The effect of the transition period and postpartum body weight loss on macrophage infiltrates in bovine subcutaneous adipose tissue

Abstract

The transition period in dairy cattle is characterized by a rapid increase in metabolic demands due to the onset of lactation in parallel with a voluntary drop in dry matter intake, which slowly increases compared with the rapidly increasing milk production. The resulting deficit in energy intake is largely met by lipolysis of adipose tissue stores liberating nonesterified fatty acids (NEFA) as energy substrates to support milk production and for the synthesis of milk fat. Previous work in cattle and other species has documented an increase in adipose tissue macrophages (ATM) during periods of feed restriction and lipolysis; however, alterations in ATM during the transition period have only recently received interest because of the role that adipose tissue remodeling and inflammation may play during this time. The primary objective of this study was to evaluate the number of macrophages in subcutaneous adipose tissue from dairy cattle at multiple time points throughout the transition period. Secondary objectives included the evaluation for potential associations of ATM with changes in body condition score (BCS) and concentrations of circulating NEFA and β-hydroxybutyrate. Holstein cows (n = 25) were enrolled in the study 28 d before expected parturition and fed the same prepartum and postpartum rations for ad libitum consumption. On d 10 before expected parturition, and on d 4 and 21 after calving, subcutaneous adipose tissue biopsies were taken from the paralumbar fossa and preserved in formalin. Paraffinembedded sections of tissue from each of the 25 cows at the 3 time points (total of 75 samples) were labeled with an immunohistochemical marker of macrophages, ionized calcium-binding adapter molecule 1 (Iba1, also known as allograft inflammatory factor 1). The number of Iba1-positive cells, the number of crown-like structures, and the number of immunopositive aggregates were enumerated in each sample. The number of Iba1positive macrophages increased by 60 and 93% on d 4 and 21, respectively, when compared with the average prepartum number. Additionally, cows that lost ≥0.50 points of BCS had a 57 and 52% higher number of ATM on d 4 and 21 postpartum, respectively, when compared with cows that lost ≤0.25 points of BCS. No association was found between ATM numbers and NEFA and β-hydroxybutyrate concentrations or milk production in early lactation. Cows experiencing a more pronounced decrease in BCS postpartum had the largest increase in adipose tissue macrophage counts, suggesting that a greater degree of adipose tissue remodeling during the period of greatest nutrient deficit may be associated with higher numbers of ATM.

Transcriptomic profiling of adipose tissue inflammation, remodeling, and lipid metabolism in periparturient dairy cows (Bos taurus)

“…Increased expression of CD14 postpartum in this group of cows provides further evidence for the enhanced trafficking of macrophages into AT during lipolysis as the CD14 protein is a macrophage marker in cattle [ 48 ]. This finding coincides with reports from different research groups demonstrating an increased number of macrophages in AT postpartum, especially in cows with high lipolysis rates using transcriptomics [ 27 ], flow cytometry [ 8 ], and immunohistochemistry [ 45 , 49 ]. A new finding of our present study is the identification of TREM2 as DEG .…”

Review: Following the smoke signals: inflammatory signaling in metabolic homeostasis and homeorhesis in dairy cattle

“…When comparing latelactation cows in either positive or negative energy balance, an increase in macrophage infiltration in adipose was noted in cows experiencing negative energy balance; however, there were minimal changes in inflammatory markers between groups (Contreras et al, 2016). Lastly, an invasion of macrophages in adipose was associated with a greater degree of body condition loss in transition dairy cows (Newman et al, 2019). Collectively, these data suggest a role for M1 macrophages in the development of a low-grade chronic inflammatory state that can occur in diseased early-lactation dairy cattle (Contreras et al, 2018).…”

Methods in isolation and characterization of bovine monocytes and macrophages

“…For formalin-fixed tissue specimens in specific cases, antigen retrieval may be necessary. Antigen retrieval methods using enzymatic or heat-based protocols vary according to each molecular target and comprise: heat-induced (heating by pressure cookers or microwave in citrate buffer for 10 to 20 min), enzymatic (0.1% trypsin or pepsin in phosphate-buffered saline for 30 min at 37°C) or proteinase K (10 μg/mL proteinase K in Tris buffer for 15 min) may be necessary [163][164][165][166][167][168].…”

“…Immunohistochemistry and immunofluorescence have been utilized to identify, enumerate and characterize tissue macrophages in formalin-fixed [160,[163][164][165][166][167][175][176][177] or frozen [168][169][170][172][173][174] sections of a variety of bovine tissue samples including adipose tissue [160,167,168,175], in the intestinal tissue of cattle with spontaneous paratuberculosis at different stages of the disease [165,166,[172][173][174], the endometrium of pregnant and post parturient dairy cows [169,170,176], fibrotic liver lesions in bovines infected with Fasciola hepatica [163], lung lesion in bovine contagious pleuropneumonia [177] and early lesions during experimental M. bovis aerosol infection [164].…”