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mRNA expression of chemerin and its receptor in a subcutaneous and a visceral fat depot of dairy cows fed with high or low portions of concentrate during the transition period
Chemerin (RARRES2) is involved in adipogenesis and in mediating fat mobilization in mature adipocytes, exerting its effects via its receptor ChemR23. In humans, circulating chemerin levels are regulated by the energy intake. We hypothesized that the expression of RARRES2 or ChemR23 in subcutaneous (SC) and retroperitoneal (RP) adipose tissue (AT) of dairy cattle will change throughout the transition period and will be affected by different portions of concentrate in the diet. Twenty pluriparous German Holstein cows were divided into a high-concentrate group (HC, n=10) receiving a diet with 60% and a low-concentrate group (LC, n=10) receiving a diet with 30% concentrate on DM basis from d 1 until d 21 post partum. The SCAT from tail head and RPAT were biopsied at d −21, 1 and 21 relative to calving. RARRES2 and ChemR23 mRNA abundance were quantified by qPCR. The statistical analyses were performed with SPSS 21.0 (P<0.05).
The mRNA abundances of both genes were not different between the HC versus the LC group neither in SCAT nor in RPAT, thus, groups were pooled for further analyses. In both tissues RARRES2 and ChemR23 mRNA expression were time-dependent, i.e. less RARRES2 and ChemR23 mRNA was observed ante partum than post partum in both AT (P<0.05). When comparing both AT depots within the individual sampling times, RPAT had 1.33-fold higher RARRES2 mRNA abundance than SCAT on d 1 (P=0.004), whereas no differences between both depots were seen on d -21 and 21. For ChemR23, RPAT and SCAT did not differ at any time point. In conclusion, the different concentrate portion and the difference in energy balance (Δ=18.5 MJ/d in the third week of lactation) between HC vs. LC group were apparently not relevant for the expression of RARRES2 or ChemR23. Considering time-related differences we observed that RARRES2 and its receptor are regulated in a likewise manner in bovine AT. Due to their functions, the higher mRNA abundances of RARRES2 and its receptor in both AT after parturition may reflect the paracrine/autocrine involvement of RARRES2 in stimulation of lipolysis to provide non-esterified fatty acids as energy source to other peripheral tissues.
Keywords:
Chemerin, Adipose tissue, Transition period