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Impacts of endocrine signals altered by heat stress on mammary gland gene expression during the dry period.

V. Ouellet



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Impacts of endocrine signals altered by heat stress on mammary gland gene expression during the dry period.
V. Ouellet*, V. Lantigua, A. L. Skibiel, T. F. Fabris, J. Laporta, G. E. Dahl. Department of Animal Sciences, University of Florida Gainesville, FL.

Late gestation heat stress increases blood prolactin (PRL) and decreases estrogen (E) concentrations in cows. These alterations may disturb mammary gland remodeling, thereby resulting in a reduction in subsequent milk yield. We investigated the effects of altered endocrine environment induced by heat stress on mammary gland gene expression at different stages of the dry period. Mammary gland biopsies of cows that were either cooled (CL, n = 7) or heat stressed (HT, n = 7) during the dry period were collected at d3 and 35 relative to dry off and equally divided in 3 explants. Tissue explants were then incubated in vitro for 24h in 1 of 3 mediums: 1) Basal (Bm): no PRL or E; 2) CL-mimic (Cm): Bm + 20ng/mL PRL + 5.8ng/mL E or 3) HT-mimic (Hm): Bm + 40 ng/mL PRL + 2.9ng/mL E. Real Time qPCR BioMark Dynamic Array Integrated Fluidic Circuits was used to assess the expression of 66 genes encompassing multiple pathways (e.g., apoptosis, autophagy, proliferation, immunity). Statistical significance between in vivo (CL, HT) and in vitro (Bm, Cm, Hm) treatments and their interaction were determined by ANOVA and assessed separately by time period. In vivo treatment impacted genes related to apoptosis (CASP3,9), cell proliferation (EGF, MAPK3, PDK1, PIK3R2), and autophagy (BECN1), which were downregulated in explants from HT cows relative to CL at d3, while immunity genes (TGFBP3, NFKB1) were upregulated. Upregulation of genes related to proliferation (CCND1), and autophagy (MAP1LC3A) was observed in explants from HT relative to CL cows at d35. Expression of proinflammatory cytokines (CXCL2, TNF, IL1A, IL1B, and IL6) increased in explants incubated in Cm and Hm relative to Bm at d35. Pro-apoptotic gene CASP8 and immune-related gene LBP were downregulated at d35 in explants from CL cows incubated in Cm relative to Bm whereas they were upregulated in explants from HT cows incubated in Cm relative to Bm. Collectively, our results indicate that heat stress influences the expression of genes involved in key cellular processes occurring during the dry period and that these modifications may be mediated by hormonal alterations.

Keywords: Fluidigm, heat stress, endocrine signal.

Biography: Veronique Ouellet completed her PhD at Laval University in Quebec, Canada. Her work focuses on the effects and strategies to mitigate heat stress and improve resilience in dairy herds. She is currently a postdoctoral fellow at the University in Florida under Dr Jimena Laporta and Dr Geoffrey Dahl.