title: The Infertility of Repeat-Breeder Cows During Summer Is Associated with Decreased Mitochondrial DNA and Increased Expression of Mitochondrial and Apoptotic Genes in Oocytes.
abstract: Oocyte quality is known to be a major cause of infertility in repeat-breeder (RB) and heat-stressed dairy cows. However, the mechanisms by which RB oocytes become less capable of supporting embryo development remain largely unknown. Thus, the aim of this study was to investigate whether the decreased oocyte competence of RB cows (RBs) during summer is associated with an altered gene expression profile and a decrease in mitochondrial DNA (mtDNA) copy number. Therefore, oocytes collected from heifers, non-RBs in peak lactation (PLs), and RBs were used to evaluate mtDNA amounts as well as the expression levels of genes associated with the mitochondria (MT-CO1, NRF1, POLG, POLG2, PPARGC1A, and TFAM), apoptosis (BAX, BCL2, and ITM2B), and oocyte maturation (BMP15, FGF8, FGF10, FGF16, FGF17, and GDF9). The oocytes retrieved from RBs during winter contained over eight times more mtDNA than those retrieved from RBs during summer. They also contained significantly less mtDNA than oocytes retrieved from heifers and PLs during summer. Moreover, the expression of mitochondria- (NRF1, POLG, POLG2, PPARGC1A, and TFAM) and apoptosis-related (BAX and ITM2B) genes, as well as of GDF9, in RB oocytes collected during summer was significantly greater than that in oocytes collected from heifers and PLs during the same season. In oocytes from heifers and PLs, the expression levels of these genes were lower in those collected during summer compared with winter, but this difference was not observed in oocytes collected from RBs. Altogether, these data provide evidence of altered gene expression and reduced mtDNA copy number in the oocytes collected from RBs during summer. This indicates a loss of fertility in RBs during summer, which might be caused by a possible mitochondrial dysfunction associated with a greater chance of oocytes to undergo apoptosis.
authors: Departamento de Reprodução Animal, Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo, São Paulo, São Paulo, Brazil Departamento de Medicina Veterinária, Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, Pirassununga, São Paulo, Brazil robertinhavet@yahoo.com.br.
authors: Roberta Machado
authors: RM
authors: Ferreira
authors: Departamento de Ciências Básicas, Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, Pirassununga, São Paulo, Brazil Departamento de Genética e Evolução, Centro de Ciências Biológicas e da Saúde, Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil.
authors: Marcos Roberto
authors: MR
authors: Chiaratti
authors: Departamento de Ciências Básicas, Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, Pirassununga, São Paulo, Brazil Departamento de Genética e Evolução, Centro de Ciências Biológicas e da Saúde, Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil.
authors: Carolina Habermann
authors: CH
authors: Macabelli
authors: Clínica Veterinária Samvet de São Carlos Ltda., São Carlos, São Paulo, Brazil.
authors: Carlos Alberto
authors: CA
authors: Rodrigues
authors: Vida Reprodutiva Consultoria, Cravinhos, São Paulo, Brazil.
authors: Márcio Leão
authors: ML
authors: Ferraz
authors: Vitrogen-WTAvet, Cravinhos, São Paulo, Brazil.
authors: Yeda Fumie
authors: YF
authors: Watanabe
authors: Centre de Recherche em Reproduction Animale, Faculté de Médecine Vétérinarie, Université de Montréal, St. Hyacinthe, Quebec, Canada.
authors: Lawrence Charles
authors: LC
authors: Smith
authors: Departamento de Medicina Veterinária, Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, Pirassununga, São Paulo, Brazil Departamento de Ciências Básicas, Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, Pirassununga, São Paulo, Brazil.
authors: Flávio Vieira
authors: FV
authors: Meirelles
authors: Departamento de Reprodução Animal, Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo, São Paulo, São Paulo, Brazil.
authors: Pietro Sampaio
authors: PS
authors: Baruselli
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002417:Cattle / Q000502:physiology*; D004272:DNA, Mitochondrial / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology; D007247:Infertility, Female; D008928:Mitochondria / Q000502:physiology; D009865:Oocytes / Q000502:physiology*; D010298:Parity; D011247:Pregnancy; D012621:Seasons
chemical_list: D004272:DNA, Mitochondrial
keywords: apoptosis; dairy cow; heat stress; mitochondria; oocyte quality; repeat breeding; reproductive efficiency