The inflammatory microenvironment of the aging prostate facilitates cellular proliferation and hypertrophy

Abstract

Benign Prostatic Hypertrophy (BPH, also known as benign prostatic hyperplasia or benign prostatic enlargement), is one of the most common benign proliferative conditions associated with aging in men and is pathologically characterized by the proliferation of fibroblast/myofibroblast and epithelial cell types in the prostate. Previous studies from our laboratory have shown that the CXC-type chemokines, CXCL5 and CXCL12, are secreted by aging prostate stroma and promote both proliferative and transcriptional responses from prostate epithelial cells. Using array-based gene expression profiling and quantitative reverse-transcriptase polymerase chain reaction, we now show that the transcriptome of the aging prostate stroma is characterized by the up-regulation of several genes that encode secreted inflammatory mediators, including secreted CXC-type chemokines (CXCL1, CXCL2, CXCL5, CXCL6, CXCL12), interleukins (IL11, IL33), and transcripts with cytokine homology (CYTL1). At the protein level, ELISA experiments demonstrated that CXCL1, CXCL5, and CXCL6 were secreted by primary prostate stromal fibroblasts explanted from aging prostate stroma. Dose-response assays confirmed that, like CXCL5 and CXCL12, CXCL1 and CXCL6 promote low-level proliferative responses from both prostate stromal fibroblasts and epithelial cells. Taken together, these data suggest that inflammatory mediators are secreted by prostatic stroma consequent to aging, that the levels of these mediators are sufficient to promote low-level increases in the proliferative rate of both epithelial and stromal fibroblast cell types. Moreover, these processes may account for the low-level, but cumulative, proliferation of both epithelial and fibroblastic/myofibroblastic cell types that characterizes the aging-associated development of benign prostatic hypertophy.

Figure 1. Inflammatory Mediators Are Expressed by Aging Prostate Stroma

A. RNA purified from primary prostate stromal fibroblasts explanted and cultured from the prostates of 5 younger (white triangles) or 4 older (black triangles) patients was subjected to quantitative reverse transcription polymerase chain reaction analysis for transcripts encoding cytokine- and chemokine-type inflammatory mediators identified through gene expression profiling experiments. The graph shows the transcript expression values after normalization to the constitutively expressed control transcript, RPLPO, plotted on a logarithmic scale (y-axis). B. Fold transcript levels for CYTL1, CXCL1, CXCL5, CXCL6 and IL11 for primary prostate stromal fibroblasts explanted and cultured from the prostates of 4 older compared to 5 younger patients. Transcript levels for CXCL6 were significantly higher (asterisk, p<.05) for prostate stromal fibroblasts explanted and cultured from older compared to younger patients. C. Protein levels (pg/ml) for the CXC-type chemokines CXCL1, CXCL5 and CXCL6 secreted into media conditioned by primary prostate stromal fibroblasts were significantly higher (*, p<.05) for cells explanted and cultured from the prostates of 5 older (black bars) compared to 4 younger (gray bars) patients. The graph shows the quantity of protein secreted in pg/ml plotted on a logarithmic scale (x-axis). D. Protein levels (pg/ml) for the CXC-type chemokines CXCL1, CXCL5 and CXCL6 secreted into media conditioned by N1 prostate stromal fibroblasts (black bars) or CXCL1 and CXCL6 by LNCaP (dark gray bars), PC3 (medium gray bars), N15C6 (light gray bars) or BPH-1 (white bars) prostate epithelial cells were determined by ELISA. The graph shows the quantity of protein secreted in pg/ml plotted on a logarithmic scale (x-axis).

Figure 2. Inflammatory Mediators Expressed by Aging Prostate Stroma Promote Fibroblast and Epithelial Cell Proliferation

A. The fold proliferation of N1 prostate stromal fibroblast cells in serum-free media supplemented with CXCL5 (light gray bars), CXCL1 (dark gray bars) or CXCL6 (black bars) at the concentrations indicated relative to proliferation in un-supplemented serum-free media (set at 1-fold) is shown. The histograms indicate average fold proliferation and standard errors obtained over replicate experiments. An asterisk indicates significant levels of proliferation (p<.05) in chemokine-supplemented serum-free media compared to proliferation in un-supplemented serum-free media. B., C. and D. The fold proliferation of N15C6 (B), LNCaP (C) or PC3 (D) prostate epithelial prostate cells in serum-free media supplemented with CXCL1 (dark gray bars) or CXCL6 (black bars) at the concentrations indicated relative to proliferation in un-supplemented serum-free media (set at 1-fold) is shown. The histograms indicate average fold proliferation and standard errors obtained over replicate experiments. An asterisk indicates significant levels of proliferation (p<.05) in chemokine-supplemented serum-free media compared to proliferation in un-supplemented serum-free media.