Studies between lipotoxicity and very low density lipoprotein (VLDL) secretion in heat-stressed chicken follicular granulosa cells

報告時間：2025-6-20
報告地點：Room 407
指導老師：Shuen-Ei Chen
學生：Nguyen Thanh Ngan
摘要

In birds, follicle atresia is initiated from granulosa cell (GC) death, which is tightly associated with ovarian regression and thereby   poor egg production and thus notable economic loss in the poultry industry. Heat stress (HS) stands out among environmental stressors as a potent cue to induce granulosa cell death and thus a higher incidence of follicle atresia and poor laying performance. Heat stress has been shown to elevate cellular ceramide (Cer) levels. Ceramide is a central molecule in sphingolipid metabolism functioning as a second messenger to activate PKC-zeta pathway. Ceramide can be synthesized through two main pathways; the de novo pathway through serine palmitoyltransferase (SPT), or via the hydrolysis of sphingomyelin (SM) by neutral and acidic sphingomyelinase (nSMase/aSMase), particularly HS. The turnover between Cer and SM is tightly associated with cell fate. Sphingomyelin is a key structural lipid in the plasma membrane that supports lipid raft formation. The generation of Cer can compromise membrane stability and initiate apoptosis. Lipotoxicity is characterized by disruption of cellular lipid homeostasis, leading to accumulation of free fatty acids, triacylglycerol, and bioactive lipid intermediates such as diacylglycerol and ceramide, which can provoke oxidative stress inflammation, and death signalling and ultimately lead to cell death. Our previous studies demonstrated that chicken follicular granulosa, theca, and epithelial cells possess functional microsomal triglyceride transfer protein (MTTP) and apolipoprotein B (apoB) to support VLDL assembly and secretion and exposure to HS promotes MTTP activity and apoB expression, and resultant VLDL secretion. Despite the well documented role of Cer to mediate HS-induced cell apoptosis, turnover between Cer and SM, significance of VLDL secretion by chicken follicle cells in response to HS, and sphingolipid metabolism and VLDL secretion in respect to lipotoxicity and cell fate under HS remains further studies. This study aims to examine the complex interactions among sphingolipids pathway, specifically focusing on the dynamics between Cer and SM turnover and their relationship with VLDL secretion in respect to lipotoxicity of GCs under HS conditions. In the present results, under exposure to HS (42 ºC) for 3 hrs and then allowed recovery (37 ºC) for 0, 2, 5 and 13 hrs, the cell viability of GCs was significantly reduced at 13 hr recovery after HS. Cellular SM and Cer levels was decreased and increased, respectively, along the time course. These findings suggest that HS operates at Cer accumulation and SM catabolism to prime GC apoptosis. Pharmacological inhibition of VLDL secretion rescued GC viability under prolonged HS over 8 hrs, suggesting that cargo lipid export is involved in HS-affected cell fate.

Keywords: chicken granulosa cell, heat stress, cell death, VLDL, lipotoxicity
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