AMPK gene expression and caspase-3 activity points to autophagy/symbiophagy as the main bleaching pathway in P. acuta
Bcl-2 gene is involved in both apoptosis and autophagy pathways (Xu et al., 2013). In order to distinguish between these two programmed cell death pathways, we analyzed activity of caspase-3, one the key apoptotic effector proteases. We performed caspase-3 activity test in thermally stressed PC and NPC corals at times 0, 3 days and 5 days, and in PC and NPC corals treated with venetoclax to exclude the switch in PCD pathways upon treatment. Both PC and NPC corals showed slightly increased caspase-3 activity under thermal stress, but significantly lower compared to colchicine-induced apoptosis (Fig. 5A).
Moreover, we analyzed expression profile of pAMPK (adenosine monophosphate-activated protein kinase), a major signal inducer of autophagy pathway, triggered by ROS(Villanueva-Paz et al., 2016).pAMPK was significantly upregulated at 6 hours post-stress in NPC vs PC (p = 0.010) and after 24 hours we observed a gradual increase in AMPK levels in NPC, peaking at 72 hours with almost three times higher mean expression than in PC corals (p = 0.077) (Fig. 5B).