The Spontaneous Ala147Thr Amino Acid Substitution within the Translocator Protein Influences Pregnenolone Production in Lymphomonocytes of Healthy Individuals

• Published in: Endocrinology (Philadelphia) 2009-12, Vol.150 (12), p.5438-5445
• Main Authors: Costa, Barbara, Pini, Stefano, Gabelloni, Pamela, Da Pozzo, Eleonora, Abelli, Marianna, Lari, Lisa, Preve, Matteo, Lucacchini, Antonio, Cassano, Giovanni B, Martini, Claudia
• Format: Article
• Language: English
• Subjects: Adult; Alleles; Amino Acid Substitution; Amino acids; Analysis of Variance; Base Sequence; Blotting, Western; Cholesterol; Cholesterol Side-Chain Cleavage Enzyme - genetics; Cholesterol Side-Chain Cleavage Enzyme - metabolism; Cytochrome P450; Cytochromes P450; Enzymatic activity; Female; Gene expression; Gene Frequency; Gene polymorphism; Genotype; Humans; Leukocytes, Mononuclear - cytology; Leukocytes, Mononuclear - metabolism; Lipoproteins; Lymphocytes - cytology; Lymphocytes - metabolism; Male; Metabolites; Middle Aged; Molecular Sequence Data; Monocytes - cytology; Monocytes - metabolism; mRNA; Neurosteroids; Nucleotides; Polymorphism; Polymorphism, Single Nucleotide; Pregnenolone; Pregnenolone - blood; Pregnenolone - metabolism; Protein transport; Proteins; Receptors, GABA - genetics; Reverse Transcriptase Polymerase Chain Reaction; Sequence Homology, Nucleic Acid; Single-nucleotide polymorphism; Steroid hormones; Steroidogenesis; Substitutes; Translocation; Young Adult
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2009-0752

The de novo production of steroids and neurosteroids begins in mitochondria by the conversion of cholesterol to pregnenolone through cytochrome P450 side-chain cleavage (CYP11A1) enzymatic activity. The C-terminal amino acid domain of the translocator protein (TSPO) has been demonstrated to bind cholesterol, thereby determining its mitochondrial translocation. The goal of the present study was to investigate the effect of the Ala147Thr single-nucleotide polymorphism localized in this TSPO region on pregnenolone production in healthy volunteers. Pregnenolone production was evaluated in a peripheral cell model, represented by circulating lymphomonocytes. First, CYP11A1 expression, both at mRNA and protein level, was demonstrated. Pregnenolone production varied among genotype groups. Comparison of pregnenolone mean values revealed that Thr147 homozygous or heterozygous individuals had significantly lower pregnenolone levels compared with Ala147 homozygous individuals. These findings suggested a dominant effect of the minor allelic variant Thr147 to produce this first metabolite of the steroidogenesis pathway. Interestingly, Ala147 homozygous individuals exhibited significant higher levels of circulating cholesterol-rich low-density lipoproteins with respect to heterozygous individuals. In conclusion, our results demonstrate that the Ala147Thr spontaneous amino acid substitution within TSPO is able to affect pregnenolone production; this should encourage further studies to investigate its potential role in polygenic dyslipidemias. The Ala147Thr single nucleotide polymorphism within TSPO affects the production of first metabolite of the steroidogenesis pathway, pregnenolone, and is associated with plasma low density lipoproteins levels.