Repeated exposure to neurotoxic levels of chlorpyrifos alters hippocampal expression of neurotrophins and neuropeptides

• Published in: Toxicology (Amsterdam) Vol. 340; pp. 53 - 62
• Main Authors: Lee, Young S, Lewis, John A, Ippolito, Danielle L, Hussainzada, Naissan, Lein, Pamela J, Jackson, David A, Stallings, Jonathan D
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier Ireland Ltd 18-01-2016
• Subjects: Animals; CA1 Region, Hippocampal - drug effects; CA1 Region, Hippocampal - metabolism; Chlorpyrifos; Chlorpyrifos - toxicity; Cholinergics; Cholinesterase; Cholinesterase inhibition; Cholinesterase Inhibitors - toxicity; Cholinesterases - metabolism; Emergency; Exposure; Gene expression; Gene Expression Profiling - methods; Gene Expression Regulation; Genes; Hippocampus; Immunohistochemistry; Insecticides - toxicity; Male; Microarray; miRNA; Nerve Growth Factors - genetics; Nerve Growth Factors - metabolism; Neuropeptides - genetics; Neuropeptides - metabolism; Neurotoxicity Syndromes - etiology; Neurotoxicity Syndromes - genetics; Neurotoxicity Syndromes - metabolism; Oligonucleotide Array Sequence Analysis; Organophosphorus pesticide; Pesticides; Rats, Long-Evans; RNA, Messenger - metabolism; RNA, Untranslated - metabolism; Signal Transduction - drug effects; Time Factors; synaptotagmin 4; cholinesterase; fold change of difference; neuropeptide Y; SEC23-related protein A; PTEN; Long Evans; Microarray; sequencing; subcutaneous; body weight; gene ontology; CRHBP; MDK; ADORA1; cadherin 13; acyl-coA oxidase 1; SRGN; MAP2K4; corticotropin-releasing factor-binding protein; gamma-aminobutyric acid receptor; brain derived neuronal factor; slit homolog 3; DYRK1A; s.c; aRNA; phosphatase and tensin homolog; Gene expression; GABRG2; SEPT3; CORT; cortistatin; ACOX1; MAP1B; MADD; CDH13; midkine; spectrin; dual specificity tyrosine-phosphorylation-regulated kinase 1A; adenosine a1 receptor; FC; SEC23A; ADCYAP1R1; a-kinase anchor protein 6; pituitary adenylate cyclase-activating polypeptide receptor; Organophosphorus pesticide; potassium ethylene diamine tetraacetic acid; AKAP6; prepronociceptin; organophosphorus; mitogen-activated protein kinase kinase 4; K 2-EDTA; multiple acyl-coA dehydrogenase deficiency; FDR; NPY; MAPK1; miRNA; SLIT3; NPTX2; false discovery rate; seq; SPTBN1; OP; ChE; SYT4; septin 3; SYT1; BDNF; DEG; antisense RNA; GO; differentially expressed gene; b.w; microtubule-associated protein 1B; synaptotagmin-1; chlorpyrifos; Cholinesterase inhibition; neuronal pentraxin II; PNOC; CPF; LE; mitogen-activated protein kinase 1; serglycin; Chlorpyrifos; K2-EDTA
• ISSN: 0300-483X; 1879-3185
• DOI: 10.1016/j.tox.2016.01.001

Abstract Chlorpyrifos (CPF), an organophosphorus pesticide (OP), is one of the most widely used pesticides in the world. Subchronic exposures to CPF that do not cause cholinergic crisis are associated with problems in cognitive function (i.e., learning and memory deficits), but the biological mechanism(s) underlying this association remain speculative. To identify potential mechanisms of subchronic CPF neurotoxicity, adult male Long Evans (LE) rats were administered CPF at 3 or 10 mg/kg/d ( s.c. ) for 21 days. We quantified mRNA and non-coding RNA (ncRNA) expression profiles by RNA-seq, microarray analysis and small ncRNA sequencing technology in the CA1 region of the hippocampus. Hippocampal slice immunohistochemistry was used to determine CPF-induced changes in protein expression and localization patterns. Neither dose of CPF caused overt clinical signs of cholinergic toxicity, although after 21 days of exposure, cholinesterase activity was decreased to 58% or 13% of control levels in the hippocampus of rats in the 3 or 10 mg/kg/d groups, respectively. Differential gene expression in the CA1 region of the hippocampus was observed only in the 10 mg/kg/d dose group relative to controls. Of the 1382 differentially expressed genes identified by RNA-seq and microarray analysis, 67 were common to both approaches. Differential expression of six of these genes ( Bdnf , Cort , Crhbp , Nptx2 , Npy and Pnoc ) was verified in an independent CPF exposure study; immunohistochemistry demonstrated that CRHBP and NPY were elevated in the CA1 region of the hippocampus at 10 mg/kg/d CPF. Gene ontology enrichment analysis suggested association of these genes with receptor-mediated cell survival signaling pathways. miR132/212 was also elevated in the CA1 hippocampal region, which may play a role in the disruption of neurotrophin-mediated cognitive processes after CPF administration. These findings identify potential mediators of CPF-induced neurobehavioral deficits following subchronic exposure to CPF at a level that inhibits hippocampal cholinesterase to less than 20% of control. An equally significant finding is that subchronic exposure to CPF at a level that produces more moderate inhibition of hippocampal cholinesterase (approximately 50% of control) does not produce a discernable change in gene expression.