Drug Ligand-Induced Activation of Translocator Protein (TSPO) Stimulates Steroid Production by Aged Brown Norway Rat Leydig Cells

Abstract

Translocator protein (TSPO; 18 kDA) is a high-affinity cholesterol-binding protein that is integrally involved in cholesterol transfer from intracellular stores into mitochondria, the rate-determining step in steroid formation. Previous studies have shown that TSPO drug ligands are able to activate steroid production by MA-10 mouse Leydig tumor cells and by mitochondria isolated from steroidogenic cells. We hypothesized herein that the direct, pharmacological activation of TSPO might induce aged Leydig cells, which are characterized by reduced T production, to produce significantly higher levels of T both in vitro and in vivo. To test this, we first examined the in vitro effects of the TSPO selective and structurally distinct drug ligands N,N-dihexyl-2-(4-fluorophenyl)indole-3-acetamide (FGIN-1-27) and benzodiazepine 4Ј-chlorodiazepam (Ro5-4864) on steroidogenesis by Leydig cells isolated from aged (21-24 months old) and young adult (3-6 months old) Brown Norway rats. The ligands stimulated Leydig cell T production significantly, and equivalently, in cells of both ages, an effect that was significantly inhibited by the specific TSPO inhibitor 17,. Additionally, we examined the in vivo effects of administering FGIN-1-27 to young and aged rats. In both cases, serum T levels increased significantly, consistent with the in vitro results. Indeed, serum T levels in aged rats administered FGIN-1-27 were equivalent to T levels in the serum of control young rats. Taken together, these results indicate that although there are reduced amounts of TSPO in aged Leydig cells, its direct activation is able to increase T production. We suggest that this approach might serve as a therapeutic means to increase steroid levels in vivo in cases of primary hypogonadism. (Endocrinology 154: 2156 -2165, 2013)

Peripheral Benzodiazepine Receptor/Translocator Protein Global Knock-out Mice Are Viable with No Effects on Steroid Hormone Biosynthesis

“…TSPO binding chemicals have been shown to increase steroid hormone production in isolated mitochondria from steroidogenic cells (35), MA-10 cells (37), and even live rats (68). Given our current findings, we can offer two possible explanations for these pharmacological effects.…”

PK11195 Effect on Steroidogenesis Is Not Mediated Through the Translocator Protein (TSPO)

“…These results provided compelling genetic evidence that TSPO physiology is not associated with steroidogenesis. However, this did not agree with TSPO pharmacology, as TSPO binding chemicals are reported to induce steroid hormone production (17,18,25).…”

Induction of Androgen Formation in the Male by a TAT-VDAC1 Fusion Peptide Blocking 14-3-3ɛ Protein Adaptor and Mitochondrial VDAC1 Interactions

“…Moreover, FGIN-1-27, a high affinity TSPO drug ligand induced acute T formation in vivo both in control and Cetrorelix-treated rats, although to a lesser extent than TVS167, in agreement with recent findings in aged Brown-Norway rat Leydig cells, a model of male hypogonadism. 40 Although the signal transduction mechanisms mediating the effect of LH on Leydig cell steroidogenesis are well known, this work suggests that alternative mechanisms via intracellular peptide mediators may be involved in the production of T. The presence of such natural intracellular peptides able to regulate protein-protein interactions and cell signal transduction was recently demonstrated. 41,42 Homo sapiens, Mus musculus, and Rattus norvegicus 14-3-3ε and VDAC1 proteins showed high degrees of homology.…”