GABA mitigates mitochondrial apoptosis induced by high temperature stress in the Pacific oyster (Crassostrea gigas)

BackgroundHigh temperature is a critical environmental factor leading to mass mortality in oyster aquaculture in China. Recent advancements highlight the physiological regulation function of gamma-aminobutyric acid (GABA) in the adaptation of environmental stress.Methods and resultsThis study examined the physiological responses of the Pacific oyster (Crassostrea gigas) upon high temperature exposure, focusing on the histopathological changes in gill, the GABA concentration, the mRNA expression and activities of apoptosis-related genes. Following 24 h of exposure to seawater at 28 degrees C, notable histopathological changes, including cellular swelling and vacuolization, along with an increase in TUNEL-positive cells were observed in the oyster gill, compared to the control group maintained at 18 degrees C. Moreover, there was a significant increase in CgCaspase-3 transcripts, Caspase-3 and Caspase-9 activities in the gills, glutamate decarboxylase CgGAD transcripts in the haemocytes, and GABA concentrations in the haemolymph supernatant. Intervention with GABA markedly ameliorated these responses, including reducing the mRNA expression levels of CgBax, CgBak, CgCaspase-3, and CgCaspase-9, as well as the activities of Caspase-3/9. Furthermore, after the treatment with GABAA and GABAB receptor antagonists, the activities and expression levels of Caspase-3 and Caspase-9 significantly up-regulated under hightemperature stress. GABA treatment also significantly diminished the increased Caspase-3 activity by mitochondrial pathway apoptosis inducers.ConclusionsHigh temperature induced mitochondrial pathway apoptosis via increased caspase activities. The transcripts of CgGAD in haemocytes and GABA concentration in hemolymph supernatant also increased after high-temperature stress. GABA countered these effects through the activation of GABAA and GABAB receptors, reducing both caspase activity and expression of apoptosis-related genes.