Developmental nicotine exposure precipitates multigenerational maternal transmission of nicotine preference and ADHD-like behavioral, rhythmometric, neuropharmacological, and epigenetic anomalies in adolescent mice

Abstract

Maternal smoking during pregnancy, a form of developmental nicotine exposure (DNE), is associated with increased nicotine use and neurodevelopmental disorders such as ADHD in children. Here, we characterize the behavioral, rhythmometric, neuropharmacological, and epigenetic consequences of DNE in the F1 (first) and F2 (second) generation adolescent offspring of mice exposed to nicotine prior to and throughout breeding. We assessed the effects of passive oral methylphenidate (MPH) administration and voluntary nicotine consumption on home cage activity rhythms and activity and risk-taking behaviors in the open field. Results imply a multigenerational predisposition to nicotine consumption in DNE mice and demonstrate ADHDlike diurnal and nocturnal hyperactivity and anomalies in the rhythmicity of home cage activity that are reversibly rescued by MPH and modulated by voluntary nicotine consumption. DNE mice are hyperactive in the open field and display increased risk-taking behaviors that are normalized by MPH. Pharmacological characterization of nicotinic and dopaminergic systems in striatum and frontal cortex reveals altered expression and dysfunction of nicotinic acetylcholine receptors (nAChRs), hypersensitivity to nicotine-induced nAChR-mediated dopamine release, and impaired dopamine transporter (DAT) function in DNE mice. Global DNA methylation assays indicate DNA methylome deficits in striatum and frontal cortex of DNE mice. Collectively, our data demonstrate that DNE enhances nicotine preference, elicits hyperactivity and risk-taking behaviors, perturbs the rhythmicity of activity, alters nAChR expression and function, impairs DAT function, and causes DNA hypomethylation in striatum and frontal cortex of both first and second-generation adolescent offspring. These findings recapitulate multiple domains of ADHD symptomatology.

Developmental nicotine exposure engenders intergenerational downregulation and aberrant posttranslational modification of cardinal epigenetic factors in the frontal cortices, striata, and hippocampi of adolescent mice

“…DNMT3A maintains and establishes DNA methylation marks, and previous research reveals co-occurring DNMT3A deficits and global DNA hypomethylation in neurodevelopmental disorder-related brain regions of first-generation DNE mice [59,73]. Therefore, we suspected that the global DNA methylome deficits which we previously reported in first-and second-generation DNE progeny may stem from the multigenerational transmission of DNE-induced DNMT3A deficits [39]. To test this hypothesis, we performed immunoblot analyses to compare DNMT3A abundance, expressed as percentage relative optical density versus the mean F1 Veh control value, in the frontal cortices, striata, and hippocampi of first-and second-generation adolescent DNE mice versus F1 Veh controls.…”

“…Previously described protocols for the breeding of mice and collection of tissues are diagrammed in Fig. 1 and detailed in "Methods" section [39,40]. Briefly, F0 dams received either nicotine (200 µg/mL in 0.2% saccharin) or vehicle (0.2% saccharin) as the sole source of fluid Procedural timeline for breeding and tissue collection.…”

“…Collectively, prior studies implicate an ensemble of DNA methylomic and histonomic alterations in the etiology of ADHD, autism, and schizophrenia, in the heightened risk for neurodevelopmental disorders in DNE children and grandchildren, and in the ADHD-, autism-, and schizophrenia-like phenotypes exhibited by first-generation DNE offspring. While we have previously demonstrated corticostriatal global DNA hypomethylation in DNE offspring and grandoffspring, no prior studies have examined the multigenerational impacts of DNE on epigenetic factors such as DNA-methylating, DNA-demethylating, methylated DNA-binding, or histone-modifying proteins [39]. Given that neurodevelopmental disorders and DNE are associated with dysfunction of DNMT3A, TET2, MeCP2, and HDAC2, we posited that dysregulation of these proteins may contribute to the increased risk of neurodevelopmental disorders in DNE children and grandchildren as well as the neurodevelopmental disorder-like phenotypes exhibited by rodent DNE offspring and grandoffspring.…”

“…Contemporary research indicates that DNE alters the transcription and expression of the epigenetic factors DNA methyltransferase 3A (DNMT3A) and ten-eleven translocase methylcytosine dioxygenase 2 (TET2) in rodent offspring [59,71,72]. Given that DNMT3A and TET2 reciprocally regulate DNA methylation via catalysis of de novo DNA methylation and demethylation, respectively, downregulation of DNMT3A and/or upregulation of TET2 could mediate the multigenerational global DNA methylome deficits and associated neurobehavioral phenotypes that we have previously identified in adolescent DNE mice [39,40,73,74]. In support of this inference, alterations in corticostriatal and hippocampal DNMT3A and TET2 expression perturb the DNA methylome and thereby disrupt neurodevelopment, neuroplasticity, and synaptogenesis, elicit neurodegeneration, impair learning, memory, and cognition, and modify anxiety, stress responsivity, and emotional behaviors, and this cascade of DNMT3A and TET2 downregulation-induced DNA methylome perturbation occurs in neurodevelopmentally disordered and DNE children as well as animal models thereof [1,35,37,38,59,67,.…”

“…Similarly, DNA methylomic alterations are also linked to BDNF and HPA axis deficits in neurodevelopmental disorders as well as in DNE children and animal models [32-34, 36-38, 67-70]. Building upon this research, we recently documented corticostriatal global DNA methylome deficits in first-and secondgeneration adolescent DNE mice that co-occur with the multigenerational transmission of neurodevelopmental disorder-like behavioral perturbations, nAChR and DAT dysfunction, proBDNF/BDNF imbalance, furin deficits, and atypical glucocorticoid receptor activity [39,40]. In light of this evidence, perturbed DNA methylation patterns represent a putative mechanistic basis for the predisposition to neurodevelopmental disorders in the children and grandchildren of maternal smokers.…”