Reduction of insulin signalling pathway IRS-1/IRS-2/AKT/mTOR and decrease of epithelial cell proliferation in the prostate of glucocorticoid-treated rats

Abstract

Previous studies by our research group using a model of insulin resistance induced by dexamethasone (DEX) showed that in the rat ventral prostate there was epithelial and smooth muscle cell atrophy and there were also alterations in fibroblasts. Proteins of the insulin signalling pathway are known to be very important for cell proliferation and development. Thus, we investigated the insulin signalling pathway and epithelial proliferation in the rat ventral prostate in this model and correlated the findings with expression of glucocorticoid (GR) and androgen (AR) receptors. Insulin resistance was induced in adult male Wistar rats by injection of DEX (1 mg/kg, ip for 5 consecutive days), whereas control (CTL) rats received saline. DEX treatment resulted in a significant decrease in body weight, but not in prostate weight. Reductions in insulin receptor 1 (IRS-1) (CTL 1.11 ± 0.06; DEX 0.85 ± 0.03), IRS-2 (CTL 0.95 ± 0.05; DEX 0.49 ± 0.04), AKT (CTL 0.98 ± 0.03; DEX 0.78 ± 0.02), mammalian target of rapamycin (mTOR; CTL 0.65 ± 0.08; DEX 0.22 ± 0.05), GR (CTL 1.30 ± 0.09; DEX 0.57 ± 0.10) and AR (CTL 1.83 ± 0.16; DEX 0.55 ± 0.08) protein levels were observed in the prostate of DEX-treated rats. The expression of the IRα-subunit, phosphoinositide 3-kinase, p-AKT, p70(S6K) , extracellular signal-regulated kinase (ERK) and p-ERK was not altered. The frequency of AR-positive cells in the epithelium of the prostate decreased in the glucocorticoid-treated group, and the intensity of the reaction for this receptor in the cell nuclei was lower in this group. Furthermore, the treatment with DEX reduced the frequency of proliferating cell nuclear antigen-positive (PCNA) cells 30-fold. This study suggests that the reduction in the insulin signalling pathway proteins IRS-1/IRS-2/AKT/mTOR in the prostate of DEX-treated rats may be associated with the morphological alterations observed previously.

Figure 1

Protein expression of insulin receptor α-subunit (a); insulin receptor substrate (IRS)-1 (b); IRS-2 (c) and phosphoinositide 3-kinase (d) in the ventral prostate of rats treated with saline (CTL) and dexamethasone (DEX). Data are reported as means ± SE. *P < 0.05 compared to control (Student’s t-test), n = 6.

Figure 2

Protein expression of AKT (a); p-AKT (b); mammalian target of rapamycin (c) and p70^S6K (d) in the ventral prostate of rats treated with saline (CTL) and dexamethasone (DEX). Data are reported as means ± SE. *P < 0.05 compared to control (Student’s t-test), n = 6.

Figure 3

Protein expression of extracellular signal-regulated kinase (ERK) (a) and p-ERK (b) in the ventral prostate of rats treated with saline (CTL) and dexamethasone (DEX). Data are reported as means ± SE, P > 0.05 (Student’s t-test), n = 6.

Figure 4

Protein expression of GR (a) and AR (b) in the ventral prostate of rats treated with saline (CTL) and dexamethasone (DEX). Data are reported as means ± SE. *P < 0.05 compared to control (Student’s t-test), n = 6.

Figure 5

Proliferating cell nuclear antigen immunocytochemistry of the intermediate region of the ventral prostate of control rats (a) or rats treated with dexamethasone (b). Proliferating cell nuclear antigen-positive cells are indicated by arrowheads. Note that proliferation in the prostate epithelium decreases significantly in the dexamethasone group (b). Scale bar: 20 μm.

Figure 6

Immunocytochemistry for AR in the ventral prostate of control rats (a–c) or rats treated with DEX (d–f). Distal region (a, b, d and e) and intermediate region of the acini (c and f). Note the reduction in the staining of the AR in the prostate epithelium of the DEX-treated group and the decreasing intensity of nuclear staining for this receptor after treatment with DEX. Scale bars = 100 μm for a and d; 20 μm for b, c, e and f.

Figure 7

Relative frequency (%) of immunoreactions for PCNA-positive cells (a) and AR-positive cells (b). Data are reported as means ± SE. *P < 0.05 compared to control (Student’s t-test).