Functional interplay between endoplasmic reticulum stress and mitochondrial activity in a post-ovulatory aging model...

To investigate whether targeting the ER-mitochondria axis can improve embryonic development in a post-ovulatory aging (POA) model by evaluating organelle-specific modulation.

Fresh oocytes were collected immediately after ovulation, and post-ovulatory aged oocytes were obtained using a mouse model. Fresh oocytes were treated with thapsigargin (an ER stress inducer) or CCCP (a mitochondrial inhibitor), and ER stress (GRP78 fluorescence) and mitochondrial superoxide status (MitoSOX™ fluorescence) were assessed. Aged oocytes were treated with salubrinal (an ER stress modulator), 5-aminolevulinic acid (5-ALA, a mitochondrial modulator), or both. Embryonic development was evaluated via blastocyst formation and cell death rates.

In fresh oocytes, CCCP increased GRP78 fluorescence, and thapsigargin increased MitoSOX fluorescence, consistent with bidirectional ER-mitochondria stress propagation. In POA oocytes, salubrinal reduced GRP78 fluorescence but not MitoSOX, whereas 5-ALA reduced MitoSOX fluorescence but not GRP78; the combined treatment showed no additive effects on either proxy marker. Despite the lack of additivity at the marker level, blastocyst formation increased and apoptosis decreased in all treatment groups, with no additional benefit of combined treatment compared with single agents.

In this POA model, ER-mitochondria coupling detected in freshly ovulated oocytes appeared attenuated. While our single-marker readouts (GRP78 and MitoSOX) are limited proxies, independent targeting of either organelle modestly improved blastocyst formation. These data support a hypothesis-generating framework for future studies in maternal aging models. Results were obtained under 20% O₂ culture and may be conservative relative to physiologic (5%) O₂ conditions.