Extracellular vesicle–derived microRNA profiling in bipolar disorder and in response to lithium treatment

Background

Bipolar disorder (BD) is a complex psychiatric condition and its etiopathogenesis is not completely understood yet. Furthermore, despite lithium treatment is the mainstay in the management of BD, still one third of patients do not show an adequate response. Micro RNAs (miRNAs), small noncoding RNAs involved in post-transcriptional regulation and in gene expression, emerged as potential biomarkers and modulators of neurobiological processes. MiRNAs can be secreted from cells into extracellular vesicles (EVs) and detected in plasma, with a non-invasive peripheral investigation. EVs and their molecular cargo, including miRNAs, mediate intercellular communication and may be altered in pathological conditions. Different studies suggest that individuals with bipolar disorder show different miRNA profile compared to controls, but only few investigations specifically focused on EVs-derived miRNA profiling. This study aims to investigate the differences in EVs-derived miRNA profile between patients with BD (n=30) and non-psychiatric controls (n=15) and, among the patients’ group, between responders (R, n=11) and non-responders (NR, n=19) to long-term lithium treatment, aiming to identify possible response biomarkers.

Methods

EVs were isolated from plasma using size exclusion chromatography (Izon Columns qEV1–70 nM), concentrated and further characterized with tunable resistive pulse sensing (TRPS) technique using Exoid instrument and TEM. RNA was extracted from EVs using the Exosomal RNA isolation Kit (Norgen Biotek Corp.), library preparation was performed using QIAseq miRNA Library Kit and sequencing was conducted on a NextSeq 2000 platform (Illumina). Data (approximately 10 million reads per sample) were QC-processed (MultiQC), aligned to the reference genome with bowtie, and miRNAs were identified with miRDeep2. TMM-normalized counts were analyzed for associations with phenotypes using edgeR.

Results

A total of 153 miRNAs were detected across samples. Only two miRNA, hsa-miR-12136 (log fold-change [logFC]= 2.11, corrected p=0.02) and hsa-miR-3679-5p (logFC= 2.32, corrected p=0.03) were overexpressed in EVs of BD patients compared to controls. Enrichment and functional analyses of differentially expressed miRNAs’ target genes are still ongoing. Preliminary analysis on TarBase (v.9) showed enrichment for different pathways including “Vesicle-mediated transport”, “Regulation of cholesterol biosynthesis by SREBP” and other pathways previously implicated in BD like “Transcriptional activation of mitochondrial biogenesis” and “Circadian Clock”. Hsa-miR-12136 abnormal expression has also been previously linked to neurodevelopmental delay and intellectual disability. Among the BD group, a total of 104 miRNAs were detected. Hsa-miR-12136 was nominally associated with response to lithium but was not statistically significant after multiple testing correction.

Conclusions

These findings need to be interpreted considering some limitations, particularly the small sample size. Given the limited functional characterization of the identified miRNAs, further studies are required to validate their targets and biological roles. In fact, while the proposed miRNA-target interactions are experimentally supported, their functional relevance in BD requires further investigation. Overall, our findings of brain relevant molecular signals in peripheral EVs support their potential role for the characterization of psychiatric conditions and more specifically bipolar disorder.

ACKNOWLEDGEMENTS

The study was funded by European Union - Next Generation EU, Missione 4 Componente 1 CUP F53D23006570006 under the PRIN 2022 call (Project ID: 20228974E8).

References

No references