Adipose tissue remodeling in late-lactation dairy cows during feed-restriction-induced negative energy balance

Abstract

Excessive rates of demand lipolysis in the adipose tissue (AT) during periods of negative energy balance (NEB) are associated with increased susceptibility to disease and limited lactation performance. Lipolysis induces a remodeling process within AT that is characterized by an inflammatory response, cellular proliferation, and changes in the extracellular matrix (ECMT). The adipose tissue macrophage (ATM) is a key component of the inflammatory response. Infiltration of ATM-forming cellular aggregates was demonstrated in transition cows, suggesting that ATM trafficking and phenotype changes may be associated with disease. However, it is currently unknown if ATM infiltration occurs in dairy cows only during NEB states related to the transition period or also during NEB-induced lipolysis at other stages of lactation. The objective of this study was to evaluate changes in ATM trafficking and inflammatory phenotypes, and the expression of genetic markers of AT remodeling in healthy late-lactation cows during feed restriction-induced NEB. After a 14-d (d −14 to d −1) preliminary period, Holstein cows were randomly assigned to 1 of 2 feeding protocols, ad libitum (AL) or feed restriction (FR), for 4 d (d 1-4). Caloric intake was reduced in FR to achieve a targeted energy balance of −15 Mcal/d of net energy for lactation. Omental and subcutaneous AT samples were collected laparoscopically to harvest stromal vascular fraction (SVF) cells on d −3 and 4. The FR induced a NEB of −14.1 ± 0.62 Mcal/d of net energy for lactation, whereas AL cows remained in positive energy balance (3.2 ± 0.66 Mcal/d of NE L ). The FR triggered a lipolytic response reflected in increased plasma nonesterified fatty acids (0.65 ± 0.05 mEq/L on d 4), enhanced phosphorylation of hormone sensitive lipase, and reduced adipocyte diameter.Flow cytometry and immunohistochemistry analysis revealed that on d 4, FR cows had increased numbers of CD172a + , an ATM (M1 and M2) surface marker, cells in SVF that were localized in aggregates. However, FR did not alter the number of SVF cells expressing M1 markers (CD14 and CD11c) or M2 markers (CD11b and CD163). This finding contrasts with the predominately M1 phenotype observed previously in ATM from clinically diseased cows. No changes were observed in the expression of ECMT-related or cell proliferation markers. In summary, an acute 4-d lipolytic stimulus in late-lactation dairy cows led to ATM infiltration with minimal changes in inflammatory phenotype and no changes in ECMT. These results underscore that physiological changes related to parturition, the onset of lactation, extended periods of lipolysis, or a combination of these can induce intense AT remodeling with enhanced ATM inflammatory phenotype expression that may impair the metabolic function of AT in transition dairy cattle.

Adipose tissue lipolysis and remodeling during the transition period of dairy cows

“…Cells of the innate and adaptive immune systems, such as macrophages, mast cells, lymphocytes, neutrophils, eosinophils, dendritic cells, and NK, exhibit active AT trafficking during health and disease in rodents and humans [80], as well as in dairy cows during the transition period and late lactation [81, 82]…”

“…In cases of displaced abomasum in transition dairy cows, macrophages exhibiting a M1 phenotype accumulate in aggregates within omental and subcutaneous depots [81]. During induced NEB in late-lactation cows, lipolysis induced ATM infiltration into subcutaneous and visceral AT, yet no phenotypic change was observed [82]. …”

“…T-cells were reported to comprise 3–5% of the SVF cells in cows, with or without displaced abomasum, during the transition period and in late lactation [81, 82, 95]. Around 4–7% of SVF cells are B lymphocytes and their numbers are higher in visceral AT than other AT.…”

“…Markers of cell cycle activation, such as CCNA2 , CCNB2 , and MKI67 have been used. In late-lactation cows, short-term intense lipolysis did not increase the expression of these genes [82]. In dairy heifers during peak lactation, Häussler et al detected a 25-fold increase in the number of preadipocytes in the retroperitoneal AT [98], compared to heifers in mid lactation (105 DIM), using immunohistochemistry with antibodies against Ki67, a cell proliferation marker, and Pref-1 (preadipocyte factor).…”

“…High rates of lipolysis observed in cancer cachexia are also associated with changes in the ECM composition that lead to enhanced inflammatory responses by adipocytes [105, 106]. In late-lactation dairy cows, ECM composition is affected by anatomical location, with higher expression of collagens I and VI in subcutaneous fat compared to omental fat [82]. Reports on the dynamics of ECM remodeling during the transition period and early lactation are limited to gene expression evaluation.…”