Purinergic signaling gene network expression in bovine polymorphonuclear neutrophils during the peripartal period

An effective immune response relies on efficient activation of polymorphonuclear neutrophilic leukocytes (PMNL). The PMNL release cellular ATP in response to inflammatory mediators. Although extracellular ATP is rapidly degraded to adenosine, both compounds can readily bind to either the purinergic receptor P1 (adenosine) or P2 (ATP). The P1 and P2 receptors are members of the G-protein-coupled receptor family. The peripartal period is characterized by marked changes in metabolic and inflammatory status that are functionally related with immune responses in the cow. We evaluated the mRNA expression of genes associated with purinergic signaling in PMNL during the peripartal period. Seven multiparous Holstein cows were dried off at d -50 relative to expected parturition and fed a controlled-energy diet (net energy for lactation=1.24 Mcal/kg of dry matter) for ad libitum intake during the entire dry period. After calving, all cows were fed a common lactation diet (net energy for lactation=1.65 Mcal/kg of dry matter) until 30 d in milk. Blood PMNL collected at -10, 3, and 21 d in milk were used to study the expression of 22 genes associated with adhesion to endothelium, chemoattractant binding at the plasma membrane, and purinergic signaling. Other blood samples around calving were used to analyze concentrations of insulin, metabolites, and whole-blood phagocytosis. The expression of purinergic receptor P2Y, G-protein coupled, 2 (P2RY2) increased on d 3 and then decreased on d 21. This response suggested that ATP could play a role in the amplification of chemotactic signals. In contrast, the expression of genes encoding cell adhesion [selectin L (SELL) and selectin P ligand (SELPLG)], chemoattractant receptors [complement component 5a receptor 1 (C5AR1), IL-8 receptor α (CXCR1), IL-8 receptor β (CXCR2), and platelet-activating factor receptor (PTAFR)], and adenosine receptors [adenosine A1 receptor (ADORA1) and adenosine A3 receptor (ADORA3)] decreased between -10 and 3 d. The decrease coincided with a marked increase in blood nonesterified fatty acids and hydroxybutyrate concentrations, and a decrease in glucose and insulin concentrations. The increase in metabolites also was associated with greater expression of leukotriene B4 receptor (LTB4R) on d 3 and 21 compared with d -10, which is involved in inflammatory prostaglandin synthesis. Most chemoattractant receptors increased by 21 d, but cell adhesion genes and blood leukocyte phagocytosis was lower. The expression of adenosine A2a receptor (ADORA2A), which is associated with immunosuppression of PMNL and that of adenosine uptake channels [solute carrier family 29 (nucleoside transporters), member 1 (SLC29A1) and member 2 (SLC29A2)] and the nucleotidase adenosine deaminase (ADA) was greater at 3 and 21 d compared with -10d. The reduction in key immune responses, such as cell adhesion and chemotaxis, by bovine PMNL could partly be a function of changes in mRNA expression of genes associated with purinergic signaling.