Epigenetic contribution to individual variation in response to lipopolysaccharide in bovine dermal fibroblasts

The innate immune signaling pathway plays a crucial role in the recognition and early response to pathogens associated with disease. Genetic analysis has been unable to completely account for individual variability in the strength of the innate immune response. The aim of this study was to determine the role of the epigenetic markers (DNA methylation or histone acetylation) in controlling bovine gene expression in relation to the response to lipopolysaccharide (LPS). To determine the impact epigenetics may have in controlling innate immunity, dermal fibroblasts from fifteen dairy heifers having previously displayed a differential response to LPS were exposed to 5-aza-2′-deoxycytidine (AZA) and trichostatin A (TSA); de-methylating and hyper-acetylating agents, respectively. The AZA-TSA exposure resulted in a loss of variability between individuals' response to LPS as measured by fibroblast IL-8 protein production. Transcriptomic analysis by microarray was used to elucidate the role of epigenetics in innate immune signaling at 2, 4, and 8 h post-LPS exposure. A subset of genes displayed altered expression due to AZA-TSA alone, suggesting an epigenetic regulatory element modifying expression under normal conditions. Treatment with AZA-TSA also led to increased expression of IL-8 (7.0-fold), IL-6 (2.5-fold), TNF-α (1.6-fold), and serum amyloid A 3 (SAA3) (11.3-fold) among other genes compared to control cultures for at least one of the measured times following LPS exposure. These data support the conclusion that epigenetic regulation significantly alters LPS-induced responses and constitutive cytokine gene expression.