Although epidemiological studies from the last years report an increase in the incidences of Leydig cell tumors (previously thought to be a rare disease), the biochemical characteristics of that tumor important for understanding its etiology, diagnosis, and therapy still remains not completely characterized. Our prior studies reported G-protein coupled estrogen receptor signaling and estrogen level disturbances in Leydig cell tumors. In addition, we found that expressions of multi-level-acting lipid balance- and steroidogenesis–controlling proteins including peroxisome proliferator-activated receptor are altered in this tumor. In order to get deeper into the other molecular mechanisms that regulate lipid homeostasis in the Leydig cell tumor, here we investigate the presence and expression of newly-described hormones responsible for lipid homeostasis balancing (leptin and adiponectin), together with expression of estrogen synthase (aromatase). Samples of Leydig cell tumors (n = 20) were obtained from patients (31–45 years old) and used for light and transmission electron microscopic, western blotting, and immunohistochemical analyses. In addition, body mass index (BMI) was calculated. In tumor mass, abundant lipid accumulation in Leydig cells and various alterations of Leydig cell shape, as well as the presence of adipocyte-like cells, were observed. Marked lipid content and various lipid droplet size, especially in obese patients, may indicate alterations in lipid homeostasis, lipid processing, and steroidogenic organelle function in response to interstitial tissue pathological changes. We revealed significantly increased expression of leptin, adiponectin and their receptors, as well as aromatase in Leydig cell tumors in comparison to control. The majority of patients (n = 13) were overweight as indicated by their BMI. Moreover, a significant increase in expression of phospholipase C (PLC), and kinases Raf, ERK which are part of adipokine transductional pathways, was demonstrated. These data expand our previous findings suggesting that in human Leydig cell tumors, estrogen level and signaling, together with lipid status, are related to each other. Increased BMI may contribute to certain biochemical characteristics and function of the Leydig cell in infertile patients with a tumor. In addition, altered adipokine-estrogen microenvironment can have an effect on proliferation, growth, and metastasis of tumor cells. We report here various targets (receptors, enzymes, hormones) controlling lipid balance and estrogen action in Leydig cell tumors indicating their possible usefulness for diagnostics and therapy.

Leydig cell tumors (LCT) are the most common type of testicular sex cord-stromal tumor. In this report, we implicate the G-coupled estrogen receptor (GPER) and peroxisome proliferator receptor (PPAR) in regulation of lipid homeostasis and the expression of steroidogenesis-controlling molecules in clinical specimens of LCTs and cell line (mouse tumor Leydig cells; MA-10). We also show the general structure and morphology of human LCTs with the use of scanning electron microscopy and light microscopy, respectively. In LCTs, protein immunoblotting and immunohistochemical analysis revealed increased expression of GPER and decreased expression of PPARα, β and γ. Concomitantly, changes in expression pattern of the lutropin receptor (LHR), protein kinase A (PKA), perilipin (PLIN), hormone sensitive lipase (HSL), steroidogenic acute regulatory protein (StAR), translocator protein (TSPO), HMG-CoA synthase (HMGCA), and HMG-CoA reductase (HMGCR) were observed. Using MA-10 cells treated with GPER and PPAR antagonists (alone and in combination), we demonstrated there is a GPER-PPAR mediated control of cholesterol concentration. In addition, GPER-PPARα regulated estradiol secretion, while GPER-PPARγ affected cGMP concentration. It is assumed that GPER and PPAR can be altered in LCT, resulting in a perturbed lipid balance and steroidogenesis. In LCTs, the phosphatidylinositol-3-kinase (PI3K)-Akt-mTOR signaling pathway was disturbed. Thus, PI3K-Akt-mTOR, together with cGMP, can play a role in LCT proliferation, growth, and metastasis as well as lipid balance control. In conclusion, we discuss the implications of GPER-PPAR interaction with lipid metabolism and steroidogenesis controlling-molecules in LCT biology that can be used in future studies as potential targets of diagnostic and therapeutic implementations.