Hypoxia Promotes Luteal Cell Death in Bovine Corpus Luteum1

Abstract

Low oxygen caused by a decreasing blood supply is known to induce various responses of cells, including apoptosis. The present study was conducted to examine whether low-oxygen conditions (hypoxia) induce luteal cell apoptosis in cattle. Bovine midluteal cells incubated under hypoxia (3% O(2)) showed significantly more cell death than did those incubated under normoxia (20% O(2)) at 24 and 48 h of culture, and had significantly lower progesterone (P4) levels starting at 8 h. Characteristic features of apoptosis, such as shrunken nuclei and DNA fragmentation, were observed in cells cultured under hypoxia for 48 h. Hypoxia increased the mRNA expressions of BNIP3 and caspase 3 at 24 and 48 h of culture. Hypoxia had no significant effect on the expressions of BCL2 and BAX mRNA. Hypoxia also increased BNIP3 protein, and activated caspase-3. Treatment of P4 attenuated cell death, caspase-3 mRNA expression, and caspase-3 activity under hypoxia. Overall results of the present study indicate that hypoxia induces luteal cell apoptosis by enhancing the expression of proapoptotic protein, BNIP3, and by activating caspase-3, and that the induction of apoptosis by hypoxia is partially caused by a decrease in P4 production. Because hypoxia suppresses P4 synthesis in bovine luteal cells, we suggest that oxygen deficiency caused by a decreasing blood supply in bovine corpus luteum is one of the major factors contributing to both functional and structural luteolysis.

Summer heat stress affects prostaglandin synthesis in the bovine oviduct

“…Each protein in the cultured bovine oviductal cells was detected by western blotting analysis as described previously (Nishimura et al 2008). Briefly, the cultured cells were lysed in 200 ml lysis buffer, and the protein concentrations were determined by the BCA method (Osnes et al 1993).…”

Multiple roles of hypoxia in ovarian function: roles of hypoxia-inducible factor-related and -unrelated signals during the luteal phase

“…The response to hypoxia is important pathologically in the ischemic tissues, and is important physiologically in the process of embryo development in organ formation Wenger 2002;Bruick 2003;Wiesener and Maxwell 2003;Lee et al 2004; 11 Hellwig-Burgel et al 2005;Chen et al 2009;Dunwoodie 2009). We have previously suggested that hypoxia plays roles in both life (luteal formation) (Nishimura and Okuda 2010) and death (luteal regression) (Nishimura et al 2008) of CL. In the formation of CL, hypoxia induces angiogenesis (Nishimura and Okuda 2010), whereas it decreases P4 synthesis (Nishimura et al 2006) and promotes apoptosis during regression of the CL (Nishimura et al 2008).…”

“…We have previously suggested that hypoxia plays roles in both life (luteal formation) (Nishimura and Okuda 2010) and death (luteal regression) (Nishimura et al 2008) of CL. In the formation of CL, hypoxia induces angiogenesis (Nishimura and Okuda 2010), whereas it decreases P4 synthesis (Nishimura et al 2006) and promotes apoptosis during regression of the CL (Nishimura et al 2008). These ideas are summarized in Figure 4.…”

“…Under hypoxic conditions, an effecter caspase in the apoptosis cascade, caspase-3, was induced in cultured luteal cells (Nishimura et al 2008). BNIP3, which facilitates apoptosis under hypoxic conditions (Bruick 2000), is also induced by hypoxia.…”

“…In cultured bovine luteal cells, the expression of HIF1 and BNIP3 are increased by incubation under hypoxic conditions (Nishimura et al 2006;Nishimura et al 2008).…”