Genome-wide DNA methylation analysis of heavy cannabis exposure in a New Zealand longitudinal cohort

Abstract

Cannabis use is of increasing public health interest globally. Here we examined the effect of heavy cannabis use, with and without tobacco, on genome-wide DNA methylation in a longitudinal birth cohort (Christchurch Health and Development Study, CHDS). A total of 48 heavy cannabis users were selected from the CHDS cohort, on the basis of their adult exposure to cannabis and tobacco, and DNA methylation assessed from whole blood samples, collected at approximately age 28. Methylation in heavy cannabis users was assessed, relative to non-users (n = 48 controls) via the Illumina Infinium® MethylationEPIC BeadChip. We found the most differentially methylated sites in cannabis with tobacco users were in the AHRR and F2RL3 genes, replicating previous studies on the effects of tobacco. Cannabis-only users had no evidence of differential methylation in these genes, or at any other loci at the epigenome-wide significance level (P < 10^-7). However, there were 521 sites differentially methylated at P < 0.001 which were enriched for genes involved in neuronal signalling (glutamatergic synapse and long-term potentiation) and cardiomyopathy. Further, the most differentially methylated loci were associated with genes with reported roles in brain function (e.g. TMEM190, MUC3L, CDC20 and SP9). We conclude that the effects of cannabis use on the mature human blood methylome differ from, and are less pronounced than, the effects of tobacco use, and that larger sample sizes are required to investigate this further.

Fig. 1. A Manhattan plot of the genome-wide CpG sites found in the cannabis with tobacco analysis.

The Y axis presents −log10(p) values with the most significantly differentially methylated sites labelled with the gene the CpG site resides in.

Fig. 2. A Manhattan plot of the genome-wide CpG sites found in the cannabis-only analysis.

The Y axis presents −log10(p) values with the most nominally significantly differentially methylated sites labelled with the gene the CpG site resides in. NB, where a gene name is near multiple points, the appropriate point is circled in black.

Fig. 3. Genetic networks enriched within the hypermethylated CpG sites identified in the cannabis-only analysis.

Pathways from KEGG 2019. Genes shown by filled cells are hypermethylated in cannabis-only users and included in named pathway.

Fig. 4. Genetic networks enriched within the hypomethylated CpG sites identified in the cannabis-only users.

Pathways from KEGG 2019. Genes shown by filled cells are hypomethylated in cannabis-only users and included in named pathway.

Fig. 5. Genetic networks enriched within the hypomethylated or hypermethylated CpG sites identified in the cannabis-only users.

Pathways from KEGG 2019. Genes shown by filled cells are hypomethylated in cannabis-only users and included in named pathway.