Autophagy and Apoptosis Act as Partners to Induce Germ Cell Death after Heat Stress in Mice

Abstract

Testicular heating suppresses spermatogenesis which is marked by germ cell loss via apoptotic pathways. Recently, it is reported that autophagy also can be induced by heat treatment in somatic cells. In this study, the status of autophagy in germ cells after heat treatment, as well as the partnership between autophagy and apoptosis in these cells was investigated. The results demonstrated that besides initiating apoptotic pathways, heat also induced autophagic pathways in germ cells. Exposure of germ cells to hyperthermia resulted in several specific features of the autophagic process, including autophagosome formation and the conversion of LC3-I to LC3-II. Furthermore, the ubiquitin-like protein conjugation system was implicated as being likely responsible for heat-induced autophagy in germ cells since all genes involving this system were found to be expressed in the testes. In addition, the upstream protein in this system, Atg7 (Autophagy-related gene 7), was found to be expressed in all types of spermatogenic cells, and its expression level was positively correlated with the level of autophagy in germ cells. As a result, Atg7 was selected as the investigative target to further analyze the role of autophagy in heat-induced germ cell death. It was shown that down expression of Atg7 protein resulted in the notable decrease in the level of autophagy in heat-treated germ cells, and this down-regulation of autophagy caused by Atg7 knockdown further reduced the apoptotic rate of germ cells. These results suggest that autophagy plays a positive role in the process of germ cell apoptosis after heat treatment. In conclusion, this study demonstrates that heat triggers autophagy and apoptosis in germ cells. These two mechanisms might act as partners, not antagonist, to induce cell death and lead to eventual destruction of spermatogenesis.

The autophagy-related protein LC3 is processed in stallion spermatozoa during short-and long-term storage and the related stressful conditions

“…In stallion spermatozoa, STF-62247 and rapamycin induced a significant decrease in viability, whereas chloroquine and 3-MA had no effect on this parameter. Our results are in accordance with those published by Zhang et al (2012), where autophagy-induced germ cell death after heat stress in mice.…”

“…LC3 protein is processed under stress in sperm Zhang et al, 2012). Therefore, our next objective was to investigate whether autophagy was activated as a survival mechanism or, in opposition, was induced to produce cell death.…”

Heat shock response and autophagy—cooperation and control

“…81 Later, by utilizing different cellular techniques and models, it was shown that heat stress, as high as 43 C, induces autophagy. 82 Heat exposure also triggers autophagy in a human hepatoma cell line, 83 rat cardiomyocytes, 84 human alveolar basal epithelial cells, 5 a mouse spermatocyte cell line, 85 and human cervical cancer cells. 86 Moreover, recent studies have shown that deletion of the heat shock transcription factor 1 (HSF1), increases basal autophagy levels.…”

NVP-BEZ235, a novel dual PI3K/mTOR inhibitor, enhances the radiosensitivity of human glioma stem cells in vitro

“…Autophagy and apoptosis together induce cell death [30] and enhance radiosensitivity [31] . Apoptosis can also be induced via enhanced autophagy [32] .…”