Reproduction in Domestic Animals

60 DJ Skarzynski, G Ferreira-Dias and K Okuda(+)(+)(+)EDN1(–)PGF 2aNO(–)(–)P4Apoptosis of steroidogenic andendothelial cells of the CLCytokines(TNFa,FAS-L,IFNg)Fig. 3. Hypothetical model of the structural and functional regressionof the CL (see text for the details; adapted from Ferreira-Dias andSkarzynski 2008)Mamluk et al. 1999; Meidan et al. 1999, 2005; Levyet al. 2000). EDN1 inhibited P4 secretion, in a dosedependent manner via selective EDN1 bindings sites(EBN A ; Girsh et al. 1996). The expression of membersof the EDN1 system (EDN1, EDN converting enzymes,and EDN A and EDN B receptors) increases during lutealregression (Ohtani et al. 1998; Klipper et al. 2004;Rosiansky-Sultan et al. 2006). Moreover, PGF 2a upregulatesEDN1 and EDN A expression within the CL(Mamluk et al. 1999). Besides EDN1, other vasoactivepeptides [i.e. angiothensin II (ANG-II), atrial natriureticpeptide (ANP)] are considered important factors inmediating PGF 2a luteolytic action (Schams and Berisha2004; Berisha and Schams 2005). These vasoactivepeptides decreased blood flow and triggered the luteolyticcascade and consequently inhibited P4 secretion(Kobayashi et al. 2002; Shirasuna et al. 2004). However,Flores with colleagues showed that the EDN1 system(EDN1, EDN A and EDN converting enzymes) exists inthe bovine CL through the oestrous cycle and PGF 2aincreased EDN1 mRNA expression in vivo only at 10 hafter treatment (Wright et al. 2001). In fact, Schamset al. (2003) showed that up-regulation of EDN1 andANG-2 occurred mainly during structural CL regression.Therefore, it has been suggested that EDN1 isinvolved in the process of structural CL regression bypromoting leucocyte migration and stimulating macrophagesto release cytokines [i.e. tumour necrosis factor a(TNF-a), interferon c (IFN-c); Meidan et al. 1999,2005].CytokinesImmune cells infiltrating the bovine CL play a centralrole in structural luteolysis of both steroidogenic andendothelial CL cells (Friedman et al. 2000; Pate andLandis Keyes 2001; Pate 2003). The number of leucocytes(i.e. T lymphocytes, macrophages) increased at thetime of structural luteolysis (Penny et al. 1999; Towsonet al. 2002). Shaw and Britt (1995) using a CL microdialysissystem showed that TNF-a is released duringspontaneous and PGF 2a -induced luteolysis in cows.Then, it was shown that the mRNAs for TNF-a and itsspecific receptors (TNFR type-I) are present in thebovine CL during luteolysis (Sakumoto et al. 2000;Neuvians et al. 2004). Tumour necrosis factor a incombination with IFN-c reduced P4 production andinduced apoptosis and PGF 2a production by luteal cellsin vitro (Sakumoto et al. 2000; Petroff et al. 2001;Korzekwa et al. 2006). Specific binding sites for TNFaare also present in endothelial cells derived frombovine CL (Okuda et al. 1999). Furthermore, TNF-ainduces EDN1 production by endothelial cells that maylead to structural regression of the CL (Okuda et al.1999; Friedman et al. 2000). Tumour necrosis factor aacting via TNFR type-I induces apoptotic death ofsteroidogenic (Petroff et al. 2001) and endothelial cells(Friedman et al. 2000) of bovine CL. However, some invitro studies indicated that TNF-a induces luteolysisonly in combination with INFc or other factors (i.e.EDN1; Petroff et al. 2001; Korzekwa et al. 2006).Therefore, we tested whether TNF-a acts as a luteolyticfactor in vivo, and whether it changes the lifespan ofbovine CL (Skarzynski et al. 2003a). Lower doses ofTNF-a increased PGF 2a and nitrite ⁄ nitrate (stablemetabolites of NO), decreased P4 level and consequentlyresulted in shortening of the oestrous cycle. Surprisingly,higher doses of TNF-a stimulated the synthesis of P4and PGE 2 and consequently resulted in prolongation ofthe oestrous cycle (Skarzynski et al. 2003a). However,inhibition of PG synthesis by indomethacin, a cyclooxygenase(COX; PTGS) inhibitor, injected into the aortaabdominalis, blocked the actions of TNF-a indicatingthat TNF-a acts mainly through mediation by arachidonicacid metabolites (Skarzynski et al. 2007). Inaddition to TNFR, other cytokine membrane receptors,second messengers, including calcium ions [Ca 2+ ] i andregulatory proteins are involved in apoptosis of steroidogenicand endothelial CL cells (Meidan et al. 1999;Petroff et al. 2001; Taniguchi et al. 2002). Fas ligand, amember of the TNF super family, primarily engages itsreceptors (Fas) to induce apoptosis (Taniguchi et al.2002; Okuda et al. 2004). The expression of Fas mRNAwas increased by IFN-c, and TNF-a augmented thestimulatory action of IFN-c on Fas expression (Taniguchiet al. 2002). Moreover, apoptotic bodies wereobserved in luteal cells treated with Fas L in thepresence of IFN-c and ⁄ or TNF-a, showing that leucocyte-derivedTNF-a and IFN-c play important roles inFas L-Fas-mediated luteal cell death in the bovine CL.Nitric oxideNADPH-d localization [a marker for nitric oxidesynthase (NOS)] and immunostaining of both isoformsof NOS [inducible (iNOS) and endothelial (eNOS)] weredetected in steroidogenic cells and in blood vessels of thebovine CL during the entire oestrous cycle withincreasing activity from the early to the late lutealphases (Skarzynski et al. 2003b). However, Rosiansky-Sultan et al. (2006) presented the highest level of eNOSand iNOS mRNA and protein expression in the earlyÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag