparous cows without further increase to d 252 of lactation. In primiparous cows of the CON group, the AQP7 mRNA abundance increased from 1 to 105 DIM in s.c. AT from the tail head and in mesenteric AT. In retroperitoneal AT, the only depot for which a significant decrease in mass was observed with DIM, AQP7 mRNA abundance was greater at 42 and 105 than 1 DIM. Comparing the different fat depots, retroperitoneal AT had the highest and mesenterial AT had the lowest AQP7 mRNA abundance, but no general difference was observed between v.c. and s.c. fat depots. The values were not affected by CLA treatment with the exception of mesenteric AT, for which lower AQP7 mRNA abundance values were recorded in the CLA than in the CON group. The longitudinal characterization of the AQP7 mRNA expression profile throughout lactation revealed differences between primiparous and pluriparous cows, with an increase of AQP7 mRNA abundance up to 105 DIM only in the primiparous cows. Due to a lack of CLA effects in pluriparous cows and the limitation to just one fat depot in primiparous cows, a modulatory effect of CLA on AQP7 mRNA abundance in dairy cows is not supported by our study.