Metformin and male reproduction: effects on Sertoli cell metabolism

Abstract

Background and purpose: Metformin is commonly used to treat type 2 diabetes (T2D). While new clinical applications have been ascribed to metformin, including treatment of anovulatory infertility, its effects on male reproduction have not been investigated. The Sertoli cell (SC) is crucial for germ cell development, exerting metabolic control of spermatogenesis, therefore, we investigated the effects of metformin on SC metabolism.

Experimental approach: Rat SCs were cultured in the absence and presence of metformin (5, 50 and 500 μM). mRNA and protein levels of glucose transporters (GLUT1 and GLUT3), phosphofructokinase 1 (PFK 1), lactate dehydrogenase (LDH) and monocarboxylate transporter 4 (MCT4) were determined by quantitative PCR and Western blot respectively. LDH activity was assessed and metabolite production/consumption determined by (1) H-NMR.

Key results: Metformin (50 μM) decreased mRNA and protein levels of GLUT1, GLUT3, MCT4 and PFK 1 but did not affect LDH mRNA or protein levels. However, although glucose consumption was maintained in metformin-treated cells, LDH activity, lactate and alanine production were increased, indicating an enhanced glycolytic flux. No metabolic cytotoxicity was detected in SCs exposed to supra-pharmacological concentration of metformin.

Conclusions and implications: Our results indicate that metformin: (i) decreases mRNA and protein levels of glycolysis-related transporters in SCs but increases their activity; and (ii) stimulates alanine production, which induces antioxidant activity and maintains the NADH/NAD(+) equilibrium. The increased lactate in metformin-treated SCs provides nutritional support and has an anti-apoptotic effect in developing germ cells. Thus, metformin can be considered as a suitable antidiabetic drug for male patients of reproductive age with T2D.

Keywords: Sertoli; glycolysis; male reproductive function; metabolism; metformin.

Figure 1

Effect of metformin (5, 50 and 500 μM) on GLUT1, GLUT3, PFK 1 mRNA (panels A, C and E) and protein levels (panels B, D and F). The figure shows pooled data of independent experiments, indicating the fold variation in mRNA and protein levels found in rat SCs cultured in the presence of metformin when compared with the control condition. Representative blots are also presented. Results are expressed as mean ± SEM (n = 5 for each condition). Significantly different results (P < 0.05) are indicated as: a – relative to control; b – relative to 5 μM; c – relative to 50 μM.

Figure 2

Effect of metformin (5, 50 and 500 μM) on LDH and MCT4 mRNA (panels A and C) and protein levels (panels B and D). The figure shows pooled data of independent experiments, indicating the fold variation in mRNA and protein levels found in rat SCs cultured in the presence of metformin when compared with the control condition. Representative blots are also presented. Results are expressed as mean ± SEM (n = 5 for each condition). Significantly different results (P < 0.05) are indicated as: a – relative to control; b – relative to 5 μM; c – relative to 50 μM.

Figure 3

Effect of metformin (5, 50 and 500 μM) on LDH activity in cultured SCs. The figure shows pooled data of independent experiments, indicating LDH activity in nmol·min⁻¹·mg⁻¹ protein. Results are expressed as mean ± SEM (n = 5 for each condition). Significantly different results (P < 0.05) are indicated as: a – relative to control.

Figure 4

Effect of metformin (5, 50 and 500 μM) on extracellular metabolites. The figure shows pooled data of independent experiments, indicating glucose consumption (panel A) and the production of lactate (panel B), alanine (panel C) and acetate (panel D) in cultured SCs. Results are expressed as mean ± SEM (n = 5 for each condition). Significantly different results (P < 0.05) are indicated as: a – relative to control; b – relative to 5 μM; c – relative to 50 μM.