Subclinical mastitis disrupts oocyte cytoplasmic maturation in association with reduced developmental competence and impaired gene expression in preimplantation bovine embryos

Abstract

Subclinical chronic mastitis was induced to examine the effects on oocyte developmental competence. Uninfected Holstein cows were intramammary administrated with serial (every 48h for 20 days) low doses of toxin of Staphylococcus aureus origin (Gram-positive; G+), endotoxin of Escherichia coli origin (Gram-negative; G-) or sterile saline (control). Follicular fluid of toxin- and saline-treated cows was aspirated from preovulatory follicles and used as maturation medium. Oocytes harvested from ovaries collected at the abattoir were matured and then fertilised and cultured for 8 days. The percentage of oocytes undergoing nuclear maturation, determined by meiotic nuclear stages, did not differ between groups. Cytoplasmic maturation, determined by cortical granule distribution, was affected by both toxins (PPPPTGS2) mRNA increased, whereas that of growth differentiation factor 9 (GDF9) decreased in matured oocytes. In addition, PTGS2 expression increased and POU class 5 homeobox 1 (POU5F1) expression decreased in 4-cell embryos developed from both G+ and G- oocytes. Thus, regardless of toxin type, subclinical mastitis disrupts oocyte cytoplasmic maturation and alters gene expression in association with reduced developmental competence.

Comparing the effects of heat stress and mastitis on ovarian function in lactating cows: basic and applied aspects

“…Follicular fluid obtained from GÀ or Gþ toxin-induced acute, clinical or subclinical mastitic cows impaired oocyte maturation and reduced cleavage rate and percentage of blastocyst formation [18,37]. Some differences and similarities between mastitic types were noted.…”

“…Subclinical mastitis induced by multiple low doses of both GÀ and Gþ increased the proportion of apoptotic oocytes and impaired cytoplasmic maturation, determined by cortical granule distribution. However, subclinical mastitis did not affect nuclear maturation, determined by the proportion of oocytes that resumed meiosis and reached the MII stage [18]. On the other hand, acute clinical mastitis induced by a single high dose of GÀ (LPS) endotoxin disrupted both nuclear and cytoplasmic maturation, whereas a single dose of Gþ toxin (S aureus exosecretions) did not alter maturation at all [37].…”

“…Lower GDF9 expression in primordial, primary, and secondary follicles of cows with subclinical mastitis was reported [53]. Oocyte maturation in follicular fluid aspirated from subclinical mastitic cows (induced by GÀ toxin) resulted in low GDF9 transcription level in MII-stage oocytes and 4-cell-stage embryos [18]. On the other hand, maturation of oocytes in follicular fluid aspirated from clinical mastitic cows (induced by GÀ) reduced expression of the genes PTGS2, HSF1, and POU5F1 [37].…”

“…Another approach is the addition of GÀ LPS or a toxin of Gþ origin such as peptidoglycan, or cytokines and other inflammatory agents, to culture various reproductive tissues [35,36]. Recently, we matured oocytes in follicular fluid aspirated from preovulatory follicles after induction of clinical and subclinical mastitis, that is, in a physiologically relevant follicular environment [18,37].…”

“…We categorize mastitis as acute short-term clinical or chronic, long-term subclinical. Such a distinction between clinical and subclinical mastitis is common in several studies dealing with mastitis effects on reproduction and fertility [6,11,[16][17][18]. In particular, we focus on the impact of clinical and subclinical mastitis on ovarian responses.…”