Chronic prostatitis alters the prostatic microenvironment and accelerates preneoplastic lesions in C57BL/6 mice

Abstract

Background: Chronic prostatitis has been supposed to be associated with preneoplastic lesions and cancer development. The objective of this study was to examine how chronic inflammation results in a prostatic microenvironment and gene mutation in C57BL/6 mice.

Methods: Immune and bacterial prostatitis mouse models were created through abdominal subcutaneous injection of rat prostate extract protein immunization (EAP group) or transurethral instillation of uropathogenic E. coli 1677 (E. coli group). Prostate histology, serum cytokine level, and genome-wide exome (GWE) sequences were examined 1, 3, and 6 months after immunization or injection.

Result: In the EAP and E. coli groups, immune cell infiltrations were observed in the first and last months of the entire experiment. After 3 months, obvious proliferative inflammatory atrophy (PIA) and prostatic intraepithelial neoplasia (PIN) were observed accompanied with fibrosis hyperplasia in stroma. The decrease in basal cells (Cytokeratin (CK) 5+/p63+) and the accumulation of luminal epithelial cells (CK8+) in the PIA or PIN area indicated that the basal cells were damaged or transformed into different luminal cells. Hic1, Zfp148, and Mfge8 gene mutations were detected in chronic prostatitis somatic cells.

Conclusion: Chronic prostatitis induced by prostate extract protein immunization or E. coli infection caused a reactive prostatic inflammation microenvironment and resulted in tissue damage, aberrant atrophy, hyperplasia, and somatic genome mutation.

Keywords: Chronic prostatitis; Proliferative inflammatory atrophy; Prostatic intraepithelial neoplasia; Prostatitis mouse model; Somatic genome mutation.

Fig. 1

Characteristic images of glandular histopathological findings in ventral prostate (VP), dorsolateral prostate (DLP), and anterior prostate (AP) lobes of mice at 1, 3, and 6 months after immunization or infection (H&E stain, Bar = 100 µm). a, b, d Naïve, CFA, and PBS groups without obvious histopathological changes. CFA group with very mild inflammation at 6 months. c, e EAP and E. coli groups with inflammation characterized by infiltration of lymphocytes, hyperplasia and heteromorphism of glandular epithelium, large and intensely stained nucleolus, and karyokinesis

Fig. 2

Serum levels of C-reactive protein (CRP) (ng/mL) in mice at 1, 3, and 6 months after immunization or infection. Comparison of serum levels of CRP (ng/mL) among a naïve, CFA, and EAP groups and b naïve, PBS, and E. coli groups (N = 6 per group, data are expressed as mean ± SEM, *P < 0.05, **P < 0.01, ***P < 0.001)

Fig. 3

Serum levels of IL-17 (ng/mL) in mice at 1, 3, and 6 months after immunization or infection. a Comparison of IL-17 (ng/mL) among naïve, CFA, and EAP groups. b Comparison of IL-17 (ng/mL) among naïve, PBS, and E. coli groups (N = 6 per group, data are expressed as mean ± SEM, *P < 0.05, **P < 0.01, ***P < 0.001)

Fig. 4

Characteristic monochrome and merged images for CK8 (red) in ventral prostate (VP), dorsolateral prostate (DLP), and anterior prostate (AP) lobes of mice at 1, 3, and 6 months after immunization or infection. Nuclei are counterstained with DAPI (blue). a, b, d Naïve, CFA, and PBS groups. A single layer of luminal cells is present, and no proliferating cells are observed. c, e EAP and E. coli groups. Multiple layers of luminal cells positive for CK8+ (in red) are observed at the third and sixth month of modeling

Fig. 5

Characteristic monochrome and merged images for CK5 (red) in ventral prostate (VP), dorsolateral prostate (DLP), and anterior prostate (AP) lobes of mice at 1, 3, and 6 months after immunization or infection. Nuclei are counterstained with DAPI (blue). a, b, d Naïve, CFA, and PBS groups. CK5+ (red) can be observed from 1 to 6 months. c EAP and E. coli groups. Basal cells positive for CK5+ (red) are observed in the first month, obviously decrease in the third month, and almost disappear in the sixth month