Molecular mechanisms involved in the response of pig ovaries to seasonal heath stress

Decreased fertility during the hot season is a common problem in pigs. Maternal hyperthermia reduces oocyte fertilizability and increases embryonic mortality. Cell biochemical thermoprotection mechanisms involve members of the heat shock protein (Hsp) family. Hsp40, also known as Mammalian Relative of DnaJ (MRJ) protein, plays a pivotal role as co-chaperone after heat shocks.. Although this protein may be involved in local thermoprotection, no information is available on the role of Hsp40 in mammalian ovary. Hsp40 in pig, was characterized by extracting RNA from ovaries, granulosa cells and from pools of 5 oocytes. The nucleotide sequence showed an homology of 95% with the human, 92% with the bovine and 84% with the mouse orthologs. Western blot analysis with anti-Hsp40 antibody, identified an immune peptide, displaying a MW 38Kda, in agreement with results obtained in other species. Immunofluorescence studies, showed that Hsp40 is found in oocytes, granulosa and theca cells of follicle at all developmental stages. Exposure of porcine ovaries to 42°C for 1 hour resulted in a significant increase (P<0.05) of Hsp40 mRNA levels (2,4 ± 0,35 fold) in oocytes, while no significant raise was detected in cumulus cells. Furthermore, pig ovaries were collected at the slaughterhouse during the cold and hot season and semi-quantitative analysis was performed. A comparison of transcript levels, revealed higher expression of Hsp40 in the hot versus cold season. To our knowledge, this is the first demonstration that Hsp40 is expressed and responds to a thermal stress in pig ovary. Since this co-chaperone acts upstream to other heat shock protein –such as Hsp70- and it is specifically up regulated in the oocytes, our findings suggest that it may play an important protective role against heat stress infertility.