Transcriptomic Changes and the Roles of Cannabinoid Receptors and PPARgamma in Developmental Toxicities Following Exposure to delta9-Tetrahydrocannabinol and Cannabidiol
Human consumption of cannabinoid-containing products during early life or pregnancy is rising. However, information about the molecular mechanisms involved in early life stage Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) toxicities is critically lacking. Here, larval zebrafish (Danio rerio) were used to measure THC and CBD-mediated changes on transcriptome and the roles of cannabinoid receptors (Cnr) 1 and 2 and peroxisome proliferator activator receptor γ (PPARγ) in developmental toxicities. Transcriptomic profiling of 96-hour post fertilization (hpf) cnr+/+ embryos exposed (6-96 hpf) to 4 μM THC or 0.5 μM CBD showed differential expression of 904 and 1095 genes for THC and CBD, respectively, with 360 in common. KEGG pathways enriched in the THC and CBD datasets included those related to drug, retinol, and steroid metabolism and PPAR signaling. THC exposure caused increased mortality and deformities (pericardial and yolk sac edemas, reduction in length) in cnr1-/- and cnr2-/- fish compared to cnr+/+ suggesting Cnr receptors are involved in protective pathways. Conversely, the cnr1-/- larvae were more resistant to CBD-induced malformations, mortality, and behavioral alteration implicating Cnr1 in CBD-mediated toxicity. Behavior (decreased distance travelled) was the most sensitive endpoint to THC and CBD exposure. Co-exposure to the PPARγ inhibitor GW9662 and CBD in cnr+/+ and cnr2-/- strains caused more adverse outcomes compared to CBD alone, but not in the cnr1-/- fish, suggesting that PPARγ plays a role in CBD metabolism downstream of Cnr1. Collectively, PPARγ, Cnr1, and Cnr2 play important roles in the developmental toxicity of cannabinoids with Cnr1 being the most critical.
Keywords: Behavior; Cannabidiol; Development; PPARγ; RNAseq; Tetrahydrocannabinol.