Effects of Staphylococcus aureus intramammary infection on the expression of estrogen receptor α and progesterone receptor in mammary glands of nonlactating cows administered estradiol and progesterone to stimulate mammary growth

摘要

Intramammary infections (IMI) are prevalent in nonlactatingdairy cattle and are known to alter mammarystructure and negatively affect the amount of mammaryepithelium in the gland. Mechanisms responsiblefor the observed changes in mammary growth duringan IMI are poorly understood, yet the importance ofthe key mammogenic hormones driving mammarygrowth is well recognized. This study’s objective wasto characterize the expression of estrogen receptor α(ESR1) and progesterone receptor (PGR) in mammaryglands stimulated to grow and develop in the presenceor absence of an IMI as well as preliminarily characterizemyoepithelial cell response to IMI. Mammarygrowth was stimulated in 18 nonpregnant, nonlactatingdairy cows using subcutaneous estradiol and progesteroneinjections, and 2 culture-negative quarters ofeach cow were subsequently infused with either saline(n = 18) or Staphylococcus aureus (n = 18). Mammaryparenchyma tissues were collected 5 d (n = 9) or 10d (n = 9) postchallenge and examined using immunofluorescencemicroscopy to quantify positive nucleiand characterize staining features. There tended to be agreater number of ESR1-positive nuclei observed across8 random mammary parenchyma fields of view in salinequarters than in Staph. Aureus quarters (201 vs. 163± 44 nuclei). Saline quarters also contained a greaternumber of PGR-positive nuclei (520 vs. 440 ± 45 nuclei)and myoepithelial cells (971 vs. 863 ± 48 nuclei)than Staph. Aureus-challenged quarters. However, whenESR1, PGR, and myoepithelial nuclei counts were adjustedfor Staph. Aureus quarters containing less epithelium,differences between quarter treatments abated.The examined ESR1 and PGR staining characteristicswere similar between saline and Staph. Aureus quartersbut were differentially affected by day of tissue collection.Additionally, nuclear staining area of myoepithelialcells was greater in Staph. Aureus quarters thanin saline quarters. These results indicate that IMI hadlittle effect on the number or staining characteristicsof ESR1- or PGR-positive nuclei relative to epithelialarea, but myoepithelial cells appear to be affected byIMI and the associated inflammation in nonlactatingmammary glands that were stimulated to grow rapidlyusing mammogenic hormones. Accordingly, reductionsin mammary epithelium in affected glands are notsuspected to be resultant of alterations in the numberor staining characteristics of ESR1- or PGR-positivemammary epithelial cells.