Benzo[a]pyrene‐decreased gap junctional intercellular communication via calcium/calmodulin signaling increases apoptosis in TM4 cells

Abstract

The mechanism of male reproductive toxicity induced by benzo[a]pyrene (BaP) is poorly understood. Gap junctional intercellular communication (GJIC) is known to play a critical role in maintaining spermatogenesis. The aim of the present study was to determine the toxic effects of BaP in Sertoli cells, and to explore the possibility and potential mechanisms of BaP-induced changes in the level of GJIC, and the relationship between GJIC and BaP-induced apoptosis. We treated mouse Sertoli cell lines (TM4) with different concentrations (0.1-100 μm) of BaP for 1-48 hours, and found that GJIC exhibited a dose- and time-dependent downregulation. Treatment with 10 μm BaP increased apoptosis, intracellular Ca level ([Ca ] ) and calmodulin (CaM) protein expression, and decreased the protein level of connexin 43 (Cx43) (also known as gap junction α-1 protein [GJA1]) in TM4 cells. However, BaP had no effect on the phosphorylation of Cx43 at Ser279/282, Ser255, Ser368 or Ser262. Downregulation of [Ca ] by BAPTA-AM significantly attenuated the BaP-induced GJIC suppression, Cx43 protein decrease and CaM protein increase. Interestingly, inhibition of CaM expression by W7 partially recovered BaP-induced GJIC inhibition, but had no effect on BaP-induced Cx43 protein decrease. Pretreatment with the GJIC activator retinoic acid significantly mitigated BaP-induced apoptosis. In conclusion, these results suggest that BaP can decrease GJIC via Ca /CaM signaling, and that BaP-induced GJIC suppression increases apoptosis in TM4 cells.

Downregulation of gap junctional intercellular communication and connexin 43 expression by bisphenol A in human granulosa cells

“…3A). It has been reported that GJIC might be affected by cell density difference of <80% [39]. When GC/M‐AO cells were exposed to 10 −7 M BPA for 24 and 48 H, the number of viable cells was ≥90% compared with controls.…”

Abnormal methylation of spermatozoa induced by benzo(a)pyrene in rats

“…BaP: benzo(a)pyrene; KEGG: Kyoto Encyclopedia of Genes and Genomes. 17 Similar studies have been done on male scallop Chlamys farreri and found that BaP affects steroid levels and induces gonadal toxicity at ambient concentrations. 18 Overall, BaP can cause damage to the male reproductive system, and its mechanism may be related to decreased sex hormone levels and increased apoptosis of reproductive cells.…”

Melatonin supplementation protects against the benzo(e)pyrene cytotoxicity and optic cup formation disruption in chicken embryos

“…It seems that the disturbance of optic cup formation caused by benzo(e)pyrene may not associate to a direct reduction of the extracellular calcium levels or the calmodulin inhibition. On the other hand, an increased cytosolic calcium and expression of calmodulin protein induced by benzo(e)pyrene trigger the post excision embryonic cells death and by this has been observed in other animal studies (59)(60). In porcine retinal arterioles, benzo(e)pyrene had a vasodilator effect caused by superoxide production and endoplasmic reticulum stress (61).…”

“…Benzo(e)pyrene increases the cytosolic calcium levels in the human T cells and endothelial HMEC-1 cells, but a reduction in the extracellular calcium levels was not observed in these cells in the in vitro systems (56)(57)(58). In mouse Sertoli cell lines (TM4) benzo(a)pyrene (0.1-100 µmol l -1 ) triggered apoptosis by increase the intracellular calcium levels and calmodulin expression (59). It seems that the disturbance of optic cup formation caused by benzo(e)pyrene may not associate to a direct reduction of the extracellular calcium levels or the calmodulin inhibition.…”