Millions of patients suffer from Major Depressive Disorder (MDD), but
many do not respond to selective serotonin reuptake inhibitor (SSRI) therapy. We
used a pharmacometabolomics-informed pharmacogenomics research strategy to
identify genes associated with metabolites that were related to SSRI response.
Specifically, 306 MDD patients were treated with citalopram or escitalopram and
blood was drawn at baseline, four and eight weeks for blood drug levels,
genome-wide single nucleotide polymorphism (SNP) genotyping and metabolomic
analyses. SSRI treatment decreased plasma serotonin concentrations
(p<0.0001). Baseline and plasma serotonin concentration changes were
associated with clinical outcomes (p<0.05). Therefore, baseline and
serotonin concentration changes were used as phenotypes for genome wide
association studies (GWAS). GWAS for baseline plasma serotonin concentrations
revealed a genome-wide significant (p=7.84E-09) SNP clusters on chromosome four
5’ of TSPAN5 and a cluster across
ERICH3 on chromosome one (p=9.28E-08) that were also
observed during GWAS for change in serotonin at four (p=5.6E-08 and p=7.54E-07,
respectively) and eight weeks (p=1.25E-06 and p=3.99E-07, respectively). The
SNPs on chromosome four were eQTLs for TSPAN5. Knockdown (KD)
and over expression (OE) of TSPAN5 in a neuroblastoma cell line significantly
altered expression of serotonin pathway genes (TPH1,
TPH2, DDC and MAOA). Chromosome one SNPs
included two ERICH3 nonsynonymous SNPs that resulted in
accelerated proteasome-mediated degradation. In addition, ERICH3 and TSPAN5 KD
and OE altered media serotonin concentrations. Application of a
pharmacometabolomics-informed pharmacogenomic research strategy, followed by
functional validation, indicated that TSPAN5 and
ERICH3 are associated with plasma serotonin concentrations
and may play a role in SSRI treatment outcomes.