Acute bacterial inflammation of the mouse prostate

Abstract

Background: Prostatic inflammation is gaining increasing attention as a potential etiologic factor in prostate cancer, benign prostatic hyperplasia, lower urinary tract symptoms, and CPPS. This study was performed to address the need for a well characterized model of acute prostatic inflammation that may be used to study the effect of acute inflammation on epithelial and stromal cell proliferation, voiding behavior, and neurovascular physiology.

Methods: Uropathogenic E. coli 1677 was instilled transurethrally into adult C57BL/6J male mice. Prostates were analyzed at 1, 2, 3, 5, 7, or 14 days post-instillation and compared to saline-instilled and naïve controls. Time course and severity of inflammation were characterized by the quantity and type of inflammatory infiltrate present, hemorrhage, proliferation, and reactive hyperplasia. RT-PCR was performed to characterize inflammatory mediators including IL-1α, IL-1β, IL-1RA, IL-18, IL-6, IL-10, IL-8, TNFα, and COX-2.

Results: Inflammation was evident in all lobes of the prostate with the DLP most severely affected. Infection consistently led to a significant increase in neutrophils and macrophages in the early stages of prostate infection, followed by lymphocytic inflammation at the later time points. Inflammation was accompanied by induction of several inflammatory genes, including IL-1 family members, IL-6, and COX-2, and induced a significant increase in epithelial proliferation and reactive hyperplasia in all three prostate lobes.

Conclusions: Transurethral inoculation of uropathogenic E. coli 1677 reliably infects the mouse prostate, produces a significant inflammatory response, and induces quantifiable epithelial proliferation and reactive hyperplasia.

Fig. 1

Representative H&E stained sections of the DLP 5 days after instillation of saline (top panels) or E. coli 1677 (bottom panels). The 10× power images are shown on the left; 40× power insets are shown on the right and specific features of inflammation are designated in the 40× image of the infected DLP: (H) indicates hyperplasia; (V) indicates vascular damage; (I) indicates inflammatory infiltrate; and (PN) indicates a pyknotic nucleus. The central lumen is filled with necrotic epithelium and inflammatory infiltrate.

Fig. 2

Comparison of hyperplasia, inflammatory infiltrate, vascular pathology and tissue damage in the VP, CG, and DLP of infected and saline control prostates 1, 2, 3, 5, 7, and 14 days post instillation (n = 3 at all time points). Inflammation scores for naïve controls (n = 3) are shown at all time points for purpose of comparison. *P < 0.05 compared to naïve, and ^#P < 0.05 compared to saline by ANOVA.

Fig. 3

Immunostaining for BrdU (green) in the DLP (20×). Co-staining for p63 (red) was performed to identify the basal cell layer. A:Naïve control; (B) saline control 2 days post-instillation; (C) saline control 5 days post-instillation; (D) infected 2 days post-inoculation; (E) Infected 5days post-inoculation.

Fig. 4

A–C: Comparison of epithelial proliferation rates determined as the number of BrdU positive cells per duct in the VP, CG, and DLP of infected and saline control prostates 1, 2, 3, 5, 7, and 14 days post instillation (n = 3 at all time points). Proliferation rates for naïve controls (n = 3) are shown at all time points for purpose of comparison. *P < 0.05 compared to naïve; #P < 0.05 compared to saline by ANOVA with a square root transformation.

Fig. 5

A–D: Characterization of DLP inflammatory infiltrate at 1–14 days post-inoculation by H&E staining and IHC presented as the mean number of cells per 20× field. A:Neutrophils, (B) Blymphocytes, (C) Tlymphocytes, (D) monocytes/macrophages. *P < 0.05 [ANOVA] compared to Day 0.

Fig. 6

RNA expression of inflammatory mediators in the DLP at selected time points after bacterial inoculation (squares) of saline instillation (diamonds) expressed as fold change from naïve: (A) IL-1α, (B) IL-1β, (C) IL-18, (D) IL-8, (E) COX-2, (F) TNFα, (G) IL-1RA, (H) IL-10, (I) IL-6. *P < 0.05 compared to naïve; ^#P < 0.05 compared to saline by ANOVA with a natural logarithmic transformation (n = 5–9 per time point).