急性热应激重塑牛颗粒细胞线粒体超微结构及时间依赖性转录组图谱

Abstract

Heat stress is a major environmental challenge that reduces fertility in dairy cows, yet the early cellular events triggered by elevated temperature remain poorly understood. To investigate the molecular and structural responses of bovine granulosa cells—the cells that surround and support the developing egg—we exposed them to a high temperature (43 °C) for short periods (10, 20, 30, and 40 min). Observations revealed that heat stress caused swelling of mitochondria, the energy-producing units of the cell, and disrupted calcium balance, with calcium levels rising first, then falling as exposure continued. Using RNA sequencing, we identified 185 genes that changed after 20 min and 831 genes after 40 min of heat exposure, revealing a dramatic time-dependent amplification of the cellular stress response. Many of the affected genes are involved in heat protection, cell survival, inflammation, and hormone production. These findings provide new insights into how heat stress impairs ovarian function at the very early stages and may help develop strategies to protect dairy cow fertility during hot summer months. Heat stress is a critical environmental factor that compromises reproductive performance in dairy cattle, primarily through deleterious effects on ovarian follicular cells. Granulosa cells (GCs), which provide essential nutritional and hormonal support for oocyte maturation, are particularly vulnerable to hyperthermic insult. However, the early molecular and subcellular events that precede overt cellular dysfunction remain inadequately characterized. This study aimed to investigate the temporal dynamics of mitochondrial morphological alterations and transcriptomic reprogramming in bovine GCs subjected to acute in vitro heat stress. Bovine GCs were exposed to 43 °C for 10, 20, 30, or 40 min, with untreated cells serving as controls. Heat shock protein expression (HSP90 and HSPA1A) was evaluated by qRT-PCR. Intracellular calcium concentration was measured using the F