Relationship between bcl-2, bax, beclin-1, and cathepsin-D proteins during postovulatory follicular regression in fish ovary

Abstract

In fish ovaries, postovulatory follicles (POFs) are key biomarkers of breeding and provide an interesting model for studying the relationship between autophagy and apoptosis. In this study, we investigated the immunohistochemical expression of autophagic and apoptotic proteins to improve the knowledge on the mechanisms regulating ovarian remodeling after spawning. Females from three neotropical fish species kept in captivity were submitted to hormonal induction. After ova stripping, ovarian sections were sampled daily until 5 days postspawning (dps). Similar events of POF regression were detected by histology, terminal transferase-mediated dUTP nick-end labeling (TUNEL), and electron microscopy in the three species: follicular cells hypertrophy, progressive disintegration of the basement membrane, gradual closing of the follicular lumen, theca thickening, and formation of large autophagic vacuoles preceding apoptosis of the follicular cells. Autophagic and apoptotic proteins were assessed by immunohistochemistry. Morphometric analysis of the immunolabeling revealed a more intense reaction for bcl-2 and beclin-1 (BECN1) in POFs at 0 to 1 dps and for bax at 2 to 3 dps (P < 0.001), the later period being the peak of apoptosis of the follicular cells. The immunostaining for cathepsin-D was more elevated until 2 to 3 dps and decreased significantly at 4 to 5 dps, when the POFs were in late stage of regression. Double labeling for BECN1 and caspase-3 indicated a shift in the relationship between autophagy and apoptosis at 2 to 3 dps, a critical period in determining the fate of follicular cells in POFs. Together, these results indicate that the bcl-2 family, BECN1, and cathepsin-D can be involved in the regulation of ovarian remodeling in teleost fish.

Autophagy and Cathepsin D mediated apoptosis contributing to ovarian follicular atresia in the Nile tilapia

“…Apoptosis can be identified through typical morphological characteristics such as chromatin condensation around the nuclear envelope, loss of cell–cell and cell–basal lamina adhesion, and cell fragmentation into apoptotic bodies (Drummond, Bazzoli, Rizzo, & Sato, ; Elmore, ; Morais et al, ; present study). The internucleosomal DNA cleavage pattern (DNA ladder) in apoptosis was also found in atretic ovaries (Santos et al, ).…”

“…In support of this hypothesis, we observed follicular cells with highly electron-lucid cytoplasm and a shortage of organelles under the electron microscope. In some models, an (Drummond, Bazzoli, Rizzo, & Sato, 2000;Elmore, 2007;Morais et al, 2016;present study). The internucleosomal DNA cleavage pattern (DNA ladder) in apoptosis was also found in atretic ovaries (Santos et al, 2008).…”

“…However, nonapoptotic processes, such as autophagy, can contribute to the efficient elimination of granulosa cells in mammals (Repnik Meng et al, 2018). In teleost fish, recent studies indicate that autophagy can be involved in follicular atresia (Cassel, Camargo, Jesus, & Borella, 2017;Morais, Thomé, Lemos, Bazzoli, & Rizzo, 2012;Morais, Thomé, Santos, Bazzoli, & Rizzo, 2016;Thomé et al, 2009), but the interactions between these signaling pathways are not fully elucidated.…”

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“…Moreover, the maintenance of breeders in small boxes in laboratory under controlled conditions promotes a higher efficiency, control and organization for directed crosses for fish stocking and for genetic improving programs (HASHIMOTO et al, 2015). From a physiological point of view, the standardization of protocols for successive breedings allows a continuous production of fingerlings, thus avoiding long ovarian resting and regression periods, which are common in tropical migratory species (ABREU et al, 2015;MORAIS et al, 2016;PEREIRA et al, 2013;KURADOMI et al, 2017), such as A. altiparanae .…”

Alisol A 24-Acetate and Alisol B 23-Acetate Induced Autophagy Mediates Apoptosis and Nephrotoxicity in Human Renal Proximal Tubular Cells

“…Under basal conditions, Bcl-2 proteins were found to be constitutively bound to Beclin-1, and allowing only basal levels of autophagy to proceed ( Oral et al, 2016 ). The dissociation of Beclin-1 from Bcl-2 could be an important event to allow autophagy while cleavage of Beclin-1 mediated by caspase might promote apoptosis ( Morais et al, 2016 ). The functional relationship between autophagy and apoptosis is complex, and the relevant molecular mechanisms remain unclear.…”