PARENT SESSION
PLATFORM SESSION 16: LUTEAL STEROIDOGENESIS AND MORPHOLOGY
Chair: Komar, Carolyn¹, ¹
Co-chair: Clamon, Laura¹, ¹
Grand Ballroom I-IV
2:00 PM-4:00 PM

(413) UNDERSTANDING SIGNALLING EVENTS DURING CL APOPTOSIS.

Dharmarajan, Arun¹, Hisheh, Susan¹, Abdo, Michael¹, ¹ School of Anatomy & Human Biology, Perth, AU

ABSTRACT- The complexities of the apoptosis pathways arise from variation in the cellular specialisation and initial stimulus. Corpus luteum (CL) regression is facilitated through apoptosis though the apoptosis pathways within the CL are poorly understood. Here we report on the role of tumor necrosis factor- (TNF) in CL apoptosis. TNF-induced cell death is governed by the presence of the two TNF receptors and several second messenger systems that include; the sphingolipids, mitogen-activated protein (MAP) kinases and caspases. These factors and their interaction were assessed in the rat CL during pregnancy and in vitro. During pregnancy TNF protein expression increased prior to the onset of CL apoptosis, which correlated with increased expression of the chemotactic factor monocyte chemoattractant protein -1 (MCP-1) and the functional regression of the CL. The functional regression of the CL was assessed by measurement of both progesterone synthesis and steroidogenic acute regulatory (StAR) protein expression. Immunohistochemical studies revealed the presence of both TNF receptors in luteal cells. Subsequently, the role of the sphingolipids ceramide and sphingosine, the MAP kinases and the caspases was examined during induced CL apoptosis in vitro. Ceramide and sphingosine were found to be potent apoptotic agents when administered in vitro (50 M). Treatment with either TNF or ceramide increased expression of the pro-apoptotic MAP kinase p38 with no change to the non-apoptotic extracellular-signal related kinase (ERK 1&2). General inhibition (10 mM - 1M) of the caspase cascade in vitro was effective in preventing apoptosis regardless of the apoptotic stimulus, though specific inhibition (50 M) of caspase 3, 6, and 8 significantly reduced the level of TNF-induced apoptosis. The results suggest that elements of the TNF cell death pathway which exist in other tissues and cell systems also play a role in rat CL apoptosis. TNF plays an integral part in CL regression through the activation of the caspases, the sphingolipids ceramide and sphingosine and the MAP kinases.

KEY WORDS: corpus luteum, apoptosis, tumor necrosis factor - alpha, signalling