PCB 37 (3,4, 4’-trichlorobiphenyl) increased apoptosis and modulated neuronal morphogenesis in primary rat cortical neuron-glia cocultures in a concentration-, sex-, age-, and CREB-dependent manner

Abstract

Higher-chlorinated (HC) polychlorinated biphenyls (PCBs) are known developmental neurotoxicants. In contrast, there are limited data regarding the developmental neurotoxicity of lower-chlorinated (LC) PCBs despite the increasing environmental prevalence and detection of LC-PCBs in contemporary human tissues, including the perinatal brain. This study characterized the neurotoxic effects of the LC-PCB congener PCB 37 in primary male and female rat cortical neuron-glia co-cultures. Cultures were exposed to varying concentrations of PCB 37 for 48 h beginning on day in vitro 0 or 7. Cell viability was assessed by measuring lactate dehydrogenase release into the culture medium and the percentage of live cells identified using Calcein-AM and Hoechst staining. Apoptosis was measured using fluorometric assays of caspase 3/7 activity and Annexin V binding. Axonal and dendritic growth were quantified in neurons immunostained for Tau-1 or transfected with MAP2B-red fluorescent protein, respectively, using automated image analysis protocols. At environmentally relevant concentrations (0.0001, 0.1, and 100 nM) that did not affect cell viability, PCB 37 caused sex-, age-, and concentration-dependent increases in apoptosis, axonal, and dendritic growth. Pretreatment with the CREB inhibitor 666–15 (500 nM) blocked the effects of PCB 37 on apoptosis and dendritic morphology but not axonal growth. These findings suggest that the pro-apoptotic and dendrite-promoting effects of PCB 37 are mediated by CREB signaling, but that CREB-independent mechanisms underlie PCB 37 effects on axonal growth. Overall, these findings identify PCB 37 as a potential developmental neurotoxicant and further support increasing evidence identifying CREB as a convergent mechanism of developmental neurotoxicity.