A Cyanobacterial Toxin, Microcystin-LR, Induces Apoptosis of Sertoli Cells by Changing the Expression Levels of Apoptosis-Related Proteins

Abstract

Toxic cyanobacterial blooms in freshwater have been considered as threats to human health. Microcystins are a family of cyclic polypeptides produced by cyanobacteria and are toxic to plants and animals. Microcystin-LR (MC-LR) is the most toxic variant among the microcystin family and could cause oxidative stress in various organs, including the reproduction system. The aim of this study was to investigate the effect of MC-LR on apoptosis of Sertoli cells that play an essential role in the development and maturation of sperm cells. Sertoli cells were isolated from healthy immature rats and cultured with MC-LR. The viability of Sertoli cells was decreased after treatment with MC-LR at 10 μg/ml for 24 h (P < 0.05). Moreover, the MC-LR-treated cells exhibited condensed chromatin and fragmented nuclei, features of apoptosis, as judged by Hoechst 33258 staining. We also analyzed the mRNA and protein levels of three apoptosis-related genes, p53, bax and bcl-2, using reverse transcription-polymerase chain reaction and Western blot analyses, respectively. Both p53 and bax function as promoters of apoptosis, while bcl-2 is an apoptotic suppressor. The mRNA and protein expression levels of p53 and bax were increased in Sertoli cells treated with MC-LR at 10 μg/ml compared with the control group (P < 0.05), while the bcl-2 protein levels were decreased in cells treated with MC-LR at 10 μg/ml (P < 0.05). Moreover, caspase-3 activity that is involved in the induction of apoptosis was significantly increased in Sertoli cells treated with MC-LR. These results indicate that MC-LR induces apoptosis of Sertoli cells.

A review of reproductive toxicity of microcystins

“…MC-LR exposure also induced TUNEL-positive testicular cells in rats following chronic, sub-chronic and acute exposure [46,64,65]. MC-LR-induced apoptosis/necrosis of rat Sertoli cells [71][72][73], spermatogonia [68], Chinese hamster ovary (CHO) cells [76,77,80,81], and ovary cells of zebrafish [85] were also observed. Apoptosis of HeLa cells was also observed following exposure to MC-RR [82].…”

“…Recently, Sertoli cells have been speculated to be a potential target of MC-LR for male reproductive toxicity [51,[70][71][72][73][74]. The primary function of testicular Sertoli cells is to support and provide necessary nutrition for spermatogenic cells to promote spermatogenesis.…”

“…Thus, damage to Sertoli cells may lead to impairment of male reproduction. Recently, Chen et al [73] and Wang et al [51] reported that MC-LR can be observed entering primary cultured Sertoli cells by immunofluorescence detection and Western blotting, resulting in oxidative stress and cell injury [70][71][72][73]. MC-LR could induce autophagy and apoptosis in a dose-dependent manner [73].…”

“…Recently, many studies showed that MCs induced the apoptosis of testicular cells and that the expression of several apoptosis-related proteins was significantly changed, suggesting the important role of apoptosis in MC-induced reproductive toxicity [33,57,58,64,[71][72][73]. An apoptotic DNA ladder was detected in cultured rat Leydig cells by exposure to MC-LR [62].…”

Cyanobacterial Toxins of the Laurentian Great Lakes, Their Toxicological Effects, and Numerical Limits in Drinking Water

“…In addition to liver damage MCs have also been shown to affect brain and reproductive tissues [158,159,160,161,162,163,164,165,166,167]. Of note for risk analysis are those studies that examine effects from repeat oral dose exposures.…”