Transcriptional regulators transforming growth factor-β1 and estrogen-related receptor-α identified as putative mediators of calf rumen epithelial tissue development and function during weaning

Abstract

Molecular mechanisms regulating rumen epithelial development remain largely unknown. To identify gene networks and regulatory factors controlling rumen development, Holstein bull calves (n=18) were fed milk replacer only (MRO) until 42 d of age. Three calves each were euthanized at 14 and 42 d of age for tissue collection to represent preweaning, and the remaining calves were provided diets of either milk replacer + orchard grass hay (MH; n=6) to initiate weaning without development of rumen papillae, or milk replacer + calf starter (MG; n=6) to initiate weaning and development of rumen papillae. At 56 and 70 d of age, 3 calves from the MH and MG groups were euthanized for collection of rumen epithelium. Total RNA and protein were extracted for microarray analysis and to validate detected changes in selected protein expression, respectively. As expected, calves fed MRO had no rumen papillae and development of papillae was greater in MG versus MH calves. Differentially expressed genes between the MRO diet at d 42 (preweaning) versus the MG or MH diets at d 56 (during weaning) were identified using permutation analysis of differential expression. Expression of 345 and 519 transcripts was uniquely responsive to MG and MH feeding, respectively. Ingenuity Pathway Analysis (Qiagen, Redwood City, CA) indicated that the top-ranked biological function affected by the MG diet was the cell cycle, and TFGB1, FBOX01, and PPARA were identified as key transcriptional regulators of genes responsive to the MG diet and associated with development of rumen papillae. Increased expressions of TGFB1 mRNA and protein in response to the MG diet were confirmed by subsequent analyses. The top-ranking biological function affected by the MH diet was energy production. Receptors for IGF-1 and insulin, ESRRA, and PPARD were identified by ingenuity pathway analysis as transcriptional regulators of genes responsive to the MH diet. Further analysis of TGFB1 and ESRRA mRNA expression in rumen epithelium obtained from a separate ontogenic study of Holstein calves (n=26) euthanized every 7d from birth to 42 d of age showed increases in transcript expression with advancing age, supporting their roles in mediating rumen epithelial development and function during weaning. Additional evaluation of gene expression in the rumen epithelium of adult cows ruminally infused with butyrate also suggested that observed changes in ESRRA mRNA expression in developing calf rumen may be mediated by increased butyrate concentration. Our results identify TGFB1 and ESRRA as likely transcriptional regulators of rumen epithelial development and energy metabolism, respectively, and provide targets for modulation of rumen development and function in the growing calf.

The periparturient period is associated with structural and transcriptomic adaptations of rumen papillae in dairy cattle

“…Screening for growth factors expressed in RE during the onset of lactation may provide a better understanding of the mechanisms controlling the adaptive growth response of the RE in early lactation. The results from the present study support previous findings that EGF, IGF-axis (Penner et al, 2011), and TGFB (Connor et al, 2014) families of growth factors are involved in RE growth and differentiation in a variety of experimental models in calves and cows.…”

“…For each microarray comparison, networks revolved around TGFB1 (Supplemental Figures S3 and S5;http://dx.doi.org/10.3168/jds.2014-8640). This understanding supports the recent finding (Connor et al, 2014) that TGFB1 may be involved in regulating growth and differentiation in the RE in early lactation.…”

“…Shen et al (2004) were the first to report differential gene expression related to IGF-1 as the transition from a lowenergy to higher energy diets in goats was associated with an increase in the expression of IGF-1 receptor. In line with this finding, Connor et al (2014) conducted a study comparing rumen tissue from milk-and grain-fed calves and found through IPA network analysis that IGF1R was a key transcriptional regulator for the observed treatment differences. Furthermore, Naeem et al (2012) reported that IGF1 and INSR mRNA expression is increased in rumen tissue in response to higher planes of nutrition being fed preweaning.…”

“…Three isoforms are present during development and have distinct overlapping expression patterns (Govinden and Bhoola, 2003). It was recently found that TGFB1 is regulated in grain induced ruminal development in dairy calves (Connor et al, 2014). In contrast, TGFB1 was shown to be downregulated in lactating dairy cattle infused with butyrate (Baldwin et al, 2012).…”

“…The mechanisms responsible for these adaptive changes are poorly understood. However, it is known that RE differentiation and proliferation is associated with growth factors of the IGF-axis (Shen et al, 2004;Steele et al, 2011aSteele et al, , 2012, epidermal growth factor family (EGF; Penner et al, 2011) and recently the transforming growth factor-β family (TGFB; Connor et al, 2014). These studies evaluated gene expression of the RE in the developing ruminant or during a high grain challenge model.…”