Histological evaluation and In situ localization of apoptosis in fresh and cryopreserved ovarian tissue

Objective:To study the feasibility of using combined morphology and terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick-end labeling (TUNEL) for apoptosis detection and the impact of cryopreservation on this process.
Materials and methods: We conducted this investigation using a porcine animal model. Bilateral oophorectomy was performed in eight sows. The ovarian tissues were divided into two parts; one part was immediately fixed while the other was cryopreserved. The cryopreserved specimens were subsequently thawed and then fixed. All the specimens were sectioned, fixed and stained with H&E. The ovarian follicles were counted, histologically categorized as healthy and atretic and evaluated for the presence of apoptosis. Then, in situ examination of apoptosis was performed using TUNEL assay.
Results: In the cryopreserved tissues: 1) the count of the primordial follicle was significantly reduced as compared to freshly- fixed samples (4.9±5.3 vs. 7.2±5.4, p=0.03 respectively) and 2) the mean values of apoptosis were insignificantly higher when compared to the freshly-fixed group (p=0.74). Moreover: 1) apoptosis was found in the atretic, but not in the healthy follicles (primordial, primary and secondary); 2) the nuclei of the granulosa cells, but not those of theca or stromal cells, were TUNEL positive; 3) some cells with histological features of necrosis and apoptosis were TUNEL negative, and 6) The distribution of apoptosis was not different between cryopreserved tissue and freshly fixed tissue.
Conclusions: the presence of apoptosis in the atretic follicles may suggest its involvement in follicular atresia; and 2) combined histology and TUNEL assay may be a useful method for detection of apoptosis.