Integration of in vivo stress reporters with transcription profiling to define chemical mixtures mechanisms of toxicity, including trans-generational effects

Humans are exposed to mixtures of chemical pollutants from various environmental sources at all stages of life. Understanding how these compounds are causally linked to population health effects is challenging because of the ethical limitations on studying controlled human exposures and the complexity of the many potential molecular mechanisms involved. We hypothesized that studies using a combination of in vivo murine stress reporter models together with non-targeted global transcriptome analysis will define the toxic mechanisms of complex chemical mixtures in a physiological context. To test this hypothesis, a panel of stress reporter mice were subjected to a mixture of polychlorinated biphenyls (PCBs), persistent environmental pollutants typified by Aroclor 1254 (A1254). In time-dependent and trans-lactational exposure studies we observed activation of stress responses in liver using reporters for Cyp1a1 (aryl hydrocarbons receptor, AHR pathway) and Hmox1 (oxidative stress and inflammation). Whole liver transcriptional analysis revealed distinct Aroclor 1254-linked signatures including xenobiotic metabolism (AHR, CAR/PXR), oxidative stress (Nrf2), cell proliferation, and carcinogenesis. A combination of genetic and biochemical approaches revealed that NRF2 does not mediate Hmox1 activation following A1254 exposure but plays a major role in regulating the expression of genes involved in mitosis. We further demonstrate the utility of our reporter approach to detect the activation of stress responses in mouse neonates exposed to A1254 by lactational transfer. Intriguingly, we observed robust Hmox1 reporter activation in neonate livers for up to two generations following initial maternal exposure. Thus, we exemplify how a combination of in vivo reporter and transcriptional analysis captures novel mechanistic insights into the effects of chemical mixtures of persistent organic pollutants in a relevant physiological context and with cellular resolution, after both primary exposure and in a transgenerational manner. This approach may be applied to understand the full spectrum of mechanisms of toxicity of other chemical mixtures of concern in the physiological context.