Activation of cGMP/PKG/p65 signaling associated with PDE5-Is downregulates CCL5 secretion by CD8 ⁺ T cells in benign...

Benign prostatic hyperplasia (BPH) is the most common urological disease in elderly men, but the underlying pathophysiological mechanisms are complex and not fully understood. Phosphodiesterase type 5 inhibitors (PDE5-Is) used to treat BPH could upregulate the cyclic guanosine monophosphate (cGMP)-dependent protein kinase G (PKG) signaling, which was shown to blunt inflammation in the prostate. Our previous findings indicate that CD8⁺ T cells promote the proliferation of BPH epithelial cells (BECs) in low androgen conditions through secretion of CCL5; however, the role of the cGMP/PKG pathway in the process is unclear.

Paraffin-embedded tissues were used for expression quantity of CD8⁺ T cells, CCL5, cyclin D1, and PDE5 protein by immunohistology in prostate specimens which were/were not treated with finasteride 5 mg daily for at least 6 months before surgery. BPH-1 cells were cocultured with or without CD8 ⁺ T cells or PDE5-Is in low androgen conditions for 4 days. The conditioned media, BPH-1 cells, and CD8 ⁺ T cells were harvested for the subsequent experiments. The quantitative polymerase chain reaction was used for assaying the level of messenger RNA expression of CCL5. CCL5 in the conditioned media was detected by the enzyme-linked immunosorbent assay. The effect of PDE5-Is on cocultured BPH-1/CD8 ⁺ T-cell proliferation was detected by the cell counting kit-8. A high-fat diet (HFD)-induced prostatic hyperplasia rat model was used to investigate the effect of cGMP/PKG activation in CD8 ⁺ T cells in vivo.

CD8⁺ T-cell infiltration into human BPH tissues was positively correlated with the expression of CCL5, cyclin D1, and PDE5, whereas in an HFD-induced prostatic hyperplasia rat model, the activation of the cGMP/PKG signaling by a PDE5-I could suppress the CD8 ⁺ T-cell infiltration and the CCL5 and cyclin D1 expression. Furthermore, the activation of the cGMP/PKG pathway inhibited CCL5 secretion by CD8 ⁺ T cells by downregulating nuclear factor-κB p65 phosphorylation, which reduced the growth of BPH-1 through CCL5/STAT5/CCND1 signaling.

Our results indicate that the upregulation of the cGMP/PKG/p65 signaling reduces CCL5 secretion in CD8 ⁺ T cells, which in turn decreases the proliferation of BECs in low androgen conditions, suggesting that the combination of 5α reductase inhibitors lowering androgen levels and PDE5-Is may be a novel, more effective treatment for BPH patients.